Copolymer optically active

Metallocenes are very versatile catalysts for the production of polyolefins, polystyrene and copolymers. Some polymers such as syndiotaetic polypropene, syndiotactic polystyrene, cycloolefin copolymers, optically active oligomers, and polymethylenecycloalkenes can be produced only by metallocene catalysts. It is possible to tailor the microstructure of polymers by changing the ligand structure of the metallocene. The effect and influence of the ligands can more and more be predicted and understood by molecular modeling and other calculations. 

The brief presents a systematic study of synthesis of optically active polymers. It discusses in detail about the syntheses of three different types of optically active polymers from helical polymers, dendronized polymers and other types of polymeric compounds. The brief also explains the syntheses of optically active azoaromatic and carbazole containing azoaromatic polymers and copolymers optically active benzodithiophene and optically active porphyrin derivatives. The final chapter of the brief discusses different properties of optically active polymers such as nonlinear optical properties, chiroptical properties, vapochromic behavior, absorption and emission properties, fabrication and photochromic properties. The intrinsic details of different properties of optically active polymers will be useful for researchers and industry personnel, who are actively engaged in application oriented investigations. 

The H and C NMR spectra of azo compounds incorporated into monomers and polymers have been measured. " Chiral methacrylic polymers containing azobenzene chromophore, epoxy-based polymers functionalized with tricyanivinylphenylazo chromophores, 4-vinylazobenzene and homo- and copolymers, microstructure of lra j-4-acrylooyloxyazo-benzene/methyl methacrylate copolymers, optically active poly[(5)-4-(2-methacryloyloxypropanoyloxy)azobenzene] and polyetherurethane pendant with azo dye by 7 T-substitution have been studied. 

The enantioselectivity was greatly improved by the copolymerization with 7- or 13-membered non-substituted lactone using lipase CA catalyst (Scheme 8) the ee value reached ca. 70% in the copolymerization of (3-BL with DDL. ft is to be noted that in the case of lipase CA catalyst, the (5 )-isomer was preferentially reacted to give the (5 )-enriched optically active copolymer. The lipase CA-catalyzed copolymerization of 8-caprolactone (6-membered) with DDL enan-tioselectively proceeded, yielding the (/ )-enriched optically active polyester with ee of 76%. 

Another significant cooperativity effect in preferential helical screw sense optically active copolymers is the majority rule phenomenon.18bl8q In this case, the screw sense of a helical main chain with unequal proportions of opposite chirality enantiopure chiral side groups is controlled by the enantiomeric excess only. Since this phenomenon was first reported from poly-a-olefins made of vinyl co-monomers bearing nonenantiopure chiral moieties by Green et al.8b and Pino et al.,16b this majority rule has been established in... 

Additionally, copolymers of 30-37 containing 20% enantiopure chiral silane units (see Chart 4.6) are optically active helical polymers which obey the sergeants-and-soldiers principle, as shown in Figure 4.18.29g Interestingly, from the observation of the CD sign in the phenyl region, the arrangement of phenyl... 

A series of optically active poly alkyl(phenyl)silane derivative copolymers with different chiral molar composition 44 and 45, are shown in Chart 4.7, along with homopolymers poly(methyl(phenyl)silane) (42) and poly(n-hexyl(m-tolyl)silane) (43). 

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

Chart 4.9 Chemical structure of optically active poly(diarylsilane) copolymers. 

Wullf and Hohn recently described several new stereochemical results (93). They reported the synthesis of a copolymer between a substituted styrene (M ) and methyl methaciylate (M2) having, at least in part, regular. . . M,M M2M MiM2. . . sequences. Polymerization involves the use of a chiral template to which the styrene monomer is loosely bound. After elimination of the template, the polymer shows notable optical activity that must be ascribed to the presence of a chiral stmcture similar to that shown in 53 (here and in other formulas methylene groups are omitted when unnecessaiy for stereochemical information). This constitutes the first stereoregular macromolecular compound having a three monomer unit periodicity. 

The trick used in asyrmnetric inclusion polymerization is to perform the reaction in a rigid and chiral environment. With more specific reference to chirality transmission, the choice between the two extreme hypotheses, influence of the starting radical (which is chiral because it comes from a PHTP molecule), or influence of the chirality of the channel (in which the monomers and the growing chain are included), was made in favor of the second by means of an experiment of block copolymerization. This reaction was conducted so as to interpose between the starting chiral radical and the chiral polypentadiene block a long nonchiral polymer block (formed of isoprene units) (352), 93. The iso-prene-pentadiene block copolymer so obtained is still optically active and the... 

Copolymers between an achiral monomer and an enantiomer of a stracturally similar monomer sometimes have optical activity higher than that derived by a simple additive mle (376). Thus, in the copolymer between 4-methylpentene and (5)-4-methylhexene the monomer units of the first type are forced to assume a conformation analogous to those of the second and contribute to the optical rotation of the polymer. 

Copolymerization of a monomer having two styrene moieties attached to a chiral template molecule with a comonomer e.g., methyl methacrylate) gives copolymers with strong optical activity after removal of the template molecules. In this case styrene diads of an S,S configuration separated from other styrene diads by comonomeric units are responsible for the optical activity. 

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],... 

Preparation of addition polymers having the oxolene (dihydrofuran) functionality can be envisioned to occur in two possible ways (Scheme 13). Both, in fact, have been observed (77MI11102). Whereas furan (53) or its derivatives do not homopolymerize under free radical conditions, 1 1 alternating copolymers possessing the 1,4-structure are produced with maleic anhydride (50). Intermediate formation of a CT complex between monomers (50) and (53) is believed to be necessary before polymerization can occur. On the other hand, cationic polymerization is quite facile. The outcome is straightforward with benzo[f>]furan derivatives, producing 1,2-polymers. Optically active poly(benzofurans) are formed when the cationic polymerizations are conducted in the presence of a chiral anion. 

The failure in separating in fractions possessing optical activity of opposite sign the stereoregular polymers of racemic 5-methyl-l-heptene, polymerized in the presence of the same catalyst as that used to prepare polymers from racemic 3-methyl-l-pentene and 4-methyl-1-hexene (75), might be an indication that, in order to obtain prevailingly (R) and (S) separable polymers instead of random copolymers from racemic vinyl monomers, the asymmetric carbon atom of the monomer must be in a or in / position with respect to the double bond. 

In fact, the copolymers of methacrylic acid with maleic anhydride (14) and the copolymers of vinyl alcohol with maleic anhydride (127) obtained respectively from optically active (l-methyl-benzyl)-methacrylate or (l-methyl-benzyl)-vinyl-ether and maleic anhydride, were optically active, but their rotatory power was rather small. 

The first success was achieved when optically active (chiral) monomeric units were combined with a nematic LC polymer 105,123,143,144). The approach was based on the idea that a cholesteric mesophase may actually be realized as a helical nematic structure. Then by chemical binding of chiral and mesogenic units into a chain, accomplished by copolymerization or copolycondensation (in case of linear polymers) of nematogenic and optically active compounds, it was found feasible to twist a nematic mesophase and obtain copolymers of cholesteric type (Table 13). 

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