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Synthesis of high transparency polyarylates containing cyclohexane group
Polymer xxx (xxxx) xxx
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Synthesis of high transparency polyarylates containing cyclohexane group Yu Zhang a, Guang-ming Yan b, Gang Zhang b, *, Sui-lin Liu b, Jie Yang b, c, ** a
College of Polymer Science and Engineering, Sichuan University, Chengdu, 610065, PR China Institute of Materials Science & Technology, Analytical & Testing Center, Sichuan University, Chengdu, 610064, PR China c State Key Laboratory of Polymer Materials Engineering (Sichuan University), Chengdu, 610065, PR China b
A R T I C L E I N F O
A B S T R A C T
Keywords: Polyarylate Cyclohexane Optical properties
A new kind of polyarylates containing different proportion of cyclohexane units in the main chain were syn thesized by using 2,2-bis (4-hydroxyphenyl) propane (BPA), 4, 40 -cyclohexane-1, 10 -diyldiphenol (BPZ), ter ephthaloyl dichloride (TPC) and isophthaloyl dichloride (IPC) through interfacial copolymerization at 25 � C. The intrinsic viscosity of resultant PZAs was 0.49–0.97 dL/g. The FT-IR, 1H NMR and XRD was used to characterize the chemical structure of polymer. The optical properties of PZAs were performed on UV–vis spectrophotometer. With the cyclohexane unit proportion in the polymer backbones increased to 40%, the transmittance at 400 nm and 450 nm can reach up to 87.41% and 88.07% respectively and the cutoff wavelength is 294 nm. These resultant copolymers were also found to have good thermal, mechanical performance and melt flowability (glass transition temperature of 194.8–197.1 � C, 5% mass loss temperature about 461 � C, tensile strength of 60–71 MPa, Young’s modulus:1.47–1.61 GPa, melt complex viscosity of 47–790 Pa s at 310 � C during the testing time (30 min)). The comprehensive properties of the resultant copolymers were similar or even much better than that of the commercial polyarylate U-100, they can be facile processed with solution or melt method and can be potential used in optical thin films and optical microlens.
1. Introduction As a kind of high-performance engineering plastic, polyarylates have good thermal stability, mechanical properties, chemical resistance and excellent transparency in the visible light region [1–3]. Owing to these advantages, commercial polyacrylates, polyiso/terephthalate of bisphenol A (U-polymer) developed by Unitika LTD, has been widely used in aerospace, electronics, automobiles, etc. However, the high melting viscosity, poor fluidity and low solubility in organic solvents limits the further application of polyarylates [4]. In the view of these existing problems, researchers have brought many strategies to over come these weaknesses, such as introducing polar side group [5–7], flexible structures [8], asymmetric elements [9–13], non-coplanar structure [14–16] and bulky pendant groups [17–23] in backbones and so on. Introduction of the bulky groups has become an important method to improve the transparency properties of polymers, such as polyimide [24,25], polyamide [26], poly (arylene sulfide sulfone) [27] and poly (aryl ether ketone) [28,29]. The incorporation of bulky pendant in the polymer chains would increase the voids between
molecular chains, thus, light can penetrate through polymer films more easily. The optical properties of polyarylate is also improved by inco porating bulky pendant into the main-chain [30–35]. Various pendant groups have been introduced in polymer chain to improve the optical properties of polymer, such as benzene ring, trifluoromethylphenyl unit and so on. As an aliphatic ring side chain, the introduction of cyclo hexane unit into the main-chain of polyarylates not only enlarge the free volume of polymer molecular chain, which results in an improved resin’s processability and optical properties, but also remain the thermal performance of polymers because of the chemical and thermal stability of the cyclohexane group. Therefore, in the last few years, incorporating cyclohexane in polymer chain has been proved to be an efficient way of increasing the transparency of polymers, such as polyimide [36], poly (arylene ether sulfone), as well as poly (arylene ether ketone) [37]. However, the introduction of cyclohexane in polyarylates to improve its transparency, to the best of our knowledge, has never been investigated. Thus, we expect to incorporate cyclohexane in the polymer backbone and improve the optical properties by increasing the free volume and reducing the interaction between the molecular chains, without loss the
* Corresponding author. ** Corresponding author. Institute of Materials Science & Technology, Analytical & Testing Center, Sichuan University, Chengdu 610064, PR China. E-mail addresses: [email protected] (G. Zhang), [email protected] (J. Yang). https://doi.org/10.1016/j.polymer.2019.122047 Received 14 October 2019; Received in revised form 26 November 2019; Accepted 1 December 2019 Available online 3 December 2019 0032-3861/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Yu Zhang, Polymer, https://doi.org/10.1016/j.polymer.2019.122047
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thermal stability of polyarylates. The monomer 4, 40 -cyclohexame-1, 10 diyldiphenol (BPZ) containing cyclohexane bulky pendant was synthe sized with the electrophilic substitution reaction of cyclohexanone and phenol. A series of polyacrylates were copolymerized by 2, 2-bis (4hydroxyphenyl) propane (BPA), 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ), 1, 4-benzenedicarbonyl chloride (TPC) and 1, 3-Benzenedicar bonyl dichloride (IPC) through interfacial polycondensation with a fixed ratio of IPC to TPC at 7: 3 which could balance the thermal per formance and processability of polyarylates. The effect of the ratio of BPZ to BPA on the thermal, mechanical as well as the optical properties of polyarylates were investigated in detail.
The typical polymerization of the copolymer was carried out as shown in Scheme 1, and the PZA46 was taken as an example to demonstrate the synthesis process. The BPZ (10.72 g, 0.04 mol), BPA (13.70 g, 0.06 mol), NaOH (8 g, 0.2 mol) and deionized water (200 ml) were all added into a 1000 mL triple-necked flask equipped with a mechanical stirrer. After the mixture dissolved, the surfactant BTEAC (0.5 g) was added and the solution of 120 ml dichloromethane con taining IPC (14.21 g, 0.07 mol) and TPC (6.09 g,0.03 mol) were added drop by drop within 10 min. The copolymerization reaction was kept for 4 h at 25 � C. Finally, the reaction solution was poured into deionized water to precipitation a white solid. The product obtained was pulver ized with crushing machine to powder and extracted with hot deionized water and ethanol. Finally, the polymer was dried in vacuum dry chamber under 100 � C for 12 h. PZA46: Yield: 33.68 g, yield: 90.0%. FT-IR (KBr, cm 1): 3052 (C–H aromatic ring), 2937 (-CH3), 2933, 2858 (–CH2–), 1741 (–CO–O-); 1H NMR (400 MHz, DMSO‑d6/TMS, ppm): 8.97–9.01 (d, 1H, H1); 8.41–8.47 (d, 2H, H2); 7.67–7.70 (t, 1H, H4); 8.30–8.33 (s, 1.7H, H4); 7.29–7.36 (d, 5.7H, H5); 7.12–7.19 (d, 5.7H, H6); 2.27–2.33 (s, 2.3H, H7); 1.69–1.77 (d, 8.6H, H8–H10). With the similar procedure, the samples PZA37, PZA28 and PZA19 containing different proportion of BPZ and BPA were also synthesized (copolymers were named PZAXY (X represents the proportion of BPZ, and Y is the proportion of BPA). The yields were as follows: PZA37, 34.71 g (93.8%), PZA28, 33.45 g (91.3%), PZA19, 33.98 g, (93.8%).
