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Synthesis and ring-opening copolymerization of cyclic aryl ester dimers
Chinese Chemical Letters 24 (2013) 897–900
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Synthesis and ring-opening copolymerization of cyclic aryl ester dimers Qing-Zhong Guo, Yi Du, Jun-Fang Guo *, Liang Li, Jiang-Yu Wu, Guo-Ping Yan School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan 430073, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2013 Received in revised form 14 May 2013 Accepted 20 May 2013 Available online 16 July 2013
Two kinds of cyclic aryl ester dimers have been synthesized by reaction of phthaloyl dichloride with bisphenols via interfacial polycondensation. The cyclic dimers readily undergo anionic ring-opening polymerization or copolymerization in the melt by using sodium benzoate as the initiator, producing linear, high molecular weight polyesters. The contents of cyclic dimers in the homopolymers P1, P2, and copolymer P12 are 13.7%, 10.2%, 2.9%, respectively, which indicates that ring-opening copolymerization of cyclic dimers may impel the conversion of cyclic dimers and decrease the content of cyclic dimers in the resulting copolymer. Moreover, the isothermal chemorheology of the ring-opening copolymerization of cyclic dimers indicates that the reactive molten mixture has low shear viscosity and the viscosity increases slowly in the initial stage of ring-opening polymerization. ß 2013 Jun-Fang Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Ring-opening polymerization Cyclic oligomer Rheological behavior
1. Introduction Ring-opening polymerization (ROP) reactions constitute an important class of polymerization reactions. The advantages of using ROP of cyclic aryl oligomers to prepare high performance aromatic thermoplastics, such as polycarbonate [1,2], poly(aryl ether ketone)s [3,4] and poly(aryl ester)s [5,6], have been widely recognized in recent years. These cyclic oligomers afford a unique combination of low melt viscosity and the possibility of undergoing controlled polymerization in the molten state without the liberation of volatile byproducts, which makes them candidates in the area of advanced thermoplastic compositions [7–9]. It is generally believed that the ROP of aromatic cyclic oligomers is essentially thermoneutral and driven by entropy changes as the cyclic oligomers have big size with little or no ring strain, which differs from the ROP of the conventional cyclic monomers, such as epoxides and e-caprolactam, which are driven by the exothermic enthalpy change. However, up to now, studies on ROP of aromatic cyclic oligomers were mainly focused on finding optimum initiators to open the cyclic structure and monitoring the change of molecular weight with time of polymerization by GPC [2–6]. Systematic research on ROP,
* Corresponding author. E-mail address: [email protected] (J.-F. Guo).
especially in the mechanism and the process of ROP, are rather scarce in the literature [9]. We have been studying the cyclization and ROP of cyclic aryl ester containing phthaloyl moiety [10,11]. The cyclic esters could be synthesized in high yield and underwent facile ROP via a transesterification reaction to form high molecular weight linear polymers. However, the content of cyclic oligomers remaining in the obtained polymer was above 10%, even when different initiators were used or the reaction time of ROP was increased. The relatively large amount of cyclic oligomers remaining in the polymers weakens the performance of the polymers and restrains the application of the cyclic aryl esters in the area of advanced thermoplastic compositions. The reason for this phenomenon is probably due to an intermolecular ring-chain equilibration reaction among the cyclic oligomers and linear high molecular weight polymers, although this ring-chain equilibration is much more favorable toward the formation of high molecular weight linear polymers. We hypothesize that copolymerization of different cyclic oligomers could favor the conversion of cyclic oligomers and decrease the content of cyclic oligomers in polymer, since the copolymer has greater entropy than the homopolymer and the ROP of aromatic cyclic oligomers is driven by entropy changes. Hence, two kinds of cyclic aryl ester dimers derived from phthaloyl dichloride have been synthesized and the ring-opening copolymerization (co-ROP) of cyclic ester dimers is investigated in this report. Data from the viscosity profile of the co-ROP is also reported, since the processibility of the resin in any
