Copolymerization chemoselectivity

Alternating polymers can be produced by taking advantage of the functional group tolerance, high activity, and chemoselectivity of 3. Copolymerization of cycloalkenes such as cyclooctene or cyclopentene with diacrylates affords regular alternating polymers (Eq. 15) [32]. Based on the different reactivity of the two monomers (class 1 and class 2, respectively) the more... 

The use of Lewis acids to impart chemoselectivity and stereoselectivity to free-radical polymerization and copolymerization is well documented [670]. Recent progress in radical reactions in organic synthesis has revealed the importance of Lewis acids in selective transformations [671,672]. Lewis acids have also been found to enhance the reactivity both of radical acceptors [673-675] and of radicals themselves [676], thus increasing the efficiency of radical reactions. 

Chemoselectivity of copolymerization (e. g., perfect alternation) with these olefins is governed by similar factors to those discussed for ethylene/CO copolymerization, although some differences are noteworthy. Whereas fi-H elimination does not take place to a significant extent with ethylene/CO copolymerization, this termination pathway can play a significant role in copolymerization with higher olefins. Another difference is that, under certain circumstances and with certain ligands, the polymers can be formed in a polyspiroketal structure (Structure 7), isomeric with polyketones [34, 35]. 

The role of back-biting coordination in governing 4-MPD polymerization chemoselectivity was subsequently confirmed using ethylene/4-MPD copolymerization In this case, a considerable amount of 1,4-enchained 4-MPD units were detected adjacent to ethylene units along the polymer chain. This suggests that the absence of a double bond in the penultimate unit of the growing chain (i.e., after ethylene insertion), and thus the impossibility of back-biting coordination, causes a decrease in chemoselectivity for 4-MPD incorporation. 

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