2. Experimental 2.1. Materials Terephthaloyl chloride (TPC), Isophthaloyl dichloride (IPC) (99.9%, Qingdao Benzo New Materials Company Ltd.), 2,2-bis (4-hydrox yphenyl) propane (BPA) (polymerization grade, Sinopec Mitsui), mer captoacetic acid (99%, Aladin Reagent Company), cyclohexanone (AR, Macklin Reagent Company), phenol (AR, Chengdu HuaXia Chemical Industry Company), sodium hydroxide (NaOH), Dichloromethane, hy drochloric acid (HCl), acetic acid, benzyltriethylammonium chloride (BTEAC) (98%, Aladin Reagent Company).The rest solvents and re agents were obtained by commercially way.
2.2.3. Measurements The HLC-8320 gel permeation chromatography (GPC) was per formed to obtain the number-average and weight-average molecular weights. The inherent viscosity of polymers was obtained with a Cannon-Ubbelodhe viscometer by single-point method. The SolomonCiuta equation [38] was shown below: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�ffiffi 2 ηsp lnηr ηint ¼ C
2.2. Synthesis of monomer 2.2.1. 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) The phenol (75.29 g, 0.8 mol) was added into a 250 ml triple-necked flask equipped with mechanical stirrer. A mixture of hydrochloric acid (60 ml) and acetic acid (30 ml) was added with mechanical stirring. Stirring continually until the temperature up to 50 � C. After adding the catalyst mercaptoacetic acid (0.5 g), cyclohexanone (19.63 g, 0.2 mol) was added dropwise. The reaction was kept for 20 h. The reaction mixture solution was filtered, and the solid product was washed with hot deionized water for 4 times. The pure product was obtained by the recrystallization procedure using the mixture of methanol/water as solvent (volume ratio was 2:1). Then the obtained monomer was dried in the vacuum dry chamber under 55 � C for 24 h. Yield: 47.44 g, yield: 88.5%. FT-IR (KBr, cm 1): 3588, 3433, 3217 – C benzene ring); 1H (-OH), 2939, 2856 (–CH2–), 1594, 1508, 1446 (C– NMR (400 MHz, DMSO‑d6/TMS, ppm): 9.08–9.15 (s, 2H, H1); 6.98–7.09 (d, 4H, H2); 6.55–6.65 (d, 4H, H3); 2.04–2.21 (s, 4H, H4); 1.32–1.51 (s, 6H, H5, H6), m/z (M ): 267.01, m/z (2M ): 535.24 (attributed to the molecular association of BPZ).
where ηr ¼ η=η0 ,ηsp ¼ η=η0 1. The 400 MHz 1H NMR spectra was measured by a Bruker Avance-400 NMR spectrometer with samples dissolved in the deuterated chloroform (CDCl3) or deuterated dimethyl sulfoxide (DMSO‑d6) as solvents. The FT-IR spectra was measured with Nicolet Nexus 670 instrument (Thermo Nicolet Corporation, USA). Liquid chromatography mass spectrometer (Hermo Fisher Scienti, TSQ Quantum Ultra) was utilized to quantify the element content in monomer. Aggregate structure was studied by X-ray diffraction (XRD) analysis with a scanning carried out from 5� to 80� on Philips electronic instrument (X’pert Pro MPD) with Cu-Kα at 40 kV and 150 mA. Differential scanning calorimetry (DSC, TA Q20) was carried out � under nitrogen atmosphere with a heat rate of 10 C/min and the test temperature is between 30 and 300 � C. Thermogravimetric analysis � (TGA) was carried out with a heating rate of 10 C/min under nitrogen � atmosphere from 30 to 800 C on the TGA Q500 V6.4 Build 193 thermal analysis instrument. Dynamic mechanical properties were tested by dynamic mechanical analyzer with tensile mode from 30 to 300 � C under a heating rate of 5 � C/min under air atmosphere and at the oscillation frequency of 1.0 Hz on TA Instruments (DMA Q800). The stress-strain behavior was measured on the MTS E50 electronic uni versal testing machine at room temperature. The load speed of tests was 2 mm/min. Each value obtained represented the average of three specimens. Parallel plate rheometer was fitted with 2.5 cm diameter stainless steel parallel plates on Bohlin Gemini 200 testing machine. The time sweep tests (0–1800 s) and the temperature sweep test (285–310 � C) were performed at a frequency of 1 Hz. The optical transmittance of the polymer films which prepared by the solution-casting method was measured by UV–Visible spectroscopy (U-2310 II) with a film thickness of 10–12 μm.
2.2.2. Synthesis of polymer In this study, polymers were synthesized by the fixed proportion of TPC and IPC (the mole ratio is 3: 7), and the polyarylates with a various proportion of BPA and BPZ (as shown in Table 1) were synthesized by the similar interfacial polymerization procedure. Table 1 GPC data and inherent viscosities of PZAs and reference sample U-100. Polymers U-100 PZA46 PZA37 PZA28 PZA19
Inherent viscosity (dL/g)a 0.52 0.49 0.66 0.67 0.97
GPC datab Mn � 104
Mw � 104
Mw/Mn
1.82 1.50 2.01 1.85 3.51
3.45 3.46 4.16 4.47 8.32
1.90 2.31 2.07 2.42 2.34
a Tested in polymer solution of 0.5 g/dL in NMP with a testing temperature of 30 � C. b Tested by GPC with samples dissolved in eluent THF.
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Scheme 1. Synthesis route of monomer 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) and copolymers (PZAs).
3. Results and discussion 3.1. Synthesis of monomer 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) The monomer was synthesized with phenol and cyclohexanone through an electrophilic substitution reaction under the acid condition for 20 h followed by the steps as shown in Scheme 1. Compared with the previous work [39,40], we have made some improvements in the syn thesis of BPZ monomer: i. The appropriate reduction of the concentra tion of the reaction system to avoid premature precipitation which will cause an inadequate reaction; ii. The addition of mercaptoacetic acid as catalyst to increase reactivity. Due to these improvements, the yield of BPZ was up to 88.5% which is much higher than that of earlier reported literature. Fig. 1 is the 1H NMR spectra and Fig. 2 is the FT-IR spectra of monomer BPZ. In the 1H NMR spectra, the signal near 9.11 ppm belongs to hydroxyl unit, and signals of proton in benzene rings are in the range from 6.60 to 7.09 ppm. Because of the different chemical condition of the proton in cyclohexyl unit, different signals in the range of 1.30–2.20 ppm are ascribed to cyclohexyl protons. The integral area of the proton signal peak is 1: 2: 2: 1.96: 3 as shown in Fig. 1, which agrees well with the theoretical protons ration of H1: H2: H3: H4: (H5–H6) (1: 2: 2: 2: 3). To further confirm the chemical structure of synthesized monomers, the FTIR spectra of monomer was obtained. As shown in Fig. 2, the absorption
Fig. 2. The FT-IR spectrum of BPZ.
