Marriage of ring-opening metathesis polymerization and thiol-maleimide chemistries: Direct polymerization of prefunctionalized monomers or postpolymerization modification?

Abstract

Two distinct synthetic methodologies to furnish polynorbornene bearing thiol-maleimide adduct side groups, namely direct ring-opening metathesis polymerization (ROMP) of prefunctionalized monomers and postpolymerization modification, were investigated and compared in this study. ROMP of thiol-maleimide adduct-containing monomers M1-M4 was performed to yield polymers PM1-PM4 with full conversion of monomers but broad molecular weight distribution. Meanwhile, narrowly distributed polymers P1-P4 were generated through postpolymerization modification of polymer P0 by using thiol-maleimide reaction. However, removal of residual monomer M0 was an indispensable step prior to postpolymerization modification since incomplete monomer conversion was observed in the previous step, synthesis of polymer P0 using ROMP of maleimide-containing monomer M0. Narrow molecular weight distribution in conjunction with good polymerization controllability renders the strategy of postpolymerization modification a seemingly more reliable synthetic protocol to achieve the goal of this contribution. Finally, polymers P0-P4 were subjected to property studies to elucidate their thermal stability, glass transition behavior, wettability and gelation using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angle measurement, and cross-linking test, respectively.