Preparation And Properties Of Novel High Thermal-Stability Polybenzoxazine Resins

Polybenzoxazines, as a novel type of phenolic resin, have the advantages of the traditional phenolic resins, such as good thermal stability, mechanical strength, excellent electrical property, and outstanding flame retardance. In addition, polybenzoxazine also provide unique characteristics like molecular design flexibility, nearly zero shrinkage, release of no byproducts upon curing, curing without using strong acid or basic catalysts etc. However, there are still some shortcomings for polybenzoxazines including much higher curing temperature, brittleness and not good film forming ability. At this moment, many novel benzoxazine monomers or precursors have been developed and most of the research has been focused on how to further improve the thermal stability or how to reduce the curing temperature.Despite polybenzoxazine as a novel phenolic resin, its application is far less than the traditional phenolic resin. It will be a very important research direction in the future about how to improve the high curing temperature and the brittleness and how to surmount the current conventional research and develop new functional polybenzoxazines.In this thesis, we considered to develop novel high thermal-stability polybenzoxazines, in which the ferrocene, polydimethylsiloxane and POSS are selected as the amino groups to prepare a series of novel benzoxazine monomers and precursors. The properties of the relative polybenzoxazines are also investigated. The research mainly consists of the following three parts: (1) Two novel benzoxazine monomers are prepared, monofunctional benzoxazine (pC-fcma) and bifunctional benzoxazine (BA-fcma). DSC results suggest that the ring-opening curing temperature is much decreased than that of BA-a benzoxazine, by nearly70℃. The much decreased ring-opening temperature is due to the electron-donating of N-ferrocen group stabilizing the zwitterionic intermediates. TGA results show that the thermal stability of polyBA-fcma is greatly improved because of incorporating the ferrocene group into the polybenzoxazine, in particular, the weight loss temperature of5%for polyBA-fcma is increased by almost100℃than that of PBA-a, and the char yield even reached60%at800℃under N2. Cyclic voltammetry studies of pC-fcma and BA-fcma show that the species undergo one reversible and one-electron redox coupling, which will make the benzoxazine containing ferrocene suitable for application in electrode modification and electrochemical sensors.(2) A series of copolybenzoxazine is obtained by copolymerization of PBA-pdms600precursor and BA-fcma monomer. The film formation ability of the copolymer is greatly improved compared with the pure polyBA-fcma due to the introduction of PBA-pdms600. DSC results show that the ring-opening curing temperature is decreased resulting from the incorporation of BA-fcma. There is no macroscopic phase separation occurs owning to the co-crosslinking of BA-fcma and PBA-pdms600. TGA results suggest that the thermal-resistance of the copolymers is higher than that of homopolymers both in the nitrogen and air. DMA results exhibit that the storage modulus (E’) of the copolymers is greatly enhanced. The three peaks in tanδ curve illustrate that there are three crosslinking structures in the copolymers. The structure and the degradation mechanism of the copolymers are deeply investigated by Pyrolysis/GC-MS technique.(3) A bi-functional benzoxazine monomer containing POSS moiety is synthesized and the monomer is copolymerization with the PBA-pdms600precursor. DSC results show that the ring-opening temperature is higher than that of BA-a monomer by nearly40℃, which is mainly due to the larger size of POSS and the lower density of oxazine ring. The thermal-resistance of pure polyBA-poss is not so good and the pure polyBA-poss also shows too brittle. However, the film formation ability of pure polyBA-poss is greatly improved by copolymerization with PBA-pdms600. The thermal stability of the copolymer is not well enhanced because of the poor thermal-resistance of isobutyl group in POSS and low crosslinking density of the copolymer. Additionally, SEM and XRD results show that the addition amount of BA-poss is less than10wt%to make sure no macroscopic phase separation occur, otherwise, BA-poss will aggregate and crystallize on the surface of the film.