RAFT dispersion polymerization of benzyl methacrylate in non-polar media using hydrogenated polybutadiene as a steric stabilizer block

A monohydroxy-capped hydrogenated polybutadiene (PhBD) is converted into a macromolecular chain transfer agent via esterification using a carboxylic acid-functionalized trithiocarbonate. H-1 NMR and UV spectroscopy studies indicated a mean degree of esterification of at least 95%. The resulting precursor is used for the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) in n-dodecane at 90 degrees C. In principle, systematic variation of the mean degree of polymerization (DP) of the insoluble structure-directing PBzMA block should enable the formation of PhBD-PBzMA spheres, worms or vesicles via polymerization-induced self-assembly (PISA). In practice, only kinetically-trapped spheres are obtained when targeting DPs of up to 300 at 25% w/w solids. However, increasing the copolymer concentration up to 40% or 45% w/w provides access to well-defined worms or vesicles, respectively. Gel permeation chromatography and H-1 NMR spectroscopy studies confirmed relatively narrow molecular weight distributions (M-w/M-n < 1.20) and high final BzMA conversions (>= 99%), respectively. These diblock copolymer nano-objects were characterized in terms of their particle size and morphology using TEM and DLS and a phase diagram was constructed. According to rheology studies, the free-standing worm gels that are formed at ambient temperature have a critical gelation concentration of approximately 5.0% w/w.