Effect of trifluoromethyl substituents on birefringence of polystyrene

Abstract

Transparent thermoplastic polymers that exhibit no birefringence are ideal for optical components such as optical films for liquid crystal displays and various lenses. Copolymerization of a positive birefringent monomer with a negative monomer is an effective technique for obtaining low birefringent polymers, especially zero‐photoelastic birefringence polymers that exhibit no photoelastic birefringence even during elastic deformation. We prepared four types of trifluoromethyl‐substituted polystyrenes. By substituting hydrogens at the ortho or meta positions of the benzene ring of polystyrene, we demonstrated that poly(2‐(trifluoromethyl)styrene), poly(3‐(trifluoromethyl)styrene), and poly(3,5‐bis(trifluoromethyl)styrene) had negative photoelastic coefficients. However, poly(4‐(trifluoromethyl)styrene) had a positive photoelastic coefficient similar to that of polystyrene. Based on these results, we synthesized a zero‐photoelastic birefringence polymer of poly(2‐(trifluoromethyl)styrene‐co‐4‐(trifluoromethyl)styrene) (55/45 wt.) exhibiting no photoelastic birefringence in elastic deformation, in which the positive photoelastic birefringence of the poly(4‐(trifluoromethyl)styrene) unit was compensated for by the negative photoelastic birefringence of the poly(2‐(trifluoromethyl)styrene) unit. The discovery of polymers having negative photoelastic coefficients is valuable for the design and synthesis of zero‐photoelastic birefringence polymers. The four types of trifluoromethyl‐substituted polystyrenes are promising optical materials because they have high transparency (transmittance > 89–92% for 27–34‐µm thickness films) in the visible and near‐infrared regions and a high decomposition temperature of approximately 400°C. Copyright © 2016 John Wiley & Sons, Ltd.

May Trifluoromethylation and Polymerization of Styrene Occur from a Perfluorinated Persistent Radical (PPFR)?

“…Moreover, for a [PPFR]/[St] molar ratio of 3/1, although the molar mass of polystyrene is higher, the obtained value (59 °C) is lower than that observed from a 3/10 molar ratio. This can be rationalized by the influence of CF 3 position in the styrene aromatic ring on the T g that has already been reported: [62, 63] when the substitution with a CF 3 group occurs on the ortho position of poly(trifluorostyrene), the T g is higher (and can reach up to 175 °C) than when it is in meta (63 °C) or para positions (101 °C). These values mean that the trifluoromethylation occurs in meta position mainly which is in agreement with results obtained from 19 F NMR spectroscopy.…”

“…Moreover,f or a[ PPFR]/[St] molar ratio of 3/1, although the molar mass of polystyrene is higher,t he obtainedv alue (59 8C) is lower than that observed from a3 /10 molar ratio. This can be rationalized by the influence of CF 3 positioni nt he styrene aromatic ring on the T g that has already been reported: [62,63] when the substitution with aC F 3 group occurs on the ortho positiono fp oly(trifluorostyrene), the T g is higher (and can reach up to 175 8C) than when it is in meta (63 8C) or para positions (101 8C). These values mean that the trifluoromethylation occursi nmeta position mainly which is in agreement with results obtained from 19 FNMR spectroscopy.M oreover, the T g values observed for such CF 3 -poly(St-CF 3 -ran-St) copolymers depend on the [PPFR]/[St] initial molar ratios, leadingt om ore St units when that ratio decreases andt hus to higher T g values.H owever,a nd as expected, these copolymers having low molar masses favor lower T g values that cannotr each 104 8C(that of PSt).…”

Boosting the Photovoltaic Performance and Thermal Stability of Organic Solar Cells via an Insulating Fluoropolymer Additive

“…PTFS was synthesized according to literature procedure. [25] The detailed synthetic procedures and characterizations of PTFS are illustrated in the Scheme S1,2 and Figure S10,11. The GPC spectra of PTFS is shown in Figure S12.…”

“…The M n and M w of PTFS is 1.16�10 6 and 3.07�10 6 , respectively, which are larger than the materials reported in the previous literature (M n : 6.04�10 5 , M w : 1.63�10 6 ). [25] The thermal properties of PTFS was investigated by thermogravimetric analysis (TGA, Figure S1a) and differential scanning calorimetry (DSC, Figure S1b). PTFS exhibits a higher glass transition temperature (119 °C) than PS (104 °C).…”

“…[20,21] Taking the aforementioned issues into consideration, together with outstanding performance of fluoropolymer additives in boosting the photovoltaic performance of OSCs, [22][23][24] in this contribution, we selected a known fluoropolymer poly-p-trifluoromethylstyrene (PTFS) as a solid additive to OSCs, which has been described in the previous literature. [25] With the addition of 4 % PTFS, a best PCE of 6.64 % was obtained for devices using PTB7-Th:PDI2 (ethylene-annulated perylene diimide dimer) as the prototype active layer. However, inferior PCEs of 5.29 % and 5.76 % were obtained for devices processed with polystyrene (PS) or without additive, respectively.…”