Acceptor monomers

Monomers that are strong electron donors may undergo spontaneous oupolymeri/.aliun with strong electron acceptor monomers by a radical mechanism. In certain cases homopolymers formed by an ionic mechanism accompany copolymer formation.312,j2s... 

While there is clear evidence for complex formation between certain electron donor and electron acceptor monomers, the evidence for participation of such complexes in copolymerization is often less compelling. One of the most studied systems is S-.V1 Al I copolymerization/8 75 However, the models have been applied to many copolymerizations of donor-acceptor pairs. Acceptor monomers have substituents such as carboxy, anhydride, ester, amide, imide or nitrile on the double bond. Donor monomers have substituents such as alkyl, vinyl, aryl, ether, sulfide and silane. A partial list of donor and acceptor monomers is provided in Table 7.6.65.-... 

Equilibrium constants for complex formation (A") have been measured for many donor-acceptor pairs. Donor-acceptor interaction can lead to formation of highly colored charge-transfer complexes and the appearance of new absorption bands in the UV-visible spectrum may be observed. More often spectroscopic evidence for complex formation takes the font) of small chemical shift differences in NMR spectra or shifts in the positions of the UV absorption maxima. In analyzing these systems it is important to take into account that some solvents might also interact with donor or acceptor monomers. 

Although it has been suggested that crosslinking in the presence of MAH involves coupling of appended MAH radicals with other appended MAH radicals or with polymer radicals (7) the former is improbable due to the tendency for disproportionation rather than coupling between radicals derived from strong electron acceptor monomers such as MAH. 

Free radical alternating 1 1 copolymerization of donor-acceptor monomer systems has been known for quite some time. Linear copolymers from donor-acceptor systems... 

Photoinduced copolymerization of donor-acceptor monomer pairs (Scheme 1) can be either self initiated by excitation of the charge transfer complex (charge transfer initiation) or by polymerization of the charge transfer complex/monomer equilibrium... 

In considering the origin of the results in Table III and the extraordinary rate exhibited by the HM/CHVE system, it is tempting to consider the role that ground-state charge transfer interaction between the donor and acceptor monomers in the... 

Each vertex of a buckyball cluster is attached by three H-bonds, and hence must have net donor (2D1A) or acceptor (1D2A) character that seems to preclude significant cooperativity. However, by suitably pairing each donor and acceptor monomer, one may produce connected dimers that are each of effective 3D3A pseudo-closed-CT character. Such cooperative dimer units may then be joined in proton-ordered fashion to form closed polyhedra that retain a high degree of cooperative stabilization. 

The monomer complex participation (MCP) mechanism suggests that alternation results from homopolymerization of a 1 1 complex formed between donor and acceptor monomers [Cowie, 1989 Furukawa, 1986] ... 

Some pairs of very strongly electron-donor and electron-acceptor monomers, such as p-methoxystyrene and dimethyl cyanofumarate, undergo spontaneous alternating copolymerizations without any added free-radical initiator, although heat may be required [Hall and Padias, 1997, 2001]. Initiation involves reaction of the comonomer pair to form a diradical,... 

As to the contributions of the ghost functions, those of s type are of the same behaviour than in the He2 dimer (see Table II, values are given for monomerl). The contributions of p functions, as expected, show a systematic trend it is to be emphasized that the contributions from monomerl in the SMOs for monomerl are usually higher than those from monomerl to monomerl. However, not so large difference can be noticed for the contributions in the corresponding CP-systems. These results also suggest that one cannot expect a similar correspondence for the correlation energy contributions in the SM- and CP-systems for the electron-donor and electron-acceptor monomers, respectively. 

The nature of the polymer is diagnostic of the nature of the initiating intermediate. The homopolymer of the donor olefin in the presence of an acceptor monomer can only be obtained by a cationic propagation mechanism, and not by a free-radical mechanism. Correspondingly, the homopolymer of the acceptor olefin... 

The Bond-Forming Initiation theory is based on the fact that cycloaddition and initiation of copolymerization compete in the reactions of donor and acceptor monomers. Experimental conditions played a great role in that dilute solutions favored cycloadditions, while high concentration favored polymerization. The main concept is that the intermediates in the cycloaddition reactions are also the initiators of the polymerization. 

Feng, Cao, and Li [9] studied the photopolymerization of acceptor monomers initiated by donor initiators, especially by aromatic amines. The proposed mechanism involved a charge-transfer interaction, followed by proton-transfer to produce two kinds of free radicals. The acrylonitrile (AN)/W,V-dimethyltoluidine (DMT) system is shown as an example ... 

The photo-induced charge-transfer copolymerization entity consists of a donor monomer and an acceptor monomer, without initiator. Reported combinations usually consist of an aryl vinyl monomer as the donor component and a 1,2-disubstituted vinyl monomer as the acceptor component. 

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 ... 

Electron donor-acceptor monomer pairs form charge-transfer complexes (CTC), which collapse to the tetramethylene intermediates through the bond-formation between the p-carbons ... 

The initiation mechanism of photo-induced charge-transfer copolymerization of donor-acceptor monomer pairs is clarified by integrating the results from organic chemistry and polymer chemistry. A reasonable suggestion for the initiating species in certain cases may be a tetramethylene 1,4-diradical. The excited complex of the donor/acceptor monomers undergoes multiple follow-up reactions to produce the... 

Complex Acceptor/Monomer ratio -N= Proportion of -NH- N+ Anion/N ratio Halogen/N O/N Conductivity (S/cm)... 

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