Fig. 1. The 1H NMR spectrum of BPZ. 3
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of –OH are the three sharp peaks from 3588 cm 1 to 3200 cm 1. These three vibration peaks between 3300 cm 1 to 3600 cm 1 is probably attributed to the absorption of hydrogen bonding multiple association of –OH group. The absorption peaks near 2939 cm 1 and 2856 cm 1 are the characteristic absorption of –CH2-, which indicates the existence of – C stretching vibration of benzene ring is near cyclohexyl units. The C– 1594 cm 1,1508 cm 1 and 1446 cm 1. From the MS data, two obvious peaks can be found at 267.01 and 535.24, which are attributed to the bisphenol anion of BPZ and bi-molecular association of BPZ. This also indicates the association role of BPZ between the hydroxyl units, which is consistent with the result of FT-IR. Combining the 1H NMR, FT-IR and MS analysis, it is safe to conclude that the monomer is successfully synthesized as we expected. 3.2. Synthesis of PZAs A series of copolymers were synthesized by acyl chloride and two kinds of bisphenol (BPZ and BPA). During the synthesis, the acyl chlo ride (IPC: TPC ¼ 7: 3) was keep constant, while the proportion of BPZ: BPA varied from 4:6 to 1:9. The properties of PZAs are shown in Table 1. The molecular weight of these polymers was estimated via the intrinsic viscosity. As shown in Table 1, the intrinsic viscosity of PZAs is 0.49–0.97 dL/g that corresponding to the number-average as well as the weight-average molecular weights of 15000–35100 and 34500–83200, respectively, which indicates that the PZAs have high molecular weight. 1 H NMR spectra and FT-IR spectrum of PZAs are shown in Fig. 3 and Fig. 4, respectively. In the 1H NMR spectra of PZAs, the signal in the range of 7.65–9.00 ppm belongs to benzene rings of TPC and IPC, and H5, H6 at 7.32 and 7.15 ppm belong to benzene rings of BPA and BPZ. The proton signals of the benzene ring shift to low field because of the strong electrical absorption effect of the carbonyl unit, so the proton chemical shift of TPC and IPC is larger than that of BPA and BPZ. The proton signals at 2.30 ppm belongs to methylene units in the cyclohexane unit. For the reason that the chemical shift of H8, H9, H10 at 1.71 ppm are largely overlapped so that they are difficult to separate. Additionally, from the peak area integral of 1H NMR spectra of PAZs, it could confirm the proportions of each component are exactly in
Fig. 4. The FT-IR spectra of PZAs.
accordance with the expectation. The FT-IR spectra showed that the peak at 1735 cm 1 is the characteristic absorptions of ester group (–COO–). In addition, from Fig. 4, it can be observed the characteristic absorption of –OH disappeared, combined with the new absorption of –COO–, suggesting that the hydroxyl has reacted with acyl chloride completely during the polymerization. The results of 1H NMR and FT-IR indicate that the polyarylates are synthesized successfully. 3.3. Aggregate structure and thermal properties of copolymers As shown in Fig. 5, there is no obvious crystallization peak can be observed, and only one dispersing diffraction peaks can be found, which suggests the prepared copolymers are amorphous. The curves of DSC and TGA was obtained to assess the thermal
Fig. 3. The 1H NMR of PZAs. 4
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Fig. 7. TGA curves of PZAs and reference sample U-100. Fig. 5. XRD diffraction patterns of the PZAs.
3.4. Dynamic mechanical properties of polymers
properties of PZAs, which are shown in Figs. 6 and 7. It could be found the glass transition temperature of the resultant copolymers were 196.0, 196.9, 197.1 and 194.8 � C, respectively, with variation of the proportion of BPZ: BPA from 1: 9 to 4: 6. This indicates that the thermal perfor mance of PZAs is similar as that of commercial product U-100 (Tg ¼ 195.4 � C). Besides, it can be found that the glass transition temperature (Tg) of PZAs increased with the increase of monomer BPZ content. This is primarily because that the introduction of non-coplanar cyclohexane group hinders the chain segment motion. However, PZA46 doesn’t comply with the above trend. The glass transition temperature of PZA46 is the lowest among the copolymer PZAs which is caused by the lowest molecular weight of PZA46. From the curves of DSC, it could be observed no endothermic melting peak during the heating process, which suggests the copolymers are amorphous. This in agreement with XRD results. As shown in Fig. 7, with the proportion of BPZ: BPA varies from 1: 9 to 4: 6, the 5% mass-loss temperature (T5%) under nitrogen atmosphere (heating rate:10 � C/ min) are 466.1, 460.6, 462.3 and 461.4 � C respectively, exhibiting a similar good thermal stability to the commercial products U-100. The exacted data mentioned above was concluded in Table 2.
The thermal mechanical properties of PZAs was evaluated with DMA measurement. As shown in Fig. 8, the glass transition temperature tested by DMA is slightly higher than the results of DSC. The difference is caused by the different response of molecular segments between the two measure ments. As the storage modulus showed in Fig. 9 and Table 2, the storage modulus of PZAs are above 1.1 GPa at room temperature. It is worth noting that the polymers still remain high storage modulus even when the temperature is and even near the glass transition temperature. The glass transition temperature and the storage modulus are listed in Table 2. As demonstrated above, the prepared PZAs are confirmed to have good thermal-mechanical performance. 3.5. Tensile properties of polymers Fig. 10 shows the mechanical properties of the PZAs and the data are summarized in Table 2. The tensile strength of polymers is in the range of 60.4–71.6 MPa when the proportion of BPZ: BPA varied from 1: 9 to 4: 6. The storage modulus are about 1.47–1.61 GPa. The elongation at break is in the range of 16.84–21.14%. Compared to commercial prod uct U-100, the mechanical properties of PZAs are good and similar or slightly lower than that of U-100. 3.6. Rheological properties of polymers The effect of the ratio of BPZ and BPA on rheological properties was studied by the parallel plate rheometer. The complex viscosity of poly mers was also measured and the plots are shown in Figs. 11 and 12. The variation of complex viscosity with temperature is shown in Fig. 11. It is apparent that the complex viscosity of PZAs and U-100 decreased dramatically with the increase of temperature from 285 to 310 � C. However, compared with the reference sample U-100, except PZA19, the complex viscosities of PZAs are both lower, and are in the range of 36–795 Pa s from 285 to 310 � C. From the curves of complex viscosities versus temperature, it also could observe the PZA46 had the lowest complex viscosity of 36–133 Pa s. It is well known that both the glass transition temperature and chemical structure have relationship with complex viscosity. The Tg values of PZA19, PZA28 and PZA37 increase gradually with the increase of cyclohexane which will lead to viscosity increment while the complex viscosity decreased obviously. It is consistent with the regularity that the introduction of large pendant group in molecular can reduce the complex viscosity of polymers, and the side groups have a greater impact on the complex viscosity of PZAs
Fig. 6. DSC curves of PZAs and reference sample U-100. 5
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Table 2 The comparison of thermal and mechanical properties of PZAs and reference sample U-100. Polymers
Tga (oC)
Tgb (oC)
T5%c (oC)
Char yield (%)
Tensile strength (MPa)
Young’s modulus (GPa)
Elongation at break (%)
Storage modulus (GPa)
U-100 PZA46 PZA 37 PZA 28 PZA 19
195.4 194.8 197.1 196.9 196.0
219.5 216.0 217.7 217.7 217.6
482.03 461.44 462.32 460.64 466.13
30.58 24.02 24.64 26.28 26.60
70.38 71.62 67.39 61.51 60.41
1.69 1.61 1.61 1.59 1.47
36.27 18.03 16.84 17.67 21.14
1.85 1.13 1.50 1.34 1.52
a b c
Tested at DSC with a heating rate of 10 � C/min. Tested at DMA with a heating rate of 5 � C/min. Tested at TGA with a heating rate of 10 � C/min.
Fig. 10. The tensile strength and tensile modulus of PZAs and reference sample U-100. Fig. 8. The DMA plots (tanδ) of PZAs and reference sample U-100.
