bluuebunny/crossref_metadata_2025 huggingface dataset:
Sm based initiators for the ring-opening polymerization of L-lactide
Authors: Agarwal Seema , Karl Marc , Dehnicke Kurt , Greiner Andreas
Published: August 2014

Ring-opening polymerizations of L-lactide were carried out in the presence of Sm(II) (SmI2/Sm) and the Sm(III) complex [Sm(m-Cl){N(SiMe3)2}2(THF)]2 (Me: CH3, THF: tetrahydrofuran). The polymerizations were performed using different mole ratios of monomer to initiator and for different time intervals. The complexes were found to be active polymerization catalysts and led to the synthesis of semicrystalline, optically active poly(L-lactide) retaining about 95.5% of the optical activity. This shows that - with the initiator systems used - polymerization proceeds with the retention of configuration at the chiral carbon atom.
Molecular weight control and end group functionalization of polynorbornene by Ni(II)-initiated polymerization of norbornene in the presence of ethylene and ɑ-olefins
Authors: Mast Christian , Krieger Matthias , Dehnicke Kurt , Greiner Andreas
Published: August 2014

High-molecular-weight vinyl-type polynorbornene (PN) was obtained in high yields by a highly active nickel-based phosphorane iminato complex in the presence of methylaluminoxane. Termination of norbornene polymerization by functionalized ɑ-olefins yielded soluble end group functionalized polynorbornenes of controlled molecular weight. The impact of the ɑ-olefins on yield and Mn depends significantly on the sterical situation at the olefins. No proof for the incorporation of the olefin at any other position than the chain end was observed. Considerations based on yields and Mn suggest that the Ni hydride species, which is most likely formed upon β-H elimination reaction in the scheme of olefin addition to the growing PN chain, initiates a new PN chain; in other words, chain transfer occurs through β-H elimination reaction.
Bis(η5-cyclopentadienyl)bistriphenylsilanolatozirconium( IV): a new precursor for ethylene polymerization catalysis
Authors: Altomare Angelina , Candian Roberta , Michelotti Marco , Pampaloni Guido , Ciardelli Francesco
Published: August 2014

Trialkylsilanols were reported to modify and also to improve the catalytic performance in ethylene polymerization when added to zirconocene/methylaluminoxane (MAO) systems. In order to obtain more information about the chemistry involved, a new stable catalytic precursor was investigated in this work. The precursor bis(h5-cyclopentadienyl)bistriphenylsilanolatozirconium(IV) [ZrCp2(OSiPh3)2] was compared to ZrCp2(CH3)2 and ZrCp4, which can generate ZrCp2(OSiPh3)2 in situ on triphenylsilanol addition. In ethylene polymerization, ZrCp2(OSiPh3)2 exibits a comparable activity and a larger stability than dicyclopentadienylzirconium complexes. On addition of triphenylsilanol to zirconocenes, the productivity increased and the molecular weight sharply decreased, thus suggesting the occurrence of ligand substitution in solution. The reported results are discussed with reference to the proposed mechanism of ethylene polymerization with the conventional ZrCp2Cl2/MAO system.
Coordination polymers from kinetically labile transitionmetal complexes: True macromolecules or only dynamic solution aggregates?
Authors: Lahn Brigitte , Rehahn Matthias
Published: August 2014

Readily soluble copper(I) and silver(I) coordination polymers have been prepared via the conversion of equimolar amounts of
Kinetic and Monte-Carlo modelling of hyperbranched polymerisation
Authors: Galina Henryk , Lechowicz Jaromir B.
Published: August 2014

After some comments on the size and conformation of dendrimer molecules, models of the polymerisation of AB2 monomers that leads to hyperbranched polymers are reviewed. The models are (i) a kinetic one that takes into account changes in the reactivity of B groups as well as intramolecular reactions, and (ii) the equivalent Monte-Carlo model. The results of application of the kinetic model to the polymerisation system AB2 + B3 are also presented.
Reactions of polystyrene radicals in a monomer-free atom transfer radical polymerization system
Authors: Yoshikawa Chiaki , Goto Atsushi , Fukuda Takeshi
Published: August 2014

Polystyrene radicals (PS•) were produced in high concentration using ω-bromopolystyrene (PS-Br) and α,ω-dibromopolystyrene (Br-PS-Br) in conjunction with Cu(I)Br following the atom transfer technique. A proper choice of the activator system led the PS-Br adduct to a maximum extent of coupling (by recombination), qmax = 0.91, as estimated by gel permeation chromatography. On the other hand, the fraction of chains terminated by disproportionation was estimated to be 0.07 ± 0.04 by 1H NMR. When the radical concentration [PS•] was not high enough, the chain transfer reaction competed with termination, and qmax remained low. For the bifunctional adduct Br-PS-Br, the coupling reaction produced ‘polymers’ of a variety of chain lengths, whose distribution obeyed the theory of random coupling, when q was lower than about 0.5. The high extent of coupling (qmax ≈ 0.9) achievable in short time (< 10 min) suggests practical applicability of this reaction.
Time-resolved FTIR/FTNIR spectroscopy: powerful tools to investigate diffusion processes in polymeric films and membranes
Authors: Musto Pellegrino , Ragosta Giuseppe , Mensitieri Giuseppe
Published: August 2014

