Sequence-controlled degradable polymers by controlled cationic copolymerization of vinyl ethers and aldehydes: precise placement of cleavable units at predetermined positions†
Sequence-controlled degradable polymers with precisely placed breakable bonds in the main chain were synthesized by controlled alternating cationic copolymerization of vinyl ethers (VEs) and aldehydes. Novel linear polymers with acid-labile acetal units derived from VE–aldehyde alternating sequences at predetermined positions were prepared by adding a small amount of p-methylbenzaldehyde during the living cationic polymerization of 2-chloroethyl VE (CEVE). The single addition of a large amount of an aldehyde, myrtenal, during the living polymerization of isobutyl VE (IBVE) produced a block-type copolymer with a completely degradable segment of myrtenal and IBVE. Furthermore, star-shaped polymers that had degradable cores composed of acetal structures were successfully prepared by two methods: addition of (i) a mixture of a bifunctional VE and a monofunctional aldehyde or (ii) a bifunctional aldehyde to the living propagating poly(VE). The resulting polymers with acid-labile units were selectively degraded and transformed into lower MW polymers with other shapes quantitatively under mildly acidic conditions.