The synthesis of ABA block copolymers by means of ‘living’/controlled radical polymerization using hydroxyl-terminated oligomers as precursor

ABA block copolymers with well-defined structure were synthesized by the combination of the end-group transformation of prefabricated hydroxyl-terminated oligomers and atom transfer radical polymerization (ATRP). The hydroxyl-terminated oligomers, such as polyether diol, polyester diol and hydroxyl-terminated polybutadiene, were reacted with chloroacetyl chloride to form α,ω–bichloroacetyl oligomers (P–Cl). After the P–Cl was characterized by IR and chlorine content analysis, it was used as macro-intiator in the bulk polymerization of styrene in the presence of CuCl/bpy, which led to a series of ABA block copolymers. The formation of block copolymers was proved by 1H-NMR. The molecular weight of the block copolymers could be designed up to 105 according to the consumed monomer and the amount of feeding P–Cl. The kinetic study showed that the relationship between the logarithm of monomer concentration and the reaction time was linear, and an induction period was observed. It suggested that the initiation is slow and the concentration of active species was constant after initiation. Moreover, the experimental molecular weight increased linearly with the monomer conversion; simultaneously, the molecular weight distribution (MWD) of the block copolymer was close to the MWD of the macro-initiator (P–Cl). The results demonstrate the polymerization is a ‘living’/controlled process.