Facilely Synthesizing Ethynyl Terminated All-Aromatic Liquid

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Applied Chemistry

Facilely Synthesizing Ethynyl Terminated All-Aromatic Liquid Crystalline Poly(esterimide)s with Good Processability and Thermal Resistance under Medium-Low Temperature via Direct Esterification Ting Huang, Qingbao Guan, Li Yuan, Guozheng Liang, and Aijuan Gu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00301 • Publication Date (Web): 09 May 2018 Downloaded from http://pubs.acs.org on May 10, 2018

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Industrial & Engineering Chemistry Research

Facilely Synthesizing Ethynyl Terminated All-Aromatic Liquid Crystalline Poly(esterimide)s with Good Processability and Thermal Resistance under Medium-Low Temperature via Direct Esterification

Ting Huang, Qingbao Guan*, Li Yuan, Guozheng Liang and Aijuan Gu*

State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application Department of Materials Science and Engineering College of Chemistry, Chemical Engineering and Materials Science Soochow University, Suzhou, 215123, P. R. China.

*Corresponding Authors Tel.: +86 512 65880967. Fax: +86 512 65880089. E-mail address: [email protected] (Aijuan Gu); [email protected] (Qingbao Guan). Address: No. 199 Ren-Ai Road, Suzhou Industrial Park, Suzhou, Jiangsu 215123, China.

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ABSTRACT Developing a facile strategy to synthesize thermosetting all-aromatic liquid crystalline poly(esterimide)s (LCPEIs) at medium-low temperature and endowing LCPEIs with good processability and high thermal resistance are still two big challenges. Herein, a new solution polymerization based on direct esterification under 120 °C is developed, overcoming bottlenecks of traditional melt and solution polymerizations. Besides, two new reactive LCPEIs (LCPEI-1 and LCPEI-2) terminated with 3-ethynylaniline (3-EA) were synthesized, their structures and properties were compared with two control samples without 3-EA end groups. LCPEI-1 and LCPEI-2 not only show good processing characteristics including low melting temperature (Tm=200 °C), low melting viscosity and good solubility in solvent, their cured samples also have high glass transition temperature (Tg = 192 and 225 °C) and high storage modulus, whereas control samples, even treated with similar thermal history as curing procedure for LCPEI-1 and LCPEI-2, have poor performances. Cured-LCPEI-2 exhibits the highest Tg among polyesters with low Tm values ( 280 °C) is so high that is close to the decomposition temperature. Another is low glass transition temperature (Tg < 120 °C), which limits their applications in advanced industrial fields that require high thermal stability and good processing features.10, 11 Several methods have been developed to address challenges mentioned above, nevertheless, which often bring new problems instead. For instance, Tm can be reduced by incorporating aliphatic monomers,12 but at the same time Tg is decreased as well.13 Aromatic bulky side-chain substituents are introduced to prepare TLCPs with improved Tg, but Tm is still very high.14 Non-linear or kinked aromatic monomers (e.g. aromatic ketone-, ether-, amide- or imide-based monomers)15,

16

are feasible to reduce the

molecular chains of symmetry, leading to decreased Tm, but also this disrupts the liquid crystallinity. The reactive end-groups, such as 4-phenylethynylphthalic anhydride (PEPA)17-20 or norbornene,21 have been applied to reduce Tm and melt viscosity (|η*|), and the cured thermosets exhibit good thermal and mechanical properties owing to the chain extension and cross-linking of the reactive end-groups during the cure procedure;



however, the curing temperatures of PEPA and norbornene are as high as 370 °C and 375 °C, respectively, greatly hindering practical applications. It is noteworthy to mention that above single modification method can improve one performance of TLCPs, but which usually tends to deteriorate other performances. Therefore, researchers tried to combine different modification methods in order to fulfill the requirements of good processability and high thermal resistance. Recently a series of reactive all-aromatic liquid crystalline poly(esterimide) (LCPEI) oligomers were synthesized via melt polycondensation at high temperature (~310 °C), as the molecular weight of thermosetting LCPEI block copolymers reduce, Tm and |η*| tend to decrease and the processability will be gradually improved, however the cured thermosets exhibit double Tg (120 and 220 °C).22,

23

In addition, the esterification or transesterification

reaction of melt polycondensation usually takes place at high temperature (250 to 320 °C), so the reactive end-groups must keep latent. Up to date, only PEPA and norbornene are two available compounds.24,

