Multiple Quantum and Dipolar Correlation Effect NMR Studies of Cross-Linking in Elastomer Systems

摘要

Physical and chemical aging of filled polydimethylsiloxane- polydimphylsiloxane (PDMS- PDPS) copolymer foams iscurrently being studied to assess engineering performance degradation and to provide fundamental understanding of aging mechanisms for predictive modeling. Nuclear Magnetic Resonance (NMR) spectroscopy has been shown to be a powerful method for the characterization of polymer aging mechanisms. NMR offers the ability to assess speciation changes and changes in motional properties caused by chemical and physical agingmechanisms. In fact, the measurement of 'H transverse relaxation times (T2) of aged silica filled PDMS/PDPS copolymers have been shown to be sensitive to bulk changes in motional processes caused by aging mechanisms such as radiation exposure. However, more subtle aging mechanisms cause only small changes in bulk relaxation times and conclusive interpretation of the NMR data can be difficult. 'H T2 studies of surveillance return samples, for example, have suffered from such an insensitivity to age and no direct correlation between age and relaxation time have been detected, mirroring solvent swelling results.