## 4 Stability of Some Fluorinated Polymers
### ADAMantane-Dr1 af  
The copolymer described here is a fluorinated side-chain copolymer, the ADAMANTANE-DR1 AF [11] with \(T_{g}\) = 148 \({}^{\circ}\)C. The synthesis of the copolymer was carried out with a molar fraction \(x\) = 73% of the \(\alpha\)-fluoroacrylate monomer bearing a heavy stabilizing diamond-like side group, the adamantane (-CH\({}_{2}\)-C\({}_{10}\)H\({}_{15}\)), and a molar fraction y = 27% of the \(\alpha\)-fluoroacrylate monomer bearing the Disperse Red 1 (DR1) chromophore (DR1 AF). The general structure is given in Figure 9(a). Also the ADAMANTANE-DR1 AF is an evolution of the DR1 PMMA (Figure 9(b)) [11], where a part of the C-H groups was substituted with C-F and with the adamantane as a supplementary side group.  
Figure 9: **(a)** chemical structure of the ADAMANTANE-DR1 AF; **(b)** chemical structure of the DR1 PMMA. Reprinted with permission from [11]. Copyright 2006, American Institute of Physics.  
The electro-optic coefficient of the sample fabricated with ADAMANTANE-DR1 AF was measured at \(\lambda\) = 1,550 nm and it becomes \(r_{33}\) = (2.8 \(\pm\) 0.3) pm/V, for a poling field of \(E_{p}\) = 43 V/\(\mu\)m.  
Thermal stability of the poling induced electro-optic coefficient was measured by means of both temperature scanning and isothermal relaxation measurements [11].  
We scanned the temperature from the ambient one up to 150 \({}^{\circ}\)C, above the \(T_{g}\), at a constant rate \(\Delta T/\Delta t\) = 5 \({}^{\circ}\)C/min. In Figure 10, the results obtained for the ADAMANTANE-DR1 AF copolymer is shown. From the measurements, the results show \(T_{dep}\) = 136 \({}^{\circ}\)C, close to, but lower than, the polymer glass-transition temperature \(T_{g}\).  
We then performed isothermal relaxation measurements on the ADAMANTANE-DR1 AF sample for different temperatures ranging between 110 \({}^{\circ}\)C and 140 \({}^{\circ}\)C. In Figure 11 we show the isothermal relaxation of the EO coefficient normalized to the initial value \(r_{33}(t)/r_{33}(0)\), for the three different fluorinated compounds presented so far, performed at the same temperatures \(T_{m}\) = 110 \({}^{\circ}\)C. The increase of the thermo-stability of the ADAMANTANE-DR1 AF copolymer with respect to the other species is evident.  
Figure 11: Isothermal relaxation measurements at \(T_{m}\) = 110 \({}^{\circ}\)C for three fluorinated copolymers: ADAMANTANE-DR1 AF, FATRIFE-DR1 AF, and HFIP-DR1 AF. Reprinted with permission from [11]. Copyright 2006, American Institute of Physics.  
Figure 10: Temperature scanning measurements on ADAMANTANE-DR1 AF. Reprinted with permission from [11]. Copyright 2006, American Institute of Physics.  
In Figure 12, we plot the values of log\(<\)\(\epsilon\)\(>\)_vs._ 1000/T for the ADAMANTANE-DR1 AF copolymer. The graph shows that relaxation of the chromophores orientation can be described by the Arrhenius law with activation energy \(E_{A}\)\(\approx\) 105 kcal/mol. This result must be compared with the value \(E_{A}\)\(\approx\) 58 kcal/mol obtained for the HFIP-DR1 AF [62] and \(E_{A}\)\(\approx\) 60 kcal/mol for the FATRIFE-DR1 AF [64]). This high activation energy, together with the high \(T_{dep}\), leads to a high thermo-stability of the EO properties even at a high operative temperature, compared with other similar fluorinated DR1 based compounds.