The application of time-resolved FTIR spectroscopy to investigate diffusion processes in polymers is described. Two thermosetting systems have been studied: a tetrafunctional epoxy resin cured with an aromatic diamine hardener, and a ternary formulation comprising the above components plus a bismaleimide co-monomer. Spectroscopic monitoring of water diffusion, both in the Mid and in the Near IR frequency ranges, yielded accurate and reproducible kinetic curves from which it was possible to evaluate the absolute parameters of diffusion (diffusivity and activation energy). These were found to compare favourably with the values obtained by conventional gravimetric methods. The molecular interactions between the penetrant molecules and the polymer networks were also investigated and it was shown that, in the system containing the bismaleimide component, the fraction of water molecules hydrogen-bonded to the network decreases significantly.
pH-Dependence of the morphology of micelles formed by poly(2-vinylpyridine)-block-poly(ethylene oxide) copolymers in water
Authors: Gohy Jean-François , Mores Sandrine , Varshney Sunil K. , Zhang Jian-Xin , Jérôme Robert
Published: August 2014

The morphology of micelles formed by two poly(2-vinylpyridine)-blockpoly( ethylene oxide) (P2VP-b-PEO) copolymers has been studied in phosphatebuffered water by dynamic light scattering and transmission electron microscopy. Spherical micelles are observed when the P2VP block is the minor component of the diblock copolymer. When P2VP dominates the composition, transition from spheres-to-rods-to-vesicles takes place in a narrow pH range that straddles the pKa of P2VP. This transition is controlled by the degree of protonation of the P2VP blocks. At high pH, the copolymer precipitates from the solution.
Interpenetrating polydicyclopentadiene/polyacrylate networks obtained by simultaneous non-interfering frontal polymerization
Authors: Fiori Stefano , Mariani Alberto , Ricco Laura , Russo Saverio
Published: August 2014

Interpenetrating polymer networks made of dicyclopentadiene and methyl methacrylate or tri(ethylene glycol) dimethacrylate have been successfully prepared by non-interfering frontal polymerization. The role of catalyst and free radical initiator relative amounts, as well as of monomer ratio, has been thoroughly studied. The conditions under which a pure frontal polymerization occurs, and the related values of both front velocity and maximum temperature reached by the reaction, are presented and discussed.
Three-dimensional radical polymerization
Authors: Korolev Gennadii V. , Bubnova Maria L.
Published: August 2014

This is an analytical review on kinetics and mechanism of threedimensional radical polymerization (TDRP) of multifunctional vinyl monomers (oligomers) having two or more double bonds per molecule. The period (1960 - 1977) of establishing the fundamental kinetic law of TDRP and the principal characteristics of its mechanism, i.e., microheterogeneity, is briefly described. New intense progress in the field of TDRP (during the recent decade) resulting from the development of new technologies based on this technique (fiber-optic engineering, information technology, etc.) has received much consideration. The methodological peculiarities of investigations on TDRP kinetics and mechanism, which are a result of the complex conditions of highly structured reaction media inherent in TDRP processes, are described. Particular attention is given to techniques of structuralphysical investigation (a consistent complex of methods including ESR, NMR, diffusion and radiation probing, mechanics and thermomechanics) sensitive to structural microheterogeneity in the range 10-6 - 10-4 cm. The perspectives of macromolecular design based on TDRP data are analyzed including latest approaches as the employment of a ‘living’ chain mode. This review covers three monographs in Russian, reflecting three sequential stages of TDRP development from 1960 till 1995 using acrylic oligomers as an example (most of the investigations were carried out at the Institute of Chemical Physics RAS). The bibliography includes 197 references.
Direct interchain exchange reaction in a polymer blend: evolution of the block weight distribution
Authors: Kudryavtsev Yaroslav V. , Govorun Elena N.
Published: August 2014

The kinetics of an interchain exchange reaction in homogeneous polymer blends is studied theoretically. A set of kinetic equations describing the evolution of the block weight distribution is derived. It is demonstrated that the process may be divided into a fast and a slow stage. The former results in the almost full disappearance of homopolymer chains. Simultaneously, the block weight distribution becomes close to the Flory distribution. In the course of the slow stage, the average block lengths decrease to values typical of a completely random copolymer. It is explicitly shown that for an initial blend of homopolymers characterized by the Flory distribution, the transient block weight distribution takes the Flory form starting from the onset of the reaction. The copolymer composition is proved to change in the course of the fast stage of the process. Previous attempts to address the problem are discussed.
Novel unsaturated ε-caprolactone polymerizable by ringopening and ring-opening metathesis mechanisms
Authors: Lou Xudong , Detrembleur Christophe , Lecomte Philippe , Jérôme Robert
Published: August 2014

Ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) of an unsaturated ε-caprolactone, 6,7-dihydro-2(3H)-oxepinone (DHO2), are alternative routes to produce unsaturated aliphatic polyesters with the same molecular structure. Polymerization of DHO2 initiated by Al isopropoxide in toluene at room temperature or at 0°C proceeds by a coordination-insertion mechanism, although intramolecular transesterification takes place beyond complete monomer conversion. The molecular weight distribution is narrow as long as monomer conversion does not exceed 90%. Ring-opening metathesis polymerization of DHO2 initiated by Schrock’s Mo-based catalyst, 1, at 60°C allows higher molecular weight unsaturated polyester to be prepared, even though an intramolecular side reaction also operates. The structure of poly(DHO2) synthesized by ROP and ROMP is the same, as confirmed by 1H, 13C NMR, and FT-IR spectra. Copolymers of DHO2 with norbornene, cis-cyclooctene, and 1,5-cyclooctadiene have been successfully prepared.
Continuous metathesis reactions by molybdenum carbene complexes supported on inorganic carriers
Authors: Preishuber-Pflügl Peter , Eder Elisabeth , Stelzer Franz
Published: August 2014

