Pendant Chain dynamics en model PDMS networks probed by spin diffusion experiments.

R.H. ACOSTA; M.B. FRANZONI; M.A. VILLAR; E.M. VALLÉS; D. A. VEGA; G.A. MONTI

Angra dos Reis

Congreso; 13th Nuclear Magnetic Resonance Users Meeting; 2011

Over the last 5 decades the dynamic response of entangled polymer melts has been an outstanding problem in polymer science. Most of the viscoelastic and diffusive properties of polymer melts and concentrated polymer solutions are profoundly influenced by topological interactions. The most successful model to deal with topological constrains is the tube model. According to this model, the topological confinement exerted on a given molecule by the surrounding media can be modeled as a hypothetical tube that severely suppress the motion perpendicular to the tube’s local axis, but permits the diffusion along the tube. Polydimethylsiloxane (PDMS) networks are ideal systems to probe chain dynamics, however, in the context of spin diffusion experiments no work has been carried out to our knowledge to the moment. The usual approach for determination of domain size probed by interaction between different structures does not apply as the whole network, entangled and dangling chains have the same chemical structure. This means that the whole sample has the same spectroscopic components. In this work we propose to use the differences between transverse relaxation times to generate the both the generation of the magnetization gradient and the determination of the spin diffusion. Two different experiments are proposed in order to obtain information on the dynamics of the pendant chains, that is, chains that are chemically attached to the network by one end while the second end is free or physically entangled with the network [1,2]. In the first experiment the pendant chains are selected by the use of a dipolar filter (DF) [3] and left to equilibrate with the network. The second approach is to select the network chains by the application of a Double Quantum Filter (DQF) [3-5] that will leave magnetization only on those chains that have a very well defined residual dipolar coupling, which arises from the restricted mobility of the chains that form the network. Detection is performed with a CPMG sequence at 0.5 T with a Bruker Minispec mq20.