1994 рік

The effects of two low-profile additives (LPA), namely poly(vinyl acetate) and poly(methyl methacrylate), on the rheokinetics and morphological changes up to gelation in the cure of unsaturated polyester (UP) resins at l l0°C were investigated by using a Haake viscometer, a differential scanning calorimeter, a Fourier-transform infra-red spectrometer and a scanning electron microscope. Adding LPA to the neat UP resins could increase the gel time and the gel conversion to differing extents, depending on the types of LPA added. The experimental results were explained by a microgel-based gelation mechanism on the basis of the integrated rheology-reaction kinetics-morphology results and by ternary static phase characteristics for styrene/UP/LPA systems at 25°C.

Детальніше...  

Oriented and non-oriented samples of two liquid-crystalline side-chain poly(vinyl ether)s, poly{4-[11- (vinyloxy)undecyloxy]-4-cyanophenylbenzoate} (poly(1)) and poly{4-rll-(vinyloxy)undecyloxy]-4-ethoxyphenylbenzoate} (poly(2)), have been studied by small-angle and wide-angle X-ray scattering techniques, polarized light microscopy and differential scanning calorimetry. The terminal group of the mesogenic unit played an important role in the organization of the side chains. With increasing temperature, poly(1) exhibited a smectic C, a transitional ordered smectic, a smectic A and finally an isotropic phase, whereas poly(2) showed a crystal B, a smectic A and an isotropic phase. Both polymers showed a glass transition at 310 K. The global alignment of the mesogenic groups did not affect the internal order of the smectic phases

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Hydroxypropyl cellulose (HPC) was incorporated & situ with silica by the sol-gel process involving various amounts of added tetraethoxysilane (TEOS), and hybrids with nanometre-sized silica particles were prepared. To determine the effect of TEOS content on the mechanical properties of the micro-hybrids, the TEOS content in the hybrids was varied from 20 to 60%. The mechanical properties of the micro-hybrids were compared with those of HPC composites mixed with various amounts of glass beads (diameters of 20-40/am) by solvent blending. The ultimate tensile strength of the micro-hybrid was improved from 6 to 18 MPa when the TEOS content reached 40 wt%. On the other hand, the strength of the blend composite decreased with glass-bead content. The ~1- (molecular motion in a highly ordered amorphous phase), ct 2- (molecular motion in a random amorphous phase) and B-relaxations (relating to molecular motion of hydroxypropyl groups) were observed in the temperature dependence of the dynamic viscoelastic properties of HPC. The level of the dynamic modulus, G', of the micro-hybrid increased with initial TEOS content. By hybridization, the cq-peak in the tan 6 curve broadened and its intensity lowered as the initial TEOS content increased. The ct2-peak was observed for the micro-hybrid composed of 20 wt% TEOS, but disappeared when the TEOS content exceeded 40 wt%. The B-peak was not observed in the hybrid. No drastic change was observed in the dynamic viscoelastic behaviour of the blend composite as the glass-bead content was varied. The mechanical properties of the in situ micro-hybrid were completely different from those of the blend composite. This difference was caused by the interaction between the filler and matrix. In the micro-hybrid, nanometre-sized ceramic particles may be dispersed in the HPC component, and strong interaction occurs via hydrogen bonding. In contrast, the interaction between the glass beads and HPC in the blend composite is weak

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Block copolymers consisting of rubbery lignin derivative components (i.e. hydroxypropyl lignin, L) and cellulose propionate (CP) segments ranging in size from degree of polymerization (DP) 5 to 60 were synthesized using chemistry described previously. The block copolymers (LCP) varied in relation to architecture and size of component. The copolymers were characterized by solution, thermal and optical techniques, and their effect on the properties of L/CP blends was determined by mechanical tests. The results suggest that copolymer properties are dictated primarily by CP segment size. Whereas copolymers with short CP segments behaved like spherical macromolecules, copolymers with large CP segments had rod-like behaviour. All block copolymers displayed T m values, even if CP arm length was as low as 5. Crystallinity was highest at CP chains of DP 60. Copolymer morphologies varied; they revealed patterns resembling dispersed fibrils, spheres and alternating lamella types depending on composition and segment geometries. The block copolymers had surprisingly little effect on L/CP blend properties. This was attributed to the overall compatibility of lignin derivatives with CP.

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Self-diffusion of water in unhardened photographic gelatin is measured by pulsed-gradient n.m.r. spectroscopy. Mutual diffusion and activity of water in hardened and unhardened gelatin is measured by step-change gravimetric sorption methods. Predictions of mutual diffusion from the self-diffusion data and published thermodynamic data by using the Vrentas-Duda theory are in agreement with the measured mutual diffusivities. Hardening (i.e. crosslinking) of the gelatin reduces the diffusivity as predicted by an extension to the Vrentas-Duda theory. The water activity increases with crosslinking.

