Synthesis and Blend Behaviour of Multi-End Capped Polyethylene

Abstract

There is an ever-growing need for polymers with specific surface properties for the production of modified materials. Recently, extremely efficient polymer surface modification has been achieved by incorporating dendritically end functionalised polymers into blends, which combine sufficient mobility, with optimal functionality, to cause dramatic changes in surface properties. This method has significant advantages over traditional coating technologies in that no additional processing step is required.
It has already been established that blends of dendritically functionalised polymers have great potential in amorphous systems, but for commercial uptake similar results in semi-crystalline materials must be achieved. Polyethylene (PE) is the world’s most widely produced polymer, coming in many grades of molecular weight, branch content, and crystallinity. Semi-crystalline materials, such as PE possess excellent bulk properties, but their surfaces are notoriously difficult to functionalise except by harsh chemical treatments, or corona discharge methods. By bridging the gap between polymer science that is well understood, and polymer modification, will add value to commercially important materials. However to do this the effect that crystalline domains have on spontaneous surface segregation must be understood. Do crystalline regions exclude lower energy additives and drive them to the surface or are the additives trapped in the bulk?
In this study new synthetic methodologies were developed for the preparation of fluoro-end-capped polymers with well defined multiple hydrophobic groups, via anionic polymerisation, resulting in analogues of end-functionalised LLDPE. Physical properties have been characterised using a variety of techniques, namely ion beam analysis (IBA), contact angle measurements and several neutron scattering measurements, including neutron reflectivity (NR), small angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS) and studies proved surface enrichment with fluoro-chain ends.
This work has shown that blends of fluoro-polymer preferentially segregate to the air surface interface and the subsequent surface free energies of these blends were near that of polytetrafluoroethylene (measured surface energy was 8.95 mNm-2) with minimal amounts of fluorine. For example blends with 12 wt% (with respect to matrix polymer) fluorocarbon end-functionalised PE, which is equivalent to ~1% fluorocarbon, result in a measured surface energy of 8.44 mNm-2.