Synthesis and characterization of poly[1,4-isoprene-b-(ethylene oxide)] and poly[ethylene-co-propylene-b-(ethylene oxide)] block copolymers

The synthesis of amphiphilic AB block copolymers, having 1,4-polydiene or corresponding hydrogenated aliphatic polyolefin blocks and poly(ethylene oxide) (PEO) blocks, is described. The materials are obtained in a two-step process. In the first step isoprene is polymerized anionically in a hydrocarbon solvent with sec-butyllithium or tert-butyllithium as initiator. The end-capping of the living polymer with ethylene oxide (EO) yields polyisoprene, which is functionalized with a hydroxyl end group (PI-OH). This product can be hydrogenated to the aliphatic polyolefin poly(ethylene-co-propylene) (PEP-OH). In the second step cumylpotassium is used to deprotonate the OH groups, leading to the macroinitiators PI-OK and PEP-OK. PI-PEG and PEP-PEO block copolymers are obtained by initiating the polymerization of EO with the macroinitiators in TKF. The characterization reveals narrow molecular weight distributions, absence of homopolymer in the block copolymers, and complete conversion of monomers in both polymerization steps. The materials form water soluble aggregates even at a PEO content of 41% and a total molecular weight of M(n) = 35400. In n-decane all block copolymers synthesized were soluble, the one with the smallest hydrophobic part having a PI content of 24% and a total molecular weight of M(n) = 17700.