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# Study of the structure-properties relationship of polymeric materials using coupled techniques

Daniel Hermida Merino

► To cite this version:

Daniel Hermida Merino. Study of the structure-properties relationship of polymeric materials using coupled techniques. Physics [physics]. Université de Lorraine, 2020. tel-03092454

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https://hal.univ-lorraine.fr/tel-03092454

Submitted on 2 Jan 2021

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Ecole Doctorale C2 MP
(Chimie Mécanique Matériaux Physique)

DE L'UNIVERSITÉ DE LORRAINE

LABORATOIRE LMOPS

Présentée et soutenue publiquement pour l'obtention du titre de

Habilitation à diriger des recherches

par

Daniel Hermida Mérino

# Etude de la relation structure-propriétés des matériaux polymères par techniques couplées

## Study of the structure-properties relationship of polymeric materials using coupled techniques.

Soutenue le 14 décembre 2020

### Membres du jury :

<table><tr><td>Pr Corine BAS, Université Savoie Mont Blanc LEPMI UMR 5279</td><td>Rapportrice</td></tr><tr><td>Pr Noëlle BILLON, CEMEF, Sophia Antipolis</td><td>Rapportrice</td></tr><tr><td>Pr Manuel Martínez Piñeiro, Universidade de Vigo, Vigo</td><td>Rapporteur</td></tr><tr><td>Pr Valérie GAUCHER, UMET, Université Lille1</td><td>Examinatrice</td></tr><tr><td>Pr Isabelle ROYAUD, IJL, Université de Lorraine, Nancy</td><td>Examinatrice</td></tr><tr><td>Dr Carlos ALONSO MORENO, Université de Castilla-La Mancha, Albacete. Espagne</td><td>Invité</td></tr><tr><td>Dr Guiseppe PORTALE, Université de Groningen, Pays-Bas</td><td>Invité</td></tr><tr><td>Pr Patrice BOURSON, LMOPS, Université de Lorraine, Metz</td><td>Parrain scientifique</td></tr></table>
# Sommaire

<table><tr><td>Resumé</td><td>4</td></tr><tr><td>Abstract</td><td>4</td></tr><tr><td>Introduction</td><td>5</td></tr><tr><td>Etat Civil</td><td>8</td></tr><tr><td>Indicateurs de la qualité de la production scientifique</td><td>8</td></tr><tr><td>Formation académique universitaire</td><td>9</td></tr><tr><td>Licences, maîtrises et diplômes d'ingénieur</td><td>9</td></tr><tr><td>Doctorats</td><td>9</td></tr><tr><td>Expérience pédagogique</td><td>9</td></tr><tr><td>Direction de thèse de doctorat ou de projets de fin d'études</td><td>9</td></tr><tr><td>Projet scientifique</td><td>11</td></tr><tr><td>1-Understanding of the structural development of polymeric materials upon extreme conditions that mimic the industrial environment</td><td>12</td></tr><tr><td>2-Investigation of the internal nanostructural development of block copolymers polymerization under polymeric sc-CO2</td><td>14</td></tr><tr><td>3-Co-proposer PhD Thesis project awarded; "Etude multi-échelle de l'impact de l'ajout de fluoroélastomère sur la structure du PVDF par des mesures in situ couplées", Université de Lorraine</td><td>16</td></tr><tr><td>4-Controlling of fibrillization for drug delivery</td><td>32</td></tr><tr><td>5-Caroline Grant (from Oct 1st 2017 to Nov. 30th 2020) in the project "NODENS" which is a Caroline Fellowship program co-founded by European Union Horizon 2020 Marie Skłodowska-Curie actions and Irish Research Council</td><td>50</td></tr><tr><td>6-Scientific granted project by Fapesp (Sao Paulo Federal Research Council) for the investigation of 'In situ studies of nanoparticles nucleation and growth assisted by simultaneous SAXS and WAXS and XAS in combination with UV-visible spectroscopy', 2017</td><td>52</td></tr><tr><td>7-Co-proposer PhD Thesis project awarded; 'Nouvelle génération de biopolymères nanostructurés pour la fabrication additive et l'électrofilage, Université de Lorraine</td><td>57</td></tr><tr><td>8-Study of the nanostructure of the fish gelatin hydrogels for drug delivery applications</td><td>65</td></tr><tr><td>9-Main applicant as well as co-applicant of a series of synchrotron proposals as well as other polymer research projects</td><td>71</td></tr><tr><td>10-Part of the scientific panel of bl11 NCD in Alba sincrotrón</td><td>71</td></tr><tr><td>11-Beamline scientist responsible of bm26/ DUBBLE at ESRF from July 2015</td><td>72</td></tr><tr><td>Conclusions</td><td>75</td></tr><tr><td>PROJETS ET PRODUCTIONS SCIENTIFIQUES</td><td>76</td></tr><tr><td>Cours et séminaires de formation pédagogique universitaire</td><td>76</td></tr><tr><td>Expérience scientifique et technologique</td><td>76</td></tr></table>
<table><tr><td>Activité scientifique ou technologique</td><td>76</td></tr><tr><td>Participation à des projets de R&D&I financés à travers des procédures concurrentielles d'organismes publics ou privés</td><td>76</td></tr><tr><td>Participation à des contrats, conventions ou projets de R&D&I ne résultant pas de procédures concurrentielles, avec des entreprises (ou dans le cadre d'entreprises) et/ou des administrations</td><td>95</td></tr><tr><td>Publications, documents scientifiques et techniques ou technologiques ou autre publication</td><td>96</td></tr><tr><td>Travaux présentés lors de congrès nationaux ou internationaux</td><td>105</td></tr><tr><td>Comités consultatifs scientifiques, sociétés scientifiques</td><td>106</td></tr><tr><td>Expérience de gestion de R&D&I</td><td>107</td></tr><tr><td>Séjour dans des centres de R&D&I ou bien des entreprises nationales ou internationales</td><td>108</td></tr><tr><td>Aides et bourses obtenues</td><td>110</td></tr><tr><td>Résumé des autres titres</td><td>110</td></tr></table>
## Resumé

Mes recherches portent principalement sur l'étude des relations structure-propriété dans le domaine de la matière molle dans différents milieux tels que le massif, la solution ainsi que les films minces. En particulier, j'ai développé mon activité de recherche scientifique en interne, en menant des expériences de diffusion de la lumière à la fois en mode transmission et en mode angle rasant, en combinaison avec plusieurs spectroscopies et techniques mécaniques dans le domaine des polymères comme la cristallisation des polymères, les polymères supramoléculaires auto-assemblés, les systèmes polymères fonctionnels avancés et les systèmes hybrides métal-organiques. En tant que chercheur travaillant sur une infrastructure scientifique de pointe (ESRF), j'ai acquis des connaissances exceptionnelles à la pointe de l'instrumentation des rayons X et j'ai ainsi bénéficié d'une interaction étroite avec les groupes de recherche les plus éminents en science des matériaux, en particulier la matière condensée molle, aux Pays-Bas et en Europe. Cela m'a encouragé à développer de nouveaux environnements d'échantillonnage et à réaliser des expériences de pointe en matière de rayons X en combinaison avec plusieurs autres techniques dans le domaine de la matière molle, telles que la microscopie, la calorimétrie, la spectroscopie et la rhéologie. Actuellement, j'ai concentré mes recherches sur le développement et la caractérisation de nouveaux copolymères blocs de biosourcés avec des blocs biocompatibles. Les nouveaux biopolymères avancés sont des candidats idéaux pour des applications dans des domaines vitaux du domaine biomédical ou pharmaceutique lorsqu'ils sont associés à des médicaments et à des nanoparticules métalliques clés.

## Abstract

The main focus of my research is the study of the structure-property relationships in the soft matter area in different medium such as bulk, solution as well as thin films. Particularly, I have developed my scientific in-house research activity, conducting scattering experiments both in transmission and grazing angle mode, in combination with several spectroscopies and mechanical techniques in the polymeric field such as polymer crystallization, self-assembled supramolecular polymers, advanced functional polymeric systems and metal-organic hybrid systems.

As a researcher working on a leading scientific infrastructure (ESRF), I have acquired an outstanding knowledge at the forefront of X-ray instrumentation and thus, I have benefited from close interaction with the most prominent research groups in materials science, specifically soft condensed matter, in the Netherlands and Europe. This has encouraged me to develop novel sample environments and performed cutting edge X-ray experiments in combination with several other leading techniques in a soft matter such as microscopy, calorimetry, spectroscopy, rheology. Currently, I have focused my research on the development and characterization of novel biosource block-copolymers with biocompatible blocks. Novel advanced biopolymers are ideal candidates with applications in vital areas of the biomedical or pharmaceutical field when coupled with drugs and key metallic nanoparticles.
Introduction

The main focus of my research is the study of the structure-property relationships in the soft matter area in different medium such as bulk, solution as well as thin films. Particularly, I have developed my scientific in-house research activity, conducting scattering experiments both in transmission and grazing angle mode, in combination with other techniques in the polymeric field such as polymer crystallization, self-assembled supramolecular polymers, advanced functional polymeric systems and metal-organic hybrid systems.

I am currently the scientist responsible for the SAXS-WAXS station in DUBBLE at the ESRF, Grenoble as an NWO employee. As a beamline scientist of bm26, I have benefited from the long-standing and extensive investigation of polymer crystallization studies in quiescent and industrial processing conditions conducted at the beamline. A wide range of polyolefins, polyamides, have been investigated at extreme conditions to understand the mechanism of crystallization and the kinetics of expected mesophases and oriented structures formations.

I have promoted further the in-situ monitoring of nanostructure development by simultaneous SAXS/WAXS under external thermal and mechanical fields by enlarging the length scale in combination with spectroscopies techniques and additional multivariate analysis due to the increase of acquired metadata per experiment. Likewise, I have successfully applied for several scientific projects in collaboration with European partners in the soft matter field to advance in the design of novel functional polymeric materials with tailored properties with particular emphasis, in the use of green approaches as well as biocompatible application due to increase by the society demands for bioenvironmental policies.

I have investigated the nanostructure formation during the synthesis of structured block copolymer under extreme conditions such as the formation of polymeric microparticles in sc-CO2 in collaboration with Professor Steven Howdle at University of Nottingham. Firstly, a novel X-ray reactor was designed that then permitted to probe in-situ the influence of sc-CO2-philicity of the different blocks in the internal structural development of polymeric block-copolymer microparticles.

In addition, I have participated to advance the polymer science research at processing conditions at the beamline particularly at relevant industrial conditions as a co-proposer of the successful DPI (Dutch Polymer Institute) project "Online Polyolefin structuring during Cast Film Extrusion" granted on June the 1st of 2018 by Dr. Portale at University of Groningen. The cast film extrusion has lately been adopted in the packing industry due to the beneficial optical properties and film thickness distribution in the cross direction obtained compare to typically blow film process. Furthermore, I have also investigated together with Dr. Portale the main parameters that defined the polymeric film formation by performing in-situ GISAXS/GIWAXS experiments that allows to describe the crystallinity and microphase separation of block copolymers as well as polymer blends. The assessment of the role of as several phenomena such as macrophase separation, nanostructure development and film percolation, occur concomitantly is crucial to control the film formation.

Moreover, I gained visiting grants as both junior and senior researcher at the "Universidad de Castilla la Mancha" to endorse the understanding of the key structural parameters to design novel molecular organic and polymeric systems with sensing applications and specially for delivery drug delivery systems.

Consequently, I have then participated as a co-applicant of the successful synthetic project "Procesos catalíticos para la conversion de CO2 en productos de interés industrial" of the science ministry of Spain in collaboration with the "Universidad de Castilla la Mancha". Particularly, the synthesis of biodegradable as well as biocompatible novel polyester by
organometallic catalysis was aimed to attain both control on the Mw and stereoregularity as well as narrow polydispersity that in turn, were evaluated as drug nanocarriers. The manuscript published with the preliminary results has been reproduced in the press for being selected for its importance in fundamental research and in the application of X-rays by the ALBA synchrotron.

https://www.sincrotronalba.es/es/actualidad/noticias/nuevas-nanoparticulas biocompatibles-contra-el-cancer-demama

Furthermore, I have studied metal-organic hybrid systems that provide a novel approach to combine the mechanical support that offers the polymeric material with the improvement of targeted properties. Likewise, I have successfully applied together with associate Professor José Fernando Queiruga to the FAPESP scientific council the support of the structural investigation by combined techniques of hybrid systems with the research project: "In situ studies of nanoparticles nucleation and growth assisted by simultaneous SAXS and WAXS and XAS in combination with UV-visible spectroscopy".

I have studied the nanostructure of Nafion-Cs nanoparticles (N-CSP) composites by simultaneous SAXS/XAS as well as SAXS/WAXS experiments in order to enhance the proton conductivity at working conditions. Hybrid metal-polymeric membranes promote the maintenance of high protonic conductivity at low humidity conditions. The Nafion-Cs nanoparticles composites nanostructural has been investigated at high temperatures to understand the increased protonic conductivity in relation to Nafion under anhydrous conditions. Moreover, I have designed a novel X-ray flow cell to probe the growth of the gold nanoparticles in mild conditions by simultaneous SAXS- UV-vis spectroscopy to correlate the changes on the plasmon with the morphological evolution minimasing the X-rays detrimental effect on the nanoparticule formation. In the next future, the nanoparticules growth will be integrated in supramolecular hydrogels to attain the desired mechanical charactestics for biomedical applications as drug nanocarriers that feature sensing capabilities.

Since the research I have developed during my PhD, I have enthusiastically involved in the design proviso of novel supramolecular polymers with responsive specific functionalities that harnessed from the dynamic and specificity of the non-covalent interactions nature. Furthermore, the hierarchical self-organization that defines the supramolecular nanostructure is commonly employed by conventional polymeric systems and thus, the understanding of key paramaters that govern their self-assembly is beneficial to advance in the development of polymeric systems.

As with conventional, covalently bonded polymers, the macroscopic properties of supramolecular polymers (such as viscosity and tensile strength) are intimately related to its nanostructure. The versatility of the supramolecular architectures offers the possibility of constructing chemical architectures displaying notable structural complexity, from linear polymeric chains to networks and hyperbranched systems. Supramolecular entities can, in turn, enable the production of new thermoplastic elastomers and tuneable polymer materials. A systematic study of the effect of supramolecular interactions of both the end group and linkers on the nanostructure of self-assembled polymers has been the aim of my research on the supramolecular field.

Furthermore, I have investigated the gelation mechanism of mainly supramolecular systems, particularly, in combination with the presence of therapeutic agents, to design drug nanocarriers for the pharmaceutical administration in corporal areas with targeted barriers. The structure-activity relationship and the gelation process that drives the self-assembly of potential supramolecular gelators into gels is not fully understood and the majority of gels are
found serendipitously. However, it has been established that gelation is mainly controlled by
the gelator architecture, gelator concentration, gelation conditions and solvent effects.
Attempts to understand the molecular assembly of a low molecular hydrogelator into
molecular-scale fibrils and the subsequent hierarchal organization of the fibrils into spanning
network that percolates the solution by fibril-fibril interaction has been investigated. The
mechanism development of a molecular solution into insoluble fibrillar gel network is a phase
separation process driven thermodynamically by solution saturation. Moreover, the acquired
understanding of the hydrogelator fibrillization, as well as their self-recognition mechanism,
has been applied to design responsive nanocarriers for targeted pharmaceutical agents that
will be encapsulated and released in a controlled fashion. Subsequently, the passive upload of
an antitumoral (Doxorubucin) and the posterior release from the hydrogelator network has
been evaluated in vitro glioblastoma cells in collaboration with the "Universidad de Castilla la
Mancha" as part of previous mentioned partnership.

In order to continue the investigation on the gelation mechanism, I successfully obtained a
joint application for Caroline Grant with Bing Wu, to spend 36 months (from Dec. 1st 2017 to
Nov. 30th 2020) working as a guest researcher in the project "NODENS" which is a Caroline
Fellowship program cofounded by European Union Horizon 2020 Marie Skłodowska-Curie
actions and Irish Research Council.

Furthermore, I have co-applied successfully to the regional Lorraine research program to co-
finance a PhD project in collaboration with Arkema and the LMOPS titled "Etude multi-échelle
de l'impact de l'ajout de fluoroélastomère sur la structure du PVDF par des mesures in situ
couplées". In addition, I have been selected in the fellowship program of the "Université de
Lorraine" as a scientific visitor for 2018, 2019 and 2020 courses. During my scientific stay, I
have gained experience in Raman spectroscopy, which offer great complementary
opportunities to be coupled with scattering techniques as well as to advance on the application
of Multivariate data analysis (MVA) for SAXS-WAXS data acquired together with Raman
spectroscopy in order to correlate complementary structural information.

Currently, I have focused my research on the development and characterization of novel
biosourced block-copolymers with biocompatible blocks. Novel advanced biopolymers are ideal
candidates with applications in vital areas of the biomedical or pharmaceutical field when
coupled with drugs and key metallic nanoparticles. I have participated together with Professor
Patrice Bourson at "Université de Lorraine" to finance a PhD project at LMOPS titled "New
generation of nanostructured biopolymers for additive manufacturing and electrospinning", to
synthetise novel block copolymer PLA stereo-complexes of high Mw for potential nanomedice
applications in collaboration with "Universidad de Castilla la Mancha".

