Structure in model PDMS networks probed by monitoring defect dynamics via TD- NMR experiments

F. CAMPISE; L. ROTH; R. H. ACOSTA; M. A. VILLAR; E. M. VALLES; G. A. MONTI; D. A. VEGA

Angra dos Reis

Congreso; 15th Nuclear Magnetic Resonance Users Meeting; 2015

Asociación de Usuarios de Resonancia Magnética de Brasil

A set of model polymer networks were synthesized with different concentration of linear (guest) soluble polymer chains. Transverse relaxation decay data were acquired using compensated CPMG pulse sequence with MLEV-4 pulse phase cycling.1,2 The fraction of elastically active material in the networks can be estimated by fitting the NMR, and accounts for not only the fraction of elastic chains but also the fractions of unrelaxed soluble and pendant material.3 The fraction of transiently trapped entanglements depends on the dynamics of the pendant and free chains, which can be probed by changing the sample temperature. The dynamics of each type of defect is simulated by considering their contribution to the relaxation modulus as a function of time, which are described by Milner and McLeish for free chains, and a modified version of Curro`s relaxation theory for pendant material proposed by Vega et al..4,5 Time-temperature superposition principle was applied to NMR data. Finally, network structure parameters were determined. The contribution of defects to mechanical relaxation in model polymer networks is studied by time-domain (TD) NMR temperature dependent experiments. Slow dynamics of network defects can be directly monitored by NMR spin relaxation of protons as a function of temperature in PDMS model networks. The contribution of pendant and free polymer chains to elasticity were described by arm retraction, reptation and contour length fluctuations processes. From the model proposed the fraction of elastic, pendant and free chains composing the polymer system can be determined.References:1. T. Guillon, D. Baker, M. Conradi; Journal of Magnetic Resonance. 1969, 89, 1990, 479-484.2. K. Saalwächter, B. Herrero, M. López-Machado; Macromolecules. 2005, 38, 4040-4042.3. D. Vega, M. Villar, E. Vallés, C. Steren, G. Monti; Macromolecules. 2001, 34, 283-288.4. S. Milner, T. McLeish; Physical Review Letters. 1998, 81, 725-728.5. D. Vega, L. Gómez, L. E. Roth, J. A. Ressia, M. Villar, E. Vallés; Physical Review Letters. 2005, 95, 166002.