Polymeric gels. NMR study of elementary chain swelling. Effect of trapped topological constraints

J.P. Cohen-Addad , M. Domard , G. Lorentz , J. Herz

This work aims at studying the progressive swelling process of three polydimethylsiloxane covalent gels, synthetized at several volume fractions, νc ; two good solvents (chloroform and heptane) and a theta-solvent (bromocyclohexane) were used as swelling agents. i) The macroscopic swelling was found to obey a simple addition law of volumes of solvent and polymer. ii) The transverse magnetic relaxation process of protons linked to PDMS chains is shown to reflect a progressive swelling process of elementary chains occurring according to two well defined steps. The first one (1 < q < qd ~ 3), is a progressive desinterspersion of chains; monomeric units are replaced by solvent molecules; the relaxation rate δ was shown to obey a superposition property : δ/ν c ∝ (qν5/8c)-0.6±0.05 ; in the second step (qd < q ≲ 12), δ was found to obey another superposition property : δ ∝ q2/3 ν 5/3c. In the swelling ratio range 1 < q ≤ qd and in the presence of good solvents, elementary chains have Gaussian properties; these are conveniently identified using a theta-solvent; these properties progressively disappear (q > qd) and an excluded volume effect arises ; this is fully observed on gels at equilibrium with a liquid solvent. Superposition properties are interpreted from a basic formula describing the transfer of localization of NMR properties from a local space-scale to a semi-local one.

Mots clés: gels; magnetic relaxation; nuclear magnetic resonance; polymer solutions; swelling

Domaines: Articles anciens

J.P. Cohen-Addad, M. Domard, G. Lorentz, J. Herz. Polymeric gels. NMR study of elementary chain swelling. Effect of trapped topological constraints. Journal de Physique, 1984, 45 (3), pp.575-586. ⟨10.1051/jphys:01984004503057500⟩. ⟨jpa-00209788⟩