Effects of glass-transition temperature on properties of photorefractive polymer composite

In this study, photorefractive polymer composites were developed in which polycarbonate was doped with a dual-function dopant and a photocharge generation sensitizer. The dual-function dopant has the function of providing both charge transport and optical nonlinearity. The composites' photoconductivity and electrooptic coefficient were investigated experimentally. The effects of the glass-transition temperature (T_g), dual-function dopant content, and electric field on the composites' photorefractive properties were studied as well. The results show that the composites' photorefractive properties are enhanced with decreasing T_g, increasing dual-function dopant content, and increasing electric field. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3302–3306, 1999     

Studies on molecular composite. III. Nano composites consisting of poly(p‐phenylene benzobisthiazole) and thermoplastic polyamide

A bulk sample of a nano composite consisting of poly(p‐phenylene benzobisthiazole) (PBZT) and a thermoplastic matrix polymer was obtained by polymer blending of a matrix polymer of thermoplastic aromatic polyamide and a reinforcing polymer of a copolymer consisting of a precursor of PBZT and a fragment in common with the matrix polymer, using organic solvent, followed by molding. The phase structure of obtained specimens was varied by controlling the molding process conditions. In particular, the mechanical properties, heat resistance, and chemical resistance of the matrix polymer of a bulk specimen which has a three‐dimensional network structure of PBZT were improved drastically, even when only a small amount of the reinforcing material was added. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 209–218, 1999     

Lessons learned from research on photorefractive polymers and molecular materials

Organic photorefractive (PR) materials are a new kind of electrooptic substance that emerged 10 years ago. These are very complicated materials that possess both electrooptic effects and photoconductivity. It is challenging to integrate these properties into a single polymer system that will exhibit this PR effect. This article highlights our efforts in the past nine years in synthesizing and characterizing fully functionalized organic PR materials. I emphasize the lessons we have learned from this research, which may be more valuable to those who are interested in this area. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2557–2564, 2001     

Studies on molecular composite. I. Processing of molecular composites using a precursor polymer for poly(p‐phenylene benzobisthiazole)

The blending of a precursor polymer for poly(p‐phenylene benzobisthiazole) (PBZT) with various matrix polymers was attempted, followed by heat conversion of the PBZT precursor polymer to obtain molecular composites consisting of PBZT and the matrix polymers. A higher concentration of mixed solution using organic solvent and milder conditions to remove the solvent could be applied to blend the polymers using the precursor polymer in place of rodlike PBZT. The dispersibility of PBZT in the matrix polymer in the blended materials obtained depended on the ability to form intermolecular hydrogen bridges between the PBZT precursor and the matrix polymer. In particular, the blended material, obtained using a nonthermoplastic aromatic polyamide as the matrix polymer having a molecular structure similar to that of the PBZT prepolymer, was transparent and showed excellent reinforcing efficiency of PBZT. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 189–197, 1999     

Properties of polyvinylchloride in solution: an hydrodynamic and vibrational spectroscopy study

The polymer polyvinylchloride has been studied in binary solvent mixtures and as a function of temperature in solution. A discontinuity of the polymer chain dimensions has been observed, as measured by hydrodynamic methods. This phenomenon is further examined by infrared and Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1351–1356, 1999     

Experimental evidence and theoretical analysis of physical aging in thin and thick amorphous glassy polymer films

Through time‐dependent gas transport properties, we have investigated the physical aging process of amorphous glassy polymer films made from a polynorbornene. By combining the concepts of free volume and the kinetic theory of glass stabilization, it was found that the time dependence of the gas permeability could be rationalized through the thickness dependence of the glass transition temperature. A mathematical relationship was developed that directly relates polymer physical aging (tracked by the gas permeability decay) and sample thickness. It was confirmed by permeation measurements with nitrogen and helium that the aging process is accelerated for thin glassy polymer films (about 8000 Å). The theoretical results show that accelerated aging for thin films compared to thick films can be qualitatively predicted, based on the decrease in the glass transition temperature when the film thickness decreases. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2239–2251, 1999     

Polybenzoxazine resins: Aspects of interaction and adsorption behavior

The technique of inverse gas chromatography (IGC) has been used to evaluate the acid–base interaction potential of two polybenzoxazines. One of these, prepared from bisphenol‐A monomer, was shown to be a net base. Another based on dihydroxybenzophenone registered as a net acid. The bisphenol‐A version was adsorbed at controlled thicknesses on α‐alumina, on fumed silica and on boron nitride, all three solids with acidic surfaces as shown by IGC data. Thin layers of the adsorbed polymer near monolayer coverage were strongly perturbed by the underlying substrate, the polymer surface now behaving as a net acid. Thicker layers of the adsorbed polymer revert to basicity, but fail to attain the acid–base interaction constants of the pure polymer. The presence of strongly interactive substrates leads to the creation of a substantial interphase, the interaction properties of the adsorbed polymer varying through the thickness of this layer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1441–1447, 1999     

