bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological control of impact toughness in poly(methyl methacrylate) /acrylonitrile‐butadiene rubber blends
Authors: Lindsay C. I. , Jenkins S. D. , Emmerson G. T. , McGrail P. T.
Published: March 2011

Toughening of PMMA by in‐situ polymerisation of methyl methacrylate/acrylonitrile‐butadiene rubber solutions to give blends with a multiple‐inclusion morphology has been achieved This contrasts with the lack of impact toughening observed upon direct blending of PMMA with the same rubber. The toughened blends are analogous to HIPS in terms of the multiple‐inclusion morphology and the observed cross‐linking within the separated elastomeric phase but possess significantly larger separated phase domains.
Chemical reactions during reactive blending of polyurethanes: Fiction or reality?
Authors: Stutz Herbert , Pötschke Petra , Mierau Uta
Published: March 2011

The extent of reactions occurring during reactive blending of thermoplastic polyurethanes (PUR) with functionalized polyolefins or reactive compatibilizers has been studied using ethylene/acrylic acid and styrene/maleic anhydride copolymers. Due to interfacial segregation effects, no reaction was found with carboxylic groups and only little with anhydrides. Here 1–2% reaction products are generated after 30 min with preferentially multiple additions at the same molecules. Therefore, with incompatible polymers, reactive coupling is negligible with PUR under realistic blending conditions.
Reactive compatibilization of poly(styrene‐Co‐maleic anhydride)/poly(phenylene oxide) blends
Authors: Koning Cor , Bruls Willie , Buijsch Frans Op Den , Vondervoort Lizette V. D.
Published: March 2011

Primary amine terminated polystyrene (PS‐NH2), with Mn=12,000 g/mol and Mw=23,000 g/mol, was applied as a reactive compatibilizer for poly(styrene‐co‐maleic anhydride)/poly(phenylene oxide) (SMA/PPO) blends, in which both an impact modifier for the continuous SMA phase, viz. ABS, and the dispersed PPO phase, viz. SEBS, was incorporated. During melt blending, SMA‐g‐PS copolymers are generated at the interface between the SMA/ABS and the PPO/SEBS phases. The addition of 10 wt % of the reactive PS‐NH2 compatibilizer to a SMA/ABS/PPO/SEBS 30/30/30/10 blend results in a more significant refinement of the dispersed PPO/SEBS particles than 10 wt % of a commercially available, bulky PS‐graft‐PMMA copolymer with Mn=45,300 and Mw=293,400 g/mol. In addition, PS‐NH2 gives a more pronounced enhancement of the yield stress, the stress at break and the notched Izod Impact than the PS‐g‐PMMA. On the other hand, the elongation at break is higher in the case of the non‐reactive PS‐g‐PMMA. It was demonstrated that surface imperfections, probably introduced by an observed strongly elastic character due to partial crosslinking of the SMA/ABS phase by difunctional H2N‐PS‐NH2, are responsible for the lower elongation at break for the PS‐NH2 based blends.
Surfactant induced mesomorphic behaviour of flexible polymers
Authors: Ikkala Olli , Ruokolainen Janne , Torkkeli Mika , Serimaa Ritva , Brinke Gerrit Ten
Published: March 2011

Conditions for micro phase separated structures based on flexible polymers associated with surfactants have been investigated. Reasonably strong attractive interactions are required to oppose macro phase separation between polymer and surfactant. In order to obtain micro phase separation, additionally a sufficiently strong polar‐nonpolar repulsion has to be present. Poly(4‐vinyl pyridine), poly(2‐vinyl pyridine) and polyamide 6 have been used as model polymers in this work. Associations based on protonation, metal coordination and hydrogen bonding are presented and shown to yield micro phase separation under suitable conditions. In the charged systems, the polar‐nonpolar repulsion easily becomes large enough to render micro phase separated structures. In hydrogen bonded (i.e. noncharged) systems a more delicate balance can be achieved in which case an order‐disorder transition takes place from a homogeneous state, exhibiting nonetheless a distinct SAXS peak due to characteristic block copolymer‐like fluctuations, to a micro phase separated ordered state.
Blends of some non‐flexible and flexible polymers: Routes to molecular composites?
Authors: Cowie John M. G. , Nakata Shoichi , Adams Gordon W.
Published: March 2011

The definition of a molecular composite is a blend of a rigid rod polymer and a flexible coil polymer that is miscible at the molecular level. This concept has been tested using systems in which the chain flexibilities differ as widely as possible as judged by the difference in glass transition temperatures (δTg). The biggest variation (δT ∼360°C) was obtained by mixing poly benzimidazole with copolymers of poly(vinyl acetate‐ran‐vinyl alcohol). It was observed that the blends were distinctly two phase when the hydroxyl content was less than 50 mol %. Above this value clear blends were obtained with finely dispersed phases although it is doubtful if mixing at the molecular level takes place.

