Complex participation copolymers

It is also possible to process copolymer composition data to obtain reactivity ratios for higher order models (e.g. penultimate model or complex participation, etc.). However, composition data have low power in model discrimination (Sections 7.3.1.2 and 7.3.1.3). There has been much published on the subject of the design of experiments for reactivity ratio determination and model discrimination.49 "8 136 137 Attention must be paid to the information that is required the optimal design for obtaining terminal model reactivity ratios may not be ideal for model discrimination.49... 

The complex participation model, like the depropagation model, predicts a variation of the copolymer composition with temperature and monomer concentration. The effect of temperature comes from the change in K, resulting in a decrease in the concentration of the comonomer complex with increasing temperature. Increasing monomer concentration at a constant/i increases the comonomer complex concentration. 

Copolymer Statistics Within the Framework of the Complex Participation Model... 

There are several cases where NMR spectroscopy has been used to investigate copolymers which deviate from the terminal model for copolymerisation (see also chapter 3). For example, Hill and co-workers [23, 24] have examined sequence distributions in a number of low conversion styrene/acrylonitrile (S/A) copolymers using carbon-13 NMR spectroscopy. Previous studies on this copolymer system, based on examination of the variation of copolymer composition with monomer feed ratio, indicated significant deviation from the terminal model. In order to explain this deviation, propagation conforming to the penultimate (second-order Markov) and antepenultimate (third-order Markov) models had been proposed [25-27]. Others had invoked the complex participation model as the cause of deviation [28]. From their own copolymer/comonomer composition data. Hill et al [23] obtained best-fit reactivity ratios for the terminal, penultimate, and the complex participation models using non-linear methods. After application of the statistical F-test, they rejected the terminal model as an inadequate description of the data in comparison to the other two models. However, they were unable to discriminate between the penultimate and complex participation models. Attention was therefore turned to the sequence distribution of the polymer. 

The formation of inter- and intrapolymer complexes has also been shown to affect the polymerization kinetics. For example, Ferguson and Shah (1968) investigated the influence of intrapolymer complexation on the kinetics of AA in the presence of copolymer matrices composed of either A-vinylpyrrolidone and acrylamide or A--vi nyl pyrrol idone and styrene. The polymerization rate reaches a maximum in the vicinity of AA to VP ratio equal to one for the VP/AAm matrix. This maximum in the polymerization rate is most pronounced in the presence of copolymer with the highest content of VP. When the hydrophilic acrylamide is replaced with the more hydrophobic styrene monomer in the copolymer matrix, the observed maximum in AA polymerization rate occurred at a lower than equimolar ratio of AA to VP. The hydrophilic groups of VP were interacting with the hydrophobic nucleus consisting of the styrene units in the VP/St copolymer, and were thus unable to participate in the formation of the complex unlike in the case of VP/AAm copolymer matrix. 

Copolymerization, on the other hand, is very easy with maleic anhydride. It copolymerizes by a free-radical reaction with a wide variety of monomers and many of the copolymers are perfectly alternating. This tendency of MA to form alternating copolymers derives from the participation of a donor-acceptor complex formed by the two reacting monomers. The term is used to describe... 

Further evidence for the participation of the charge transfer complex in these terpolymerization systems was obtained by dilution experiments (12). The effect of dilution with various solvents on the AN content of the terpolymer is shown in Figure 4. Except for chloroform, the AN content of the copolymer increases with dilution. This suggests a higher order dependence of monomer consumption on monomer concentration... 

The virtually unlimited availability of CO renders it extremely appealing as a monomer in copolymerization reactions. Herrmann and co-workers [21] reported the copolymerization of CO and ethene using dicationic chelating carbene complexes of palladium(II) (Fig. 2). Given the large molecular weight of the obtained copolymer and the relatively modest TONs they observed, the authors postulated that only a small percentage of palladium pre-catalyst actually participates in the production of copolymer. 

Iwatsuki and Yamashita (46, 48, 50, 52) have provided evidence for the participation of a charge transfer complex in the formation of alternating copolymers from the free radical copolymerization of p-dioxene or vinyl ethers with maleic anhydride. Terpolymerization of the monomer pairs which form alternating copolymers with a third monomer which had little interaction with either monomer of the pair, indicated that the polymerization was actually a copolymerization of the third monomer with the complex (45, 47, 51, 52). Similarly, copolymerization kinetics have been found to be applicable to the free radical polymerization of ternary mixtures of sulfur dioxide, an electron donor monomer, and an electron acceptor monomer (25, 44, 61, 88), as well as sulfur dioxide and two electron donor monomers (42, 80). 

