Synthesis of well-defined block copolymers of n-hexyl isocyanate with isoprene by living anionic polymerization

Abstract

n-Hexyl isocyanate (HIC) was polymerized at different reaction temperatures and times, using alkali metal naphthalenide, via anionic polymerization in THF. To prevent the formation of trimers, the polymerization of HIC was also performed utilizing sodium tetraphenylborate (NaBPh 4) as a common ion salt. As the reaction temperature decreases, yield of the polymer increases due to stabilization of the active amidate anion at low temperature. In the absence of the additive, a quantitative yield was obtained at −98 °C. However, after most of the monomer was polymerized, further reaction led to trimerization. This was prevented in the presence of NaBPh 4 effectively and the living polymerization was performed successfully at −98 °C. The reaction rate retarded with increasing concentration of NaBPh 4, the optimum concentration of NaBPh 4 was 10 times the concentration of the initiator for the living polymerization of HIC. The living system led to the polymers of molecular weight (MW) as high as 50,000 g/mol. The observed MW was well in agreement with the calculated one. At the higher reaction temperature, −78 °C, the quantitative yield was obtained at 2 min of the reaction time, however the living character was not observed at longer reaction time. The study indicated that the amidate anion was stabilized using NaBPh 4 having bulky contact ion pair. The block copolymer of HIC with isoprene, poly(HIC- b-isoprene- b-HIC), was synthesized with help of the living character of polyisoprene and NaBPh 4. The morphology and composition of the block copolymers were investigated using TEM and 1H NMR, respectively.