Controlled polymerization of a cyclic diene prepared from the ring-closing metathesis of a naturally occurring monoterpene

(Chemical Equation Presented) The diene 3-methylenecyclopentene (2) was synthesized from the naturally occurring monoterpene myrcene (1) by ring-closing metathesis using Grubbs second generation catalyst. Radical, anionic, and cationic polymerizations of 2 were investigated. The anionic polymerization of 2 with sec-butyllithium (s-BuLi) in cyclohexane gave poly-2 in quantitative yield, with a narrow molecular weight distribution and predictable molecular weight based on the molar ratio of 2 and s-BuLi. Radical polymerization of 2 was also successful using AIBN as the initiator. Samples of poly-2 obtained from the anionic and radical polymerization of 2 possessed mixed regiochemistry (i.e., 4,3 and 1,4 addition). The cationic polymerization of 2 proceeded smoothly to afford regiopure 1,4-poly-2. For example, the i-BuOCH(Cl)Me/ ZnCl₂/Et₂O initiating system afforded 1,4-poly-2 with controlled molecular weight and narrow molecular weight distribution. Samples of 1,4-poly-2 were semicrystalline as determined by differential scanning calorimetry.