1993 рік

We investigate the small-angle light scattering from dilute polystyrene (PS)-poly(dimethylsiloxane) (PDMS) diblock copolymers in semidilute isorefractive PDMS/tetrahydrofuran (THF) solutions. We compare the results with those obtained on PS/PDMS homopolymer mixtures and analyse the data quantitatively in terms of the only available theoretical results based on the mean-field approach. We also obtain measurements of diffusion coefficients of probe PS molecules and probe PS-PDMS diblock molecules in semidilute PDMS/THF solutions by dynamic light scattering and show the different coupling that occurs between the probe molecule and the semidilute matrix

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The phase structure and the dynamic-mechanical properties of isotropic films of isotactic polypropylene (iPP)/hydrogenated oligocyclopentadiene (HOCP) blends are reported. It is found that the phase diagram presents both the lower critical solution temperature and the upper critical solution temperature. The dynamic-mechanical tests (performed at a frequency of 1 Hz and at a heating rate of 4°C min-1) show that the addition of HOCP> 20 wt% causes an increase of the storage modulus at low temperatures; the curves of storage modulus and loss modulus of the isotropic films containing HOCP> 20 wt% show the transition of the smectic form of iPP to the crystalline ct form.

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Partial base molal volume values obtained from high-precision density measurements, in conjunction with heats of dilution data, derived from flow calorimetry measurements, have been obtained for a series of samples of poly(oxyethylene) (POE) of different molar masses, ranging from 200 to 35 000 Da. The results show that the state of solution of the POE is very much dependent upon the molar mass of the polymer; at low molar masses, pair and triplet interaction coefficients suggest that the hydrophobic interaction controls solution behaviour, while at higher molar masses, a helical conformation appears the most likely explanation.

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Segmented poly(ether esteramide) copolymers with short (M = 382) partially aromatic esteramide units of uniform length and segments of poly(tetramethylene oxide) (PTMO) have beem synthesized in the melt. The polymers show phase separation into two or three phases. The influence of the PTMO segment length on the following properties was studied: the Tg of the amorphous phase, the T m of the crystalline PTMO and the melting and crystallization behaviour of the uniform polyesteramide units. Volume fraction and density of each phase were determined. The polyesteramide units crystallize in lamellar structures; their sizes were studied using WAXD and SAXS. The polymers were melt processed and their mechanical properties were investigated using dynamic mechanical thermal analysis (d.m.t.a.) and tensile tests. Polyesteramide crystallinity, crystalline structure and crystallite size were found to be almost independent of PTMO segment length. The decrease in hard-segment melting temperature with increasing PTMO segment length is explained as being due to a 'solvent' effect of the soft phase, The copolymers crystallize very fast, and the modulus in the rubber region is essentially independent of temperature. The copolymers with long PTMO segments (M= 2000 and 2900) have a low glass transition temperature (-65°C); the materials are very soft and have an elongation at break of over 1000%. The copolymer with the shortest PTMO segments (M = 250) has a glass transition temperature of 43°C and the material is hard at room temperature

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The effect of compatibilizing polyethylene and nylon-6 on the morphology and mechanical properties of their blends is investigated. A maleic anhydride functionalized styrene-(ethylene-co-butylene)-styrene block copolymer (MA/SEBS) is added to the blends as the compatibilizer. The compatibilizer is found to play a dual interfacial function. On the one hand, it reduces the interfacial tension of the system, resulting in reduction of the particle size of the dispersed polyethylene phase. On the other hand, it enhances the interfacial adhesion through the formation of micro-bridges. The fine polyethylene phase thus coupled to the matrix in compatibilized blends can carry load and deform co-continuously along with the matrix. This causes extensive yielding of the blend prior to its failure and high ultimate elongations. Unexpectedly, at MA/SEBS contents higher than 10%, the ductility of the blends drops sharply. This is attributed to flow-induced discontinuities within a large core in the tensile specimens. The lines of instabilities act as large notches within the specimen, causing brittle failure of the otherwise ductile blend.

