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A high‐temperature radical scavenger, 2,2‐diphenyl‐l‐picryl hydrazyl (DPPH), has been used to study the reaction mechanisms of polyacrylonitrile (PAN) on thermal treatment. The effect of DPPH on the cyclization reaction of PAN in both air and nitrogen, investigated by differential scanning calorimetry (DSC), helped to verify the proposed reaction mechanisms, i.e., the free radical and the ionic ones. For PAN homopolymer, the peak temperature of the reaction exotherm shifted to higher temperatures and the heat of reaction was decreased with increasing DPPH concentration. For PAN copolymer with methylacrylate and itaconic acid, however, the effects of DPPH on DSC thermograms were insignificant. The effects of IPPH suggest that the reaction of the nitrile groups proceeds by free radicals for the homopolymer while by ions for the copolymer. The activation energies for the thermal reactions of PAN in both air and nitrogen were also estimated by the dynamic DSC method, and they proved to be highly dependent on reaction mechanism, environment of thermal treatment, and DPPH concentration.

Multiple melting characteristics of a highly isotactic polypropylene (iPP) were studied by means of differential scanning calorimetry (DSC). Double melting characteristics were observed on melting iPP crystallized isothermally at temperatures ranging from 110 to 140°C. iPP crystallized below and above 125°C exhibited different double melting characteristics from each other. For iPP crystallized below 125°C, the single melting peak split into two peaks during slow DSC heating scans without changing the total crystallinity in the polymer. On the other hand, the double melting endotherm of iPP crystallized above 125°C seemed to come from two preexisting crystal fractions having different Tm. There existed an optimum annealing temperature range where the five‐minute annealing of iPP raised Tm of the polymer significantly. The treatment also increased the crystallinity of iPP crystallized isothermally at 110°C by 12%.

A new class of thermotropic side-chain liquid crystalline polymers containing a poly(1,6heptadiyne) main chain was prepared by metathesis polymerization with transition-metal catalysts. It was found that the MoCU-based catalyst systems were very effective for the cyclopolymerization of presently investigated monomers. Resulting polymers exhibited good solubility in common organic solvents such as tetrahydrofuran (THF), chloroform, etc., and could be easily cast on glass plates to give black shiny thin films. The structure of the products was confirmed by IR, MS, UV-visible, and *H and 13C NMR. The numberaverage molecular weight (Af") values of the polymers were in the range of 4.9 X lO3-!.! X 106 relative to polystyrene standards by GPC. Thermal behavior, morphology, and electrical conductivity were investigated by using differential scanning calorimetry (DSC), croes-polarized optical microscopy, X-ray diffraction analysis, and an LCR meter. Both monomer and polymer displayed enantiotropic liquid crystallinity showing the reversible phase transitions. Room-temperature conductivities of the undoped and L-doped polymers were found to be about 10~u and 1CH-10"3 S/cm, respectively.

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