1992 рік

Blends containing polyacetal and a random styrene-vinyl phenol copolymer consisting of 35 mol% vinyl phenol segments were prepared by melt mixing and found to exhibit miscibility within the amorphous phase. The blends exhibited a single, composition-dependent glass transition temperature as determined by dynamic mechanical measurements. Thermal analysis revealed a significant depression of the melting point and, in certain cases, a lowering of the degree of crystallinity of the polyacetal phase upon blending with the styrene vinyl phenol copolymer.

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Electron spin resonance (e.s.r.) spectra of the vanadyl probe VO(H20)~ + in chemically cross-linked polyacrylamide (PAA) gels with pore diameters of 7-58 A were used to analyse the changes in gel structure as a function of temperature and solvent composition. The PAA networks were swollen by water and acetone/water mixtures containing 0.1-0.6 volume fraction of acetone. Spectroscopic evidence has been obtained that indicates the absence of bulk water in all the networks studied. Depending upon experimental conditions, bimodal distributions of pore sizes have been detected for all networks. The appearance of this distribution is triggered by lowering the gel temperature in networks swollen by water; alternatively, the bimodal distribution appears for a homogeneous gel at a constant temperature, by adding acetone to the swelling fluid. Unlike the ionic gels, the transition from a homogeneous PAA gel to a gel having a bimodal distribution of pore sizes is gradual as a function of temperature in water swollen gels, and of the acetone content in gels swollen by the solvent mixtures. The microviscosity in the pores appears to depend on the free volume in the pores; this is evident from the Fujita-Dolittle plots in PAA swollen by water, at three different temperatures.

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A new approach to prepare blends of polystyrene (PS) and poly (2,6-dimethyl-l,4-phenylene ether) (PPE) directly in the reactor is presented. The key step in this new route is the in situ 'cold' end-capping of PPE, dissolved in styrene, but the acetylation of the reactive phenolic end group of PPE. Without isolation of the PPE-acetyl (Ac), the reaction mixture is subjected to a classical styrene suspension polymerization procedure, yielding homogeneous beads of PS/PPE-Ac. The presence of PPE-Ac does not interfere chemically with the styrene polymerization as demonstrated by g.p.c, analysis of the separated constituents of the blend. A series of blends with different compositions was prepared. The maximum content of PPE in these reaction blends is 35 wt%, due to a limitation in viscosity of the PPE-styrene solution. Homogeneous transparent amorphous beads of PS/PPE-Ac were obtained, possessing a single glass transition temperature between 105°C and 140°C, depending on the composition.

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A new efficient monofunctional initiator transfer (minifer) system, comprising 2-cyclohexyl-2-propanol, BC13 and 1-methyl-2-pyrrolidinone, has been investigated for the first time in CH2CI 2 diluent at -40°C for the living polymerization of isobutylene. The use of this new minifer system has led to the synthesis of low molecular weight, living (near-monodisperse), new ~t-cyclohexyl-og(tert-chloro)polyisobutylenes. The structural analysis of these polymers by 13C n.m.r, spectroscopy confirmed the nature of the head and end groups to be a cyclohexyl and a tert-chloro, respectively. The living nature of these polymers has been demonstrated by kinetic investigations as well as by their low polydispersity (Mw/M, = 1.18-1.43 ) values from g.p.c, studies

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The spatial distribution of a short-chain amphiphilic diblock copolymer (i.e. block oligomer), used as an emulsifier during the preparation of a latex, is determined by low temperature transmission electron microscopy and differential scanning calorimetry (d,s.c.). The main question is whether intermixing of the amphiphilic block oligomer and latex core materials actually takes place to a significant extent. Electron microscopy gives a clear indication that a surfactant-rich layer exists in all latex samples examined. At very high surfactant concentration ( > 6%, not typically used in commercial latexes), electron beam radiation damage reveals the presence of a surfactant gradient from the particle surface to its core. These results are in good agreement with our d.s.c, data.

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Poly (arylene ether)s containing quinoxaline units were prepared by the aromatic nucleophilic displacement reaction of novel bis(phenolquinoxaline) compounds with activated aromatic difluoro compounds. Polymers prepared from bis(phenoiquinoxaline)s that had configurational isomers were amorphous with inherent viscosity (~/inh) from 0.34 to 1.30 dl g- 1 and glass transition temperature (Tg) from 213 to 283°C. Several polymers prepared from bis (phenolquinoxaline)s that did not contain configurational isrmers were semicrystalline with r/i,h from 0.24 to 0.83 dl g-l, Tgs from 179 to 240°C and Tins from 365 to 388. The molecular weights of the semicrystalline polymers were limited by their solubility in the reaction media

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The crystallization and morphology of binary mixtures of a low-molecular-mass (M, = 2500; Mw/M, = 1.15) linear polyethylene and a high-molecular-mass (_/~, = 166 000 ; ~,/M. = 6.1 ) branched polyethylene grade with 1.5 mol% of ethyl branches have been studied by polarized light microscopy and differential scanning calorimetry. The linear growth rate and the supermolecular structure were found to be highly sensitive to composition. The pronounced increase in linear growth rate with increasing content of the linear fraction may be explained by an increased rate of diffusion of crystallizable segments due to a reduction in chain entanglement. The introduction of the linear polyethylene fraction changed the originally spherulitic structure into a predominantly axialitic texture.

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Glycidyl methacrylate-ethylene dimethacrylate (GMA-EDMA) copolymer particles were synthesized by both conventional suspension polymerization and a two-step swelling technique. Oxirane groups in the products were modified by reaction with a mixture of 2,2,6,6-tetramethyl-4-aminopiperidine and its 1-oxyl paramagnetic derivative. The characteristics of the synthesized copolymer particles and the modified oxirane groups were studied with respect to the type of synthesis and the type and content of diluent.

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We report a wide angle neutron scattering experiment on atactic polystyrene, recently performed on the novel small angle neutron diffractometer for amorphous and liquid samples (SANDALS) commissioned at the pulsed neutron facility ISIS (UK). The use of SANDALS allows for the first time true quantitative neutron scattering data to be obtained over a large scattering vector range for hydrogenous polymers. Results for samples of both totally deuterated and totally protonated polystyrene are presented and compared with predictions from statistical models for the chain configuration. The possibility offered by SANDALS of investigating the local structure of hydrogenous polymers offers exciting prospects, particularly in the study of polymers of technological or commercial importance.

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The crystallization and morphology of binary mixtures of a low-molecular-mass (M, = 2500; Mw/M, = 1.15) linear polyethylene and a high-molecular-mass (_/~, = 166 000 ; ~,/M. = 6.1 ) branched polyethylene grade with 1.5 mol% of ethyl branches have been studied by polarized light microscopy and differential scanning calorimetry. The linear growth rate and the supermolecular structure were found to be highly sensitive to composition. The pronounced increase in linear growth rate with increasing content of the linear fraction may be explained by an increased rate of diffusion of crystallizable segments due to a reduction in chain entanglement. The introduction of the linear polyethylene fraction changed the originally spherulitic structure into a predominantly axialitic texture

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