Supramolecular association of acid-terminated polydimethylsiloxanes. IV. NMR investigation of hydrogen bonding interactions and apparent molecular weight in the bulk state

Carbon-13 spin-lattice relaxation time measurements were used to probe the existence of hydrogen bonding interactions in bulk for a diacid-terminated oligosiloxane at temperatures well above its glass transition and melting temperatures. The behavior of the corresponding monoacid-terminated oligosiloxane, which can form dimers only, diester-terminated oligosiloxane, which cannot undergo any hydrogen bonding interactions, and two higher molecular weight covalent polymers, which serve as models for the supramolecular polymer, was also studied. The degree of association of the diacid-terminated oligosiloxane was estimated by investigating its transverse relaxation derived from 1H NMR and comparing the results thus obtained with data from a series of polydimethylsiloxane samples with different molecular weights.