Moreover, I have initiated the study of gelatin from fish sources to develop pharmaceutical
drug delivery systems as well as promoting the valorization of value-added products derived
from fisheries waste sources to enhance the environmental sustainability and as a contribution
to the circular economy. The research is conducted in collaboration with both "Universidade
de Vigo" and "Instituto de investigacions mariñas" at the CSIC (Spanish scientific council).
Furthermore, the mechanical properties of the generated gelatin hydrogels were enhanced by
the formation of double network gel using a cohydrogelator as ionic liquids (ILs) that are
considered green solvents due to their biodegradability and low toxicity.
# Etat Civil

**Nom:** Hermida Merino
**Prénoms:** Daniel
**DNI:** 36157638M
**ORCID:** 0000-0002-8181-158X
**Sexe:** Homme
**Nationalité:** Espagne
**Pays de naissance:** Espagne
**Communauté autonome ou région de naissance:** Galice
**Ville de naissance:** Vigo
8a Rue du Jura
**Adresse de contact:**
**Code postal:** 74160
**Pays :** France
**Ville:** St Julien en Genevois
**Téléphone fixe:** (0033) 0476882375
**Adresse électronique:** d.hermida@gmail.com
**Téléphone portable:** (0033) 0601794459

**Situation professionnelle actuelle uniquement si vous travaillez (pas si vous êtes au chômage)**

**Nom de l'établissement:** DUBBLE
**Type d'établissement:** Centre de R&D
**Département, service,...:** ESRF
**Catégorie / fonction ou poste:** Scientifique Senior Beamline en DUBBLE à E.S.R.F / Responsable bm26
**Date de début:** 01/01/2015
**Modalité de contrat:** Contrat professionnel à durée indéterminée

# Indicateurs de la qualité de la production scientifique

**H index** 20

i-10 index 43

Près de 1950 citations

> 74 proposals in synchrotrons across Europe such as ESRF, ILL, Diamond, Alba, Daresbury, PETRA III, ISIS y Hasylab

> 90 publications

34% D1

39% Q1

73% D1+Q1
## Licences, maîtrises et diplômes d'ingénieur

Titulaire d'une maîtrise dans Sciences Chimiques Modalité Chimique Physique

Université Universidade de Vigo (Espagne)

Date d'obtention du diplôme: 21/06/2003

## Doctorats

Doctor of Philosophy/Programme officiel de doctorat en nanoscience et nanotechnologie

PhD Thermo-responsive reversible supramolecular polymers

Jury : Professeur Anthony J. Ryan et Professeur Howard Colquhoun

Université de Reading (UK)

Date d'obtention du diplôme: 12/2010

## Expérience pédagogique

Type d'enseignement: Enseignement officiel dans le cadre de ma thèse (environ 100 h/an, donc 300h d'enseignement)

Nom de la matière/intitulé du cours: Cours TD TP de pratique de laboratoire en physico-chimie

Type de programme: Maîtrise

Diplôme: University of Reading

Date de début: 05/02/2007

Date de fin: 01/06/2009

Date du dernier cours: 01/06/2009

University of Reading, Faculté, institut, centre: School of Chemistry

Département: School of Chemistry

Ville: Reading, Royaume-Uni

Langue d'enseignement: Anglais

## Direction de thèse de doctorat ou de projets de fin d'études

1. Thèse de doctorat : Carmen Moya López-Peláez

Titre "New generation of nanostructured biopolymers for additive manufacturing and electrospinning",

Co-directeur de thèse: Patrice Bourson; Daniel Hermida Merino (33%); David Chapron
Université: Université de Lorraine, Laboratoire LMOPS Metz

Date de soutenance: 01/09/2022

2. Thèse de doctorat : **Federico Di Sacco**

Titre "Polyolefin structuring during Cast Film Extrusion Polyolefin structuring during Cast Film Extrusion"

Co-encadrant des expériences synchrotron Online Polyolefin structuring during Cast Film Extrusion"

Co-encadrant de thèse sur le meausures de synchrotron: G. Portale

Université: Université de Groningen

Date de soutenance: 30/09/2021

3. Master : **Murillo Donizeti dos Santos Rosa**

Titre "Nucleação e crescimento de nanopartículas de ouro incorporado em hidrogel/ Trabajo para tener obtención del master"

Co-directeur de thèse: Jose Fernando Queiruga Rey; Daniel Hermida Merino

Université: Universidade Fedaral do ABC, Santo André, Brésil

Date de soutenance: 01/06/2021

4. Master : **Victor Cruz de Souza**

Titre "SAXS-WAXS/ EXAFS in situ studies of thermal activated nucleation and growth process of CsHSO₄ in Nafion"

Co-directeur de thèse: Jose Fernando Queiruga Rey; Daniel Hermida Merino

Université: Universidade Fedaral do ABC, Santo André, Brésil

Date de soutenance: 01/02/2021

5. Thèse de doctorat : **Sarah Saidi**

Titre "Etude multi-échelle de l'impact de l'ajout de fluoroélastomère sur la structure du PVDF par des mesures in situ couplées"

Co-directeur de thèse: Patrice Bourson; David Chapron;

Coencadrants: Daniel Hermida Merino

Université de Lorraine LMOPS Metz

Date de soutenance: 01/11/2020

6. Post-doc : **Bing Wu**

Titre: "Novel pOlymeric materials DEsigNed for drug delivery System (NODENS)/CAROLINE"

Université: Royal College of Science for Ireland

Co-encadrant Andreas Heise; Bing Wu; Daniel Hermida Merino; Kay Saalwaechter

Fin du projet: 30/09/2020

7. Post-Doc : **Carolina Hermida Merino**

Titre "Etude de gels de sources biologiques en combinaison avec des liquides ioniques"

Université de Vigo

Co-encadrant: Daniel Hermida Merino, Ana B Pereiro

Fin du projet: 31/12/2020
# Projet scientifique

I have started by scientific career by completing a Ph.D. in supramolecular polymers under the supervision of Prof. Ian Hamley and Prof. Wayne Hayes at Reading University, entitled “Thermo-responsive reversible supramolecular polymers”. My Ph.D. was focussed on the synthesis and characterization of novel thermo-responsive self-assembled supramolecular polymers. In particular, the main aim was the study of the dynamic mechanism of the self-assembly mechanism in supramolecular polymers under thermal stimuli understanding the interplay between mechanical properties and the nanostructure of these smart tuneable materials.

I then joined the DUBBLE beamline (SAXS/WAXS) at ESRF as a post-doctoral fellow from Eindhoven Technical University first and then from the Dutch Polymer Institute (DPI) to promote the research of polymer materials structure under processing conditions. I was responsible for scientific contact between the Dutch polymer groups and DUBBLE for the application of X-rays in combination with other techniques for the study of structural and morphological changes during polymerization and polymer processing.

The role involved:

* The development of new experiments to study polymer structure and dynamics with X-rays.

* Attract new DPI groups to the beamline and apply for beamtime for novel experiments.

* Local contact during the experiments at DUBBLE.

* Development of sample environment for the specific requirements of combining different techniques in combination with X-rays techniques.

* Modeling of polymer morphology.

Currently, I am employed by the Netherlands Council for Scientific Research (NWO) as the beamline scientist responsible for the Dutch-Belgium SAXS/WAXS beamline at ESRF. I am responsible for leading and coordinating beamline BM26 staff in order to design and validate new experiments. I manage the beamtime schedule. Moreover, I advise visitor scientists on experimental strategy, including support on data collection and interpretation. I ensure continuous development of novel sample environments by performing cutting edge X-rays experiments in combination with other techniques, developing my research on the structure-property relationship of novel materials of soft matter by SAXS-WAXS, GISAXS, and GIWAXS techniques.

During my scientific career, I have applied for projects to industrial and governmental grants in order to develop my research.

The fund-raising was essential to strengthen and enlarge my research activities in the different areas of the knowledge process. Through my research, I have obtained financial support to design and manufacture novel samples environments. I have been actively applying for beamtime in different synchrotrons across Europe to perform cutting edge experiments. Moreover, I have collaborated closely with leading groups in the soft matter area to successfully applied to national and international grants to fund long term research projects and thus, to fulfill independently the research responsibilities.
I will list my scientific achievements in different areas of my research activities. Particularly, herein, I will focus on the research conducted recently in my scientific career. I have selected a series of my current research projects that are presented briefly along with a significant manuscript according to the subject matter. Particularly, I expanded the updated scientific projects in collaboration with the "Université de Lorraine" as well as biomaterials with nanomedicine applications.

# 1-Understanding of the structural development of polymeric materials upon extreme conditions that mimic the industrial environment.

My main scientific aim during the postdoc period in DUBBLE was the application of time-resolved X-ray diffraction techniques for studying structural and morphological changes during polymerization and processing. Polymers undergo extreme thermal quenching and high shear rates, during processing that affects the nanostructure and thus, the mechanical properties of the final polymeric materials. The high flux and collimated beam together with the new detector technology have enabled us to perform in situ simultaneous SAXS/WAXS experiments during polymer processing to understand the parameters that govern the structural evolution upon industrial conditions (Figure 1.1). I have spent 3 months in the Department of Chemical Engineering and Chemistry of the Eindhoven University of Technology to identify scientific projects that could be benefited from X-ray characterization.

<figure><img src="image_2.png" /><figcaption>**Figure 1.1.** Pictures of in situ time-resolved scattering experiments in combination with other relevant techniques to monitor the polymer nanostructuration at extreme conditions that mimic real industrial environments</figcaption></figure>

I have participated in the investigation of both commodity polymers, as well as specialty polymers at different thermal and/or shear conditions that lead us to tens of publications in the field. Particularly, we have published a series of reviews on the area to summarized the advances on the structure-property relationship of polymeric materials under extreme conditions:

1. Giuseppe Portale, **Daniel Hermida-Merino** and Wim Bras, "Polymer research and synchrotron radiation perspectives"; European Polymer Journal (2016) (online) DOI: 10.1016/j.eurpolymj.2016.04.015

2. Anthony J. Ryan, Wim Bras, **Daniel Hermida-Merino**, Dario Cavallo; "The interaction between fundamental and industrial research and experimental developments in the field of polymer crystallization"; Journal of Non-Crystalline Solids (in press) (2016) http://dx.doi.org/10.1016/j.jnoncrysol.2016.07.039
3. Benny Luijsterburg, Peter Jobse, **Daniel Hermida Merino**, Ton Peijs, Han Goossens; *Solid-state Drawing of β-nucleated Polypropylene: Effect of Additives on Drawability and Mechanical Properties*; J. Polym. Sci. B Polym. Phys., 52: 1071–1082. doi: 10.1002/polb.23533

4. Giuseppe Portale, Dario Cavallo, Giovanni Carlo Alfonso, **Daniel Hermida-Merino**, Martin van Drongelen, Luigi Balzano, G. W. M. Peters, J. G. P. Goossens and Wim Bras, *Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF*, J. Appl. Cryst. (2013). 46, 1681–1689
<figure><img src="image_3.png" /></figure>

ELSEVIER

Contents lists available at ScienceDirect

European Polymer Journal

journal homepage: www.elsevier.com/locate/europolj

<figure><img src="image_4.png" /></figure>

Feature Article

Polymer research and synchrotron radiation perspectives

Giuseppe Portale<sup>a</sup>, Daniel Hermida-Merino<sup>b</sup>, Wim Bras<sup>b,*</sup>

<figure><img src="image_5.png" /></figure>

CrossMark

ARTICLE INFO

Article history:

Received 18 January 2016

Received in revised form 8 April 2016

Accepted 14 April 2016

Available online 26 April 2016

Keywords:

Synchrotron radiation

On-line processing

Polymers

X-ray scattering

ABSTRACT

The developments in synchrotron radiation based polymer research have been profound over the last two decades. Not only have many more beamlines suitable for soft condensed matter research become available since the pioneering days but also the technical developments with respect to X-ray beam quality and position sensitive X-ray detectors have been very substantial. This has allowed to increase the degree of experimental sophistication considerably by introducing sample environments which not only allow the materials to be studied outside of equilibrium conditions but in fact in conditions which closely start to resemble realistic processing conditions. These developments now allow polymer researchers to bring synchrotron radiation based tools to the whole spectrum from academic relevant characterisations to trying to understand the effects that desired processing parameters have on the final materials.

In this manuscript, which is not intended as a comprehensive history, it is described how the historic interplay between technical developments and the experimental desires has generated the soft condensed matter synchrotron radiation toolbox that is at present available by following some of the major areas that have been the subject of polymers in the last two decades.

© 2016 Elsevier Ltd. All rights reserved.

Contents

<table><tr><td>1.</td><td>Introduction</td><td>416</td></tr><tr><td>1.1.</td><td>Combinations of techniques</td><td>416</td></tr><tr><td>1.2.</td><td>Sample environments</td><td>417</td></tr><tr><td>2.</td><td>Commodity polymers</td><td>418</td></tr><tr><td>2.1.</td><td>Quiescent crystallization studies</td><td>420</td></tr><tr><td>2.2.</td><td>Crystallisation studies under processing conditions</td><td>420</td></tr><tr><td>2.3.</td><td>On-line chemistry</td><td>422</td></tr><tr><td>3.</td><td>Specialty polymers</td><td>423</td></tr><tr><td>3.1.</td><td>Conventional block copolymers</td><td>423</td></tr><tr><td>3.2.</td><td>Conductive polymers</td><td>424</td></tr><tr><td>4.</td><td>Developments in synchrotron sources and beamline equipment</td><td>426</td></tr><tr><td>4.1.</td><td>SR sources</td><td>426</td></tr><tr><td>4.2.</td><td>Developments in data handling</td><td>428</td></tr></table>

<footnote><sup>a</sup>Univ Groningen, Zernike Inst. Adv. Mat., Macromol Chem & New Polymer Mat, Nijenborgh 4, NL-9747 AG Groningen, The Netherlands</footnote>

<footnote><sup>b</sup>Netherlands Organisation for Scientific Research (NWO), DUBBLE@ESRF BP CS40220, 38043 Grenoble, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: wim.bras@esrf.eu (W. Bras).</footnote>
<table><tr><td>5. Conclusions</td><td>428</td></tr><tr><td>Acknowledgements</td><td>428</td></tr><tr><td>References</td><td>428</td></tr></table>

# 1. Introduction

Polymer research using synchrotron radiation based X-ray scattering beam lines has an extended history which is characterized by an ever increasing level of experimental sophistication. Where in the early day's synchrotron sources were still required to obtain simple data required for morphological and phase determination of bulk polymers we now see that this role has been taken over by home laboratory based sources which have benefitted from the improvements in X-ray generator, X-ray optics and detector technology. The polymer research area where the more powerful and well collimated X-ray beams of synchrotron sources are still a requirement for successful experiments has therefore shifted. In this we can discern two main directions in which the experiments have developed. In the first place the development of time-resolved experiments with second and sub-second time resolution and in the second place the increased spatial resolution achieved by drastically reducing the beam size from hundreds of micros to few tens of nanometers without the detrimental lack of intensity to map the structure of polymeric samples (i.e. thin films and fibers).

The commodity polymers like for instance the different polyolefins have formed an important part of polymer based synchrotron radiation (SR) research since the start. Initially this was mainly a matter of semi static characterisations where the main sophistication was that slow thermally induced structural changes could be followed with data framing rates in the minutes. The limitations here were mainly due to the available detectors which were lacking in detection efficiency, could only handle limited count rates and had rather long read-out times. Over the years this gradually improved and time framing on the order of seconds per frame became feasible [1,2].

However, the field really took off when combined small and wide angle X-ray scattering experiments (SAXS/WAXS) became routinely available. In the early years these instrumentation combinations were mainly used for determinations of phase diagrams and slow crystallization kinetics. This is to some degree still an important subject due to the better control over materials manufacturing which allows for instance to create blends from the same mother material but with a sharp bimodal distribution in the molecular weights. The improved control over tacticity and molecular weight now allows for enhanced processing pathways which can be studied on the beamlines. This requires the more specialised sample environments which can mimic the processing conditions generally encountered in the industrial context. This is not only a matter of controlling pressure, volume and temperature (P, V, T) but in general the appropriate combinations of these parameters. Although this falls outside of the traditionally named 'extreme conditions' experiments, like high pressure, magnetic field or temperature, the combined set of parameters and the time scale over which such experiments can be carried out should also qualify for the category of 'extreme conditions'. This type of experiment can now also be used to validate the simulation code of which the development has also progressed considerably over the years.

Specialty polymers only have a limited commercial market share but a disproportional large amount of experiments in soft condensed matter are dedicated to this category of materials. Whereas the emphasis of the commodity experiments has shifted towards what to do with the materials for the specialty materials a large proportion of the research is still mainly dedicated to characterisation studies. However, thanks to the earlier experimental developments in commodity polymer research, and the communal expertise build up over the years on how to perform more complicated experiments, the transition from pure academic research of specialty polymers towards actual processing can be foreseen to be much faster compared to the commodity materials. The developments in beamlines and detector technology allow the implementation of experiments with the sample environments that are required for these materials. This can range from on-line thin layer coating to fuel cells or batteries, where the operating cycle of the devices for which these polymers are intended, can be simulated.

## 1.1. Combinations of techniques

The low electron density contrast in polymeric materials was in the early years of synchrotron radiation scattering beam lines one of the main motivations to leave the home laboratory, with its Kratky camera, and make the travel to a central facility where the same static experiments could be done faster and with a higher data quality. Soon, however, it was realised that the several orders higher flux also allowed to follow the evolution of samples in time as function of external parameters [3,4].