1001-8417/$ – see front matter ß 2013 Jun-Fang Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.05.039
Q.-Z. Guo et al. / Chinese Chemical Letters 24 (2013) 897–900
898
formation of a single molecular weight product. The spectroscopic results (MALDI-TOF MS, FTIR and 1H NMR) confirmed that the product was a cyclic dimer (Scheme 1). DSC analyses show that the cyclic ester dimers 1 and 2 are highly crystalline and the Tms are 306.0 8C and 306.2 8C, respectively. The 5% weight loss temperatures of cyclic dimers from TGA tests are above 400 8C. The mixture of cyclic dimer 1 and 2 (1:1 by mol) has a Tm peak at 285.0 8C. The melt viscosities of cyclic dimers 1 and 2 are about 1.8 Pa S and remain stable during the test period of 40 min at 310 8C. This suggests that they are thermally stable at melt temperature under N2. The cyclic dimers could be converted to a high molecular weight linear polymer through ROP in the presence of a small amount of initiator via an ester exchange reaction [7,10]. Melt polymerizations have been performed on cyclic dimer 1, dimer 2 and mixture of dimer 1 and 2 (1:1 by mol) using sodium benzoate (0.1 mol %) as the initiator for 40 min at 310 8C, 310 8C and 290 8C, respectively, to give high molecular weight polymers P1, P2, and P12 (Scheme 1). The melt co-ROP can proceed at lower temperatures, which is significant for molding and processing strategies. The polyesters are brown, tough and easily dissolved in common solvents such as THF, CHCl3 and dimethylformamide. The structures of P1, P2, and P12 have been fully confirmed by 1H NMR, and are consistent with the corresponding cyclic dimers. The GPC traces of P1, P2, and P12 are presented in Fig. 1. It shows clearly the formation of high molecular weight linear polymers. P1, P2, P12 have Mws of 94.3 k, 108.8 k, 79.9 k and Mns of 66.8 k, 77.0 k, 58.0 k, respectively (using polystyrene as standards). It is worth noting that the polydispersity (Mw/Mn) of molecular weight for the polyesters resulting from ROP is relatively small (about 1.4) compared with those from the traditional condensation polymerization (usually above 2.0) (see Table 1). This phenomenon is probably due to an intermolecular chain–chain equilibration reaction. We hypothesize that the transesterification reactions are indiscriminate with regard to cyclic or linear chains and the interchain equilibration is also a facile process during polymerization, as little or no ring strain exists in the cyclic oligomers. GPC analysis also shows that about 13.7%, 10.2%, 2.9% of the cyclic oligomers remained in the final polymers P1, P2, and P12, respectively. This result indicates that ROP of a cyclic mixture may improve the conversion of cyclic oligomers and decrease the content of cyclic oligomers in the polymers. The copolymer P12
application will be largely dependent on its rheological properties. 2. Experimental 2.1. Preparation of cyclic aryl ester dimer The cyclization reaction was conducted according to the reported method [11]. The cyclic dimer was recrystallized from THF. Cyclic aryl ester dimer 1: yield, 63%; MS (FAB) (m/z): 717 (M+, 100), 702 (M-CH3, 70); 1H NMR (300 MHz, CDCl3): d 7.98 (m, 1H, J = 5.6 Hz), 7.70 (m, 1H, J = 5.6 Hz), 7.20 (d, 2H, J = 8.8 Hz), 7.08 (d, 2H, J = 8.8 Hz), 1.67 (s, 3H); Tm, 306.0 8C (by DSC). Cyclic aryl ester dimer 2: yield, 55%; MS (MALDI-TOF) (m/z): 935 ([M+H]+, 100), 957 ([M+Na]+, 20); 1H NMR (300 MHz, CDCl3): d 8.02 (m, 1H, J = 5.6 Hz), 7.76 (m, 1H, J = 5.6 Hz), 7.48 (d, 2H, J = 8.8 Hz), 7.30 (d, 2H, J = 8.8 Hz); Tm, 306.2 8C (by DSC). 