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Crystal structure, morphology and thermal effects of poly(1,4-phenylene-oxy-l,4rphenylene-oxy-l,4- phenylene pyromeilitimide) (PMDA-TPE-Q), synthesized from N,N'-dimethyl pyromellitic bisimide and 1,4-bis(4-aminophenoxy) benzene in the melt, have been studied by transmission electron microscopy (TEM), electron diffraction (ED) and wide angle X-ray diffraction (WAXD) measurements. The unit cell of PMDA-TPE-Q is determined by ED and WAXD to be a two-chain orthorhombic lattice with dimensions of a =0.823 nm, b =0.558 nm and c =2.209 nm. The observed crystal morphology from TEM is primarily lamellar with extended chain conformations. The thickness of the lamellar crystals varies with the polymerization conditions. Possible thermal effects on PMDA-TPE-Q have been studied by annealing the crystals at different temperatures. The results indicate that with increasing annealing temperature, the lateral dimensions of the lattice expand, primarily along the a-axis. The c-axis shrinks slightly with increasing the reflection intensities of (0 0/) planes when l = odd. This is confirmed by using order correlation changes along these directions measured by WAXD experiments. Crystal defects are found in dark field TEM observations

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Modified silicone rubber intended mainly for biomedical applications was obtained by in situ polymerization. The process involved swelling of the rubber with a mixture of solvent and monomers, polymerization, and finally evaporating the solvent under reduced pressure. The polymerization system selected was the stepwise hydrogen-transfer polyaddition of 1,4-piperazinediyl diethanethiol to ethylene glycol dimethacrylate, leading to a poly(ester thioether amine). The modified silicone was physically and mechanically characterized by several analytical techniques (Fourier-transform infra-red spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, dynamic contact angle and scanning electron microscopy), and the results obtained were compared with those relative to both the linear guest polymer and the unmodified rubber

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Certain structurally different polyisophthalamides containing pendent phthalimide groups were synthesized from 5-(phthalimide)isophthalic acid and aromatic diamines by the phosphorylation method. Their chemical, physical and thermal properties were determined and compared with those of the corresponding unsubstituted polyisophthalamides. The polymers were characterized by FTi.r., 1H n.m.r., thermogravimetric analysis, isothermal gravimetric analysis and inherent viscosity measurements. The modified polyisophthalamides showed enhanced solubilities in some solvents, such as 1,4-dioxane, m-cresol and trichloroacetic acid, in comparison to the unmodified analogues. In addition, the incorporation of the pendent phthalimide groups in the polyisophthalamide backbone increased remarkably the thermal stability of the polymer. The modified polyamides were stable up to 317-351°C in N2 or air and afforded anaerobic char yields of 55-66% at 800°C. Water absorption and X-ray measurements were also performed.

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Differential scanning calorimetry (d.s.c.) has been applied to characterize the miscibility of blends of a high T~ polyester, synthesized by condensation polymerization from 4,4'-(2-norbornylidene)diphenol and terephthalic acid/azelaic acid in a 60/40 molar ratio (this polyester will be denoted T(40)C-GJ), with bisphenol-A polycarbonate. The theoretical development to determine the Flory-Huggins interaction parameter (Z) of phase-separated polymer blends from their phase compositions is described. The glass transition temperature (Tg) of a miscible blend of T(40)C-GJ and a low molecular weight polycarbonate (Lexan) can be accurately described by both the Gordon-Taylor equation with k = 1.7 and the Couchman equation. These equations were used to determine the phase compositions of a phase-separated blend of T(40)C-GJ and a high molecular weight polycarbonate (Makrolon) from the Tg data. The Z values for these blends are in the range (8.4-9.9) x 10-3 and are slightly composition dependent. The miscibility of these blends can be quantitatively understood in terms of the X results from the d.s.c, measurements. The morphology observed by transmission electron microscopy for 50/50wt% blends of T(40)C-GJ and polycarbonate is consistent with the d.s.c, results.

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In electron-beam lithography, charging on the photoresist usually causes image distortion and placement error. To dissipate the charge, a conductive polymeric layer can be introduced either over or under the photoresist coating. In this paper, we will discuss the approach of using toluene and xylene-soluble poly(alkylthiophene) in combination with a photoacid generator as a discharge underlayer or interlayer beneath the photoresist to dissipate the accumulated charge during electron-beam exposure. We will also discuss the use of water-soluble acid or ammonium salt forms of polyl-3-(ethanesulfonate)thiophene] as the discharge top layer. During the resist image developing process, the top layer will be removed by aqueous base. Therefore, it is advantageous to use a discharge top layer owing to its simplicity. In this study, the salt and acid forms ofpoly[3-(ethanesulfonate)thiophene] were synthesized through chemical polymerization of the corresponding methanesulfonate ester. They exhibit the same properties as those of electrochemically synthesized polymer reported in the literature.

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