Synthesis of a biodegradable, halochromic polymer via end- functionalization of poly(lactic acid) G.V.W. Kularatne , D.C. Aluthge Department of Chemistry, University of Colombo, Sri Lanka In this study, a poly – (lactic acid) (PLA) based halochromic pH-sensitive biodegradable polymer was developed and characterized. Low molecular weight PLA was synthesized via the ring-opening polymerization of lactide using a simple air- and moisture-tolerant catalyst SnCl 2 and benzyl alcohol as the initiator. 1 At first, phenolphthalein was used as the initiator instead of benzyl alcohol for the ring-opening polymerization mechanism, and it successfully initiated the reaction, and phenolphthalein incorporated PLA polymer was synthesized. However, the phenolphthalein incorporated PLA did not show any halochromism. This was likely due to both phenolic residues in phenolphthalein initiating the polymerization, thus losing its pH responsiveness. Therefore, the indicator methyl red was used to synthesize the halochromic/pH-responsive polymer. Methyl red was incorporated successfully into the chain–end of neat PLA through a Fischer esterification. Methyl red is an azo dye in which the protonation occurs in the azo group of the molecule. 2 Therefore, the carboxylic end of the methyl red was used for the Fischer esterification in this study without affecting the halochromic effect and with no significant change in the azo group in the methyl red molecule. The successful incorporation of methyl red into the polymer was confirmed by the observation of its halochromic effect. The indicator-incorporated polymer represented visual color changes from light red (at pH 2) to light yellow (at pH 10). 1 HNMR and FTIR were used to determine the molecular structure of the monomer, polymer, and pH-sensitive polymer. The successful covalent binding of methyl red to poly- (lactic acid) was identified through thin-layer chromatography (TLC) analysis. 3 References 1. Cunha, B. L. C.; Bahú, J. O.; Xavier, L. F.; Crivellin, S.; de Souza, S. D. A.; Lodi, L.; Jardini, A. L.; Filho, R. M.; Schiavon, M. I. R. B.; Concha, V. O. C.; Severino, P.; Souto, E. B. Lactide: Production Routes, Properties, and Applications.Bioengineering (Basel, Switzerland) 2022 ,9(4), 164. 2. Kuwabara, T.; Nakajima, H.; Nanasawa, M.; Ueno, A. Color Change Indicators for Molecules Using Methyl Red-Modified Cyclodextrins.Analytical Chemistry 1999 ,71(14), 2844–2849. 3. Fleischmann, C.; Cheng, J.; Tabatabai, M.; Ritter, H. Extended Applicability of Classical Phenolphthalein: Color Changing Polymeric Materials Derived from PH-Sensitive Acrylated Phenolphthalein Derivatives.Macromolecules 2012 ,45(13), 5343–5346.
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