Chain copolymerization cyclopolymerization

Cyclopolymerization of bifunctional monomers is an effective method of chirality induction. Optically active vinyl homopolymers and copolymers have been synthesized by using optically active distyrenic monomers (41) based on a readily removable chiral template moiety. Free-radical copolymerization of 41a with styrene and removal of the chiral template moiety from the obtained copolymer led to polystyrene, which showed optical activity ([Oc]365 -0.5-3.5°) (Scheme 11.6) [84], The optical activity was explained in terms of chiral (S,S)-diad units generated in the polymer chain through cyclopolymerization of 41a [85], Several different bifunctional monomers have been synthesized and used for this type of copolymerization [86-90]. 

In attempts to copolymerize various diallyl esters with styrene it was found that the reactivity was quite low. Further, the rate and degree of copolymerization was roughly inversely related to the concentration of diallyl ester. With increasing styrene levels, the tendency toward cyclopolymerization decreased [47]. In effect, the diallyl esters act as chain-transfer agents for the polymerization of styrene. Table V gives the chain-transfer constants and the reactivity ratios for the copolymerization with styrene. 

Miilhaupt and coworkers studied homo- and copolymerizations of 1,5-HD with ethylene and styrene using the MAO-activated constrained geometry catalyst 8. This catalyst system afforded very high 1,5-HD incorporation (reaching 52 mol%) with randomly distributed cis- and transcyclopentane rings in the homo- and copolymer backbones. The ratio of vinyl side chains to cyclic rings was controlled by the 1,5-HD concentration, where low concentrations of 1,5-HD promoted cyclopolymerization. 

Copolymerization of pent-1,4-diene or hex-1,5-diene with CO results in the cyclopolymerization to produce copolymers including cyclopentanone or cyclohexanone in the middle of the chain (Scheme 8). 

Al-Phenyl-iV-allylmethacrylamide (23) gives a polymer with a five-membered ring structure with true asymmetric centers in the main chain by free-radical cyclopolymerization [63]. When the polymerization is carried out in the presence of SnCl4/(-)-menthol, the resulting polymer was optically active ([a]] -5.6°). Chiral induction was also observed in the copolymerization of 23 with MMA. Cationic cyclopolymerization of 24 using a ZnClJ 10-camphorsulfonic acid (25) initiator system gives an optically active polymer having a 1,3-dioxane structure in the main chain([a]435-17°)[64]. 

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