Synthesis And Application Of Hydroxyl-terminated Polybutadiene

Hydroxyl-terminated polybutadiene is a common binder of composite solid propellantand coating layer material. By curing reaction between hydroxyl groups and isocyanate canform conventional polyurethane system. But conventional curing method of polyurethanesystem is sensitive to moisture, thus limiting its scope of application. The elastomer madeof alkyne and azido through click-chemistry crosslinking reaction improve thedisadvantages of traditional polyurethane elastomer, and has a big advantage in terms ofwater resistance and weather resistance.In the thesis, with hydroxyl-terminated polybutadiene (HTPB) as reaction substrate,azido-terminated polybutadiene (ATPB) was prepared through two step reactions ofchloride and azide. And the synthesis process of ATPB was deeply discussed. The structureof HTPB and ATPB were characterized in detail.Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance of carbonspectroscopy (13C-NMR) and hydrogen spectroscopy (1H-NMR), gel permeationchromatography (GPC), elemental analysis (EA), thermogravimetry (TG), differentialscanning calorimetry (DSC), and viscosity analysis were carried out to characterize thestructure and performance of the product. FTIR and NMR analysis indicated that theconversion rate of hydroxyl groups were complete. GPC spectrum showed that molecularweight and molecular weight distribution of ATPB were the same as HTPB prepolymers·,and no chain scission or crosslinking reaction happened. EA results showed that themeasured azide value of the product was very close to the theoretical one. Thus, it come tothe conclusion that end group conversion of HTPB was very thoroughly.Thermogravimetric (TG) curve revealed that thermal decomposition temperature of ATPBdecreased slightly compared wtih HTPB. Differential scanning calorimetry (DSC) showedthat the glass transition temperature of ATPB was slightly lower than HTPB. Viscosityanalysis indicated that HTPB and ATPB were belong to pseudoplastic fluid, and theviscosity decreased after hydroxy groups were converted to azido groups.With substances containing alkynyl molecules as curing agents, different conditions·influences on click-chemistry elastomers of ATPB were studied. After the discussion ofinfluences to elastomers· mechanical properties by the contents of curing catalysts, the typeof curing catalysts, curing parameters of R value and different functionality of curing agents, it come to the conclusion that curing reaction was suitable when adding0.5%curingcatalyst3#, three-functionality curing agent in R=1.0and50℃conditions. Swellingexperienments were carried out to discuss the effect of the R values on the structureintegrity of cross-linked network. When the R value was1.0, the ATPB elastomers curingsystem had better mechanical properties. Crosslinking network generated the highestdensity when R=1.0, and the average molecular weight between the cross-linking point wasthe smallest. It meaned that, at this time, the network structure of the cross-linked elastomerwas the most complete. FTIR analysis showed the changes of crosslinking networkstructure of ATPB elastomers with different R value.TG curve indicated that little effect on the change of the thermal performance indifferent R value of the elastomers. Compared with HTPB elastomers, heat stability ofATPB elastomers were significantly improved. DSC analysis realved that the value of Rhad small changes on Tg. Comparing contact angle of different R values of ATPBelastomers with water could be found that along with the increase of the R value ofelastomers, water contact angle first increased and then decreased, and the contact anglewas at the maximum when R=1.0. Compared with HTPB elastomers, contact angle ofATPB elastomers were increased, thus laid the foundation for the study of anti-polarplasticizermigration.The result of the viscosity test in different temperatures and different time indicatedthat ATPB could transform to elastomer through self-crosslinking reaction, and suitablepreservation condition of ATPB was put forward according to viscosity result. Fourierinfrared spectrum (FTIR) and nuclear magnetic hydrogen spectroscopy (1H-NMR) analysisexplained the mechanism of self-curing reaction of ATPB. By measuring the elasticmodulus of cured elastomer under different temperature could determine the completecuring time.