Anionic polymerization, furans

When undiluted 2-vinylfuran was added to metallic sodium (mirror or particles) an orange colour developed and some resinous material was deposited on the metal surface. On prolonged contact much of the monomer was converted into a partly-insoluble reddish resin with spectra unrelated to those of standard poly(2-vinyl-furan). Reaction of diluted monomer with sodium gave a milder interaction, but no evidence of living anionic polymerization. 

Synthesis of monodisperse PHOST was first reported by Nakahama et al. [145], who demonstrated that 4-terf-butyl(dimethyl)silyloxystyrene undergoes living anionic polymerization with butyllithium as the initiator in tetrahydro-furan (THF) at cryogenic temperatures under high vacuum and that desilyla-tion of the resulting polymer with HC1 cleanly yields monodisperse PHOST. It... 

Anionic polymerization is a useful alternative to free-radical and Ziegler-Natta procedures for certain polymers. Adding butyllithium to a solution of styrene in tetrahydro-furan (THF), for example, gives polystyrene. 

Singha et al. reported DA cross-linked products [158] using furan-modified polymethacrylate (PFMA) as the polymeric precursor, which was prepared through atom transfer radical polymerization (ATRP) and free-radical polymerization (FRP). Furthermore, the self-healing behavior of a triblock copolymer (PFMA-co-MMA) prepared by ATRP was demonstrated by means of scanning electron microscopy (SEM). With the modification, an almost fully recovered surface from knife-cut samples has been observed [159]. Chen et al. also reported the DA polymer product of PFMA-BM possessing thermal reversibility, whereas the homopolymer was prepared from anionic polymerization [160]. 

Although cyanoacrylate polymers are most commonly prepared by anionic polymerization, they may also be prepared by free-radical polymerization using conventional radical initiators (36-38), provided adequate amounts of anionic polymerization inhibitors are employed. Bulk photoanionic polymerization of cyanoacrylates has also been described by a number of workers (39-43). These systems rely on the in situ generation of an anionic initiator from a neutral species, following absorption of light of an appropriate wavelength. The zwitterionic and radical copolymerization of cyanoacrylates has also been reported for a number of comonomers including vinyl ethers (44), ketene acetals (45), furan (46), vinyl ketones (47), and ethylene (48). 

Higashi et al. [262] investigated the anionic polymerization of / -MeSt with -amylsodium in -hexane at 0°C. The polymer obtained could be fractionated in benzene-soluble, acetone-soluble, and insoluble fractions. The IR spectra of these fractions showed distinct differences, but no further explanation was given. Hirohara et al. [263,264] reported on the kinetics of anionic polymerization of o-, m-, and /7-methylstyrene in methyltetrahydro-furan at 25°C using several organometallic initiators. 

In 1956 Szwarc and his associates discovered an anionic polymerization of styrene without chain transfer and termination , and this reaction was called living polymerization. Subsequent studies revealed a number of examples of living anionic systems . In the field of cationic polymerization, two research groups reported in 1965 that the propagating species in ring-opening polymerization of tetrahydro-furan have an unusually extended lifetime . ... 

Recent work on the synthesis, structure and some properties of macromolecules bearing furan rings is discussed. Two basic sources of monomers are considered, viz. furfural for monomers apt to undergo chain polymerization and hydroxymethylfurfural for monomers suitable for step polymerization.Within the first context, free radical, catiomc and anionic systems are reviewed and the peculiarities arising from the presence of furan moieties in the monomer and/or the polymer examined in detail. As for the second context, the polymers considered are polyesters, polyethers, polyamides and polyurethanes. Finally, the chemical modification of aU these oligomers, polymers and copolymers is envisaged on the basis of the unique reactivity of the furan heterocycle. 

Radiation-induced polymerization of nitroethylene in the liquid state was studied by Yamaoka and one of the present authors (K. H.). They verified that nitroethylene polymerizes in the anionic mechanism by radiation too, from the following three observations (7). Tetrahydro-furan is the most favorable solvent for the polymerization, among nitro-ethane, ethylether and tetrahydrofuran. The addition of hydrogen chloride remarkably retards the polymerization. Finally, nitroethylene copolymerizes with acrylonitrile. 

Preparation of addition polymers having the oxolene (dihydrofuran) functionality can be envisioned to occur in two possible ways (Scheme 13). Both, in fact, have been observed (77MI11102). Whereas furan (53) or its derivatives do not homopolymerize under free radical conditions, 1 1 alternating copolymers possessing the 1,4-structure are produced with maleic anhydride (50). Intermediate formation of a CT complex between monomers (50) and (53) is believed to be necessary before polymerization can occur. On the other hand, cationic polymerization is quite facile. The outcome is straightforward with benzo[f>]furan derivatives, producing 1,2-polymers. Optically active poly(benzofurans) are formed when the cationic polymerizations are conducted in the presence of a chiral anion. 

Initiation by Electron Transfer. This mechanism of initiation operates in polymerizations by alkali metals or their complexes and was best elucidated in the case of the sodium naphthalene complex (13). which was used to form the well-known "living" polymers. In these complexes, the naphthalene is a radical anion (35) formed by transfer of an electron from sodium in the presence of a highly solvating solvent such as H -furan ... 

More recently, acrylonitrile dissolved in vitreous methyltetrahydro-furan was irradiated at —196 °C. and found to polymerize by an anionic mechanism (3, 4). Here again the rates exhibited a maximum at low monomer concentrations. 

Potentially, there are greater numbers of monomers that are suitable for cationic polymerization than for anionic, but the cationic method is less successful in block copolymer synthesis because, in many systems, the existence of a living carbocationic species is doubtful. Consequently, the involvement of carbocations in block copolymer synthesis tends to be limited to mixed reactions, e.g., the couphng of poly(tetrahydro-furan) cations with polystyryl anions to give an (A - B) diblock (Equation 5.19). 

As two non-petroleum chemicals readily accessible from renewable resources, both furfural and HMF are suitable starting materials for the preparation of versatile fine chemicals [14, 102-106] and can also serve as renewable monomers for preparation of sustainable polymer products [107]. Schemes 3, 4, and 5 depict the stmctures of the selected furan-based monomers [107-113]. As a typical precursor, furfural can be converted to a vast array of furan-based monomers bearing a moiety which can normally be polymerized by chain-growth polymerization mechanisms [108-113]. As shown in Scheme 3, these monomers are all readily polymerizable by chain-growth reactions. However, depending on their specific structure, the nature of the polymerization mechanism is different, ranging from free radical, cationic, anionic, to stereospecific initiation [108-113]. On the other hand, furfuryl... 

The first mention of polythiophenes as potential conducting polymers can be found in the literature in 1967. A. G. Davies and coauthors investigated the acid catalyzed polymerization of furan, pyrrole, and thiophene hetero-cycles. Although this polymerization reaction was known before, several new and interesting facts could be elucidated. Besides the confirmation of the cyclic structure of the polymer units (instead of ring opened), the electric conductivity was investigated. In contrast to the already known types of electronically conducting polymers (polyaniline and polypyrrole, see Chapter 1), the conductivity of all polyheterocycles in Armour s paper, isolated as trichloro- or trifluoroacetates (triflate), is ionic. In the case of the polythiophene, ion pairs formed by the reaction of polythiophene with trifluoro acetic acid dissociated in methylene chloride solution to the protonated polymer and triflate anions. The polythiophene triflate decomposed at relatively low temperatures (60°C-80°C). ... 

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