25

Liquid crystalline polymers terminated with PEPA or

norbornene have a curing temperature up to 370 °C,26 which severely restricts their practical applications. Furthermore, in order to make sure the polymerization proceed completely, a vacuum atmosphere is required at the end of the melt polycondensation to remove the small molar mass by-products such as acetic acid or water, this requests extremely high standard polymerization equipment. Besides melt polycondensation, solution polymerization is an alternative method to synthesize poly(esterimide)s. Generally, poly(esterimide)s are synthesized through a twostep procedure, the first step is the reaction between ester-amine based compounds and anhydride derivatives to form poly(ester amic acid) precursors; and the second step is


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imidization that needs high temperature (250~300 °C)27 or long reaction time (~24 h under a nitrogen atmosphere)28, 29. Up to date, through a direct esterification to synthesize all-aromatic thermosetting LCPEIs under medium-low polymerization temperature is still a big challenge. The aim of our research not only includes developing a new kind of high performance thermosetting LCPEIs that simultaneously possessing good processability (high Tm, low Tg and low |η*|) and high thermal resistance, but also contains building a new solution polymerization under medium-low temperature. Herein, two new reactive LCPEIs (LCPEI-1 and LCPEI-2) terminated with 3ethynylaniline (3-EA) groups were designed and synthesized, which have target molecular weight (Mn) of 5000 g/mol but different contents of imide monomer with kinked structure. The effects of aromatic imide-based moiety and reactive end-groups on chemical structure, processability and thermomechanical properties of LCPEIs have been systematically investigated. The discussion on the mechanism behind outstanding performances demonstrate that simultaneously employing non-linear aromatic monomer and reactive end-groups is capable of obtaining LCPEIs with good processability and high thermal resistance. 2. EXPERIMENTAL SECTION 2.1 Materials p-Hydroxybenzoic acid (HBA, 99%), 6-hydroxy-2-naphthoic acid (HNA, 98%), 1,2,4benzenetricarboxylic anhydride (TMA) and diphenyl phosphoryl chloride (DPCP) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd, China. 3Aminophenol (3-AP) was obtained from Thermo Fisher Scientific Technology Co., Ltd,



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China. 3-Ethynylaniline (3-EA) with a purity of 98% was purchased from Beijing Yinuokai Technology Co., Ltd, China. Anhydrous lithium chloride (LiCl) was bought from J&K Scientific Ltd, China, and dried under vacuum at 150 °C for 15 h prior to use. Glacial acetic acid, acetic anhydride, pyridine (Py) and methanol with analytical grades were obtained from Jiangsu Qiangsheng Functional Chemical Co. Ltd, China, and used without further purification. 2.2 Synthesis of 2-(3-ethynylphenyl)-1,3-dioxoisoindoline-5-carboxylic acid (EPDDCA) 1,2,4-Benzenetricarboxylic anhydride (0.1 mol, 19.21 g) was dissolved in glacial acetic acid (250 mL) with stirring at 120 °C to obtain a clear solution. 3-Ethynylaniline (0.1 mol, 11.72 g) was added to above solution and followed by refluxing for 4 h at 130 °C to obtain a bright yellow suspension, which was then cooled down to 70 °C and filtrated. After that, the precipitated product was washed with acetic acid and ethanol, successively, and followed by drying. Yield: 24.76 g (85%). Fourier transform infrared (FTIR): 1785 cm-1 (C=O asymmetrical stretching), 1724 cm-1 (C=O asymmetric stretching), 717 cm-1 (C-N-C bending vibrations of imide), 3270 cm−1 (carboxylic hydroxyl), 1600 cm-1 and 1420 cm-1 (carboxyl). 1H nuclear magnetic resonance (1H NMR, 400 MHz, DMSO-d6) (Figure S1): δ 4.29 (s, 1H, C≡CH), 7.49−7.57 (m, 4H, Ar H), 8.06−8.07 (d, 1H, Ar H), 8.29 (s, 1H, Ar H), 8.39−8.40 (d, 1H, Ar H), 13.74 (s, 1H, COOH).

