Environment-friendly stimulus-sensitive polyurethanes based on cationic aminoglycosides for the controlled release of phytohormones

Controlled release systems are an efficient alternative for the effective use of agricultural supplies. Among the most versatile controlled release systems are intelligent or stimulus-sensitive polymeric materials, since these materials are multipurpose and adaptable alternatives that offer great adaptability for agricultural applications. The objective of this work was to develop stimulus-sensitive polyurethanes (PUs) based on cationic aminoglycosides (CAG) to be used as an active phase for the manufacture of systems for the controlled release of phytohormones such as naphthalene acetic acid (NAA). The synthesis of stimulus-sensitive PUs was carried out by a polycondensation reaction using CAGs and methylene diphenyl isocyanate (MDI) as precursors. The NAA retention and release experiments were performed at different pH values and ionic forces to include the acidity and salinity of agricultural soils. The results demonstrate that PUs can be obtained from CAG and MDI using the one-step method. The retention of NAA increased as the CAG content increased in the polymer structure, while it is seen that the effect of pH is weak compared to the effect of ionic strength. On the other hand, the release of NAA from cationic PUs can be accomplished by small changes in ionic strength that are mainly affected by the composition of the PU and the pH. The results suggest that, for developed systems, retention and release of NAA is affected by other interaction mechanisms that could probably be related to p-aromatic interactions. Findings are limited to controlled conditions and the expanding of results to extensive crops should be analyzed in next research studies. The practical implications of this study are improving of control for the dosage of phytohormones in stake propagation crops, greenhouse crops, optimization of reseeding operations, among others. The social implication of this study is reduction of pollution by addition of excess of NAA, in consequence, production costs are decreased. Originality and value of this research is the use of PUs based on CAG, and in consequence, the possibility to build novel environment-friendly systems for phytohormone dosage.