A new fluorinated poly(ether amide) bearing xanthene group

Ting Li, Shou Ri Sheng *, Mei Hong Wei, Cheng Chen, Cai Sheng Song

College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, China

Received 19 January 2010

Abstract

A new fluorinated poly(ether amide) bearing xanthene group was prepared from 9,9-bis[4-(2-trifluoromethyl-4-aminophenox-

y)phenyl]xanthene (BTFAPX) with 9,9-bis[4-(4-carboxyphenoxy)phenyl]xanthene (BCAPX) in the presence of triphenyl phos-

phate and pyridine (Py). The polymer had the weight-average molecular weight (Mw) of 69,000 and number-average molecular

weight (Mn) of 39,000, showed the glass transition temperature (Tg) of 267 8C, 5% weight loss temperature (Td5) over 460 8C both in

N2 and air, and char yield of 62% at 800 8C in N2. This polymer was amorphous and readily soluble in amide-type solvents such as

N,N-dimethylacetamide (DMAc), and even in m-cressol, Py and tetrahydrofuran (THF) at room temperature, and exhibited tensile

strength of 74 MPa, elongation at break of 6%, tensile moduli of 2.2 GPa. The polymer had low dielectric constant of 3.69 (100 Hz),

low moisture absorption of 0.56%, and high transparency with an ultraviolet–visible absorption cut-off wavelength at 334 nm.

# 2010 Shou Ri Sheng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Keywords: Fluorinated polyamide; Xanthene group; Trifluoromethyl substituents

Aromatic polyamides are characterized as highly thermally stable polymers with a favorable balance of physical

and chemical properties [1]. But these polymers are usually difficult to process due to their high softening

temperatures and their insoluble nature in most organic solvents. Current or prior numerous attempts have been made

to improve their processability by the introduction of flexible linkage [2], molecular asymmetry [3], or substituted

group [4] into the backbone of polyamides. Introducing cardo groups such as tert-butylcyclohexylidene [5] is a

successful approach for improving the processability of aromatic polyamides without an extreme loss of their

outstanding properties. Furthermore, it is well known that the incorporation of trifluoromethyl substituents into

polyamide backbones resulted in great benefits for improving polymer solubility and photoelectric properties [6]. In a

continuation of our interest in the polyamide containing xanthene cardo group [7], we here report another aromatic

polyamide with trifluoromethyl and xanthene pendent groups (Fig. 1), based on a novel diamine monomer, 9,9-bis[4-

(2-trifluoromethyl-4-aminophenoxy)phenyl]xanthene (BTFAPX) (Fig. 2). The solubility, tensile property, crystal-

linity, thermal property, moisture absorption, dielectric constant, as well as optical transparency of the resulting

polymer were investigated.

Treatment of potassium phenolate of 9,9-bis(4-hydroxyphenyl)xanthene [7] in N,N-dimethylformamide (DMF)

with 2-chloro-5-nitrobenzotrifluoride afforded 9,9-bis[4-(2-trifluoromethyl-4-nitrophenoxy)phenyl]xanthene [8],

followed by reduction with hydrazine hydrate and Pd/C catalyst in refluxing ethanol to give BTFAPX [9]. The

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Chinese Chemical Letters 21 (2010) 1247–1250

* Corresponding author.

E-mail address: shengsr@jxnu.edu.cn (S.R. Sheng).

1001-8417/$ – see front matter # 2010 Shou Ri Sheng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

doi:10.1016/j.cclet.2010.04.017

polyamide was obtained in almost quantitative yield by the polycondensation reaction of BTFAPX with 9,9-bis[4-(4-

carboxyphenoxy)phenyl]xanthene [10] according to the literature method [11]. The polymerization proceeded

homogeneously throughout the reaction and gave highly viscous polymer solution. Seen from Table 1, the polyamide

with inherent viscosity of 0.65 dL/g exhibited weight-average molecular weight (Mw) and number-average molecular

weight (Mn) of 69,000 and 39,000, relative to standard polystyrene, respectively.

