Living Cationic Isomerization Polymerization of β-Pinene. 1. Initiation with HCl−2-Chloroethyl Vinyl Ether Adduct/TiCl₃(OiPr) in Conjunction with nBu₄NCl

The first example of living cationic isomerization polymerization of β-pinene was achieved with an initiating system that consists of the HCl−2-chloroethyl vinyl ether adduct [1a; CH3CH(OCH2CH2Cl)Cl] and isopropoxytitanium trichloride [TiCl3(OiPr)] in the presence of tetra-n-butylammonium chloride (nBu4NCl) in CH2Cl2 at −40 and −78 °C. The number-average molecular weight of the polymers (M̄n ≤ 5 × 103) increased in direct proportion to monomer conversion, and the molecular weight distribution of the polymers was relatively narrow (M̄w/M̄n ∼ 1.3). The living nature of the polymerization was further demonstrated by monomer-addition experiments. A similar living polymerization was also feasible with the HCl−styrene adduct or 1-phenylethyl chloride [1b; CH3CH(Ph)Cl] in conjunction with TiCl3(OiPr) and nBu4NCl. 1H NMR analysis of the polymers from 1a showed that 1a serves as an initiator and generates poly(β-pinene) chains consisting of the 1-(2-chloroethoxy)ethyl head group, a tert-chloride tail group, and isomerized β-pinene repeat units with a cyclohexene ring.