1994 рік

A new polymeric support was synthesized using the co-oligomer of 1,3-butadiene-acrylic acid crosslinked with 2-hydroxyethylmethacrylate. Tannic acid was later attached to this product as a ligand, through a spacer arm of nine carbon atoms. Different assays were carried out in order to characterize this product, and preliminary experiments were performed to determine its potential application in the capture of proteins.

Детальніше...  

Differential scanning calorimetry [d.s.c.) measurements on the 50/50 blends of well-defined multibranched polystyrenes and linear polystyrenes were carried out to investigate the miscibility between polymer components having the same constitutional repeating units but different molecular architectures. Multibranched polystyrenes with different branch number and length were prepared by the radical polymerization of polystyrene macromonomers of different molecular weights possessing a different polymerizable end group, i.e. a vinylbenzyl end group and methacryloyl end group. D.s.c. curves showed one or two thermal transitions corresponding to the glass transitions depending on both the branching architecture of the muhibranched polystyrene, namely poly(macromonomer)s, and the molecular weight of the linear polystyrenes. The miscibility between the poly(macromonomer) and the linear polystyrenes decreased with increase in both branch number of poly(macromonomer)s and the molecular weight of the linear polystyrene. The miscibility increases with increase in the branch length but was not much influenced by the chemical structure of the central backbone of the poly(macromonomerjs. These results indicate that the miscibility in the athermal binary multibranched-linear polystyrene blends is influenced by the branching architecture, and the blends locate near the miscible/immiscible boundary.

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Experimental evidence is discussed indicating that in the case of polypivalolactone (PPVL), the time spent in the melt, and the melt temperature from which the samples are quenched to the crystallization temperature, both affect the subsequent crystallization process, and specifically the relative proportions of the ~- and 7-modifications. Neither thermal degradation nor heterogeneous nucleation by extraneous substances appear to account fully for the observed phenomena. The results suggest that the surprising features of the polymorphic behaviour of PPVL, as reported, may relate to the persistence of structural organization, the most likely being nuclei of different crystalline forms, at a temperature which is more than 40°C above the phenomenological melting point, i.e. at temperatures comparable to the proposed equilibrium melting temperature of ~t-PPVL

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Ionic association in complexes of lithium trifluoromethanesulfonate with low-molecular-weight poly(ethylene oxide) dimethyl ethers was studied using Raman and infra-red vibrational spectroscopy. The relative concentrations of ion pairs and more highly associated ionic species are quite dependent on chain length. This dependence was measured in both the CF 3 symmetric deformation mode and the SO3 symmetric stretching mode. The effect of the terminating group was considered by comparing the dimethyl ethers with hydroxy-terminated poly(ethylene oxide) at comparable chain lengths. Hydrogen bonding effects in the hydroxy-terminated poly(ethylene oxide) compounds were also found to depend on chain length.

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The u.v. photolysis of statistical methyl methacrylate-methyl vinyl ketone copolymers containing relatively small amounts of methyl vinyl ketone is shown, by n.m.r, and g.p.c, analysis, to give rise to oligo(methyl methacrylate)s with allylic end-groups that are not readily polymerizable. Thus it is concluded that the photolysis proceeds predominantly via a Norrish type I process rather than by a modified Norrish type II process as previously suggested. The Norrish type II process, however, is a minor contributor to the overall reaction and gives rise to some oligomeric fragments with acrylic end-groups.

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A general equation is derived for the critical conversion at the gel point in free radical crosslinking polymerizations by omitting the equal reactivity assumption from the Stockmayer criterion of gelation. Calculations show that the monomer depletion, the volume contraction during polymerization and the initiator depletion have to be taken into account when the pre-gelation period is sufficiently large. The nucleation and growth of the gel molecule are described using kinetic differential rate equations. If the assumptions of equal vinyl group reactivity and random crosslinking are introduced, the resulting equations are equal to those of the statistical theories.

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Block copolymers of various compositions, consisting of poly(4-vinylpyridine) (P4VP) and poly(dimethylsiloxane) (PDMS) blocks, were prepared by anionic polymerization. These samples were modified by the addition of various amounts of iodine in solution. The electrical conductivities of the doped materials were measured by the four-probe method and were found to be as high as 10- s S cm- 1. The optimum ratio of iodine to pyridine which gave the highest conductivity was determined

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Atomic force microscopy (AFM) was used to study the morphology and nanostructure of mechanically oriented, isotactic polypropylene (i-PP). AFM images of cleaved samples on the micrometre scale unveiled microfibrils with a diameter of 100-150nm. Chain orientation and imperfections of chain packing were visualized in the (1 10) crystal facet at the surface of the microfibrils. Paracrystalline disorder and twisting of macromolecules were observed. Resolution of individual methyl groups with unprecedented quality allowed us to identify the handedness of the helices in the crystalline i-PP matrix. The packing of the methyl groups, visualized by AFM, was compared with the computer-visualized structure. The agreement between the expected and the experimentally determined parameters of the crystal structure was perfect within experimental accuracy

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Epoxy resins (EP)/poly(ethylene oxide) (PEO) blends cured with phthalic anhydride were studied by differential scanning calorimetry and dynamic mechanical analysis. Single glass transition temperatures were observed for all blends before and after curing, indicating a high degree of miscibility. At the same time, a marked deviation from the empirical equation (e.g. the Fox equation) was noticed after curing. This is ascribed to the dilution effect of the PEO component and participation of PEO in the cure reaction resulting in incomplete crosslinking, i.e. the formation of imperfect crosslinking network structures. Fourier transform infra-red spectroscopy provided strong evidence that there is a specific interaction between the EP and PEO molecules

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Styrene(S)--isoprene(l) multibiock copolymers of the (SI), type (n = 1, 2, 3, 4) were prepared by a multistep monomer addition technique of anionic polymerization. Molecular weights of SI diblock units are almost the same and the total polystyrene volume fractions are about 0.5. All the film specimens cast from toluene solutions were found to have alternating lamellar structures. The lameUar domain spacing monotonically decreases and approaches an asymptotic value with increasing the number of blocks.

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