Triphenylmethyl methacrylate conformational asymmetric polymerization

Another result of great importance—the conformational asymmetric polymerization of triphenylmethyl methacrylate realized in Osaka (223, 364, 365)— has already been discussed in Sect. IV-C. The polymerization was carried out in the presence of the complex butyllithium-sparteine or butyllithium-6-ben-zylsparteine. The use of benzylsparteine as cocatalyst leads to a completely soluble low molecular weight polymer with optical activity [a]o around 340° its structure was ascertained by conversion into (optically inactive) isotactic poly(methyl methacrylate). To the best of my knowledge this is the first example of an asymmetric synthesis in which the chirality of the product derives finom hindered rotation around carbon-carbon single bonds. 

Vinyl polymers with a stable helical conformation are obtained from methacrylates with a bulky side group by isotactic specific anionic or radical polymerization.13,34 This type of polymer was first synthesized by asymmetric anionic polymerization (helix-sense-selective polymerization) of triphenylmethyl methacrylate (TrMA, 5) using a complex of n-BuLi with (—( sparteine (Sp, 6).13 Although, as discussed... 

Optically active oligomers of methyl methacrylate were obtained by the asymmetric polymerization of triphenylmethyl methacrylate, followed by the substitution of methyl for triphenylmethyl, and subsequent GPC separation275 and optical resolution.276 Detailed study on the stereostructure of the oligomer made it possible to discuss precisely the mechanism of polymerization leading to the formation of polymer with one-handed helical conformation. 

Some isotactic polymers such as polychloral and poly(triphenylmethyl methacrylate)289 are known to exist only in purely helical conformation. The helical structure of the polymers is rigid even in solution, owing to the bulkiness of the side-groups. This has been demonstrated by the measurement of high optical activity of the polymers prepared by asymmetric polymerizations the optical activity is based on a one-handed helical conformation of the polymer chain. 

We have been studying the helix-sense-selective polymerization of bulky methacrylates such as triphenylmethyl methacrylate (TrMA), diphenyl-2-pyridylmethyl methacrylate (D2PyMA)phenyl-2-pyridyl-o- and m-tolylmethyl methacrylates (PPyoTMA and PPymTMA), and (S)-(-)-diphenyl(1-methylpyrrolidin-2-yl)methyl methacrylate (DMPMA) with chiral anionic initiators. In these polymerizations, optically active polymers with one-handed helical structure have been obtained and some of the polymers exhibited characteristic conformational transition in solution. In the present paper, we describe helix-sense-selective polymerization of 1 -phenyidibenzosuberyl methacrylate (PDBSMA), diphenyl-3-pyridylmethyl methacrylate (D3PyMA) and phenyl[bis(2-pyridyl)]methyl methacrylate (PB2PyMA) by means of chiral anionic initiators and conformational transition of the obtained polymers. Asymmetric radical polymerization of PDBSMA is also reported because this monomer can also afford a helical, highly isotactic polymer by radical mechanism. 

---