Grain growth kinetics of a _nB _n star block copolymers in supercritical carbon dioxide

Using a series of A _nB _n miktoarm star block copolymers with different numbers of arms (n = 1, 2, 4, and 16), the effect of molecular architecture on the grain growth kinetics was investigated by annealing in supercritical carbon dioxide. Across this entire series of materials, all the A arms were polystyrene (PS) blocks from the same anionically synthesized batch, and all the B arms were polyisoprene (PI) blocks from the same anionically synthesized batch. Thus, all the star block copolymers employed in this study were composed of the same A and B arms linked together in symmetric numbers. The grain growth kinetics was monitored in real space by transmission electron microscopy (TEM), followed by subsequent micrograph image analysis. It was found that the molecular architecture influenced the grain growth kinetics of these A _nB _n star block copolymers significantly. The grain growth kinetics of these A _nB _n stars annealed in supercritical CO ₂ was compared to a previously completed grain growth study of the same materials under simple thermal annealing. It was found that the grain growth kinetics for the A _nB _n stars with n = 2, 4, and 16 were similar for both supercritical CO ₂ and thermal annealing. However, the grain growth kinetics of the diblock (A _nB _n with n = 1) was dramatically enhanced in supercritical CO ₂ relative to thermal annealing.