Influence of the stereoregularity on the crystallization of the trans planar mesomorphic form of syndiotactic polypropylene

The crystallization of the trans-planar mesomorphic form of syndiotactic po lypropylene by quenching the melt at 0 degreesC is investigated as a functi on of the stereoregularity of the samples. The formation of the trans-plana r mesomorphic form at 0 degreesC is followed as a function of the permanenc e times at 0 degreesC by X-ray diffraction and FTIR spectroscopy. Samples k ept at 0 degreesC for short time rapidly crystallize into the helical form I at room temperature, whereas longer permanence times at 0 degreesC increa se the stability of the trans-planar mesomorphic phase which remains stable and inhibits the normal crystallization of the sample into the helical for m at room temperature. The stereoregularity of the polymer sample strongly influences the rate of formation of the mesomorphic form at 0 degreesC, Hig her the syndiotacticity, easier the formation of trans-planar mesomorphic f orm. Very short permanence times (few hours) at 0 degreesC are enough to fo rm and stabilize the mesomorphic form for highly syndiotactic samples, wher eas for stereo-irregular samples the amount of mesomorphic form observed wh en the sample is removed from the 0 degreesC bath and heated to room temper ature, remains always very low, even for very long permanence times (months ) at 0 degreesC and the crystallization into the normal helical form is not inhibited. (C) 2001 Elsevier Science Ltd. All rights reserved.