Study of pendant chain dynamics in model PDMS networks

FLORENCIA CAMPISE; ENRIQUE VALLÉS; DANIEL VEGA; MARCELO VILLAR; RODOLFO ACOSTA; GUSTAVO MONTI

Rosario

Congreso; Taller fronteras en Resonancia Magnética: de los materiales a los sistemas biológicos; 2013

Regarding polymeric materials, it is important to be able to predict its mechanical, viscoelastic and diffusive properties. This is achieved by understanding the physical-chemical interaction of the polymeric chains which are profoundly influenced by topological interactions. We intend to study chain dynamics as well as the contribution of network defects to such dynamics, the effects of physical entanglements and chemical crosslinks on microstuctural and viscoelastic properties of polymer networks by means of proton relaxation NMR experiments in model tri and tetra functional polydimethylsiloxane (PDMS) networks with low concentrations of pendant chains of different molecular weight. In this work, we have studied the entanglement dynamics of the chains that form the network applying a CPMG pulse sequence at different temperatures. For the analysis of the data we have considered that for the proton NMR time scale, the physical entanglements behave as crosslink points. It could be observed that the contribution of non relaxed pendant material to the NMR signal decreases with temperature and responds to an Arrhenius process enabling the determination of activation energies. The activation energies obtained are in the same range of the obtained in a previous work in which we monitored the magnetization transfer via Nuclear Overhauser Effect (NOE) between pendant and elastic chains. Besides the decrease in the NMR data shows a similar behavior to the rheological data of the relaxation modulus G(t), which would imply that the origin of both behaviors is the same. On the other hand, we present some results of Double Quantum Coherence experiments which might contribute to the analysis of the previous results. This is an ongoing experiment.