A series of end-linked polymer networks with varying contents of linear guest chains were investigated through swelling and time-domain NMR temperature dependent experiments. Taking advantage of the thermorheological simplicity of polydimethylsiloxane polymers, time temperature superposition (TTS) was employed to expand the characteristic time scales of NMR exploration by about 2 orders of magnitude. A comparison between swelling data and tube model predictions reveals that NMR captures the dominant features of the equilibrium and dynamic properties of defects trapped in slightly cross-linked, entanglement-dominated polymer networks. As high-temperature experiments ensures a complete relaxation of the guest linear chains on the millisecond time scale of the NMR experiments, an accurate description of the network architecture can be provided. Contents of guest chains determined by NMR were found to agree within a 1 wt % accuracy with data of swelling experiments.

We analyze the dynamic response of end-linked poly(dimethylsiloxane) networks containing entangled unattached guest linear polymers. Upon increasing the content of unattached guest polymers there is an increasing dissipation and a reduction in the network elasticity. It was found that the width of the relaxation spectrum is nearly insensitive to the content of guest chains, indicating that the network structure is not affected by the presence of these defects and that the effective number of entanglements associated to guest chains is independent of the equilibrium elastic modulus of the networks.The inhibition of the constraints release mechanism for molecules trapped in polymer networks have enormous consequences on the dynamic response, producing a dramatic slowing down in the relaxational dynamics of defects. The presence of different structures of defects in polymer networks is physically unavoidable, even under optimum reaction conditions. Here we found that the slow dynamics of soluble branched structures or dangling molecules can easily hide the contribution of linear unattached molecules. (C) 2015 Elsevier Ltd. All rights reserved.

The structure and viscoelastic response of polymer networks are highly sensitive to the presence of pendant chains. These imperfections, that are unavoidable produced during a cross-linking reaction, reduce the cross-linking density and affect the damping response of elastomers. In this work the dynamics of pendant chains present in a cross-linked network is investigated using end-linked poly(dimethyl-siloxane) networks with well defined structure. For this purpose, model networks containing 10 and 20 wt% of two different monodisperse pendant chains with molecular weights well above the critical entanglement molecular weight and some of their blends were prepared. It was found that, within this range of concentration of pendant chains, the long-time dynamic response of the networks was nearly insensitive to the content of pendant material but deeply influenced by the average molar mass of these defects. While the equilibrium behavior of the networks can be well described by a mean field theory for rubber elasticity, the long time relaxational dynamics can be rationalized in terms of the Pearson-Helfand picture for the arm retraction process. Within this theoretical picture, the dynamics can be explained in terms of the molecular architecture of the network, the Rouse time and the weight average molar mass of the pendant material. (C) 2014 Elsevier Ltd. All rights reserved.