Donor monomers thermal initiation

This section describes polymerizations of monomer(s) where the initiating radicals are formed from the monomer(s) by a purely thermal reaction (/.e. no other reagents are involved). The adjectives, thermal, self-initialed and spontaneous, are used interchangeably to describe these polymerizations which have been reported for many monomers and monomer combinations. While homopolymerizations of this class typically require above ambient temperatures, copolymerizations involving certain electron-acceptor-electron-donor monomer pairs can occur at or below ambient temperature. 

Complexes of monomers with acceptors can initiate polymerizations of the respective monomers even without photoexcitation. The properties of DA complexes and the conditions of the thermal activation are determined by the type of donor (monomer), acceptor, and solvent [300,303]. Ion radicals from the monomer, dipolar intermediates (zwitterions), as well as the relatively... 

Dibenzothiophene derivatives have been used as co-catalysts in the addition polymerization of vinyl and diene monomers. Dibenzothiophene itself, in conjunction with vanadium oxychloride, is effective in initiating the polymerization of isobutylene, - although when incorporated in a Ziegler catalyst system, competition between donor and monomer for the most electrophilic sites results in deactivation of the catalyst. Despite the fact that 2-vinyl- - - and 4-vinyldibenzothiophene - readily undergo thermal polymerization,... 

Photopolymerization induced by donor-acceptor interaction has several characteristic differences from conventional photopolymerization. Firstly, the initiation is very selective. Appropriate strength of donor and acceptor is essential since the CT interaction might bring about spontaneous thermal polymerization if it is too strong. Although most charge transfer processes must be photosensitive, practically important systems are limited to those which conduct thermal reactions with negligible rates. The photopolymerization of MMA by triphenyl-phosphine should be called photoacceleration rather than photoinitiation since the rate of spontaneous photopolymerization of MMA is about half of that of polymerization photosensitized by 4 x 10 4 M of triphenyl-phosphine. Secondly, an ionic mechanism is expected. Thirdly, when both donor and acceptor are polymerizable monomers, the polymerization mixture is entirely solid and clean after polymerization. There is no initiator and no solvent. 

Before discussing the tetramethylenes in the photoreactions of donor/acceptor monomer pairs, we would like to recall the results of thermal copolymerizations of such pairs, from which enlightment may be gained for our proposal. In all discussions we will deal only with spontaneous polymerizations, i.e., in the absence of initiators. 

Many donor-acceptor monomer pairs spontaneously undergo thermal copolymerizations. Hall [86-88] studied the thermal addition and polymerization reaction of such combinations systematically and postulated a Bond-Formation Initiation theory. The most important points of this theory may be summarized as follows ... 

A trifunctional initiator was used to synthesize a (PIB- -PS)3 star-block copolymer using ring-substituted tricumyl chloride as initiator and TrCU as coinitiator via the sequential monomer addition methodology. The polymerization was conducted at -80 °C, in the presence of pyridine (electron donor) and 2,6-di-tert-butylpytidine (proton trap) in a 60/40 (v/v) methylcy-clohexane-methyl chloride solvent mixture. The copolymer synthesized exhibited a rather low PDI (1.17) and their mechanical, thermal, and morphological properties were examined extensively. 

Thermal and UV-initiated cyclo-polymerizations of mixed allyl-butenedioate monomers with both donor and acceptor unsaturations such as methyl allyl fumarate or maleate were recently described. Hyperbranched macromolecules were obtained by free radical alternating copolymerization of bifunctional monomers containing two polymerizable double bonds of allyl and vinylene type with styrene or maleic anhydride. Thanks to their original structure, this new class of liquid blends exhibit improved mechanical and physical properties useful for a wide range of coating applications. ... 

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