Molybdenum carbene complexes supported on Al2O3/methylaluminoxane/ diol based carriers were tested in continuous metathesis reactions. For investigations on the stability of the heterogenized complexes, a small tubular reactor filled with catalyst powder was used. When mixing cyclic monomers with chain-transfer agents, we were able to run ring-opening metathesis polymerization (ROMP) via the supported carbenes in a continuous process. Furthermore, continuous acyclic metathesis reaction (ACM) and ring-closing metathesis reaction (RCM) were investigated. Results show that the stability of these molybdenum carbene complexes depends on the concentration of methylidene carbenes formed during the reactions.
Synthesis of rodlike ruthenium(II) coordination polymers having metal-nitrogen and metal-carbon bonds in their main chains
Authors: Schmelz Oliver , Rehahn Matthias
Published: August 2014

Well-defined coordination polymers are described whose main chains are held together by pseudo-octahedral ruthenium(II) complexes in which five ligands are nitrogen and one ligand is carbon. In the first step of polymer synthesis, the bis-tridentate ligand 4,4''-bis[4'-(2,2':6',2''-terpyridine)]-2',5'-dihexyl-p-terphenyl is treated with two equivalents of ruthenium(III) chloride. The resulting dinuclear metal-monomer is subsequently activated by exchanging the remaining three chloro ligands at each ruthenium center by acetone as a more easily substitutable ligand. The activated metal monomer is treated with equimolar amounts of 4,4''- bis[4'-(6'-phenyl-2,2'-bipyridine)]-2',5'-dihexyl-p-terphenyl as a bis-tridentate ligand monomer. During this conversion, rodlike chains grow through the formation of two further metal-nitrogen bonds and one carbon-nitrogen bond at every ruthenium center. The homogeneous constitution of the readily soluble polymers is proven, and their degrees of polycondensation are roughly estimated to be Pn ≥ 20, using 1H and 13C NMR spectroscopy. UV-vis absorption spectra show the polymers to behave like chains of electronically independent metal complexes. Due to the carbon-ruthenium bond, however, λmax appears at a longer wavelength (approx. 530 nm) than in the related coordination compounds with only nitrogen-ruthenium bonds. There, λmax is around 500 nm.
Two-dimensional chromatography of complex polymers. 3. Full analysis of polystyrene-poly(methyl methacrylate) diblock copolymers
Authors: Pasch Harald , Mequanint Kibret , Jörg Adrian
Published: August 2014

Poly(styrene-block-methyl methacrylate)s were fully analyzed by liquid chromatography at the critical point of adsorption (LC-CC) and two-dimensional chromatography. Operating at chromatographic conditions corresponding to the critical points of the homopolymers polystyrene and poly(methyl methacrylate), the block lengths distributions for the different blocks of the block copolymers were determined quantitatively. Information on the amounts and molar mass distributions of homopolymers and coupling products that were identified in the samples as by-products was obtained by on-line coupled 2D chromatography. It was shown that a complete picture of the molecular heterogeneity of block copolymers can be obtained only when information from different chromatographic experiments is combined. Size exclusion chromatography alone is inappropriate for evaluating the molecular heterogeneity of such samples.
Multiblock silicones, 1 Vinyl functionalized polydimethylsiloxane a
Authors: Ivanenko Carine , Maitre Catherine , Ganachaud François , Hémery Patrick
Published: August 2014

The first part of this series is devoted to the preparation of vinyl functionalized multiblock silicones by the process of anionic ring opening polymerization in miniemulsion. The advantage of working in dispersed media is that different scales of reactivities are found between one-chain reactions, taking place at the interface (propagation, backbiting), and two-chain reactions, located in the bulk of the particles (polycondensation and intermolecular redistribution). First, homopolymerizations of octamethylcyclotetrasiloxane (D4) and tetramethyltetravinylcyclotetrasiloxane (D4 V) were carried out and compared, focusing specifically on the rates of polymerization, backbiting and polycondensation processes. Copolymerization of D4 with D4 V then gave insight into the extent of mixed cycles’ formation and particularly how to avoid these. On this basis, recipes were carefully selected so that homopolymerization and scarce co-polycondensation and redistribution progress at the expense of backbiting reactions and thus multiblock copolymers are formed, the microstructure of which was confirmed with 29Si NMR.
Porous structure formation via phase separation of two polymers Blends of aromatic polyoxalates and poly(lactic acid)
Authors: Zorin Ivan , Ovcharenko Nadja , Batuto Yan , Bilibin Alexander
Published: August 2014

A new method of porous polymer structure formation by means of phase separation of two polymers with different degradation rates is proposed. Aromatic polyesters of oxalic acid as fast degradable polymers were synthesized and their degradation properties under alkaline conditions were studied. Heterogeneous mixtures of poly(phenolphthalein oxalate) with poly(lactic acid) were prepared by solution phase separation and co-precipitation, and porous poly(lactic acid) samples were produced by polyoxalate leaching due to its fast degradation.
Grafting of methyl methacrylate onto natural keratin
Authors: Martínez-Hernández Ana Laura , Velasco-Santos Carlos , Icaza Miguel de , Castaño Victor M.
Published: August 2014

