Synthesis and mechanical properties of semi-flexible polymer networks

We have synthesized a range of polymer networks containing varying amounts of the flexible molecule 1,3-divinyltetramethyldisiloxane (B-2) and the rig id mesogenic molecule, di-(4 oxyallyl-(methyl)-phenyl)4-terephthalate. Netw orks were prepared using hydrosilylation chemistry, by crosslinking the vin yl terminated B-2 and the mesogen, with the tetrafunctional crosslinker tet rakis(dimethylsiloxy) silane (A(4)). The elastic modulus (G(e)) increased w ith the incorporation of the rigid mesogen into the network structure, and also increased as the ratio of silane hydrogens (Si-H) to vinyl groups in t he preparation was increased from 1 to 1.5, Complementary swelling experime nts in toluene showed the soluble fraction (w(sol)) decreased with an incre ase in this ratio. Also, a maximum value of the polymer volume fraction, up silon(2), was obtained with the stoichiometry r = 1,5. Network properties w ere analyzed using the Flory-Rehner expression from which values of the ave rage interaction parameter, chi, were extracted. (C) 1998 Published by Else vier Science Ltd. All rights reserved.