Block Copolymerisation of Oxiranes and

3 Block Copolymerisation of Oxiranes and Lactones or Cyclic Acid Anhydrides 

Block copolymers characterised by different backbone structures of well-defined block lengths have been obtained from oxiranes and other heterocyclic monomers in the presence of catalysts that are effective at bringing about living polymerisations. Aida et al. [127,188,189,195,196] applied aluminium porphyrins and Teyssie et al. [125,197,198] applied bimetallic /i-oxoalkoxidcs for block copolymerisations in systems involving oxirane lactone, oxirane oxirane/cyclic acid anhydride, and oxirane/cyclic acid anhydride lactone as block forming units and obtained respective polyether polyester and polyester polyester block copolymers. Such copolymers seem to be of exceptionally wide potential utility [53]. 

The growing species in living block copolymerisation systems may change when changing the comonomer to build the next block or they may retain their structure. For instance, the polymerisation of /J-butyrolactonc with an aluminium porphyrin catalyst such as (tpp)AlCl proceeds via aluminium carboxylate species [scheme (10)] which are converted to aluminium alcoholate species when the polymerisation of propylene epoxide is carried out from the living polyester as shown schematically below [195]  

On the other hand, when propylene oxide polymerisation is carried out from the living polyester afforded by the polymerisation of /i-butyrolactonc with (tpp)AlOMe, the growing aluminium alcoholate species [scheme (9)] remain unchanged. 

Copolymerisations of heterocyclic and heterounsaturated monomers generally lead to random copolymers with a prevailing content of the heterocyclic monomer and to alternating or nearly alternating copolymers, depending on the kind 

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