Although the Diels-Alder reaction of a conjugated diene, such as butadiene or isoprene, with maleic anhydride, has been known to yield tetrahydrophthalic anhydride, it has recently been shown (81, 85) that alternating copolymers are prepared under the influence of ionizing radiation (81) or free radical initiators (81, 85). The participation of the charge transfer complex as a common intermediate in both adduct... 

The participation of Diels-Alder type intermediates in polymerization was considered by Hill et ah (26) in 1939 as a result of the elucidation of the structures of the butadiene homopolymer and the butadiene-methyl methacrylate copolymer resulting from thermal polymerization in emulsion. The considerable amount of alternating 1,4 and 1,2 structures in the homopolymer and the predominantly 1,4 structure of the butadiene in the copolymer which contained more than 50% alternating units of butadiene and methyl methacrylate led to the proposal that the reaction proceeded through a Diels-Alder dimer complex or activated complex. Chain initiation involved a thermal reaction in which the activated com-... 

Owing to the insolubility of the polar monomer-zinc chloride complex, handling of the reaction mixture is difficult. However, a second patent (73) describes an improved process wherein the polar monomer is utilized in considerable excess with no effect on the polar monomer content of the resulting copolymer, in contrast to the results from a conventional free radical polymerization. This is consistent with the mechanism shown in Reaction 23 and essentially eliminates the participation of a polar monomer-complexed polar monomer complex. 

A reflex with chemical shift at 8 = 0.35 ppm typical of -CH2-CH2-group is observed in ll NMR spectrum of copolymer 1 (Table 3). This indicates that polyaddition proceeds pursuant to the Farmer rule. A duplet centered at 8=1.06 ppm, corresponded to methyl protons in =CH-CH3 group, is also observed in the spectrum. Based on the ratio of intensities, it was concluded [20, 21] that polyaddition partly proceeds by the Markovnikov mechanism (6 -8%). A complex multiplet with chemical shift at 8=5.6 - 6.2 ppm typical of vinyl protons not entered polyaddition reaction, and a singlet for =Si-H protons with chemical shift at 8 = 4.4 ppm, not participated in the reaction, too, were observed in the spectra. 

Cationic polymerizations induced by thermally and photochemically latent N-benzyl and IV-alkoxy pyridinium salts, respectively, are reviewed. IV-Benzyl pyridinium salts with a wide range of substituents of phenyl, benzylic carbon and pyridine moiety act as thermally latent catalysts to initiate the cationic polymerization of various monomers. Their initiation activities were evaluated with the emphasis on the structure-activity relationship. The mechanisms of photoinitiation by direct and indirect sensitization of IV-alkoxy pyridinium salts are presented. The indirect action can be based on electron transfer reactions between pyridinium salt and (a) photochemically generated free radicals, (b) photoexcited sensitizer, and (c) electron rich compounds in the photoexcited charge transfer complexes. IV-Alkoxy pyridinium salts also participate in ascorbate assisted redox reactions to generate reactive species capable of initiating cationic polymerization. The application of pyridinium salts to the synthesis of block copolymers of monomers polymerizable with different mechanisms are described. 

In a large number of investigations the possibility of the formation of polymer-polymer complexes with the participation of alternating and random copolymers has been shown. So, using the viscometric method58, the complex formation of iso-PMAA and methyl methacrylate and methacrylic add copolymer has been reported. The stability of the stereocomplex decreases with increasing add content in the copolymer. 

As is seen from Table 4, the complexes containing an alternating copolymer as one of the interacting components are rich in the nonionic component (PVP or PEG). Probably part of the PVP(PEG) groups does not participate in the complex formation, due both to the increase of the distance between the active groups in the copolymer and the steric difficulties caused by the bulky anhydride groups. 

The rate of polymerization of polar monomers, for example, maleic anhydride, acrylonitrile, or methyl methacrylate, can be enhanced by coraplexing them with a metal halide (zinc or vanadium chloride) or an organoaluminum halide (ethyl aluminum sesqui-chloride). These complexed monomers participate in a one-electron transfer reaction with either an uncomplexed monomer or another electron-donor monomer, for example, olefin, diene, or styrene, and thus form alternating copolymers (11) with free-radical initiators. An alternating styrene/acrylonitrile copolymer (12) has been prepared by free-radical initiation of equimolar mixtures of the monomers in the presence of nitrile-coraplexing agents such as aluminum alkyls. 

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