The degree of crystallinity of a set of monoclinic (alpha) isotactic poly(p
ropylenes), prepared by a metallocene-type catalyst, were determined at roo
m temperature. Three different methods were used: density, enthalpy of fusi
on, and wide-angle X-ray scattering, and the results compared. The relation
between the heat effusion and the specific volume of these poly(propylenes
) was found to be nonlinear, thus precluding any linear extrapolation to ob
tain the heat of fusion of the pure crystal (Delta H-u). The value of Delta
H-u obtained from depression of the melting temperature by diluents is use
d. Based on the unit cell density of monoclinic crystals formed from a low
defected fraction, the density obtained crystallinity levels were found to
be between 0.15-0.25 higher than those calculated from the heat of fusion.
This relatively large difference holds for the isothermally crystallized an
d quenched isotactic poly(propylenes), and reflects the contribution of the
interphase to the density determined crystallinity, which does not contrib
ute to the heat of fusion. Paralleling results found in other systems, the
crystallinity levels obtained from wide-angle X-ray scattering agree with t
hose obtained from density, indicating a significant contribution of the pa
rtially ordered phase to the total diffraction. Emphasis is given on the ne
ed to account for the large differences in the crystallinities of poly(prop
ylene) measured by different techniques when evaluating the dependence of p
roperties on this quantity. (C) 1999 John Wiley & Sons, Inc.