1992 рік

The swelling equilibrium behaviour of N-n-butyl-N,N-dimethyl-4-vinyl benzylammonium bromide (BBABr) gel was measured in aqueous solutions of various inorganic electrolytes: HBr, LiBr, NaBr, KBr, NH4Br, NaC1, NaI and NaC104. The equilibrium swelling volume of BBABr gel does not depend strongly on the cationic species but on the anionic species. In aqueous solutions containing I- and C10~ ions, the volume-phase transitions of the BBABr gel were induced by a change in the concentration of the electrolytes. It was verified experimentally with 79Br n.m.r, and an ion electrode that the volume-phase transition is controlled by the change in the association state of the charged groups in the gel.

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The predominantly hydrocarbon macrocycles bis(p-phenylene)-32-crown-4 and bis(m-phenylene)-30- crown-4 have been synthesized in one step from hydroquinone and resorcinol, respectively, and 1,10-dibromodecane in the presence of sodium hydroxide in dioxane/1-butanol.

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Optically controlled ligand delivery systems would be useful for the design and development of biosensors. We synthesized a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing sidechains terminated in model ligand (Boc-Gly), bound via photocleavable 2-nitrobenzyl bonds. To study photocleavage at solid liquid interfaces, the HPMA copolymer was covalently attached to 3-aminopropyl triethoxy silane (APS)-coated porous silica beads, which were modified with ct,~o-diaminopoly(ethylene oxide) of molecular weight 1000 or 5000. The influence of the poly (ethylene oxide) (PEO) spacer on the rate of photolysis and on the minimization of non-specific adsorption was determined. The results show that the photolytic rates are faster for copolymer-derivatized silicas with PEO spacers compared to that without spacer and that the PEO spacer reduces the non-specific adsorption of HPMA copolymer on the silica surface.

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The effect of particle size on the fracture behaviour of cured epoxy resin filled with spherical silica particles was studied. Five kinds of spherical silica particles prepared by hydrolysis of silicon tetrachloride having different mean sizes, ranging from 6 to 42/~m, were used. The critical stress intensity factor (Kc) and the critical strain energy release rate (G?) of the cured epoxy resins filled with the silica particles were measured. Both Kc and Gc values increased with particle size. Scanning electron microscope observation shows that the main crack propagation was hampered by large particles and a damage zone was formed at the main crack tip region in the large particle filled resin due to crack diversion and debonding of particle/matrix interfaces. The higher K c and G c values seem to be derived from these phenomena.

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Apparent gelation rates t~-ed, defined as the reciprocal of the gelation time, are measured for poly(vinyl alcohol) solutions as functions of polymer concentration, Cp, and quenching temperature, TQ. Here the measurements are limited to the case of homogeneous gelation where T o is below 0°C. The critical gelation concentration, C*= oo, extrapolated to t~ = 0 is independent of TQ, and is identical to the polymer chain overlap concentration, C*g. In order to represent the degree of polymer chain overlap a reduced concentration, ?= (Cp-C*~)/C*8, is introduced. An experimental relation, tg-d =A(TQ) ?2, is obtained where A(TQ) is the temperature factor. The ? dependence of the equation can be explained using the chain overlap concept for gelation and random bond percolation theory, and the temperature factor A(TQ) is analysed by the crystal nucleation theory.

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Poly (3-chlorodiphenylamine) was prepared by electrochemical and chemical polymerization in acetonitrile solutions. The as-synthesized polymers are soluble in organic solvents and concentrated acid and exhibited a room temperature electrical conductivity of 1.6 x 10 -3 S cm-1. Electropolymerized and solution cast films are electroactive and displayed reversible colour changes when cycled in organic or acid electrolytes between 0.0 V and 1.3 V versus Ag/AgCI.

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MgC12 supported Ti and Hf catalysts were comparatively tested with respect to the polymerization of differently shaped monoalkenes. The ratio between the average polymerization rates of Ti and Hf catalysts during the first 120 rain ( V~i/Vpn f) is 10 for ethylene,i ncreases to 63 for propylene and returns to ~ 12-20 for higher or bulkier monoalkenes, suggesting a distinct shape selectivity of active sites

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The crystallization of cis-l,4-polyisoprene (PIP) in miscible blends with atactic poly (vinylethylene) (PVE) was investigated. Normalized to the PIP content, the extent of crystallization and the crystallization rate were suppressed in the mixtures. A reduction in the degree of crystallinity is contrary to the behaviour usually exhibited by blends in the absence of crosslinking. More anomalous was the observation that the magnitude of the crystallization suppression in the uncrosslinked PIP was independent of PVE concentration over a range from 5 to 50% PVE. Furthermore, whereas ~-lamellae predominate for pure PIP crystallization, blending with high-molecular-weight PVE caused preferential development of the/~-lamellar form. This bias may be a reflection of the known ability of the /~-lamellae to incorporate non-crystallizing entities more readily into the fold plane at the crystal surface. Changes in heat capacity at T~ measured before and after melting were consistent with the notion that PVE chains are trapped between the lamellae of the crystallizing PIP, with the extent of entrapment substantially greater for higher-molecular-weight PVE. The degree of crystallinity in the blends also varied with the molecular weight of the PVE, suggesting that suppression of the crystallization was a consequence of the entrapment of the PVE. In networks the suppression of crystallization significantly exceeded that observed in uncrosslinked blends and pure PIP networks. For free-radical crosslinking the presence of PVE increases the crosslink density of the PIP segments, contributing to the lower crystallinity in the crosslinked mixtures

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Copolymerizations of propylene and 4-(~o-alkenyl)-2,6-di-t-butylphenol were performed at 70°C over a high-activity supported TiC14/MgC12 Ziegler-Natta catalyst, using AI(C2Hs) 3 as cocatalyst and diphenyldimethoxysilane as external electron donor. The 4- (og-alkenyl)-2,6-di-t-butylphenol was pretreated with a stoichiometric molar amount of triethylaluminium prior to copolymerization. After the copolymerization the protecting group was removed by converting the phenol aluminium compound to - OH functionality by HCl/ethanol treatment. The copolymerizability of 4- (~o-alkenyl)-2,6-di-t-butylphenol as a function of the number of methylene group spacers between the double bond and the phenol moiety was determined for four different spacers. The results show that the copolymerization yield as well as the phenol content of the produced copolymer increased with an increase of spacer chain length. The produced copolymers exhibited good thermo-oxidative stabilities also after a prolonged extraction with n-heptane

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In suspension vinyl polymerization of water immiscible monomers, the polymer yield is very low when water soluble initiator is used, because the free radicals generated in the aqueous phase do not get the opportunity to initiate polymerization. However, in conjunction with a phase transfer catalyst, the radical precursor is transferred into the organic phase, where the generated free radicals cause vinyl polymerization, just as an organic soluble initiator does.

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