ISSN:
1022-1352
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The temperature dependences of the associated fraction of PVC units were determined from measurements of integrated intensities of high-resolution 1H NMR spectra in thermoreversible gels of PVC and chemically modified PVC in diethyl oxalate (DEO) and dibutyl oxalate (DBO). The existence of two types of associates of different thermal stability, completely melting at 55°C and 90-130°C, was indicated by these measurements. While the associated fraction and the thermal stability of the associates increase with increasing polymer concentration, a significant reduction in the associated fraction is observed in samples where ≈5% of chlorine atoms are replaced by phenylthio groups or hydrogen. Because the chemical modification takes places only on isotactic and heterotactic triads, this result confirms the important role of these sequences in interactions associated with the gel formation. In DBO gels, the values of the associated fraction are lower than in DEO gels. A complete parallelism was found for temperature dependences of the associated fraction and viscoelastic storage modulus. From measurements of selective and nonselective 1H spin-lattice relaxation times of the solvent, the existence of PVC/DEO complex was confirmed. The life-time of bound solvent molecules which could bridge different chains is shorter than 1 s. Both polymer/solvent complex and polymer-polymer interactions seem to act as physical crosslinks.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
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