Crystallinity and microstructure of plasticized poly(vinyl chloride).: A 13C and 1H solid state NMR study

The combination of C-13 solution NMR and C-13 solid-state NMR (CP/MAS and MAS) is used to reveal the relative amount of rigid (crystalline) PVC in two PVC/DOP (50/50 wt % of poly(vinyl chloride)/di-2-ethylhexyl phthalate) samples with tacticities, or, of 0.52 and 0.575, respectively. For both samples the crystallinity decreases with increasing temperature, from about 30% at 90 degrees C to approximately 6% at 180 degrees C. By means of a careful spectral deconvolution of the C-13 solid-state NMR spectra, the relative amounts of different triad sequences in the crystallites of PVC were obtained. The relative fractions of rr and rm sequences, about 0.5 and 0.4 respectively, are found to be constant as a function of temperatures above 90 degrees C. On the basis of proton low resolution T-2 experiments the mean average amorphous chain length between crystals was estimated at 50 monomer units at 160-180 degrees C. All results can be well understood by assuming the existence of crystallites which on average consist of only a few syndiotactic sequences in the chain direction.