Living carbocationic polymerization

Living carbocationic polymerization of styrene (St) has been achieved by the use of the 1(p-methylphenyl)ethyl acetate (pMePhEtOAc)·BCl3 complex in CH3Cl solvent at −30°C using both the IMA and AMI techniques. The living nature of the polymerizations has been demonstrated by linear Mn versus WPSt (weight of polystyrene) plots passing through the origin and horizontal N (moles of PSt) versus WPSt plots starting at N=Io (the number of moles of initiator used). The molecular weight distribution MWD of the PSts is broad (Mw/Mn=~5–6) due to slow initiation and/or slow exchange between dormant and active species relative to propagation. The structure of the ester initiator strongly affects the rate and outcome of living polymerization, e.g., cumyl acetate (CumOAc), cumyl propionate (CumOPr), and 2,4,6-trimethylphenylethyl acetate (TMePhEtOAc), do not lead to truly living St polymerizations. The findings with the latter esters is explained in terms of a two path process comprising a slow living polymerization and a faster conventional cationic chain reaction. With phenylethyl acetate (PhEtOAc) living polymerization is achieved, however, initiation (cation generation) is slow. Forced termination by pyridine or methanol, or heating to ambient temperature leads to-CH2CH(C6H5)Cl end groups.