Preparation Of Silane End-capped Polyurea And Its Application On Sealants

Polyurea is a polymer which contains urea group in the mainchain derived from the chemical reaction between diisocyanates and diamines.Compared with other polymer materials,polyurea can be used under harsh conditions because it has high mechanical strength,good elongation at break and thermal stability,in addition,polyurea has the advantages of corrosion resistance,wear resistance properties.However,there are some disadvantages of polyurea.The application of polyurea has been restricted by the weak stability of chemical structure,normal water resistance and low adhesion to the substrate.Organo-silicon compounds have the advantages of low surface energy,good high temperature resistance and oxidative resistance.The chemical stability,thermal stability and dielectric resistance of polyurea are enhanced after introducing organo-silicon compounds.In this paper,polyurea was end-capping modified by organo-silicon compounds.The detailed research contents and results are summarized as follows:Silane end-cappde polyurea(SPUA)was prepared by two step.Firstly,PUA prepolymer was prepared by using polyether amine and different types of diisocyanates as raw materials.Secondly,SPUA was prepared by end-capping PUA using silane coupling agent KH550 as modifier.The 5% weight loss temperature rise 20~30℃ after modification,which prove the enhancement of thermal stability.The thermal stability of SPUA films increases with the decrease of NCO/NH2 molar ratio or the increase of SPUA chain stiffness.The glass-transition temperature drops and the cold resistance is better when NCO/NH2 molar ratio decreases or the SPUA chain gets more softer.The lowest Tg is-65.8℃ when using HDI as raw materials and NCO/NH2 molar ratio is 1.1.Tensile strength and elongation at break are both increase with the decrease of NCO/NH2 molar ratio,tensile strength is 4.14 MPa and elongation at break is 420% when the NCO/NH2 molar ratio is 1.05.Tensile strength increases while elongation at break decreases when the SPUA chain gets stiffer,tensile strength is 4.8 MPa using the stiffest raw material MDI;elongation at break is 335% using the softest raw material HDI.Water absorption of SPUA films decreases and the water contact angle increases after modification,which prove the enhancement of water resistance.The increase of SPUA chain stiffness and NCO/NH2 molar ratio make water absorption decrease and water contact angle increase.The influence of chain stiffness is more obvious.SPUA sealants were prepared using SPUA as base polymer,nano SiO2 as filler and curing catalyst,adhesion promoter as additives.Mechanical property,adhesion property,dielectric resistance and thermal stability of SPUA sealant were analyzed.The results show that the filler can improve the strength of SPUA sealants evidently,while decrease the flexibility.Tensile strength and adhesion strength reach the maximum(tensile strength: 6.16 MPa;adhesion strength: 3.08 MPa)when filler content is 15 wt%.Water absorption decreases after adding filler.The retention ratio of tensile strength and elongation at break of SPUA sealants are more than 80% after immersing in deionized water,5 wt% hydrochloric acid and 5 wt% NaOH solution for 14 days,proving that SPUA sealants exhibit outstanding water,acid and basic resistance.The rise of residue,5% and 50% weight loss temperature suggest the improvement of thermal stability of SPUA sealants after adding filler.