Preparation And Performance Of Self-Healable Polysulfide-Based Elastomers

Self-healing materials have become a research hotspot in the field of green chemistry and functional materials in recent years due to their ability to autonomously heal cracks and local damages.Disulfide bond is one of the most important reversible covalent chemical bonds for the construction of self-healing materials because of their ability to exchange under moderate conditions and respond to various stimuli.The main chain of thiol-terminated polysulfide resin is a saturated structure containing abundant disulfide bonds.It is commonly used in the preparation of various adhesive and sealing materials thanks to its excellent adhesion,high elasticity and aging resistance.However,its application in the preparation of self-healable materials has not been reported.In this paper,several self-healable polysulfide-based elastomers were developed by the reaction of oxide,epoxy resin and isocyanate with thiol-terminated liquid polysulfide resin,and the molecular structure,mechanical property and self-healing ability of the obtained elastomers were investigated.The main contents and results are summarized as follows:(1)Preparation and performance of self-healable oxide cured polysulfide sealantThe self-healing ability of the general oxide cured polysulfide sealant is studied for the first time.The oxide cured polysulfide sealant was prepared by the reaction of thiol-terminated liquid polysulfide resin with manganese dioxide.The effects of manganese dioxide dosage,filler type and dosage on the mechanical property and self-healing ability were investigated.The results showed that with the dosage of manganese dioxide increased from 1.75 wt%,2 wt%and 2.5 wt%to 3 wt%,the tensile strength increased while the self-healing ability decreased.The optimal sample LP55-2 exhibited a tensile strength of 1.15 MPa and an ultimate elongation of 478%.After healing at 75 ℃ for 48 h,the healing efficiencies of tensile strength and ultimate elongation were 92.2%and 86.4%,respectively.Furthmore,the spray carbon black,titanium dioxide and fumed sili;con dioxide were used to modify LP55-2.When 2.5 wt%filler was added,the tensile strength corresponding to spray carbon black is highest.The healing efficiency corresponding to titanium dioxide is optimal and the obtained sample exhibited a tensile strength of 1.25 MPa and an ultimate elongation of 507%.After healing at 75 ℃ for 48 h,the corresponding healing efficiencies reached 89.6%and 84%,respectively.(2)Preparation and performance of self-healable epoxy cured polysulfide sealantSelf-healable epoxy resin cured polysulfide sealant can be prepared,avoiding the influence of metal oxide and improving the healing ability.The epoxy cured polysulfide sealant was prepared by the reaction of thiol-terminated liquid polysulfide resin with bisphenol F and bisphenol A epoxy resin.The effects.of molecular weight and cross-linking degree of polysulfide resin on the mechanical property and self-healing ability were investigated.The results showed that by changing the molecular weight(Mn= 1000 N～4000)and cross-linking degree(0.05%～2%)of polysulfide resin,the polysulfide sealants exhibited flexible and adjustable mechanical property,with tensile strength of 1.02～0.75 MPa and ultimate elongation of 157%～478%.The higher molecular weight and lower degree of cross-linking of polysulfide resin are favorable for improving the self-healing ability.The optimal sample LP55-F exhibited a tensile strength of 0.75 MPa and an ultimate elongation of 478%.After healing at 75 ℃ for 60 min,the healing efficiencies of tensile strength and ultimate elongation both reached 91%.The sample also exhibited excellent reprocessing ability.After repeated chopping and hot pressing events(75 ℃,5 MPa,20 min)for three times,the tensile strength remained 0.75,0.72 and 0.68 MPa,respectively.The obtained sealants exhibited good self-healing and reprocessing abilities under a moderate thermal stimula.(3)Preparation and performance of self-healable polysulfide poly(urethane-urea)By using poly(urethane-urea)structure,a reinforced self-healable polysulfide poly(urethane-urea)with high tensile strength as well as good self-healing and reprocessing abilities was prepared.The isocyanate-terminated prepolymer was obtained by the reaction of thiol-terminated liquid polysulfide resin with IPDI,and then reacted with an aromatic amine to prepare polysulfide poly(urethane-urea).The effects of hard segment content and soft segment molecular weight of polysulfide resin on the mechanical property and self-healing ability were investigated.The results showed that by changing the hard segment content(15%～25%),the polysulfide poly(urethane-urea)s had the tensile strength of 2.62～5.80 MPa.The lower hard segment content and higher soft segment molecular weight are favorable for improving the self-healing ability.The optimal sample PSPU-15 with a hard segment content of 15%exhibited a tensile strength of 2.62 MPa and an ultimate elongation of 787%.After healing at 75 ℃ for 48 h,the healing efficiency deduced from tensile strength reached 95%,about twice the value of PTMG-based polyurethane.The sample PSPU-15 also exhibited excellent reprocessing ability.After repeated chopping and hot pressing events for three times,the tensile strength only decreased by 8.4%.(4)Preparation and performance of self-healable polysulfide polyureaA new method for synthesizing aromatic amine-terminated polysulfide oligomer was proposed based on the dynamic reversibility of disulfide bonds.The polyurea structure was introduced into the polysulfide elastomer,which further improved the tensile strength of self-healing polysulfide materials.A novel aromatic amine-terminated polysulfide oligomer was synthesized by the reaction of thiol-terminated liquid polysulfide resin with bis(4-aminophenyl)disulfide and oxidative coupling of thiols.The resulting oligomer was reacted with isocyanates(IPDI and TDI)to prepare polysulfide polyureas and the mechanical property and self-healing ability were investigated.The results showed that the use of alicyclic isocyanate is favorable for improving the self-healing ability.The IPDI cured sample A-LP23-I exhibited a tensile strength of 3.32 MPa and an ultimate elongation of 396%.After healing at 75 ℃ for 48 h,the healing efficiencies of tensile strength and ultimate elongation both reached 91%.