“Charge transfer” polymerization—and the absence thereof!

Abstract

ABSTRACT:Mechanisms for "charge-transfer" spontaneous polymerizations and cycloadditions between electron-rich olefins and electron-poor olefins were reviewed. As for propagation, literature proposals involving chargetransfer complexes were rejected. Instead, alternating copolymerization is ascribed to polar effects in free-radical reactions. As for spontaneous initiation, literature proposals involving charge-transfer complexes, with or without proton transfer, were rejected. Instead, the initiating species is postulated to be a tetramethylene zwitterion biradical, which may initiate either ionic homopolymerization or freeradical copolymerization. A new hypothesis proposes that any interaction that brings vinyl monomers close together may facilitate tetramethylene formation and spontaneous polymerization. These interactions include Coulombic, acidbase, hydrophobic-hydrophilic and templating-tethering interactions.

Synthesis and characterization of double hydrophilic block copolymers containing semi‐rigid and flexible segments

“…The increase in polymerization rate of alternating copolymers where the electron-rich monomer (donor monomer) is rendered more electron-rich and/or the electronpoor monomer (acceptor monomer) is made more electronpoor is well documented in the literature. 38,39 For example, the copolymerization of p-methoxystyrene with MAn has a faster polymerization rate than the copolymerization of styrene and MAn. 20 Like styrene homopolymerizations with dithiobenzoate CTAs, a retardation period (2 h) appeared due to the over-stabilization of the RAFT adduct arising from the dithiobenzoate Zgroup of CDB.…”

Photoinitiator‐free UV grafting of styrene, a weak donor, with various electron‐poor vinyl monomers to polypropylene film

“…Advantages associated with PI-free systems have been discussed in a previous publication. 7 The role of styrene as an electron donor has been documented in a number of publications, 2,18,19 but its copolymerization with strong acceptors, such as MA, 18 diisopropyl fumarate 19 and maleimides 20 were carried out in the presence of additives such as initiators 19,20 or Lewis acid. 18 In this study, the possibility of styrene, a poor electron donor, forming D/A pairs with electronpoor (EP) vinyl monomers as acceptors in initiating spontaneous polymerization and grafting under the influence of a UV source with PP as the substrate was investigated.…”

“…However, several mechanisms have been proposed and these include (a) the interaction of a donor/acceptor (D/A) pair producing a tetramethylene intermediate species which initiates spontaneous polymerization, 2 (b) a CT complex acts as a monomer which polymerises in a certain order forming alternating polymer, 2 (c) matrix polymerization in which the donors and acceptors are thought to realign in an alternative order in the monomer solution producing an alternating polymer, 2 and (d) an electron transfer mechanism in which interaction between electron donors and acceptors are thought to lead to complete electron transfer from donors to acceptors producing cationic/anionic radical pairs which are capable of initiating spontaneous polymerization. 1,2 The most widely accepted mechanism is mechanism (a) which involves the theory of the polymerization initiated by tetramethylene intermediates. 1,2 According to this theory, strong interactions between donors and acceptors under the influence of a UV source produce tetramethylene intermediates which can be of a pure ionic Zwitterion nature or a 1,4 biradical nature.…”

“…1,2 The most widely accepted mechanism is mechanism (a) which involves the theory of the polymerization initiated by tetramethylene intermediates. 1,2 According to this theory, strong interactions between donors and acceptors under the influence of a UV source produce tetramethylene intermediates which can be of a pure ionic Zwitterion nature or a 1,4 biradical nature. These intermediate species can initiate free-radical or ionic polymerization.…”

“…For example, the two derivatives of styrene, p-methoxy styrene and p-glycidyloxy styrene, are strong electron donors. 1,2 Styrene undergoes slow radical polymerization and thus can be considered to be a suitable monomer for UV grafting to substrates as long UV exposures, which are normally required for grafting, can be applied. 14,17 It has been used as a comonomer with MMA in order to reduce homopolymerization of MMA and improve grafting of this monomer to cellulose and PP substrates under the influence of either ionising or UV radiation, with photoinitiators (PIs) normally being required in the latter technique.…”