On the preferential extraction of the more isotactic parts of PVC with acetone. A verification by ¹³C NMR analysis

Abstract

Acetone-soluble and -insoluble fractions were obtained from two different PVC samples: a polymer prepared in our laboratory at 60 "C using 2,2 '-azoisobutyronitrile (AIBN) as initiator (sample A) and a commercial polymer prepared at 70 "C (sample B). The content of isotactic, syndiotactic and heterotactic triads was accurately measured by high resolution 13C NMR. From the obtained data it follows that the isotactic triads accumulate preferably in the soluble fraction, the amount of which depends on the type of polymer. In agreement with earlier results, the soluble fraction is about 40% less stable than the insoluble fraction. The reasons for this behaviour are discussed in the light of the higher content of both isotactic triads and some defect structures, as found in the low molecular weight soluble extracts of PVC.

Experimental and Theoretical Evaluation of the Reactions Leading to Formation of Internal Double Bonds in Suspension PVC

“…In Figure 3, the lower content of syndiotactic triads and higher content of isotactic triads in low molecular weight extracts of the 87.2 and 96.4% conversion polymers can be clearly seen. The higher content of isotactic triads in low molecular weight extracts is not an artifact of the isolation procedure, 31 as the same preference for isotactic triads was also seen in ether extracts and in some low molecular weight material obtained by fractionation. The differences in the sequence distribution of the low molecular weight part and complete PVC (samples of conversion above 87%) indicate that some portion of the syndiotactic triads is destroyed at the time when these short chains are formed.…”