2.2. General procedure of the measurements of isothermal chemorheology The dimer and 0.1 mol% sodium benzoate as the initiator were mixed and pressed into disks with diameter of about 20 mm and thickness of 0.3 mm at room temperature. Rheological measurements were performed using an MCR 300 type rheometer with 25 mm parallel plates at a constant shear rate of 0.05 rad/s under N2 by the rotation test methods. The gap between the upper and lower plates was set as 0.2 mm and the sample was thus forced to be thinner by the rotating upper plate at the experimental temperature. The viscosity’s change with time during the ROP course at a constant angular frequency was measured. 3. Results and discussion The cyclization reactions were conducted by the interfacial polycondensation of phthaloyl dichloride with bisphenol A or 4, 40 (hexafluoroisopropylidene)diphenol under pseudo-high dilution conditions. The pseudo-high dilution conditions were achieved by slowly adding the solutions of two reactants over 8 h from separate dropping funnels to a large amount of solvent containing phase transfer catalyst. GPC chromatography of the isolated product showed a very narrow single peak suggesting the exclusive
CH3
O C
C
C
CH3
x
+
CH3 C
O
O
O
CH3
CF3
O
O O
O
C
CF3
y
CF3
C
C
O
O
C
O
O
O
CF3 2
1 0.1 mol%
nitrogen
COONa
CH3 O
O O
O
O
O
O
C
C
40 min
CF3 O
O CF3
P 2: x = m = 0;
O
C
C n
m CH3
P1: y = n = 0;
O
P 12: x / y = 1
Scheme 1. Chemical structures and ROP of cyclic aryl ester dimers.
Q.-Z. Guo et al. / Chinese Chemical Letters 24 (2013) 897–900
899
800
dimer 1 mixture of dimers 20
Viscosity (Pas)
Viscosity (Pa S)
600
400
15
10
5
0
200
0
5
10 Time (min)
15
20
0 0
10
20 Time (min)
30
40
Fig. 1. GPC curves of P1, P2, and P12.
Fig. 2. Viscosity profiles for the ROP of dimer 1 and mixture of dimers in the presence of 0.1 mol% sodium benzoate as an initiator at 310 8C, 290 8C, respectively.
obtained by co-ROP of cyclic dimers has greater entropy than the homopolymer, which promotes the chain-ring equilibration toward the formation of linear polymers since the ROP of aromatic cyclic oligomers is driven by entropy changes. DSC analysis (Table 1) shows that the resulting polyesters P1, P2, unlike the corresponding cyclic dimers, are amorphous, showing glass transition at 151.3 8C and 158.8 8C, respectively. The single glass transition of copolymer P12 occurs at 155.1 8C, which indicates that the copolymer is random and the relationship between Tgs of homopolymers and the copolymer is in accordance with the FOX equation. Fig. 2 shows the viscosity profiles for the ROP of cyclic ester dimer 1 and co-ROP mixture of dimers with 0.1 mol % sodium benzoate as an initiator at a constant shear rate of 0.05 rad/s and at 310 8C, 290 8C, respectively. Because of the low viscosity of the molten reactive mixture in the initial stage of ROP, a low shear rate and a gap between the parallel plates of 0.2 mm were selected. The shear viscosity of the molten mixture is lower than 10 Pa S at a constant shear rate of 0.05 rad/s and increases slowly in the initial stage of ROP (inset of Fig. 2). This phenomenon suggests that the molecular weight of the mixture is below the critical molecular weight Mc and there are no entanglements between polymer chains. Furthermore, it may reflect that there are a high proportion of cyclic oligomers still remaining in this period and the cyclic oligomers may act as a kind of ‘‘lubricant’’ or ‘‘plasticizer’’ among high molecular weight linear chains. The initial stages of ROP and co-ROP are 15 and 10 min, which imply that the conversion of cyclic dimers in co-ROP is faster than that of ROP. This maybe attribute to a greater entropy change in the process of co-ROP. With the reaction going on, the molecular weight exceeds Mc and the further increase of molecular weight causes entanglements between polymer chains, which results in a dramatic increase of melt viscosity of the resin. The shear viscosities of the products
obtained by ROP of cyclic dimer 1 and co-ROP of mixture of dimers at 35 min are 433.8 Pa S and 693.6 Pa S, which indicates that the content of cyclic dimers remaining in copolymer is lower than that of the former, consistent with the GPC analysis. The initial slow increase of viscosity during ROP provides a processing timewindow, which allow the resin be processed at a lower shear rate and much lower pressure. This would be a significant advantage for the fabrication of thermoplastic compositions.
