1994 рік

A new 4-ethynyl-substituted monomer, bis(4-ethynyl phenyl) 1,4,5,8-naphthalimide (EPNI) was synthesized and characterized. EPNI is a crystalline material which, when thermally polymerized under N 2 in the solid state, yielded a highly crosslinked resin. The progress of polymerization was followed by Fourier transform i.r. spectroscopy, differential scanning calorimetry and wide-angle X-ray diffraction. It was found that EPNI reacted completely thermally to yield an extended polyene structure. Polymer plates were made by solid-state polymerization of EPNI under 4.8 MPa for 1.5 h at 300°C. Because EPNI is ordered and polymerized in the crystalline state, it showed zero polymerization shrinkage (EPNI had the same density as the well consolidated polymer, 1.40gml-1). EPNI polymerized to high conversion in spite of its very rigid matrix, probably because of the localization of its polymerizable ethynyl groups. A plate of polymeric EPNI (PEPNI) with 10% voids had a storage modulus of 2.2GPa at room temperature, a glass transition temperature, T~, of 309°C and a linear coefficient of thermal expansion of 4.28 x 10- 5 K- 1. PEPNI has excellent thermal and thermooxidative stabilities since it retained over 83% of its initial weight after 105 h at 427°C in air

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Mechanical damping spectra have been measured between the fl and ~ transitions on specimens of polycarbonate deformed by traction or cold pressing in the pre-yield region and left thereafter to recover at room temperature for given periods of time. The deformation is always applied to samples previously aged for 2 years at room temperature after quenching from above the glass transition temperature. The deageing effect induced by small applied deformation is apparent on the damping spectra by the enhancement of two peaks: the :t' peak precursor of the ~ transition and the :t" peak partially merging with the :t' peak and at a lower temperature with the fl loss process. Several experimental parameters such as the mode, amount of deformation and the recovery time after release of the stress are chosen to investigate the enhancement conditions and the relaxation behaviours of the :t' and :t" loss processes. The location of the :~' peak is well understood in terms of a classical formalism together with the hypothesis that a change in the structural temperature of the sample occurs as a result of the small deformation. At present, no interpretation of the ~" loss process has been proposed, but it is obvious from the present data that the existence of a strain-induced ~t" loss process contributes significantly to the deageing and further physical ageing effects probed in the vicinity of room temperature by mechanical damping measurements.

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Using the techniques of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS), the morphology of polyimide thin films thermally imidized from several photosensitive polyimide (PSPI) precursors has been investigated and compared with that of the thin films prepared from the corresponding poly(amic acid) precursors: poly(4,4'-oxydiphenylene pyromellitimide) (PMDA-ODA), poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(4,4'-oxydiphenylene benzophenonetetracarboximide) (BTDA-ODA). The WAXD results indicate that regardless of the precursor origin, the BTDA-ODA polyimide is amorphous, whereas the other polyimides exhibit a molecular order. For both the PMDA-ODA and the BPDA-PDA, the molecular order is relatively higher in the films prepared from the PSPI precursors than in those from the corresponding poly(amic acid)s, indicating that during thermal imidization, the photosensitive groups play an important role to improve the mobility of the polymer chains, which may be critically needed to make better molecular packing, in spite of their bulkiness having the potential to hinder the molecular packing. In Lorentz-corrected SAXS analyses, a long period (130-156/~ mean periodicity) was observed for all the polyimides except the PMDA-ODA. In particular, the microstructure in the BPDA-PDA could be described by an extended chain-based two-phase (ordered and less ordered phase) model with diffuse boundaries because of its high chain rigidity. In addition, the Guinier SAXS analyses indicate the presence of voids in all the polyimide films, regardless of the precursor origin. The size of voids was 251-349/~ in radius, depending upon the type of polyimide

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Poly(4-mercaptobenzoyl) (PMB) whiskers were obtained from S-acetyl-4-mercaptobenzoic acid by hightemperature solution polymerization. The whisker prepared in liquid paraffin at a concentration of 1.0% at 300°C has an almost uniform width of 0.34).5/~m and a length of 5-8 #m. These whiskers show radial growth from the centre. The optimal conditions for preparing them are by using liquid paraffin as a solvent and polymerization temperatures of 260-300°C. Electron diffraction reveals that the PMB whiskers show single crystal nature and the polymer chains are aligned along the long axis of the whisker. D.s.c. analysis of the PMB whiskers shows the presence of the reversible solid-solid transition as already reported by Kricheldorf et al. The transition temperature and enthalpy of the PMB whiskers are higher and larger than those of PMB crystals with other morphologies. Another endotherm is found at ~420°C, but only when measurement is carried out using a faster heating rate of 100°Cmin - 1. This is deduced to be a solid-liquid crystal transition from the observation of the nematic domain structure in a quenched specimen using an optical microscope. Finally, the formation mechanism of the PMB whiskers is discussed from the polymerization time dependencies of the length, the degree of polymerization and the yield.

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The criteria for internal cavitation of rubber particles have been evaluated. It is shown that internal rubber cavitation can be considered as an energy balance between the strain energy relieved by cavitation and the surface energy associated with the generation of a new surface. The model predicts that there exists a critical particle size for cavitation. Very small particles (100-200nm) are not able to cavitate. This critical-particle-size concept explains the decrease in toughening efficiency in different rubber-modified systems involving very small particles.