Several years later the first successful combinations of X-ray scattering with other techniques were pioneered. In the first place the logical combination of SAXS with WAXS but at later times also with non X-ray based techniques like Differential Scanning Calorimetry (DSC) and a variety of spectroscopic methods. This was combined with an ever increasing sophistication in the sample handling. The developments in this have been reviewed several times in the past [5,6] and we therefore will not dwell on this subject for too long.

Important to realise, however, is that in contrast to the general perception the increase in available X-ray flux has not been the main stimulus for the developments described above. Although not irrelevant, once the flux has reached a threshold, increases are less relevant but the collimation of the beam becomes the more important parameter. For instance in the early days of SAXS/WAXS combinations one could not place two separate detectors at more than 2–3 m from each other
since otherwise the over-underfocus of the optics would render heavily distorted scattering patterns on one or both detectors. With the increase in collimation the focal depth of field has increased that much that it is now possible to place the SAXS and WAXS detector 20–30 m apart and place several detectors in between which allows to cover a very large scattering vector range [7]. Similar considerations can be made for the installation of more complex sample environments where the use of a small, less divergent, beam simplifies the installation considerably.

In fact the ever increasing flux densities that beamlines can generate could be seen as an inconvenience for a large body of experiments. The onset of radiation damage is in general recognisable and acknowledged but rarely reported in the literature. Therefore a comprehensive understanding of the damaging effects of X-rays, and the solutions to the problems that are caused by the interactions of X-rays with polymeric materials, is at the moment still elusive. The same is true for radiation induced modifications of materials which one maybe cannot strictly classify as 'damage'. These effects are less common and not always recognised but do occur over a large range of materials with a tendency to be more pronounced in samples containing solvents [8] or which are amorphous [9] and might play a role in crystallization experiments where crystallization nuclei could potentially be formed due to the interaction of the X-rays with the material. It is clear, however, that the tendency of X-ray beams to get brighter and smaller through the years should be handled with care for conventional polymer research.

## 1.2. Sample environments

At present there are not many valid reasons anymore for performing static polymer experiments on a synchrotron radiation source. Even though heating/cooling cycles, in time/temperature resolved experiments, are still probably the most commonly carried out experiments, the tendency has become to introduce more complicated sample environments which can bring the materials in a variety of ways out of their equilibrium. What is becoming even more common is that there is not a single parameter which is varied but that a combination of parameters is changed. One can think for instance of the multitude of shear induced crystallization experiments where during the cooling a brief shear pulse is applied and subsequently the crystallization kinetics is investigated.

Taking this a step further are the environments where one either tries to mimic industrial processing conditions, where cooling/deformation and shear are often applied partially in sequence or simultaneous, or very highly controlled experiments where accurate control is maintained over pressure, volume and temperature. Similar steps have been seen in the developments of environments for reactive processing.

With improved synthesis techniques more well defined block copolymer systems have started to be used. The fascinating self assembly properties of these molecules initially saw many studies into the fundamentals of phase diagrams as function of temperature and composition [10–12]. The time for the shift between fundamental research and more applied work [13], around 10 years, has been much shorter than the comparable time in the case of the commodity style polymers which was around 20 years. We can attribute this to both the technical developments on the beamlines, the increase in expertise how to conduct more complicated experiments and the improvements in polymer synthesis.

A similar story can probably be told for the development of organic photovoltaic cells and other organic electronics. By the nature of the applications which mainly is in the field of thin films there has been a further shift towards techniques suitable for investigating these thin layers like grazing incidence X-ray scattering. Between the advent of this field, around 2000, and present one has progressed from phase determinations to on-line roll-roll processing.

In the remainder of this text we will mainly concentrate on experiments done in the transmission geometry. This is not because the grazing incidence configuration is deemed to be less important but due to the fact that this has become field in

<figure><img src="image_6.png" /><figcaption>**Fig. 1.** Time-resolved SAXS (left panel) and WAXS (right panel) patterns obtained in a combined experiment where the PE-PEE diblock copolymers were cooled from the melt [14]. Even though the detectors and X-ray intensity in this experiment from 1995 were not of the same quality/intensity as is available at present high data quality could be achieved in time frames of 1–5 s/frame (reproduced with permission).</figcaption></figure>
itself and deserves to be treated separately. However, many research issues are tackled by a combination of both experimen-
tal configurations and where appropriate we will indicate where this is the case.

**2. Commodity polymers**

The crystallization behaviour of polyolefins and blends of different polyolefins has long been an important research area
not only because of the fundamental interest in how some of these long molecules still manage to escape the disordered
spaghetti state they form in the melt towards a much more ordered phase, but also because of the industrial background.

The kinetics of crystallization could be followed with reasonable accuracy by either WAXS or SAXS experiments. In the case of WAXS one could use the peak intensities and follow how these grew from the disordered melt. By using SAXS one could follow the increase of electron density and use this as a probe for the increase in degree of crystallinity. However, with these independent methods the details of what occurred at the very early stages, where the crystallization was initiated, remained elusive. One of the most important steps in these studies was the introduction of combined SAXS/WAXS experiments. This enabled for the first time to observe the events taking place at the different length scales that were involved.

An example of early SAXS/WAXS results is a study [14] of structure development in semicrystalline poly(ethylene)-poly (ethylethylene) and poly-(ethylenel-poly(ethylene-propylene) diblock copolymers when crystallizing from the ordered melt. Representative SAXS and WAXS data are shown in Fig. 1.

For these experiments a nominal cooling rate of 40 °C min⁻¹ was used. The main limitation with respect to the cooling rate was the thermal control of the sample and was not due to the X-ray experimental equipment. Even with the rather low count rate proportional gas detectors sufficient statistics could be accumulated in time-frame lengths of 1–5 s/frame. The derived parameters, like the scattering invariant, $Q = \int_0^\infty q^2 I(q) dq$, from the SAXS data and the integrated intensity of the most intense WAXS peak (1 1 0), $Q = \int_{q_1}^{q_2} I(q) dq$, are shown in Fig. 2.

When comparing the combined SAXS/WAXS data as obtained in the 90's with a similar experiment carried out 15 years
before we can see the improvement in data quality. For the X-ray based experiments this can mainly be attributed to the
improvements in detector quality in that period. Where once limited count rate gas wire chambers or high background noise
level CCD detectors with a limited dynamic range were used, we nowadays can benefit from photon counting pixel detectors
which combine the single photon counting capability of the gas wire chambers with the high count rate capacities of CCD
detectors but with a much improved dynamic range with respect to counting statistics.

An example of this much improved data quality is shown in Fig. 3. This shows results from a combined SAXS/WAXS/DSC/
conductivity experiment on poly(epsilon-caprolactone) to which multiwalled carbon nanotubes were added in order to form
a nanocomposite [15]. Where in the data shown in Fig. 2 certainly the WAXS data obtained in 1995 was still rather noisy,
for the experiment similar in time evolution and X-ray scattering power performed in 2014, the noise level has fallen to
insignificant levels.

What is maybe less noticeable at first sight, but certainly true in the experience of the researchers working on the beam-
lines, is the much reduced time and effort required to reduce the data and to perform the type of analysis that one requires.
Although it is deplorable that still no wide spread data package exists that is recognised to be a kind of standard, software
packages like Matlab etc. allow even less software oriented researchers to be able to extract the parameters that one wants to
obtain from a data set many times faster than was possible only a decade ago.

<figure><img src="image_7.png" /><figcaption>**Fig. 2.** The derived data obtained from the SAXS and WAXS raw data shown in Fig. 1. The scattering invariant $Q = \int_0^\infty q^2 I(q) dq$ (open symbols) and the integrated intensity of the WAXS (1 1 0) peak (closed symbols) are given as function of time and temperature. The data quality is remarkably good even though the WAXS data is intrinsically more noisy than the SAXS data.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 3.** Derived parameters from a SAXS/WAXS/DSC/calometric/conductivity experiment [15] obtained during thermal treatments of a polymer sample doped with Multi Walled Carbon Nano Tubes. (A) Thermal profile, (B) raw data, (C) derived electron density data (SAXS), (D) Raw WAXS data, (E) degree of crystallinity derived from WAXS data, (F) thermal diffusivity, (G) electrical conductivity. Data obtained with modern detectors and sample environments.</figcaption></figure>

The improvement in data quality between combinations of X-ray based experiments and non X-ray based experiments, like for instance SAXS in combination with Thermal Analysis methods, e.g. DSC, has in some areas also made great strides. DSC was one of the first sample environments/technique combinations that was utilised on line [16–18]. One of the major problems with DSC is that in order to obtain the highest quality data one requires the sample to be thermally shielded. Experimentally this is in disagreement with the requirement to have X-ray access. The higher X-ray intensity and the introduction of flash DSC type of instruments has allowed more accurate and faster experiments [15,19,20]. In Fig. 4 the right hand panel describes one of the earlier SAXS/DSC experiments with a conventional heating rate of several 10's of

<figure><img src="image_9.png" /><figcaption>**Fig. 4.** Combined X-ray scattering and thermal analysis data. The left hand panel shows the slow cooling and crystallization from a polyethylene sample [16] obtained around 1985. The right hand panel shows a similar experiment [20] using a flash DSC, well collimated beamline and efficient photon counting detectors performed in 2015. The differences in data quality are clearly visible.</figcaption></figure>
degrees/minute. In the right hand panel WAXS/flash DSC data are shown. If we keep in mind that to obtain good quality WAXS data is more difficult than to obtain a good quality SAXS invariant, a theme which we will explore in more detail, then we can see a remarkable improvement in data quality.

Many other examples of improvements, over the last decades, in experimental results on commodity polymers can be found in the literature. The main reason why this has become possible is the fact that the quality of X-ray position sensitive detector has finally come up to the level that one can fully benefit from the available synchrotron beams. The limiting step at present has become the X-ray dose that materials can handle before their physical structure and their physical/chemical interactions are being changed by the X-ray doses.

## 2.1. Quiescent crystallization studies

The development of crystallinity when pure semi-crystalline polymers are quenched below their melting temperature has long been an important subject not only because of the pure scientific interest how long chain molecules behave in such conditions but also because of the potential industrial interest. In the case of quiescent crystallization where the only parameter is the degree of under-cooling the interest is mainly fundamental since this is hardly a condition that will be encountered in an industrial processing environment where other factors like shear and the addition of different crystallization enhancers and clearing agents also have to be considered. However, the fundamental data that can be obtained is still interesting.

In this area we encounter an issue which highlights the limits to which X-ray scattering and diffraction can play a role. In the extended debate about the initial stages of polymer crystallization it was postulated that one could distinguish between a nucleation and growth model and a model by which density fluctuations would precede the crystallization event which would be some kind of spinodal decomposition process. The arguments used were that the density fluctuations would generate a SAXS intensity and this would precede the occurrence of diffraction peaks, evidencing the formation of crystalline regions, if a spinodal type of crystallization would take place. If the more conventional model of nucleation and growth would be true the SAXS intensity due to the formation of lamellae containing crystalline regions, and the diffraction peaks, would start to grow at the same time [21–24]. The early results were probably hampered by detector issues where sensitivity, efficiency and electronic noise levels all played a role. It would be a mistake, however, to assume that with the present generation of highly effective photon counting detectors [25] this issue could be settled by relying on scattering data alone. One should realise that crystallinity can exist even though it is not detected by WAXS. Very small and/or disordered crystallites with a low volume fraction will not render diffraction peaks that will be noticeable in the experimental noise. However, these will constitute volumes with a slightly different density with length scales detectable with SAXS. This will not be distinguishable from the intensity generated by fluctuations. In other words, even with the best detectors, one will always find that the SAXS intensity increases before the WAXS intensity.

It is at times puzzling to notice that one is willing to accept the fact that there are different sensitivities to crystallization effects between for instance DSC, Raman or dielectric spectroscopy [26] but that when comparing two techniques based upon X-ray interactions one immediately assumes that the sensitivities between the techniques will be identical. This also should not be interpreted as a statement that X-rays cannot play a role here since by utilising the crystallization kinetics data one can compare this with the theoretical studies and simulations [22,27,28].

An issue that has not been thoroughly investigated in this context is if the interaction of the samples with the intense synchrotron X-ray beams does not have an effect on the crystallization kinetics. In general one associates synchrotron beams with radiation damage but there is growing evidence that in disordered materials the absorption of the photons can cause unexpected effects due to the creation of electronic defects in glassy matter [9,29], hydrolysis products in solutions [8], etc. It is not unthinkable that free radical created by X-ray absorption induce cross linking between the polymer molecules and thus alter the crystallization rate.

## 2.2. Crystallisation studies under processing conditions

The introduction of large scale equipment on beamlines that could mimic some aspects of polymer processing has a long history [22,30,31]. Initially the main problem was to have the infrastructure in a SAXS/WAXS experimental hutch that allowed to install these sometimes rather voluminous sample environments on a beamline. Issues with lack of space, inflexible optical benches and lack of pressure lines and exhausts were numerous. Once these problems were sorted [22,32,33] to some degree, the main problem, in contrast to the popular belief, was not the lack of X-ray flux but the lack of suitable detectors that could handle the data at framing rates and with low enough noise levels. This had as a consequence that even though industrial inspired sample environments were used the cooling/extension rates etc. were mainly of academic interest. There they’ve played an important part in the rekindling of the fundamentals of the polymer crystallization debate [21–23,34].

In real industrial life, the crystallizing polymer melt is subjected to a combination of high cooling rates and shear forces during the most common production processes such as injection molding, film blowing and fiber spinning. These conditions are often extreme and cooling rates as high as 100–1000 °C/s and shear rates ranging from 1 to 1000 s⁻¹ can be attained. The most illustrative example is injection molding. During injection molding, the polymer is melted in an extruder and subsequently injected, into a cold mold where it solidifies acquiring the mold shape. The thermo-mechanical history to which
the polymer melt is subjected determines the formation of complex skin-core morphologies, where the formation of mesomorphic, highly oriented/highly crystalline and isotropic structures occurs simultaneously.

Due to the high cooling rates and to the enhancing of crystallization rate due to shear, the structural evolution of semicrystalline polymers in processing conditions can last few seconds. High brilliance X-ray synchrotron sources are thus a unique tool to study on-line and in-situ polymer crystallization in relevant industrial conditions, offering the possibility to perform measurements with micro and millisecond resolution. Among the other techniques, microscopy techniques are certainly valuable for visualizing in real space the final structure, but they are destructive and cannot be applied for in-situ studies. On the other hand, fast chip calorimetry can study melting and crystallization events at cooling rates well comparable to the ones find in industrial processing, however the sample quantity required for fast chip calorimetry (nanograms) is far too small be comparable with real specimen. FTIR and laser scattering can also be performed with millisecond time resolution, however they require samples much thinner than the ones used in reality. On the contrary, synchrotron X-ray scattering techniques such as SAXS and WAXD can be performed with micro and milliseconds resolution on samples with thickness ranging from microns to some millimetres. Moreover, complex sample environment mimicking real processing machines can be used.

The effect of fast cooling on polymer structure has been long studied in literature. Semicrystalline polymers are generally characterized by a certain amount of defects such as variation in chemical composition, different configuration of neighbouring repeating units and different conformation of portions of the chains. These defects hinder chain packing and a large amount of structural disorder is generated when melt is rapidly cooled below its melting temperature. The highly defective structures generated in these conditions are intermediate between the crystalline and amorphous ones and are usually called mesomorphic phases, or simply mesophases. Mesomorphic phases have been observed for a large number of homopolymers such as iPP [35–37] polyamides [38] and polyesters [39,40] Due to its industrial relevance, iPP mesophase is one of the most studied and well characterized. Though the observation of mesophase occurrence can be achieved by off-line X-ray diffraction of a polymer quenched from the melt, observation of mesophase development in real time is a more challenging task. Traditionally, mesomorphic structuring from the melt has been studied by calorimetric techniques. Wunderlich et al. [41] showed first the occurrence of the mesophase between 60 and 0 °C in iPP when cooled at 70 °C/s. For polymers characterized by high crystallization rates and low degree of defects, it is however difficult to obtain pure mesophase using conventional calorimetry. Cooling rates as high as –4000 °C/s can currently be achieved by using the so-called fast chip calorimetry [42,43]. However, calorimetric techniques cannot provide directly information about what phases develop and off-line spectroscopic or diffraction measurements are required. Moreover, quantitative analysis always requires the knowledge of thermal data from pure phases. On the other hand, X-ray diffraction experiments during fast cooling would provide quantitative and exhaustive information on phase formation.

With the very high cooling rates mentioned above, and realising that, in the industrial context, this also will be accompanied by preceding shear and rapid volume changes we remind the reader here about the statement in the introduction regarding the study of extreme conditions. Not a single parameter is changed very rapidly here but a combination of several.

