Effect of Polymerization Initiator on Early Colour of Poly(Vinyl Chloride)

The development of early color and the dehydrochlorination rate were compared for poly(vinyl chloride) samples obtained by suspension polymerization using two different initiators, dicetylperoxydicarbonate and butylperoxyneodecanoate. The degree of discoloration was measured on pressed plates and expressed as yellowness index (YI), the polyene sequence distribution was monitored by UV/Vis-spectroscopy, and the degration rate was determined by measuring evolved HCl conductometrically. The PVC sample initiated by dicetylperoxydicarbonate exhibited more extensive early color and a higher dehydrochlorination rate as compared to the sample obtained with butylperoxyneodecanoate as initiator. The UV/Vis-spectra showed that the early color originates from polyene sequences. After extraction of the PVC resins with heptane: acetone (85:15) the early color turned out to be almost the same for the two samples. From 13C-NMR measurements it was found that the extract of the sample polymerized with dicetylperoxydicarbonate contains unreacted initiator. We suggest that the radicals formed when the remaining initiator decomposes initiate dehydrochlorination. Our results also indicate that radicals from dicetylperoxydicarbonate may cause long-chain branches during polymerization. The radicals formed from butylperoxyneodecanoate, on the other hand, do not seem to react with the polymer molecules.