Flame-retarding High Performance Thermosetting Resins And Their Glass Fibre Composites

Bismaleimide(BMI) and cyanate ester(CE) resins are two representative high performance thermosetting resins due to their outstanding integrated properties including high thermal and thermal-oxidative resistance, good mechanical properties, outstanding moisture resistance and excellent dielectric properties, and thus showing great potential in many cutting-edge fields, especially aerospace, electric and electronic industries. However, being polymers, BMI and CE resins generally have poor flame retardancy, which is also the major disadvantage for restricting their applications in Copper Clad Laminates(CCLs) field. In fact, improving flame retardancy has been the main subject associated with the investigations of BMI and CE resins for many years. To date, many approaches have been developed to effectively improve the flame retardancy of BMI and CE resins; however they tend to sacrifice the outstanding properties of original BMI and CE resins, and thus can not meet the harsh requirements on high performance resins proposed by the rapid development of modern industries. Therefore, how to develop new high performance halogen-free flame retarding BMI and CE resins without sacrificing orighnal outstanding performances is still an interesting and important subject. Our project that reported in this thesis focused on designing and preparing halogen-free flame retarding high performance thermosetting resins and their glass fabrics(GF) reinforced composites as well as studying the structure-property relationship.First, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) was introduced into 4,4’-bismaleimidodi-phenylmethane/2,2’-diallyl bisphenol A(BD) resin, and a series of BDP resins were prepared. The effect of the concentration of DOPO on the curing behavior and integrated properties of cure BDP resins and their GF composites were systematically evaluated. Results disclose that properties of cured BDP resins and their GF composites are dependant on the content of DOPO. Essentially, the content of DOPO has significant influence on the structure of polymer chain and that of aggregation state for the crosslinked networks. Compared with BD resin and its GF composite, the BDP resins and their composites with suitable content of DOPO have significantly improved integrated properties including mechanical properties, flame retardancy as well as dielectric properties.Second, [(6-oxido-6H-dibenz [c, e] [1,2] oxaphosphorin-6-yl)-methyl]-butanedioic acid(DDP) was employed to modify BD resin, and BDDP resins and their GF composites were prepared. It is found that DDP can catalyze the homo-polymerization of BDM, which is beneficial to make BDDP resins have higher crosslinking density and thermal resistance Tg. Besides, BDDP resins can be dissolved in low boiling solvents(such as acetone), solving the bottleneck problem that BDP resin can only be dissolved in high boiling solvents. In addition, the presence of DDP makes the resin and GF have better interfacial adhesion, thus endowing BDDP composites with higher flexural strength, impact strength and lower dielectric loss. At the same time, the flame retardancy of GF/BDDP composite belongs to the UL94 V-0 grade, showing decreased heat release rate(HRR) and improved limited oxygen index(LOI).Third, a series of modified CE resins were prepared by introducing 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DPDP), DPDP/CE resins, and then corresponding GF composites were fabricated. The effect of the loading of DPDP on the curing behavior and crosslinking structure as well as the integrated properties(including thermal resistance, dielectric properties, mechanical properties, thermal water resistance, thermal expansion coefficient(CTE) and flame retardant mechanism), were systematically evaluated. Compared with CE resin, DPDP/CE resins have 21-76 oC lowed curing temperature, and the exothermic enthalpy remarkely decreases. The presence of DPDP improves the humidity resistance of the DPDP/CE resins and their GF/DPDP composites, especially, improves the stability of dielectric properties of DPDP/CE resins in the wet environment. This is because-OH groups in DPDP can catalyze the self-polymerization of CE and co-react with CE, reducing or eliminating the amount of-OCN left(as-OCN groups easily hydrolyzes to form carbamates or subammonia carbonates, which is easy to decompose into CO2). In addition, DPDP contains phosphaphenanthrene-containing structure and nonflammable benzene structure, which endows the modified resins and GF composites with better flame retardancy and self-extinguishing. A suitable amount of DPDP can significantly improve the impact strength, flexural strength and modulus of DPDP/CE resins and GF/DPDP/CE composites, but the glass transition temperature(Tg) and thermogravimetric temperature(TG) slightly decrease.Finally, a new BMI resin system based on novel phosphaphenanthrene-containing ladderlike polysiloxane(PN-PSQ) and BD resin was developed. From the view of the gelation time and rheology, PN-PSQ/BD resin with good processing feature was selected, and corresponding GF composite was prepared. The structure-property relationship of GF composite was discussed and correlated with that of PN-PSQ/BD resin. The results show that the content of PN-PSQ on resins and composites has important influences on the thermal properties and CTE. The main reasons behind this phenomen on can be explained from following two aspects. On one hand, PN-PSQ possesses regular ladder structure and Si-O linkage with high bond energy, this is beneficial to improve the thermal stability and CTE of the crosslinked network. However, on the other hand, the Michael addition between-NH2 groups and imide rings reduces the amount of homopolymerization of BDM; and the product of Michael addition reaction has poorer thermal stability, compact and rigid structure than the homopolymerization of BDM, so the thermal stability and CTE of the PN-PSQ/BD resin and GF composite are related to the content of PN-PSQ. Thereby, the appropriate content of PN-PSQ can endow PN-PSQ/BD resin and its GF composite with better thermal resistance and CTE. In addition, the PN-PSQ/BD resin has better thermal resistance than GF/PN-PSQ/BD composite. For example, the Tg value of PN-PSQ/BD resin increases 10-23 oC, however, the Tg value of GF/PN-PSQ/BD composite only increases 3-11 oC. This is because the-NH2 groups on GF worsen the decrease of the homopolymerization of BDM. In addition, GF/PN-PSQ/BD composites have much better flame retardancy than the GF/BD composite, and PN-PSQ/BD resins have better flame retardancy than their GF composites due to the “candle effect”. The introduction of PN-PSQ to BD resin and its GF composite significantly improves the dielectric properties and moisture resistance. However, their impact strength, flexural strength and modulus slightly decrease.