Small angle neutron scattering and transmission electron microscopy studies of interpenetrating polymer networks from thermoplastic elastomers

Abstract

The formation of interpenetrating polymer networks (IPNs) may allow the production of materials with controlled morphologies and greater probability of synergistic property enhancement. IPNs were made by the in situ polymerisation/crosslinking of styrene in the dispersed styrene-rich phase of block copolymers with a crosslinked elastomeric matrix. Such networks when optimally prepared can combine stiffness with toughness. In this work the ratio of stiff and hard segments (controlled by styrene/isoprene or butadiene ratio) and morphology have been altered, and two families of block copolymers, with linear and radial structures are compared. The morphology of a brittle IPN is compared with a tough analogue, using small angle neutron scattering (SANS) and transmission electron microscopy (TEM). The former reveals substantial orientation in the drawn material, whereas the TEM shows similar structures for both. When radial thermoplastic elastomer IPNs are prepared, the structure is found to be isometric by SANS, as shown by intensity versus scattering vector, q, data for sample sections cut in two directions. The linear thermoplastic elastomer IPNs show quite different scattering, consistent with the rod-like dispersed phases previously established by TEM. The size of the hard, dispersed domains appears to be comparable using TEM and SANS, the latter giving a more sensitive indication of orientation. This possibly reflects the advantages of strong signal generation from a bulk sample, which has undergone little alteration during characterization.