It is only in the last 5 years that real time X-ray diffraction during ultrafast cooling became feasible thanks to the development of ultrasensitive noiseless X-ray detectors for synchrotron radiation and thanks to the development of novel sample environments [44]. The first real time detection of iPP mesophase using WAXD has been reported by Cavallo et al. in 2010 [45] using a simple and effective apparatus to produce ballistic cooling with cooling rates from 20 °C/s to 300 °C/s. This simple approach allowed the authors to follow the polymer structuring process during fast cooling by simultaneous thermal and X-ray analysis. Moreover, by using the so-called continuous cooling curve (CCC) diagrams, the time and temperature coordinates for the formation of the mesophase with respect to the most stable phase can be identified clearly [45]. Fig. 5a shows the temperature directly measured inside the sample together with the evolution of the crystallinity calculated from WAXD during a ballistic non isothermal cooling experiment. Deviation of the sample temperature from the natural cooling curve reveals sample crystallization. Thus the derivative of the sample temperature, i.e. the instantaneous sample cooling rate, shows a peak at the crystallization temperature. Comparing the instantaneous cooling rate with the crystallinity evolution as a function of time or temperature demonstrate that the peak in the thermal analysis curve occurs at the maximum rate of phase formation (Fig. 5b). By cooling at different rates iPP and propene/ethylene random copolymers with increasing

<figure><img src="image_10.png" /><figcaption>**Fig. 5.** (a) Comparison of the instantaneous sample temperature and the X-ray crystallinity developed during cooling at 30 °C/s as a function of time. (b) Comparison of the instantaneous sample cooling rate and the X-ray crystallinity developed during cooling at 30 °C/s as a function of sample temperature. (c) CCC diagrams for propene-ethylene random copolymers. (black circles) pure iPP, (grey circles) 3.4% of ethylene counts, (open circles) 7.3% of ethylene counts, (open circles). (a) and (b) are reprinted with permission from [45] and (c) is adapted with permission from [46].</figcaption></figure>
ethylene co-unit content and plotting the temperature when the maximum rate of phase formation is attained versus time CCC diagrams can be constructed (Fig. 5c). The CCC diagrams in Fig. 5c have a double “nose” shape, with the top region related to the formation of the most stable alpha form and the bottom region related to the mesophase formation. Given a certain cooling history, the prevailing structure that will form can be predicted from the CCC diagrams.

This approach has been successfully applied also to polyamides [47] and polyesters [48].

Most recently, simultaneous fast chip calorimetry (flash DSC) and WAXD measurements also became feasible making possible quantitative analysis of polymer structuring at even higher cooling rates and also isothermal experiments after rapid quenching that could not be performed using ballistic devices [20].

The other important parameter in industrial polymer processing is flow. The effect of flow on polymer crystallization during polymer processing is dramatic and flow-induced crystallization is a complex phenomenon that is still extensively studied nowadays. Application of flow to a polymer melt can cause substantial transitions in kinetics and morphology of the polymers. The well-known shish-kebab morphology is often formed during flow-induced crystallization where long crystalline fibers (shish) serve as nuclei for further crystallization of lamellae growing perpendicularly to the fibrils (kebab).

Shearing apparatus using slit flow geometry have been recently developed in order to elucidate the mechanism of formation of thread-like precursors, shish and kebabs in real time [49,50]. These machines allow to reach the high stress regime with well-defined flow conditions and closely mimic industrial conditions. In-situ WAXD and SAXS measurements during and after flow in the high flow regime showed that not only thread-like precursors but even elongated crystalline fibers can be formed during quite short flow pulses, resulting in a dramatic viscosity change [51]. Due to the pressure that builds up during the injection phase in injection molding, polymer structuring is also expected to be influenced by pressure. This has been recently demonstrated experimentally for linear low-density polyethylene (LLDPE) [52].

Thanks to the possibility to host large apparatus in a synchrotron beamline, extruders, fiber spinning apparatus and even very large film blower can be used to collect online data during a polymer processing experiment with conditions virtually equal to the ones encountered in industry. For instance, the structural evolution during melt spinning of polyethylene, nylon and PVDF has been extensively studied in the past using both SAXS and WAXS [31,53]. Recently, systematic data on the LLDPE structural evolution during film blowing have been produced by SAXS and WAXD [54,55]. See Fig. 6.

In order to be able to install large scale sample environments like the film blowing unit shown in Fig. 6 the experimental infrastructure to handle this should be available. There are only a few SAXS/WAXS beamlines where this is the case and for future generations of beamlines, when one intends to carry out a program in polymer processing, one is well advised to make this infrastructure part of the initial design. The experimental hutch should for instance be large enough to accommodate encumbering machinery as well as possess motorised dispositives such as cranes, linear stages, goniometers and cradle motors that are able to handle heavy instruments. Moreover, exhausting systems are required to conduct safely synthesis in situ involving gases. For SAXS experiments, extra care should be taken to reduce the air absorption/scattering and specially customized exit/entrance windows should be designed to limit the air gap, whilst still hosting large equipment around the sample (see the shallow 60 cm long cone of the SAXS vacuum line in Fig. 6).

## 2.3. On-line chemistry

The synthesis of novel materials is commonly hampered by the lack of knowledge on the fine control of complex synthetic steps. A chemical synthesis is a thermodynamic system that involves generally several chemical reactions of reagents

<figure><img src="image_11.png" /><figcaption>**Fig. 6.** Film blowing unit installed on beamline BM26A at the ESRF [56]. 1-blown film, 2-fedding hopper, 3-extruder, 4-film blow die, 5-X-ray beam, 6-WAXS detector, 7-SAXS detector. This set-up was used to collect data on the structural evolution of LLDPE [55,57]. With the appropriate infrastructure in place this type of sample environment can be installed in a couple of hours.</figcaption></figure>
with subsequent intermediates as well as their different relationship with the synthetic medium. Commonly, the monitoring of the chemical synthesis is predominantly followed by sampling aliquots and offline spectroscopic techniques and frequently focused on kinetic studies. However, online structural investigations are crucial in order to understand the dependence of the final product on the mechanism of formation.

Great efforts have been carried out to develop novel X-ray cells that permit the monitoring in situ by simultaneous SAXS-WAXS experiments in combination with other techniques such as FT-IR spectroscopy to elucidate the dependency of the phase separation onset and the reaction kinetics [58].

Particularly, polymer science has significantly advanced along with the development of the X-rays cells for synchrotron studies as provides time resolved structural information during that mimic real polymer processing extreme conditions.

Hydrogen bonding was considered to drive the phase separation in segmented polyurethanes as studied by FT-IR. However, in situ SAXS experiments in combination with FT-IR of a series of polyurethane reactions have been shown that free energy of mixing as the molecular weight increased led to the microphase separation morphology that preceded the kinetics of hydrogen bonding formation [58].

Reaction injection molding (RIM) [59] is a widely employed operating method in the industry of a wide broad of segmented block copolymers such as copolyurethanes [60], copoly(urethane-urea)s [61,62], copolyureas [63–65] and copoly(ether-amide)s to generate complex polymer elements in a fast and malleable processing routine. The polymer reaction by RIM comprises concomitantly phase separation, crystallization and cross-linking of the copolymer obtained as a kinetic competition that defined the development of the final structure [66]. The initial low viscosity monomers mixture reacts instantly that subsequently develops from a glassy solution during the mold filling as a result of the cross-linking of the ongoing copolymerization to a highly cross-linked stiff polymer material. In situ structural investigations of the morphology development of a RIM copoly(iscyanurate-urea) reaction by SAXS have shown that at a critical isocyanate conversion a microphase separation transition occurred [67]. The growth of the microphase separation has been found to progress by a spinodal decomposition and deterred by the glassy polyisocyanurate phase. Similarly, the polymerization of water-flown flexible polyurethane foams have been investigated by in situ SAXS experiments as well as by FT-IR spectroscopy and rheology [68]. The concomitant synthesis of a polyether polyol and water with diisocyante lead to a homogenous solution of reagents, homopolymer, hard segment segments and water reacted isocyanate mixture [69]. The complex system was simultaneously blown by the release of CO₂ of the water-diiasocyanate into a foam and thus, maintaining the core of the foam in quasi-adiabatic state. The microphase separated morphology evolved through a spinodal decomposition following a time dependent Ginzburg-Landau model that was detained at a glassy state when the Tg of the complex system attained the reaction temperature, the so-called Berghmans point. As a result, the vitrification of the reaction system deterred the foam expansion [69].

Recently, supercritical CO₂ (sc-CO₂) has largely been employed as a green reacting medium that offers advantages to traditional organic solvents. Sc-CO₂ is inexpensive and recoverable after use that eliminate the need for tedious drying steps and it is also inert to free radical reactions. However, the lack of solubility of most of the block copolymer in sc-CO₂ has prevented the applicability in industrial polymer applications. Dispersion polymerization of block copolymers in one pot synthesis in sc-CO₂ by reversible addition-fragmentation chain-transfer (RAFT) have shown to be an easy alternative method to produce microparticules with a wide array of internal well-defined structures [70]. However, the nature of the reacting medium (high pressure) have limited the understanding of polymerization kinetics, morphological development mechanism as well as phase behaviour of the block copolymer obtained in sc-CO₂.

Several block copolymers synthesised by dispersion polymerization in sc-CO₂ in which one of the blocks was consistently poly(methyl methacrylate) (PMMA) whilst the second block differed in CO₂-philicity have monitored by SAXS experiments [71]. The obtained morphology has been found to shift on the predicted phase diagram depending on the CO₂-philicity of the second block. The difference in CO₂-philicity defined the absorption of CO₂ by the different blocks that leads to the formation of kinetically-trapped morphologies.

Obviously also in the study of structure formation by on-line chemistry one will look for the opportunities to push the boundaries farther. For very fast reactions one probably has to revert to microfocus techniques and stop flow or ballistic coalescence of bubbles containing the reagents [72–74]. However, there are two issues that one should take into consideration here. The first one is the possibility that too high a local radiation dose can influence the chemical reactions. The second issue is that the reduction in size might render results that might be less relevant in an industrial context. The first issue requires conscientious cross checks to eliminate artefacts. The second should be assessed on a case to case basis and definitely should not stop one performing experiments which have mainly academic interest.

### 3. Specialty polymers

#### 3.1. Conventional block copolymers

The morphological richness which is displayed by block copolymers is by now well established. Where in the 90's synchrotron radiation SAXS/WAXS was an excellent tool for the determination of phase diagrams [10,11] the developments in beamline instrumentation pioneered with the polymer processing experiments, in combination with improved synthesis control, have created the know-how and materials that allows the transition from characterisation to processing to be
speeded up manifold for this class of materials. As an example of this recent developments in polymeric organic conductors and semiconductors in combination with synchrotron radiation beamlines will be discussed more extensively in the next section. However, the developments discussed in the next section are not limited to conducting systems but parallel developments on specialised processing to other specialty polymers start to appear more abundantly [75,76].

Another important development, due to the area in which these organic materials might be used, like electronic components, but above all like cheap devices for energy generation, the emphasis in this area is also shifting from the bulk characterisation and processing, to more thin films. The developments in grazing incidence scattering, both technical as well as in data analysis, which in the early years were quite slow [77] have in recent years been very fast [78].

## 3.2. Conductive polymers

The global need for energy stimulates the development of new technology to extract more efficiently energy from renewable sources. Among the different renewable sources, solar energy represent a fabulous opportunity with its estimated energy potential of 23,000 TW/year. Solar energy can be converted into electricity using photovoltaic devices. Despite the higher efficiency of silicon based photovoltaic devices, organic photovoltaic devices (OPVs) represent an interesting alternative due to their low cost and easy processing and have received massive attention in the last years. Among the OPVs, polymer based OPVs are particularly interesting as they allow easy fabrication and integration of the photoactive polymer layer into light-weight and flexible substrates, also made out from polymers like PET.

The most classical polymer based OPV, is the bulk heterojunction (BHJ) OPV device. Here, the active layer is composed by a blend of a semiconducting polymer that acts as electron donor and a small molecule with function of electron acceptor. The fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester known as PCBM is usually used as electron acceptor, whilst poly(3-hexyl thiophene) known as P3HT is the mostly used electron donor polymer. Other polymers are also used such as poly(diketopyrrolopyrrole) (DPP) [79] or poly(benzothiadiazole) [80] based derivatives an efficiency of the order of 10% have been reported [81].

In order to achieve high efficiency, two aspects of the active layer have to be considered: (i) the chemical structure of the acceptor and donor materials and (ii) the characteristic length scale of the local morphology. The chemical structure has to be fine-tuned such that the highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) levels allows the material to achieve a high open-circuit voltage with a small energy bandgap, whilst maintaining a LUMO level high enough for efficient charge separation [82]. On the other hand, due to the very limited diffusion length of the exciton (about 10 nm), a local morphology with characteristic length scale of the order of 10–20 nm and with a large interface between the donor and acceptor materials is desirable. Thus, the study of the nanostructure of the active materials is crucial to understand and establish the structure-property relationship in OPVs.

Several microscopy techniques have been employed to visualize in real space the structure of OPV materials. In particular bright-field TEM [83] and 3D electron tomography have showed the network nature of the active material composed by PCBM and crystalline P3HT interpenetrated domains [84]. On the other hand, scattering techniques can be successfully used to investigate the morphology in OPV in the range of 0.1–100 nm. Due to the thin film nature of the OPV active layer (typically 100–200 nm), the use of transmission SAXS remains quite limited [85] and surface sensitive scattering techniques such as GISAXS and GIWAXS have proven to be the best techniques to investigate the active layer morphology [86]. Moreover, GISAXS/ GIWAXS data acquired using 2D detectors offer the possibility to extract from one single image information about the structure of the conjugated polymer (i.e. lamellar), the size of crystallites, the degree of crystallinity and the orientation of the crystalline domains [86,87]. Static GISAXS/GIWAXS are nowadays routine techniques to study the structure of the OPV active layer. Fig. 7 shows the connection between the structure and the GIWAXS patterns for a typical pi-conjugated polymer with lamellar-like structure. It is clear how sensitive is a GIWAXS measurement to the mosaicity of the thin polymer film. From the orientation of the diffraction peaks, especially the 100 reflection for the P3HT lamellar structure, the average orientation of the P3HT crystals in the thin film can be extracted (edge-on or flat-on configuration).

Advanced methods to measure with extract the full pole figure for the conjugated polymer crystals in grazing incidence geometry has been developed [89]. When performed at synchrotrons, GISAXS/GIWAXS can be used to study in real time the process of structuring of the active layer.

Initial real time studies of the structure development of the active layer morphology have been conducted during film drying of P3HT/PCBM(reference of Docsh group) as well as pDPP/PC71BM (where pDPP is a copolymer of diketopyrrolopyrrole and quaterthiophene) by the group of Russell [90] and during a roll-to-roll coating prototype process of P3HT/PCBM [91,92].

The final structure of the polymeric materials during the formation of thin layers from solution is a complex multistage mechanism that involves concomitant physical and chemical processes.

During solvent casting of pDPP/PC71BM from a 1,2-dichlorobenzene: chloroform (DCB:CF) 1:4 w/w solution, four different stages have been observed [90] (see Fig. 8c). Firstly, The onset of pDPP precipitation/crystallization during CF evaporation occurs whilst PCBM is still completely dissolved (appearance of the 100 diffraction signal). Further crystallization of pDPP into a better defined semicrystalline fibrillar network (increase in the scattered GIWAXS and GISAXS intensity, see Figure). pDPP crystallization forces segregation of PCBM to form a phase segregated structure with better defined scattering entities. Finally the phase separation becomes more and more enhanced and the crystalline structure more perfect. Similar multistage process for the phase separation are believed to occur during spin coating [93]. The evolution of the structural
<figure><img src="image_12.png" /><figcaption>**Fig. 7.** Overview of the structural information that can be extracted from GIWAXS images. (i) Random crystallites orientation; (ii) crystallites with partial orientation; (iii) crystallites highly oriented with the (0 0 1) plane parallel to the substrate. Reprint with permission from [88].</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Fig. 8.** In situ GIWAXS (a) and GISAXS (b) of pDPP and PC71BM blends processed from a DCB:CF solvent mixture. (c) Summary of the in-situ GIWAXS and GISAXS results during solvent evaporation. Adapted with permission from [90].</figcaption></figure>

parameters, the extent of phase separation and the final morphology are strongly influenced by the presence of co-solvent [94], composition of the starting solution [93] and processing conditions [95].

GIWAXS data acquired during a fast combinatorial study on a pre-coated tape produced using a roll-to-roll process showed that a critical concentration of P3HT in the drying film has to be reached before P3HT crystallization sets in (see Figs. 9 and 10) [91].

Representative results obtained with the experimental set-up depicted in Fig. 9 are shown in Fig. 10. The effect of adding a high boiling point co-solved such as orthodichlorobenzene (ODCB) to a drying P3HT/chloroform solution during roll-to-roll processing has been elucidated (see Fig. 10a and b). As expected, the drying process is slowed down significantly as a result of the ODCB addition and P3HT crystallization is significantly delayed and higher P3HT crystalline degree could be attained at the end of the drying (Fig. 10b). The onset of P3HT crystallization changes from 0.6 s to 18 s due to the ODCB presence. PCBM addition further delays the P3HT crystallization, as the time for the P3HT to reach the critical concentration for its crystallization is delayed [92] At the same time, PCBM has a negative effect on the P3HT crystallization and lower crystallinity is obtained (Fig. 10c).

Other in-situ GISAXS/GIWAXS works have been conducted during in-situ GISAXS/GIWAXS works during spin coating [93], blade-coating [96] slot-die coating [97] and during printing [98].

In-situ synchrotron GISAXS and GIWAXS investigation have helped researchers to understand what the mechanism of structuring during film formation is and provided crucial information on what is the best formulation of the starting solution and how to control solvent evaporation to achieve the optimized morphology for the best power conversion performances.

