Kinetics behind a Strategy for Modulation of Sustainable Benzoxazines: Experimental Study and Its Theoretical Verification

Abstract

A series of benzoxazine monomers with varied benzoxazine functionality from 1 to 3 (mono, bis, and tris) is prepared by reacting agrowaste-derived cardanol with higher functionality amines. The ring opening polymerization study of cardanol-based benzoxazine monomers is investigated by three modes, namely, solution (nuclear magnetic resonance and gel permeation chromatography), bulk (differential scanning calorimetry), and theoretical (B3LYP and 6–31+G**) calculations to analyze the role of number of benzoxazine functionality in curing behavior of the monomers. It is found that the presence of higher and close vicinity of benzoxazine functionality in the monomer promotes faster ring opening, rapid polymerization conversion, and enhancement in the average molecular weight buildup. The activation energy for the curing process is found to decrease from 144–113 kJ mol−1 from mono- to tris-benzo­xazine monomer. Thermodynamically, the presence of higher benzoxazine moiety reveals the curing process is highly exergonic as supported by theoretical calculations. Free energy for successive protonation varies from −9.54 to −24.68 eV for mono- to tris-functionalized monomer. The effect of number of functionality in monomer on its curing behavior – a complete study is reported to offer sustainable monomers/polymers for futuristic materials applications. (Figure presented.) . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim