INFLUENCE OF THE TACTICITY DEPENDENT MICROSTRUCTURE ON THE SPACE-CHARGE DISTRIBUTION OF POLYPROPYLENE - PART 1 - A FIRST TENTATIVE APPROACH

Space charge trapping has been studied by the thermal step (TS) method for four samples of polypropylene (PP) of different tacticities, prep ared by selective extractions from an additive-free commercial polymer with mixtures of a non-polar/polar pair of solvents of various compos itions. The experimental currents derived from the application of the TS method to the samples after submitting them to an electrical field are proved to depend both on the isotactic content and on the electrod e. In particular, the current intensity increases markedly as the isot actic content decreases, without diverging from non-bernoullian isotac ticity. Similarly, the space charge distribution obtained through the deconvolution of the measured current curves usually utilized in the T S method, exhibits a decrease of the whole space charge in the materia l, as the isotactic content increases. It is of the type obtained when heterocharges and homocharges accumulate in the anode and the cathode , respectively. The results are discussed on the basis of the tacticit y based molecular microstructure, as defined in earlier work, in parti cular the frequency of occurrence of isotactic mmr tetrads associated with isotactic sequences. In addition, they are the first indication t hat the space charge/tacticity-microstructure relationships found for poly(vinylchloride) in earlier work, apply to PP. (C) 1998 SCI.