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 AUREMN meeting; 2015

Asociación de Usuarios de Resonancia Magnética de Brasil

     The contribution of defectsto mechanical relaxation in model polymer networks is studied by time-domain(TD) NMR temperature dependent experiments. Slow dynamics of network defectscan be directly monitored by NMR spin relaxation of protons as a function oftemperature in PDMS model networks. The contribution of pendant and freepolymer chains to elasticity were described by arm retraction, reptation andcontour length fluctuations processes.      A set of model polymernetworks were synthesized with different concentration of linear (guest)soluble polymer chains. Transverse relaxation decay data were acquired usingcompensated CPMG pulse sequence with MLEV-4 pulse phase cycling.1,2 The fraction of elastically active material in the networks can beestimated by fitting the NMR data, and accounts for not only the fraction ofelastic chains but also the fractions of unrelaxed soluble and pendant material.3 The fraction of transiently trapped entanglements dependson the dynamics of the pendant and free chains, which can be probed by changingthe sample temperature. The dynamics of each type of defect is simulated byconsidering their contribution to the relaxation modulus as a function of time,which are described by Milner and McLeish for free chains, and a modifiedversion of Curro`s relaxation theory for pendant material proposed by Vega etal..4,5Time-temperature superposition principle was applied to NMR data. Finally,network structure parameters were determined.