Abstract
This work is concerned with the investigation of the toughness of novel poly(bisbenzoxazine)s by examining, through a combination of synthesis, evaluation of the materials, and computational simulations, their thermal and mechanical properties and the relation of these to the structure. Through these means it may be possible to predict the properties of new benzoxazine materials purely through analysis of the structure. A number of novel bisbenzoxazine monomers were prepared through one of two synthetic routes, in good yield and purity. The solvent free synthesis was chosen as the preferred route due to reduced experimental time and improved results. Characterisation of these monomers was accomplished using spectroscopic techniques, including FTIR and various NMR spectroscopic techniques, which was particularly useful in evaluating the structure and purity of the products, and elemental analysis. Thermal analysis, using DSC, carried out on the homopolymers produced provided information of the polymerisation of each material and the glass transition temperature of them. It was observed that the PK3-a and BisA-m materials remained in the molten state over the longest temperature range, improving their processability and that varying the amine used in production of the monomer has a predictable affect on the thermal properties of the resultant polymer. Allyl and benzyl materials typically displayed higher glass transition temperatures than methyl and aryl. The mechanical properties of the polymers were tested using DMA, TMA and a number of “in-house” techniques at Hitachi Chemical Company Ltd. The damping of the materials tested was investigated, using the α transition peak on the tan δ curves to assess the toughness of these materials. It was found that the aryl derivatives performed the best, on comparison to the other materials produced, and in particular the PK3 and BisAF6 materials. Conversely, the materials containing benzylamine performed the worst, displaying the lowest damping, with shallow and broad peaks for the a transition. Polymers containing flexible backbones, i.e. the BisT, DHPE and PK3, materials showed improved damping, as increased flexibility allows for greater segmental motions. While the more restricted DHAMS and biphenol materials displayed the lowest damping, due to lower segmental rotation and fewer relaxing species. Through comparison of the results obtained from benzoxazine materials produced with data acquired from commercially available competitors it was found that poly(bisbenzoxazine)s perform well, rivalling, if not improving on, the properties seen for these commercially available materials. Using novel methods of computational simulations the mechanical properties of selected poly(bisbenzoxazine)s can be predicted. A reliable and reproducible technique for these predictions has been developed during the course of this work, validated by comparison of the results of the Tg simulation and density prediction against experimental and literature data. The predicted data include a Young’s modulus value which can be used to evaluate the toughness of the material by evaluation of the stress-strain curve suggested. The groups exhibiting greater degrees of flexibility have been found to display the highest Young’s modulus values, suggesting greater toughness. Conversely, materials containing bulky pendant groups and less flexible backbones produce low values for the Young’s modulus, suggesting lower toughness.