| Popis: |
A new class of high-performance resins combining the molecular structure of both traditional phenolics and benzoxazines is developed. The monomers are synthesized through Mannich condensation reaction of methylol-functional phenols and primary amines, in the presence of paraformaldehyde. The network structure is built utilizing simultaneous addition and condensation polymerization through benzoxazine and resole chemistry. The presence of methylol groups accelerates the polymerization with improved thermal properties of the produced polymer. The polymers show high glass transition temperature, Tg (274-311°C) and excellent thermal stability compared to the traditional polybenzoxazines. The non-isothermal DSC analysis using Kissinger and Ozawa methods show that polymerization reactions of methylol monomer exhibits lower apparent non-elementary activation energy (83.6 and 93.5 KJ/mol) compared to the unfunctionalized monomer (94.1 and 101.4 KJ/mol). The thesis shows an optimum solution to overcome the historic limitations of using phenolic/urethane materials. The limitations include the slow reaction kinetics of the isocyanate and phenolic compounds along with poor thermal stability of the produced urethane linkages. The new approach is based on reacting methylol benzoxazines with isocyanates and polyols to form polybenzoxazine/polyurethane copolymers. The incorporation of benzoxazine in the copolymer shifted the decomposition temperature to (285-300 °C) with char yield of (18-53%), depending on the benzoxazine content.In addition, the thesis deals with the preparation of high thermally conductive coating for electronic components. For this purpose, boron nitride nanosheet (BNNS) is used as a model system to be dispersed in benzoxazine monomer. Composite of the commercial BN embedded into methylol benzoxazine monomer was used as a control. BNNS systems exhibit higher thermal conductivity values than the BN systems. The SEM images show that dispersion and distribution of BNNS systems are better than BN systems. Theoretical models based on Lewis-Nielsen expression are used to predict the thermal conductivity of polymer composites. Distinct micro- and nano-structured models fit the experimental data of BN and BNNS systems, respectively. The water uptake measurements shows that BNNS system exhibits more hydrophilic nature compared to BN system. The thermal stability and char yield of BNNS nanocomposites are significantly improved by the presence of small amounts of BN. |
