Photoinduced living cationic polymerization of tetrahydrofuran. I. Living nature of the system and its application to the diblock copolymer synthesis

Abstract

ABSTRACT:The living nature of cationic polytetrahydrofuran (THF), photoinduced in the presence of diphenyliodonium hexafluorophosphate (initiator), was investigated. In the bulk polymerization of THF, the linear relationship between percent conversion and the number-average molecular weight of the resulting polymer strongly suggests the living nature of this polymer and this was confirmed by the monomer addition technique, that is, cationic poly(THF) is capable of initiating a newly added monomer. The loss of the living nature of the cationic poly(THF) in a polar solvent, dichloromethane, is explained in terms of the stabilization of the five-membered cyclic oxonium ion, a propagating species of cationic polymerization of THF, by ion-pair formation with a less nucleophilic counterion, hexafluorophosphate. Based on the living nature of cationic poly(THF), a diblock copolymer, composed of THF and N-2-(hydroxyethyl)ethyleneimine (HEEI) was synthesized by subsequent monomer addition method; however, it was found that the HEEI block of the compolymer has a nonlinear structure. The factors affecting the structure of the HEEI block are also discussed.

Photoinduced living cationic polymerization of tetrahydrofuran(IV): Syringe method

“…The results of the direct polymerization method are also shown for the sake of comparison. It shows that the percentage of conversion increases linearly with the reaction time in both cases, which means that THF is initiated by the photolytic products of the initiator, presumably hexafluorophosphoric acid, as reported by Crivello and Lam12–16; however, the rate of polymerization in the syringe method is lower than that of the corresponding direct polymerization method, as reported in our previous article 8…”

“…Stabilization of cationic propagating species by ion pair formation with the less‐nucleophilic complex (PF) is attained as follows8: …”

“…In our previous investigations on photoinduced cationic polymerization of tetrahydrofuran (THF) in the presence of diphenyliodonium hexafluorophosphate (initiator),8–10 we reported that a cationic polymerization of THF is initiated by the addition of a proton, a photolytic product of the initiator 11–17. The living nature of the system is from the stabilization of the propagating cationic species, a five‐membered cyclic oxonium ion, by ion pair formation with a complex metal halide anion supplied by the initiator 9.…”

Photoinduced living cationic polymerization of tetrahydrofuran. II: Synthesis of four-armed star-shaped poly(tetrahydrofuran)

“…Monomers, THF, and epichlorohydrin (ECH) were purified by the conventional fractionation method 1. Diphenyliodonium hexafluorophosphate, a well‐known photocationic initiator, was synthesized by the method described elsewhere 7…”

“…In an earlier article1 we investigated the living nature of the photoinduced cationic poly(tetrahydrofuran) [poly(THF)] and based on this study a THF‐based diblock copolymer was synthesized by the sequential monomer addition method. A linear relationship between the conversion and the number average molecular weight of the resulting polymer indicates that the cationic poly(THF) has a living nature (i.e., the chain transfer or termination process is absent in this system) and this was ascribed to the stabilization of the five‐membered cyclic oxonium ion, which is responsible for the cationic polymerization of THF, by ion pair formation with the less nucleophilic complex metal halide anion.…”