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The influence of crystalline morphology on the dynamic mechanical relaxation properties of poly(ether ether ketone) (PEEK) has been investigated for the glass-rubber (~) and sub-glass (fl) relaxations; a series of both cold-crystallized and melt-crystallized specimens were examined. The presence of crystailinity had a marked influence on the glass-rubber relaxation characteristics of PEEK owing to the relative constraint imposed on the amorphous-phase motions by the crystallites. Above Tg, a progressive relaxation of rigid amorphous-phase material was evident, as well as a small incremental decrease in modulus reflecting the onset of the low-temperature melting component. The sub-glass mechanical relaxation was bimodal, comprising a lower-temperature (fix) component, which originated in the bulk of the amorphous material, and a higher-temperature (f12) component, which originated in organized regions of the amorphous phase (i.e. at the crystal-amorphous interphase). Both the dynamic mechanical and corresponding dielectric results displayed morphological sensitivity in the fl relaxation region, with the mechanical results encompassing motions of a more complex (i.e. cooperative) nature.

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Free-radical cyclopolymerization of six ether dimers of ~-(hydroxymethyl)acrylic acid and its alkyl esters was kinetically investigated to evaluate the factors that control the cyclopolymerizability. A strong effect of ester substituent on cyclopolymerizability was observed and cyclization efficiency at 80°C increased in the following order: methyl, ethyl, isobornyl, t-butyl and adamantyl esters. That is, cyclization efficiency is found to be affected by the number of carbons linked to the central ester carbon (which defines the 'effective' bulkiness) rather than by the 'apparent' bulkiness, which encompasses the total mass or size of the whole substituent. Kinetic considerations of the temperature dependence of cyclization efficiency indicated that a strong contribution of the steric factor for bulky substituents (which inhibits intermolecular monomer addition) resulted in high cyclization efficiency despite a disadvantage in activation energy for cyclization. A linear relationship between the difference of activation energies (E?-Ei) and the logarithm of the ratio of collision frequency factors On(Ac/Ai)) observed for various esters led to recognition of an iso-efficiency point at which all esters show the same cyclization efficiency (k?/ki = 2.0 moll-1 at -45°C). This phenomenon is caused by the fact that both parameters change in proportion to the bulkiness of the ester substituent. The ether dimer of 0t-(hydroxymethyl)acrylic acid showed unexpectedly high cyclization efficiency (intermediate between secondary and tertiary esters) despite having the lowest substituent bulkiness. The kinetic parameters obtained showed some deviation from the linearity observed for the ester derivatives. The large A?/Ai obtained was attributed to the capability of hydrogen-bond formation between acid groups, which causes a favourable conformation for cyclization. Microstructures of the cyclopolymers were investigated by observation of carbonyl carbon peaks in the 13C nuclear magnetic resonance spectra. The peaks observed were assigned to four microstructures based on the combination of trans/cis configuration of the tetrahydropyran ring and racemic/meso configuration between the rings. Both the trans and racemic ratios increased with the bulkiness of the ester substituent. The values of Eci,-E, .... and At,°,~/Aci, for the t-butyl ester cyclopolymer indicated that trans formation is slightly favourable in both activation energy and steric factor, a result similar to that reported for the racemic/meso ratio in radical polymerization of some alkyl methacrylates. On the other hand, racemic formation between rings was suggested to be sterically unfavourable by the A ..... iJAm,,o ratio = 0.55. The glass transition temperatures for the cyclopolymers were found to be much higher than for the corresponding acrylates or methacrylates, and the thermal stabilities of some of the derivatives, especially the adamantyl compound, were also high

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Real-time stress-whitening experiments were performed on initially transparent poly(vinyl chloride) (PVC)/ methyl methacrylate-butadiene-styrene graft copolymer (MBS) blends containing very small MBS rubber particles. The chemical composition of the different MBS rubber particles was held constant and it was found that the onset of internal rubber cavitation in the blends during a tensile test depends only on the size of the rubber particles. The real-time, stress-whitening experiments indicate that the resistance against cavitation increases with decreasing rubber particle size. Small particles are unable to cavitate. This is further confirmed independently on the basis of transmission electron microscopy observations and density measurements on the deformed samples.

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Dielectric relaxation properties of amorphous poly(propylene oxide)s with nominal molecular weights of 1000 and 2000 have been studied as a function of temperature at gigahertz frequencies using a time-domain reflectometry method. Two relaxation processes were observed in the dielectric spectra. The dielectric relaxation parameters were quantitatively estimated by the Havriliak-Negami equation. At the lower frequency side of the main dispersion, a normal-mode relaxation was seen and the relaxation times obtained from the spectra were found to be approximately one decade longer than the values calculated assuming the Rouse-Zimm theory. The hydrogen-bonded structures in the system are discussed. The relaxation strength is also discussed in terms of chain conformation. The relaxation times of the higher frequency process were found to be independent of the molecular weight. The shortest possible relaxation times estimated by the Vogel-Fucher-Tamman equation were in good agreement with those reported before.

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N-Antipyryl acrylamide monomer [2,3-dimethyl-l-phenyl-5-oxo-3-pyrazolin-4-ylacryloylamine) was synthesized by the reaction of 4-aminoantipyrine with either acryloyl chloride or acrylic acid in the presence of N,N'-dicyclohexyl carbodiimide as the dehydrating agent. Binary copolymerizations of this new monomer with methyl acrylate, ethyl acrylate, butyl acrylate and styrene were performed in dimethylformamide at 65°C using 1 mol% azobisisobutyronitrile as the initiator. The copolymer compositions were determined from the nitrogen analyses. Copolymerization parameters for each system were calculated by the Fineman-Ross and Kelen-Tiid6s methods.

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