Modification Of Bismaleimide Resins By Hyperbranched Polysiloxanes

Advanced polymer matrix composites (APCs) have been one kind of high-tech materials owing to their light weight, large specific strength and modulus, outstanding thermal resistance, and high designability. The matrice is a key factor to determine the performances of a composite. Bismaleimide (BMI) resin has the advantages of polyimide such as including outstanding thermal and radiation resistance, and the similar processing characteristics of epoxy (EP) resins. BMI meets the requirements of the APCs in many aspects. However,BMI has big brittleness and poor processing characteristics including high melting point, poor solubility, and high curing temperature. Among them, brittleness becomes the biggest barrier to impede the applications of BMI. Therefore, the toughening is one of the most important subject on the modification of BMIs.In general, APCs should have not only excellent mechanical properties (especially fracture toughness),heat resistance,damp-heat,anti-aging,corrosion resistance and so on,but also have excellent processability. However,it seem not possible to overcome the contradiction between the processability.and performances of cured resins such as thermal resistancance, moisture resistance, and toughness.Polysiloxane is a kind of high performance polymers with outstanding heat resistance, toughness and dielectric properties, so it is expected to be used as an excellent tougher of thermosetting resins. But polysiloxane has big viscosity, poor compatibility with BMI, so the toughening effect of polysiloxane is difficult to be taken effect.Hyperbranched polymers are a class of polymers with low structural regularity, wide mass distribution, and a large number of active groups, which have been a hot spot of researches in the field of polymer materialsin recent years due to their unique structure and properties as well as simple polymerization conditions. Some hyperbranched polymers have been used for toughening of epoxy resins,but no similar researches are carried out for the modification of BMIs. More importantly, toughening of BMI resins should be carried out without sacrificing the original advantages of BMI resins including outstanding heat resistance and excellent dielectric properties, etc, whether the modification of BMIs by hyperbranched polymers can get the target is a worthy subject to be addresses, this is the object of this research.Three hyperbranched polysiloxanes (HBPSi) with different active end groups (epoxy, C=C double bonds and amine groups) are designed and synthesized by the hydrolyzation. These hyperbranched polysiloxanes are expected to combine the advantages of both hyperbranched polymers and polysiloxanes, but also get good compatibility with BMI through active-terminated groups. On this basis, new method for preparing HBPSi modified BMI resins is developed, and the structure-property relationship of modified resins is evaluated. Results show that the addition of HBPSi into BMI can effectively improve the impact strength and therma resistance of the resin, so that the overall performances of resins are greatly enhanced.