Abstract
Due to the growing concerns over the use of organic solvents for spray coatings, carbon dioxide has been used as a supercritical fluid for studies of spray coatings in this project. The aim of this project was to synthesise copolymers of methyl methacrylate and poly(dimethylsiloxane) monomethacrylate (PDMS-mMA) macromonomer, for use as dispersion stabilisers to re-disperse preformed poly(methyl methacrylate) (PMMA) in supercritical carbon dioxide (scCO2) that can subsequently be used in spray coatings. The PDMS-mMA macromonomers of different molar masses, 10, 5, and 2 kg have been successful in synthesising copolymer stabilisers (PDMS-mMA/PMMA) in which concentrations of the macromonomers was varied from 5 wt%-50 wt% (wrt monomer) in the copolymer. PDMS-mMA/PMMA have also been used to carry out stirred and non-stirred polymerisation in SCCO2. The products from the polymerisations have been analysed by scanning electron microscopy (SEM) and 1H NMR spectroscopy. Non-stirred polymerisations with stabilisers containing a molar mass of 10 kg at 0.5% stabiliser concentration and 5% macromonomer concentration in the copolymer stabiliser have proved to be most efficient. Commercial stabilisers such as Krytox (157 FSL, DuPont) and Galden (HT55, Ausimont) and PDMS-mMA/PMMA have been used as dispersion stabiliser for re-dispersion of preformed PMMA in SCCO2. Re-dispersed PMMA particles containing the stabilisers Krytox and Galden were analysed by 13C NMR, 19F NMR spectroscopy and EDX analyses. Products containing PDMS-mMA/PMMA stabilisers were analysed by 1H NMR and 29Si NMR spectroscopy and EDX analyses. This re-dispersion process was not successful with any of the stabilisers, but some stabilisers have been successful in coating the PMMA particles. Macromonomer grafting was carried out in SCCO2 with preformed PMMA and PDMS-mMA macromonomer with a molar mass of 10 kg by free radical polymerisation where AIBN was used as an initiator.1H NMR analysis was performed to analyse the products from this process, which shows the presence of the proton containing silicon group (Si-CH3) in products containing 10% AIBN, 50% PDMS-mMA (wt% PMMA) and 5% AIBN, 50% PDMS-mMA (wt% PMMA).