Chain conformation alternating copolymers

PolyCACN) has a rigid chain structure yet can form excimers with alternate units along the chain (8), or by stacking in a helical conformation. Excimer formation has been reported for alternate copolymers of ACN with styrene (9) and for ACN with maleic anhydride CIO). The situation is different for 2-vinylnaphthalene since alternating copolymers of 2VN with methyl methacrylate or methacrylic acid did not form excimers, yet random copolymers of the same systems showed excimer fluorescence Cll). Only random copolymers of ACN were prepared in this work. 

Homonuclear correlation via the nuclear Overhauser effect (NOESY). The NOESY experiment correlates peaks by means of the nuclear Overhauser enhancement and so identifies pairs of nuclei which are sufficiently close together in space to relax by their dipole-dipole interaction. This technique is not so applicable in determining stereochemical assignments as those described previously, but may be extremely useful in determining the chain conformation as demonstrated by Mirau et al. in a study of the alternating copolymer of styrene and methyl methacrylate [45] (see chapter 4). 

Alternating copolymers of acrylates and styrenes have, in effect, two rotational states per main chain bond. The splittings in the fine structure of the methoxy protons of methyl acrylate and methyl methacrylate repeat units is shown to arise from the anisotropic aromatic shielding, as modified by conformational probabilities. When C shifts are treated, the y effect between carbon atoms 3 bonds apart is usually deemed the only factor sensitive to conformation, though other possible terms have been considered. ... 

Alginates are linear copolymers of non-branched P-n-mannuronic acid (M) and a-L-guluronic acid (G) linked by (1 4) glyco-sidic bonds (4-176). Residues of mannuronic acid are in the conformation, while residues of guluronic acid are in the conformation. The chain contains alternating sections of different... 

Fig, 6. Chain conformation and symmetry elements for a) Isotactic alternate copolymer of ethylene and bute ne-2. b) Polymethylene,... 

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