Thin polymer films are important in many areas of biomaterials research, biomedical devices, and biological sensors. The accurate <i>in situ</i> measurement of multiple physicochemical properties of thin polymer films is critical in understanding biocompatibility, polymer function, and performance. In this work we demonstrate a facile spectroscopic methodology for accurately measuring the micro-polarity and hydrogen-bond donor/acceptor ability for a series of relatively hydrophilic thermoresponsive copolymers. The micro-polarity of the <i>N</i>-isopropylacrylamide (NIPAM) and <i>N</i>-tert-butylacrylamide (NtBA) co-polymers was evaluated by means of the <i>E</i><sub>T</sub>(30), α, β, and π* empirical solvatochromic polarity parameters. The data shows that increasing the NtBA fraction in the dry copolymer film reduces polarity and hydrogen-bonding ability. Within the Kamlet–Taft polarity framework, the NIPAM/NtBA copolymer films are strong hydrogen-bond acceptors, strongly dipolar/polarizable, and rather moderate hydrogen-bond donors. This characterization provides a more comprehensive physicochemical description of polymers, which aids the interpretation of film performance. Comparison of the measured <i>E</i><sub>T</sub>(30) values with literature data for other water-soluble polymers show that dry NIPAM/NtBA copolymers are slightly more polar than poly(ethylene oxide), less polar than polyvinylalcohol, and approximately the same polarity as poly(<i>N</i>-vinyl-2-pyrrolidone). These findings indicate that this spectroscopic method is a facile, rapid, and nondestructive methodology for measuring polymer properties <i>in situ</i>, suitable for most biomaterials research laboratories.
Vol. 4, Iss. 6 Virtual Journal for Biomedical Optics
Boguslaw Szczupak, Alan G. Ryder, Denisio M. Togashi, Yuri A. Rochev, Alexander V. Gorelov, and Thomas J. Glynn, "Measuring the Micro-Polarity and Hydrogen-Bond Donor/Acceptor Ability of Thermoresponsive N-Isopropylacrylamide/N-tert-Butylacrylamide Copolymer Films Using Solvatochromic Indicators," Appl. Spectrosc. 63, 442-449 (2009)