Whilst all the above cited works have showed the feasibility of synchrotron GISAXS/GIWAXS experiments during processing, structural investigation during real processing conditions (namely industrial roll-to-roll process) is still a challenge. The feasibility of these studies has been showed already [91,92] and, soon, structuring of the OPV active layer in real processing conditions will be unrevealed. GISAXS and GIWAXS remain probably the most versatile and powerful techniques to study organic semiconductors in thin films.
<figure><img src="image_14.png" /><figcaption>**Fig. 9.** Panel (a) shows the physical set up for a roll to roll printer installed on beamline 7.3.3. at the Advanced Light Source (ALS, Berkeley) [119]. Panel (b) shows the overall lay-out for in-situ GISAXS/GIWAXS investigation of the experiment with respect to the X-ray storage ring.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>**Fig. 10.** Summary of the in-situ GIWAXS results during drying in a roll-to-roll processing express in terms of relative P3HT concentration. The top panel shows the integrated intensity of the (100) WAXS diffraction peak. The middle panel shows the coherence length derived from the WAXS data. The bottom panel shows the shift of the (100) diffraction peak as function of concentration. Adapted with permission from [91].</figcaption></figure>

# 4. Developments in synchrotron sources and beamline equipment

## 4.1. SR sources

One of the questions that one can ask is if there is still a future for synchrotron radiation based polymer research? The developments in conventional X-ray sources, for instance using liquid metal targets [99] and focussing optics [100] have brought very highly performing systems to the home laboratory. Although not at the level yet of what SR sources can do this has reduced the number of required visits for routine experiments to SR beamlines considerably. Alternative X-ray sources based upon strong pulsed laser systems have seen developments in recent years as well. There are several different schemes which can be used but these are for the moment still lacking in the required low beam divergence required for scattering and diffraction although for imaging purposes some of these methods are already well suitable [101,102]. Since the underlying physics of these X-ray generation techniques has been worked out it probably will become an engineering effort to increase the beam quality. This, in combination with the requirement to develop user models instead of prototypes, set up a sales and after sales organisation and bring down the price to a level that it is affordable for a university department or industrial laboratory will require probably around 10–15 years. The beam quality, with respect to intensity and divergence, that probably will be achievable, will be comparable to a second generation synchrotron radiation source [32,103,104].

Another perceived 'threat' is the development of Free Electron Lasers (FEL's). For some these are seen as the snake oil for every experiment but in reality these facilities are unlikely to play a role in the present materials science research setting due to the too high temporal flux which will make time-resolved experiments slower than the nanosecond level impossible since the samples will be destroyed in that time scale. The fact that we can study a chemical reaction on the nano-femto second time scale is very interesting as such but hardly relevant for, among else, polymer crystallization and deformation.
The developments in detector technology in recent years are nearly as astounding as the progress made with the X-ray sources. Where efficient high count rate position sensitive detectors were less than a decade either Charge Coupled Devices which suffered from read out noise [105] or gas based chambers which required elaborate gas handling systems [106], these have virtually now all been superseded by the hybrid pixel detectors [107,108] which offer both high count rate as well as single photon counting. Even though the pixel sizes are still relatively large one can expect this issue to be tackled by the manufacturers in the near future and then these detectors will also be usable for microfocus experiments. Although these developments have also been useful for conventional lab set ups, the synchrotron beamlines have benefitted most from the increased detector efficiency and count rate due to the fact that the disparity between the number of to be detected photons and maximum detector count rates was higher on SR beamlines than in home laboratory set ups.

In the meantime the introduction of more complex sample environments increased the demand for access by a larger number of research groups which are still benefitting from the higher flux and better collimation of even the best conventional X-ray sources.

Further developments of the X-ray sources with respect to photon flux can be made possible by the SR machine and beamline developers but it becomes questionable if this should be the main driving force for developments. During a materials science experiment lasting beyond several minutes the radiation load on samples can easily exceed the maximum dose rate during beyond which the samples either are damaged to a sufficiently large degree that the experimental results are not representative of the samples any more or that structure formation is influenced by the creation of a larger number of crystallization nucleation sites [8,29] or by cross linking which even becomes apparent when measuring thermodynamic data [109].

If we take the above considerations into account it appears that for the foreseeable future (i.e. 8–10 years) the difference in beam quality between SR beamlines and home laboratory sources will ensure the need for synchrotron beam lines for X-ray scattering and diffraction of soft condensed matter systems even though the quality of both home sources as well as SR sources have increased over the years. The X-ray flux threshold required to be able to do time-resolved experiments, which is a combination of X-ray flux, X-ray contrast and required time resolution and statistical data quality, is for some slow experiments and with specific samples reached even with home sources. For fast experiments, weak scatterers and when using complicated sample environments this is not reached yet and maybe will remain elusive even in the coming years.

Since sample preparation methods have become more elaborate there is a tendency not only to take a look at the finished materials and the processing but move research forwards in the production time line where the materials are being synthesized. Since this synthesis often entails catalysts with active metallic sites it can be foreseen that techniques like X-ray Absorption Spectroscopy (XAS) which can shed light on the changing electronic environment around these metallic sites, will gain in popularity as well. This might be in combination with the scattering techniques which can simultaneously render more structural information [110]. XAS experiments, which in soft condensed matter research took many hours for each scan years ago [111,112], can now be done in minutes. This offers promises in for instance the area of supramolecular chemistry. See Fig. 11.

Especially when such spectroscopic techniques can be combined with techniques that can render structural information like SAXS and WAXS, or other non X-ray based experimental approaches, this has the promise to become a new area in polymer and soft condensed matter research [110,112,113].

X-ray spectroscopy using soft- or tender X-rays, with photon energies <5 keV, are benefitting at present from the development of some new beamlines and are very useful in the elucidation of more complicated structural issues in block copolymers [114]. Developments in this area are unfortunately limited to the synchrotron radiation laboratories specialised in soft X-ray generation which are much less in number than the storage rings generating hard X-rays.

<figure><img src="image_16.png" /><figcaption>**Fig. 11.** An X-ray Absorption Spectroscopy scan from a Ruthenium containing soft condensed matter sample. This kind of data can be used to shine light on the coordination of metallic complexes with the surrounding organic medium. The graph shows the data and the inset the derived data. These experiments using reasonable time scales and X-ray doses were hardly feasible 10 years ago but have moved into the realm of reality in the last number of years.</figcaption></figure>
## 4.2. Developments in data handling

An emerging trend in the handling of data is to combine experiments, both as a post experiment analysis technique as well as in real time, with numerical simulations. The tremendous increase in available computing power in the last decade has enabled this [115]. Although such attempts are tempting, and this path should definitely be investigated, there are also risks inherent to this approach in that it is most unlikely that this can be done in a completely model independent fashion.

Other promising approaches, which are still on the primary data side, are attempts to co-analyse the data obtained from different techniques instead of considering these data sets as independent data sets and only combine them after the full analysis on both techniques is done [116,117].

Inspired by experiments that can be performed on Free Electron Lasers one can also imagine some progress using fluctuation scattering [118]. Such approaches, just like protein solution scattering however, should be developed with a clear understanding of the theoretical limitations of the information contents of the scattering data as well as how the convolution of the theoretical mathematical world intersects with the real data world where data points have error bars, background subtraction issues and non ideal detector systems.

## 5. Conclusions

With respect to the commodity polymers one can draw the conclusion that over the last twenty years the emphasis of research has shifted from the more academic studies towards experiments which are more application directed. In this we can think of the approaches where very controlled, with respect to molecular weight, or molecular weight distributions, and well characterized samples are brought into environments where the parameters like pressure, shear, thermal quenches and volume can be set in such a fashion that industrial conditions are mimicked.

For the non-commodity polymers the time-line between the initial characterisations and phase diagram determinations towards these materials under operando, in devices, or in processing conditions, can be much shorter. The available instrumentation has much improved in recent years but also the collective experience of performing SR based experiments among polymer researchers has grown thanks to more beamlines becoming available and the passing on of the expertise from the pioneers towards new generations of students.

Grazing incidence scattering has shown to be a powerful tool in the studies of block copolymer films. Where in the early years [77] both the technical as well as software developments in this area were rather slow in the last decade this has accelerated considerably [78]. With the ever increasing world energy consumption and the high interest there is in energy generation in which these OPV blockcopolymers potentially it looks like two developments have come together at the right time. It might be interesting to see for future students of the history of technological development whether these were indeed separate developments or if the interplay between X-ray scattering technology and specialty polymer processing needs had been the main driving force.

## Acknowledgements

Although the emphasis of the examples given in this manuscript are centered around examples from the beamlines that we are best acquainted with we would like to acknowledge the fact that the communal expertise both in the international polymer community as well as in the synchrotron instrumentation community has grown at a very fast pace in the last decades. We gratefully acknowledge collaborations and inspirations regarding instrumentation developments with Gerrit Peters, Han Goossens, Han Meijer, Dario Cavallo, Alex Hexemer, Cheng Wang, Nick Terrill, Tony Ryan, Patrick Fairclough, Oleg Mykhaylyk and many others. The Dutch Polymer Institute is gratefully acknowledged for the financial support for DHM in specific and the long term support in general.

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<figure><img src="image_17.png" /></figure>

Giuseppe Portale graduated and received his PhD in chemistry from the University of Rome "La Sapienza". After a PhD in polymer physics using synchrotron radiation, he moved to the ESRF for a post-doc funded by the Dutch Polymer Institute (DPI) in 2006 to develop new experiments to study polymer structure and dynamics with X-rays. In 2009 he became beam line scientist for the Netherlands Organization for Scientific Research at the ESRF, where he was the responsible for the SAXS/WAXS BM26B beam line. From 2015, he is Assistant Professor at the Zernike Institute for Advanced Materials in Groningen where he leads the group of polymer physics with focus on the structure-property relationships in polymers for energy applications and in organic/inorganic hybrid systems.
<figure><img src="image_18.png" /></figure>

**Daniel Hermida-Merino** received his Master of Science in Chemistry at the University of Vigo. He completed a PhD in supramolecular polymers under the supervision of Prof. Ian Hamley and Prof. Wayne Hayes at Reading University. He then joined the ESRF as a post-doctoral fellow from Eindhoven Technical University first and then from Dutch Polymer Institute (DPI) to promote the research of polymer materials under processing conditions. Currently, He is employed by the Netherlands Council for Scientific Research (NWO) as the beamline scientist responsible of the Dutch-Belgium SAXS/WAXS beamline (BM26b) at ESRF.

<figure><img src="image_19.png" /></figure>

**Wim Bras** is a physics graduate from Groningen University (Netherlands). After graduation he was employed by the Netherlands Council for Scientific Research (NWO) to work as a beam line scientist in Daresbury Laboratory (UK). Based on his work there he obtained a PhD from Liverpool John Moores University. In close collaboration with the polymer groups from Tony (AJ) Ryan an extensive portfolio of experimental possibilities for soft condensed matter and X-ray scattering was created. After 7 years he was transferred by NWO to the ESRF in Grenoble to construct a new beamline for the DUBBLE project and then appointed as project leader. For the last 10 years he also has spend two months per year in Lawrence Berkeley Lab as advisor and visiting scientist with the X-ray scattering beamlines.
## 2-Investigation of the internal nanostructural development of block copolymers polymerization under polymeric sc-CO₂.

The investigation of novel block polymers possesses great interest to enlarge the number of tuneable applications arising from the nature of their self-assembly. Block copolymer synthesis has become simpler in recent years as a result of the advent of controlled radical polymerizations. Simple methodology, combined with industrially relevant conditions, lead to more widespread applications. Supercritical carbon dioxide (sc-CO₂) is an environmentally "Green" solvent with unique properties such as considerable changes in solvent density achieved by changing the temperature and pressure. The medium has been exploited extensively for a wide range of polymerizations, but especially for dispersion polymerization.

The nature of sc-CO₂, its low dielectric constant and low polarizability per unit volume, results in low solubility potential of many polymers which can be exploited for dispersion polymerization. A new route to block copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization in a dispersion polymerization in supercritical CO₂ has been developed in order to afford the growth of the microparticles with internal structure in sc-CO₂. will be able to resolve the incipient morphology of the microparticle system, especially the internal structure, as a result of the contrast matching. Also, I have gained an insight into the structural changes that occur upon temperature and pressure modification. Understanding complex systems in sc-CO₂ is crucial for its employment as an alternative green solvent. Polymer synthesis with blocks with different CO₂phicity has been carried out to understand the effect of the different affinities to sc-CO₂ has an impact on the phase diagram of the block copolymers during the polymerization. However, there was a lack of knowledge on the morphological evolution during the polymerizations as a result of the synthetic conditions that deter the understanding of the parameters that affect the final morphology. I have firstly designed a novel X-ray vessel to allow the study of chemical reactions upon sc-CO₂ together with the group of prof. Steven M. Howdle at Nottingham University (see Figure 2.1). Consequently, I have been a visiting scientist in Howdle's groups in order to gain a deep understanding on the polymerizations in sc-CO₂ as well as sharing my expertise in X-ray experiments to manufacture the X-ray vessel. Moreover, I have spent a month in the Physical Chemistry and Soft Matter department of Wageningen University under the supervision of prof. Martien Cohen Stuart in order to prepare offline future experiments at the synchrotron.

<figure><img src="image_20.png" /><figcaption>Figure 1. Time-resolved in situ SAXS data collected during the chain extension of PMMA(31) to form PMMA(31)-PS(25) (experiment 5) via dispersion polymerisation in TEM scCO₂ b) Post mortem samples</figcaption></figure>
Figure 1.2. Summary of the polymerization of block copolymers under sc-CO2 in a novel X-ray vessel.

High impact papers were published to follow the technical manuscript about the design and manufacturing of the X-ray vessel designed for conducting the polymerizations in situ.

Publications of the Project :

1. Daniel Hermida-Merino, Giuseppe Portale, Peter Fields, Richard Wilson, Simon P. Bassett, James Jennings, Martin Dellar, Cedric Gommes, Steven M. Howdle, Benno C. M. Vrolijk, and Wim Bras; "A high pressure cell for supercritical CO2 on-line chemical reactions studied with x-ray techniques"; Review of Scientific Instruments, **85**, 093905 (2014), DOI: http://dx.doi.org/10.1063/1.4895717.

2. David Alaimo, Daniel Hermida Merino, Bruno Grignard, Wim Bras, Christine Jérôme, Antoine Debuigne, Cedric J Gommes: Small-Angle X-ray Scattering Insights into the Architecture-dependent Emulsifying Properties of Amphiphilic Copolymers in Supercritical CO2. The Journal of Physical Chemistry B 12/2014; 119(4), DOI:10.1021/jp5086558

3. J. Jennings, S. P. Bassett, **D. Hermida-Merino**, G. Portale, W. Bras, L. Knight, J. J. Titman, T. Higuchi, H. Jinnai and S. M. Howdle; *"How does dense phase CO2 influence the phase behaviour of block copolymers synthesised by dispersion polymerisation?"*; Polym. Chem., (2016) 7, 905-916; DOI: 10.1039/C5PY01823.

4. Mohammad Alauhdin, Thomas M Bennett, Guping He, Simon P. Bassett, Giuseppe Portale, Wim Bras, **Daniel Hermida-Merino***, Steven M Howdle: *Monitoring Morphology Evolution within Block Copolymer Microparticles during Dispersion Polymerisation in Supercritical Carbon Dioxide: A High Pressure SAXS Study*. Polymer Chemistry 12/2018; 10(7), DOI:10.1039/C8PY01578C.
<figure><img src="image_21.png" /></figure>

Cite this: Polym. Chem., 2019, 10, 860

# Monitoring morphology evolution within block copolymer microparticles during dispersion polymerisation in supercritical carbon dioxide: a high pressure SAXS study†

Mohammad Alauhdin,‡ª Thomas M. Bennett, ID‡ª Guping He,ª Simon P. Bassett,ª Giuseppe Portale, IDc Wim Bras, IDd Daniel Hermida-Merino*b and Steven M. Howdle ID*ª

Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerisation in supercritical carbon dioxide is an effective process for creating block copolymer microparticles with internal nanostructures. Here we report an alternative synthesis route involving completely independent steps by exploiting the livingness of RAFT-terminated PMMA microparticles and their unique ability to be redispersed in scCO₂. This not only enables a series of block copolymers to be created from a single RAFT dispersion synthesised PMMA homopolymer batch, thus improving reproducibility, but also adds flexibility by allowing the time and concentration requirements for each stage to be decoupled. The internal morphology development and evolution for a series of poly(methyl methacrylate-*block*–styrene) (PMMA-*b*–PS) block copolymer microparticles synthesised *via* this route was monitored *via* in situ small-angle X-ray scattering (SAXS) using an autoclave with diamond windows. Together with offline kinetics experiments and post-mortem transmission electron microscopy imaging, this study provides remarkably detailed insights into block copolymer self-organisation phenomena in scCO₂. Specifically, the time period over which this block copolymer undergoes phase separation before progressing from an arrangement of spheres to lamellae *via* the hexagonal cylinder phase is elucidated, and the data are used to plot a detailed empirical phase diagram for this block copolymer system in scCO₂.