Keratin fibers from chicken feathers were modified through graft copolymerization with methyl methacrylate in an aqueous medium, using a KMnO4 / malic acid redox system. Original and grafted fibers were characterized by IR and Raman spectroscopy and their thermal behavior was studied by both differential scanning calorimetry and thermogravimetric analysis. The grafted fiber surface was characterized by scanning electron microscopy. The characterization results show that grafting was effectively achieved and this was confirmed by a ninhydrin test after acidic hydrolysis of the grafted keratin.
Impact modification of polyamide-12 through blending with liquid polybutadiene, 2 a Compatibilization of blends of PA12 and liquid polybutadiene with pyromellitic anhydride
Authors: Talon Olivier , Couvercelle Jean-Pierre , Bunel Claude
Published: August 2014

The compatibilizing effect of pyromellitic anhydride (APy) in blends of PA12 and liquid polybutadiene (HTPB) was investigated. Blends were prepared, with or without APy, and the efficiency of this route of compatibilization was evidenced by observation of their morphologies. The addition of APy led to a finer dispersion of HTPB in the PA12 matrix. The formation of a compatibilizing block copolymer was proven by the evolution of the torque, the amine functionality and the size of the particles during blending, and by extraction of the dispersed phase followed by FTIR analysis. The effect of the mixing procedure was also investigated, and it was shown that the best dispersions were obtained when APy was added to a pre-blend of PA12 and HTPB.
Distribution of molecular weight and composition in diblock copolymers
Authors: Tobita Hidetaka , Zhu Shiping
Published: August 2014

The distribution of molecular weight (MW) and composition of diblock copolymers is considered theoretically. Assuming that the chain end of each block is coupled randomly, the weight-average MW of the block copolymers is given by Mw = w1 (Mw,1 + Mn,2) + w2 (Mw,2 + Mn,1), irrespective of the shape of the distribution of each block, where wi is the weight fraction, and Mn,i and Mw,i are the number- and weight-average MW of each block. In copolymer chains, the chemical compositions as well as the MWs cannot be identical for all polymers, and there exists a bivariate distribution of MW and composition. When the MW distribution (MWD) of both blocks follows the Schulz-Zimm distribution, the bivariate distribution can be obtained analytically. In addition to the bivariate distribution, the full MWD, the average composition as a function of MW, the composition distribution of copolymers having a specified MW, and the overall composition distribution are obtained. The composition distribution, as well as the average composition, becomes independent of MW under the condition σ1/Mn,1 = σ2/Mn,2, where σ i is a parameter indicating the narrowness of the Schulz-Zimm distribution. The present theoretical analysis provides new insight into the design of diblock copolymers.
Adsorption of monodisperse polybutadienes on carbon black, 1 Adsorption from dilute and semi-dilute solutions
Authors: Vuillaume Kathy , Haidar Bassel , Vidal Alain
Published: August 2014

A series of polybutadienes (PBs) of different molecular weights (in the range of 3000 to 120 000) but of identical microstructure (1,2-PB content ≈ 80%) was synthesized via anionic polymerization. The adsorption in solution of the various monodisperse PBs on carbon black (CB) was studied for different polymer/ CB ratios as well as for polymer and CB concentrations in the range of 0.1 to 100 g/l. The amount of adsorbed polymer was followed and was found to be essentially governed by the polymer concentration, which determines also the conformation of the polymer chain on the filler surface. CB concentration didn’t prove to be a pertinent parameter, whereas the polymer/filler ratio was found to control the formation of the three-dimensional polymer-filler network on the basis of a percolation process. Results are discussed with respect to the available theories.
Phase inversion and co-continuity domain in immiscible polyethylene/polystyrene blends
Authors: Prochazka Frédéric , Dima Romulus , Majesté Jean-Charles , Carrot Christian
Published: August 2014

Blends of polystyrene and high-density or linear low-density polyethylene have been prepared in an internal mixer and studied in a wide range of compositions. Phase inversion compositions have been determined using selective extraction and scanning electron microscopy. It appears that phase inversion can occur in a domain of compositions rather than at a single point. The existing models of phase inversion are not complete enough to explain the entire phenomenon, and percolation of each component may be considered to describe the formation of co-continuity.
Artificial muscles based on conducting polymers
Authors: Cortés María Teresa , Moreno Juan Carlos
Published: August 2014

Natural muscles have mechanical properties that conventional actuators do not possess. These natural machines show large strain, moderate stress, high efficiency and stability, fast response time, high power/weight ratio, long lifetime, etc. In the last years a great interest has arisen to develop materials that mimic natural mechanisms. Conducting polymers have an array of potential applications as artificial muscles since they are capable to produce a moderate displacement when submitted to an electrochemical reaction. This property has been used to fabricate actuator devices that imitate and even improve the performance of natural muscles. For example, conducting polymers show stresses 15 times higher than those generated by mammalian muscles, a high power/weight ratio and a high degree of compliance. However, there are also several responses that need improvement in the actuators based on conducting polymers. Strains are still c. 50% lower than in natural muscles. Most of this kind of actuators only work in liquid media. It is necessary to increase the response time and obtain more durable actuators with longer lifetime and higher stability. In spite of these disadvantages, the first actuators based on conducting polymers are being commercialized. This paper presents a brief summary of some of the actuators based on these polymers, focusing on their design, performance and actuation mechanism.
Living free radical polymerization of styrene with 2-cyanoprop-2-yl dithionaphthalate as RAFT agent
Authors: Jian Zhu , Xiulin Zhu , Di Zhou , Jianying Chen
Published: August 2014

