Synthesis and characterization of styrene/butyl acrylate linear and star block copolymers via atom transfer radical polymerization

Well-defined styrene (S) and butyl acrylate (BA) linear and star-like block copolymers are synthesized via atom transfer radical polymerization (ATRP) using di- and trifunctional alkyl halide initiators employing the Cu/ PMDETA (N,N,N′N″,N″-pentamethyldiethylenetriamine) catalyst system. Initial addition of Cu^II deactivator and utilization of halogen exchange techniques suppresses the coupling of radicals and improves cross-propagation to a large extent, which results in better control over the polymerization. Two types of star-like PBA/PS block copolymers are prepared by using core-first techniques: a trifunctional PBA or PS macroinitiator extended with the other monomer. Block copolymers with a well-defined structure and low polydispersity (PDI=M̄_w/M̄_n) are obtained in both cases. A trifunctional PBA₃ macroinitiator with M̄_n = 136 000 g · mol^-1 and PDI= 1.15 is extended to (PBA-PS)₃ star-like block copolymer with M̄_n = 171 100 g · mol ^-1 and PDI = 1.15. A trifunctional PS₃ macroinitiator with M̄_n = 27 000 g · mor^-1 and PDI= 1.16 g-mol^-1 is extended to (PS-PBA)₃ with M̄_n = 91 500 g · mol ^-1 and PDI = 1.40. The individual star-like macromolecules as well as their aggregates are visualized by atomic force microscopy (AFM) where the PS and PBA adopt the globular and extended conformation, respectively. For the PBA core star block copolymers, PS segments tend to aggregate either intramolecularly or intermolecularly. PS core star block copolymers form aggregates with a PS core and emanating PBA chains. Most aggregates have 'n × 3' arms but minor amounts of 'defective' stars with 4,5,8, or 11 arms are also observed. The AFM analysis shows that PS core star block copolymers contain about 92% threearm block copolymers, and the efficiency of cross-propagation is 97.3%.