Studies On Polyurethanc Modiifed Silyl-terminated Polyether Sealants

Silyl-terminated polyether (MS) sealant has been attracting considerable attention andwidely used in construction, automotive and other fields for its excellent performances andgood balance of properties such as good durability, weather resistance, heat and coldresistance, adhesion, surface finishing and storage stability etc. In this paper the effect ofcatalysts on the performances of a transparent MS sealant was first studied, and then theisocyanate-terminated and siloxy-terminated polyurethane were separately used to modify theabove MS sealant. The main contents and results of the thesis are as follows:First, a transparent MS sealant was prepared through adding the catalyst dioctyltinS,S’-bis(isooctyl mercaptoacetate)(TMA) to the silyl-terminated polyether resin, and thegenerated sealant exhibited better adhesion and mechanical properties. Compared to thatcatalyzed by dibutyl tin dilaurate (DBT), the tack free time of the sealant reduced from33h to2h; the fully cured time was shortened from8days to4days; the tensile strength reached to0.41MPa; the tensile shear strength increased from0.32MPa to0.45MPa, and showedcohesive failure under external force.Second, the isocyanate-terminated polyurethane (PU) was used to modify the above MSsealant to obtain the transparent PU-MS sealant, which exhibited better mechanical propertiesand adhesion in comparison with MS sealant. When the mass ratio of PU and MS is3:7, thetransmittance of the cured sealant was82%; the tensile strength and elongation at break wereup to0.91MPa and312%, which were122%and142%higher than that of MS sealantrespectively; the tensile shear strength with42%increase was0.64MPa; experienced onlyvery slight discoloration after7days outdoor exposure; the glass transition temperature(Tg)and peak of tanδ were-70.5℃and0.95respectively, which indicated good low temperatureflexibility of the cured sealant.Third, the siloxy-capped polyurethane (SPU) was further used to modify MS sealant toprepare the transparent SPU-MS sealant, in comparison with PU-MS sealant, which not onlyhad the single curing mechanism, but also contained the increased degree of Si-O-Si crosslinkage, and thus showed improved transparency and mechanical strength. When the massratio of SPU and MS is3:7, the sealant achieved the transmittance of91%after curing; tensile strength of1.23MPa,0.32MPa higher than that of the PU-MS sealant; elongation atbreak of256%; tensile shear strength of0.75MPa,0.11MPa increase, underwent only veryslight discoloration after7days outdoor exposure, the glass transition temperature(Tg) andpeak of tanδ were-67.7℃and1.03respectively, which demonstrated good low temperatureflexibility of the PU-MS sealant.