Table 1 Physical properties of polymers prepared by ROP or co-ROP.
P1 P2 P12
Mna
Mwa
Mw/Mn
Tgb (8C)
TGAc (8C)
Content of cyclic dimer
66.8 77.0 58.0
94.3 108.8 79.9
1.41 1.41 1.38
152.5 162.4 156.8
371 384 393
13.7% 10.2% 2.9%
a Measured by GPC and calibrated against polystyrene standard, unit in 103 g/ mol. b Measured by DSC under nitrogen atmosphere; heating rate was 10 8C/min. c Temperature at 5% weight loss under nitrogen atmosphere; heating rate was 20 8C/min.
4. Conclusion In conclusion, the content of cyclic dimers in polyester produced by ROP has been decreased successfully. This suggests that co-ROP of cyclic dimers may promote the chain-ring equilibration toward the formation of linear polymers. The rheological behaviors during ROP of cyclic dimers show that the shear viscosity is lower than 10 Pa S at a constant shear rate of 0.05 rad/s and increases slowly in the initial stage of ROP. These results make cyclic ester dimers applicable for preparation of advanced thermoplastic compositions. Acknowledgments The work described in this paper was supported by grants from the National Natural Science Foundation of China (Nos. 21001085, 20904045), the Natural Science Foundation of Hubei Province (No. 2010CDB11104) and Doctoral Program Foundation of Wuhan Institute of Technology (No. 11105032). References [1] D.J. Brunelle, E.P. Boden, T.G. Shannon, Remarkably selective formation of macrocyclic aromatic carbonates: versatile new intermediates for the synthesis of aromatic polycarbonates, J. Am. Chem. Soc. 112 (1990) 2399–2402. [2] P. Hodge, S.D. Kamau, A. Ben-Haida, R.T. Williams, Cyclo-depolymerizations of polycarbonates in solution: use of the macrocyclic oligomers obtained in entropically-driven ring-opening polymerizations and copolymerizations to give carbonate–carbonate and carbonate–carboxylate ester copolymers, React. Funct. Polym. 11 (2012) 868–877. [3] Q.Z. Guo, H.H. Wang, J.Y. Wu, D. Guo, T.L. Chen, Synthesis and ring-opening polymerization of macrocyclic aryl ketone oligomers, Polym. Adv. Technol. 21 (2010) 290–295. [4] H.H. Wang, J.Y. Ding, T.L. Chen, Cyclic oligomers of phenolphthalein polyarylene ether sulfone (ketone): preparation through cyclo-depolymerisation of corresponding polymers, Chin. Chem. Lett. 15 (11) (2004) 1377–1379. [5] N. Gonza´lez-Vidal, A.M.D. Ilarduya, S. Mun˜oz-Guerra, Poly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate) copolyesters obtained by ring opening polymerization, J. Polym. Sci. Part A: Polym. Chem. 47 (2009) 5954–5966.