13

C nuclear magnetic

resonance (13C NMR, 151 MHz, DMSO-d6): δ 82.15, 82.91, 122.73, 123.87, 124.30, 128.41, 129.84, 130.74, 131.82, 132.47, 135.28, 135.96, 136.91, 166.20, 166.48. 2.3 Synthesis of LCPEIs N-(3’-Hydroxyphenyl)trimellitimide (IM) was synthesized according to the method reported previously.22, 23 Typically, glacial acetic acid (130 mL) and trimellitic anhydride


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(0.05 mol, 10.51 g) were mixed at 120 °C until all solids were dissolved, and then 3aminophenol (0.05 mol, 5.46 g) was added. A thick suspension was formed almost immediately and this reaction mixture was refluxed for 4 h at 120 °C. After cooling the reaction mixture, the precipitated product was isolated by filtration and washed with acetic acid and ethanol, followed by drying under vacuum at 100 °C for 24 h to get offwhite product, which is N-(3’-hydroxyphenyl)trimellitimide (IM). Yield: 12.31 g (87%). 1

H NMR (400 MHz, DMSO-d6) (Figure S2): δ 6.80−6.84 (m, 3H, Ar H), 7.30 (t, 1H, Ar

H), 8.04 (d, 1H, Ar H), 8.26 (s, 1H, Ar H), 8.38 (dd, 1H, Ar H), 9.73 (s, 1H, Ar-OH), 13.67 (s, 1H, Ar-COOH).

13

C NMR (151 MHz, DMSO-d6): δ 114.30, 115.20, 117.73,

123.32, 123.66, 129.45, 131.93, 132.55, 134.80, 135.34, 136.32, 157.59, 165.74, 166.13, 166.15. DPCP (34.4 g) and LiCl (4 g) were added into Py (200 mL) with stirring at 25 °C for 30 min to obtain a clear solution A. IM (0.022 mol, 6.23 g), HBA (0.051 mol, 7.04 g), HNA (0.027 mol, 5.08 g), 3-EA (0.0034 mol, 0.40 g), EPDDCA (0.0034 mol, 1.00 g) and Py (100 mL) were preheated at 120 °C for 5 min to get a clear solution B. Solution A was added dropwise to solution B within 1 h. The resultant suspension was refluxed for 3 h at 120 °C. The white polymer powder was filtered from Py and mixed with 400 mL of methanol. The obtained precipitate was then washed thoroughly with methanol and hot water for 3 times, followed by filtration and drying at 100 °C under vacuum for 24 h. The resultant product was coded as LCPEI-1. Yield: 16.75 g (93 %). LCPEI-2 with higher concentration of IM was prepared according to the reactant contents listed in Table 1 and above procedure of LCPEI-1. Figure S3 demonstrates the



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reason of selecting molar ratios of HBA, HNA and IM as 0.051/0.027/0.022 and 0.029/0.027/0.044. Table 1. Reactants for synthesizing LCPEIs HBA

HNA

IM

3-EA

EPDDCA

Sample g

mol

g

mol

g

mol

g

mol

g

mol

LCPEI-1-c

7.04

0.051

5.08

0.027

6.23

0.022

-

-

LCPEI-2-c

4.00

0.029

5.08

0.027

12.46

0.044

-

-

LCPEI-1

7.04

0.051

5.08

0.027

6.23

0.022

0.40

0.0034

1.00

0.0034

LCPEI-2

4.00

0.029

5.08

0.027

12.46

0.044

0.48

0.0041

1.20

0.0041

The high molecular weight control samples (LCPEI-1-c and LCPEI-2-c) were synthesized under identical conditions but without 3-EA and EPDDCA. FTIR: 1784 cm-1 (C=O symmetric stretching of imide), 1723 cm-1 (C=O asymmetric stretching), 724 cm-1 (C-N-C bending vibrations of imide). 2.4 Preparation of thin Films LCPEI-1-c or LCPEI-2-c powders were placed between two Kapton films and consolidated in a preheated hot press at 250 °C for 15 min with a pressure of 20 MPa, followed by cooling down to 30 °C, and thus a control LCPEI film was obtained. LCPEI-1 or LCPEI-2 powders were placed between two Kapton films and consolidated in a preheated hot press at 250 °C for 15 min with a pressure of 20 MPa, and then cooled down to 30 °C, followed by curing with the procedure of 200 °C/1 h + 230 °C/1 h + 270 °C/1 h + 300 °C/1 h in an oven to get a thermosetting film, coded as CuredLCPEI-1 or Cured-LCPEI-2. Thermoplastic LCPEI-1-c and LCPEI-2-c have been applied


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the same “cure” procedure to Cured-LCPEI-1 and Cured-LCPEI-2, and the resultant samples are coded as Heated-LCPEI-1-c and Heated-LCPEI-2-c, respectively.