Received 6th November 2018,

Accepted 21st December 2018

DOI: 10.1039/c8py01578c

rsc.li/polymers

## Introduction

Block copolymers are a remarkable class of materials because of their ability to spontaneously self-organise into a variety of ordered mesoscopic morphologies. It is well understood that three parameters dictate this process: the volume fraction of each block (*f*), the Flory–Huggins polymer–polymer interaction parameter (γ) and the degree of polymerisation (*N*).¹,² For a linear A–B diblock copolymer the various morphologies that can be formed in this way include lamellae (LAM), cylin-

ders (CYL), gyroids (GYR) and spheres (SPH), each of which can influence the physical properties of the overall material.³⁻⁵ This has given rise to numerous studies aiming to exploit these structures for a diverse range of applications including drug delivery,⁶ polyelectrolytes,⁷,⁸ nanoporous membranes,⁹ photonics,¹⁰,¹¹ thin film nanolithography,¹²⁻¹⁴ organic photo-voltaics¹⁵ and as templates for inorganic materials.¹⁶⁻¹⁸

In more recent years the concept of confining self-assembled block copolymers within three dimensional micron-size structures such as spheres or worms has received considerable interest.¹⁹ This is because the resulting hierarchically structured materials exhibit multiple levels of structural organisation simultaneously over disparate length scales, thus providing synergies between mechanical properties, transport properties and enhanced surface area.²⁰,²¹ A variety of novel approaches towards the synthesis of such materials have been actively investigated in the literature to date. The most common of these exploit solvent evaporation processes, typically from block copolymer solutions in solvent/nonsolvent mixtures such as the self-organised reprecipitation (SORP)²²⁻²⁴ and evaporation-induced self-assembly (EISA)²⁵⁻²⁷ methods, or dispersed

<footnote>ªSchool of Chemistry, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK. E-mail: steve.howdle@nottingham.ac.uk</footnote>

<footnote>ᵇNetherlands Organisation for Scientific Research (N.W.O), DUBBLE@ESRF, CS40220, 38043 Grenoble Cedex 9, France</footnote>

<footnote>ᶜZernike Institute for Advanced Materials, University of Groningen, Nijemborg 4, 9747 AG, The Netherlands</footnote>

<footnote>ᵈOak Ridge National Laboratory, Chemical Sciences Division, One Bethel Valley Road, Oak Ridge, Tennessee 37831, USA</footnote>

<footnote>†Electronic supplementary information (ESI) available. See DOI: 10.1039/c8py01578c</footnote>

<footnote>‡These authors contributed equally to this work.</footnote>
in particles²⁸ or aerosols.²⁹ However, the drawbacks of these methods include the requirement for multiple steps, the use of volatile organic solvents and unrealistic reaction conditions (nano-object concentration typically <1 wt%) for scaled-up use.

An alternative route is the use of emulsion, miniemulsion or dispersion polymerisation, in which self-organisation occurs within a particle as the block copolymers are synthesised, typically using controlled/living radical polymerisation (CLRP) techniques. CLRP in dispersed systems can advantageously be prepared at high concentration or solid content (up to 40 wt%) and overall presents a simpler and potentially commercial route to block copolymer particles because the synthesis and self-organisation steps take place simultaneously.¹⁹ RAFT polymerisation is one of the CLRP techniques that has received considerable attention in the preparation of functional block copolymers in this way.³⁰ In particular, RAFT dispersion polymerisation has been successfully applied in producing amphiphilic block copolymer nano-objects of controlled size and morphology through the robust and efficient polymerisation-induced self-assembly (PISA) route.³¹⁻³³ Recently, our group has reported a block copolymer synthesis route via RAFT dispersion polymerisation in supercritical carbon dioxide (scCO₂) which allowed the one-pot fabrication of unique nano-structured-block copolymer microparticles that would not normally be obtained in conventional media.³⁴⁻³⁷

Dispersion polymerisation in scCO₂ is an effective technique in this regard because scCO₂ is a good solvent for most common vinyl monomers and a non-solvent for their polymers. This process also allows the size and morphology of the resulting polymer particles to be readily tuned.³⁸ Moreover, scCO₂ as a polymerisation medium is not only beneficial as an alternative 'green' solvent, but also provides additional advantages such as simplified product recovery, lower processing temperature, and the absence of solvent residue.³⁹⁻⁴² These advantages arise from the ability of scCO₂ to swell and plasticise various polymers as a function of pressure.³⁹,⁴³,⁴⁴ This allows the block copolymers to self-organise during the polymerisation process, even at moderate temperatures, thereby circumventing the need for time consuming post polymerisation annealing and/or mixing steps. It has also been observed that blocking efficiencies obtained in scCO₂ are comparable with, and often favourable to, those observed in other CRP reactions in heterogeneous media. This was attributed to the high diffusivity of scCO₂ improving access of the second monomer to the polymerization loci.³⁵ However, one potential consequence of this phenomenon is a deviation of the internal morphology of the block copolymer systems investigated from that expected for a block copolymer of equivalent fA in the melt state. This has been attributed to changes in the apparent volume fraction of the segments in a scCO₂ environment due to variations in the CO₂-philicity of each block, thus altering and even inducing morphological transitions.³⁶,⁴⁵,⁴⁶ This effect was clearly evident after dissolving and solvent casting the as-synthesised block copolymer microparticles into bulk films, which after annealing returned to their predicted equilibrium morphologies.³⁴

The phase separation behaviour of block copolymers is often studied using small angle X-ray scattering (SAXS) because it is a relatively non-destructive and high-throughput technique that can probe structural features on the nano-scale and also permits in situ measurements.³³,⁴⁷⁻⁴⁹ SAXS is commonly used in corroboration with other techniques, such as electron microscopy, because although it provides more representative information of the structural properties of a sample, the data can often be ambiguous when considering samples with unconventional and/or intermixed morphologies. A combination of transmission electron microscopy (TEM) and SAXS analysis has been utilised previously to fully characterise the microphase separation within block copolymer microparticles prepared in scCO₂ and confirm the persistence of the observed morphology throughout an entire sample.³⁴,³⁶ Recently, synchrotron radiation SAXS studies were undertaken for the first time to investigate the morphological transitions that occur in situ during the non-aqueous PISA synthesis of poly(stearyl methacrylate)-b-poly(benzyl methacrylate) (PSMA-b-PBzMA) diblock copolymers.⁵⁰ An in situ SAXS kinetics study has also demonstrated that morphology changes during the synthesis of a PMMA-b-PBzMA block copolymer microparticle sample via RAFT dispersion polymerisation in scCO₂ could be detected, but no interpretation of the order development and thermodynamics of the system were discussed.⁵¹

Given that many of the desirable properties of block copolymers originate from their well-defined nanostructures, the ability to precisely predict when an ordered morphology will form and what structure it will take are crucial pieces of information. This article describes several advances in the synthesis of block copolymer microparticles via dispersion polymerisation in scCO₂ and the characterisation of their internal structures. Most importantly, we demonstrate that the synthesis of nano-structured block copolymer microparticles can be separated into two completely independent steps. We exploit the livingness of RAFT-terminated macro chain transfer agent (macroCTA) PMMA microparticles, which retain activity even after storage for several months, and their ability to be redispersed in scCO₂. This enables a series of block copolymers to be created from a single RAFT dispersion synthesised PMMA homopolymer batch, thus improving reproducibility and also increasing flexibility by allowing the time and concentration requirements for each stage to be decoupled. We then monitored the internal morphology development and subsequent evolution for a series of PMMA-b-PS block copolymer microparticles synthesised using this route via in situ SAXS. Together with offline kinetics experiments and TEM characterisation this approach provides remarkably detailed insights of the self-organisation process occurring within block copolymer microparticles in scCO₂.

## Experimental

### Materials

S-Dodecyl-S'-(α,α'-dimethyl-α''-acetic acid) trithiocarbonate (DATC) was synthesised following literature procedures.⁵²
α-Azobisisobutyronitrile (AIBN, Wako, 97%) was purified by recrystallising twice from methanol. Methyl methacrylate (MMA, Fisher, >99%) and styrene (Alfa Aesar, 99%) were purified by eluting through a column of basic alumina prior to use. Poly(dimethylsiloxane monomethyl methacrylate) (PDMS-MA, ABCR, number-average molecular weight ($M_n$) = 10 000 g mol⁻¹) and ruthenium tetroxide (RuO₄, Acros, 0.5% solution in water) was used as received. Dry CO₂ (SFC grade, 99.99%) was purchased from BOC or Air Liquide. HPLC grade THF (Fisher) and HPLC grade chloroform (Aldrich) were used without further purification. For TEM, Agar 100 epoxy resin (Agar Scientific) was used as received, and mixed to target a formulation of medium hardness for embedding samples before being allowed to set at 50 °C for 48 hours.

## RAFT dispersion polymerisation of MMA in scCO₂

The RAFT dispersion polymerisation of PMMA has been reported previously.⁵³ In a typical procedure targeting PMMA with a molecular weight of 25 kDa, RAFT agent (DATC, 165 mg, 0.45 mmol), AIBN (73 mg, 0.23 mmol) and macro-monomer stabiliser (PDMS-MA, 5 wt% relative to MMA) were added to a standard 60 mL autoclave. The autoclave was purged with CO₂ for 30 minutes, during which time MMA (11.3 g, 112.7 mmol) was degassed by bubbling with argon at 0 °C before being charged into the autoclave under a positive flow of CO₂. The autoclave was then sealed and pressurised to 50 bar, heated to 65 °C and then the pressure was topped up to 275 bar. The reaction was stirred at 300 rpm for 18 hours, after which time the heating jacket was switched off and the autoclave was vented over a period of 15 minutes upon cooling to ambient temperature. In all cases the PMMA product was collected as a fine, pale yellow powder with gravimetric conversions >95%.

## X-ray autoclave characteristics

An improved version of the X-ray autoclave previously developed by the Howdle group⁵¹ was constructed in-house at the University of Nottingham and used for all of the SAXS monitored reactions (see ESI Fig. S1†). The features of this design are a 60 mL capacity and working pressure and temperature limits of 300 bar and 120 °C, respectively. In addition, the X-ray windows are mounted in a small, independent holder that facilitates efficient stirring throughout the vessel, crucial for *in situ* polymerisation studies, and also aids product collection and cleaning when removed post reaction.

## Small-angle X-ray scattering setup

Time-resolved SAXS experiments were conducted at the Dutch-Belgian Beamline (DUBBLE) station BM26-B of the European Synchrotron and Radiation Facility (ESRF) in Grenoble, France.⁵⁴ Experiments were performed using a wavelength (λ) of 0.6526 Å (15 KeV) and a sample-to-detector distance of 3000 m. A Dectris-Pilatus 1 M detector with a resolution of 981 × 1043 pixels and a pixel size of 172 × 172 µm was employed to record the 2D scattering profiles, covering a scattering angle range $q = 0.07–3.65$ nm⁻¹, where the modulus of the scattering

vector *q* is defined as $q = 4π/λ \sin θ$, with $2θ$ being the scattering angle. SAXS profiles of the reaction mixtures were collected every 2.5 minutes, with an exposure time of 30 seconds. The diffraction rings from a Silver Behenate powder standard were used to calibrate the scattering angle scale. The SAXS images were normalised with respect to the incident beam intensity and were corrected for absorption and background scattering from the diamond windows and scCO₂ within the autoclave. After correction, radial averaging around the beam centre was conducted in order to covert the SAXS images into the *I(q)* vs. *q* curves.

## Chain extension of PMMA microparticles with styrene monitored *via* *in situ* small-angle X-ray scattering in scCO₂

The polymers described here are designated with the generalised label PMMA(*X*) and PS(*X*), where *X* denotes the $M_n$ values in kDa. In a typical reaction, the chain extension of PMMA(31) with PS(25) was monitored *in situ* via time resolved SAXS. MacroCTA PMMA microparticles (5.94 g, 0.192 mmol), synthesised as described above, were added to the X-ray autoclave along with the PDMS-MA (5 wt% relative to styrene monomer) stabiliser. After gently purging the X-ray autoclave with CO₂ for 30 minutes, the vessel was sealed, pressurised to 50 bar and then heated to 65 °C before finally topping up the pressure to 275 bar. After stirring for at least 2 hours at 300 rpm under these conditions, the pressure inside the X-ray autoclave was reduced to 200 bar and styrene (5.45 g, 52.3 mmol) containing AIBN (30 mg, 0.093 mmol), which had been degassed by bubbling with argon for 30 minutes, was injected through the head of the autoclave at a rate of 1 mL min⁻¹ using a HPLC pump (Jasco). The styrene was allowed to polymerise for 64 hours, during which time SAXS profiles of the reaction mixture were collected every 2.5 minutes with an exposure time of 30 seconds. On completion, the temperature was reduced to ambient over a period of approximately 1 hour, and the X-ray autoclave was vented over an additional period of approximately 15 minutes. In each case involving styrene monomer the products were collected as pale yellow and slightly clumped powders due to microparticle surface dissolution and partial fusion by the residual monomer. For the reaction involving the synthesis of PMMA-*b*-PMMA a homogeneous fine pale yellow powder was obtained instead.

## Offline kinetics investigation of the chain extension of macroCTA PMMA microparticles with styrene *via* reaction sampling

The representative chain extension of PMMA(25) (3.34 g, 0.134 mmol) with styrene (10 g, 96.0 mmol) was repeated offline in a 60 mL stainless steel autoclave with a sampling tap on the base to collect the polymer product at various times throughout the polymerisation. This was performed as described above for the *in situ* experiments using AIBN (25 mg, 0.077 mmol), with the exception that at time periods of 21, 37, 53, 60 and 84 hours, a ~1 mL closed sampling pipe was screwed onto the bottom of the reactor and the sampling tap was opened to the reaction for 5 seconds.
## Polymer characterisation

PMMA-*b*-PS block copolymers were analysed by ¹H NMR in CDCl₃ on a Bruker DPX 400 MHz spectrometer in order to determine the molecular weight of the polystyrene blocks (*M*<sub>n</sub>, ¹H NMR) and the overall mass fraction of the block copolymers. This was converted to the PMMA volume fraction (*f*<sub>PMMA</sub>) using the reported melt densities of the individual homopolymers: PMMA = 1.17 g cm⁻³ and PS = 1.05 g cm⁻³.⁵⁵ The molecular weight (*M*<sub>n</sub>, GPC) and the dispersity (*D*) of the homo and block copolymers were also determined by GPC using either an Agilent PL GPC 120 in THF or a PL GPC 50 in chloroform. Analyses were run at 40 °C with flow rates of 1 mL min⁻¹ and 0.5 mL min⁻¹, respectively, and the columns were calibrated with narrow dispersity PMMA standards.

## Transmission electron microscopy (TEM)

Block copolymer particles were embedded in epoxy resin (Agar 100) and set at 50 °C for 48 hours before being ultramicromoted at room temperature to ~100 nm slices with a diamond knife (Leica Diatome Ultra 45°) and collected on copper grids. Where specified, the PMMA-*b*-PS particle sections were stained prior to imaging with RuO₄ for 2 hours, which adsorbs selectively to PS. Imaging of particle samples was completed using a FEI Tecnai TEM operating at an accelerating voltage of 100 kV.

## Results and discussion

### Synthesis and characterisation of PMMA microparticles in scCO₂

In previous publications we reported on the one pot RAFT dispersion synthesis of structured block copolymer microparticles in scCO₂. In this scenario the second monomer was injected under pressure once the MMA polymerisation had reached high conversion.³⁵,³⁶ Here we explore a much improved “two-pot” route that separates the block copolymer synthesis into two independent pressurisation/polymerisation/depressurisation stages. The success of this approach hinges on retaining the “livingness” of the PMMA seed particles and successfully redispersing them in scCO₂ prior to adding the second monomer. Such redispersion can be achieved by incorporating additional PDMS-MA stabiliser into the vessel to account for the volume increase of the particles as *M*<sub>n</sub> increases, allowing a series of previously synthesised PMMA particles to be chain extended.⁵³ The role of the additional PDMS-MA stabiliser in improving the redispersion process was determined through a series of test polymerisations undertaken prior to the reactions described here. In these cases, chain extension of the macroCTA PMMA microparticles was still observed, but the block copolymer microparticle products were very poorly defined (ESI Fig. S2†).

In the first stage of the process, a series of PMMA microparticle batches with varying *M*<sub>n</sub> values (Table 1) were synthesised *via* RAFT dispersion polymerisation in scCO₂, and then used for chain extension experiments monitored *via* in situ SAXS

<table><caption>**Table 1** Characteristics of the PMMA particles prepared *via* dispersion polymerisation in scCO₂</caption><thead><tr><th>Exp.</th><th>Name</th><th><i>M</i><sub>n, theo.</sub><sup>a</sup><br>(kDa)</th><th><i>M</i><sub>n, exp.</sub><sup>b</sup><br>(kDa)</th><th><i>D</i><sup>b</sup></th><th>Conv.<sup>c</sup><br>(%)</th></tr></thead><tbody><tr><td>1</td><td>PMMA(31)</td><td>30</td><td>31</td><td>1.16</td><td>96</td></tr><tr><td>2</td><td>PMMA(25)</td><td>25</td><td>25</td><td>1.19</td><td>95</td></tr><tr><td>3</td><td>PMMA(58)</td><td>50</td><td>58</td><td>1.39</td><td>98</td></tr><tr><td>4</td><td>PMMA(54)</td><td>50</td><td>54</td><td>1.19</td><td>98</td></tr></tbody></table>

(Scheme 1a).⁵³ In each case excellent molecular weight control and narrow dispersity values were achieved as confirmed by the GPC traces (ESI Fig. S3†), demonstrating that the DATC RAFT agent in the seed particles was active and able to control the polymerisations effectively. Analysis of each product with SEM revealed that discrete spherical particles were formed in all cases with sizes ranging between 1.7–2.2 µm (ESI Fig. S4†).

