Self-Assembly of Poly(styrene-block-acrylated epoxidized soybean oil) Star-Brush-Like Block Copolymers

Here we report dynamic and thermodynamic aspects of the self-assembly in a series of branched-chain soybean-oil-derived styrenic block copolymers produced via reversible addition–fragmentation chain transfer (RAFT) polymerization. These biobased materials display unusual domain expansion which has not been seen in conventional petroleum-based block copolymers. The chain architecture of poly­(styrene-b-acrylated epoxidized soybean oil) (PS–PAESO) block copolymers varies from star-like to star-brush-like owing to the bulk and multifunctionality of the PAESO repeat unit. The self-assembly behavior is evaluated through a combination of (ultra) small-angle X-ray scattering (SAXS), transmission electron microscopy, and dynamic shear rheology. Microphase separation in PS–PAESO is kinetically limited due to sluggish chain dynamics that cannot be thermally accelerated due to interference from cross-linking reactions. Selective hydrogenation of the residual PAESO vinyl groups retards but does not eliminate cross-linking reactions, indicating that transesterification is also at play. SAXS experiments show that the PS–PAESO domain size scales nearly linearly with the number of statistical segments, with structures as large as d = 155 nm observed. We believe that domain dilation is related to bulky aliphatic side chains in PAESO domains that extend the primary chain backbone to produce a brush-like conformation. The understanding of the structure–property relationships of these new biobased block copolymers gives insights on the design of novel polymer architectures benefiting new applications.