Polymer modification is a cost-effective alternative to developing new polymers with tailored properties. It has been practiced for centuries, as exemplified by weaving cotton/wool into fabrics, tanning leather, vulcanizing rubber, and lacquering. For biopolymers, modification is particularly important to expand their range of applications. Traditionally, chemical modification of polymers has been performed in liquid media using solvents. While solvents ensure good heat and mass transfer, they also result in waste streams, additional post-processing steps, health hazards, increased costs, and challenges to industrial scaling. Solvent-lean and solvent-free techniques offer a promising approach to mitigate these issues. Solvent-lean techniques utilize a small amount of solvent to intimately mix the reactants, while solvent-free techniques employ one of the reactants as the solvent itself. These techniques are typically used for esterification, amidization, carboxymethylation, and nucleophilic substitution reactions of polymers [1,2]. Another strategy involves the exposure of solid polymers to vapours of the modifying agent. This method is widely used for silanization of hydroxyl-containing substrates and crosslinking of polymers with amine/hydroxyl functionality using aldehydes and epichlorohydrin [3]. In addition to solvent-lean, solvent-less, and vapor-phase techniques, solid-state reactions between functional polymers and modifying agents have also been investigated for the chemical modification of polymers. A notable example is the mechanochemical synthesis of polymeric Schiff bases. Additionally, efforts have been made to perform esterification and deacetylation reactions by heating a mixture of the polymer and modifying agent in solid state [4]. This presentation will delve into some of the chemical modification techniques for functional polymers without the use of solvents, with a particular focus on strategies for modifying biopolymers.
References
[1] Parvathy, K. S., Susheelamma, N. S., Tharanathan, R. N., & Gaonkar, A. K. Carbohydrate Polymers, 2005, 62(2), 137 – 141.
[2] Ravishankar, K., Shelly, K., Desingh, R. P., Subramaniyam, R., Narayanan, A., & Dhamodharan, R. ACS Sustainable Chemistry & Engineering, 2018, 6(11), 15191 – 15200.
[3] Jiang, F., & Hsieh, Y. L. Journal of Materials Chemistry A, 2014, 2(18), 6337 – 6342.
[4] Akopova, T. A., Demina, T. S., Cherkaev, G. V., Khavpachev, M. A., Bardakova, K. N., Grachev, A. V., Vladimirov, L. V., Zelenetskii, A. N. & Timashev, P. S. RSC Advances, 2019, 9, 20968 – 20975.