| Autor: |
Yu.Ya. Gotlib, M.I. Lifshits, V. A. Shevelev |
| Rok vydání: |
1975 |
| Předmět: |
|
| Zdroj: |
Polymer Science U.S.S.R.. 17:2132-2142 |
| ISSN: |
0032-3950 |
| DOI: |
10.1016/0032-3950(75)90112-4 |
| Popis: |
Studies were made of the temperature relations of proton magnetic relaxation times T1 and T2 at a resonant frequency of 18·6 Mc/s for solutions of PMMA fractions (M = 3×104−1·7×106) in proton free solvents with polymer concentration of 5–80 mole%. It was shown that the minimum on the curve of the temperature dependence T1 observed in PMMA solutions with polymer concentrations of 5–30% is due to superposition of two coexisting ranges of relaxation caused by the motion of the main chain and the natural rotation of α-methyl groups. The effective activation energy of the relaxation process, of which the correlation times determine T2, increases with a reduction of temperature from 4–5 to 8–10 kcal/mole. Time T1 is independent of M in the range of M values studied. Starting from a polymer concentration of 10% time T2 depends on M at high temperatures; the higher the concentration, the more marked is this dependence and on lowering temperature, dependence on M ceases. An assumption is proposed, according to which an increase in the effective activation energy for T2 and a weakening of the dependence of T2 on M are due to intensification of interaction between the chains as temperature decreases. The nuclear intermolecular effect for high polymer concentrations is ∼20% of the total effect, i.e. relaxation is basically due to intramolecular nuclear interactions. Molecular mobility decreases with an increase of viscosity and a deterioration of the thermodynamic quality of the solvent. The effect of solvent properties on T2 is stronger than on T1. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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