Synthesis of miktoarm star (μ-star) polymers

The synthetic strategies available for the synthesis of miktoarm star (μ-star) polymers with molecular weight, chemical, or topological asymmetry are reviewed. All strategies are based on functional living polymer chains and linking agents. Although each strategy has its weak and strong points, it seems that anionic polymerization combined with chlorosilane methodology yields the widest variety of model single and double μ-stars. These novel architectures open new horizons in polymer science and technology. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 857–871, 1999     

Comparison of methods for the determination of diffusion coefficients of polymers in dilute solutions: The influence of polydispersity

A comparison between various methods to determine diffusion coefficients of polymers in dilute solutions has been made. It is shown that Taylor dispersion analysis (TDA), dynamic light scattering (DLS), hydrodynamic chromatography (HDC), and size exclusion chromatography (SEC) can all be used to accurately determine diffusion coefficients when the polymer samples have low polydispersities. By the analysis of a series of practically representative styrene acrylonitrile copolymer (SAN) samples, it is shown that polydispersity of the samples and the presence of low‐molecular‐mass material cause considerable differences between the methods. It was found that TDA is mostly disturbed by the presence of low‐molecular‐mass material, whereas DLS is more sensitive to the polydispersity of the polymer. With broad samples, DLS gives the Z‐average diffusion coefficient. SEC can be used to obtain a diffusion coefficient distribution as well as an average diffusion coefficient of a polydisperse sample. Although, the same was expected for HDC, it was found that this method could only be successfully used for polymer samples having low polydispersities. Deviations between SEC, HDC, and TDA found for narrow samples were not related to the chemical composition of the samples. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 593–603, 1999     

Degradation and stabilization of polycyanoacrylates

Polycyanoacrylates were found to be inherently unstable. Even in the absence of a deliberately added strong base, their molecular weights decreased drastically on standing in solution in accord with observations by Ryan and McCann (Makromol Chem Rapid Commun 1996, 17, 217). The initial high molecular weight polymer disappeared over the course of a few hours in solution and was replaced by a much lower molecular weight material. For polymers made by anionic polymerization, the entire sample degraded, but for polymers made by free-radical polymerization, only a portion of the sample was affected. This behavior was consistent with the mechanism proposed by Ryan and McCann, in which the polymer chains are in dynamic equilibrium with their monomers and the polymer degrades from its chain terminus. Surprisingly, the degradation in molecular weight even occurred slowly in the solid state. The degradation was inhibited by acids and could be prevented by free-radical copolymerization with small amounts of more stable monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4570–4581, 1999     

Electrical conductivity of heat treated polyacrylonitrile and its copper halide complexes

The electrical conductivity of polyacrylonitrile homopolymer and polymer complexes of acrylonitrile (PAN) with CuCl₂, CuBr₂, and Cul₂ was measured at different temperatures. It was found that the electrical conductivity increased with temperature. Cyclic voltammetry was used for measuring the shift of the reduction peaks upon heat treatment of the polymer complexes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3057–3062, 1999     

Synthesis and properties of nonlinear optical side chain soluble polyimides for photonics applications

Aromatic polyimides with side chain nonlinear optical chromophores have been investigated through a facile two-step synthetic route. First, various poly(hydroxy imide)s have been synthesized by direct thermal imidization of diaminophenol dihydrochloride salt and aromatic dianhydride monomers. The resulting polyimides bearing phenolic hydroxy groups were found to react easily with the terminal hydroxy group on the chromophores via the Mitsunobu condensation to give corresponding polyimides with high optical nonlinearities and good solubility in common organic solvents. Detailed physical properties showed that these polyimides have a molecular weight (M_w) of 31,000 and high glass transition temperature above 220°C, ensuring a long-term alignment stability at elevated temperature. The electrooptic coefficients, r₃₃, of the electrically poled polymer films were in the range 1.8–7.6 pm/V at 1.3 μm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 301–307, 1998     

A 3‐D numerical simulation of AC electrical properties of short fiber composites

The relation between microstructure and electrical properties of polymer reinforced by electrically conducting nanofibers is investigated using a RC type simulation. Real and imaginary parts of the conductivity vs. the frequency and the filler fraction are presented both for two‐ and three‐dimensional systems. In the latter case, resistor and capacitor values are deduced from a random microstructure and the measured macroscopic properties of each component. These results are compared with experimental data obtained on a nanocomposite material composed of electrically conductive fillers dispersed in an insulating matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 805–814, 1999     

Coarsening of the phase structure in immiscible polymer blends. Coalescence or ostwald ripening?