2.5 Characterizations FTIR spectra were recorded on a Bruker Vertex 70 spectrometer (USA) over the wavenumber ranging from 600 to 4000 cm-1. 1

H NMR spectra were obtained on a 400 MHz Bruker AVANCE III superconducting

magnetic resonance spectrometer (USA) at 25 °C.

13

C NMR spectra were recorded with

an Agilent DD2-600 MHz spectrometer (USA) at 25 °C. A solvent mixture of CDCl3 and pentafluorophenol (v/v = 4/1) or DMSO-d6 was used as the solvent, and tetramethylsilane (TMS) as the internal standard at room temperature. Molecular weights and polydispersities (PDIs) relative to polymethylmethacrylate were measured at 30 °C using a Agilent Technologies PL-GPC 50 Integrated GPC System (USA) with the mixture solvent of CHCl3 and pentafluorophenol (v/v = 4/1) as the mobile phase at a flow rate of 1.0 mL/min. Thermal behaviors were investigated using differential scanning calorimetry (DSC) on a TA instrument Q200 (USA) with a flowing rate of 50 mL/min under a nitrogen atmosphere. The samples were analysed from 45 to 360 °C at a heating rate of 20 °C/min. The liquid crystalline phase behaviours were observed using a polarizing microscope (POM) equipped with hot-stage at a heating rate of 50 °C/min under an air atmosphere. Rheological behaviours were studied using an Anton Paar MCR302 (Anton Paar Trading Co., Ltd., Austria) equipped with a force-rebalanced transducer in a parallel plate geometry. Parallel plates of 20 mm were used, and samples were prepared by



compression molding, their dimensions are 20 mm in diameter and 0.2 mm in thickness. Tests were conducted under a nitrogen atmosphere with a temperature ramping (3 °C/min) from 180 to 310 °C followed by an isothermal hold at 310 °C for 1 h. All experiments were performed at a frequency of 1 Hz and a strain amplitude of 0.1%, which were well within the linear viscoelastic range. Dynamic mechanical analyses (DMA) were performed with a TA DMA Q800 (USA) in tension mode, under air atmosphere and at a heating rate of 3 °C/min from 30 to 380 °C. The dimensions of each thin film were (20 ± 0.2) mm × (5 ± 0.2) mm × (0.15 ± 0.05) mm. All experiments were performed at a frequency of 1 Hz, the preload force was 20 mN and the amplitude was 5 µm. X-ray diffraction (XRD) patterns were recorded in the range of 2θ = 5-90° using a X’Pert-Pro MPD (Holland) with Cu-Kα radiation source. UV-visible absorption spectra were recorded on a PerkinElmer (USA) over the wavelength ranging from 200 to 800 nm. Thermogravimetric analyses (TGA) were performed on a TA Discovery TGA (USA) from 50 to 700 °C under a nitrogen atmosphere at a flowing rate of 50 mL/min and a heating rate of 10 °C/min.

3. RESULTS AND DISCUSSION 3.1 Synthesis and characterization of liquid crystalline poly(esterimide)s A new series of thermosetting all-aromatic LCPEIs based on HBA, HNA and IM were synthesized in the presence of DPCP and Py as the condensing agents at medium-low temperature (120 °C) as shown in Figure 1. Because diphenylchlorophosphate (DPCP) can


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form N-phosphonium salt in pyridine, which reacts with carboxylic acid to give activated acyloxy N-phosphonium salt (Figure 2), so the direct esterification can take place under mediumlow temperature.14, 30 Compared to high polymerization temperature (310 °C) of traditional melt polycondensation, the solution polymerization in present work is new and much more facile and controllable.

Figure 1. Synthesis of LCPEIs (Route A) and control ones (Route B).

Figure 2. DPCP-activated direct esterification mechanism.