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[6] K. Pang, R. Kotec, A. Tonelli, Ring-opening polymerization of the cyclic dimer of poly(trimethylene terephthalate), J. Polym. Sci. Part A: Polym. Chem. 44 (2006) 6801–6809. [7] H.L. Chen, W. Yu, C.X. Zhou, Entropically-driven ring-opening polymerization of cyclic butylene terephthalate: rheology and kinetics, Poly. Eng. Sci. 52 (2012) 91–101. [8] D.J. Brunelle, Cyclic oligomer chemistry, J. Polym. Sci. Part A: Polym. Chem. 46 (2008) 1151–1164. [9] H.L. Chen, C.W. Huang, W. Yu, C.X. Zhou, Effect of thermally reduced graphite oxide (TrGO) on the polymerization kinetics of poly(butylene terephthalate)
(pCBT)/TrGO nanocomposites prepared by in situ ring-opening polymerization of cyclic butylene terephthalate, Polymer 54 (2013) 1603–1611. [10] H.Y. Jiang, T.L. Chen, J.P. Xu, Synthesis, structure, and ring-opening polymerization of macrocyclic aromatic esters: a new route to high-performance polyarylates, Macromolecules 30 (1997) 2839–2842. [11] Q.Z. Guo, C. Liu, H. Lu, S.F. Hu, Synthesis, characterization and ring-opening polymerization of cyclic aryl ester dimer containing hexafluoroisopropylidene unit, J. Wuhan Inst. Technol. 33 (5) (2011) 41–44.
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Synthesis and ring-opening copolymerization of cyclic aryl ester dimers Qing-Zhong Guo, Yi Du, Jun-Fang Guo *, Liang Li, Jiang-Yu Wu, Guo-Ping Yan School of Materials Science and Engineering, Wuhan Institute of Technology, Wuhan 430073, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 April 2013 Received in revised form 14 May 2013 Accepted 20 May 2013 Available online 16 July 2013
Two kinds of cyclic aryl ester dimers have been synthesized by reaction of phthaloyl dichloride with bisphenols via interfacial polycondensation. The cyclic dimers readily undergo anionic ring-opening polymerization or copolymerization in the melt by using sodium benzoate as the initiator, producing linear, high molecular weight polyesters. The contents of cyclic dimers in the homopolymers P1, P2, and copolymer P12 are 13.7%, 10.2%, 2.9%, respectively, which indicates that ring-opening copolymerization of cyclic dimers may impel the conversion of cyclic dimers and decrease the content of cyclic dimers in the resulting copolymer. Moreover, the isothermal chemorheology of the ring-opening copolymerization of cyclic dimers indicates that the reactive molten mixture has low shear viscosity and the viscosity increases slowly in the initial stage of ring-opening polymerization. ß 2013 Jun-Fang Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Ring-opening polymerization Cyclic oligomer Rheological behavior
1. Introduction Ring-opening polymerization (ROP) reactions constitute an important class of polymerization reactions. The advantages of using ROP of cyclic aryl oligomers to prepare high performance aromatic thermoplastics, such as polycarbonate [1,2], poly(aryl ether ketone)s [3,4] and poly(aryl ester)s [5,6], have been widely recognized in recent years. These cyclic oligomers afford a unique combination of low melt viscosity and the possibility of undergoing controlled polymerization in the molten state without the liberation of volatile byproducts, which makes them candidates in the area of advanced thermoplastic compositions [7–9]. It is generally believed that the ROP of aromatic cyclic oligomers is essentially thermoneutral and driven by entropy changes as the cyclic oligomers have big size with little or no ring strain, which differs from the ROP of the conventional cyclic monomers, such as epoxides and e-caprolactam, which are driven by the exothermic enthalpy change. However, up to now, studies on ROP of aromatic cyclic oligomers were mainly focused on finding optimum initiators to open the cyclic structure and monitoring the change of molecular weight with time of polymerization by GPC [2–6]. Systematic research on ROP,
* Corresponding author. E-mail address: [email protected] (J.-F. Guo).
