Regioselective cross metathesis for block and heterotelechelic polymer synthesis

Abstract

Ring-opening metathesis polymerization (ROMP) of 3-substituted cyclooctene (3RCOE) monomers with Grubbs 2^nd and 3^rd generation catalysts (G2 and G3) has been shown to occur with high head-to-tail regioregularity and E-stereoregularity. Cross metathesis (CM) between the resultant polymer chains, a secondary metathesis reaction during ROMP, also results in head-to-tail regioregularity and E-stereoregularity. The selectivity of the CM is demonstrated in the reaction between polymers of various molar masses or with different R substituents. In the latter case, monitoring by DSC reveals the change from a multiblock polymer to a statistical copolymer by displaying first two, then one T_g. The regioregularity of both the ROMP and CM reactions is exploited for the synthesis of heterotelechelic polyolefins through the use of an asymmetric, allylically-substituted chain transfer agent alongside the 3RCOE monomer.