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LCPEIs reported by melt polycondensation are insoluble in all but corrosive solvents,22, 23 whereas LCPEIs synthesized via solution polymerization in present work are soluble in the solvent mixture of chloroform and pentafluorophenol (v/v = 4/1). The good solubility of LCPEIs not only provides rich choice of processing methods, but also facilitates the characterization of chemical structures. Figure 3 shows 1H NMR and 13C NMR spectra of LCPEI-1-c, LCPEI-1 and LCPEI-2. The characteristic signals of benzene ring at 112-138 ppm in

13

C NMR spectra and 6-9

ppm in 1H NMR spectra are observed for all three samples. The characteristic signals of 3-EA at 81 ppm in

13

C NMR spectra31, 32 and 3.1-3.2 ppm in 1H NMR spectra 8 are found in

LCPEI-1 and LCPEI-2 samples, but not in LCPEI-1-c. Therefore, it is reasonable to state that acetylene group of 3-EA is attached to the main chain of LCPEI-1 and LCPEI-2. In addition, HBA, HNA, EPDDCA and IM contain carboxylic acid group, but no characteristic signal of carboxylic acid group is observed in the spectra, so the final products are not mixed with 3-EA and other reactants.


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Figure 3. 1H NMR (a) and 13C NMR (b) spectra of LCPEIs. It is known that the poor solubility of all-aromatic oligomeric species readily leads to early precipitation within the reaction solution and thus precluding further polymerization, so only low molecular weight (1000~8000 g/mol) polymers can be obtained.17, 33-35 From GPC results shown in Figure 4, it can be seen that LCPEI-1-c exhibits a number molecular weight (Mn) of 6075 g/mol, meanwhile the Mn values of LCPEI-1 and LCPEI-2 are 5195 g/mol and 4925 g/mol, respectively, which are consistent with the theoretical value (Mn = 5000 g/mol).



Figure 4. GPC results of LCPEIs. 3.2 Curing reactivity and liquid crystalline behavior Figure 5a shows DSC curves of samples, each curve of two control samples (LCPEI-1-c and LCPEI-2-c) does not show an exothermic peak, whereas the curve of either LCPEI-1 or LCPEI-2 has a broad exothermic peak (cure reaction) ranging from 230 to 360 °C, and reaching the maximum at 310 °C. The exothermic peak disappears after the samples were cured with a multi-step curing procedure (200 °C/1 h + 230 °C/1 h + 270 °C/1 h + 300 °C/1 h) (Figure 5b), indicating that LCPEIs can be completely cured at 300 °C, which is far lower than the cure temperature (370 °C) of LCPEIs synthesized by traditional high temperature melt polycondensation.23


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Figure 5. DSC curves of LCPEIs (a) and cured ones (b). The liquid crystalline phase transition of LCPEIs was investigated under a hot-stage polarizing microscope. The photographs were taken with different magnifications, but the scale bar stands for the same size (50 µm) in Figure 6 and Figure 7. The LC (nematic) phase transition temperature (also Tm) of LCPEI-1-c or LCPEI-2-c is 220 °C or 240 °C (Figure 6), whereas LCPEI-1 and LCPEI-2 have same Tm (~200 °C) as shown in Figure 7, suggesting that the incorporation of reactive end-groups reduces the molecular weight of polymer chain, this is beneficial to reduce Tm. In contrast to high Tm (280 °C) of commercial LC polyester (Vectra A) consisting of HBA and HNA,36 the incorporation of imide monomer (IM) with kinked structure reduces the backbone symmetry and suppresses the Tm of LCPEIs as well.37-39



Figure 6. Optical micrographs of LCPEI-1-c (top) and LCPEI-2-c (bottom), the scale bar stands for the same size (50 µm).

Figure 7. Optical micrographs of LCPEI-1 (a1-h1) and LCPEI-2 (a2-h2) at different cuing stages with a heating rate of 50 °C/min, the scale bar stands for the same size (50 µm) (a. 150 °C; b. 200 °C; c. 200 °C/1 h; d. 200 °C/1 h + 230 °C/1 h; e. 200 °C/1 h + 230 °C/1 h + 270 °C/1 h; f. 200 °C/1 h + 230 °C/1 h + 270 °C/1 h + 300 °C/1 h; g. ramping sample f to 350 °C; h. ramping sample g to 400 °C). In addition, all poly(esterimide)s exhibit a typical nematic texture from Tm up to the decomposition temperature (∼460 °C). A nematic to isotropic transition (N−I) could not be detected, so LCPEIs are processable over a broad temperature range. Furthermore, the curing reaction does not affect the liquid crystallinity of LCPEIs. After a multi-step


