Menthyl-, polymerization

The polymerization of MMA has been shown to be subject to enantiomorphic site control when the Ci-symmetric a .va-lanthanocene complexes (196) and (197) are employed as initiators.463 When the (T)-neomenthyl catalyst (196) is used, highly isotactic PMMA is produced (94% mm at — 35 °C), whereas the (-)menthyl derived (197) affords syndiorich PMMA (73% rr at 25 °C). NMR statistical analysis suggests that conjugate addition of monomer competes with enolate isomerization processes, and the relative rate of the two pathways determines the tacticity. 

A special case of asymmetric enantiomer-differentiating polymerization is the isoselective copolymerization of optically active 3-methyl-1-pentene with racemic 3,7-dimethyl-1-octene by TiCl4 and diisobutylzinc [Ciardelli et al., 1969]. The copolymer is optically active with respect to both comonomer units as the incorporated optically active 3-methyl-l-pentene directs the preferential entry of only one enantiomer of the racemic monomer. The directing effect of a chiral center in one monomer unit on the second monomer, referred to as asymmetric induction, is also observed in radical and ionic copolymerizations. The radical copolymerization of optically active a-methylbenzyl methacrylate with maleic anhydride yields a copolymer that is optically active even after hydrolytic cleavage of the optically active a-methylbenzyl group from the polymer [Kurokawa and Minoura, 1979]. Similar results were obtained in the copolymerizations of mono- and di-/-menthyl fumarate and (—)-3-(P-styryloxy)menthane with styrene [Kurokawa et al., 1982],... 

In the case of the polymerization of methyl and butyl sorbates optical purity varies by varying the type of asymmetric complex used as catalyst. In non-systematic runs carried out with catalysts prepared from lithium-butyl and (—)-menthyl-ethyl-ether, [M]n increases... 

The most widely investigated optically active poly-acrylic-esters are the polymers of bomyl and menthyl acrylate and methacrylate in this case the monomers have been polymerized by radical polymerization using benzoyl-peroxide (135), A. I. B. N. (134, 135), y-rays (131, 135), U. V. rays (4) in the presence of benzoin (134), and by anionic polymerization using LiC4H9 (4, 135) or C6H5MgBr (134, 135) as catalyst. 

In the case of poly-menthyl-methacrylate, an evaluation of the type and degree of stereoregularity of the unfractionated polymers, obtained by different polymerization processes, has been made by converting poly-menthyl-methacrylate into polymethyl-methacrylate and then determining the stereoregularity of the methyl derivative thus obtained by N. M. R. analysis (135). 

In fact sorbic acid (XXXIII) has been transformed in menthyl-sorbate and the ester (XXXIV) has been polymerized (36) by butyl-lithium (Scheme 6) the prevalence of asymmetric carbon atoms having one of the possible configurations in the main chain of the polysorbic acid (XXXV), not isolated by the authors, has been proved by oxidizing the polymer and measuring the optical activity of the obtained methyl succinic acid, which actually was optically active and had an optical purity of 6% (36). 

Section II, 1. Theoretical aspects of asymmetric polymerization have been discussed by Fueno and Furdkawa [T. Fueno, J. Furukawa J. Polymer Sci., Part A, 2, 3681 (1964)]. 1-phenyl-l,3-butadiene has been polymerized using (R)-2-methyl-butyl-lithium or butyl-lithium complexed with menthyl-ethyl-ether, yielding optically active polymers with [a] f, referred to one monomeric unit, between +0.71 and —1.79. Optical rotation dispersion between 589 m u and 365 mft is normal and the Drude equation constant is comprised between 255 raft and 280 raft [A. D. Aliev, B. A. Krenisel, T. N. Fedoiova Vysokomol. Soed. 7, 1442 (1965)]. 

Diene Polymers Polymerization of a 1,3-diene yields a polymer having true asymmetric centers in the main chain and ozonolysis of the polymer gives a chiral diacid compound (12) whose analysis of optical purity discloses the extent of chiral induction in the polymerization (Scheme 11.2) [12,35-39], The polymerization of methyl and butyl sorbates methyl and butyl styrylacrylates and methyl, ethyl, butyl, and /-butyl 1,3-butadiene-1-carboxylates using (+)-2-methylbutyllithium, butyllithium/(-)-menthyl ethyl ether, butyllithium/menthoxy-Na, butyllithium/bomeoxy-Na, butyllithium/Ti((-)-menthoxy)4, and butyllithium/bomyl ethyl ether initiators [35-37] and that of 1,3-pentadiene in the presence of... 

Natta, Farina and Donati (123) found that optically active menthyl ethyl ether complexed with butyl lithium initiated asymmetric polymerization of optically inactive sorbic and /9-styryl acrylic esters. This strongly suggests that monomer orientation occurs during coordination with lithium by steric interaction with the asymmetric ligand. Similarly, asymmetric polymers were obtained using optically active 2-methyl-butyl lithium wherein the asymmetric polymer chain directed the monomer orientation. 

In order to investigate in more detail the relationships between structure and photoinitiation activity in the polymeric systems based on benzoin methyl ether moieties, poly(MBA) and copolymers of MBA with menthyl acrylate [poly(MBA-co-MtA)s] have also been checked as photoinitiators and compared with the homopolymer of ot-vinyloxymethylbenzoin methyl ether and its copolymers with menthyl vinyl ether [poly(MBVE) and poly(MBVE-co-MtVE)s, respectively] [61,84]. 

Scheme 103 Efficient synthesis of isopropenyl menthyl carbonate for the manufacture of polymeric menthol-release agents.

Cp TiCl2(OR) (Cp =Cp, C3H4CHMe2, G5H4CH2GH2OMe R = menthyl, fenchyl) have been synthesized, characterized, and tested as catalyst precursors for the syndiospecific polymerization of styrene.859... 

When an enantiopure menthyl-substituted monomer is first oligomerized, the resulting single-handed helical oligomer complex can be used as an enantioselective catalyst for the polymerization of achiral isocyanides. 

K10 montmorillonites exchanged with different cations, dried at 120°C or calcined at 550°C, are used as catalysts in Diels-Alder reactions of methyl and (-)-menthyl acrylates with cyclopentadiene. In general, calcined clays give rise to better conversions and selectivities. Zr(IV) and specially Ti(IV) clays display the best catalytic activities. However, the best asymmetric induction is achieved with Cr(lll) and Ca(ll) calcined clays. Clays containing easily reducible cations behave differently due to the cyclopentadiene polymerization via radical cations. 

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