especially in the mechanism and the process of ROP, are rather scarce in the literature [9]. We have been studying the cyclization and ROP of cyclic aryl ester containing phthaloyl moiety [10,11]. The cyclic esters could be synthesized in high yield and underwent facile ROP via a transesterification reaction to form high molecular weight linear polymers. However, the content of cyclic oligomers remaining in the obtained polymer was above 10%, even when different initiators were used or the reaction time of ROP was increased. The relatively large amount of cyclic oligomers remaining in the polymers weakens the performance of the polymers and restrains the application of the cyclic aryl esters in the area of advanced thermoplastic compositions. The reason for this phenomenon is probably due to an intermolecular ring-chain equilibration reaction among the cyclic oligomers and linear high molecular weight polymers, although this ring-chain equilibration is much more favorable toward the formation of high molecular weight linear polymers. We hypothesize that copolymerization of different cyclic oligomers could favor the conversion of cyclic oligomers and decrease the content of cyclic oligomers in polymer, since the copolymer has greater entropy than the homopolymer and the ROP of aromatic cyclic oligomers is driven by entropy changes. Hence, two kinds of cyclic aryl ester dimers derived from phthaloyl dichloride have been synthesized and the ring-opening copolymerization (co-ROP) of cyclic ester dimers is investigated in this report. Data from the viscosity profile of the co-ROP is also reported, since the processibility of the resin in any
1001-8417/$ – see front matter ß 2013 Jun-Fang Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.05.039
Q.-Z. Guo et al. / Chinese Chemical Letters 24 (2013) 897–900
898
formation of a single molecular weight product. The spectroscopic results (MALDI-TOF MS, FTIR and 1H NMR) confirmed that the product was a cyclic dimer (Scheme 1). DSC analyses show that the cyclic ester dimers 1 and 2 are highly crystalline and the Tms are 306.0 8C and 306.2 8C, respectively. The 5% weight loss temperatures of cyclic dimers from TGA tests are above 400 8C. The mixture of cyclic dimer 1 and 2 (1:1 by mol) has a Tm peak at 285.0 8C. The melt viscosities of cyclic dimers 1 and 2 are about 1.8 Pa S and remain stable during the test period of 40 min at 310 8C. This suggests that they are thermally stable at melt temperature under N2. The cyclic dimers could be converted to a high molecular weight linear polymer through ROP in the presence of a small amount of initiator via an ester exchange reaction [7,10]. Melt polymerizations have been performed on cyclic dimer 1, dimer 2 and mixture of dimer 1 and 2 (1:1 by mol) using sodium benzoate (0.1 mol %) as the initiator for 40 min at 310 8C, 310 8C and 290 8C, respectively, to give high molecular weight polymers P1, P2, and P12 (Scheme 1). The melt co-ROP can proceed at lower temperatures, which is significant for molding and processing strategies. The polyesters are brown, tough and easily dissolved in common solvents such as THF, CHCl3 and dimethylformamide. The structures of P1, P2, and P12 have been fully confirmed by 1H NMR, and are consistent with the corresponding cyclic dimers. The GPC traces of P1, P2, and P12 are presented in Fig. 1. It shows clearly the formation of high molecular weight linear polymers. P1, P2, P12 have Mws of 94.3 k, 108.8 k, 79.9 k and Mns of 66.8 k, 77.0 k, 58.0 k, respectively (using polystyrene as standards). It is worth noting that the polydispersity (Mw/Mn) of molecular weight for the polyesters resulting from ROP is relatively small (about 1.4) compared with those from the traditional condensation polymerization (usually above 2.0) (see Table 1). This phenomenon is probably due to an intermolecular chain–chain equilibration reaction. We hypothesize that the transesterification reactions are indiscriminate with regard to cyclic or linear chains and the interchain equilibration is also a facile process during polymerization, as little or no ring strain exists in the cyclic oligomers. GPC analysis also shows that about 13.7%, 10.2%, 2.9% of the cyclic oligomers remained in the final polymers P1, P2, and P12, respectively. This result indicates that ROP of a cyclic mixture may improve the conversion of cyclic oligomers and decrease the content of cyclic oligomers in the polymers. The copolymer P12
application will be largely dependent on its rheological properties. 2. Experimental 2.1. Preparation of cyclic aryl ester dimer The cyclization reaction was conducted according to the reported method [11]. The cyclic dimer was recrystallized from THF. