1999 рік

Polyethylenes (PE) with long chain branching (LCB) densities up to 0.44 carbons/10 000 carbons and narrow molecular weight distributions were synthesized using a continuous stirred-tank reactor (CSTR) with the Dow Chemical’s constrained geometry catalyst system, CGCTi/TPFPB/MMAO, in Isopar E solution at 500 psig and 140–190°C. Rheological properties of these metallocene polyethylenes (mPE) were evaluated and correlated to the LCB density. Measurements included steady-state viscosity, dynamic viscoelasticity, melt flow index and extrudate swell. Compared to their linear counterparts with the same molecular weights, LCB PEs gave higher viscosities at low shear rates and lower viscosities at high shear rates. These shear-thinning properties measured by a melt flow index ratio I 10/I 2 strongly depended on the LCB density. PE with an average of fewer than one branch per six polymer molecules exhibited a I 10/I 2 value of 25.7 compared to linear PEs I 10/I 2 ¼ 6~8 having similar molecular weights. An increase in the LCB density also significantly reduced the ratio of loss modulus over storage modulus, and yielded longer relaxation lifetime and higher level of extrudate swell. In contrast to the rheological properties, tensile strength, melting temperature, and other physical and mechanical properties were not noticeably affected by LCB.

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Hydrolytic activity of molecularly imprinted polymeric mimics of chymotrypsin was evaluated against N-acetyl tyrosyl para nitrophenyl ester and N-benzoyl tyrosyl para nitrophenyl ester, respectively. The mimic grafted on hydrophilic support exhibited high kcat and high Km values for N-acetyl tyrosyl para nitrophenyl ester. But, for N-benzoyl tyrosyl para nitrophenyl ester, the mimic exhibited low kcat as well as low Km values, consistent with the nonproductive binding exhibited by natural chymotrypsin for hydrophobic substrate. The same mimic when grafted on hydrophobic support exhibited trends consistent with Michaelis–Menten kinetics and also higher catalytic activity than that exhibited by the mimic on hydrophilic support. Thus in the case of mimics nonproductive substrate binding could be eliminated by the choice of appropriate support. This helped to enhance the mimic activity towards a specific substrate. This discretion is not available in the case of native enzyme

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A series of all sol–gel organic–inorganic nonlinear optical materials based on the prepolymers of melamines and an alkoxysilane dye (ASD) were investigated. The NLO-active ASD containing nitroazobenzene was incorporated into the melamine matrices with different weight ratios. This all sol–gel type is shown to have the advantages of simultaneous polymerizations, and better compatibility between two components due to residual hydroxyl and silanol groups after curing. The simultaneous route is often used to avoid significant phase separation in a multi-component system. SEM results indicate that the inorganic networks are distributed uniformly throughout the organic networks on a molecular scale. The silica particle sizes are well under 1 mm. This series of all sol–gel materials exhibits large second-order optical nonlinearity (d33 ˆ 10–54 pm/V at 1064 nm, and 3–17 pm/V at 1542 nm) after poling and curing. Temporal stability of the effective second harmonic coefficient at 1008C is also reported.

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The spin probe technique was systematically applied to study a family of high permeability and high free volume glassy polymers. Rotation correlation times t c or frequencies n ¼ 1/t c of 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) were measured in amorphous teflons — random copolymers of tetrafluoroethylene and 2,2-bistrifluoromethyle-4,5-difluoro-1,3-dioxole, polyacetylenes and polynorbornenes. Polymers distinguished by unusually high, for the glassy state, permeability and free volume exhibit large rotational mobility of TEMPO. The correlation times correspond to fast rotation of the spin probe previously observed only in rubbery polymers. Correlations between the frequency n and gas permeability and diffusion coefficients were observed. However, in some polymers, the spin probe’s rotation rate is also sensitive to side-chain local mobility, which does not affect translational diffusion coefficients of gas molecules in polymers.

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Various solvents and cocatalysts were examined for the purpose of achieving high initiator efficiency in the living polymerization of substituted acetylenes catalyzed by MoOCl4-based catalysts. Eventually, anisole and n-Bu4Sn were found to be very useful as solvent and cocatalyst, respectively. The initiator efficiency of the MoOCl4 –n-Bu4Sn–EtOH (1:1:2)/anisole system was as high as 40% in the polymerization of o-CF3-phenylacetylene, whereas the value for the corresponding toluene system was no more than 10%. o-Me3Si-phenylacetylene, 1-chloro-1-octyne, 2-octyne, and 1-chloro-2-phenylacetylene and a few other monomers were also polymerized in a living manner by the present catalyst/solvent system, the initiator efficiencies being 20–40% and larger than those of the previous systems.