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curing procedure, Cured-LCPEI-1 and Cured-LCPEI-2 also show stable nematic texture (Figure 7), thus endowing the cured poly(esterimide)s with unique LC property. 3.3 Rheology Understanding the melting behavior of polymers is of great significance to define the processing window. The complex melt viscosity (|η*|)-temperature-time curves for LCPEIs are shown in Figure 8. The |η*| of LCPEI-1-c starts decreasing at Tm (220 °C) where the polymer chains become mobile, thus the lowest value (|η*|min) is obtained at 310 °C (326 Pa·s). LCPEI-2-c shows much higher |η*|min (7982 Pa·s) at 252 °C, because its larger IM concentration brings higher intermolecular force, and thus restricting the mobility of polymer chains.

Figure 8. Plots of complex melt viscosities of LCPEIs as functions of temperature and time. Note that the |η*|min of LCPEI-1 is only 184 Pa·s at 230 °C, which is the lowest value among four LCPEIs samples, this is because the incorporation of reactive end-groups (3EA) limits the molecular weight of LCPEI-1. LCPEI-2 shows higher |η*|min than LCPEI-1



due to the larger intermolecular force. Although the |η*|min of LCPEI-2 is 5576 Pa·s at 217 °C, which only decreases by 30% compared to that of LCPEI-2-c without endgroups, the |η*| of LCPEI-2-c is 13754 Pa·s at 217 °C. The rheology results suggest that introducing reactive end-groups is beneficial to improve processability. During the 1 h isothermal hold at 310 °C, the |η*| of LCPEI-1-c increases from 346 to 568 Pa·s; while that of LCPEI-1 shows a rapid increase from 184 to 8236 Pa·s. This is because the chain extension and cross-linking take place during the 1 h isothermal hold at 310 °C in LCPEI-1, whereas LCPEI-1-c does not have this curing process. LCPEI-2 shows a more complex rheological behaviour, the increases in |η*| are attributed to the cure reaction whereas the decreases in |η*| are more likely related to the loosed intermolecular force during heating. Eventually, the |η*| of LCPEI-2 levels off at the similar range as that of LCPEI-2-c. Reminding that thermosetting LCPEI from high temperature melt polycondensation exhibited a |η*| about 5×105 Pa·s at 217 °C,23 which is almost 100 times of LCPEI-2 (5576 Pa·s) at the same temperature, meaning that the solution polymerization established in present work has significant advantage in synthesizing LCPEIs with low Tm and low |η*|. 3.4 Thermomechanical properties To study thermodynamic properties of LCPEIs, the film samples were tested by DMA. In general, Tg is defined as the peak temperature of the tan delta-temperature curve.40, 41 Figure 9a and Table 2 show that the Tg values of LCPEI-1-c and LCPEI-2-c are severally 161 °C and 205 °C, whereas those of Cured-LCPEI-1 and Cured-LCPEI-2 are 192 °C and 225 °C, respectively. These results reveal that the higher IM content or the presence of


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reactive end-groups can afford higher Tg, specifically, higher IM content is favourable for improving the rigidity of the aromatic main chain and the interaction force between molecular chains;23,

42

the existence of reactive end-groups can bring cross-linking

structure, restricting the activity of molecular chain segments.43 Table 2. Thermal properties of LCPEIs Tg (°C) a

E' at 50 °C (GPa)

Tdi (°C) b

LCPEI-1-c

161

3.3

465

LCPEI-2-c

205

2.3

460

Cured-LCPEI-1

192

2.9

460

Cured-LCPEI-2

225

2.9

473

Sample

a

Tg data were obtained from DMA experiments using melt pressed films, defined by the

maximum of the Tan delta peak. The tests were carried out under a nitrogen atmosphere with a heating rate of 3 °C/min and a frequency of 1 Hz. b

The initial degradation temperature at which the weight loss of sample was 5 wt%. The

property was evaluated using dynamic TGA technique with a heating rate of 10 °C/min at a nitrogen atmosphere.

Through reviewing polyesters, poly(esterimide)s or poly(esteramide)s reported previously (Table S1), it can be found that polyesters are divided into three kinds according to their Tm and Tg. The first kind exhibits high Tm (>270 °C) and high Tg (~170 °C); the second kind shows low Tm (~200 °C) and low Tg (

Facilely Synthesizing Ethynyl Terminated All-Aromatic Liquid

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