Stimulus-sensitive Cationic Tannin-basedPolyurethanes for Controlled Release ofPhytohormones

Cationic polyurethanes are attractive polymers for application as phytohormone dispensers; however, these are generally synthesized using polyols from petrochemical sources that are not environmentally friendly.To solve this problem, the objective was to develop cationic polyurethanes based on tannins (CTPUs) since these are secondary metabolites of plants and have a polyphenolic nature.For this, tricomponent synthesis was performed with N-carboxymethyl-N,N,N-triethylammonium chloride (CMtEACl), 4,4'diphenylmethane diisocyanate (MDI), and low molecular weight tannins as precursors of cationic groups, isocyanate and hydroxyls respectively.Nine materials were synthesized in total.The structural characterization using various spectroscopic techniques showed that the three-component reaction was successfully executed.The thermal evaluation of the materials allowed to show that the CTPUs that were synthesized with greater molar fraction of MDI have improved thermal properties; however, the presence of ammonium quaternary groups deteriorated these properties.The retention and release experiments were performed using naphthaleneacetic acid (NAA) as a phytohormone model, showing that the CTPU that was synthesized with the highest molar ratio of MDI and CMtEACl, exhibited high retention values at pH = 5.5 and at an ionic strength of 0.50 %, while the release experiments allowed to denote optimal percentage at pH = 8.5 and at an ionic strength also of 0.50 %.These results showed that CTPU are polymers that, in addition to being used as phytohormone dispensers, allow conventional polyols to be replaced with precursors from natural sources, concluding that the eventual application of these materials has a positive environmental impact.