Impact of Precision Sequence on Microphase Separation of Graft Copolymers Bearing Immiscible Polymer Chains: Alternating versus Random Architectures

Graft alternating copolymers bearing polystyrene (PS) and polylactide (PLA) graft chains were precisely synthesized via selective cyclopolymerization of a pendant-transformable divinyl monomer followed by postpolymerization modification for chain incorporation via a grafting-to and grafting-from approach. The number-averaged polymerization degrees (DPn’s) of both the backbone and graft chains were precisely controlled. Importantly, the corresponding graft “random” copolymers as well as the PS-PLA block copolymers of identical DPn’s were also synthesized to enable direct comparison of their microphase separation behaviors. The graft alternating copolymers with a volume fraction of approximately 5:5 exhibited periodic scattering peaks attributable to a lamellar morphology in the SAXS profile. These peaks of the graft alternating copolymers were significantly sharper than those observed for the random and block architectures, and the domain spacing was smaller than those observed for the random architectures. This trend became even more pronounced at a volume fraction of approximately 7:3, where a cylindrical morphology was formed.