The reversible addition-fragmentation chain transfer (RAFT) bulk polymerization of styrene was studied using 2-cyanoprop-2-yl dithionaphthalate (CPDN) as RAFT agent in the presence or absence of 2,2’-azoisobutyronitrile (AIBN). The results of both thermally and AIBN-initiated styrene (St) polymerizations show that St can be polymerized in a controlled way using CPDN as RAFT agent; i.e., the polymerization rate is first order with respect to monomer concentration, and molecular weight increases linearly with monomer conversion. The molecular weights obtained from gel permeation chromatography are close to the theoretical values and molecular weight distributions are relatively narrow (Mw/Mn < 1.2). It is confirmed by chain extension reaction that the polymer prepared via RAFT polymerization can be used as a macroRAFT agent. The effects of reaction temperature and mole ratios [St]0/[CPDN]0/[AIBN]0 on the polymerization were investigated. The results indicate that the reaction temperature has a positive effect on the polymerization rate, but little effect on molecular weight and molecular weight distribution, and the optimum mole ratios were found to be [CPDN]0/[AIBN]0 > 4/3 and [St]0/[CPDN]0 < 800.
Cholesteric copolymers and mixtures containing dithienylethene photochromic fragments
Authors: Semenova Dasha , Bobrovsky Alexey , Boiko Natalia , Shibaev Valery , Zavarzin Igor , Kalik Marina , Krayushkin Mikhail
Published: August 2014

The phase behaviour and optical properties of mixtures based on cholesteric copolymers with 3 - 6 wt.-% of photochromic dithienylethene dopants as well as a cholesteric copolymer containing dithienylethene side groups were studied. It was shown that planar-oriented films of the mixtures and of the copolymer possess a selective light reflection in the visible or near IR regions of the spectrum. UV irradiation of the mixture films leads to the appearance of an intense absorbance peak in the spectral range coinciding with the selective reflection band (λmax ≈ 522 - 615 nm depending on the chemical structure of the photochromic fragment). This process is associated with the photocyclization of dopants and photochromic side groups and the ‘degeneration’ of the selective light reflection. The photoinduced coloured form of dopants and photochromic side groups is thermally stable at room temperature, but subsequent irradiation of the film by visible light (550 or 633 nm) induces a decoloration process. The influence of temperature on the rates of forward and back photoprocesses in such polymeric liquid crystalline films was studied. The potentialities of the use of such type of materials for reversible data recording and storage were demonstrated.
Combination of supramolecular cross-linking with covalent cross-linking through epoxide ring-opening including gel studies
Authors: Hofmeier Harald , El-ghayoury Abdelkrim , Schubert Ulrich S.
Published: August 2014

Terpolymers based on poly(methyl methacrylate), containing terpyridinemoieties as well as epoxide groups, were synthesized via free-radical polymerization. The products were cross-linked non-covalently with iron(II) ions and covalently by treatment with AlCl3. Both steps could be combined in different order. The non-covalent cross-linking could be reversed by applying a strong competing ligand. The swelling behaviour of the polymers was investigated.
Relevance of purification procedures in the direct synthesis of poly(p-phenyleneterephthalamide) from its dimer
Authors: Mariani Alberto , Monticelli Orietta , Fiori Stefano , Russo Saverio
Published: August 2014

The direct synthesis of poly(p-phenyleneterephthalamide) has been successfully performed by polymerizing its dimer, N-(4-aminophenyl)terephthalamic acid, instead of p-phenylenediamine and terephthaloyl chloride or terephthalic acid, as commonly carried out. An intrinsic viscosity much higher than those typical of the commercial fibres (Kevlar®) has been obtained. The procedure and the advantages of the method are highlighted.
Impact modification of polyamide-12 through blending with liquid polybutadiene, 1 Binary blends of PA 12 and liquid polybutadiene
Authors: Talon Olivier , Couvercelle Jean-Pierre , Bunel Claude
Published: August 2014

Blends of polyamide 12 (PA12) with liquid polybutadiene (HTPB) were prepared by melt blending over a composition range varying from 0 to 20% of polybutadiene. A study of the potential reactions led to the conclusion that the system undergoes no chemical reaction under the processing conditions used. Scanning electron micrographs of the blends showed a good dispersibility of HTPB in the PA12 matrix. Charpy impact tests and tensile tests demonstrated that the dispersion of HTPB in PA12 provides a good impact toughness enhancement but leads to a decrease of Young's modulus.
Synthesis and characterization of alternating poly(amide urea)s and poly(amide urethane urethane)s from ε-caprolactam, diamines, and diphenyl carbonate or ethylene carbonate
Authors: Ubaghs Luc , Sharma Bhaskar , Keul Helmut , Höcker Hartwig , Loontjens Ton , Benthem Rolf van
Published: August 2014

