1992 рік

The preparation of hetero difunctional oligodimethylsiloxanes (ODMSs) was carried out. The ODMSs contained 2-(4-pyridyl)ethyl (Py) or 2-(2,6-di-t-butyl-4-pyridyl)ethyl (DBPy) at one end and a reactive group, such as 3-methacryloxypropyl (MP) or hydrosilyl (H), at the other end. These oligosiloxanes were prepared by anionic ring-opening polymerization of hexamethylcyclotrisiloxane (D3) initiated with silanolate anions containing pyridyl groups. To obtain the initiators, novel silanol compounds containing Py or DBPy groups were prepared from 4-methylpyridine and 2,6-di-t-butyl-4-methylpyridine, respectively. The average degree of polymerization could be controlled by changing the ratio of D3 and the initiator. Py-ODMS-MP and DBPy-ODMS-MP were copolymerized with methyl methacrylate or butyl methacrylate to yield the desired graft copolymers containing pyridyl groups at the side chain ends. Also, the hydrosilylation of DBPy-ODMS-H with vinyldimethylsilylated polysulphone (PSF) was carried out to afford PSF/DBPy-ODMS graft copolymer. The gas permeability coefficients of nitrogen, oxygen and carbon dioxide for the copolymer membranes were evaluated.

Детальніше...  

Copolymer films (100 pm thick) were prepared by cast polymerization of methacryloyl-L-alanine methyl ester (MA-L-AIaOMe) and diethyleneglycol-bis-allylcarbonate (CR-39). The films swell in water at temperatures below 60°C. The degree of swelling increases with decreasing temperature down to 0°C. The swelling capacity of the films increases with increasing MA-L-AlaOMe content. The thermal response is reversible. Swelling and shrinkage have different time constants of ~24 h for swelling and ~ 10 min for shrinkage. The films were subject to an ion track etching process consisting of a heavy ion irradiation using gold ions of 11.4 MeV per nucleon specific energy followed by subsequent etching of the latent ion tracks in NaOH solution. The resulting porous membranes show a reversible change of the pore diameters of ~ 12% between 0°C and 60°C for a copolymer with 70 vol% MA-L-AlaOMe

Детальніше...  

Intrinsic viscosities ([q]) of polystyrene solutions in cyclohexane above and below the 0 temperature have been measured using a capillary viscometer. The viscosity measurements were performed on five polystyrene samples with molecular weights of 6.3 ? 104, 9.0 x 104, 6.0 x 105, 2.8 ? 106 and 10 ? 106. A smooth and continuous contraction was observed below the 0 temperature (34.5°C). The temperature dependence of It/] can be represented by a master curve in a ot3lzlM 1/2 (gl/2 mol-1/2) versus IzlM 1/2 (gl/2 mol-1/2) plot, where ~,= [q(T)]/[q(O)] 1/a is a viscosity expansion factor and T= (T-O)/T is the reduced temperature. A universal plot of reduced viscosity (ct,) versus reduced blob parameter (N/Nc) shows the achievement of the collapsed state for the T < 0 region. The prediction of the temperature blob theory is also verified for the T> 0 region.

Детальніше...  

A series of sequentially ordered copolyesters were prepared from isomeric naphthylene bis(4-hydroxybenzoate) s (NBHBs) and ct,oJ-bis (4-carboxyphenoxy) alkanes (BCPAs) with varying length of =?o-alkylene units. All of the copolyesters were composed of naphthalenediol (NAPH), BCPA and p-hydroxybenzoic acid (POB) (1:1:2molar ratio). The polymer chains were made up of-POB-NAPH-POB-BCPAsegments. The naphthalene units were derived from 1,5-, 1,6-, 2,6- and 2,7-naphthalenediols. The BCPAs employed were 1,4-butane, 1,5-pentane and 1,10-decane derivatives. The melting points and crystallizability of these copolyesters were found to be much higher than those of the corresponding random copolyesters having the same overall compositions. All of the polymers, with the exception of the polyester derived from 2,7-naphthalenediol and 1,5-pentane spacers, formed nematic phases in melts. The ordered sequence copolyesters were found to undergo a rapid sequence randomization at temperatures higher than their melting points. A model compound of a copolyester, 2,7-naphthylene bis[4-(4-n-butoxybenzoyloxy)- benzoate], was also synthesized and its thermal behaviour and liquid crystal properties were studied

Детальніше...  