Miscible blends could be obtained from combinations of the sodium salt of poly(phenylene terephthalamide) with poly(4‐vinylpyridine) and mixtures of poly(phenyl imino‐1,4‐phenyleneoxyterephthalate) with poly(styrene‐stat‐hydroxylstyrene) where coulombic interactions and hydrogen bonding respectively promoted the miscibility.
On the extension of polysoaps: The Gaussian approximation
Authors: Borisov Oleg V. , Halperin Avraham
Published: March 2011

Polysoaps are linear hydrophilic chains that incorporate, at intervals, covalently bound amphiphilic monomers. In water, the amphiphilic monomers self assemble into intrachain micelles thus endowing the chain with a secondary structure. The relaxation of the secondary structure upon deformation qualitatively modifies the elastic behaviour of polysoaps in accordance with the LeChatelier principle. For long polysoaps a regime in which the tension in the chain, f, is independent of the end to end distance R, f ˜ R° is predicted. The extension of long polysoaps is analysed for the particularly simple case when the backbone obeys Gaussian statistics and excluded volume interactions are neglected.
ABC and BAC triblock copolymers ‐ morphological engineering by variation of the block sequence
Authors: Abetz Volker , Stadler Reimund
Published: March 2011

Different morphologies and phase transitions of ternary triblock copolymers with different block sequences (ABC and BAC) are discussed qualitatively. The interplay between interfacial energies and elastic energies of the different blocks leads to various morphologies and enhances or prevents mixing of different blocks, depending on composition and topology.
Electrooptical properties of mesogenic chain molecules in solution and in nematic state
Authors: Tsvetkov Victor N. , Tsvetkov Nikolay V. , Kant Rama
Published: March 2011

Electrooptical characteristics of mesogenic chain molecules in solution and in mesophase can be described in terms of intra‐ and intermolecular orientational orders. The value and sign of electric birefringence δn in a solution of kinetically rigid chain molecules are determined by the combination of two factors: intramolecular orientational order which depends on the dipolar and anisotropic architecture of the molecule and intermolecular orientational order caused by the action of the external electric field E. The value and sign of the dielectric anisotropy δε of the polymer nematic phase are also determined by the combination of intra‐ and intermolecular orders. However, in this case the latter is not maintained by the external field but by the nematic potential of the mesophase. Therefore, comparative investigations of electrooptical properties of polymers in solutions and in nematic melts make it possible to obtain information about the intra‐ and intermolecular orientational orders of the molecules under investigation in these two states. These investigations were carried out using the method of electric birefringence in solutions and the method of orientational deformations of nematic textures in an electric field. The objects being investigated were nematogenic dimers and trimers. Experimental data obtained for these compounds showed the presence of intramolecular order in their molecules, which is manifested in the odd‐even oscillations of the value and sign of Kerr constant K≈δn/E2 in solution and δε in the nematic phase when the number of C‐C bonds in the methylene spacers of these molecules is varied. This effect is particularly dramatic in the mesophase where it is enhanced by intermolecular nematic potential.
Fluctuation, relaxation and “super‐structure” in liquids the conformon model
Authors: Kilian Hanns‐Georg
Published: March 2011

The conformon model of liquids postulates a heterogeneous dynamic superstructure in liquids. The model predicts a universal reduced energy‐ and entropy‐density distribution (Planck distribution) which typify together the thermodynamics of fluctuations. The mean reduced energy‐ and entropy density distributions are identical and invariant at all temperatures, independently of the type of molecules the liquid is comprised of. The model predicts therefore a unique superstructure at the quasi‐static glass‐transition temperature. Tapping‐mode atomic force experiments on monolayers of bottle‐brush molecules reveal a type of a superstructure which is, in fact, in good accord with the conformon model. Relaxation experiments can be described as superposition of a broad set of intra‐conformon Debye‐processes which is consequently related to the heterogeneous equilibrium structure. Principal aspects of the results are reflected in the paper.
Nuclear magnetic relaxation in solutions of poly(fluoromethylene) and poly(vinyl fluoride); segmental mobility of fluorinated ethylene polymers
Authors: Stockmayer Walter H. , Yang Henry W.‐H. , Matsuo Keizo
Published: March 2011

1H and 19F spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for solutions of poly(fluoromethylene) in DMSO, and for poly(vinyl fluoride) in DMF. These results, together with literature values for other fluorinated ethylene polymers, show that substitutions of F for H on the chain backbone produce only mild changes in segmental mobility.
Reversible thermothickening of aqueous solutions of polycations from natural origin
Authors: Desbrières Jacques , Rinaudo Marguerite , Chtcheglova Lilia
Published: March 2011

This paper concerns our first set of experimental data on alkyl chitosans in acidic medium allowing to compare the roles of the degree of alkylation and that of the length of the alkyl chains on their physicochemical properties in aqueous solution. The balance between electrostatic repulsion (related to the fraction of ‐NH3+) and the hydrophobic attraction is discussed on the CC12 sample, a chitosan modified with a C12 aliphatic chain. A phase diagram is established separating the conditions for gel‐like structure formation and phase separation. The roles of the net charge and that of the temperature on the formation of hydrophobic aggregates are examined.
Spreading of polymer molecules on solid surfaces
Authors: Stuart Martien A. Cohen , van Eijk Marcel C.P. , Dijt Jaap C. , Hoogeveen Nynke G.
Published: March 2011

