Investigation of the properties of fully reacted unstoichiometric polydimethylsiloxane networks and their extracted network fractions

Abstract

We investigated the linear dynamic response of a series of fully reacted unstoichiometric polydimethylsiloxane (PDMS) networks and of the two corresponding network fractions namely the sol and the washed network. The sol and the washed network were separated by a simple extraction process. This way it was possible to obtain rheological data from the washed network without interference from the sol fraction, and furthermore from the sol fraction without interference from the elastic washed network. When the stoichiometry increased towards perfectly reacted networks and beyond we observed harder networks both qualitatively and by rheology and the properties of the two fractions became more and more different. At the gel point, the sol fraction and the washed network have more or less identical properties which our data also shows. The storage and loss moduli, G ′ and G ′′ , were analysed with the gel equation as proposed by Winter and Chambon(1986;1987). We observed that one of the investigated samples which before the swelling experiment did not show any elastic response gave an elastic washed network after swelling, this was verified by analysis with the gel equation. We also calculated the weight fraction of the sol fraction by using the theory by Villar et al. (1996) and compared these with experimentally found values.

Novel cross-linkers for PDMS networks for controlled and well distributed grafting of functionalities by click chemistry

“…The swelling experiments performed are therefore more suitable for comparison with previously performed PDMS swelling experiments. 30,31 Optimized PDMS elastomers usually have gel fractions of 95-97% whereas stoichiometrical PDMS networks usually have gel fractions around 90%. This can be explained by the optimized PDMS elastomers having a stoichiometry of 1.1-1.4 which means that the cross-linker is in excess and that all cross-linker sites do not need to react thus reducing steric hindrance.…”

Silicone elastomers with high dielectric permittivity and high dielectric breakdown strength based on tunable functionalized copolymers

“…Viscous losses (tan δ) remain low for all films expect for those prepared with copolymers with the highest concentration of 1-ethynyl-4-nitrobenzene (Co-1c and Co-2c). For these films the viscous losses increased six-fold, indicating increased damping behavior, which is partly or fully due to the larger fractions of extractable substructures 30 .…”

Control of PDMS crosslinking by encapsulating a hydride crosslinker in a PMMA microcapsule

“…Moving towards the situation at 120 C, the temperature was higher than the T g of the PMMA (T g ¼ 100 C), 13 resulting in the soening of the PMMA shell in the microcapsule and the release of HMS-301. Consequently, this release of HMS-301 reacted with V35 in the presence of a catalyst, yielding a PDMS network.…”

“…Since the inactive species were identical for all samples, the difference in soluble fraction between the MP10H10C + V35 network and referenced network arises from different degrees of imperfections in the networks. 13 The PMMA is not distinguishable soluble in heptane and is thus not washed out of the networks. The difference in the imperfections in the network could be explained as follows: Upon the heating of the mixture containing MP10H10C and V35, the HMS-301 diffused out from the microcapsule and reacted with V35, yielding crosslinked PDMS network around the microcapsule.…”

“…the perfection of the PDMS network. 11,[13][14][15][16] Thus, the inuence of stoichiometric imbalance on the equilibrium storage modulus will be investigated, in order to determine the optimum amount of microcapsules and sensitivity of the storage modulus on stoichiometric imbalance in controlled PDMS crosslinking reaction. This paper, which is devoted to studying the crosslinking reaction between a hydride crosslinker and a vinyl-terminated PDMS polymer controlled by releasing the hydride crosslinker from a PMMA shell, is divided into the following parts: in the rst part, we describe the preparation and the characterisation of a PMMA microcapsule containing a multifunctional methylhydrosiloxane-dimethylsiloxane copolymer crosslinker.…”