Synthesis of Propargyl‐Terminated Polybutadiene and Properties of Polytriazole Elastomers

Abstract

Compared with the traditional polyurethane curing system with polyisocyanate group and hydroxyl group prepolymer, the click chemistry curing system with the polyazide group and the terminal alkyne prepolymer has the advantages of single reaction selectivity and insensitivity to oxygen and water. In this paper, the propargyl‐terminated polybutadiene (PTPB) has been synthesized by using hydroxyl terminated polybutadiene (HTPB), potassium t‐butoxide and bromopropyne as raw materials, and the yield is 98.6 %. The polytriazole elastomers have been prepared through copper‐catalyzed azide‐alkyne huisgen [3+2] dipolar cycloaddition reactions between the propargyl‐terminated polybutadiene (PTPB) as binder and azide (−N3) compound as curing agent. Furthermore, the effects of catalyst type, azide functionality and curing parameters (R value) on elastomer properties are investigated by FTIR, DMA, TG, DSC and mechanical tests. It has been obtained that the crosslinking elastomer formed with the PTPB and azide of 3.8 functionality has better mechanical properties and thermal stability. When the molar ratio R of azide group to alkyne group in curing the PTPB is equal to 1, the PTPB elastomer has the biggest tensile strength and smallest tensile strain, and the change of the R value has little effect on the glass transition temperature and thermal stability of the PTPB elastomers.

Click Chemistry Reactions between Hydroxyl‐Terminated or Alkynyl‐Terminated Polybutadiene and Benzyl Azide

“…FTIR, 1 H-NMR, 13 C-NMR, and Elemental analysis are used to track the reactivities of the C=C and C�C bonds in HTPB or ATPB with the azide group with or without Cu (I) catalyst. It is verified that the C=C bonds of HTPB can react with the azide group without the Cu (I) catalyst, quantitative 13 C-NMR determines that the 1,2-vinyl, 1,4-cis, and 1,4-trans structure reactions in HTPB are more than 10 %. With the Cu (I) catalyst, the reaction degree of the C=C bonds and -N 3 in HTPB was significantly reduced than that without the Cu (I) catalyst.…”

“…A Bruker 600 MHz spectrometer was used to measure the 1 H-NMR and 13 C-NMR spectra of S1-S4 samples with the reaction time. Tetramethylsilane was used as the internal standard, and CDCl 3 was used as the solvent.…”

“…In order to determine the degree of inhibition of C=C and -N 3 by copper (I) catalyst, the remaining percentage of three different C=C structures in HTPB molecule was monitored by quantitative 13 C-NMR integral calculation. The remaining percentages of the three structure types C=C are shown in Table 2.…”

“…The PTPB-GAP system was not sensitive to humidity and has good compatibility with other new green high-energy oxidants. Gao et al [13] successfully prepared alkynyl-terminated polybutadiene and polytriazole elastomers with different formulations. They investigated the effects of catalyst type, azide function, and curing parameters on the properties of the elastomer.…”

“…Currently, the activity level of -N 3 reacting with the C�C or C=C has not been reported yet. In this work, FTIR, 1 H-NMR, 13 C-NMR were used to study the reactivity of C=C in HTPB and C�C, C=C in PTPB with azide groups. At the same time, the impact of the copper (I) catalyst on the reaction between C�C/C=C bonds and azide was explored.…”