Synthesis and characterization of novel dumbbell shaped copolymers poly(ethylene oxide)x-b-polystyrene-b-poly(ethylene oxide)x with tunable side arms by combination of efficient thiol-ene addition reaction with living polymerization mechanism

A series of novel dumbbell shaped copolymers poly(ethylene oxide)x-b-polystyrene-b-poly(ethylene oxide)x (PEOx-b-PS-b-PEOx, x = 1, 2, 3) composed of different numbers of hydrophilic PEO and hydrophobic PS segments were prepared by combination of living anionic polymerization (LAP) and ring opening polymerization (ROP) mechanisms, and the efficient thiol-ene addition reaction was also adopted. First, the functional polystyrene with one hydroxyl group and one allyl group at each end (AGE-PS-AGE) was synthesized by the LAP of St monomers followed by the capping reaction with allyl glycidyl ether (AGE). Subsequently, by thiol-ene addition reaction with 2-mercaptoethanol (ME) and 3-mercapto-1,2-propanediol (MP), one allyl group on the AGE-PS-AGE was transformed into one or two hydroxyl groups to synthesize the functional polystyrene with two hydroxyl groups at both ends (ME-PS-ME) or three hydroxyl groups at both ends (MP-PS-MP). Then, the copolymers PEOx-b-PS-b-PEOx were achieved by ROP of EO monomers using AGE-PS-AGE, ME-PS-ME and MP-PS-MP as macro-initiators. The target copolymers and their precursors were fully characterized by GPC, 1H NMR and 13C NMR measurements. The crystallization behavior of copolymers with different topologies and compositions was investigated by DSC, XRD and POM instruments, and the results showed that the topologies (compared to the compositions) tend to make the primary contribution to the crystallization behavior.