Polymer, Vol.43, No.6, 1857-1865, 2002
Measurement of the C-13 spin-lattice relaxation time of the non-crystalline regions of semicrystalline polymers by a cp MAS-based method
The non-crystalline C-13 spin-lattice relaxation times of atactic and isotactic polypropylene and those of an ethylene-l-octene copolymer of low crystallinity have been measured by classical inversion and saturation recovery methods as well as by a cp MAS-based pulse sequence. The latter is a saturation recovery-type sequence that involves cross-polarization. It samples preferentially the soft non-crystalline regions of semicrystalline polymers. The method is found to be useful in determining T-1C of the amorphous regions of semicrystalline iPP at room temperature. It is found that the atactic PP molecule and the non-crystalline iPP regions have the same average segmental relaxation rate. The T-1C of some of the carbons investigated was