Fig. 11. Plots of complex viscosities versus temperature for PZAs and reference sample U-100. Fig. 9. The DMA plots (storage modulus) of PZAs and reference sample U-100.
during the testing time (0–1800 s at 310 � C) whereas the complex vis cosity of U-100 increases slowly. This suggests that the PZAs have good melting stability. Combined the results of Figs. 11 and 12, it can be concluded that the PZAs, especially PZA46, has both good melting processability and melting stability which makes these resins much easier to process, especially for the super-thin optical transparency films.
than Tgs. What’s more, the glass transition temperature of PZAs differs by 2–3 � C, and it has less effect on complex viscosity. As a result, we think large pendant group plays a leading role rather than Tg in the reduction of complex viscosity. The introduction of the bulky cyclo hexane unit decreases the interaction between the molecular backbones, and the hindrance of the molecular reduce, which then results in an easier molecular chains’ motivation. With the increase of BPZ content, the improvement of fluidity is more significant, indicating that the resultant polyarylates (PZAs) have good melting processability. As shown in Fig. 12, the complex viscosity of PZAs is almost unchanged
3.7. Optical properties of PZAs The obtained polyarylates have good solubility. Then they were casted into films with the solution method. Fig. 13 shows the images of PZAs films. The thickness of films is about 10–12 μm and all of them are 6
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Fig. 12. Plots of complex viscosities versus time (at 310 � C) for PZAs and reference sample U-100.
Fig. 13. The images of PZAs and reference sample U-100 films with the thickness of 10–12 μm.
colorless and transparent. The films were detected by UV–vis. The transmittance of samples at 400 nm (T400), 450 nm (T450) and cut off wavelength (λ0) are listed in Table 3. As demonstrated in Fig. 14 and Table 3, it is obviously observed that the PZA46 has the best optical properties among these copolymers, and the transparency is better than commercial product U-100. The transmittance of PZA46 at 400 nm and 450 nm are both higher than that of U-100. In addition, the cut off wavelength is further lower (about 26 nm) than U-100. As the propor tion of BPZ increased, the optical properties of copolymers increased distinctly both of T400, T450 and cut off wavelength. This higher light transmittance is explained by the existence of large pendant group Table 3 The transmittance at 400 nm (T400), 450 nm (T450) and cut off wavelength (λ0) of PZAs and reference sample U-100 films. Polymer
T400 (nm)
T450 (nm)
Tcutoff (nm)
U-100 PZA46 PZA37 PZA28 PZA19
86.65 87.41 86.82 86.82 83.96
87.95 88.07 87.70 87.81 85.24
320 294 300 300 308
Fig. 14. The UV–vis spectra of PZAs and reference sample U-100 films.
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cyclohexyl, which increases the free volume of the copolymer molecular chains.
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Wadgaonkar, Aromatic polyesters containing pendant azido groups: synthesis, characterization, chemical modification and thermal cross-linking, Eur. Polym. J. 116 (2019) 180–189. [19] Y.K. Chamkure, R.K. Sharma, New organosoluble polyarylates containing pendent fluorene units: synthesis, characterization and thermal behaviour, J. Polym. Res. 26 (1) (2019) 17. [20] F. Akutsu, M. Inoki, K.I. Takahashi, T. Yonemura, Y. Kasashima, K. Naruchi, Synthesis and properties of polyarylates derived from 4,400 -Dihydroxy-o-terphenyl, Polym. J. 28 (12) (1996) 1107–1109. [21] H.J. Jeong, M.A. Kakimoto, Y. Imai, Synthesis and characterization of novel polyarylates from 2,5-bis(4-hydroxyphenyl)-3,4-diphenylfuran and aromatic diacid chlorides, J. Polym. Sci., Polym. Chem. Ed. 29 (9) (1991) 1293–1299. [22] B. Tamami, H. Yeganeh, G.A. Kohmareh, Synthesis and characterization of novel polyesters derived from 4-aryl-2,6-bis (4-chlorocarbonyl phenyl) pyridines and various aromatic diols, Eur. Polym. J. 40 (8) (2004) 1651–1657. [23] P.W. Morgan, Aromatic polyesters with large cross-planar substituents, Macromolecules 3 (5) (1970) 536–544. [24] X. Zhao, C. Wang, L. Chen, M. Zhu, Novel poly (fluorinated imide)s containing naphthalene pendant group: synthesis and characterization, Colloid Polym. Sci. 287 (11) (2009) 1331–1337. [25] C. Wang, X. Zhao, G. Li, J. Jiang, High solubility and optical transparency of novel polyimides containing 3, 3’, 5, 5’-tetramethyl pendant groups and 4-tert-butylto luene moiety, Polym. Degrad. Stab. 94 (9) (2009) 1526–1532. [26] G. Zhang, M.L. Zhang, X.J. Wang, S.R. Long, J. Yang, Synthesis of high refractive index polyamides containing thio-ether units, J. Macromol. Sci. 47 (9) (2010) 892–902. [27] G. Zhang, H.H. Ren, D.S. Li, S.R. Long, J. Yang, Synthesis of highly refractive and transparent poly (arylene sulfide sulfone) based on 4,6-dichloropyrimidine and 3,6-dichloropyridazine, Polymer 54 (2) (2013) 601–606. [28] H. Ohno, S. Takeoka, K. Oyaizu, Synthesis of novel fluorine-containing poly (aryl ether ketone)s, Polym. Adv. Technol. 11 (8-12) (2015) 757–765. [29] Y. Du, S. Zhang, X. Jiang, K. Zhu, Z. Geng, Y. Fang, P. Huo, C. Liu, Y. Song, G. Wang, Synthesis and optical properties of poly (aryl ether ketone)s incorporating porphyrins in the backbones, J. Polym. Sci., Polym. Chem. Ed. 52 (9) (2014) 1282–1290. [30] G.S. Liou, C.W. Chang, H.M. Huang, S.H. Hsiao, Synthesis and electrochromism of novel organosoluble polyarylates bearing triphenylamine moieties, J. Polym. Sci., Polym. Chem. Ed. 45 (10) (2007) 2004–2014. [31] Z.Z. Huang, X.L. Pei, T. Wu, S.R. Sheng, S.Y. Lin, C.S. Song, Synthesis and characterization of new fluorinated aromatic polyesters containing trifluoromethylphenoxy pendant groups, J. Appl. Polym. Sci. 119 (2) (2010) 702–708.
4. Conclusions The Bisphenol-monomer containing cyclohexane unit was synthe sized successfully. It was conducted to polymerize with BPA, TPC and IPC at room temperature to yield a series high transparent polyarylates. These obtained copolymers were proved to have good thermal proper ties: the T5% can up to 461 � C, similar glass transition temperature (Tg) with commercial product U-100. We also found that the glass transition temperature increased gradually with the addition of monomer BPZ due to the existence of the large cyclohexane side group. It was also recog nized that the optical transmittance can be thoroughly improved by introducing the large cyclohexyl side group. The transmittance at T400 increased from 83.96 (PZA19) to 87.41 nm (PZA46), and that of T450 increased from 85.24 to 88.07 nm, so as the cutoff wavelength decreased from 308 to 294 nm with the increase of the proportion of BPZ. Addi tionally, from the rheological testing, it was apparent that the PZAs especially PZA46 had better melting fluidity and stability of 47–70 Pa s at 310 � C and 133-36 Pa s with the testing temperature increased from 285 to 310 � C than that of commercial product U-100. With the increase of cyclohexyl units in molecular chain, the melting fluidity of PZAs improved. As mentioned above, the resultant polyarylates have excel lent comprehensive properties, and can be potential widely used as a new optical material in industry, especially in the application of microlens and optical thin films. Author contribution Gang Zhang: Conceptualization, Methodology, Writing- Reviewing and Editing, Supervision. Jie Yang: Supervision. Yu Zhang: Writing- Original draft preparation, Investigation, Soft ware, Resources. Guangming Yan: Data curation, Software. Suilin Liu: Visualization, Validation, Reviewing and Editing. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was supported by the department of science and tech nology of Jiangsu province (BE2019008-4), Natural Science Foundation of China (NSFC-21304060, 51573103), the Fundamental Research Funds for the Central Universities, and the Outstanding Young Scholars Fund of Sichuan University 2015SCU04A25. References [1] P.K. Bhowmik, H. Han, Fully aromatic liquid-crystalline polyesters of phenylsubstituted 4, 4’-biphenols and 1, 1’-binaphthyl-4, 4’-diol with either 2-bromo terephthalic acid or 2-phenylterephthalic aci, Macromolecules 26 (20) (1993) 5287–5294. [2] Z. Ping, W. Linbo, L. Bo-Geng, Thermal stability of aromatic polyesters prepared from diphenolic acid and its esters, Polym. Degrad. Stabil. 94 (8) (2009) 1261–1266. [3] G. Liou, Synthesis and photoluminescence of novel organo-soluble polyarylates bearing (N-carbazolyl) triphenylamine moieties, Polym. J. 39 (5) (2007) 448–457. [4] P. Liu, T. Wu, M. Shi, G. Ye, J. Xu, Synthesis and characterization of readily soluble polyarylates derived from either 1,1-bis(4-hydroxyphenyl)-1-phenylethane or tetramethylbisphenol A and aromatic diacid chlorides, J. Appl. Polym. Sci. 119 (4) (2011) 1923–1930.
