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Poly N-isopropylacrylamide and N-isopropylacrylamide / N-tert-butylacrylamide copolymer nanoparticles of 50 to 70 nm were prepared by free radical polymerisation. The particle sizes of the copolymer nanoparticles were measured in the test media MilliQ water, Algae Media, Daphnia Media and Microtox Diluent as a function of temperature. Whereas in MilliQ water the particle size was seen to decrease above the lower critical solution temperature of the thermoresponsive polymer, in the test media it was seen to increase significantly, indicative of aggregation. At the temperatures employed for the ecotoxicological studies all particles, with the exception of the 50:50copolymer existed as nanoparticles, however. The zeta potential of Poly N-isopropylacrylamide and N-isopropylacrylamide / N-tert-butylacrylamide copolymer particles measured in the different media was seen to correlate well with the ratio of N-tert-butylacrylamide monomer and therefore the hydrophobicity of the particles. Ecotoxicological studies of the copolymer nanoparticles was performed using four test species Vibrio fischeri, Pseudokirchneriella subcapitata, Daphnia magna, Thamnocephalus platyurus and the cytotoxicity of the 100% Poly N-isopropylacrylamide and 85:15 N-isopropylacrylamide / N-tert-butylacrylamide copolymer nanoparticles was evaluated using a salmonid cell line. Although no significant cytotoxicological response was recorded, significant ecotoxicological response was observed at particle concentrations of up to 1000 mg l-1. The ecotoxicological response was seen to correlate well with the ratio of N-tert-butylacrylamide monomer and therefore with the zeta potential of the nanoparticles. The toxic response in Daphnia Magna was seen to further correlate with the reduction in zeta potential pointing towards a contribution of secondary effects due to modification of the medium. No correlation with particle size was observed. The sensitivity of the test species was seen to vary depending on co-polymer composition. The relevance of the derived structure activity relationships is discussed.
Naha, P., Casy, A., Tenuta, T., Lynch, I., Dawson, K., Byrne, H., Davoren, M.: Preparation, Characterization of NIPAM and NIPAM/BAM copolymer nanoparticles and their acute toxicity testing using an aquatic test battery. Aquatic Toxicology, 92, 146-154. 2009.