A new unsymmetrical diamine monomer containing two trifluoromethyl (CF 3 ) groups is prepared from 2-bromo-5nitro-1,3-bis(trifluoromethyl)benzene. The monomer is polymerized with typical dianhydrides, in this case PMDA, BPDA, BTDA, ODPA, and 6-FDA, using a one-pot synthetic method to obtain corresponding polyimides. All of the prepared polyimides are readily soluble in many organic solvents and can be solution-cast into transparent, flexible, and tough films. These films have a UV-vis absorption cut-off wavelength at 340-375 nm and light transparencies of 87-91% at a wavelength of 550 nm. Incorporation of two CF 3 groups unsymmetrically into rigid polyimides improves their solubility and transparencies without decreasing their physical properties. The polymers V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4413-4422

Transparent polymers that can match the optical and thermal expansion properties of glass were synthesized for flexible devices.

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High-molecular-weight poly(biphenylene oxide)s (PBPO) were prepared from AB-type monomers, 4′(3′)hydroxy-4-nitro-2,6-bis(trifluoromethyl)biphenyl, through a meta-activated nitro displacement reaction. The displacement of nitro leaving group activated by the two trifluoromethyl groups at the meta-position produced high-molecular-weight polymers, which implies that nucleophilic aromatic substitution reaction of the nitro leaving group proceeded very effectively with two activating groups at the meta-position. The obtained polymers have weight-average molecular weight of 20 800−143 300 g/mol and molecular weight distribution of 1.68−2.85. While two homopolymers of 4′-or 3′-hydroxy-4-nitro-2,6-bis(trifluoromethyl)biphenyl, p-PBPO and m-PBPO, showed a semicrystalline morphology, copolymers of the two monomers were amorphous and dissolved in a wide range of organic solvents. The PBPOs possessed a high glass transition temperature (T g ) in the range of 169 to 208 °C depending on their structure and high thermal stability with 10% weight loss temperatures from 486 to 542 °C in nitrogen and from 465 to 516 °C in air. Moreover, PBPOs containing two trifluoromethyl groups showed low refractive indices in the range of 1.4979−1.5052 as well as low birefringence values of 0.0095−0.0148.

P olymers with a lower critical solution temperature (LCST) undergo an entropy-driven phase transition from a soluble coiled state at temperatures below the LCST to an insoluble aggregated globular state at temperatures above the LCST. 1 Owing to thermoresponsiveness, polymers exhibiting LCST behavior have found a diverse range of applications spanning advanced "smart" materials, drug delivery, and catalysis. 2 Poly(Nisopropylacrylamide) is a typical substance which displays LCST behavior. Its derivatives have been widely studied due to their good biocompatibility and easy adjustment of the phase transition temperature to near body temperature. 3 These polymers have a flexible main-chain conformation and respond to temperature changes in a water medium by varying their hydrogen bonds. In recent years, few examples of new LCST systems utilizing organic media have been reported, in which those LCST behaviors were induced by host−guest, 4 chargetransfer, 5 and hydrogen-bonding 6 interactions with additives. Although these demonstrations broaden the scope of the design of LCST polymers, they use ternary systems with various additives and are still illustrated with the polymers having a flexible main-chain conformation.Aromatic polyimides (PIs) are typical rigid polymers and high-performance polymeric materials with excellent thermal, mechanical, and electrical properties. 7 However, most PIs are insoluble and infusible as a result of their rod-like chain conformation and strong interchain interactions. Therefore, much research effort on PIs has been devoted to synthesizing soluble polymers in a fully imidized form without a deterioration of their thermal and mechanical properties. 8 Among the many approaches attempted thus far, the incorporation of trifluoromethyl (CF 3 ) groups onto polymer chains is considered as an effective means of realizing soluble PIs without deteriorating their useful properties. 9 Recently, we reported new soluble PIs which were prepared by introducing two CF 3 groups onto the repeating units of the chain. 10 These polymers showed good solubility while retaining their good thermal and optical properties due to the existence of CF 3 groups as substituents. Against all expectations, we noted that the PIs showed LCST behavior in organic media. This phenomenon was very interesting because LCST behavior in rigid polymers such as PIs is unprecedented to date.In this context, we describe herein the observation of novel LCST behavior in rigid polymers. The polymers were prepared from 4-(4′-aminophenoxy)-3,5-bis(trifluoromethyl)aniline and two aromatic dianhydrides, 4,4′-oxidiphthalic anhydride (PI1) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (PI2), via a one-pot solution imidization method (Scheme 1).These polymers showed good solubility in various organic solvents such as tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, m-cresol, anisole, ethyl acetate, and acetone. Among these solvents, ethyl acetate and acetone solutions exhibit...

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A diamine monomer with trifl uoromethyl groups, 3,3′-bis(trifl uoromethyl)-4,4′-diamino-1,1′-biphenyl, is synthesized from 5-bromo-2-nitrobenzotrifl uoride with two steps. The model reaction with monofunctional benzoyl chloride at room temperature gives the model compound with a quantitative yield. The results of the model reaction indicate that the amine groups have suffi cient reactivity in spite of the presence of electron-withdrawing and bulky trifl uoromethyl group at the ortho position. The monomer is polymerized with terephthaloyl chloride and isophthaloyl chloride in N,N -dimethylacetamide (DMAc) or DMAc containing LiCl using pyridine as an acid acceptor at room temperature. All synthesized polymers are somewhat crystalline and colorless. While the meta-linked polyamide ( PA2 ) shows excellent solubility in polar aprotic solvents, the para-linked one ( PA1 ) is dissolved in polar aprotic solvents containing LiCl and concentrated H 2 SO 4 . They show good thermal and thermooxidative stability as well as high melting temperatures.

Fluorinated polyimides were prepared from the twisted benzidine monomer containing two trifluoromethyl (CF 3) groups on one aromatic ring. The diamine monomer having a rigid and nonplanar structure was polymerized with typical dianhydride monomers including BPDA, BTDA, ODPA, 6-FDA, and PMDA, to obtain the corresponding polyimides. Most polyimides are soluble in organic solvents due to their twisted chain structure and can be solution cast into flexible and tough films. These films have a UV-vis absorption cutoff wavelength at 354-398 nm and a light transparency of 34-90% at a wavelength of 550 nm. They also have tensile strengths of 92-145 MPa and coefficients of thermal expansion (CTE) of 6.8-63.1 ppm/°C. The polymers exhibited high thermal stability with 5% weight loss at temperatures ranging from 535 to 605°C in nitrogen and from 523 to 594°C in air, and high glass temperature (T g) values in the range of 345-366°C. Interestingly, some of the soluble polyimides showed thermo-responsive behaviors in organic solvents presumably due to the multiple hydrogen bondings with unsymmetrically positioned two CF 3 groups along the polymer chains.