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[32] G.S. Liou, S.M. Lin, H.J. Yen, Synthesis and photoluminescence properties of novel polyarylates bearing pendent naphthylamine chromophores, Eur. Polym. J. 44 (8) (2008) 2608–2618. [33] I. Zadro_zna, M. Mysłek, Novel optical material: polyarylates with azomethine sidechain groups, J. Appl. Polym. Sci. 80 (9) (2001) 9. [34] J. Liu, L. Wang, Z. Zhen, X. Liu, Synthesis of novel polyarylate with elecrooptical chromophores as side chain as electro-optic host polymer, Colloid Polym. Sci. 290 (12) (2012) 1215–1220. [35] G. Zhang, Y. Zhou, Y. Li, X.J. Wang, S.R. Long, J. Yang, Investigation of the synthesis and properties of isophorone and ether units based semi-aromatic polyamides, RSC Adv. 5 (62) (2015) 49958–49967. [36] D.J. Liaw, C.C. Huang, W.H. Chen, Optically transparency and light color of novel highly organosoluble alicyclic polyimides with 4-tert-butylcyclohexyl group, Macromol. Chem. Phys. 207 (4) (2010) 434–443.
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Synthesis of high transparency polyarylates containing cyclohexane group Yu Zhang a, Guang-ming Yan b, Gang Zhang b, *, Sui-lin Liu b, Jie Yang b, c, ** a
College of Polymer Science and Engineering, Sichuan University, Chengdu, 610065, PR China Institute of Materials Science & Technology, Analytical & Testing Center, Sichuan University, Chengdu, 610064, PR China c State Key Laboratory of Polymer Materials Engineering (Sichuan University), Chengdu, 610065, PR China b
A R T I C L E I N F O
A B S T R A C T
Keywords: Polyarylate Cyclohexane Optical properties
A new kind of polyarylates containing different proportion of cyclohexane units in the main chain were syn thesized by using 2,2-bis (4-hydroxyphenyl) propane (BPA), 4, 40 -cyclohexane-1, 10 -diyldiphenol (BPZ), ter ephthaloyl dichloride (TPC) and isophthaloyl dichloride (IPC) through interfacial copolymerization at 25 � C. The intrinsic viscosity of resultant PZAs was 0.49–0.97 dL/g. The FT-IR, 1H NMR and XRD was used to characterize the chemical structure of polymer. The optical properties of PZAs were performed on UV–vis spectrophotometer. With the cyclohexane unit proportion in the polymer backbones increased to 40%, the transmittance at 400 nm and 450 nm can reach up to 87.41% and 88.07% respectively and the cutoff wavelength is 294 nm. These resultant copolymers were also found to have good thermal, mechanical performance and melt flowability (glass transition temperature of 194.8–197.1 � C, 5% mass loss temperature about 461 � C, tensile strength of 60–71 MPa, Young’s modulus:1.47–1.61 GPa, melt complex viscosity of 47–790 Pa s at 310 � C during the testing time (30 min)). The comprehensive properties of the resultant copolymers were similar or even much better than that of the commercial polyarylate U-100, they can be facile processed with solution or melt method and can be potential used in optical thin films and optical microlens.
1. Introduction As a kind of high-performance engineering plastic, polyarylates have good thermal stability, mechanical properties, chemical resistance and excellent transparency in the visible light region [1–3]. Owing to these advantages, commercial polyacrylates, polyiso/terephthalate of bisphenol A (U-polymer) developed by Unitika LTD, has been widely used in aerospace, electronics, automobiles, etc. However, the high melting viscosity, poor fluidity and low solubility in organic solvents limits the further application of polyarylates [4]. In the view of these existing problems, researchers have brought many strategies to over come these weaknesses, such as introducing polar side group [5–7], flexible structures [8], asymmetric elements [9–13], non-coplanar structure [14–16] and bulky pendant groups [17–23] in backbones and so on. Introduction of the bulky groups has become an important method to improve the transparency properties of polymers, such as polyimide [24,25], polyamide [26], poly (arylene sulfide sulfone) [27] and poly (aryl ether ketone) [28,29]. The incorporation of bulky pendant in the polymer chains would increase the voids between
molecular chains, thus, light can penetrate through polymer films more easily. The optical properties of polyarylate is also improved by inco porating bulky pendant into the main-chain [30–35]. Various pendant groups have been introduced in polymer chain to improve the optical properties of polymer, such as benzene ring, trifluoromethylphenyl unit and so on. As an aliphatic ring side chain, the introduction of cyclo hexane unit into the main-chain of polyarylates not only enlarge the free volume of polymer molecular chain, which results in an improved resin’s processability and optical properties, but also remain the thermal performance of polymers because of the chemical and thermal stability of the cyclohexane group. Therefore, in the last few years, incorporating cyclohexane in polymer chain has been proved to be an efficient way of increasing the transparency of polymers, such as polyimide [36], poly (arylene ether sulfone), as well as poly (arylene ether ketone) [37]. However, the introduction of cyclohexane in polyarylates to improve its transparency, to the best of our knowledge, has never been investigated. Thus, we expect to incorporate cyclohexane in the polymer backbone and improve the optical properties by increasing the free volume and reducing the interaction between the molecular chains, without loss the
* Corresponding author. ** Corresponding author. Institute of Materials Science & Technology, Analytical & Testing Center, Sichuan University, Chengdu 610064, PR China. E-mail addresses: [email protected] (G. Zhang), [email protected] (J. Yang). https://doi.org/10.1016/j.polymer.2019.122047 Received 14 October 2019; Received in revised form 26 November 2019; Accepted 1 December 2019 Available online 3 December 2019 0032-3861/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: Yu Zhang, Polymer, https://doi.org/10.1016/j.polymer.2019.122047
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thermal stability of polyarylates. The monomer 4, 40 -cyclohexame-1, 10 diyldiphenol (BPZ) containing cyclohexane bulky pendant was synthe sized with the electrophilic substitution reaction of cyclohexanone and phenol. A series of polyacrylates were copolymerized by 2, 2-bis (4hydroxyphenyl) propane (BPA), 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ), 1, 4-benzenedicarbonyl chloride (TPC) and 1, 3-Benzenedicar bonyl dichloride (IPC) through interfacial polycondensation with a fixed ratio of IPC to TPC at 7: 3 which could balance the thermal per formance and processability of polyarylates. The effect of the ratio of BPZ to BPA on the thermal, mechanical as well as the optical properties of polyarylates were investigated in detail.
