1992 рік

Polymerizations of propene and 1-hexene were conducted with two sets of catalyst systems with completely different stereospecificity : aspecific catalyst, TiC13/MgCI2/A12 (C2H 5)3C13/A1 (C2H 5) 3 (s°lid) and Cp2ZrCI2/MAO (soluble); isospecific catalyst, Solvay type TiCI3/Cp2Ti(CH3) 2 (solid) and rac- Et[IndH4]2ZrC12/MAO (soluble). The molecular mass distributions (MMDs) of both oligomers and high polymers obtained with these catalysts were measured by mass spectrometer and g.p.c. The pattern of oligomer distributions was found to be markedly different between the aspecific and isospecific catalysts. The aspecific catalyst gave a continuous distribution in a wide mass range, whereas the isospecific catalyst gave a discontinuous distribution, i.e. oligomers having more than 10-20 monomer units could not be detected. On the other hand, short periods of polymerization gave high polymers, the MMDs of which did not change so much with increasing the polymerization time. These results suggest that atactic polymerization proceeds steadily while the propagation rate of isotactic polymerization becomes very fast after the polymer chains grow to a critical number of monomer units (10-20).

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Lipopeptides and liposaccharide macromonomers with acrylamide, methacrylamide, acrylate and methacrylate polymerizable groups have been synthesized and polymerized. Depending upon the molecular characteristics of the macromonomers, lamellar (smectic), cylindrical and nematic architectures have been obtained and characterized by X-ray diffraction. The utilization of these systems as models of biological systems and their biomedical applications are discussed

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In irreversible step-growth polymerization, the molecular-weight distribution (MWD) of the polymers produced can be controlled via the reaction path. In this paper, the effect of intermediate monomer feed on MWD in batch reactors or continuous plug flow reactors is investigated using a kinetic approach. It is found that the polydispersity index (Pw/PN) of the MWD can be made larger than 2 and that its magnitude can be controlled by the extent of reaction in the first stage (before additional monomers are fed), Pl, the final extent of reaction, pf, and the amount of monomer fed additionally, qS. For non-linear polymerization, the effect of intermediate monomer feed is more significant than that for linear polymers, and the extent of reaction at the gel point, Pc, can be lowered significantly.

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Chain dimensions of the polystyrene-d8 parts of a styrene-ds-2-vinylpyridine block copolymer (DP-33) and a styrene-da-styrene-hs block copolymer (DH-44), both with 50:50 compositions, were measured in dilute solutions of pyridine (a common good solvent) benzene (a selective solvent ) and methyl ethyl ketone (a poor solvent) by small-angle neutron scattering. The conformation of one block chain within a diblock copolymer is not affected by the existence of another block chain, regardless of the solvent power at least when the composition of the diblock copolymer is 50: 50, and the molecular weight is not high

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We present a novel utilization of chemical doping in stereospecific chlorination to z-conjugated polyene. It has been verified that not only prolonged FeC13 doping but also iodine doping followed by chlorine addition to one-dimensional conjugated polyene (polyacetylene, (CH)x) produce a stereoregular chlorinated polyacetylene, (CHCI)x, i.e. di-syndiotactic poly(1,2-dichloroethylene). In the latter case, tacticity of the polymer, defined as the ratio of stereoregular to atactic segments in the (CHC1)x, strictly depends upon the dopant concentration of iodine before the chlorine addition. Thus chemical doping is a promising method to control the tacticity of (CHC1)x without polymerization. We demonstrate that the positively charged polyene segment generated by the chemical doping plays an essential role in governing stereospecific chlorination.

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Fluoresence probe techniques have been employed to monitor interactions of sodium carboxymethylamylose (NaCMA) with cationic and anionic surfactants in aqueous solution in both the absence and the presence of added salt. The changes of the 11/13 ratio of the fluorescence of pyrene in NaCMA solution were measured as a function of hexadecyltrimethylammonium chloride (HTAC) and sodium dodecyl sulphate (SDS) concentration. In the absence of added salt, mixed micelle formation of NaCMA with both HTAC and SDS was observed with an apparent critical micelle concentration (CMC) of 1 ? 10 -4 and 3 x 10- 3 M respectively. These are the first observations of mixed micelle formation between an anionic surfactant and an anionic polyelectrolyte. The average aggregation numbers of the mixed micelles were measured by the analysis of the fluoresence decay curve of the micelle-solubilized pyrene to be smaller than that for the micelles in the absence of NaCMA. In the presence of 2% NaCI the apparent CMC values of the surfactants are greater than those in the absence of NaCMA, suggesting that NaCMA forms inclusion complexes with both HTAC and SDS. The association constant of NaCMA with HTAC is 4.1 ? 104 M -1, and the maximum amount of bound HTAC per anhydroglucose residue is 0.014. This result is consistent with the model of interrupted 6-helix conformation of NaCMA.

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Reductions of TiC14 by organoaluminium compounds were carried out in hydrocarbon and halogenated hydrocarbon solvents using various ethers as donor. Under appropriate conditions, TiC14 was quantitatively reduced by trialkylaluminium to give a homogeneous black solution of TiCl3.~AICla.ether complex. Catalyst systems of the soluble TiC13 and A1 (i-Bu)3 (cocatalyst) showed high catalytic activities for random copolymerization of ethylene with propylene. The resulting copolymers were superior elastomers with low crystallinity and had outstandingly high tensile strength and elongation at break in comparison with copolymers prepared from a conventional VOCla/AI(Et)I.5Cll.5 catalyst system. Characterization data of copolymers suggest that the excellent tensile properties are due to microblock-type sequences of ethylene and propylene in a polymer chain.

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The effect of immersion in a non-swelling liquid under pressure on time-dependent crack growth has been studied for various elastomers. A large effect of pressure is observed, with the rate of growth decreasing by approaching three orders of magnitude per kbar. It appears that the effect is mainly associated with the change in glass transition temperature although other factors may also be involved, such as the tendency of the failing material at the tip to separate into filaments. Measurements of strains at the crack tip suggest that this tendency may be associated with the presence of stresses through the thickness of the material.

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The conformational properties of bacterially synthesized copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV), P(3HB-co-3HV), have been studied using the MM2 molecular mechanics method. The MM2 calculation is applied to some model compounds having carefully selected initial geometries and finite chain length. The present calculation reveals that the isolated copolymer chain of P(3HB-co-3HV) has some types of stable 21 helices over the whole comonomer composition range, and that the distortion induced on the helical conformation is much greater when 3HV units are incorporated into the 3HB helix than when 3HB units are incorporated into the 3HV helix. On the basis of these results, the crystalline morphology is discussed.

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2-Hydroxy-4-methacryloxyacetophenone (2H4MAP) was prepared and polymerized in methyl ethyl ketone using benzoyl peroxide as initiator. Poly (2H4MAP) was characterized by infra-red and 1H nuclear magnetic resonance spectroscopic techniques. The molecular weight of the polymer was determined by gel permeation chromatography. Cu(II) and Ni(n) chelates of poly(2H4MAP) were synthesized. Elemental analysis of the polychelates suggests a metal-to-ligand ratio of 1:2. The polychelates were further characterized by infra-red and electronic spectral studies, and electrical conductivity measurements. Thermogravimetric analysis of the polychelates has been carried out in air.

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