When a homopolymer adsorbs from dilute solution onto a solid surface it first attaches and then maximises its number of contacts with the substrate by means of a spreading process. Evidence for this spreading process can be obtained from experiments on the adsorption kinetics. We report on a case where the adsorption kinetics depend on the rate at which the polymer was supplied to the surface (a protein adsorbing onto silica). Also, we discuss competitive adsorption experiments in which one kind of chain molecule attempts to displace another one from the surface. In these experiments, the desorption rate of the displaced species reflects the spreading rate of the displacer. When this rate is slower than the supply of displacer molecules, oversaturated layers result that spontaneously eject polymer. We have measured the rate of these displacement‐driven desorption processes in various cases and conclude that it depends strongly on the energy of the segment‐surface bond. A model involving the diffusion of defects over the surface may account for this finding.
Interfaces between coexisting phases of polymer mixtures: Comparison between Monte Carlo simulations and theoretical predictions
Authors: Binder Kurt , Müller Marcus
Published: March 2011

Large scale Monte Carlo investigations of the interface between A‐rich and B‐rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144<T/Tc0.759, includes both the strong and the weak segregation limit. Interfacial free energy and interfacial structure are studied, and compared to predictions based on the selfconsistent field theory. Also the broadening of the interfacial width due to capillary waves is considered, and finite size effects due to the confinement of interfaces in thin films of polymer blends are discussed.
Structures of “crew‐cut” aggregates of polystyrene‐b‐poly(acrylic acid) diblock copolymers
Authors: Zhang Lifeng , Eisenberg Adi
Published: March 2011

“Crew‐cut” aggregates of polystyrene‐b‐poly(acrylic acid) block copolymers can be prepared by dissolving the copolymers in N,N‐dimethylformamide (DMF) and adding water to the solution to induce aggregation of the styrene segments of the copolymer chains. The aggregates are formed at near‐equilibrium conditions, and their structures are subsequently frozen by isolating them into aqueous solution by dialysis. Aggregates of a number of different morphologies have been prepared. The morphologies, identified by transmission electron microscopy, consist of spheres, rods, vesicles, lamellae, large compound vesicles, large compound micelles, etc. The formation of aggregates of different morphologies can be controlled by varying the copolymer composition, by changing the initial copolymer concentration in DMF, by adding ions (e.g. NaCl, CaCl2, HCl and NaOH, etc), or by adding homopolystyrene.
Polymer‐solvent co‐crystallization during thermoreversible gelation in solutions of the helical polypeptide PBLG
Authors: Tadmor Rafi , Dagan Anca , Cohen Yachin
Published: March 2011

Macromolecular aggregation during thermoreversible gelation in solutions of the helical polypeptide poly(γ‐benzyl‐L‐glutamate) [PBLG] in benzyl alcohol [BA] were studied by small angle neutron and small angle X‐ray scattering. Gelation is apparent as a large increase in the intensity scattered at low angles, signifying formation of a microfibrillar PBLG network. The aggregated phase in isotropic gels from semidilute solutions contains about 28% solvent. A periodic structure is observed when gelation is induced by rapid cooling to a low temperature, but not by slow cooling or gelation at a higher temperature. In gels from concentrated liquid crystal solutions, two crystalline structures are observed, depending on whether the solution is rapidly quenched and then annealed or slowly gelled at an elevated temperature. A phase diagram for the PBLG/BA system is presented and the observed microstructural transitions are rationalized in terms of a gelation mechanism involving a combination of liquid‐liquid phase separation and crystallization in the form of polymer‐solvent co‐crystals.
Syndiotactic polystyrene/ethylbenzene complex: Chain conformations and phase behaviour
Authors: Spells Stephen J.
Published: March 2011

Syndiotactic polystyrene (sPS) has been studied, primarily in the δ (solvent‐stabilised) and γ phases. Crystallisation from dilute ethylbenzene solution at 40°C leads to a lamellar morphology, with a similar unit cell for the polymer/solvent complex as that proposed by Chatani et al for the sPS/toluene complex [1]. As the temperature is raised, the X‐ray long period increases in the temperature range of decomplexation, becoming constant in the y phase before increasing again on annealing in the α phase.

Neutron scattering measurements show negligible isotopic fractionation and only a small increase in the radius of gyration in the plane of the sedimented δ phase mats (Rxy) with increasing molecular weight. Together with model simulations which reproduce satisfactorily both the form of Kratky plots and the values for Rxy, this evidence points strongly towards a sheetlike structure (as is obtained for other non‐complexing solution‐grown polymer crystals). Increases in Rxy and changes in the scattering curves from those characteristic of sheetlike structures in the γ phase are interpreted as indicating movement of crystal stems out of the sheets.
Thermoreversible gelation of syndiotactic polystyrene: Effect of solvent type
Authors: Daniel C. , Menelle A. , Brulet A. , Guenet J.M.
Published: March 2011

The temperature‐concentration phase diagrams of syndiotactic polystyrene (sPS)/benzene gels and sPS/toluene gels establish the existence of two polymer‐solvent compounds in both systems. In particular it is found that the sto ichiometries of the compounds differ with the type of solvent: The stoichiometrics, expressed as solvent molecules/monomer are respectively for the benzene 4/1 and 1/1 and for the toluene 0.8/1 and 1/4. Neutron diffraction patterns allow us to confirm the existence of differents compounds in sPS/toluene gel and sPS/benzene gel.
Transient electric birefringence study of agarose aggregates in water‐dimethyl sulphoxide mixtures
Authors: Ramzi M. , Mendes E. , Rochas C. , Guenet J.‐M.
Published: March 2011

