Two-step degradable ABAC-type periodic poly(cyclic acetal)s synthesized by sequence-programmed monomer formation and subsequent polyaddition based on cyclotrimerization of one vinyl monomer and two aldehydes

ABAC-type periodic polymer, Poly(cyclic acetal)s, Two-step degradation ABAC-type periodic poly(cyclic acetal)s were synthesized via a two-step method consisting of the synthesis of a sequence-programmed cyclic trimers from one vinyl monomer and two bifunctional aldehydes (isophthalaldehyde or terephthalaldehyde) and the successive cyclotrimerization of the cyclic trimer with another vinyl monomer. The use of 1,1-diphenylethylene (DPE) was important for synthesizing the cyclic trimer in high yield because the successive cyclotrimerization and other side reactions were suppressed due to the steric hindrance of DPE. The ABA-type sequence-programmed cyclic trimer consisting of one DPE molecule (unit B) and two dialdehydes (unit A) possesses two unreacted aldehyde moieties; hence, the cyclic trimer successfully underwent successive cyclotrimerization with vinyl ethers (VEs) (unit C), such as 2-chloroethyl VE (CEVE) and ethyl 2-methyl-1-propenyl ether (EMPE). As a result, ABAC-type periodic poly(cyclic acetal)s with alternately arranged two phenyl rings and VEderived side chains were produced. The two types of cyclic acetal structures in the main chain exhibited different acid degradability. Indeed, the CEVE-derived cyclic acetal structures were selectively degraded under acidic conditions at 60 degrees C for 15 min, which was followed by the subsequent degradation of the DPE-derived cyclic acetal structures in 24 h. In addition, the ABAC-type periodic polymers exhibited good thermal properties, which were attributed to the cyclic acetal structures.