Charge-transfer polymerization methacrylate

The photo copolymerization of N-vinylpyrrolidone with methyl methacrylate in the presence of zinc chloride was mentioned in passing in Section 3F above [78]. While the thermal copolymerization of these two monomers does not take place in vacuoy it does take place in the presence of oxygen, after an induction period. Thus oxygen seems to participate in the formation of an active species. The rate is increased in the presence of zinc chloride. It has been postulated that a charge-transfer polymerization process is involved here [78]. 

In the presence of maleic anhydride, the ultraviolet-induced terpolymer-ization of A/-vinylpyrrolidone, methyl methacrylate, and maleic anhydride exhibits charge-transfer polymerization characteristics without any zinc chloride being present [90]. The mixture of N-vinylpyrrolidone and maleic anhydride, on exposure to ultraviolet radiation, changes color from yellowish through pink to scarlet. The ultraviolet spectrum indicates the formation of a one-to-one complex. 

Thermal polymerization of the VCZ-AN system was studied by Ellinger and it was reported that the homopolymer of poly VCZ alone was obtained (28). Due to the small electron affinity of weak acceptors such as AN and methyl methacrylate (MMA), total charge transfer from VCZ to acceptor was thought impossible this induced Ellinger to propose a new polymerization mechanism assuming mesomeric polarization between VCZ and acceptor to initiate and control the propagating step. The finding that AN did not copolymerize with VCZ seemed to support his mechanism. Later, spontaneous copolymerization of VCZ with MMA was reported by the same author. 

Irradiation of an acceptor monomer-electron donor charge transfer complex initiates anionic polymerization in the case of nitroethylene-tetrahydrofuran ( ) and radical polymerization in the case of methyl methacrylate-triphenylphosphine (6). 

Cellulose-water may act as a matrix and promote the development of arrays of comonomer charge transfer complexes (19). The cellulose acts not only as a substrate for such alignment but also as a complexing agent. The matrix of complexes may be represented as shown in I (styrene-methyl methacrylate) and II (butadiene-acrylonitrile). The radical-, thermal-, and radiation-induced graft polymerizations involve homopolymerization of comonomer complexes rather than copolymerization of uncomplexed monomers. 

A similarly detailed study of the polymerization of methyl methacrylate by diphenyliodonium chloride in aq. AN using various aromatic ketone sensitizers has recently been carried out by Timpe s group [103a]. On the one hand the results were not complicated by monomer quenching of excited ketone sensitizer, but were complicated by operation of simultaneous singlet and triplet pathways for the electron-transfer sensitization. In this study the data were analyzed without reference to the possibility of triplet energy transfer sensitization of the iodonium salt photolysis [22], or the possible involvement of charge transfer complexes. 

The photopolymerization of methyl methacrylate using a quinoline-chlorine charge-transfer complex has been investigated. Bulk polymerization was found to follow normal free-radical kinetics, whereas in solution variable monomer exponents were observed depending on the nature of the solvent. The kinetic nonideality in solution was attributed to retardation and initiator termination via degradative chain-transfer involving solvent-modified initiating complexes and chain radicals. 

Strongly redshifted fluorescence, as the solvent polarity was increased, demonstrated the formation of an intramolecular charge transfer state. Compounds under study were used as fluorescence probes for monitoring the kinetics of thermally initiated polymerization of methyl methacrylate and photoinitiated polymerization of 2-ethyl-2-(hydroxymethyl)propane-l,3-diol triacrylate. 

The RUCI3-catalysed polymerization of methyl methacrylate CH2=C(Me)C02Me, initiated by Bu"NH2 in the presence of CCI4 in DMSO, has been investigated with the aid of a dilatometric technique at 60 °C. The kinetic data thus obtained suggest the formation of a charge-transfer complex between Bu"NH2, Ru(III), and CCI4. 

The effects of Lewis acids upon radical polymerizations are distinct from those interpreted as caused by formation of charge transfer complexes between polymer radicals and certain solvents consideration of these latter effects has been extended to the polymerizations of phenyl methacrylate and vinyl benzoate in aromatic solvents. 

Unsaturated polyesters (see Section 16.7) can be used in UV curing as well, but only in combination with a special reactive diluent system, which is based on vinyl ethers. Kinetic analysis has revealed that in that specific case the fumarate forms a charge transfer complex with the vinyl ether and a homopolymerization of this charge-transfer complex takes place as depicted in Scheme 16.34. An advantage of a charge-transfer complex radical polymerization is that it is less susceptible toward oxygen inhibition than methacrylate systems. This is illustrated by the fact that the first commercial UV powder system, in which the powder is sprayed (much oxygen), melted, and then UV-cured, was based on a fumarate-vinyl ether system. 

Compositional determinations for the methyl methacrylate-MA-methyl acrylate terpolymers, prepared with BPO in 2-butanone solvent at 60°C, showed the reactivity of the methacrylate monomer toward the anhydride macroradical is approximately four times greater than that of the acrylate. " " Even though evidence for charge-transfer complexes between the anhydride-acrylate and anhydride-methacrylate pairs exist (see Chapter 10), there is no evidence that the kinetics of the polymerization is affected by these complexes. 

---