Synthesis of block copolymers by radical polymerization in presence of Si-based chain transfer agent

Abstract

A new versatile method of block-copolymer synthesis is based on classic radical polymerization with a multifunctional Si-organic chain transfer agent. This method provides a wider choice of monomers and is universal for obtaining block copolymers with wide molecular weight distribution. The synthesis can be conducted as fast as in several hours at moderate temperatures (approx. 70 °C). The process does not involve sulfur-based or metalorganic compounds. This can be important for bio- or chemical compatibility in various applications. To implement the method, amphiphilic di-block copolymers based on styrene (hydrophobic) monomer and either 4-vinylpyridine or N,N-dimethylaminoethyl methacrylate monomers (hydrophilic) were synthesized by means of classic radical polymerization in the presence of either trichlorosilane or dimethylchlorosilane as a chain transfer agent. The molecular mass distributions of both the intermediate homopolymers and the final block copolymers were measured. By changing the concentrations of the initiator and Si–Cl-based agent, the resulting polymer molecular weight can be controlled. Maximal molecular weight of 4.4 × 10⁵ was obtained in the experiment. Depending on the nature of the solvent, micelle-like structures and micro-phase separation were observed by scanning electron microscopy and atomic force microscopy in the films of the synthesized block copolymers.