INVESTIGATION OF NETWORKS WITH LOW CONCENTRATION OF PENDANT CHAINS BY DOUBLE QUANTUM NMR

R. H. ACOSTA; GUSTAVO MONTI; M.A. VILLAR; E.M. VALLÉS

Córdoba, Argentina

Congreso; Archipol05, III Argentina-Chilenean Polymer Symposium; 2005

Mechanical properties of a polymeric material can be directly related to its structure. In the particular case of polymer networks, chemical or physical cross-linking points gave distinctive characteristics to these materials such as high elongation, better thermal stability and insolubility. Model silicone networks have been extensively studied in order to explain the influence of molecular structure on mechanical properties. Free chains and pendant chains are the more common defects in real networks. In particular, pendant chains have a strong influence on the viscoelastic properties of these networks, changing considerably the spectrum of relaxation times. In this work we will try to probe the ability of NMR to detect the influence of defects on the polymer network.  Proton residual dipolar interacctions measured by NMR provide information about the structure and molecular dynamics in soft solids like elastomers. Therefore changes in the structure and molecular dynamic can be investigated via changes induced in the residual dipolar couplings by cross-link density, the presence of fillers, the action of mechanical deformation forces, and other defects. One approach to model-free access to the residual dipolar couplings and dynamical order parameters uses multiple-quantum (MQ) buildup and decay curves (Voda, 2005).