### PMMA microparticle chain extensions in scCO₂ monitored *via* in situ SAXS

Four different chain extension reactions were monitored *via* time-resolved SAXS *in situ*. The characteristics of the final products (GPC, ¹H NMR, DSC and TEM analysis of the morphology) are listed in Table 2 (see ESI Fig. S3 and S5† for the GPC and DSC traces for each sample, respectively). Here the experiment numbers 5–8 correspond respectively with chain extension reactions of PMMA homopolymers 1–4 (Table 1). Styrene was selected as the second monomer because (a) PMMA and PS domains have high X-ray contrast, (b) the Flory-Huggins polymer-polymer interaction parameter (χ) of this diblock copolymer is known,⁵⁶ and (c) the phase behaviour has been widely investigated both in the bulk¹²,⁵⁷ and solution states,⁵⁸,⁵⁹ including in scCO₂.³⁴ Furthermore, PMMA and PS have considerably different CO₂-affinities,⁶⁰ and the small *k*<sub>p</sub> for styrene means the polymerisation proceeds over a greater time period,⁶¹ allowing subtle or slow changes in the phase behaviour due to molecular weight or scCO₂ swelling to be tracked and potentially decoupled more effectively using the SAXS profiles.

For each polymerisation, a constant PMMA loading of 5 grams was used along with 5 wt% of PDMS-MA stabiliser, which were stirred together at the reaction temperature and pressure (65 °C and 275 bar) for a minimum of 2 hours in order to redisperse the microparticles prior to adding the styrene monomer (Scheme 1b). The styrene polymerization kinetics were studied for experiments 5 and 6 in a standard 60 mL sampling autoclave, as described further in the ESI (see also ESI Fig. S6 and S7†). These reactions revealed that the styrene polymerisation ultimately takes >72 hours to reach high conversion (>90%), meaning that achieving full conversion at the beamline was not possible in the time frame available. This explains the discrepancy between the targeted and obtained *M*<sub>n</sub> values for each polymer synthesized during *in situ*

<footnote><sup>a</sup> *M*<sub>n, theo</sub> was calculated by: [MMA]/[RAFT] × 100.11. <sup>b</sup> Determined by GPC in THF against PMMA standards. <sup>c</sup> Determined gravimetrically.</footnote>
<figure><img src="image_22.png" /><figcaption>**Scheme 1** The "two pot" synthesis method used to prepare the block copolymers monitored via time resolved SAXS. (a) Preparation of PMMA particles via dispersion polymerisation and (b) PMMA particle redispersion with additional PDMS-MA stabiliser and subsequent chain extension with styrene at the beamline.</figcaption></figure>

<table><caption>**Table 2** Characteristics of the PMMA-b-PS products synthesised during the in situ SAXS characterisation</caption><thead><tr><th>Exp.</th><th>Name</th><th>Block 2 reaction time (h)</th><th>M<sub>n</sub> theo (BCP, kDa)<sup>a</sup></th><th>M<sub>n</sub> exp. (BCP, kDa)<sup>c</sup></th><th>f<sub>PMMA</sub><sup>c</sup></th><th>B<sup>b</sup></th><th>Morph.<sup>d</sup></th><th>T<sub>g,PMMA</sub><sup>e</sup> (°C)</th><th>T<sub>g,PS</sub><sup>e</sup> (°C)</th><th>Conv.<sup>f</sup> (%)</th></tr></thead><tbody><tr><td>5</td><td>PMMA(31)-PS(25)</td><td>64</td><td>70</td><td>55.7</td><td>0.53</td><td>1.5</td><td>CYL</td><td>118.4</td><td>95.5</td><td>79</td></tr><tr><td>6</td><td>PMMA(25)-PS(50)</td><td>63</td><td>100</td><td>75</td><td>0.31</td><td>1.84</td><td>CYL/LAM</td><td>118.2</td><td>95.1</td><td>80</td></tr><tr><td>7</td><td>PMMA(58)-PS(12)</td><td>71</td><td>80</td><td>70.2</td><td>0.81</td><td>1.51</td><td>DIS</td><td>122.5</td><td>N/O</td><td>76</td></tr><tr><td>8</td><td>PMMA(54)-PMMA(44)</td><td>23</td><td>100</td><td>95.4</td><td>1.00</td><td>1.45</td><td>DIS</td><td>123.0</td><td>N/A</td><td>97</td></tr></tbody></table>

<sup>a</sup> $M_{n,th}$ was calculated by: [Monomer][PMMA macroCTA] × MW monomer. <sup>b</sup> Determined by GPC in THF against PMMA standards. <sup>c</sup> From ¹H NMR. <sup>d</sup> From TEM images. <sup>e</sup> Measured by DSC, N/O = not observed due to a lack of phase separation. <sup>f</sup> Determined gravimetrically, residual monomer present.

SAXS monitoring (Table 2). We also note here that the molar mass dispersity values for the block copolymers synthesised here are typically higher than for analogous homogeneous solution based syntheses. However, these values are comparable to results reported previously for this block copolymer system by our group using the one-pot approach,³⁵ as well as other examples of heterogeneous syntheses in the literature. This is attributed to the higher tendency of styrenic monomers to terminate by combination, particularly under monomer starved conditions, as is the case in the latter stages of the polymerisations reactions undertaken here.⁶² In order to understand the influence of block copolymer composition on order development and phase transitions in these systems, the molecular weights of the PS blocks across the three polymerisations were targeted to obtain block ratios in the final products of $f_{PMMA} \approx f_{PS}$ (experiment 5), $f_{PMMA} \ll f_{PS}$ (experiment 6) and $f_{PMMA} \gg f_{PS}$ (experiment 7). A control experiment in which PMMA was chain extended with a second PMMA block of comparable $M_n$ was also completed (experiment 8).

## Internal morphology development and evolution during the polymerisation of PMMA(31)-PS(25)

Time-resolved SAXS profiles were recorded during the chain extension of PMMA(31) to PMMA(31)-PS(25) and plotted as a 3-dimensional *q* (nm⁻¹) versus intensity (*I*(*q*)) versus time (*t*) plot to illustrate the morphological transitions throughout the polymerisation (Fig. 1). A large number of SAXS profiles were removed to improve the overall visibility of the data, with the remaining profiles being separated by approximately 30 minutes intervals. A second 2-dimensional plot of the data at 10 hours intervals was also created to further highlight the changes in the scattering patterns that occurred throughout the duration of the polymerisation (ESI Fig. S8†). The small gaps in the data are due to brief pauses during the data acquisition to either adjust the pressure or due to beam loss. The SAXS profiles are initially featureless and exhibit Porod scattering with $I(q) \propto q^{-4}$, indicating the presence of many large structures with sharp interfaces between them that are consistent
<figure><img src="image_23.png" /><figcaption>Fig. 1 Time-resolved *in situ* SAXS data collected during the chain extension of PMMA(31) to form PMMA(31)-PS(25) (experiment 5) via dispersion polymerisation in scCO₂. The time between the individual profiles included is approximately 30 minutes.</figcaption></figure>

ent with the overall size of the polymer microparticles without any internal nanostructure.⁶³ This is highlighted in the ESI,† where the SAXS profile for the sample taken at *t* = 0 is plotted alongside the $q^{-4}$ decay data (ESI Fig. S9†). After polymerising for approximately 6 hours the first evidence of the formation of a block copolymer disordered phase is distinguishable by the formation of a very broad primary scattering ($q^*$) peak centred at $0.232 \text{ nm}^{-1}$ due to correlation hole scattering between the PMMA and PS segments enforced by their connectivity (Fig. 1, $q^*$) (see ESI eqn (S1)† for the peak fitting function used to derive the peak positions).¹,⁶⁴

The intensity of this peak then continues to increase over the next 10 hours and it simultaneously becomes narrower, as expected for a system that is progressing towards a more ordered state (Fig. 1). After 16 hours the block copolymer undergoes a disorder-to-order transition (DOT) as evidenced by the appearance of an additional higher order scattering peak centred at $\sqrt{3}q^*$ (Fig. 1, $\sqrt{3}q^*$). A secondary peak in this position is characteristic of a hexagonally packed cylindrical morphology, an assignment that was further validated by the appearance of a third characteristic peak for this morphology centred at $\sqrt{4} = 2q^*$ after approximately 30 hours (Fig. 1, $2q^*$). The intensity of these three SAXS peaks continues to increase throughout the remainder of the polymerisation and the domain spacing of the cylindrical morphology also continues to grow at a steady rate, culminating in a $q^*$ peak at $0.110 \text{ nm}^{-1}$. This corresponds with an average characteristic spacing of the cylindrical BCP morphology ($d_{CYL}$) in scCO₂ of 57.1 nm, as determined using Bragg's law:

$$d = 2\pi/q^* \quad (1)$$

The increase of $d_{CYL}$ during the PS polymerization indicates that the value of $\chi N$ for the system increased continuously

until the time when the reaction was discontinued, in agreement with our kinetic studies (ESI Fig. S6 and S7†). We also note that the SAXS maxima throughout the course of the reaction remain relatively broad. This phenomenon has been previously reported in SAXS studies on these systems and suggests that the internal morphology is composed of a distribution of domain sizes that only persist over a relatively short range order, given that the peak width is inversely proportional to the degree of ordering.³⁶

TEM images were acquired from thin sections of the final polymer product to corroborate the hexagonally packed cylinder internal morphology of the microparticles indicated by the SAXS profiles toward the end of the reaction (Fig. 2). These images verify the occurrence of this morphology, in agreement with previous studies on this block copolymer system with comparable values of $f_{PMMA}$.³⁴,³⁶ Domain size measurements taken from the TEM images returned a value of approximately 44.2 nm from 50 measurements (cylinder-to-cylinder distance of $(2/\sqrt{3}) \times 44.2 \text{ nm} = 51.0 \text{ nm}$), but some variation in the domain size throughout each particle was observed, as expected from the broad nature of the reflections in the SAXS data. Nevertheless, this average value is slightly smaller than the 57.1 nm domain size calculated from the primary scattering peak in the final SAXS profile for the sample prior to depressurisation. To confirm whether the TEM measured value was representative of the sample as a whole or an artefact of the microtoming process, a post reaction SAXS profile was recorded after the final product had been collected (ESI Fig. S10†). This profile returned a value of 53.3 nm that was more comparable to that obtained prior to venting the CO₂, suggesting the discrepancy between the SAXS and TEM domain size measurements is most likely the result of sample distortion during the microtoming process, which can be difficult to avoid.³⁴
<figure><img src="image_24.png" /><figcaption>Fig. 2 (a) TEM images of a representative cross-sectioned PMMA-b-PS particle obtained following the chain extension of PMMA(31) with PS(25) in the X-ray autoclave. (b) A hexagonally packed cylinder morphology can be observed throughout the sample with a cylinder-to-cylinder distance of ~51 nm. The PS domains appear dark in both images due to staining with RuO₄.</figcaption></figure>

## Internal morphology development and evolution during the polymerisation of PMMA(25)-PS(50)

A three dimensional *q* (nm⁻¹) *versus* *I*(*q*) *versus* *t* plot was generated from the SAXS data obtained during the chain extension of PMMA(25) with PS(50), with a large number of SAXS profiles again being removed to improve the overall visibility of the data (Fig. 3a). A second 2-dimensional plot of the data at 10 hours intervals was also created to further highlight the changes in the scattering patterns that occurred throughout the duration of the polymerisation (ESI Fig. S11†). As was observed for PMMA(31)-PS(25), the SAXS profiles near the beginning of the reaction exhibit the characteristic Porod scat-

tering of a microparticulate sample without internal structure. After 13.5 hours of PS polymerization, a broad and low intensity peak at around 0.22 nm⁻¹ appears and continues to develop over the next 10–15 hours (Fig. 3). As in the previous case, this peak is due to correlation hole scattering between the PMMA and PS segments, not able to show ordering due to the low *χ*N value at this point of the reaction. As the polymerization reaction progresses this peak gradually becomes more intense, forming a broad correlation peak that extends from 0.140–0.185 nm⁻¹ (Fig. 3a). This broad peak shows similarities with correlation peaks usually observed in systems comprised of interacting but poorly ordered spherical objects.⁵⁰ Thus, at the early stages of the reaction (before 30 hours) it appears

<figure><img src="image_25.png" /><figcaption>Fig. 3 (a) Time-resolved *in situ* SAXS profiles collected throughout the dispersion polymerisation of PMMA(25)-PS(50) in scCO₂. (b) TEM images of representative cross-sectioned PMMA(25)-PS(50) microparticles synthesised in the X-ray autoclave and collected at the end of the reaction. The majority of microparticles exhibit a coexisting mix of both morphologies, with lamellar being predominant towards the particle exterior. The PS domains appear dark due to staining with RuO₄. The time between the individual profiles included is approximately 30 minutes.</figcaption></figure>
that spherical PS domains were beginning to form within the PMMA microparticles.

Over time this peak then continuously shifts towards lower *q*-values, again indicating that the molecular weight of the polystyrene block was gradually increasing. From approximat-
ley 35 hours onwards this peak then gradually begins to sepa-
rate into two distinct maxima at 0.0167 nm⁻¹ and 0.0194 nm⁻¹.
This is indicative of a morphology transition within the
sample, the specific nature of which cannot be assigned from
this information alone. Finally, a third reflection with a much
higher *q* value in the range of 0.48 nm⁻¹ also becomes appar-
ent from approximately 50 hours onwards (Fig. 3a, 3q*). A
peak in this range is expected to be a higher order scattering
reflection that suggests the sample has progressed to a more
ordered state in which the domain spacing and/or morphology
is more consistent throughout the microparticles. An offline
SAXS profile was also recorded for the final product upon
venting the autoclave, confirming almost no change in the
domain size of these samples after removing the scCO₂, as for
experiment 5 above (ESI Fig. S12†).

TEM images were taken from ~100 nm thick sections of the final product to validate the morphological transitions throughout the polymerisation (Fig. 3b). Intriguingly, the majority of the microparticles exhibit internal morphologies in which the lamellar phase is predominant, but occurs alongside a smaller population of cylindrical domains located towards the centre of many particles (Fig. 3b). In many cases the variability of the lamellar domain spacing as measured from the TEM images was small, and an average domain spacing of ~40 nm (SD = 5 nm) was obtained from 50 measurements. This value corresponds with an expected primary scattering peak position at *q* = 0.156 nm⁻¹ that closely matches the higher *q* portion of the broad *q*\* scattering reflection in the SAXS profiles recorded for this sample prior to terminating the reaction (Fig. 3a, *d* = 40 nm peak), suggesting that this reflection corresponds to the formation of the lamellar morphology. There are also many lamellar regions within these particles that appear to be trapped in an incomplete transition state from the hexagonal cylinder morphology, as identified by their wavy edges, irregular appearance and larger domain spacing values that we partially attribute to the broadening of the lamellar *q*\* peak to lower values of *q* (Fig. 3b, *d* = 49 nm peak).

By contrast, the regions of the particle interiors that
possess a hexagonal cylinder morphology show a much
broader range of domain sizes that are more difficult to
accurately measure from the TEM images because of uneven
stretching that occurs during the transition to a lamellar
morphology. In spite of this, we estimate an average cylinder-
to-cylinder distance of ~50 nm for the domains from
50 measurements, and also attribute the consistent broaden-
ing of the primary SAXS scattering peak to lower *q* values to
their presence. Taking the midpoint of this broad peak as the
primary *q*\* scattering reflection also enables the higher order
reflection that forms towards the end of the reaction at higher
*q* to be assigned as the expected 3*q*\* reflection for a lamellar

morphology (Fig. 3a, 3q* peak). This is further evidence
that the lamellar phase forms during the reaction and
gradually becomes more prevalent. Such a transition is also
anticipated based on the stability window for the lamellar
phase in the classical diblock copolymer phase diagram and
the f<sub>PMMA</sub> value of the final product.² However, because of a
lack of higher order scattering reflections in this sample
during the earlier stages of the reaction, the exact sequence of
transitions that eventually culminate in the formation of the
lamellar morphology could not be identified from these data
alone.

Offline evaluation of morphology evolution for PMMA(25)-PS(50)

To further elucidate the complex phase behaviour during the
polymerisation and to estimate a time frame for when the
spherical to lamellar phase transition (via hexagonal cylinders)
occurs, additional TEM images and single shot SAXS data were
acquired from the polymer aliquots collected during the
offline kinetics evaluation of this reaction (Fig. 4). After react-
ing for 21 hours an internal morphology of spheres is present
throughout the entirety of each particle. By 37 hours the lamel-
lar phase becomes apparent around the edges of some
particles alongside the majority spherical phase, and there are
also areas within certain particles where arrays of more
ordered circular domains indicative of a hexagonally packed
cylinder morphology are present.