The dynamical behavior of agarose aggregates in a mixture of water and dimethyl sulphoxide (DMSO) has been investigated using a Transient Electric Birefringence (TEB) set up. Different agarose concentrations for different water/DMSO proportions were considered. The relaxation of the birefringence curves can be fitted with a stretched exponential of the form Δn(t) = Δn0 exp(‐(Dt)0.5). The exponent 0.5 suggests a high polydispersity of the aggregates. The rotational diffusion coefficient, D, depends strongly on the water/DMSO proportion. For small values of the applied electric field it presents a maximum for a water volume fraction equal to 0.5. A strong dependence of D on the applied electric field is also observed. However, the same kind of behavior as for weak fields is recovered when a subtle representation of the data is used. Differential Scanning Calorimetry (DSC) results also show a maximum in the temperature of fusion of the aggregates for a water volume fraction of 0.5. This set of results suggest strongly that « complexes » of water/DMSO/agarose are formed in the mixture and that the process of aggregate formation is more « efficient » for a water/DMSO mixture of same proportions.
The solvation of poly(vinyl alcohol)
Authors: Assender Hazel E. , Windle Alan H.
Published: March 2011

The possible incorporation of water molecules within the crystal structure of poly(vinyl alcohol) is discussed. Modelling of the crystal structure suggested that water could be incorporated without severe disruption, and the effect on the X‐ray powder diffraction trace was simulated. The effect of variation in tacticity is discussed in terms of the nature of the hydrogen bonding. Simulated traces are compared with experimental data from atactic samples in which a change in the diffraction peak intensities is observed for samples crystallised with water present. This is compared with samples produced from nonaqueous solutions.
The effect of temperature on the curing of unsaturated polyester resins modified with a liquid polymer
Authors: de la Caba Koro , Guerrero Pedro , Franco Merche , Mondragon Iñaki
Published: March 2011

The effect of temperature on the cure kinetics of two different unsaturated polyester resins, Estratil 1.112 and G102, modified with a liquid polymer, has been studied by Fourier transform infrared (FTIR) spectroscopy in the range of 60–80°C and 70–90°C, respectively. The experimental results have been related to the rheological changes during cure.
Acrylonitrile‐sodium methallylsulfonate copolymer solutions. NMR approach to phase diagrams and ordering processes
Authors: Margulies Monique Marie , Viallat Annie , Addad Jean‐Pierre Cohen
Published: March 2011

The physical behavior of solutions of an acrylonitrile‐sodium methallylsulfonate copolymer in dimethyl sulfoxide is described from NMR and calorimetric observations by varying concentration, temperature and thermal history of the systems. Both the solvent and the polymer can crystallize in the studied range of temperature. A method is proposed to determine the composition of the phases present in solution. At high polymer concentration, we observe that the physical state of a given solution depends on its thermodynamic history and that three distinct phases can coexist over a large temperature interval.
Complex formation in poly(vinyl chloride) thermoreversible gels
Authors: Reinecke H. , Guenet J.‐M. , Mijangos C.
Published: March 2011

The molecular structure of gels formed by poly(vinyl chloride) with different solvents is analyzed by neutron diffraction and neutron scattering techniques. Structure parameters are determined from the scattering functions and discussed in the light of the fibrillar model. Arguments are given in favour of the formation of PVC‐solvent complexes.
The role of triplet repulsion in elementary steps of cyclic chain termination of oxidizing polymers and other substances
Authors: Denisov Evguenii T.
Published: March 2011

Parabolic model of the transition state was used for analysis of activation energies of reduction of benzoquinone (Q), aminyl (Am*), and nitroxyl (AmO*) radicals by peroxyl radicals of different structure. It was proved that radicals HO2* and R2C(OH)O2* reduce Am*, and AmO* with zero activation energy due to low triplet repulsion in the transition state. On the contrary alkylperoxyl radicals reduce Am* and AmO* slowly due to high triplet repulsion and sufficiently high activation energy. That is why AmH and AmOH perform cyclic chain termination in oxidizing substances where peroxyls with OH‐group are generated.
Interactions of stabilizers during oxidation processes
Authors: Habicher Wolf D. , Bauer Ingmar , Scheim Kerstin , Rautenberg Claudia , Loßack Annett , Yamaguchi Kazuo
Published: March 2011

The antioxidative action of mixtures of phenols, phosphites, HALS, a) and some of their transformation products in various compositions has been studied in the thermo‐ and photo‐oxidation of hydrocarbons and polypropylene under different conditions. In the AIBN‐initiated oxidation of hydrocarbons at low temperatures (< 80°C), hindered phenols, hindered aryl phosphites and the nitroxyl derivatives of HALS act antioxidatively when used individually in appropriate concentrations. Secondary HALS do not show any induction period, but a certain retardation of the oxidation process after some reaction time. The inhibiting efficiency of nitroxyls observed cannot be explained completely by the currently accepted action mechanisms of HALS, but is also related to the reaction of the nitroxyls with alkylperoxyl radicals.

In mixtures with hindered phenols, HALS have almost no influence on the rate of thermooxidation at low temperatures. Their nitroxyl derivatives, however, always exhibit synergism, most pronounced when both stabilizers are used in equimolar ratios. During the photooxidation phenols lower the efficiency of HALS.

