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

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 alpha- and omega-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 degrees C and -59 degrees C, whereas the PLLA-domains exhibit a higher T-g of 41 degrees C to 49 degrees 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.