The results of theories of the Ostwald ripening and coalescence applied to molten quiescent polymer blends with dispersed phase structure were analyzed. From a comparison of predictions of the theories with available experimental results follows that coarsening of the phase structure in quiescent polymer blends with medium or high interfacial tension is induced by the coalescence. Both the mechanisms play a role in coarsening of the phase structure in blends with low interfacial tensions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 181–187, 1999     

Energy transfer from phenanthrene to anthracene in a dye-labeled (ethylene-methyl acrylate) copolymer

We describe the synthesis of a branched polyethylene-based polymer containing randomly spaced fluorescent dyes (phenanthrene or anthracene) along the polymer backbone. The dyes were introduced via ester exchange into the ethylene-methyl acrylate copolymer. Fluorescence and fluorescence-decay experiments indicated that the dyes were distributed randomly in a purely amorphous matrix. There was no indication of dye aggregation or of an enhanced local dye concentration of the sort that might be expected in a semicrystalline matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4169–4175, 1999     

Mechanical properties of polymers containing fillers

The addition of fillers can significantly change the mechanical characteristics of a material. In this paper, a general, mechanistic model is established to determine the moduli, relaxation moduli, break strengths, and break strains for polymer films containing liquid and solid micro fillers. Based on rigorous continuum mechanics principles, this model considers the filler/filler interactions, incorporates the nonlinear synergistic effects of fillers, and provides accurate predictions in comparison with experimental data. The analytical model developed provides information that is not available or extremely difficult to obtain experimentally. The model can be applied to determine the filler/matrix adhesion and filler modulus using measured modulus of a filled polymer film (a filled polymer is a polymer containing fillers). It is found that the compression moduli of polymer films containing liquid fillers differ significantly from the tension moduli, especially when the volume fraction of the filler is high. The difference in compression and tension Young's moduli normalized by the tension Young's modulus is as high as 35%. The relative error in maximum pressure calculation during Hertzian contact caused by using the tension moduli is as high as 48%. The relaxation modulus of a filled polymer film is determined through inverse Laplace transforms of its composite modulus in the s‐space. For a filled polymer film containing liquid phase fillers, a closed form solution for its relaxation modulus has been obtained. It is found that the composite relaxation modulus of the filled polymer is proportional to the relaxation modulus of the matrix polymer multiplied by a factor related to the volume fraction of the liquid filler. The break strength of the filled polymer is found to be proportional to the break strength of the polymer matrix material multiplied by a power function of the modulus ratio of filled polymer to polymer matrix, R. The break strain of the filled polymer is proportional to the break strain of the polymer matrix multiplied by a power function of 1/R. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 155–172, 1999     

In situ measurement of the thermal expansion behavior of benzocyclobutene films

In situ measurement techniques suitable for determination of the coefficient of thermal expansion (CTE) in thin, spin‐cast polymer films in both the in‐plane and through‐plane directions are presented. An examination of the thermal expansion behavior of cyclotene thin films has been performed. In particular, the effect of film thickness on the in‐plane and through‐plane CTE and in‐plane Young's modulus of spin‐coated cyclotene films was examined. It is shown that the mechanical response of in situ cyclotene films can be adequately described by isotropic film properties. It was also demonstrated that there is no thickness dependence on the free‐standing mechanical properties or on the resulting through‐plane thermal strain in an in situ film. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 311–321, 1999     

Biodegradable aliphatic thermoplastic polyurethane based on poly(ε‐caprolactone) and L‐lysine diisocyanate

A biodegradable aliphatic thermoplastic polyurethane based on L ‐lysine diisocyanate and 1,4‐butanediol hard block segments, and 2000 g/mol poly(ε‐caprolactone) diol soft block segments was synthesized. The resulting polymer was a tough thermoplastic with ultimate tensile strength of 33 MPa and elongation of 1000%. The polymer displayed classic segmented thermoplastic elastomer morphology with distinct hard block and soft block phases. Thermal and dynamic mechanical analyses determined that the material has a useful service temperature range of around ?40 °C to +40 °C, making it an excellent candidate for low‐temperature elastomer and film applications, and potentially as a material for use in temporary orthopedic implant devices. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2990–3000, 2006     

New materials for optical rectification and electrooptic sampling of ultrashort pulses in the terahertz regime

The synthesis and nonlinear optical characterization of new electrooptic (EO) materials useful for terahertz (THz) applications is presented. Semiempirical calculations were used to guide the development of a series of chromophores on the basis of 2‐dicyanomethylen‐3‐cyano‐4,5,5‐trimethyl‐2,5‐dihydrofuran acceptors acting as guests in polymer films used in the generation of THz radiation via optical rectification. Amorphous films, 65–250 μm thick, with EO coefficients as high as 52 pm/V at 785 nm were used to generate sub‐picosecond pulses with bandwidths up to 3 THz. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2492–2500, 2003     

Desulfonylation of poly(4‐hydroxystyrene sulfone) by vapor phase silylation

Vapor phase silylation of poly(4‐hydroxystyrene sulfone) (PHOSS) film was carried out with (trimethylsilyl)dimethylamine (TMSDMA) as a silylation reagent. Infrared spectroscopy was used to follow the silylation. Phenolic hydroxyl groups were trimethylsilylated, but desulfonylation of PHOSS was greatly enhanced simultaneously. The reaction rates were investigated at reaction temperatures of 50, 60, and 70°C. The rate of silylation increased with increasing reaction temperature. However, the rate of desulfonylation was very fast in the presence of TMSDMA and was virtually invariant with reaction temperature. It was confirmed that trimethylsilylation in the polymer side chain of PHOSS enhanced desulfonylation in the main chain. Trimethylsilylation might be expected to lower the ceiling temperature of the polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1549–1554, 1999