Radical polymerization asymmetric

The low efficiency of the steric control of the propagation, in radical polymerization, by the asymmetric groups present in the monomer has been indirectly confirmed by the synthesis of copolymers containing carbon atoms that are asymmetric owing to the different chemical nature of all the 4 groups directly bound to each of them. 

The substituted carbon atoms in the polymer chain are asymmetric. Stereoregular polymers are produced if all these carbon atoms have the same configuiation (all d or all I) or if the d and 1 configurations occur alternately pronounced stereo-regularity is seldom achieved in radical polymerizations except perhaps at very low temperatures. When dienes are polymerized by a radical mechanism, the resulting polymers contain several distinct types of monomer unit, thus butadiene can give rise to -CH2 C(CH CH2)-, -CH CH CH CH2- cis, and -CH CH.CH CH2- trans. 

Asymmetric induction to main-chain chiral centers can also be achieved by the radical polymerization of sorbates having chiral ester groups [80,81] and 1,3-butadiene-l-carboxylic acid complexed with optically active amines [82,83]. 

The strategy is impressively simple the phthalazine derivative 15 can readily be prepared from quinine in one step. Being a divinyl derivative, it can be submitted as a cross-linking unit in the radical polymerization of methyl methacrylate (MMA) or 2-hydroxy methacrylate (HEMA). Thereby, an immobilized (DHQ-PHAL) derivative 16 is obtained, which is suited for the asymmetric dihydroxylation of frantr-stilbene (>99 % ee) and ( )-cinnamic acid methyl ester (>99 % ee. Table 1). The insoluble catalyst can be recovered by simple filtration, and its repeated... 

Preparation of Polymeric Catalyst. A c inindAcrylonitrile copolymer has been successfully synthesized via radical polymerization using Azobisisobutyronitrile (AIBN) as initiator (eq 15). The polymer can be prepared such that the vinyl group is the connecting site and the amino alcohol portion can either be free or protected. These copolymers are thermally stable and are soluble in polar aprotic solvents such as DMF and DMSO, but insoluble in common organic solvents. Preliminary experiments have shown that these copolymers can be used as asymmetric catalysts. ... 

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... 

Free-Radical Polymerization of Asymmetric Vinyl Monomers. . 156... 

One important application of Lewis acid to asymmetric radical reactions is in the control of tacticity in free radical polymerizations. Recently, Porter [38] showed that Sc(OTf)3 modulates the polymerization of oxazolidinone acrylamides to produce highly isotactic copolymers (Scheme 12). The same study described homopolymerizations in which the m/r dyad ratio was dependent on the reaction temperature. 

I Ls containing a chiral cation ora chiral anion have been reported and are thought to play an important role for asymmetric synthesis or for chiral separation (6-9) [32-37]. A chiral IL based on l-((-)-menthoxycarbonylmethylene)-3-mefhylimida-zolium) hexafluorophosphate has been applied in stereospecific free-radical polymerization of vinyl monomers. The asymmetric environment of chiral ILs is believed to have some effect on the stereostructure of polymers [38]. 

This application of DEC chromophores requires synthesis of asymmetrically functionalized chromophores as illustrated in Fig. 1. In this example, the hydroxyl terminated end of the chromophore is capable of condensation polymerization reactions while the acrylate functionality is capable of undergoing free radical polymerization. In Fig. 2, we illustrate schematically the stepwise synthesis of a highly crosslinked polymer matrix where both ends of the chromophore are coupled to polymer main chains. The first step in the scheme shown is accomplished by free radical polymerization yielding a soluble and processible polymer with flexible pendant chromophore groups. This polymer is spin cast into an optical quality film (0.5-1.5 micron thickness) and is heated near the glass transition temperature, poled and subsequently crosslinked by a thermal crosslinking reaction involving... 

DBPAMA) ([a]365+74° using (+)-NMT [a]36s -53° using (-)-NMT) was obtained. The specific rotation values suggest that the helical-sense excess (ee) may be -30-40%. In contrast to the asymmetric radical polymerization of PDBSMA, the optically active product was completely soluble in this case. 

Recent work by several research groups has shown that supercritical fluids can be superior to other solvents for several chemical processes. For example, DeSimone has demonstrated the ability of supercritical CO2 to replace Freons in the free radical polymerization of fluorinatkl acrylate monomers. 34) Noyori has shown that significant rate enhancements can be achieved in supercritical carbon dioxide relative to other solvents for the homogeneous catalytic hydrogenation of carbon dioxide to either formic acid or its derivatives in the presence of triethylamine or triethylamine/methanol respectively, (equation 1). (55-57) As discussed below, we have recently demonstrated that improved enantioselectivities can be achieved in supercritical carbon dioxide for the catalytic asymmetric hydrogenation of several enamides. 5 8)... 

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