Preparation, Characterization of Propargyl Terminal Polybutadiene and Its Crosslinked Elastomers Properties

Abstract

Propargyl terminal Polybutadiene (PTPB) was successfully prepared through hydroxyl terminal polybutadiene (HTPB) end-capping modification. The FTIR and 13 C NMR results indicated that the HTPB terminal hydroxyl was thoroughly replaced and yielded the target product, PTPB, with a theoretical propargyl content of 0.66 mmol g −1 . In comparison with HTPB, PTPB has a lower viscosity. Using 1,6-diazide hexane as a curing agent, polytriazole crosslinked polybutadiene (PT ri PB) elastomers with various functional molar ratios (R) were prepared by CuAAC reaction, and the glass transition temperatures of the resultant PT ri PB elastomers were approximately −75 • C, measured by differential scanning calorimetry (DSC), nearly independent of elastomer R values. Mechanical tests indicated, that with the increase in R, the mechanical properties of PT ri PB elastomers exhibit a parabolic dependence on R. In addition, the thermal stability of PT ri PB elastomers were also studied. The findings revealed some fundamental features of polytriazole crosslinking elastomer prepared by CuAAC reaction.Polymers 2020, 12, 748 2 of 11 complex of CuBr and PMDETA (n,n,n ,n ,n -pentamethyldiethylenetriamine) as a catalyst. Under a nitrogen atmosphere, the mixture solution was stirred at ambient temperature for 1.5 h, achieving a hydroxyl-containing double-chain polymer [10]. Similarly, Shingu first dissolved CuBr and PMDETA in DMF (dimethylformamide) solvent, and then a solution of triazido-triethynyl-containing polymer in DMF was added into the solution, using a syringe pump, at an extremely slow rate, at 100 • C, under a nitrogen atmosphere. By the intramolecular CuAAC reaction, a µ-ABC tricyclic miktoarm star polymer was prepared [11].Unlike solution reactions, conventional cuprous catalysts for CuAAC reactions are not fit for the polymer bulk reaction. Moszner mixed multifunctional azides, alkynes and copper (II) acetate together and realized CuAAC bulk step-growth copolymerization in virtue of copper (II) acetate photoreduction under the light irradiation [12]. Schubert directly used CuOAc as the catalyst, and bulk polymerized multifunctional alkynes and azides through CuAAC reaction, and obtained a series of step-growth polymers [13]. However, these polymers contain a great quantity of triazole ring structure with a high glass transition temperature and cannot be used as elastomers. Reshmi used a little amount of cuprous iodide (CuI) solution of acetonitrile as a catalyst and prepared a CuAAC end-crosslinked propargyl terminated polytetramethylene oxide elastomer, using glycidyl azide polymer as a cross-linker [14]. Nevertheless, the strong toxicity of acetonitrile seriously restricts its application scope.We envisioned that some cuprous organic complexes could meet the demand of miscibility with prepolymer and proper chemical stability and would be effective catalysts to bulk prepare triazole crosslinked elastomer. Moreover, we found that a copper(I) hexafluoroacetylacetonate cyclooctadiene complex can decrease the activation energy of ...

The effect of mixed soft segment on the microstructure of thermoplastic polyurethane

“…HTPB has better flexibility and non‐polarity, 17,18 so HTPB‐type TPU has excellent solvent resistance and low‐temperature compliance. The researches on HTPB‐type TPU mainly focus on the improvement of its mechanical properties.…”