The influence of mixtures of stabilizers on the oxidative stability of polypropylene is rather different and depends on the oxidation conditions, the structure, the concentration and the ratio of the stabilizers. Synergistic as well as antagonistic effects are observed. Both aliphatic and aromatic phosphites studied act synergistically when used together and with phenols. This demonstrates that for acting as synergist for phenols, the hydrogen peroxide decomposing capability of the phosphites, but not their chain breaking activity is important. HALS‐phosphites and phosphonites, containing amine and phosphorus units in one molecule, are highly effective inhibitors of photo‐ and thermooxidation and exhibit lower critical antioxidant concentrations and longer induction periods than phosphites alone. They even exceed the efficiency of phenols in many cases.

Transformation products of phenolic antioxidants investigated act differently and in many cases contrarily under photo‐ and thermooxidative conditions. Therefore, they influence the efficiency of stabilizer mixtures also in a different way.
Stabilization beyond the year 2000
Authors: Zweifel Hans
Published: March 2011

A variety of chemical reactions lead to the oxidative deterioration of polymers upon processing and during end‐use of plastic articles. To inhibit the autoxidation cycle, stabilizers interfering at the various steps of the degradation are needed. Complex stabilizer systems which are able to suppress oxidative degradation have been developed recently. Special emphasis is given to radical scavenging, including alkyl radicals. UV absorbers with inherent photostability have led to an enhanced stability of polymers, such as engineering thermoplastics.
Fluorescence‐resolved hole burning of squaraine dyes in polymer matrices at low temperature
Authors: Wolf Joachim , Myers Anne B.
Published: March 2011

A new technique that combines nonphotochemical hole burning with multichannel detected fluorescence line narrowing has been used to obtain vibrationally resolved fluorescence spectra of squaraine chromophores in polymer matrices at 1.4 K. At a fixed excitation frequency, the intensities of the zero‐phonon lines decay with time due to nonphotochemical hole burning, leaving behind a broader background attributed to emission from molecules excited into phonon sidebands. Subtracting the spectrum of the hole‐burned sample from the initial one leaves predominantly a zero‐phonon line excited spectrum exhibiting enhanced vibrational structure. Spectra of the same squaraine in polystyrene and polyethylene matrices show differences in the frequencies and intensities of the phonon sidebands, indicating differences in the frequencies and strengths of the matrix modes coupled to the electronic transition of the chromophore. The phonon densities of states inferred through different measurement techniques are compared and related to electronic dephasing rates.
Pyridine‐based conjugated polymers: Photophysical properties and light‐emitting devices
Authors: Epstein Arthur J. , Wang YunZhang , Jessen Scott W. , Blatchford James W. , Gebler Darren D. , Lin Liang‐Bih , Gustafson Terry. L. , Swager Timothy M. , Macdiarmid Alan G.
Published: March 2011

We study the photophysical properties of the pyridine‐based polymers: poly(p‐pyridyl vinylene) (PPyV) and poly(p‐pyridine) (PPy). The primary photoexcitations in the pyridine‐based polymers are singlet excitons. We observe direct intersystem crossing (ISC) on picosecond time scales with the volume density of triplet excitons varying with the sample morphology (film or powder). These effects are demonstrated clearly by examining the millisecond photoinduced absorption characteristics of powder and film forms of PPyV. The pyridine‐based polymers have been shown to be promising candidates for polymer light‐emitting devices, both “conventional” diode device and symmetrically configured ac light‐emitting (SCALE) device. Here we examine the role of “insulating” layers and their interfaces with the emitting layer and electrodes in the SCALE device operation, with emphasis on the central role of the polymer‐polymer interfaces.
Photoinduced charge transfer in poly(phenylene‐vinylene) and its derivatives
Authors: Conwell Esther M.
Published: March 2011

Photoinduced absorption measurements on poly(phenylenevinylene), PPV, or its derivatives, illuminated with photons of energy past the absorption edge revealed that some percentage of the photons create a long‐lived excitation rather than the expected excitons. We present the evidence that these excitations are polaron pairs, which are essentially excimers. The reasons why this percentage varies from sample to sample are discussed. Also discussed are the reasons why polaron pairs in some derivatives of PPV emit light while in others they do not. Calculations with a relatively simple Hamiltonian can account well for the peaks in the photoinduced absorption produced by these pairs.
Hole transport in triarylamine doped polymers
Authors: Borsenberger Paul M. , Magin Edward H. , Heun Susanne
Published: March 2011

Hole mobilities have been measured in a series of triarylamine molecules doped into a poly(styrene) host. The results are described by a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. According to the model, the width is comprised of a dipolar component and a van der Waals component. The dipolar component is in good agreement with the recent analysis of Young. The results show that the van der Waals component increases with decreasing dopant concentration. This effect, which is not predicted from first order treatment arguments, is attributed to increasing structural randomness with dilution.
Femtosecond photoexcitation dynamics in polydiacetylene 4BCMU film
Authors: Zheng L. X. , Feng Z. G. , Knopf F. Carl
Published: March 2011

Femtosecond pulses were used to study photoexcitation dynamics in polydiacetylene 4BCMU film. Ultrafast photoinduced dichroism and optical Kerr gate responses were observed. These measurements allowed estimation of the diffusion constant (D ∼ 0.1 cm2/s), the nonlinear index of refraction (n2 ∼ 10−8 esu), and third‐order susceptibility (δχ(3) ∼ 6 × 10−10 esu), in the film. We also found that the sign of the photoinduced transmission signal was dependent on the pump energy at the low energy absorption edge of the film. Possible explanations are proposed.
Charge‐transfer interaction in liquid‐crystalline materials and their application to photonics
Authors: Tsutsumi Osamu , Kanazawa Akihiko , Shino Takeshi , Ikeda Tomiki
Published: March 2011