Alternating poly(amide urea)s from ε-caprolactam, diamines H2N-(CH2)x- NH2 (x = 2 - 4), and diphenyl carbonate were prepared in two steps. The microstructure of the poly(amide urea)s, as determined by means of 1H NMR spectroscopy, reveals a strictly alternating sequence of the building blocks. The molecular weights and polydispersities obtained were 7500 < Mn < 10 000 and 1.48 < Mw/Mn < 1.56, respectively. Thermal properties were determined by means of differential scanning calorimetry (DSC) (163.9°C < Tm < 197.2°C; 55.5°C < Tg (2nd heating) < 72.2°C), and thermogravimetric analysis (TGA). TGA shows a three-step decomposition at 200, 350, and 450°C, which was attributed to the cleavage of O-phenyl urethane end groups, as well as urea and amide linkages. These assignments were made by comparison with model compounds. Furthermore, alternating poly- (amide urethane urethane)s from ε-caprolactam, diamines, and ethylene carbonate were prepared in three steps. The microstructure of the poly(amide urethane urethane)s, as determined by means of 1H NMR spectroscopy, reveals imperfections. The molecular weights and polydispersities obtained were 5400 < Mn < 17 000 and 2.08 < Mw/Mn < 2.99, respectively. Thermal properties were determined by means of DSC (155.9°C < Tm < 159.0°C; 35.5°C < Tg (2nd heating) < 39.0°C) and TGA. TGA shows a complex decomposition due to the formation of ethylene carbonate by cleavage of the urethane groups (at approx. 230°C) and formation of poly(amide urea)s. The newly formed poly(amide urea)s decompose in a similar way as the poly(amide urea)s.
Characterization of an isophorone-based polyisocyanate
Authors: Burel Fabrice , Feldman Adeline , Loutelier-Bourhis Corinne , Bunel Claude
Published: August 2014

After chemical modification with methanol, a polyisocyanate based on the isocyanurate of isophorone diisocyanate was analysed. MALDI-TOF MS and sizeexclusion chromatography were chosen and indirectly coupled to identify and quantify the different species. While, as expected, the isocyanate trimer and pentamer are the two main components, homologues until the tridecamer could be identified with MS. Moreover, the isocyanurate cycle occurs preferentially on the primary isocyanate group. According to the calculated composition, a numberaverage molecular weight of 775 and a number-average isocyanate functionality of 3,24 were determined.
Binary frontal polymerization: Velocity dependence on initial composition
Authors: Pojman John A. , Griffith Jerry , Nichols H. Archie
Published: August 2014

Frontal polymerization is a mode of polymerization in which a localized zone of reaction propagates through the coupling of thermal diffusion and the Arrhenius dependence of the reaction rate. The dependence of the front propagation velocity on the initial composition has been determined in initially miscible binary systems of a free-radically cured diacrylate and an amine- or cationically cured epoxy resin. A minimum of the velocity as a function of the monomer mole fraction is observed if the two polymerizations occur independently. Excellent agreement with an analytical description was found with the diacrylate and an amine-cured epoxy but not for a diacrylate and a cationically cured one because of the effect of HCl impurities on the peroxide.
Synthesis of a novel poly(p-phenylene-vinylene) derivative and its application in chemiresistive sensors for electronic noses with an unusual response to organic vapours
Authors: Gruber Jonas , Yoshikawa Eduardo K. C. , Bao Ying , Geise Herman J.
Published: August 2014

We report the synthesis of a novel poly(p-phenylene-vinylene) derivative bearing dodecanoylsulfanyl side-groups (12COS-PPV). Good solubility in organic solvents was achieved. The average molecular weight was around 30 000, the energy gap 2.8 eV and the thermal stability up to 130°C. Doping with iodine vapours rose conductivity to 2·10-6 S/cm. Gas sensors made from FeCl3-doped 12COS-PPV showed an unusual behaviour responding to only four of the eight different organic solvent vapours tested. Recoveries from the responses are not complete, but are reproducible and can be used to discriminate between the four solvents. Quantitative analyses are also possible since there is a good linear correlation between relative response and concentration.
Preparation and swelling behaviour of a novel anti-salt superabsorbent hydrogel based on kappa-carrageenan and sodium alginate grafted with polyacrylamide
Authors: Pourjavadi Ali , Ghasemzadeh Hossein , Hosseinzadeh Hossein
Published: August 2014

A novel superabsorbent hydrogel was synthesized via crosslinking graft copolymerization of acrylamide (AAm) onto kappa-carrageenan (κC) and sodium alginate (Na-Alg) backbones in a homogeneous solution. Methylenebisacrylamide (MBA) and potassium persulfate (KPS) were applied as water-soluble crosslinker and initiator, respectively. FTIR spectroscopy was used for confirming the structure of the final product. A mechanism for superabsorbent hydrogel formation was also suggested. The parameters affecting the swelling capacity of the synthesized hydrogel, i.e., κC-Alg weight ratio, concentration of AAm, MBA and KPS, as well as reaction temperature were systematically optimized for obtaining maximum absorbency. The swelling capacity of hydrogels was also measured in various salt solutions (LiCl, NaCl, KCl, MgCl2, CaCl2, SrCl2, BaCl2, and AlCl3). Due to their high swelling ability in salt solutions, the hydrogels may be referred to as ‘anti-salt superabsorbent’ polymers. The overall activation energy for the graft copolymerization reaction was found to be 374 kJ/mol. The swelling kinetics of the hydrogels in distilled water and in saline solution (0.9 wt.-% NaCl) was investigated.
Characteristics of non-isothermal crystallization of polypropylene with and without talc
Authors: Albano Carmen , Papa José , Ichazo Miren , González Jeanette , Ustariz Carmen
Published: August 2014

The non-isothermal behaviour of crystallization of polypropylene (PP) and its talc-filled composites was investigated by means of differential scanning calorimetry. Different analytical methods were used to describe the crystallization process. According to the behaviour of crystallization temperature, crystallization activation energy and crystallization parameters and coefficient, talc results in an increase in PP crystallization rate and in a decrease in total energy opposing to homogeneous crystallization. Velisaris-Seferis’ kinetic equation was found to describe reasonably well the non-isothermal behaviour of crystallization of PP and its filled composites.
Removal of copper-based catalyst in atom transfer radical polymerization using different extraction techniques
Authors: Ydens Isabelle , Moins Sébastien , Botteman François , Degée Philippe , Dubois Philippe
Published: August 2014

