Synthesis of phase-separated super-H-shaped triblock architectures: poly(l-lactide) grafted from telechelic polyisoprene

Abstract

In the field of carbanionic polymerization bifunctional initiators permit the synthesis of complex triblock copolymer structures. Using 1,3-bis(1-phenylethenyl)benzene (PEB), isoprene was polymerized in cyclohexane, yielding a high content of 1,4-PI units of 93%. Subsequently, 3 hydroxyl groups were introduced simultaneously both in α- and ω-position by means of end-functionalization of the living anionic di-lithiated polyisoprene (PI) chains with 1,2-isopropylidene glyceryl glycidyl ether (IGG) and subsequent acidic deprotection. The resulting hexa-hydroxy functional PI-macroinitiators were then used to initiate L-lactide (LLA) in a DBU-catalysed polymerisation, ultimately yielding super-H-shaped (PLLA)₃-b-PI-b-(PLLA)₃ triblock structures with molecular weights of 23–49 kg mol⁻¹. Narrow molecular weight distributions with dispersity in the range of 1.19–1.35 were obtained, and thermal characterisation revealed two distinct glass transition temperatures (T_g), indicating phase separation. The PI-domains feature a low T_g between −55 °C and −59 °C, whereas the PLLA-domains exhibit a higher T_g of 41 °C to 49 °C. Further, the block copolymers were analyzed by TEM and SAXS, confirming clearly phase-separated cylindrical and lamellar morphologies. The reported bifunctional approach combining carbanionic polymerization with the ROP of lactones represents an efficient and general synthesis pathway for a large variety of complex polymer architectures.