Photochemical phase transition of push‐pull type azobenzene liquid crystal (LC), which contains both an electron donor and an acceptor in both ends of the azobenzene moiety, has been explored. Polymer azobenzene LCs were prepared, which show nematic (N) LC behavior in the trans form while no LC phase in the cis isomer. Photoirradiation of a very thin film of the azobenzene LCs (∼ 200 nm) in the trans form resulted in disappearance of the N phase due to transcis photoisomerization of each mesogen, and the N phase recovered quickly when the irradiated sample was kept in the dark because of cis‐trans thermal isomerization and reorientation of trans‐azobenzenes. Time‐resolved measurements by the use of a laser pulse (355 nm; 10 ns FWHM) revealed that the N to isotropic (I) phase transition took place in 200 μs. The thermal I‐N phase transition of the push‐pull type azobenzene LC occurred in 800 ms at 135 °C. This response is faster by one order of magnitude than the response of azobenzene LCs without charge‐transfer interaction.
Photo‐fabrication of surface relief gratings on polymer films
Authors: Kim Dong‐Yu , Lee Taek‐Seung , Tripathy Sukant K. , Li Jiang Xin , Li Lian , Kumar Jayant
Published: March 2011

Surface relief gratings were optically produced on a number of azobenzene‐based polymer films. The surface grating formation was investigated by monitoring the diffraction efficiency and using atomic force microscopy. The effect of the structure of the chromophores on surface modulation was investigated. The surface deformation process depended on the polarization state of the writing beams. The localized variations of the light intensity and alteration of the resulting electric field polarization were essential writing conditions to the formation of the surface relief gratings. The surface pattern from straight edge diffraction established that the surface profile of the recorded gratings is proportional to negative gradient of the intensity pattern incident on the polymer film.
Charge transfer interactions in polymers and the fabrication of high frequency electro‐optic modulators
Authors: Dalton Larry R. , Harper Aaron W. , Sun Shajing , Steier William H. , Mustacich Robert V. , Jen Alex K‐Y.
Published: March 2011

The synthesis and processing of second order nonlinear optical polymeric materials for application in electro‐optic devices is described with particular emphasis on (1) the synthesis and incorporation into hardened polymer lattices of chromophores characterized by large μβ (where μ is the dipole moment and β is the molecular first hyperpolarizability) values; (2) the synthesis and incorporation into hardened polymer lattices of chromophores which are capable of undergoing photo‐induced conformational changes and which can be processed by new multi‐color photolithography techniques into buried channel active waveguides; and (3) the processing of polymeric nonlinear optical materials appropriate for the realization of full integration with very large scale integration (VLSI) drive electronics and with silica fiber optic transmission lines. Prototype modulators have been fabricated and shown to be suitable for broadband operation from 0 to 113 GHz. Optical losses associated with waveguide wall roughness and with mode mismatch in transitioning between silica and polymeric waveguides are reduced by control of the conditions of reactive ion etching and by use of the new technique of multi‐color photochemical lithography.
The challenge of assembling molecules into materials
Authors: Stupp Samuel I.
Published: March 2011

Linear organic chains and their architectural derivatives such as branched and crosslinked macromolecules have been the main focus of polymer science for many decades. A new direction which should be pursued in the field is the exploration of polymers as “nanostructures”. This exploration would study synthetic polymers as shape invariant objects with nanoscale dimensions which resemble the folded proteins of nature. Such synthetic macromolecules would have well defined shapes which may even include topographical features. Ideally, the definition of shape could include well defined dimensions as well, but molecular objects of common shape but varying dimensions could also exhibit interesting properties. One could for example envision polymers as flat plates (two‐dimensional polymers), discs, ellipsoids, spheres with cavities, parallelepipeds, among many other possible shapes. Such objects must have fairly high molar masses, possibly in the range of hundreds to thousands of kilodaltons, and would therefore not be accessible as chemical compounds synthesized by conventional methods. At the same time, the prospects of learning “folding rules” for synthetic chemical sequences in a biomimetic approach to molecular nanostructures seems to be an extremely difficult goal at the present time. This is suggested given our contemporary difficulties in understanding the protein folding problem.
Coupling and memory in liquid crystal elastomers
Authors: Mitchell Geoffrey R. , Roberts Philip M.S , Ahn Kyung‐hwa , Davis Frederick J. , Hasson Craig , Hirschmann Harald , Pople John A.
Published: March 2011

The polymer backbone of a side‐chain liquid crystal polymer exhibits an anisotropic shape due to the coupling of the liquid crystal orientational order of the mesogenic side‐chains to the backbone. The magnitude and sign of this coupling may be controlled by chemical design. The introduction of chemical cross‐links in to such a system provides both a memory of the anisotropic organisation and a mechanism by which the microscopic anisotropy can be realised at a macroscopic level. We show how this anisotropic network structure yields new phenomena when electric or mechanical fields are applied.
Non‐rigid liquid crystalline networks based on linear, segmented‐chain mesogenic polymers
Authors: Caruso Ugo , Iannelli Pio , Pragliola Stefania , Roviello Antonio , Sirigu Augusto
Published: March 2011

