Kinetic analysis of the grafting thermal ring-opening polymerization reaction of benzoxazine with sulfonyl-ester functionalized…

This project will explore the fundamental mechanistic details and kinetics of a grafting polymerization reaction that occurs with blended benzoxazine monomers (or resins) and polymers functionalized with reactive sulfonyl-ester leaving groups [such as tosylate (Ts), nosylate (Ns) or mesylate (Ms) groups]. Isoconversional analysis (ICA) is one of the most important methods for establishing the kinetics of the complex reactions associated with curing thermosets. In the case of ICA, activation energy is measured at fixed values of reaction conversion.26 For thermosets the data are typically based on differential scanning calorimetry (DSC). The combinatorial approach not only provides uncertainty associated with modeling thermoset cure kinetics but also allows for an assessment of the extend of cure acceleration by sulfonyl ester derived reagents that lower the activation energy for cure. Benzoxazine is a thermoset that displays excellent properties such as near-zero volumetric cure shrinkage, high glass transition temperatures, low flammability, low water absorption, and tunable thermal and mechanical properties and has demonstrated success in the aerospace and microelectronics industries.4-6 The heterocyclic ring undergoes a cationic thermal ring-opening polymerization (TROP) upon heating the benzoxazine monomer. In 2017, our group discovered that solubilizing a benzoxazine monomer in reactive end-group tosylate polyethylene glycols (PEGOTs) leads to a thermoset resin with a reduced cure temperature (by up to 75⁰C) and affords a new graft copolymer that is more stable than the parent benzoxazine or its analogous blends made without the tosylated polymers.14 Here we vary the different molecular weights and end groups of the polymers blended with benzoxazine. The DSC is used at different ramp rates and data fit to the Vyazovkin kinetic model methods using MATLAB software. We extracted the activation energy (Eα) for the grafting TROP for all the benzoxazine blends. Each sulfonyl ester functionalized PEG reduced the cure temperature of benzoxazine and trends in Eα with molecular weight are examined. Characterization of the mechanical properties of the curing resins using rheometry confirmed lower polymerization temperatures and indicated that damping increases as the molecular weight of the PEG is increased.