Studies on cross-linking network structure of GAP binder system

To improve the network structure of glycidyl azide polymer (GAP) binder system, the effects of the prepolymerization of GAP with difunctional isocyanates (TDI or IPDI), the ratio of N-100 and different curing agent on the mechanical properties, network parameters, integrity of the network, and the morphology of tensile fracture surfaces of elastomers were studied. The experimental results showed that the integrity of the network was improved by the prepolymerization of GAP with TDI, the tensile strength and elongation were improved accordingly. Defined amount of difunctional isocyanate in system can also improve the integrity of the network. By the reason of the difference of structure and reactivity between TDI and IPDI, for GAP/TDI/N-100 elastomers, the network structure was the most complete when the weight ratio of N-100 and TDI was 7:3, while the most complete network structure appeared when the weight ratio of N-100 and IPDI was 5:5 for GAP/IPDI/N-100 elastomers. The tensile strength of GAP/IPDI/N-100 elastomers was larger than that of GAP/TDI/N-100 elastomers at the same N-100 ratio, and the elongation was lower. With the decreasing content of N-100, the tensile strength of GAP/TDI/N-100 elastomers decreased from 0.66 MPa to 0.32 MPa, the elongation increased from 104.6% to 506.3%, while GAP/IPDI/N-100 elastomers exhibited maximum tensile strength of 0.69 MPa when the weight ratio of N-100 and IPDI was 7:3, and the elongation increased from 103.2% to 391.4% with decreasing N-100 content. SEM results showed that the morphology of tensile fracture surfaces of elastomers has a good corresponding relation with the integrity of the network and mechanical properties.