Nuclear magnetic resonance radical polymerization

A-carboxyanhydride neocarzinostatin n-hydroxysuccinimide A-isopropylacrylamide nuclear magnetic resonance nitroxide-mediated radical polymerization nuclear Overhauser effect nitrilotriacetic acid... 

The proportion of head-to-head structures can be considerable in some cases. For example, in free-radical-polymerized poly(vinylidene fluoride), -fOH2—CF2 fi, there are about 10-12% of such links according to nuclear magnetic resonance measurements ( H and F). The proportion is as high as 6-10% in poly(vinyl fluoride). Admittedly, these physical methods... 

In radical polymerizations, the mean sequence length can be calculated, given certain assumptions (cf. Section 22.1.4). As a rule, it is not directly obtainable from experiments. However, in many copolymers, the fraction /ab of all the ab groups (i.e., a bonded to b and b to a) can be determined by nuclear magnetic resonance spectroscopy / b is defined by... 

The inhibiting effect of radical acceptors, however, suggests that polymerization proceeds by a radical mechanism. The yield of polymer from such reactions depends on the tendency of the different monomers to be polymerized by ionic and radical catalysts. The reactivity ratio on grinding for styrene plus methyl methacrylate is similar to that for peroxy-initiated polymerization. Nuclear magnetic resonance data, however, show a different stereochemical configuration for the copolymers [200]. 

Lutz J-F, Matyjaszewski K. Nuclear magnetic resonance monitoring of chain-end functionahty in the atom transfer radical polymerization of styrene. J Polym Sci A Polym Chem 2005 43 897-910. 

Many radical polymerizations have been examined from the point of view of establishing the stereosequence distribution. For most systems, it is claimed that the tacticity is predictable within experimental error by Bemoullian statistics (i.e., by the single parameter P m] - see Section 3.04.3.1.1). It should be noted that, in some studies, deviations of 5-10% in expected and measured nuclear magnetic resonance (NMR) peak intensities have been ascribed to experimental error. Such error is sufficient to hide significant departures from Bemoullian statistics. ... 

The cyclic structure of the polymers [31] was substantiated by infrared and chemical evidence. The fact that they were soluble (acetone, methyl ethyl ketone, acetic acid, dioxane) confirms their linear character. The polymerizations were also initiated by other radical initiators [peroxides, azobis(iso-butyronitrile)]. Carbinols with aliphatic, cycloaliphatic, and aromatic substituents were polymerized (104,106,109, 111, 113,119-121). Cyclic polymers are also obtained from their acetates and ethers (107, 113). Nuclear magnetic resonance has been employed to study transitions in these polymers (75, 76). Polymers possessing molecular weights of over 1,000,000 resulted in some cases. The kinetics of polymerization (11-14) were studied (111, 112). Copolymerization with vinyl monomers (108, 145) yielded linear, soluble polymers that contained cyclic structures derived from the vinylethynyl carbinol. 

In the free radical polymerization proeess, conducted usually at elevated temperatures, these effects are insignificant and the reaction usually leads to the formation of atactic polymer only. However, in some cases, like, for example, in free radical polymerization of methyl methacrylate at temperature below 0°C one obtains a crystalline polymer with syndiotactic structure, as it was proven by the high resolution nuclear magnetic resonance spectroscopy. These results confirm the rule that according to which the degree of stereoregularity decreases with increasing temperature. 

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