The low-polar polymerization of isobutylene (IB) in the presence of BCl3 was carried out in CH2Cl2 ([IB] = 7 mol/l) at -78, -20 and +20 degrees C in the presence of vinyl chloride/2-chloropropene (VC/2CP) copolymer, representing PVC resin enriched in structures with chlorine atoms bonded to the tertiary carbons. The polymerization products consist of mixtures of polyisobutylenes (PIE) and grafted VC/2CP-g-PIB copolymer. Attention was focused on evaluation of the extent of the grafting reaction. VC/2CP-g-PIB was analyzed by GPC, H-1-NMR and C-13-NMR spectroscopies and elemental analysis. The results obtained indicate that the rate of polymerization of IB decreases with increasing temperature but that the grafting efficiency increases. The experiments demonstrated that the VC/2CP copolymer induces strong grafting, compared with PVC, and that it might therefore be assumed that the C-Cl bonds with chlorine atoms bound to tertiary carbons directly initiate the polymerization of IB. The effect of the C-Cl bonds is discussed in terms of their catalytic and initiation activities.