Living and Alternating Cationic Copolymerization of o-Phthalaldehyde and Various Bulky Enol Ethers: Elucidation of the “Limit” of Polymerizable Monomers

Abstract

Cationic copolymerization of various bulky enol ethers, which have been difficult to homopolymerize and/or copolymerize, was shown to proceed when o-phthalaldehyde (OPA) was used as a comonomer. A series of enol ethers with various substituents on the β-carbon was synthesized from aliphatic aldehydes and alcohols. The relationships between the structures of the enol ethers and the copolymerization behavior were systematically investigated. As a result, monomers with one or two methyl and/or primary alkyl groups on the β-carbon were found to undergo alternating copolymerization with OPA. Moreover, living cationic copolymerization of enol ethers and OPA yielded alternating copolymers under appropriate polymerization conditions. To elucidate the limit of polymerizable monomers, the copolymerization of very bulky enol ethers such as β-t-butylor norbornenylidene-type monomers with OPA was also examined. OPA was found to be copolymerizable even with such very bulky monomers, indicating that the unique reactivity of the OPA-derived propagating carbocation with small steric hindrance is the key factor for successful copolymerization.

Anionic Copolymerization of o-Phthalaldehyde with Epoxides: Facile Access to Degradable Polyacetals and Their Copolymers under Ambient Conditions

“…13,16,24,25 Recently, Aoshima and co-workers carried out at −78 °C the synthesis of various alternating copolymers via cationic copolymerization of OPA with vinyl ethers. 10,26,27 In all cases all the (co)polymerizations have to be carried out at lower temperature than T c (−36 °C) 9 of OPA irrespective of the comonomers used.…”

“…They have to be end-capped after polymerization to avoid depolymerization under ambient conditions. − Molar masses as high as 200 kg/mol were obtained . Some works report the modification of the thermal, mechanical, and chemical properties of PPA through their copolymerization with substituted benzaldyhyde, glyoxylate, − and phthalaldehyde derivative monomers; ,,− the synthesis of block copolymers through the macroinitiator approach has also been considered. ,,, Recently, Aoshima and co-workers carried out at −78 °C the synthesis of various alternating copolymers via cationic copolymerization of OPA with vinyl ethers. ,, In all cases all the (co)­polymerizations have to be carried out at lower temperature than T c (−36 °C) of OPA irrespective of the comonomers used.…”

Cationic Copolymerization of o-Phthalaldehyde and Vinyl Monomers with Various Substituents on the Vinyl Group or in the Pendant: Effects of the Structure and Reactivity of Vinyl Monomers on Copolymerization Behavior

“…As reported in our previous study, alternating copolymerization of OPA with EMPE, which is a β , β -dimethyl VE, successfully proceeded (entry 7 in Table ; Figure D). Based on this result, the copolymerizations of various β , β -disubstituted VEs and OPA were investigated …”

“…Based on this result, the copolymerizations of various β,β-disubstituted VEs and OPA were investigated. 23 The copolymerization of OPA with VEs that have a methyl group at the α-carbon did not proceed (entry 8 in Table 2). This result is due to the unstable ketal structure derived from the crossover reaction from the VE-derived carbocation to OPA (Scheme 6).…”

“…In our previous study, we reported the exceptional copolymerizability of o -phthalaldehyde (OPA) with vinyl monomers. , Living copolymerization, alternating copolymerization, and successful copolymerization with bulky monomers such as β , β -dimethyl vinyl ether and 1,1-diphenylethylene (DPE) were demonstrated to proceed due to the special reactivity of the OPA-derived cyclic propagating carbocation with small steric hindrance. In this study, to extend the range of copolymerizable monomers and systematically elucidate the relationships between the structure and reactivity of vinyl monomers and the copolymerization behavior, the copolymerization of OPA with various St derivatives and vinyl ethers (VEs) was investigated (Scheme ).…”