NEW FEATURES OF ROMP BY HETEROGENIZATION OF MOLYBDENUM CARBENE COMPLEXES

An inorganic carrier based on alumina covered with methylaluminoxane ( MAO) which had been crosslinked by various diols was used to immobiliz e molybdenum carbene complexes of the type Mo(CH-t-Bu)(NAr)(OC(CH3)(2) CF3)(2) (1) and Mo(CH-t-Bu)(NAr)(OTf)(2)(dme) (2) (Ar=2,6-C6H3-i-Pr-2) . Employment of fluorinated diols heavily increased the activity in ri ng-opening metathesis polymerization (ROMP) of different substituted n orbornenes, 2-azanorbornene, cyclooctene, cyclooctadiene and metathesi s reaction of acyclic alkenes. Investigations were made on differences in stereochemistry of polymers obtained by these new supported comple xes compared with homogeneous polymerization initiated by (1). The imm obilized initiators produced polymers with a higher content of trans v inylene, particularly when monomers were substituted with bulky groups . Terminal alkenes like l-hexene worked as chain transfer agents. Thus regulation of molecular weight was possible. Ln addition these suppor ted carbene complexes showed a surprisingly high stability of the alky lidene species in suspension-even after 30 days of polymerization the activity was still about 15% of the initial value. (C) 1998 Elsevier S cience B.V. All rights reserved.