Poly(itaconate) esters as marine antifoulants
A series of fluorinated and non-fluorinated poly(mono- and diitoaconate)s and a perfluorinated acrylate, poly(2-(N-ethylperfluorooctanesulfanamido)ethyl acrylate) have been synthesised, by both solution and bulk chain growth polymerisation methods, characterised and some of their properties (thermal behaviour, surface energy and marine antifouling peformance) have been investigated. Chemical structures were confirmed by Gourier-transform infrared (FTIR) and nuclear magnetic resonance (1H & 13C NMR) spectroscopies, as well as mass spectrometry. Poly(itaconate)s prepared by solution chain growth polymerisation resulted in low average relative molecular mass (Mw <15000), whereas those prepared by bulk chain-growth polymerisation were of high average molecular mass (Mw ca 60000). The thermal degradation behaviour of polu(monoitaconate)s, Mwca60000, was dominated by dehydration/de-esterification reaction at ca 170 deg.C which yielded a poly(anhydride) structure. Poly(diitaconate)s Mwca 60000, were thermally stable up to ca 285 deg.C above which a chain-unzipping process resulted in the formation of monomer as the major degradation product. Glass transition temperatures (Tg) were not observed for poly(monotaconate)s; for poly(hexanoyl diitaconate) Tg was ca -18 deg.C whereas poly(1H,1H,2H,2H-perfluorodecanoyl diitaconate) exhibited two glass transition temperatures, attributed respectively to the relaxation of the alkyl side chain (ca 5 deg.C) and the overall polymer transition (ca 35 deg.C). Poly(hexadecanoyl diitaconate) was the only dditaconate to exhibit a melting endotherm. Surface energy contributions were calculated using the surface tension component (Good-Girafalco-Fowkes) theory. Recently-advanced and recently-receded contact angle measurements were performed at 25.0 + or - 0.2 deg.C for drops of water, diiodomethane and ethylene glycol on the itaconates that could be formed into films. Both recently-advanced and recently-retarded contact angles demonstrated the time-dependency of the wetting behaviour for drops of water, attributed to the slow, stepwise absorption of water by the polymer. Contact angles for drops of diiodomethane and ethylene glycol remained constant over time. Poly(1H,1H,2H,2H-perfluorodecanoyl diitaconate), PI-2, possessed the most hydrophobic surface (initial recently-advanced water contact angle: ca 120 degrees), whereas the least hydrophobic material was poly(hexadecanoyl diitaconate), PH-2; initial recently-advanced contact angle: ca 96 deg. Poly(1H,1H,2H,2H-perfluorodecanoyl diitaconate), PI-2, exhibited the lowest surface energy (advanced ca 7 mJm-2; receded: mean 9.7 mJm-2), whereas poly(hexadecanoyl diitaconate), PH-2 had the highest (advanced: ca 31-37 mJ m-2; receded 39.7 mJm-2). Poly(dodecanoyl monoitaconate), PA-5/6 exhibited surface energies of ca 22 mJ m-2 (advanced) and ca 31 mJ m-2 (receded). The low surface energy of poly(1H,1H,2H,2H-perfluorodecanoyl diitaconate), PI-2 is attributed to both the high hydrophobicity of the surface and the presence of pendent fluorocarbon side chains, which prevent the interaction of diiodomethane molecules with the polymer backbone. The relatively high surface energy of poly(hecadecanoyl diitaconate), PI-2, is due to the lower contact angles measured for this material. Increases in the basic contribution over time and its larger value relative to corresponding acidic contributions are attributed to the uptake of water by the polymer; hydrogen bonding with oxygen atoms of the ester linking group may provide the driving force behind the observed phenomenon. Antifouling performances were evaluated in seawater exposure trials over two fouling seasons. The sequence of fouling events was similar in both seasons: initial settlement by barnacles and algae follwed by settlement of tunicates. In the 1995 exposure trial polymers prepared by solution chain-growth polymerisation as well as a selection of commercial materials were evaluated. All samples exhibited almost no resistance to marine fouling. Suggested contributory factors to their poor performance was their low average relative molecular mass (Mw <15000), a variability of sample coatings or the ineffectiveness of the samples against the inhibition/prevention of settlement/attachment by marine fouling organisms. In the 1996 trial, high average molecular mass poly(itaconate) films prepared by bulk chain-growth polymerisation reactions were exposed. Poly(dodecanoyl monoitaconate)(PA-6), poly(1H,1H,2H,2H-perfluorodecanoyl monoitaconate) (PE-6) and poly(hexadecanoyl diitaconate) (PH-2) exhibited slight resistance to marine fouling, with resistances for these materials after seven months of exposure, of 13%, 18% and 34% respectively (control surfaces had fouling resistances of -5%). Areas free from coverage by fouling organisms were observed on all samples. The overall low resistance of poly(itaconate) can most likely be attributed to the absorption of water by these polymer films.