Crystallinity of side-chain fatty acid containing block copolymers with polyisobutylene segment

Block copolymers of polyisobutylene (PIB) with side-chain fatty acid-containing polymethacrylate segment with varying n-alkyl side-chains were synthesized by the combination of living cationic and reversible addition-fragmentation chain transfer (RAFT) polymerizations. Hydroxyl-terminated PIB (PIB-OH) was converted into macro-chain transfer agent (PIB-CDP macro-CTA) and used during the RAFT polymerization of fatty ester methacrylate (FEMA) monomers to obtain the block copolymers. Block copolymers were characterized by 1H NMR spectroscopy, size exclusion chromatography (SEC), and thermogravimetric analysis (TGA). The block copolymers showed varied crystalline behaviour depending on the chain length of the fatty acids in the polymethacrylate segment, confirmed by differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), polarized optical microscopy (POM), and transmission electron microscopy (TEM). SAXS and POM analysis above the crystalline melting temperature (Tm) of the block copolymers showed crystalline to amorphous phase transformation, which upon cooling below their Tm regenerated crystalline morphology (lamella-like structure). Density functional theory (DFT) calculations were performed to support interlamellar distances determined from the SAXS study. Overall the modification in the orderliness of the lamellar orientation due to the amorphous PIB segment within the fatty acid-containing block copolymer leads to a new direction toward materials with modified physical properties.