Han Goossens (J.G.P.Goossens@) tue.nl
The basic research theme is structuring of polymers on different length scales for ultimate properties. During synthesis, properties can be varied by controlling the polymer chain structure, but in some cases post-modification steps are more useful, either for improving mechanical properties or processing characteristics. The interplay between phase separation processes and chemistry is investigated to control morphologies for specific properties.
Current work includes:
Intrinsic properties of both amorphous and semi-crystalline polymers not experienced macroscopically due to localization effects. A number of approaches are used to prepare systems which promote delocalization of the stress, primarily focusing on the role of cavitation and the transition from crazing to shear yielding, based on self-assembly of block copolymers, either starting from monomer-block copolymer solutions followed by in-situ polymerization or by reactive coupling of block copolymers with the matrix in the melt.
Modification in confined spaces. In solid-state modification reactions occur below the melting temperature of the polymer to be modified, either in the amorphous phase or in the pores of porous, nascent reactor powders. Non-random molecular structures are prepared, in which crystallizable blocks are retained, while other material properties can be enhanced. This approach has been combined with a sol-gel technique to obtain well-dispersed, nano-sized silica particles with controllable adhesion, of which the morphology is stable after processing.
When polyolefins are used in combination with polar functional groups, microphase separated materials can be obtained. On modifying these functional groups with different cross-linking methods, ranging from ionic interactions, hydrogen bonding, and reversible covalent bonds, interesting properties can be achieved while maintaining processability. The focus has been on randomly grafted polar groups in amorphous polymers, but the strategy was also extended to semi-crystalline polymers, modified in the solid-state to induce a non-random distribution of the functional groups.
Since control of polymer morphology is a recurrent theme, insight in and ways to intervene morphology development is a prerequisite to make further progress. Therefore, time-resolved scattering techniques (SAXS and WAXD) using synchrotron facilities and small-angle light scattering (SALS), have been developed and used extensively to probe structure development at different length scales during polymerization, flow, or deformation in-situ. Therefore, special sample environments have been developed in-house to be used at the European Synchrotron Radiation Facility (ESRF), Grenoble, France . This is in many cases complemented with studies using vibrational spectroscopic techniques, viz. FTIR and Raman spectroscopy, for molecular information during in-situ polymerization, flow, or deformation.