Synthesis of liquid crystalline-amorphous block copolymers by combination of CFRP and ATRP mechanisms

Block copolymers of liquid crystalline 6-(4-cyanobiphenyl-4′-oxy) hexyl acrylate (LC6) and styrene (St) were obtained by the combination of two different freeradical polymerization mechanisms namely conventional free-radical polymerization (CFRP) and atom transfer radical polymerization (ATRP). In the first part, thermosensitive azo alkyl halide, difunctional initiator (AI), was prepared and then used for CFRP of LC6 monomer. The obtained bromine-ended difunctional liquid crystalline polymers (PLC6) were used as initiators in ATRP of St, in bulk in conjunction with CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst. In the second part, AI was firstly polymerized by CFRP in the presence of St and then the obtained difunctional bromine ended polystyrenes (PSt) were used as initiators in ATRP of LC6 in diphenylether solvent in conjuction with CuBr/PMDETA. The spectral, thermal, and optical measurements confirmed a fully controlled living polymerization, which results in formation of ABA-type block copolymers with very narrow polydispersities. In both cases, blocks of the different chemical composition were segregated in the solid and melt phases. The mesophase transition temperatures of the liquid crystalline block were found to be very similar to those of the corresponding homopolymers.