Several methods allowing the removal of copper-based ATRP active complexes from crude amino-functionalized polymethacrylate chains are compared. Among them, precipitation in basic medium is one of the most efficient techniques since it allows high recovery yields (above 90%) with a residual metal content as low as 5 ppm. Extraction methods such as liquid-liquid phase separation and dialysis but also selective adsorption on acidic macroporous ion exchange resin constitute other attractive alternatives. As far as water-insoluble polymers are concerned, catalyst adsorption on alumina remains the most universal method and provides acceptable recovery efficiency. However, we want to stress the key-importance of the experimental adsorption conditions and above all the relative content of alumina used for catalyst extraction.
Molecular dynamics in polymeric systems
Authors: Dionísio Madalena , Alves Natália M. , Mano João F.
Published: August 2014

It is well known that the properties of polymeric materials depend strongly upon their chemical structure. Other more specific factors that may be related to the chemical structure also determine the macroscopic behaviour of such materials, namely the relative position of the different segments of the polymeric chain, the molecular architecture (molecular weight distribution, branching, copolymer organisation, cross-linking extent, etc.), the crystalline environment and the pressure/temperature conditions. All these factors have a common impact in the material: they are strongly correlated to the mobility on the molecular level. That is why a huge amount of work has been devoted to the study of translational/rotational mobility that occurs within the polymeric chains. This review is intended to provide a brief survey on such kinds of mobilities, how they can be studied and what are their main characteristics. Examples on systems studied in our groups will be provided, obtained by dielectric and mechanical spectroscopies and differential scanning calorimetry. It will be mainly focused on molecular motions that occur in the solid phase (i.e., to temperatures up to the rubbery plateau). The dynamics in blends or copolymers will be avoided here, as they would deserve a special discussion in their own context. Special attention will be paid to the glass transition and the mobility that occurs below and above it. The dynamics that are observed in peculiar systems, such as semi-crystalline or liquid crystalline polymers, will be addressed.
Preparation of chitosan-containing nanofibres by electrospinning of chitosan/poly(ethylene oxide) blend solutions
Authors: Spasova Maria , Manolova Nevena , Paneva Dilyana , Rashkov Iliya
Published: August 2014

The first successful preparation of chitosan-containing nanofibres was achieved by electrospinning of chitosan/poly(ethylene oxide) (PEO) blend aqueous solutions. The diameters of the nanofibres were in the range 40 - 290 nm and decreased with increasing chitosan content and decreasing total concentration. An increase of the applied field strength leads to an increase of the diameter of the nanofibres and to a broadening of the size distribution. The possibility to prepare nanofibres containing a model drug - potassium 5-nitro-8-quinolinolate (K5N8Q), a broad-spectrum antimicrobial and antimycotic agent - was shown. The incorporation of K5N8Q in the nanofibres resulted in a decrease of the nanofibre diameters and the appearance of bead-shaped defects. Non-woven mats from the drugloaded nanofibres with composition chitosan : PEO = 1:1 (w/w) and 1% K5N8Q showed antibacterial and antimycotic activity against E. coli, S. aureus and C.albicans.
Molecular deformation mechanisms and mechanical properties of polymers simulated by molecular dynamics
Authors: Simões Ricardo , Cunha António M. , Brostow Witold
Published: August 2014

Virtual polymeric materials were created and used in computer simulations to study their behavior under uniaxial loads. Both single-phase materials of amorphous chains and two-phase polymer liquid crystals (PLCs) have been simulated using the molecular dynamics method. This analysis enables a better understanding of the molecular deformation mechanisms in these materials. It was confirmed that chain uncoiling and chain slippage occur concurrently in the materials studied following predominantly a mechanism dependent on the spatial arrangement of the chains (such as their orientation). The presence of entanglements between chains constrains the mechanical response of the material. The presence of a rigid second phase dispersed in the flexible amorphous matrix influences the mechanical behavior and properties. The role of this phase in reinforcement is dependent on its concentration and spatial distribution. However, this is achieved with the cost of increased material brittleness, as crack formation and propagation is favored. Results of our simulations are visualized in five animations.
Molecular and supramolecular approaches for tuning properties of new polyketanils
Authors: Sęk Danuta , Iwan Agnieszka
Published: August 2014

A new family of π-conjugated polyketanils was synthesized and thermal and optical properties of the polymers were tuned by ‘chain engineering’, consisting of the appropriate design of chain building blocks using diamines and diketones with various chemical structures, and ‘dopant engineering’ in which a specially designed multifunctional dopant was used, 1,2-(di-2-ethylhexyl) ester of 4-sulfophthalic acid, capable of specific interaction with the host polymer. The structure of the dopant creates a new type of supramolecular comb-shaped architecture in which the lateral groups, anions of the sulfophthalic acid residue, are ionically bonded to the main chain via protonation of ketimine nitrogen atoms. This specific interaction of the dopant with the host polymer influences the polyketanils’ properties and the following changes were observed: decreasing glass transition temperature and improvement of polymer film flexibility, as well as a bathochromic shift of the photoluminescence emission band.
Relationship between structural evolution and rheological measurements for polymer + organoclay nanocomposites
Authors: Kim Hee Bong , Hyun Yang Hoon , Lim Sung Taek , Choi Hyoung Jin , Jhon Myung S.
Published: August 2014