At 53 hours the prevalence of the spherical phase has
declined dramatically, whereas the hexagonally packed cylin-
der and lamellar morphologies have become abundant to the
point where both morphologies are present in roughly equal
proportions within the microparticles (see ESI Fig. S13† for a
higher magnification TEM image). These observations are
qualitatively comparable to those for the microparticles col-
lected at both the 60 hours kinetic time point and from the
X-ray autoclave after polymerising for 64 hours during *in situ*
SAXS monitoring. This further highlights the very gradual and
somewhat sporadic nature of the transitions through phase
space for this system and also validates the expected gradual
transition of the samples away from the spherical phase and
into the morphologies expected for a more symmetrical block
copolymer system.² To probe the morphology transitions at
even higher conversion values than possible at the synchrotron
due to time limitations, the kinetics experiment was continued
for a further 24 hours beyond the 60 hours time point to gain
further insight of the morphological transitions at very high
conversion. The final TEM images taken of the product col-
lected after depressurising the autoclave indicated an even
higher proportion of particles with a pure lamellar mor-
phology, as expected for this reaction based on the final mor-
phology analysis from previous reports on PMMA-b-PS block
copolymer microparticles of similar f<sub>PMMA</sub> values.³⁴

Together these data demonstrate that the hexagonal cylin-
der morphology is a distinct intermediate stage formed during
the transition to a lamellar morphology, but that the specific
scattering reflection is obscured in the *in situ* SAXS profiles. Its
<figure><img src="image_26.png" /><figcaption>Fig. 4 TEM images of representative cross-sectioned PMMA-*b*-PS particles taken from the kinetic aliquots of the offline chain extension of PMMA(25) with PS(50) at time points of 21, 37, 53, 60 and 84 hours.</figcaption></figure>

appearance within certain particles as elongated and partially
fused cylinders also match those described previously by
Sakurai et al.⁶⁵ when a polystyrene-*b*-polybutadiene-*b*-poly-
styrene (PS-*b*-PB-*b*-PS) block copolymer was thermally induced
to undergo a transition from cylinders to lamellae. This
occurred through a process in which neighbouring cylinders
gradually approached each other before zipping into uninter-
rupted lamellae.⁶⁵ A similar mechanism has also been
reported during the transition from high to low order struc-
tures in a polystyrene-*b*-polyethylene-*co*-polybutylene-*b*-poly-
styrene (PS-*b*-PE-*co*-PB-*b*-PS) block copolymer.⁶⁶ In this case
the cylindrical structure breaks up and forms rippled cylinders
as an intermediate prior to transforming into a spherical struc-
ture in a selective solvent, which accurately describes the
reverse of the transitions observed here. It can therefore be
concluded that this spherical to lamellar transition *via* the
intermediate hexagonal cylinder morphology initially begins at
some point during the 16 hours window between 21–37 hours,
corresponding with a PS molecular weight range between
~15–27 kDa based on the kinetics monitoring data (ESI
Fig. S6†). These results also suggest that the same transition is
likely to have occurred during the early stages of the
PMMA(31)-PS(25) polymerisation, immediately after phase
separation but prior to formation of the higher order peaks
characteristic of a the hexagonal cylinder morphology. For
PMMA(31)-PS(25) this occurs after approximately 35 hours of
polymerisation and a PS molecular weight of ~15 kDa,
suggesting further agreement between the morphology tran-
sitions of the two reactions that is obscured in the SAXS data
alone due to the lack of higher order scattering information
owing to the domain size variation within the microparticles.

Control polymerisations testing the limits of block copolymer
self-organisation in scCO₂: synthesis of PMMA(58)-PS(12) and
PMMA(54)-PMMA(44) monitored *via* *in situ* SAXS

As expected, the *q* (nm⁻¹) *versus* *I*(*q*) *versus* time plots obtained
during the synthesis of the second blocks for PMMA(58)-
PS(12) and PMMA(54)-PMMA(44) are both initially featureless
(Fig. 5a and ESI Fig. S14,† respectively). This remains the case
for the entirety of the PMMA(54)-PMMA(44) polymerisation,
indicating that no phase separation occurs during the poly-
merisation of the second block, and was subsequently corrobo-
rated *via* the TEM images taken of the sample post-polymeris-
ation (ESI Fig. S14b†). On the other hand, a single broad scat-
tering peak develops at 0.136 nm⁻¹ quite late into the poly-
merisation of PMMA(58)-PS(12) at approximately 65 hours (see
also ESI Fig. S15† for the corresponding 2-dimensional plot of
the SAXS profiles at 10 hours intervals). In conjunction with
the corresponding TEM images of the final product (Fig. 5b),
which lack any evidence of internal phase separated structures,
this was assigned as the correlation hole scattering peak
indicative of the disordered phase. We attribute the lack of
order in this sample to its high degree of block asymmetry
(f<sub>PMMA</sub> = 0.81), positioning it towards the edges of the phase
diagram where the formation of ordered structures becomes
thermodynamically unfavourable.²

Empirical phase diagram of PMMA-*b*-PS derived from *in situ*
SAXS measurements

Block copolymer phase diagrams are powerful tools for
researchers needing to target specific morphologies for a
system in order to meet an application need. Although both
<figure><img src="image_27.png" /><figcaption>Fig. 5 (a) Time-resolved *in situ* SAXS data recorded during the chain extension of PMMA(58) to form PMMA(58)-PS(12) *via* dispersion polymerisation in scCO₂. The time between the individual profiles included is approximately 30 minutes. (b) TEM images taken of the final product.</figcaption></figure>

theoretically and experimentally derived phase diagrams have been extensively studied and mapped out for neat diblock copolymer systems in the bulk and thin film states, their applicability to ternary systems that contain additives or dopants is often limited.²,⁵,¹² This is because the additives almost always exhibit preferential affinity for one block, leading to uneven swelling and significantly more complex system thermodynamics. As a result, phase diagrams of such systems must be plotted manually using empirical data taken from static samples, which is a time consuming and experimentally tedious task.³⁴,⁵⁸,⁶⁷

Previously, Jennings *et al*. have used this approach to plot initial phase diagrams from several static samples of two block copolymer systems, PMMA-*b*-PS and PMMA-*b*-poly(benzyl methacrylate), synthesised *via* one-pot RAFT dispersion polymerisation in scCO₂.³⁴ Although comprised of only a limited number of data points, the diagrams were a more quantitative representation of previous findings that scCO₂ preferentially swells methacrylate based polymers over those comprised of styrene units.³⁶,⁶⁰ As a consequence, PMMA-*b*-PS block copolymers synthesised in scCO₂ demonstrate markedly different morphologies when compared with those in the melt state (see Fig. 6 for the reproduced data). These morphologies are preserved upon venting the CO₂ because the block copolymers rapidly revert to a glassy, immobile state at the synthesis temperature (65 °C). For example, at $\chi N$ and $f_{PMMA}$ values of ~30 and ~0.5, respectively, a lamellar morphology is anticipated for a neat diblock copolymer,² however, a spherical morphology was observed in an equivalent PMMA-*b*-PS block copolymer synthesised in scCO₂.³⁴

The rich morphology data that are recorded during a RAFT dispersion polymerisation monitored *in situ* using SAXS are therefore a convenient method for plotting highly accurate empirical phase diagrams from a much smaller subset of polymerisation reactions, when combined with kinetically monitored sample characteristic data. The resulting diagram was plotted using the data points taken from each of the three

<figure><img src="image_28.png" /><figcaption>Fig. 6 Empirical phase diagram for PMMA-*b*-PS in scCO₂ derived from the SAXS and kinetics data for PMMA(31)-PS(25) (squares), PMMA(25)-PS(50) (circles) and PMMA(58)-PS(12) (triangles). The data points represented by stars are taken from a previous report by Jennings *et al*. for the same system in scCO₂.³⁴ Where exact time points for morphology transitions could not be determined the phase boundaries were taken at the midpoint between the available data points. The blue checked region is an assumed stability region for the cylindrical morphology that was not observed in the data available.</figcaption></figure>

block copolymer reactions undertaken here at 10 hours intervals (Fig. 6). The data previously reported by Jennings *et al*. for eight static samples of this block copolymer synthesised in scCO₂ are also included for easy comparison.³⁴ In each case, the molecular weight and composition data from GPC and ¹H NMR spectroscopy, respectively, were used to calculate values of *N* and $f_{PMMA}$, while the value of $\chi$ at 65 °C was taken from the literature as 0.0395⁵⁶ ($\chi$ = 0.0411 for data plotted from Jennings *et al*).³⁴ For simplicity, the molecular weight growth for the reaction of PMMA(58)-PS(12) reaction was assumed to be linear with time with a slope equal to that for PMMA(31)-PS(25).
Very good agreement between the morphology transitions for the three reactions undertaken here and the previous data was observed, thereby solidifying the validity of this approach as being on par with the more conventional approach. This is in spite of additional variables in the scCO₂ system, such as temperature, and more importantly, the presence of unreacted monomer, showing that overall their contributions in these systems are low relative to the effects of the scCO₂.

## Conclusions

In conclusion, we have demonstrated that the synthesis of nanostructured block copolymer microparticles *via* RAFT dispersion polymerisation in scCO₂ can be decoupled into completely independent steps. This was achieved by exploiting the living chain ends of RAFT synthesised PMMA homopolymers, even after storage for months, and their ability to be quickly redispersed in scCO₂ using a small quantity of additional PDMS-MA stabiliser. Using this process a series of three PMMA-*b*-PS block copolymers with varying *f*<sub>PMMA</sub> ratios were synthesised and the development of order and subsequent morphology evolution was monitored throughout the polymerisation *via* *in situ* SAXS and corroborated using post-mortem TEM imaging. For the polymerisation of PMMA(31)-PS(25) a SAXS pattern consistent with a hexagonal cylinder morphology was gradually formed following phase separation at approximately 16 hours. The characteristic spacing then gradually increased with time in response to the growing PS block until the end of the reaction and no further morphology transitions occurred. TEM imaging confirmed the presence of this morphology and additional SAXS analysis of the final product revealed that the domain size of the sample following depressurisation was almost the same value prior to venting the autoclave at the end of the reaction. This indicates that the increase in domain size of the internal morphology brought about by the swelling effects of scCO₂ are mostly retained by the sample upon its removal.

By contrast, the SAXS profiles obtained during the synthesis of PMMA(25)-PS(50) were considerably more complex. Initially a single broad peak was discernible in the SAXS profiles of this sample at 13.5 hours, which from the TEM images taken at a slightly later time was revealed to be due to the initial formation of a spherical morphology. As the polymerisation progressed this SAXS peak became progressively broader and slightly bimodal in appearance as the spheres gradually transitioned into a mixed cylindrical/lamellar phase. To further elucidate the nature and time period of this transition the reaction was repeated in a sampling autoclave and aliquots were taken at various time points for TEM analysis. These images revealed that the transition from spheres begins to occur over a 16 hours window between 21–37 hours *via* a hexagonally packed cylinder morphology intermediate. This is a slow and somewhat sporadic process that remains partially incomplete until the very late stages of the polymerisation (*t* > 64 hours). Finally, for PMMA(58)-PS(12) a disordered peak appeared late into the poly-

merisation but no self-organisation occurred due to the highly asymmetric composition of this sample, while for PMMA(54)-PMMA(44) there was no evidence of phase separation.

## Conflicts of interest

There are no conflicts to declare.

## Acknowledgements

SAXS experiments were undertaken at Beamline 26B (DUBBLE) of the European Synchrotron and Radiation Facility (ESRF) in Grenoble, France. We thank the N.W.O for providing the beam time for our experiments. We gratefully acknowledge the University of Nottingham Nanoscale and Microscale Research Centre (NMRC) for access to their instrumentation, in particular Ms Denise McClean for assistance with the FEI Tecnai TEM. MA, TMB, GH and SMH are indebted to the very high quality technical and high pressure safety support at the University of Nottingham from Peter Fields, Richard Wilson and Martin Dellar. This research was supported in part under the Leverhulme Grant Award Scheme (RPG-2014-034, for TMB, GH and SMH) as well a UNNES-IDB PhD scholarship for MA.

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## 3- Co-proposer PhD Thesis project awarded; "Etude multi-échelle de l'impact de l'ajout de fluoroélastomère sur la structure du PVDF par des mesures in situ couplées", Université de Lorraine.

I have co-applied successfully for a Ph.D. project to the Region of Lorraine together with prof. Patrice Bourson but also, we have fund-raised from an industrial partner (ARKEMA) in order to investigate by time resolved simultaneous DSC-SAXS-WAXS experiments in combination with Raman spectroscopy the effect on the nanostructure of PVDF the addition of a fluoroelastomer to enhance the mechanical properties. The total financial support was 135000 Euros. Importantly, the data simultaneously acquired by different techniques have been studied by chemometrics analysis in order to correlate subtle differences among the enormous metadata recorded. Chemometrics analysis is largely employed in the spectroscopic field but has scarcely used with X-ray data and/or in combination with spectroscopic techniques. I consider that the use of X-rays techniques with other relevant spectroscopies is crucial to correlate different length-scales. However, the enormous amount of data generated at acquisition times close to second or millisecond requires the employ of a mathematical tool that allows associating the data and its multiple interconnections. I have successfully applied for a visitor scientist grant in 2018, 2019 and 2020 at the Université de Lorraine to expand my knowledge on multivariate analysis. The grant was valued around 2500 euros in order to support my trip and stay for a month within prof. Patrice Bourson. The thesis student (Sarah Saidi) is in her last Ph.D. year and I will be the corresponding author of the 3 manuscripts under preparation. Sarah Saidi has spent most of her Ph.D in DUBBLE, supervised by me.

The student has already presented her work at ISPAC, the 32nd International Symposium on Polymer Analysis and Characterization, June 2-5, 2019 with an oral contribution entitled 'Multi-scale study of the impact of fluoroelastomer addition on the PVDF structure by coupled in situ measurements'.

Poly (vinylidene fluoride) (PVDF) is an interesting material largely employed in a wide range of applications such as architectural, offshore materials, solar panels, and chemical engineering. The PVDF materials undergo extreme conditions for these applications such as high or low pressure, high and low temperature, cold or hot bending and blistering. The manufacturing of the polymeric materials must meet strict ambivalent specifications because of the variable conditions depending on the work environment. PVDF properties depend on its semi-crystalline nanostructure. Indeed, PVDF crystallizes readily and presents a polymorphism. PVDF is well known to crystallize, in a polar phase (β-) which exhibits interesting electrical properties, such as pyroelectricity or piezoelectricity and in a non-polar phase (α-), the more mechanical resistant and stable phase. Moreover, PVDF has been blended with a fluoroelastomer (in weight fraction lower than 50wt%) in order to improve the viscoelastic behavior of the final material by changing the nanostructure of the initial neat PVDF. The understanding of PVDF
blends crystallization under conditions that mimic their life cycle is crucial to optimize and design novel PVDF derivatives to enhance the performance of the material under real conditions. With this goal, it has to be established the relation between the crystallinity, phase content and the crystallite size of a pure PVDF and a PVDF/fluoroelastomer blends. The composition of the blend influences the overall crystallinity. More precisely, different PVDF/fluoroelastomer blends have been studied to probe the influence of fluoroelastomer mixed to PVDF matrix. Raman spectroscopy imaging and time-resolved simultaneous DSC-SAXS-WAXS experiments in combination with Raman spectroscopy have been performed to identify the structure, crystallinity, shape and crystallite size. Moreover, chemometrics analysis has been performed to correlate the simultaneous data acquired.

In a first stage of the project, I have focused on the experimental optimization of the combination of scattering techniques with Raman spectroscopy.

Time-resolved small-angle X-ray scattering (SAXS) and/or wide-angle X-ray scattering (WAXS) are currently employed (Portale et al., 2016a) as ordinary structural characterization techniques in the synchrotron radiation community. Moreover, SAXS lab sources have been extended throughout the solid-state physics departments as a result of the great improvement at the covered angular range, the enhancement in flux, the detectors development and the standardization of complex sample environments. However, novel technical implementations are required to design complex experimental with fine control to further study the dynamic morphological evolution upon external stimuli in a multi-technique approach. The Dutch-Belgian Beamline (DUBBLE) beamline is particularly optimized for the study of polymer science under extreme conditions, as reported by Bras et al. (Bras et al., 2003). The versatility of DUBBLE to accommodate complex experimental setup (Portale et al., 2013) with applicable advances on combined techniques has been proved to be crucial to monitor the polymer crystallization under processing-relevant conditions that mimic industrial environments. Particularly, great efforts have been focused on the crystallization understanding of the interplay of the different flow fields and thermal treatments that replicate the industrial conditions at which polymers are subjected in processing such as extrusion, injection molding, blow molding, fiber spinning, drop casting, filament deposition modeling and inkjet printing. The characterization of the crystallization mechanism of semicrystalline polymers from the melt have been largely benefited upon quiescent and non-isothermal conditions with mild cooling rates by combining DSC optical microscopy equipment (Russell & Koberstein, 1985) (Bras, Derbyshire, Devine et al., 1995) with simultaneous SAXS/WAXS experiments. Moreover, the nanostructuration of semicrystalline polymers upon fast quenching cooling rates relevant to industrial environments, has been characterized upon scattering techniques subjected to ballistic cooling and recently, in combination with flash chip calorimetry (Portale et al., 2016b). Likewise, the effect of shear forces on the crystallization mechanism of semicrystalline polymers has greatly probed by scattering techniques to reproduce the industrial conditions. (Ryan et al., 2016) Solid-state drawability of β nucleated iPP films has been evaluated (Luijsterburg et al., 2014) by in situ 2D WAXS measurements under uniaxial stretching at different temperatures by heated godet drawing roll units fitted with an oven that mimic industrial conditions. The mechanical and optical properties of polymeric films depend on