Study On The Preparation And Fire Resistance Of Polyimide-modified Silicone Foams

The main chain and side chain in silicone foam materials are composed by-Si-O-Si-and organic functional groups respectively.The particular structure makes silicone foam materials get perfect thermal stability,hydrophobicity,damp-proof,physiological inert and biocompatible.They can be used continuously under high temperature.This article presents a new method to prepare silicone foams.The fire resistance and thermal stability of the foams were improved through mixing with polyimide(PI).The effects of different conditions,including polymerization time,polymerization temperature and catalyst dosage,on the degree of polymerization of HO-PDMS-OH with low viscosity were studied.Results showed that the degree of polymerization of HO-PDMS-OH increased,with the increase in polymerization temperature,as well as with the increase in amount of catalyst added.The effects of the viscosity of HO-PDMS-OH,amount of polymethylhydrosiloxane,addition of catalyst proportion,and foaming temperature on the foaming process and foam properties were also determined.With gradual increase in viscosity of HO-PDMS-OH,well as with increasing amount of polymethylhydrosiloxane,catalyst proportion and foaming temperature,the density of the silicone foams decreased initially and then increased.The prepared silicone foams are white closed cell foamed materials that have regular size,uniform cellular structure.They have perfect thermal stability and the value of LOI is 19.5%.The density is 0.05g/cm~3~0.15g/cm~3.The foaming ratio is 4.5~10 and water absorption is approximately1.0%.PI-modified silicone foams with regular cellular structure were prepared through a method that utilizes PI precursor powder,which was synthesized using different kinds of aromatic anhydride and aromatic diamine dispersed into HO-PDMS-OH with high viscosity.Results indicated that adding PI not only improved thermal stability but also enhanced the fire resistance of the silicone foams.When the amount of PI precursor reaches 7.5%,the initial decomposition temperature and limiting oxygen index increased to 80?and 7%,respectively.Meanwhile,micrographs obtained using a scanning electron microscope showed obvious differences in cellular structure because PI precursor and silicone have different foaming temperatures.