Enhancing the formation of the new trigonal polymorph in isotactic propene-1-pentene copolymers: Determination of the X-ray crystallinity

A metallocene copolymer of isotactic propene and 1-pentene was subjected to different crystallization conditions with 13 mol% of 1-pentene counits, aiming to enhance the formation of a new trigonal modification of iPP. Since it was not possible to obtain a diffractogram for the amorphous sample of cPPe13 at room temperature, the X-ray crystallinity was determined using the profile of the molten polymer, extrapolated to room temperature according to the resulting temperature coefficients. The X-ray diffraction results indicate a very interesting polymorphism in this copolymer; when crystallized from solution, amazingly high degrees of crystallinity — as high as 65% — are obtained, and this value is similar to those obtained for the iPP homopolymer. Further, the enthalpy of melting for a 100% crystalline sample of the trigonal modification was estimated from those crystallinities and the actual enthalpies of melting.