Supramolecular Polyurethanes and their Composites: Properties and Engineering Performance

A major challenge in the development of more sustainable polymeric materials for industrial manufacturing processes (such as coating or molding) for commodity products is how to ameliorate the need to manipulate the material at elevated temperatures (so it can flow and be shaped as a liquid) whilst maintaining desirable mechanical properties of the polymer (e.g. strength and toughness) at room temperature in the finished article. Processes such as injection molding or hot-melt adhesive application require elevated temperatures (often greater than 200 degrees Celsius) and thus represent capital-intensive, energy-consuming, production technologies which in turn inflate the cost and carbon-footprint of the final product. The ability to manipulate polymers at relatively modest, and controllable, elevated temperatures (sub 100 degrees Celsius) would represent significant savings of energy and cost. This proposal describes a route to novel supramolecular materials that can be processed in this manner and will also offer recyclable characteristics. The project will investigate the physical and mechanical properties of new supramolecular polyurethanes and their composite materials in order to generate a new generation of adhesives and surface coatings. Supramolecular polymers are relatively short chain organic materials that are held together by many non-covalent interactions such as hydrogen bonding, to afford polymers of far higher molecular mass and, as a consequence, these systems exhibit many solid-state characteristics common to 'traditional' covalent bonded polymers (e.g. strength and stiffness). However, as a consequence of the relatively weak non-covalent interactions that hold the supramolecular polymers together, these materials can be dissociated easily into their individual contributing components by the application of a suitable (relatively modest) stimulus - e.g. heat or light.
In this project we will also harness the thermal cycling potential of supramolecular polyurethanes in conjunction with the enhanced strength and toughness offered by fibrous and particulate fillers by developing novel supramolecular polymer composites. Such materials are potentially attractive as easily-applied adhesives and tough, corrosion resistant and healable coatings for metals and electronic components. The field of supramolecular composites is in its infancy and has yet to gain significant coverage in the literature and thus this proposal is very timely. Furthermore, the well-defined chemistry of the supramolecular polyurethanes and the composites formed from them will be used in conjunction with mechanical measurements to construct a solid-melt constitutive model parameterized in terms of the chemical structure of the supramolecular polyurethanes. In doing so, a predictive tool will be generated, suitable for design of further supramolecular materials, targeted at specific thermo-mechanical properties.

The objective of the project is to underpin the development of a new generation of self-assembling thermoreversible polymers and polymer composites that will find application in the field of adaptive coatings and adhesives, pharmaceutical dressings and healable materials, with potential to benefit the UK economy by aiding the improvement of a range of products, creating wealth in a range of markets. The new materials will offer significant advantages over current adhesive and coatings technologies in terms of reduced production costs and increased performance. One identifiable product type that will benefit is that of coatings designed to protect delicate devices, for example electronics in hostile environments. Here the property of self-healing of the supramolecular polyurethanes will be especially valuable: it will mean that damage can be repaired without replacement of the entire coating. The project will facilitate this outcome by including a study of the development of mechanical integrity of interfaces between layers of the PUs, and using the results to inform and guide design of the chemical architectures. Another product type to benefit will be pressure-sensitive adhesives. Here success in-use will hinge on the mechanical performance of the adhesives, especially under demanding load applications, such as in impact situations. The aim of the applicants in these activities is to achieve novel chemical structures optimised for their impact in various market sectors. A specific objective during the project will be to develop the capability to model thermorheological and solid-state mechanical responses of the supramolecular polymers and composites based on them. The purpose is to facilitate the further development of these materials in industry, to meet the needs of particular products. Patentable discoveries that emerge will be exploited by the University of Reading Research and Enterprise development team office, and Isis Innovation at Oxford University, in order to protect and commercialize these findings, and thereby to make the knowledge widely available to industry. In particular, the project team will also promote the research in the local cluster of polymer-based companies in the Thames Valley through existing extensive contacts (for example, to contacts at potential beneficiary companies such as Henkel Adhesives and Akzo-Nobel Paints, both located at Slough, Berkshire and Qinetiq, Farnborough). To help the project achieve its potential industrial impact, these and other companies will be encouraged to participate in project review meetings held during the project, and to attend the two half-day Showcase Meeting to be held at Oxford near to the end of the project, to discuss the research outcomes, potential for exploitation, and any follow-on knowledge-transfer activities. In addition to generating publications in high impact journals using results from this project, the applicants will present their research at national and international symposia and will use these opportunities to forge new links with other companies with a view to commercial uptake of the supramolecular polyurethanes. In addition, via collaboration with the Reading KTP office and the Materials KTN network, the applicants will seek to collaborate with SMEs who need new adhesive and coatings technologies.