The Degree of Crystallinity of Monoclinic Isotactic Poly(propylene)

J. R ISASI; L. MANDELKERN; M.J .GALANTE; R.G. ALAMO

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

JOHN WILEY & SONS INC

Lugar: New York; Año: 1999 vol. 37 p. 323 - 334

0887-6266

The degree of crystallinity of a set of monoclinic (alpha) isotactic poly(propylenes),prepared by a metallocene-type catalyst, were determined at room temperature.Three different methods were used: density, enthalpy of fusion, and wide-angleX-ray scattering, and the results compared. The relation between the heat of fusion andthe specific volume of these poly(propylenes) was found to be nonlinear, thus precludingany linear extrapolation to obtain the heat of fusion of the pure crystal (DHu). The valueof DHu obtained from depression of the melting temperature by diluents is used. Basedon the unit cell density of monoclinic crystals formed from a low defected fraction, thedensity obtained crystallinity levels were found to be between 0.l5?0.25 higher thanthose calculated from the heat of fusion. This relatively large difference holds for theisothermally crystallized and quenched isotactic poly(propylenes), and reflects thecontribution of the interphase to the density determined crystallinity, which does notcontribute to the heat of fusion. Paralleling results found in other systems, the crystallinitylevels obtained from wide-angle X-ray scattering agree with those obtainedfrom density, indicating a significant contribution of the partially ordered phase to thetotal diffraction. Emphasis is given on the need to account for the large differences inthe crystallinities of poly(propylene) measured by different techniques when evaluatingthe dependence of properties on this quantity.