Donor-acceptor type copolymerization

Peculiarities of Copolymerization of Donor-Acceptor Type MCMs.145... 

Owing to the versatile nature of the random copolymerization-based approach involving terpolymers, it could be readily extended to other conjugated polymeric systems, either upon optimizing the side-chain ratio or the donor-acceptor type to achieve significantly improved performance and highly tunable morphology in PSCs. 

The second type of nonideal models takes into account the possible formation of donor-acceptor complexes between monomers. Essentially, along with individual entry of these latter into a polymer chain, the possibility arises for their addition to this chain as a binary complex. A theoretical analysis of copolymerization in the framework of this model revealed (Korolev and Kuchanov, 1982) that the statistics of the succession of units in macromolecules is not Markovian even at fixed monomer mixture composition in a reactor. Nevertheless, an approach based on the "labeling-erasing" procedure has been developed (Kuchanov et al., 1984), enabling the calculation of any statistical characteristics of such non-Markovian copolymers. 

In fact, recent theoreticaP and experimental studies of small radical addition reactions indicate that charge separation does occur in the transition state when highly electrophilic and nucleophilic species are involved. It is also known that copolymerization of electron donor-acceptor monomer pairs are solvent sensitive, although this solvent effect has in the past been attributed to other causes, such as a Bootstrap effect (see Section 13.2.3.4). Examples of this type include the copolymerization of styrene with maleic anhydride and with acrylonitrile. Hence, in these systems, the variation in reactivity ratios with the solvent may (at least in part) be caused by the variation of the polarity of the solvent. In any case, this type of solvent effect cannot be discounted, and should thus be considered when analyzing the copolymerization data of systems involving strongly electrophilic and nucleophilic monomer pairs. 

The free-radical copolymerization of electron-donor olefinic monomers, including commercial allyl and vinyl ethers, was quite frequently reported and studied during last years and seems to present interesting potentialities for the synthesis of new bio-sourced polymers. However the only publication devoted to donor-acceptor copolymerization of monomers from biomass was focused on the photopolymerization of divi-nylfumarate, a bifunctional monomer bearing both type of double... 

In order to minimize the influence of irradiation conditions on possible side reactions, photochemical initiation has been conducted under mild conditions at room temperature, in the absence of oxygen, under low to medium intensity 365 nm irradiation, and in absence of short wavelength contribution. The reactivity of both types of olefinic monomers in copolymerization with acceptor monomers was studied. Several competing processes previously presented can possibly occur. For this reason, the consumption rate of each comonomer as well as the molecular weight of the final polymers were considered with attention and compared for both types of donor function. 

Using the CTC equilibrium constants (table in the appendix to this chapter) it is possible to calculate the true reactivity values for the CTC and for the neutral monomer. Raetzsch and coworkers used this procedure for the cyclopentene-MA and norbornene-MA copolymerizations with acrylonitrile (Table 10.23). The same technique was also used to determine the reactivity constants for several other donor-acceptor-neutral monomer polymerizations (Table 10.23). For the NVP-MA-methyl methacrylate system the true reactivity ratios show the NVP-MA CTC is about 3 000 times the reactivity of NVP and 600 times the reactivity of methyl methacrylate toward the propagating radical ending in methyl methylacrylate.Results of this type support the concept of alternating copolymerization of a CTC with neutral monomer. 

Zwitterionic Polymerizations. Zwitterionic intermediates also appear to be responsible for the spontaneous specific 1 1 copolymerizations of some acrylate-type monomers with cyclic nucleophilic species reported by Saegusa and his CO-workers.In many ways these resemble the spontaneous polymerizations of strong donor and acceptor vinyl moities mentioned earlier. s —... 

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. ... 

For the many alternating copolymer systems briefly discussed in this chapter, MA (Mi) is adjacent to some comonomer M2, and M2 is adjacent to Ml. The respective MiMi and M2M2 segments, resulting from Eqs. (16) and (19), are essentially nonexistent. Only the cross-propagation reactions, Eqs. (17) and (18), are observed. This very special copolymerization reaction occurs readily between the strong electron-acceptor MA and many different types of electron-donor monomers. 

Copolymerizations of the monodonor-diacceptor type, where MA is one of the acceptor monomers, have received much less study. 2-Chloroethyl vinyl ether (CEVE)-MA-fumaronitrile (FN) mixtures polymerize to give terpoly-mers containing 50% CEVE, the donor monomer. This system was examined by both the free propagation and complexomer mechanism concepts. ... 

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