Previous work has shown that blends of a maleic anhydride functionalized triblock copolymer (with an ethylene/butene mid-block and styrene end-blocks, or SEBS-g-MA) with nylon-6,6 gives super-tough materials with complex-shaped rubber particles that are just below the upper critical particle size for toughening. Similar blends of SEBS-g-MA with nylon-6 are not toughened because the rubber particles are evidently too small, i.e. below a proposed lower critical size for toughening. It was further proposed that this difference in morphology stems from the difunctional (nylon-6,6) versus monofunctional (nylon-6) character of these polyamides for reaction with anhydrides. This proposal is supported here by the observation that blends of SEBS-g-MA with nylon-12,12 give large complex rubber particles like those in nylon-6,6 while nylon-ll and nylon-12 give smaller particles like nylon-6. Further support of this notion is provided by blending nylon-6 with other polyamides in an attempt to produce a chemically modified matrix. Addition of 10% nylon-6,6, poly(m-xylene adipamide) (MXD6) and nylon-12,12 to the nylon-6 matrix (under conditions that cause phase homogenization by interchange reactions) leads to rubber particle enlargement and toughening, while addition of nylon-11 or nylon-12 does not lead to either particle enlargement or toughening. Possible effects of rheological factors, extent of interchange reactions, interfacial tension and end-group contents are discussed

Детальніше...  

Membranes were prepared from modified Udel P-3500 polysulphone having methyl carboxylate groups, of which the degree of substitution ranged from 0.05 to 1.90 ester groups per repeat unit. The membranes showed permselectivity towards water in the pervaporation of aqueous alcohol solutions

Детальніше...  

Cresol and benzaldehyde oligomers have been condensed in organic solvents with oxalic acid as catalyst. The influence of some reaction factors such as the mole ratio between initial monomers, reaction medium and duration of the polycondensation on the yield, softening temperature, content of free cresol and molecular weight characteristics of the cresol-benzaldehyde oligomers is described in the present paper. The products obtained were investigated by means of i.r. and n.m.r, spectroscopy. On the.basis of the data obtained a mechanism for the interaction between cresol and benzaldehyde and a probable structure of the oligomers are proposed.

Детальніше...  

We have studied the evolution of crystalline order during drawing of poly(ethylene terephthalate) at 90°C and at strain rates in the range 0.01-2.1 s- ~. The onset of crystallization always occurs at the inflection point in the stress-strain relationship, which shifts to higher strain levels and lower stress levels as strain rate decreases. Crystallinity develops in two regimes: in the low stress regime (regime 1) crystallinity increases more rapidly than in the high stress regime (regime 2). The onset of regime 2 occurs in the region of the sharp upturn in the stress-strain relationship, which shifts to higher strain levels as strain rate decreases, and at a characteristic level of crystallinity, which is independent of strain rate. We suggest that regime 1 involves the formation of a crystallite network which, at the characteristic level of crystallinity, has sufficiently crosslinked and reinforced the polymer that further deformation generates large stresses. WAXS determinations of lateral crystallite dimensions, normal to the 010 and 100 planes, reveal that crystallization in regime 2 involves modest growth of small crystallites (~ 2.5-3.5 nm), with preferential growth occurring normal to 010. A preliminary investigation of the influence of molecular weight indicates that a lower rate of molecular relaxation at higher molecular weight reduces the strain-rate dependent shift in the onset of crystallization

Детальніше...  

Poly (~-methylstyrene) and poly(vinyl methyl ether) do not form one-phase blends when mixed together. This situation can be changed if the poly(~-methylstyrene) is modified by introducing hydrogen-bond donor groups into the phenyl ring. Two groups of differing donor strength, methylcarbinol and trifluoromethylcarbinol, were selected, and modified poly (~-methylstyrene) samples, with varying degrees of substitution of these groups, were prepared. If the amount of the modifying group incorporated exceeded 4 mol% then one-phase blends of these copolymers with poly(vinyl methyl ether) could be prepared. The effect of the number and strength of these hydrogen-bonding sites on the phase stability of the blends was measured by locating the lower critical phase separation temperature in each blend. The glass transitions of the blends were found to be normally higher than those predicted from a simple rule of mixtures and reflect the extent of hydrogen-bond formation in the blends. This behaviour could, in part, be described by the Kwei equation.

Детальніше...  

The effects of a finite volume fraction of polymer on the reduced osmotic pressure and the reduced diffusion coefficient in solutions, covering an extended concentration range, are analysed in the framework of a recent theoretical approach, which incorporates a renormalization group treatment of a modified interaction Hamiltonian. The resulting analytical functions are consistent with the large amount of experimental data accumulated from the literature. In the interpretation of the diffusion behaviour, over a large concentration interval, the concept of hydrodynamic screening plays a crucial role in obtaining a uniform picture. In the region of strongly overlapping chains a breakdown of the universal features of the reduced osmotic pressure and the reduced diffusion coefficient can be inferred from the theoretical relations.

Детальніше...