Five linear mesogenic polyesters, containing terephthalic groups, and bearing different amounts of unsaturated substituents were prepared and their phase behaviour characterised by calorimetric and X‐ray diffraction means. Networks based on these polymers were obtained by thermally activated radical polymerisation. Some optical and structural features of these networks were investigated both in the bulk and in the swollen state.
Ferroelectric LC‐elastomers
Authors: Brehmer M. , Zentel R.
Published: March 2011

Ferroelectric liquid crystalline elastomers combine the rubber elasticity of polymer networks with liquid crystalline phases and ferroelectric ordering. Ferroelectric switching leads therefore to a deformation of the polymer network and an elastic stress. The coupling between both effects can be varied by changing the topology of the netpoints.
Can tandem interactions give rise to motion?
Authors: Prost Jacques
Published: March 2011

We outline the simplest principles which, taking advantage of tandem interaction, can give rise to long range motion with the use only short range forces.
Polysoaps: The signatures of intrachain self assembly in θ solvents
Authors: Borisov Oleg. V. , Halperin Avraham
Published: March 2011

Polysoaps are linear hydrophilic chains that incorporate, at intervals, covalently bound amphiphilic monomers. In water, the amphiphilic monomers self assemble into intrachain micelles thus endowing the chain with a secondary structure. Long polysoaps adopt a variety of configurations involving many intrachain micelles. While the stable configuration is that of a dense globule of closely packed micelles, it is also important to consider metastable configurations such as linear and branched strings of micelles. Theoretical discussion of these issues is presented for the case of a θ solvent for the hydrophilic backbone.
Block copolymers and liquid crystalline block copolymers: A bird's‐eye view
Authors: Galli Giancarlo
Published: March 2011

Block copolymers and liquid crystals are separately known to order at different length scales. Various types of molecular interactions in liquid crystalline block copolymers determine complex phase behaviors and states of order, and thereby can provide a way of tailoring the material properties. Examples of liquid crystalline block copolymers will be discussed as they may offer unique opportunities for both theoretical and experimental research.
Block copolymers with liquid crystalline segments
Authors: Schulze Uwe , Reichelt Norbert , Schmidt Hans‐Werner
Published: March 2011

This paper describes the synthesis and characterization of polystyrene‐block‐poly(2,2'‐dimethyl‐4,4'‐biphenylene phenylterephthalate)‐block‐polystyrene and of poly(ethylene glycol)‐black‐poly(2,2'‐dimethyl‐4,4'‐biphenylene phenylterephthalate)‐block‐poly (ethylene glycol) block copolymers. The ABA‐triblock copolymers were synthesized by condensation reaction of telechelic poly(2,2'‐dimethyl‐4,4'‐biphenylene phenylterephthalate) with ω‐hydroxy polystyrene and ω‐hydroxy poly(ethylene glycol) methyl ether of different molecular weights prepared by anionic polymerization. Some aspects of the liquid crystalline behavior and the phase transitions with respect to the block copolymer composition will be discussed.
Multiple length scale self‐organization in liquid crystalline block copolymers
Authors: Ober Christopher K. , Wang Jianguo , Mao Guoping , Kramer Edward J. , Chen John T. , Thomas Edwin L.
Published: March 2011

A series of block copolymers were prepared consisting of a block of poly(styrene) and a block in which a mesogenic group was attached by polymer analogous chemistry to a flexible backbone. Two types of mesogenic groups which produced a range of mesophases were investigated: (i) an azobenzene mesogenic group and (ii) a semifluorinated group. Organization caused by liquid crystallinity and phase separation leads to simultaneous organization on a variety of length scales. Comparison of the ordering behavior of these two types of mesogenic groups and more conventional flexible chain diblocks are made.
Tandem interactions in the self‐assembly of ionic block copolymers
Authors: Moffitt Matthew , Eisenberg Adi
Published: March 2011

The aim of the present review is to show how the phenomena of block copolymer self‐assembly and interactions of ionic (or ionizable) groups in polymer systems can be combined to produce materials with versatile and unique behavior. In our discussion, we consider two classes of tandem interactions. First, block copolymers containing short ionic blocks and long nonionic blocks are investigated in organic media. In systems of this type, block copolymer self‐assembly and short‐range electrostatic interactions act in tandem, forming regular and highly‐stable spherical structures. Next, we consider ionic (or ionizable) block copolymers dissolved in aqueous media. In this case, block copolymer self‐assembly acts in tandem with the hydrophilic nature of the soluble blocks, resulting in a wide range of unique morphologies.
Liquid‐crystalline ionomers
Authors: Wilbert Götz , Zentel Rudolf
Published: March 2011

Liquid‐crystalline (LC) ionomers combine the properties of ionomers (cluster formation of the ionic groups) with LC phases. They can be prepared with LC main‐chain and LC side‐chain polymers.
Effect of flow on topological interactions in polymers
Authors: Marrucci Giuseppe , Ianniruberto Giovanni
Published: March 2011