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For the cure process of a thermoset/thermoplastic blend, tetrafunctional epoxy resin/poly(ether sulfone)/dicyandiamide (100/25/5), we established a new time-temperature-transformation (TTT) cure diagram. The transformation here involves (1) onset of phase separation, (2) gelation, (3) fixation of the dimension of phase-separated structure, (4) end of phase separation and (5) vitrification. The onset and end of phase separation were characterized by the time variation of the invariant of light scattering (V 0 and the spatial fixation of phase-separated structure was by levelling off the decrease of scattering peak angle. The gelation and vitrification points were determined conventionally by rheological measurements, i.e. by a cross-over of dynamic storage modulus and dynamic loss modulus curves, and by torsional braid analysis curve, respectively. The epoxy/poly(ether sulfone) mixture was shown to exhibit lower critical solution temperature (LCST)-type phase behaviour (LCST= 265°C). In the early stage of curing, the ternary system was at a single-phase regime. After an induction period, phase separation started by the spinodal decomposition mode, then the domain spacing increased with time, i.e. the structure grew self-similarly. When the system was gelled, the spacing simultaneously ceased to increase. Even after that, the invariant still continued to increase, implying further growth in concentration fluctuation. The invariant then levelled off and finally the whole system was vitrified by the increase in glass transition temperature of the epoxy-rich phase. This situation was described in terms of the new TTT cure diagram in wide ranges of cure temperature (130-250°C) and cure time (6 h).

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Calculations of intramolecular and intermolecular interactions, giving the contributions to the nuclear magnetic resonance second moment for poly(p-phenylene sulfide) (PPS), have been carried out. Second-moment values of the PPS rigid lattice before and after heat treatment have been measured. Good agreement between theoretical and experimental data has been obtained. The parameters of the unit cell for the PPS 'asymmetric model' have been determined.

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The thermal stability, mechanical properties and electrical conduction of nylon-6/polypyrrole composite films are reported, where nylon-6 films were predoped with various concentrations (0.5, 1.25, 2.5, 5 and 12.5 % w/w) of copper chloride. The thermal behaviour of the composite films was studied using differential thermal analysis. The mechanical properties, namely the elongation at break and breaking strength, were measured. The results show that there is an improvement in the mechanical properties of the composite films for the nylon-6 film doped with up to 2.5% of copper chloride. The thermal stability of the composite films, however, does not show any improvement. The melting point and the degradation temperature both reduce as the concentration of copper chloride in nylon-6 is increased. The electrical conductivity (a) of these films was measured in vacuum as a function of temperature. The plots of log (a) versus temperature (T) show that the conduction mechanism is quite complicated.

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Branched polymers were prepared from the bifunctional 4,4'-diglycidyloxy-2,2odiphenylpropane( diglycidyl ether of bisphenol A) and hexafunctional poly(oxypropylene) diamine (Jeffamine T-403) at different distances from the gel point in the absence and presence of a diluent. Polymers with different amounts ofintramolecular cycles were prepared by dilution during polymerization of the epoxide system with diglyme/butanol mixed solvent. The static and dynamic light scattering from dilute solutions of these epoxide samples was measured. The results are discussed in terms of existing gelation theories. The critical exponents of M, lie between the values predicted by the Flory-Stockmayer and percolation theories and are shifted towards the percolation value with increasing fraction of intramolecular cycles. Polymer growth near the gelation threshold is discussed

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Carbon-13 relaxation measurements were performed on vinyl chloride-vinylidene chloride copolymers in solution. The variations of T1 and nuclear Overhauser enhancement were analysed over a wide temperature range including Tx minimum. The data were analysed in terms of several motional models, including both correlation time distribution and diffusional models. Only those models that involve motion on two well separated time scales were successful. The slower motion corresponds to a damped diffusion along the chain; the faster motions are librations of limited extent about the rest position

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