Study On The Preparation And Thermal Properties Of Siloxane-containing Benzoxazines

Benzoxazine is a new type of thermosetting resin that synthesized from amines,phenols and formaldehyde compounds,containing nitrogen and oxygen six-membered heterocyclic rings.Benzoxazines can generate ring-opening polymerization under heating or catalyst treatment to form a crosslinked network like phenolic resin.This crosslinked network brings many advantages for benzoxazines:high glass transition temperature,good flame retardant,excellent electrical insulation and excellent mechanical properties.The concern is that the different amine and phenol sources can be used to prepare benzoxazine monomers with distinct characteristics according to the flexibility of monomer molecule design.That is,it can be targeted to design the monomer structure with the desired characteristics,which also brings a huge space for the development of the benzoxazine field.After continuous research by many researchers,benzoxazine resin has been used as an important engineering material in high-tech fields such as aerospace and microelectronics.Although benzoxazine has many advantages,its research is not mature.There are still many deficiencies to be improved,such as its heat resistance,flame retardancy and mechanical properties etc.In this dissertation,diphenylsiloxane benzoxazine(BADPS-Ba),dimethylsiloxane benzoxazine(BADMS-Ba),methylphenylsiloxane benzoxazine(BAMPS-Ba)were successfully prepared in order to improve the heat resistance of benzoxazine resins,basing on the flexible design of the benzoxazine molecule.In situ IR and non-isothermal DSC methods were used to investigate the curing behavior and kinetics of the three benzoxazines.The Kissinger and Ozawa methods were taken advantage of studing the activation energy and pre-exponential factors of the three benzoxazine systems.According to the Friedman method,it is determined that the three systems of BADPS-Ba,BADMS-Ba and BAMPS-Ba are all autocatalytic reaction mechanisms.Based on the calculated values of the curing parameters m and n,simulations of curing processes at different heating rates were performed.The results show that the theoretical curve simulates the experimental curve successfully.In order to explore the thermal properties of siloxane-containing benzoxazine resins,studies were conducted using modulated DSC,TGA,and Py-GC/MS.Due to the presence of a large number of silicon oxygen bonds in the main chain,the flexibility of the main chain is increased.Therefore the three of benzoxazines have a low glass transition temperature,yet within theoretical expectations.Thermal performance has improved a lot compared with the alkane-type siloxane benzoxazines in the main chain in thermal performance.Because of the presence of silicon and higher content of benzene rings,p(BADPS-Ba),p(BADMS-Ba)and p(BAMPS-Ba)have relatively higher decomposition temperatures and carbon residue ratio than those of p(MDA-Ba)and alkyl benzoxazines in the main chain.The char residue at 800? were found to be 74%,67%,and 62%,respectively.After Py-GC/MS testing,the degradation products of the three siloxane-containing benzoxazine polymers at 800? were analyzed.Then according to the degraded compounds,their thermal degradation mechanism was studied.