Generally, fluorine substitution almost resulted in lower water absorption. The similar result of the resulting

polyamide with slight moisture absorption of 0.56% was also determined. The new polyamide exhibited characteristic

IR absorption bands of the amide group around 3369 cm�1 (N–H stretching), 1678 cm�1 (C O stretching), and

1137 cm�1 (C–F stretching), along with the characteristic absorption bands of aryl ether stretching near 1244 cm�1,

demonstrating the formation of amide linkages. The thermal property of polymer is summarized in Table 1. No

endothermic peak above its Tg (267 8C) was observed in DSC scan (Fig. 3), which may be attributed to the amorphous

structure, further confirmed by wide-angle X-ray diffraction (WAXD) analysis. Shown in Table 1, the 5% weight loss

temperature was 492 8C and 463 8C in nitrogen and air atmosphere, respectively, and 62% weight was retained even at

800 8C.

The polyamide was readily soluble (3.0%, w/v) in amide-type solvents such as DMAc and dimethyl sulfoxide

(DMSO), and even in m-cressol, Py and THF at room temperature, attributable to the presence of cardo xanthene

T. Li et al. / Chinese Chemical Letters 21 (2010) 1247–12501248[(Fig._1)TD$FIG]

Fig. 1. The structure of novel fluorinated polyamide.

[(Fig._2)TD$FIG]

Fig. 2. The structure of novel diamine BTFAPX.

Table 1

The polymerization and thermal properties of polyamide.

hinha (dL/g) Mw

b Mnb PDIc Tg

d (8C) Td5e (8C) Td5

f (8C) Td10g (8C) Td10

h (8C) Rwi %

0.65 69,000 39,000 1.77 267 492 463 532 510 62

a Detected in DMAc with a concentration of 0.5 g/dL at 30 8C.b Measured by GPC in THF, polystyrene was used as standard.c The polydispersity index (PDI) was obtained by Mw/Mn.d Detected by DSC at a heating rate of 10 8C/min in N2.e 5% weight loss temperature in N2.f 5% weight loss temperature in air.g 10% weight loss temperature in N2.h 10% weight loss temperature in air.i Residual weight (%) when heated to 800 8C (TGA with a heating rate of 20 8C/min).

groups, trifluoromethyl substituents and flexible ether linkages. Thin film (approximately 0.05 mm thick and 0.5 cm

wide with 6 cm long) cast from its DMAc solution according to the reported method [5] was tested for mechanical

property with tensile strength of 74 MPa, elongation at break of 6%, and tensile modulus of 2.2 GPa. The thermal and

mechanical properties of the new resulting polyamide were compared with those of the fluorinated fluorene-containing

polyamides [6].

The dielectric constant of this polyamide was 3.69 (100 Hz), which was lower than those of commercially available

polyamides [Amodel1 (Solvay Advanced Polymers, 4.2–5.7 at 100 Hz)] [12]. This result could be attributed to the

small dipole and the low polarizability of the C–F bond as well as the increase in the free volume and also because of

the lowering of the moisture absorption [13]. In addition, the incorporation of bulky xanthene increase the free volume

of polymer and further decrease the number of polarizable groups per unit volume, resulting in lower values for

dielectric constant of atomic and dipolar.

The UV–vis data of the polyamide film at various wavelengths are also listed in Table 2. As observed, the cut-off

wavelength was 334 nm, indicating that the polyamide was colorless and had high transmittance. This might be

attributed to the bulky xanthene group both in the diacid and the diamine units, and the trifluoromethyl substituents in

the diamine, which separated the chromophoric groups and interrupted the intramolecular conjugation.

Acknowledgments

We thank the National Natural Science Foundation of China (No. 20664001) and the Research Program of Jiangxi

Province Department of Education (No. 2007–123, GJJ08166 and GJJ09138) for the financial support.

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T. Li et al. / Chinese Chemical Letters 21 (2010) 1247–1250 1249[(Fig._3)TD$FIG]

Fig. 3. DSC and TGA (a in N2; b in air) curves of the polyamide.

Table 2

Optical transparency of the polyamide film at the wavelength range of UV from 200 to 800 nm.

400 nm 500 nm 600 nm 700 nm 800 nm Cut-off (nm)

84 90 90 91 92 334

[8] Mp 195–196 8C; IR (KBr): 1531, 1353 cm�1 (–NO2 stretch), 1289, 1267 cm�1 (C–O–C stretch), 1141, 1118 cm�1 (C–F stretch); 1H NMR

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