Nanocomposites with synthetic biodegradable aliphatic polyesters (BAP) were synthesized by the solution intercalation method with addition of organically modified montmorillonite. The hybrid structural evolution, caused by nanoscopic interaction between matrix polymer and layered silicate, was analyzed using viscoelastic properties obtained from oscillatory rheological measurements. Changes of viscoelastic properties to more solid-like, especially in the terminal region, were explained by both formation of specific BAP chain mesostructures with organoclay incorporated and a rheological percolation threshold. This behaviour was analyzed via a modified Cole-Cole plot evaluating the structural changes with filler concentration as well as the frequency dependence of dynamic modulus, complex modulus, and phase angle. Furthermore, the stress relaxation behaviour successfully demonstrated structural changes and critical concentration of nanocomposites with a jump shift of the longest relaxation time towards longer time.
Wetting of bioactive glass surfaces by poly(α-hydroxyacid) melts: interaction between Bioglass® and biodegradable polymers
Authors: Blaker Jonny J. , Maquet Véronique , Boccaccini Aldo R. , Jérôme Robert , Bismarck Alexander
Published: August 2014

The interfacial characteristics between bioactive glass (45S5 Bioglass®) surfaces and poly(α-hydroxyacid) melts have been assessed by direct wetting measurements. In particular, the wettability of Bioglass® powder by poly(D,Llactide) (PDLLA) and poly(D,L-lactide-co-glycolide) (PLGA) was assessed by imbibition measurements. Additionally, the equilibrium contact angles of PDLLA and PLGA melts on a sintered Bioglass® surface were measured. The surface energy of the bioactive glass and the polymers was determined from contact angles measured using various test liquids on PDLLA, PLGA and Bioglass® solid substrates. There are sufficient adhesive interactions between the polymers and Bioglass®. A simple heat treatment of the bioactive glass in an inert gas atmosphere leads to an improved wetting behaviour, indicating increased adhesive interactions. Scanning electron micrographs of the polymer + Bioglass® composites formed by polymer penetration into the powder bed show the formation of a ‘good quality’ interface.
Modification of polymers by ultrasound treatment in aqueous solution
Authors: Rokita Bozena , Czechowska-Biskup Renata , Ulanski Piotr , Rosiak Janusz M.
Published: August 2014

Ultrasound treatment, as an alternative to chemical and radiation-based processes, is an interesting technique for the modification of average molecular weights of natural and synthetic polymers in aqueous solution. Degradation is the observed main effect for strongly hydrophilic compounds - poly(acrylic acid) and chitosan. It is demonstrated that this process is caused by OH radicals as well as mechanochemical effects. Studies on more hydrophobic polymers - poly(ethylene oxide) and poly(ethylene glycol)s - indicate that here cross-linking and degradation occur side-by-side. The net effect of these competing reactions depends on the length of the polymer chains.
Potentials of solvation of macromolecules as a measure of intermolecular interactions under viscous flow conditions
Authors: Filimoshkin Anatoliy , Safronov Sergey , Safronova Marina , Chernov Eugene
Published: August 2014

Viscous flow of polymer solutions is depicted as a combined totality of elementary acts of flow within the bounds of the thermodynamic Joule cycle. Intrinsic viscosity of polymer solutions is represented as an energetical function of intermolecular interactions rather than a measure of additional loss of energy due to the rotational and viscoelastic deformations of macromolecules in the flow. A new theoretical concept in the light of the thermodynamic cycle analogous to that of Joule is brought forward to describe the viscous flow of polymer solutions. The concept is represented as a sequence of elementary cyclic processes described by equations, which establish a relationship between solvation potentials (E) and thermodynamic parameters such as temperature and volume. Solvation potentials are identified with the value of maximal solvation work and allow evaluating the energy of the corresponding intermolecular interactions via E, individually of electrostatic (Ea) and covalent (Eb1, Eb2) nature.
Novel, biocompatible polyether(meth)acrylate-based formulations for stereolithography – A new flexible material class for three-dimensional applications
Authors: Bens Arthur Thomas , Tille Carsten , Bermes Günter , Emons Moritz , Seitz Hermann
Published: August 2014

Herein we present a novel polyether(meth)acrylate-based resin material for stereolithography and other photolithographic applications with outstanding flexible material characteristics. This group of photopolymeric resin products combines the advantages of a non-toxic (meth)acrylate-based process material with a broad spectrum of adjustable low Young’s modulus material characteristics. In contrast to the mostly rigid and non-flexible process materials used at the moment in the engineering world, these formulations are able to fulfil the extended need for a very flexible and also biocompatible engineering material, especially for threedimensional models or prototypes in the medical technology area. A short overview over the bandwidth of possible material characteristics is given in this publication.
Scanning electron microscopy investigation of tooth/filling bonding
Authors: Siejka-Kulczyk Joanna , Lewandowska Małgorzata , Raczyńska Marta , Jodkowska Elżbieta , Kurzydłowski Krzysztof J.
Published: August 2014

Scanning electron microscopy (SEM) investigations have been conducted to determine the influence of selected material on tissue/material bonding. Extracted human teeth were used in this study. Several resin composites were tested as dental fillings. To reveal the structure of the tissue/filling interface, the teeth were cut parallel to the long axis. Bonding quality was determined by direct SEM observation and microanalysis with X-ray energy spectrometry (EDX). The investigated materials show good bonding with enamel.