Elastic Properties of Nonstoichiometric Reacted PDMS Networks

Abstract

The influence of stoichiometry on the elastic modulus of eight-functional end-linked poly-(dimethylsiloxane) (PDMS) networks was investigated by extensional rheometry with extensions up to more than 100%, and the stress-strain relation was found to be almost linearsa characteristic property for a network structure with an eight-functional cross-linker. The experimental data were compared to a stochastic model taking into account entanglements and to Monte Carlo simulations. The Mooney-Rivlin model was furthermore used to fit the data, and the dependency of C 1 and C2 parameters on the stoichiometric ratio was investigated in order to clarify especially the influence of trapped entanglements acting either as chemical cross-links or as sliding links. It was found that including a locking factor dividing trapped entanglements into locked entanglements and slip-links could explain our data obtained for the Mooney-Rivlin constants. It was furthermore found that trapped entanglements dominate when there is an excess of cross-linker, ensuring that all long difunctional DMS chains are bound to the infinite network in both ends.

Low moduli elastomers with low viscous dissipation

“…Finally, the pre-premixes are mixed in different mass ratios corresponding to different stoichiometric imbalances. The stoichiometric imbalance, r, is defined as the ratio of the reactive groups of the 70 PDMS (-CH=CH2) to the reactive groups of the crosslinker (-Si-H) 1 .…”

“…Most model elastomers are prepared by an end-linking process using a crosslinker with a certain functionality f and a linear polymer 30 with functional groups in both ends, and the resulting networks are so-called unimodal networks where unimodal refers to the number of polymers with different average molecular weights (in the unimodal case one polymer is used). The resulting network contains different structures, namely 1) the elastically active 35 network chains, 2) the dangling chains and substructures, and 3) the so-called sol fraction where the latter structure is not chemically attached to the network but rather acts as a solvent 1,2 . The dangling chains and the sol fractions are contributing to the softness of the network and result in higher extensibility but 40 lower the mechanical breakdown strength significantly.…”

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

“…The chemicals were used as received. The networks were prepared in two rounds with use Larsen et al(2003) The networks were made by mixing predetermined amounts of mixture A and B thoroughly and leave the mixture to cure for 12 hours. Mixture A and B were combined in different ratios resulting in networks with different r-values.…”

Front Matter: Volume 8340

“…The mechanical properties of polymer networks may be tuned by changing the molecular weight of the polymer chains and by varying the stoichiometric imbalance given by the molar ratio between the reactive groups of the crosslinker and the vinyl groups of the PDMS [8][9][10][11][12][13] :…”