1992 рік

Radical copolymerizations of cationic, surface-active monomers, such as lauryl (C~2Br), octyl (CsBr) and cetyl (C~6Br) bromide salts of 2-dimethylaminoethyl methacrylate with methyl methacrylate (MMA) or styrene (ST) have been studied in water and N,N-dimethylformamide (DMF) as solvent, giving an anisotropic and an isotropic solution, respectively. For both comonomer systems, the copolymerizations of C12Br in water were faster and exhibited a higher tendency toward alternation compared to those in DMF. It was deduced that the copolymerization in water mainly takes place at palisade layers of micelles of the cationic monomer, being responsible for increased rate and alternation of the copolymerization. The Q and e values of C~2Br were determined on the results of the copolymerization in DMF and both were found to be higher than those of 2-dimethylaminoethyl methacrylate (DMAEMA). Such higher Q and e values for the cationic monomer could be due to an intramolecular interaction of the oxygen atom of carbonyl group with the positively charged ammonium group. The copolymers of C12Br prepared here were characterized by solubility in water, solution viscosity and solubilization of azobenzene in the aqueous solution. Other micelle-forming monomers, CsBr and Cl6Br , were also used to study the effect of alkyl chain length on the copolymerization

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Model network polymers derived from narrow distribution ct,og-dihydroxypoly(propylene oxide) and a triisocyanate, tris(4-isocyanatophenyl)thiophosphate, were used. Dielectric relaxation measurements were carried out on these networks with different molecular weights between crosslink points. Two relaxation processes were identified and the complex permittivity was assumed to be the sum of two Havriliak-Negami contributions to obtain relaxation parameters. The relaxation strength of the higher frequency process was found to be proportional to the estimated concentration of the ether oxygen group, on the other hand, the relaxation strength of the lower frequency process was found to be proportional to that of the urethane group. From this result, it is reasonable to consider that the higher frequency process is due to motions involving the ether oxygen group and the lower frequency process is due to motions involving the urethane group.

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The crosslinking reactions that occur in unsaturated polyester resins result in a heterogeneous structure of highly crosslinked domains separated by less highly crosslinked material. This structure is a result of the formation of gel particles, which are initiated at free radicals during the curing reaction. Controlling the concentration of free radicals present in the system enables the heterogeneity within the resin to be varied, and its influence on the thermomechanical properties to be studied.

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A novel high-temperature non-aqueous dispersion polymerization route to liquid crystal polymers based on poly(4-oxybenzoate-co-2,6-oxynaphthoate) is described. Novel combinations of polymeric and hydrophobic inorganic stabilizers are shown to give stable dispersions at temperatures up to 320°C. A possible mechanism of stabilization is discussed.

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Amorphous network polymer electrolytes were derived from poly(propylene oxide) and tris(4- isocyanatophenyl)thiophosphate complexed with lithium perchlorate. The complex impedance diagrams of the higher crosslink density samples were found to be a superposition of two semicircles having different relaxation times. On the other hand, the diagrams of the lowest crosslink density samples were a single semicircle. The Cole-Cole equation was employed to evaluate the relaxation parameters. The higher frequency process was assigned to ionic motions associated with segmental motions of the propylene oxide chain, and the lower frequency process was assigned to ionic motions associated with segmental motions of the urethane group. Dynamic mechanical thermal spectra show two relaxation peaks in the higher crosslink density samples and Tip as a function of temperature obtained by 7Li n.m.r, study has a well defined minimum. These results indicate the correlation between the ionic mobility and the molecular motions of the network system.

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The crystallization conditions for the preparation of different modifications of the orthorhombic form (fl form) of syndiotactic polystyrene (s-PS) are described. Crystallizing from the melt produces the fl' or form depending on the cooling rate. Crystallization by casting a film from o-dichlorobenzene solutions produces clathrate structures (6 form) at low temperatures (T < 130°C) and ordered fl" modifications at higher temperatures. In particular, modification very close to the fl" limiting one are obtained in the temperature range 130-140°C. Recrystallization of the fl form has been detected by differential scanning calorimetry and studied by X-ray diffraction analysis of the annealed samples. These studies indicate that the recrystallization of the fl' form in the melting region does not involve a fl' to fl" transition, but only morphological changes. Models for the chain packing of the limiting modifications of the fl form are suggested, by quantitative comparisons of the X-ray diffraction intensities and calculated structure factors.

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Acetylene polymerizes under the action of chlorine-bridged Rh (I) complexes such as [Rh (1,5-Cod)Cl] z or [Rh (NBD)CI] 2, in the presence of sodium ethoxide as co-catalyst. The microstructure of polyacetylene obtained at different temperatures has been studied by means of i.r. spectroscopy, and its thermal behaviour by t.g.a./d.t.a. The soluble oligomers obtained as secondary products of acetylene polymerization have been studied by u.v. spectroscopy. Moreover, the chlorinated derivative of polyacetylene has been prepared

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The influence of the neutralizing cation on the response of model polyurethane ionomers to uniaxial extension is investigated by small-angle X-ray scattering. Anisotropic scattering patterns are observed for ionomers neutralized with Na+, Sr 2 + and Ca 2 + upon elongation, with the precise nature of the response depending on the neutralizing cation. Scattering patterns of elongated ionomers neutralized with Ni 2 + and Cd 2+ display little or no anisotropy up to extension ratios of 2 = 5.0 and 3.0, respectively. A model invoking ionic aggregate spatial rearrangement within the polymer matrix and removal of ionic groups from the aggregates to the polymer matrix or to other aggregates is postulated to explain the results.

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For low molecular mass poly(ethylene oxide) (PEO) and ~,cn-methoxy poly(ethylene oxide) (MPEO) fractions, extended chain crystals can grow when isothermal crystallization temperatures are near their melting temperatures (supercooling AT= T m -T c is in the range of a few degrees). Experimentally, observed lamellar thicknesses of the extended chain crystals are constants in this supercooling region. Linear relationships between crystal growth rate (G) and supercooling (AT) can be observed. Absolute values of the slopes of these relationships decrease with increasing molecular length. Additionally, MPEO fractions generally have higher slope values when compared with their PEO counterparts. Nevertheless, this difference between PEO and MPEO fractions gradually vanishes with increasing molecular length. Extended chain single lamellar crystals are highly faceted in these temperature regions, and their aspect ratios vary with supercooling as well as molecular length. Nucleation theory for the growth of extended chain crystals is applied. The transient chain-end surface free energy, tr', and the lateral surface free energy, o, for the PEO and MPEO fractions possess entropic origins. The rough surface growth model is also discussed.

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The Paris law describing slow crack propagation behaviour in several materials is deduced for craze-prone polymers from schematic considerations matching the craze fibril breakdown statistics, first introduced by Yang and co-workers, with the Dugdale-Barenblatt model of the plastic zone at the crack tip. The exponent in the Paris law is shown to be simply equal to 2p,,, where Pw is the Weibull modulus of the fibril breakdown statistics. A promising, if not definitive, agreement between the two parameters is found from literature data for several craze-prone polymers.

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