Precision vinyl acetate/ethylene (VAE) copolymers by ROMP of acetoxy-substituted cyclic alkenes

Precision linear vinyl acetate/ethylene (VAE) copolymers containing acetoxy groups on precisely every eighth backbone carbon were synthesized by ring-opening metathesis polymerization (ROMP) of racemic 3-acetoxy cyclooctene (3AcCOE) followed by hydrogenation. The use of enantiomerically pure 3AcCOE resulted in an optically active polyalkenamer that afforded isotactic precision VAE materials after hydrogenation. Both of these VAE polymers are semicrystalline (by differential scanning calorimetry and wide-angle X-ray scattering) due to their high degrees of regioregularity and the isotactic VAE samples exhibited a higher apparent degree of crystallinity and melting point compared to the atactic version. In contrast, analogous linear VAE copolymers derived from ROMP-hydrogenation of racemic 4- or 5-acetoxy cyclooctenes were regio-irregular and completely amorphous. The ROMP-hydrogenation of 3-acetoxy cycloheptene also affords precision linear VAE copolymers with acetoxy groups on every seventh carbon, but this polymer was noncrystalline. Mechanical characterization showed that the precision 3AcCOE-derived VAE samples possess improved mechanical properties compared to the compositionally similar commercial VAE copolymers produced by radical copolymerization.