The typical polymerization of the copolymer was carried out as shown in Scheme 1, and the PZA46 was taken as an example to demonstrate the synthesis process. The BPZ (10.72 g, 0.04 mol), BPA (13.70 g, 0.06 mol), NaOH (8 g, 0.2 mol) and deionized water (200 ml) were all added into a 1000 mL triple-necked flask equipped with a mechanical stirrer. After the mixture dissolved, the surfactant BTEAC (0.5 g) was added and the solution of 120 ml dichloromethane con taining IPC (14.21 g, 0.07 mol) and TPC (6.09 g,0.03 mol) were added drop by drop within 10 min. The copolymerization reaction was kept for 4 h at 25 � C. Finally, the reaction solution was poured into deionized water to precipitation a white solid. The product obtained was pulver ized with crushing machine to powder and extracted with hot deionized water and ethanol. Finally, the polymer was dried in vacuum dry chamber under 100 � C for 12 h. PZA46: Yield: 33.68 g, yield: 90.0%. FT-IR (KBr, cm 1): 3052 (C–H aromatic ring), 2937 (-CH3), 2933, 2858 (–CH2–), 1741 (–CO–O-); 1H NMR (400 MHz, DMSO‑d6/TMS, ppm): 8.97–9.01 (d, 1H, H1); 8.41–8.47 (d, 2H, H2); 7.67–7.70 (t, 1H, H4); 8.30–8.33 (s, 1.7H, H4); 7.29–7.36 (d, 5.7H, H5); 7.12–7.19 (d, 5.7H, H6); 2.27–2.33 (s, 2.3H, H7); 1.69–1.77 (d, 8.6H, H8–H10). With the similar procedure, the samples PZA37, PZA28 and PZA19 containing different proportion of BPZ and BPA were also synthesized (copolymers were named PZAXY (X represents the proportion of BPZ, and Y is the proportion of BPA). The yields were as follows: PZA37, 34.71 g (93.8%), PZA28, 33.45 g (91.3%), PZA19, 33.98 g, (93.8%).
2. Experimental 2.1. Materials Terephthaloyl chloride (TPC), Isophthaloyl dichloride (IPC) (99.9%, Qingdao Benzo New Materials Company Ltd.), 2,2-bis (4-hydrox yphenyl) propane (BPA) (polymerization grade, Sinopec Mitsui), mer captoacetic acid (99%, Aladin Reagent Company), cyclohexanone (AR, Macklin Reagent Company), phenol (AR, Chengdu HuaXia Chemical Industry Company), sodium hydroxide (NaOH), Dichloromethane, hy drochloric acid (HCl), acetic acid, benzyltriethylammonium chloride (BTEAC) (98%, Aladin Reagent Company).The rest solvents and re agents were obtained by commercially way.
2.2.3. Measurements The HLC-8320 gel permeation chromatography (GPC) was per formed to obtain the number-average and weight-average molecular weights. The inherent viscosity of polymers was obtained with a Cannon-Ubbelodhe viscometer by single-point method. The SolomonCiuta equation [38] was shown below: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�ffiffi 2 ηsp lnηr ηint ¼ C
2.2. Synthesis of monomer 2.2.1. 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) The phenol (75.29 g, 0.8 mol) was added into a 250 ml triple-necked flask equipped with mechanical stirrer. A mixture of hydrochloric acid (60 ml) and acetic acid (30 ml) was added with mechanical stirring. Stirring continually until the temperature up to 50 � C. After adding the catalyst mercaptoacetic acid (0.5 g), cyclohexanone (19.63 g, 0.2 mol) was added dropwise. The reaction was kept for 20 h. The reaction mixture solution was filtered, and the solid product was washed with hot deionized water for 4 times. The pure product was obtained by the recrystallization procedure using the mixture of methanol/water as solvent (volume ratio was 2:1). Then the obtained monomer was dried in the vacuum dry chamber under 55 � C for 24 h. Yield: 47.44 g, yield: 88.5%. FT-IR (KBr, cm 1): 3588, 3433, 3217 – C benzene ring); 1H (-OH), 2939, 2856 (–CH2–), 1594, 1508, 1446 (C– NMR (400 MHz, DMSO‑d6/TMS, ppm): 9.08–9.15 (s, 2H, H1); 6.98–7.09 (d, 4H, H2); 6.55–6.65 (d, 4H, H3); 2.04–2.21 (s, 4H, H4); 1.32–1.51 (s, 6H, H5, H6), m/z (M ): 267.01, m/z (2M ): 535.24 (attributed to the molecular association of BPZ).
where ηr ¼ η=η0 ,ηsp ¼ η=η0 1. The 400 MHz 1H NMR spectra was measured by a Bruker Avance-400 NMR spectrometer with samples dissolved in the deuterated chloroform (CDCl3) or deuterated dimethyl sulfoxide (DMSO‑d6) as solvents. The FT-IR spectra was measured with Nicolet Nexus 670 instrument (Thermo Nicolet Corporation, USA). Liquid chromatography mass spectrometer (Hermo Fisher Scienti, TSQ Quantum Ultra) was utilized to quantify the element content in monomer. Aggregate structure was studied by X-ray diffraction (XRD) analysis with a scanning carried out from 5� to 80� on Philips electronic instrument (X’pert Pro MPD) with Cu-Kα at 40 kV and 150 mA. Differential scanning calorimetry (DSC, TA Q20) was carried out � under nitrogen atmosphere with a heat rate of 10 C/min and the test temperature is between 30 and 300 � C. Thermogravimetric analysis � (TGA) was carried out with a heating rate of 10 C/min under nitrogen � atmosphere from 30 to 800 C on the TGA Q500 V6.4 Build 193 thermal analysis instrument. Dynamic mechanical properties were tested by dynamic mechanical analyzer with tensile mode from 30 to 300 � C under a heating rate of 5 � C/min under air atmosphere and at the oscillation frequency of 1.0 Hz on TA Instruments (DMA Q800). The stress-strain behavior was measured on the MTS E50 electronic uni versal testing machine at room temperature. The load speed of tests was 2 mm/min. Each value obtained represented the average of three specimens. Parallel plate rheometer was fitted with 2.5 cm diameter stainless steel parallel plates on Bohlin Gemini 200 testing machine. The time sweep tests (0–1800 s) and the temperature sweep test (285–310 � C) were performed at a frequency of 1 Hz. The optical transmittance of the polymer films which prepared by the solution-casting method was measured by UV–Visible spectroscopy (U-2310 II) with a film thickness of 10–12 μm.
2.2.2. Synthesis of polymer In this study, polymers were synthesized by the fixed proportion of TPC and IPC (the mole ratio is 3: 7), and the polyarylates with a various proportion of BPA and BPZ (as shown in Table 1) were synthesized by the similar interfacial polymerization procedure. Table 1 GPC data and inherent viscosities of PZAs and reference sample U-100. Polymers U-100 PZA46 PZA37 PZA28 PZA19
Inherent viscosity (dL/g)a 0.52 0.49 0.66 0.67 0.97
GPC datab Mn � 104
Mw � 104
Mw/Mn
1.82 1.50 2.01 1.85 3.51
3.45 3.46 4.16 4.47 8.32
1.90 2.31 2.07 2.42 2.34
a Tested in polymer solution of 0.5 g/dL in NMP with a testing temperature of 30 � C. b Tested by GPC with samples dissolved in eluent THF.
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Scheme 1. Synthesis route of monomer 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) and copolymers (PZAs).
