Synthesizing isoprene and methyl methacrylate triblock copolymers using peculiar living free radical polymerization with difunctional t-BuLi initiator

Abstract

A peculiar living free radical polymerization process for the preparation of poly(methyl methacrylate)-b-poly(isoprene)-b-poly(methyl methacrylate) (MIM) triblock copolymers using anionic living polymerization (ALP) combined with mercaptan/ε-caprolactam living polymerization (MLP) is developed. Polyisoprene (PI) is first synthesized by ALP using a difunctional t-BuLi initiator with tetrahydrofuran as the polar regulator. Then, a PI with a controlled isomeric unit is end-group functionalized with mercaptans to form an α,ω-bismercaptan-functionalized PI precursor polymer, which is characterized by MALDI-TOF mass spectrometry, after which a thiolamide-structured MIM is formed by MLP at 90 °C. Living characteristics are confirmed by GPC, which reveals that MIMs with Mn values of 42.1–81.3 kDa are prepared. The polymers are also characterized by NMR spectroscopy, and gradient polymer elution chromatography. In addition, two Tgs are observed for each polymer by DSC: between −57.2 and 10.4 °C, and 99.4 and 119.8 °C, which correspond to the separated microphases within each MIM.