Synthesis of poly(β-pinene)-b-polytetrahydrofuran from β-pinene-based macroinitiator

The living cationic polymerization of β-pinene was carried out with 1-phenylethyl chloride/Ti(OiPr)4/TiCl4 (Ti(OiPr)4/TiCl4 mole ratio 1:3) in the presence of nBu4NCl in CH2Cl2 at −40°C. Styrene was added to cap the living poly(β-pinene) just before β-pinene had been consumed almost completely (conversion ∼98%) and then the reaction was stopped at low conversion of styrene to give β-pinene macroinitiator with benzyl chloride terminal. 1H NMR analysis of the obtained polymer showed that one macroinitiator possessed almost one benzyl chloride end group. The macroinitiator in conjunction with silver salt, AgClO4 or AgSbF6, could readily initiate the ring-opening polymerization of THF in the presence of small amounts of propylene oxide. The macroinitiator/AgSbF6 system gave an almost pure block copolymer of β-pinene/THF (weight content: 45% for β-pinene segments and 55% for THF segments) with a relatively narrow molecular weight distribution. In contrast, homopolyTHF and unblocked macroinitiator formed along with the block copolymer with the macroinitiator/AgClO4 system owing to the competing side reactions.