UNIAXIAL ELONGATION OF DESWOLLEN POLYDIMETHYLSILOXANE NETWORKS WITH SUPERCOILED STRUCTURE

The mechanical properties of polydimethylsiloxane networks with a supe rcoiled structure, which are prepared by removing solvent from the net works crosslinked at low concentration, have been investigated. The fr actal dimension D of the supercoiled structure has been estimated to b e D = 2.5 from the dependence of stress on the elongation ratio lambda on the basis of the concept of the Pincus blob. The obtained D is lar ger than for Gaussian chains (D = 2), and smaller than for 'polymer ch ain in an array of obstacles' (PCAO) models (D = 3 or 4). The deswolle n network prepared at ca 9% has exhibited a remarkable high extensibil ity reaching lambda congruent to 18, as a result of the reduction of t he distance between network junctions on deswelling and the decrease o f trapped entanglements due to the low concentration at crosslinking. From comparison of the stress-elongation relationships in the deswolle n and preparation state, the deswollen networks with a supercoiled str ucture after a large elongation are expected to have the same topologi cal structure for the network chains as the original networks under el ongation. (C) 1997 Elsevier Science Ltd.