Temperature triggered alternating copolymerization of epoxides and lactones via pre-sequenced spiroorthoester intermediates.

We report the alternating copolymerization of caprolactone and epoxide through the in situ formation of pre-sequenced spiroorthoester monomer. The reaction is catalyzed by the temperature triggered, bifunctional cationic indium complex (±)-[(NN i O tBu )In(CH 2 SiMe 3 )][B(C 6 F 5 ) 4 ] (1). 1 can catalyze the coupling of epoxide and lactone to form spiroorthoester at 60 °C and its double ring-opening polymerization at 110 °C to form poly(ether- alt -ester). The post-polymerization modification and degradation of the poly(ether- alt -ester) are further investigated.