Copolymerization of ethene with cyclic and other sterically hindered olefins

Sterically hindered olefins like norbornene, dimethanooctahydronaphthalene (DMON), 4-methylpentene, and 3-methylbutene can be copolymerised with ethene by metallocene/MAO catalysts. Different C2-, Cs- and C1-symmetric and meso-zirconocenes were used. Only isolated and alternating norbornene sequences but no norbornene blocks are formed by substituted [Me2C(Cp-R)(Flu)]ZrCl2 catalysts. The alternating microstructure leads to melting points up to 270°C for ethene-norbornene copolymers and up to 380°C for the semi-crystalline alternating copolymer of ethene and DMON. Other sterically hindered olefins such as 3-methylpentene build more blocky structures with high glass transition temperatures. The mechanism for the insertion reaction of the different catalysts is discussed.