Polymerization of vinyl chloride catalyzed by a titanium complex with an anionic oxygen tripod ligand

Poly(vinyl chloride) (PVC) was prepared using a titanium complex with an anionic oxygen tripod ligand [CpCo{P(O)(OEt)2}3]− (LOEt-) as catalyst and methyl aluminoxane (MAO) as cocatalyst. The polymerization behavior was compared with that of pentamethyl cyclopentadienyl titanium trichloride (Me5CpTiCl3). It is observed that LOEtTiCl3 can polymerize vinyl chloride with activity comparable to that of Me5CpTiCl3. The PVC samples prepared with LOEtTiCl3/MAO exhibit bimodal molecular weight distribution and the fraction of high molecular weight peak decreases with polymerization temperature. The microstructure and thermal decomposition of the PVC obtained were studied. Five types of structural defect were detected by 1H-NMR. Only saturated structural defects are found at low polymerization temperature, but at high polymerization temperature unsaturated structural defects, possibly resulting from dehydrochlorination of the saturated structural defects, appear as well. No head-to-head structural defect is observed. 13C-NMR shows that the PVC prepared by LOEtTiCl3 has an atactic stereostructure. Compared with the PVC from radical polymerization and anionic polymerization, the PVC samples prepared with LOEtTiCl3 show improved thermal stability.