Benzo-oxazine Benzoxazine Resin / Montmorillonite Hybrid Materials Synthesis, Characterization And Curing Behavior Of The Study

In this paper, polybenzoxazine, a novel kind of thermosetting resin, which comes from heterocyclic compounds, is synthesized successfully, in order to get the new polymers that could provide excellent comprehensive performance in mechanical integrity and thermal stabilities as well as high glass transition. It is also superior to conventional thermosetting resins such as phenolic resin.Bis(3,4-dihydro-3-phenyl-l,3-benzoxazines)(abbreviated as benzoxazine hereafter) are synthesized by the reaction of the corresponding phenols, primary amines, and formaldehyde. Several methods in synthesis of benzoxazine have been adopted and compared herein. As a result, one step solution system using toluene as solvent, a new method, is preferred because it has reduced the cycle of the production and make the products less expensive, furthermore, the products have high amount of monomer , compared with two steps solution system.As we know, on the course of formulation of benzoxazine, there are many side reactions, so the 100% conversion has not reached and the products contains side products which includes dimers, trimers and higher oligmers due to the broken ring. It is therefore necessary to keep an eye on the structure of the products of benzoxazine and find the main factor of influence. By using 1H-NMR, FT-IR, and GPC to investigate the structure of benzoxazine intensively, one main factor, the solvent polarity, has been found which could change the stability of ring structure. The more polarity the solvent has, the more unstable the benzoxazine ring is, which also means if solvent is of high polarity, the products contain less monomer. In addition, the characteristic phenomena in "living polymerization" are discovered when the dioxane is employed.The behaviors of ring-opening polymerization, which play very important role in the properties of polybenzoxazine, have been studied in detail by isothermal and dynamic differential scanning calorimetry (DSC) and torsional braid analysis (TBA). In the dynamic DSC analysis, the activation energy and the order of the reaction are determined by using the difference-differentiation computational method, and theactivation energy and order of the reaction would not keep the same as the scanning rate is changed. The faster the scanning rate is, the smaller both activation energy and order of the reaction are.In the isothermal DSC analysis, two models of isothermal curing reaction, which include the nth order kinetics model and autocatalytic kinetics model, have been applied to characterize the behavior of isothermal curing reaction of benzoxazine. Both of the models have successfully copied the isothermal curing behavior in certain stage over the whole range of conversion. The nth-order kinetics model could only describe the curing behavior in diffusion control, while the autocatalytic model with two rate constants and two reaction orders, provides a good phenomenological description of the isothermal curing behavior up to the point of diffusion control for this model does not consider the diffusion control factor. In addition, as the curing temperature is high, the autocatalytic model could successfully copy the whole range of isothermal curing behavior for the diffusion control is small in high curing temperature.By using the torsional braid analysis (TBA), the isothermal and dynamic curing behaviors of the benzoxazine have been studied intensively. During the cure, the phase of benzoxazine changes from liquid to glass, which is accompanied by two phenomena, gelation and vitrification. Gelation occurs at a definite conversion for a particular formulation, which corresponds, to the incipient formation of infinite molecules and rubber-like elasticity arises after the gelation. On the course of curing from the gelation to vitrification, there are something that happens unexpectedly during the curing temperature is below 200. Before the vitrification, two kinds of sub-vitrification occur due to the special molecular interaction which becomes strong enough to change the unit of molecular movement...