ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
1H NMR spectra of alternating copolymers of methyl acrylate with styrene, methyl acrylate with α-methylstyrene, and methyl methacrylate with α-methylstyrene show triplet splittings at the methoxyl protons regions, which apparently reflect the cotacticity of triad sequences having a (meth)acrylate unit in the center. The two intervals between two neighboring peaks of the triplet are nearly equivalent for each alternating copolymer, whereas the absolute value of the splitting width is significantly different from one alternating copolymer to another. A theoretical interpretation is given for this observation by calculating the chemical shifts of the methoxyl protons in combination with a conformational analysis of the copolymers. The chemical shift of the protons in meso or racemic type dyad sequence is assigned by averaging the shieldings over all the preferred conformations for the dyad and is accumulated to give the shifts in triad sequences: iso = meso + meso, hetero = meso + racemic, syndio = racemic + racemic. The cotacticity-dependent splittings thus calculated are quantitatively in accordance with the observed spectra and discussed in terms of conformational variation of the copolymers depending on the presence of α-methyl group(s) in neither, either, or both of the monomeric unit(s).
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1980.021810414
