Interpenetrating polymer networks (IPNs) of polystyrene-polybutadiene-polystyrene (SBS) block copolymers and polystyrene (PS) were prepared using sequential network formation with the polybutadiene (PB) of the SBS crosslinked thermally and the styrene network formed thermally or by ??-radiation. The use of ??-radiation to cure the added PS network at room temperature successfully avoided thermal degradation of the butadiene segments within the SBS which had been observed in earlier studies. Both linear SBS and radial SB4 IPNs were studied to compare the influence of linear or branched block copolymers on the IPN morphology. The molecular morphology was examined using a suite of techniques including thermal analysis (DSC and DMA), transmission electron microscopy (TEM), atomic force microscopy (AFM) and smallangle X-ray and neutron scattering (SAXS and SANS). The primary SBS/SB4 network morphology was found to dominate the IPN morphology with the secondary styrene network limited to selectively swelling the PS domains. The linear SBS IPNs displayed a more ordered morphology than the radial SB4 IPNs, and this morphology was investigated in pseudo three-dimensions by sectioning samples in two perpendicular directions. The morphology was found to be consistent with thermally formed systems prepared in previous studies, and contained styrenic domains of 20-50 nm within a continuous butadiene matrix. The weight of evidence suggested that the lamella structure dominated the linear SBS IPNs and a cylindrical structure for the radial SB4 IPNs. Maximum values of tensile strength and elongation at break (20 MPa and 140% respectively) were observed in samples with a styrene cure ??-radiation dose of 200 kGy. The SANS analysis of these polymer systems was expanded to investigate the thermal formation of the added PS network in real time. Time-resolved SANS allowed the development of nanostructures in the bulk samples to be measured, and compared to previous time-independent TEM studies on thin sections. The formation of the styrene network was most noticeably observed in a linear SBS IPN system, in which an increase in long-range order was observed and attributed to movement of styrene monomer into the styrenic domains and sharpening of the phase boundaries between the PS and the PB regions.
| Identifer | oai:union.ndltd.org:ADTP/215664 |
| Date | January 2005 |
| Creators | Markotsis, Martin G., School of Chemical Engineering & Industrial Chemistry, UNSW |
| Publisher | Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Martin G. Markotsis, http://unsworks.unsw.edu.au/copyright |
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