GAP prepolymer

GAP is synthesized by replacing C-Cl bonds of polyepichlorohydrin with C-N3 bonds.The three nitrogen atoms of the N3 moiety are attached linearly with ionic and covalent bonds in every GAP monomer unit, as shown in Fig. 4.6. The bond energy of N3 is reported to be 378 kj mol per azide group. Since GAP is a liquid at room temperature, it is polymerized by allowing the terminal -OH groups to react with hexamethylene diisocyanate (HMDl) so as to formulate GAP copolymer, as shown in Fig. 4.7, and crosslinked with trimethylolpropane (TMP) as shown in Fig. 4.8. The physicochemical properhes of GAP prepolymer and GAP copolymer are shown in Table 4.4 and Table 4.5, respectively.I ]... 

Double-base propellants containing azide polymers are termed nitro-azide polymer propellants. DEP used as a plasticizer of double-base propellants is replaced with azide polymers in order to increase energy density. The compatibility of GAP prepolymer with NG serves to suitably desensitize the mechanical sensitivity of NG and gives superior mechanical properties in the formulation of rocket propellant grains. 

The terminal OH groups of GAP prepolymer are cured with the NCO groups of hexamethylene diisocyanate (HMDI) and crosslinked with triethylolpropane (TMP)... 

As described in Section 4.2.2.3 of Chapter 4 and section 5.2.2 of Chapter 5, GAP is a unique energetic material which bums very rapidly without any oxidation reaction. When N 3 groups are decomposed to produce nitrogen gas, a significant amount of heat is released by the thermal decomposition. The heat of formation is positive, 0.957 MJ/kg at 293 K. The GAP prepolymer is polymerized to form GAP copolymer with HMD I and... 

Figure C.6. Overview of the fabrication process. Two coverslips are placed at the top and bottom of a transparency (a) and prepolymer solution is dropped in the center (b). A thick glass slide is positioned on top of the prepolymer solution, allowing it to rest on the coverslips, and causing the prepolymer solution to flow and fill the gap (c). A photomask is aligned on top of the glass slide (d), a second glass slide is placed on top of the photomask to keep it in place, and the exposed photoresist is polymerized using UV light. After rinsing, an insoluble, patterned polymer results (e).

The 2,4-TDI prepolymers were cast as films on glass plates using a 0.762 mm drawdown bar (a draw-down bar is a metal bar with a gap, which is pulled down a glass plate leaving a thin film of prepolymer. The prepolymer is then moisture-cured to form the polymer film). The films were cured/conditioned at 23 °C and 50% relative humidity for at least four weeks prior to testing. 

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