The dynamics of concentrated polymers of high molecular mass is dominated by topological interactions (or entanglements). The nonlinear effects shown by these systems in fast flows are still poorly understood, however. We have recently noted that a mechanism of convective constraint release should play a significant role in the nonlinear range, and preliminary calculations have been made both for a simple dumbbell model and for the tube model of Doi and Edwards. Here we show that further elaboration of the simple dumbbell model can predict quite complex rheological behaviours such as those observed by Navard and coworkers in semi‐dilute solutions of ultrahigh molecular mass polymers.
Influence of a liquid crystalline block on the microdomain structure of block copolymers
Authors: Thomas Edwin L. , Chen John T. , O'Rourke Mary Jane E. , Ober Christopher K. , Mao Guoping
Published: March 2011

We report on the phase behavior and microdomain structure of two types of diblock copolymers containing a liquid crystal (LC) block joined to a flexible coil block. Consideration of the symmetry groups of the liquid crystalline phases and of the block copolymer microdomain structures provides a rationale for predicting the possible types of liquid crystalline block copolymer morphologies. Both previously reported and newly discovered structural types are identified. Possible organizational schemes are developed for the mesogens and periodic disclination defects with respect to the intermaterial dividing surfaces separating the liquid crystalline and flexible coil domains. The first type of copolymer investigated has a rod‐like LC block whereas the second type copolymer has a side chain LC block. Five different rod‐coil diblocks based on poly(hexyl isocyanate‐b‐styrene) P(HIC‐b‐S) were synthesized by anionic polymerization. Wavy lamellae, zig‐zag and arrowhead microdomain morphologies corresponding to smectic‐C and smectic‐O structures were observed depending on the composition. These layered phases have the director (PHIC chain axis) tilted at various orientations with respect to the layer normal. Side‐chain LC diblocks based on functionalized poly(isoprene‐b‐styrene) P(I‐b‐S) were also investigated. These polymers were synthesized using polymer analogous chemistry from P(I‐b‐S) precursors. Three different mesogenic groups were attached to the PI blocks: one based on biphenyl benzoate and two based on azobenzene. The microdomain structures found for the functionalized poly(isoprene side‐chain LC‐b‐styrene) P(ILC‐b‐S) diblocks are typical of traditional coil‐coil diblocks (lamellae and cylinders). However, these morphologies possess an additional smectic layering of the mesogens within the microdomains of the LC block. In the case of the rod‐coil diblocks, the transformation from an initially isotropic state to the final microphase separated solid state occurs via nematic and then smectic liquid crystalline states, whereas for the side‐chain LC‐coil cases, the microphase separation transition occurs prior to development of orientational order. The long‐range microdomain order of LC block‐coil block copolymers can extend over very large distances due to the influence of the orientational ordering of the LC block.
Liquid crystals 100 years later. What are the new concepts used in the design of molecular, macromolecular and supramolecular liquid crystals?
Authors: Percec Virgil
Published: March 2011

A brief discussion of selected synthetic strategies pursued in the field of molecular, macromolecular and supramolecular liquid crystals is made by reviewing some tandem historical events of the past 100 years of activity in this field. This survey will try to suggest the rational for the discovery, evolution and investigation of some of these new concepts. Also a brief and speculative forecast of the future of this field will be presented.
Design and construction of supramolecular and macromolecular architectures by tandem interactions
Authors: Rowan Alan E. , Sommerdijk Nico A. J. , Reek Joost N. H. , Zwanenburg Binne , Feiters Martinus C. , Nolte Roeland J. M.
Published: March 2011

The self‐assembling behaviour of several molecular building blocks are used to construct a variety of chiral and nonchiral supra‐molecular and macromolecular architectures. These structures can be finely tuned by slight changes in e.g. the shape of the building blocks, the pH and by the addition of guest molecules.
Spatial configuration of chain molecules incorporated in liquid crystals and thermodynamic significance
Authors: Abe Akihiro
Published: March 2011

The conformation of chain molecules participating variously in the formation of liquid crystalline mesophase has been elucidated. Two examples are mentioned: (1) the side chain flanking the α‐helical backbone of polypeptides, and (2) the spacer joining mesogenic units in mainchain liquid crystals. Flexible segments play an important role in determining thermodynamic properties of these systems.
Direct synthesis of aromatic polyamides
Authors: Russo Saverio , Mariani Alberto , Mazzanti Sabina L. E.
Published: March 2011

The synthesis of aromatic polyamides, namely poly(p‐phenylenetere‐phthalamide) and poly(p‐benzamide), via phosphorylation reaction has been thoroughly investigated. The effect of reaction temperature, concentration of monomers and reactants, type and concentration of salts, amount of the activator and its stepwise addition have been considered and the optimum reaction conditions found. The resultant synthesis of the above polymers, also in connection with the high purification techniques of all components of the reaction mixture, allowed to reach the highest molecular weights obtained so far by this synthetic way.
Synthesis and properties of polyesters containing naphthalenetetracarboxylic imide
Authors: Kim Woo‐Sik , Kim Sang‐Youl , Park Nam‐Kyu
Published: March 2011

Poly(ethylene naphthalates) containing small contents of N, N'‐bis(ω‐hydroxypropyl)naphthalene‐1, 4, 5, 8‐tetracarboxylic imide(HPNTI) unit as the photostabilizing component, which are stable to ultraviolet lights, were synthesized from dimethyl naphthalate, ethylene glycol, and HPNTI. The polyesters obtained were characterized by fluorescence spectroscopy and measurements of molecular weights and thermal properties.