3. Results and discussion 3.1. Synthesis of monomer 4, 40 -cyclohexame-1, 10 -diyldiphenol (BPZ) The monomer was synthesized with phenol and cyclohexanone through an electrophilic substitution reaction under the acid condition for 20 h followed by the steps as shown in Scheme 1. Compared with the previous work [39,40], we have made some improvements in the syn thesis of BPZ monomer: i. The appropriate reduction of the concentra tion of the reaction system to avoid premature precipitation which will cause an inadequate reaction; ii. The addition of mercaptoacetic acid as catalyst to increase reactivity. Due to these improvements, the yield of BPZ was up to 88.5% which is much higher than that of earlier reported literature. Fig. 1 is the 1H NMR spectra and Fig. 2 is the FT-IR spectra of monomer BPZ. In the 1H NMR spectra, the signal near 9.11 ppm belongs to hydroxyl unit, and signals of proton in benzene rings are in the range from 6.60 to 7.09 ppm. Because of the different chemical condition of the proton in cyclohexyl unit, different signals in the range of 1.30–2.20 ppm are ascribed to cyclohexyl protons. The integral area of the proton signal peak is 1: 2: 2: 1.96: 3 as shown in Fig. 1, which agrees well with the theoretical protons ration of H1: H2: H3: H4: (H5–H6) (1: 2: 2: 2: 3). To further confirm the chemical structure of synthesized monomers, the FTIR spectra of monomer was obtained. As shown in Fig. 2, the absorption
Fig. 2. The FT-IR spectrum of BPZ.
Fig. 1. The 1H NMR spectrum of BPZ. 3
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of –OH are the three sharp peaks from 3588 cm 1 to 3200 cm 1. These three vibration peaks between 3300 cm 1 to 3600 cm 1 is probably attributed to the absorption of hydrogen bonding multiple association of –OH group. The absorption peaks near 2939 cm 1 and 2856 cm 1 are the characteristic absorption of –CH2-, which indicates the existence of – C stretching vibration of benzene ring is near cyclohexyl units. The C– 1594 cm 1,1508 cm 1 and 1446 cm 1. From the MS data, two obvious peaks can be found at 267.01 and 535.24, which are attributed to the bisphenol anion of BPZ and bi-molecular association of BPZ. This also indicates the association role of BPZ between the hydroxyl units, which is consistent with the result of FT-IR. Combining the 1H NMR, FT-IR and MS analysis, it is safe to conclude that the monomer is successfully synthesized as we expected. 3.2. Synthesis of PZAs A series of copolymers were synthesized by acyl chloride and two kinds of bisphenol (BPZ and BPA). During the synthesis, the acyl chlo ride (IPC: TPC ¼ 7: 3) was keep constant, while the proportion of BPZ: BPA varied from 4:6 to 1:9. The properties of PZAs are shown in Table 1. The molecular weight of these polymers was estimated via the intrinsic viscosity. As shown in Table 1, the intrinsic viscosity of PZAs is 0.49–0.97 dL/g that corresponding to the number-average as well as the weight-average molecular weights of 15000–35100 and 34500–83200, respectively, which indicates that the PZAs have high molecular weight. 1 H NMR spectra and FT-IR spectrum of PZAs are shown in Fig. 3 and Fig. 4, respectively. In the 1H NMR spectra of PZAs, the signal in the range of 7.65–9.00 ppm belongs to benzene rings of TPC and IPC, and H5, H6 at 7.32 and 7.15 ppm belong to benzene rings of BPA and BPZ. The proton signals of the benzene ring shift to low field because of the strong electrical absorption effect of the carbonyl unit, so the proton chemical shift of TPC and IPC is larger than that of BPA and BPZ. The proton signals at 2.30 ppm belongs to methylene units in the cyclohexane unit. For the reason that the chemical shift of H8, H9, H10 at 1.71 ppm are largely overlapped so that they are difficult to separate. Additionally, from the peak area integral of 1H NMR spectra of PAZs, it could confirm the proportions of each component are exactly in
Fig. 4. The FT-IR spectra of PZAs.
accordance with the expectation. The FT-IR spectra showed that the peak at 1735 cm 1 is the characteristic absorptions of ester group (–COO–). In addition, from Fig. 4, it can be observed the characteristic absorption of –OH disappeared, combined with the new absorption of –COO–, suggesting that the hydroxyl has reacted with acyl chloride completely during the polymerization. The results of 1H NMR and FT-IR indicate that the polyarylates are synthesized successfully. 3.3. Aggregate structure and thermal properties of copolymers As shown in Fig. 5, there is no obvious crystallization peak can be observed, and only one dispersing diffraction peaks can be found, which suggests the prepared copolymers are amorphous. The curves of DSC and TGA was obtained to assess the thermal
Fig. 3. The 1H NMR of PZAs. 4
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Fig. 7. TGA curves of PZAs and reference sample U-100. Fig. 5. XRD diffraction patterns of the PZAs.
3.4. Dynamic mechanical properties of polymers
properties of PZAs, which are shown in Figs. 6 and 7. It could be found the glass transition temperature of the resultant copolymers were 196.0, 196.9, 197.1 and 194.8 � C, respectively, with variation of the proportion of BPZ: BPA from 1: 9 to 4: 6. This indicates that the thermal perfor mance of PZAs is similar as that of commercial product U-100 (Tg ¼ 195.4 � C). Besides, it can be found that the glass transition temperature (Tg) of PZAs increased with the increase of monomer BPZ content. This is primarily because that the introduction of non-coplanar cyclohexane group hinders the chain segment motion. However, PZA46 doesn’t comply with the above trend. The glass transition temperature of PZA46 is the lowest among the copolymer PZAs which is caused by the lowest molecular weight of PZA46. From the curves of DSC, it could be observed no endothermic melting peak during the heating process, which suggests the copolymers are amorphous. This in agreement with XRD results. As shown in Fig. 7, with the proportion of BPZ: BPA varies from 1: 9 to 4: 6, the 5% mass-loss temperature (T5%) under nitrogen atmosphere (heating rate:10 � C/ min) are 466.1, 460.6, 462.3 and 461.4 � C respectively, exhibiting a similar good thermal stability to the commercial products U-100. The exacted data mentioned above was concluded in Table 2.
