Synthesis and characterization of poly(isobutylene-b-pivalolactone) diblock and poly(pivalolactone-b-isobutylene-b-pivalolactone) triblock copolymers

The synthesis of poly(isobutylene-b-pivalolactone) block copolymers comprised of amorphous rubbery/crystalline block segments was accomplished by site transformation from living cationic polymerization of isobutylene (IB) to anionic ring-opening polymerization (AROP) of pivalolactone (PVL). First, polyisobutylene (PIB) with omega-carboxylate potassium salt was prepared by capping living PIB with 1,1-diphenylethylene followed by quenching with 1-methoxy-1-trimethylsiloxypropene and hydrolysis of omega-methoxycarbonyl end groups. The resulting PIB omega-carboxylate potassium salt was successfully used as a macroinitiator for the AROP of PVL in conjunction with 18-crown-6 in tetrahydrofuran, giving poly(IB-b-PVL) copolymers. Furthermore, the same methodology was applied toward poly(PVL-b-IB-b-PVL) copolymers using PIB alpha,omega-carboxylate potassium salt as a difunctional macroinitiator. Characterization of the block copolymers by high-temperature GPC, H-1 and C-13 NMR spectroscopies, DSC, AFM, and polarized optical microscopy confirmed that the block copolymers were comprised of microphase-separated low glass transition amorphous rubbery PIB and high melting crystalline PPVL block segments with predetermined composition and high structural integrity. Comparison of DSC results with morphological studies using AFM and POM indicated that crystallization of PPVL was constrained to the cylindrical and spherical microdomains preexisting in the melt for certain di- and triblock samples.