GAP copolymer

Q Zhou, Q Hou, L Zheng, X Deng, G Yu, and Y Cao, Fluorene-based low band-gap copolymers for high performance photovoltaic devices, Appl. Phys. Lett., 84 1653-1655, 2004. 

PL and EL emissions from a very low band-gap copolymer 330 (Eg 1.27eV) was demonstrated by Swedish researchers [411]. The material has two absorption peaks at 400 and 780 nm and emits light in the NIR region. The PL spectrum of thin films has one peak at 1035 nm, which is blue-shifted by ca. 60 nm on annealing at 200°C for 10min. The ITO/PEDOT/330/Ca/Al diode was positively biased when the Al/Ca electrode was connected to lower potential and the EL emission became observable at 1.1 V (AEL = 970 nm). The d>KLfor a nonoptimized device was quite low (0.03-0.05%), nevertheless demonstration of EL from PLED in the NIR can be important for communication and sensor technologies (Chart 2.85). 

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 ]... 

The adiabatic flame temperature of GAP copolymer is 1370 K at 5 MPa and large amounts of C(g), H2, and Nj are formed as initial combustion products. Fuel components such as C(s), CO, and Hj predominate, with only very small amounts of CO2 and H2O being formed. 

A thermally degraded GAP copolymer is produced at 532 K, accompanied by 3 = 0.25, where 3 is the mass fraction loss obtained by thermal degradation.The ex-... 

Infrared analysis of GAP copolymer before and after thermal degradation monitored by TG shows that the absorption of die azide bond of the starting GAP copolymer (P = 0.0) is seen at about v = 2150 cm"fI This azide bond absorption is completely lost following thermal degradation (P = 0.41). The -N3 bonds within the GAP copolymer decompose thermally above 537 K to produce Nj. Thus, the gasification of the GAP copolymer observed as the first reaction stage occurs due to spHt-... 

The burning rate of GAP copolymer increases linearly with increasing pressure in an In rversus Inp plot, as shown in Fig. 5.17. The pressure exponent of burning rateat a constant initial temperature, as defined in Eq. (3.71), is 0.44. The temperature sensitivity of burning rate at constant pressure, as defined in Eq. (3.73), is 0.010 K"h... 

The combustion wave of GAP copolymer is divided into three zones zone I is a non-reactive heat-conduction zone, zone II is a condensed-phase reaction zone. 

Fig. 5.17 Burning rates of GAP copolymer at three different initial temperatures.

Fig. 5.18 Heat flux transferred back from the gas phase to the burning surface and heat flux produced at the burning surface of GAP copolymer as a function of pressure.

Fig. 7.44 Effect of catalyst on the burning rate of GAP copolymer, showing no burning rate increase by the addition of lead citrate and/or carbon black.

When HNF or ADN particles are mixed with a GAP copolymer containing aluminum particles, HNF-GAP and ADN-GAP composite propellants are formed, respectively. A higher theoretical specific impulse is obtained as compared to those of aluminized AP-HTPB composite propellants.However, the ballistic properties of ADN, HNIW, and HNF composite propellants, such as pressure exponent, temperature sensitivity, combustion instability, and mechanical properties, still need to be improved if they are to be used as rocket propellants. 

Azide polymers contain -N3 bonds within their molecular structures and burn by themselves to produce heat and nitrogen gas. Energetic azide polymers burn very rapidly without any oxidation reaction by oxygen atoms. GAP, BAMO, and AM-MOare typical energetic azide polymers. The appropriate monomers are cross-Hnked and co-polymerized with other polymeric materials in order to obtain optimized properties, such as viscosity, mechanical strength and elongation, and temperature sensitivities. The physicochemical properties GAP and GAP copolymers are described in Section 4.2.4. 

As described in Sections 4.2.4.1 and 5.2.2, GAP is a unique energetic material that burns very rapidly without any oxidation reaction. When the azide bond is cleaved to produce nitrogen gas, a significant amount of heat is released by the thermal decomposition. Glycidyl azide prepolymer is polymerized with HMDI to form GAP copolymer, which is crosslinked with TMP. The physicochemical properties of the GAP pyrolants used in VFDR are shown in Table 15.3.PI The major fuel components are H2, GO, and G(g), which are combustible fragments when mixed with air in the ramburner. The remaining products consist mainly of Nj with minor amounts of GOj and HjO. 

Fig. 15.8 shows a typical set of burning rate versus pressure plots for GAP pyrolants composed of GAP copolymer with and without burning-rate modifiers. The burning rate decreases as the mass fraction of the burning-rate modifier, denoted by (G), is increased. Graphite particles of diameter 0.03 pm are used as the burn-... 

Fig. 15.8 Burning rate characteristics of a GAP copolymer with and without burning-rate modifier (graphite), showing that the pressure exponent increases with increasing amount of burning-rate modifier.

Using Eqs. (5.1) and (5.2), the heat flitx in zone II, n, and the heat flux in zone III (Ajii) are determined from temperature profile data in the combustion wave. As shown in Fig. 5.18, both n and Am increase linearly with increasing pressure in a log-log plot n p0 75 nd Am po-8o he heat of reaction in zone II, Qji, is determined as 624 kj kg b[44] It is noteworthy that the heat of reaction of HMX in zone II is 300 kJ kg even though the adiabatic flame temperature of HMX is 1900 K higher than that of GAP copolymer. Furthermore, Am of GAP is of the same order of magnitude as Am of HMX, despite the fact that n of GAP is approximately ten times larger than the n of HMX shown in Fig. 5.6. 

Zhou Q, Hou Q, Zheng L, Deng X, Yu G, Cao Y (2004) Fluorene-based low band-gap copolymers for high performance. Appl Phys Lett 84 1653... 

A thermally degraded GAP copolymer is made at 532 K with p = 0.25, where (3 is the mass fraction loss obtained by thermal degradation1291. The exothermic peak is reduced and the first stage reaction is complete at 529 K with (3 = 0.21 as shown in Fig. 5-8. The thermally degraded GAP copolymer which is obtained by the interruption of heating at the end of the first stage reaction (537 K with p = 0.42) shows no exothermic peak. The exothermic reaction of GAP copolymer occurs only in the... 

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