The thermal mechanical properties of PZAs was evaluated with DMA measurement. As shown in Fig. 8, the glass transition temperature tested by DMA is slightly higher than the results of DSC. The difference is caused by the different response of molecular segments between the two measure ments. As the storage modulus showed in Fig. 9 and Table 2, the storage modulus of PZAs are above 1.1 GPa at room temperature. It is worth noting that the polymers still remain high storage modulus even when the temperature is and even near the glass transition temperature. The glass transition temperature and the storage modulus are listed in Table 2. As demonstrated above, the prepared PZAs are confirmed to have good thermal-mechanical performance. 3.5. Tensile properties of polymers Fig. 10 shows the mechanical properties of the PZAs and the data are summarized in Table 2. The tensile strength of polymers is in the range of 60.4–71.6 MPa when the proportion of BPZ: BPA varied from 1: 9 to 4: 6. The storage modulus are about 1.47–1.61 GPa. The elongation at break is in the range of 16.84–21.14%. Compared to commercial prod uct U-100, the mechanical properties of PZAs are good and similar or slightly lower than that of U-100. 3.6. Rheological properties of polymers The effect of the ratio of BPZ and BPA on rheological properties was studied by the parallel plate rheometer. The complex viscosity of poly mers was also measured and the plots are shown in Figs. 11 and 12. The variation of complex viscosity with temperature is shown in Fig. 11. It is apparent that the complex viscosity of PZAs and U-100 decreased dramatically with the increase of temperature from 285 to 310 � C. However, compared with the reference sample U-100, except PZA19, the complex viscosities of PZAs are both lower, and are in the range of 36–795 Pa s from 285 to 310 � C. From the curves of complex viscosities versus temperature, it also could observe the PZA46 had the lowest complex viscosity of 36–133 Pa s. It is well known that both the glass transition temperature and chemical structure have relationship with complex viscosity. The Tg values of PZA19, PZA28 and PZA37 increase gradually with the increase of cyclohexane which will lead to viscosity increment while the complex viscosity decreased obviously. It is consistent with the regularity that the introduction of large pendant group in molecular can reduce the complex viscosity of polymers, and the side groups have a greater impact on the complex viscosity of PZAs
Fig. 6. DSC curves of PZAs and reference sample U-100. 5
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Table 2 The comparison of thermal and mechanical properties of PZAs and reference sample U-100. Polymers
Tga (oC)
Tgb (oC)
T5%c (oC)
Char yield (%)
Tensile strength (MPa)
Young’s modulus (GPa)
Elongation at break (%)
Storage modulus (GPa)
U-100 PZA46 PZA 37 PZA 28 PZA 19
195.4 194.8 197.1 196.9 196.0
219.5 216.0 217.7 217.7 217.6
482.03 461.44 462.32 460.64 466.13
30.58 24.02 24.64 26.28 26.60
70.38 71.62 67.39 61.51 60.41
1.69 1.61 1.61 1.59 1.47
36.27 18.03 16.84 17.67 21.14
1.85 1.13 1.50 1.34 1.52
a b c
Tested at DSC with a heating rate of 10 � C/min. Tested at DMA with a heating rate of 5 � C/min. Tested at TGA with a heating rate of 10 � C/min.
Fig. 10. The tensile strength and tensile modulus of PZAs and reference sample U-100. Fig. 8. The DMA plots (tanδ) of PZAs and reference sample U-100.
Fig. 11. Plots of complex viscosities versus temperature for PZAs and reference sample U-100. Fig. 9. The DMA plots (storage modulus) of PZAs and reference sample U-100.
during the testing time (0–1800 s at 310 � C) whereas the complex vis cosity of U-100 increases slowly. This suggests that the PZAs have good melting stability. Combined the results of Figs. 11 and 12, it can be concluded that the PZAs, especially PZA46, has both good melting processability and melting stability which makes these resins much easier to process, especially for the super-thin optical transparency films.
than Tgs. What’s more, the glass transition temperature of PZAs differs by 2–3 � C, and it has less effect on complex viscosity. As a result, we think large pendant group plays a leading role rather than Tg in the reduction of complex viscosity. The introduction of the bulky cyclo hexane unit decreases the interaction between the molecular backbones, and the hindrance of the molecular reduce, which then results in an easier molecular chains’ motivation. With the increase of BPZ content, the improvement of fluidity is more significant, indicating that the resultant polyarylates (PZAs) have good melting processability. As shown in Fig. 12, the complex viscosity of PZAs is almost unchanged
3.7. Optical properties of PZAs The obtained polyarylates have good solubility. Then they were casted into films with the solution method. Fig. 13 shows the images of PZAs films. The thickness of films is about 10–12 μm and all of them are 6
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Fig. 12. Plots of complex viscosities versus time (at 310 � C) for PZAs and reference sample U-100.
Fig. 13. The images of PZAs and reference sample U-100 films with the thickness of 10–12 μm.
colorless and transparent. The films were detected by UV–vis. The transmittance of samples at 400 nm (T400), 450 nm (T450) and cut off wavelength (λ0) are listed in Table 3. As demonstrated in Fig. 14 and Table 3, it is obviously observed that the PZA46 has the best optical properties among these copolymers, and the transparency is better than commercial product U-100. The transmittance of PZA46 at 400 nm and 450 nm are both higher than that of U-100. In addition, the cut off wavelength is further lower (about 26 nm) than U-100. As the propor tion of BPZ increased, the optical properties of copolymers increased distinctly both of T400, T450 and cut off wavelength. This higher light transmittance is explained by the existence of large pendant group Table 3 The transmittance at 400 nm (T400), 450 nm (T450) and cut off wavelength (λ0) of PZAs and reference sample U-100 films. Polymer
T400 (nm)
T450 (nm)
Tcutoff (nm)
U-100 PZA46 PZA37 PZA28 PZA19
86.65 87.41 86.82 86.82 83.96
87.95 88.07 87.70 87.81 85.24
320 294 300 300 308
Fig. 14. The UV–vis spectra of PZAs and reference sample U-100 films.
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cyclohexyl, which increases the free volume of the copolymer molecular chains.
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4. Conclusions The Bisphenol-monomer containing cyclohexane unit was synthe sized successfully. It was conducted to polymerize with BPA, TPC and IPC at room temperature to yield a series high transparent polyarylates. These obtained copolymers were proved to have good thermal proper ties: the T5% can up to 461 � C, similar glass transition temperature (Tg) with commercial product U-100. We also found that the glass transition temperature increased gradually with the addition of monomer BPZ due to the existence of the large cyclohexane side group. It was also recog nized that the optical transmittance can be thoroughly improved by introducing the large cyclohexyl side group. The transmittance at T400 increased from 83.96 (PZA19) to 87.41 nm (PZA46), and that of T450 increased from 85.24 to 88.07 nm, so as the cutoff wavelength decreased from 308 to 294 nm with the increase of the proportion of BPZ. Addi tionally, from the rheological testing, it was apparent that the PZAs especially PZA46 had better melting fluidity and stability of 47–70 Pa s at 310 � C and 133-36 Pa s with the testing temperature increased from 285 to 310 � C than that of commercial product U-100. With the increase of cyclohexyl units in molecular chain, the melting fluidity of PZAs improved. As mentioned above, the resultant polyarylates have excel lent comprehensive properties, and can be potential widely used as a new optical material in industry, especially in the application of microlens and optical thin films. Author contribution Gang Zhang: Conceptualization, Methodology, Writing- Reviewing and Editing, Supervision. Jie Yang: Supervision. Yu Zhang: Writing- Original draft preparation, Investigation, Soft ware, Resources. Guangming Yan: Data curation, Software. Suilin Liu: Visualization, Validation, Reviewing and Editing. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was supported by the department of science and tech nology of Jiangsu province (BE2019008-4), Natural Science Foundation of China (NSFC-21304060, 51573103), the Fundamental Research Funds for the Central Universities, and the Outstanding Young Scholars Fund of Sichuan University 2015SCU04A25. References [1] P.K. Bhowmik, H. Han, Fully aromatic liquid-crystalline polyesters of phenylsubstituted 4, 4’-biphenols and 1, 1’-binaphthyl-4, 4’-diol with either 2-bromo terephthalic acid or 2-phenylterephthalic aci, Macromolecules 26 (20) (1993) 5287–5294. [2] Z. Ping, W. Linbo, L. Bo-Geng, Thermal stability of aromatic polyesters prepared from diphenolic acid and its esters, Polym. Degrad. Stabil. 94 (8) (2009) 1261–1266. [3] G. Liou, Synthesis and photoluminescence of novel organo-soluble polyarylates bearing (N-carbazolyl) triphenylamine moieties, Polym. J. 39 (5) (2007) 448–457. [4] P. Liu, T. Wu, M. Shi, G. Ye, J. Xu, Synthesis and characterization of readily soluble polyarylates derived from either 1,1-bis(4-hydroxyphenyl)-1-phenylethane or tetramethylbisphenol A and aromatic diacid chlorides, J. Appl. Polym. Sci. 119 (4) (2011) 1923–1930.
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