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Insoluble polyelectrolyte complexes were produced by admixture of (0.2 M) aq. solutions of poly(sodium phosphate) (PSP) and poly(4vinylpyridinium chloride) (P4VPC) over the whole range of composition. Independent of the order of addition, the weights of isolated complex were approximately equal to those calculated on the basis of reaction stoichiometry. Stoichiometry was also confirmed by analysis of the supernatant liquid in conjunction with the weights of initial components and complex. Dissolution of the complex required a certain minimum hydrogen ion concentration obtained by using either a strong acid/base or a weak acid. Analysis showed that the starting materials were thereby regenerated. In dilute (1 × 10 24 M) aq. solutions, the complex did not precipitate, but UV spectroscopy demonstrated its presence and its change of shape with time.

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Superabsorbent polymers have been prepared by inverse suspension and solution polymerisation techniques using different acrylic monomer compositions and different amounts of crosslinking agents. The particle size distributions of products made by inverse suspension polymerisation were determined and the dependence of absorption characteristics on particle size was investigated. As the particle size became smaller, the rate of absorption and ultimate degree of absorption both increased. These observations drew attention to the importance of particle morphology in optimising superabsorbent performance. The experimental data provided further support for a two-parameter Voigt model of the rate of absorption. The effect of increasing the salinity of the water on absorption was also determined.

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In this work, the effects of the polymer–solvent interaction on the aggregation behavior of polyvinyl chloride (PVC) solutions were studied through elastic light scattering and viscosity measurements. The result in Zimm plots of PVC solutions showed that the second viral coefficient, A2, value of PVC/BrBz solutions is higher than that of PVC/DOA solutions at the same temperature. The radius of gyration, Rg, in PVC/BrBz solutions is larger than that in PVC/DOA solutions, indicating that PVC chains in a good solvent BrBz must be more extended than those in a poor solvent, DOA. The u -temperatures are about 32°C and 68°C for PVC/BrBz and PVC/DOA solutions, respectively. The result in the temperature dependence of Rg value showed that PVC/BrBz solution exhibits the coil–globule transition, while no transition is observed in PVC/DOA solution in the measured temperature range. The chain overlapping concept was used to discuss the heterogeneous degree of PVC solution. The result showed that PVC/DOA solution is more heterogeneous than PVC/BrBz solution. The time-resolved light scattering measurements indicated that the spinodal decomposition rate of PVC/DOA solution was faster than that of PVC/BrBz solution. However, the gelation time of PVC/BrBz solution was shorter than that of PVC/DOA solution. These facts may imply that the more extended chains in PVC/BrBz solution are advantageous to the intermolecular association for the gelation. The scattered profiles (I(q) vs. q) showed that the scattered intensity of PVC/DOA solution is much higher than that of PVC/BrBz solution at the same concentration. A scattered maximum was observed in PVC/DOA solution while no other peak appeared in PVC/BrBz solution. The various aggregation or the gelation behaviors between PVC/DOA and PVC/BrBz solutions must be concerned with different degrees of spinodal decomposition in the solution state, which is mainly related to different degrees of the polymer–solvent interaction.

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Composite systems of Kevlar, poly(p-phenylene terephthalamide), and Santoprene, a polyolefin-based thermoplastic elastomer, were studied. Kevlar pulp was used as-received in one system, and modified in the other. The as-received Kevlar pulp was found to reinforce Santoprene to a certain degree. It was found that with increasing amount of Kevlar in the composite, low-strain modulus and tensile strength increased, while the elongation at break decreased sharply. To improve mechanical properties of the composite, hydrolysis of Kevlar pulp surface was employed in conjunction with maleic anhydride-grafted-polypropylene (MA-g-PP), a reactive compatibiliser. It was found that the treated Kevlar pulp greatly improved the low-strain modulus, tensile strength, and elongation at break of the composite. Dynamic mechanical analysis showed that the storage modulus of the Kevlar/MA-g-PP/Santoprene composite was significantly higher than the asreceived Kevlar composite. A slight increase in transition temperatures of polypropylene matrix was also observed. As a result of the fact that low-strain modulus and tensile strength of the composite were improved when hydrolysed Kevlar pulp and MA-g-PP were used, it is suggested that such a combination might have increased the interfacial adhesion of the fibre and the matrix, and effective fibre volume fraction, resulting in a better distribution of stress along the reinforcing fibre.

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Apparent reactive coupling of CaCO 3 to polypropylene (PP) was achieved with the application of aminofunctional silane coupling agents. The strong coupling effect could be attributed to increased CaCO 3/silane and PP/silane interaction. A detailed study has shown that aminofunctional silanes bond strongly to the surface of the filler, but in the case of multilayer coverage also to the previous layers. Experiments were carried out to determine the mechanism of interaction between the silane coupling agents and the apolar polypropylene, which does not contain reactive groups. Model reactions followed by (Fourier Transform Infrared Spectroscopy) FTIR analysis demonstrated that during processing at elevated temperatures, oxidation of the polymer takes place in spite of the presence of stabilizers. Reactive carbonyl groups form as a result, which enter into chemical reactions with the amino functionality of the silane, resulting in strong amide bonds.

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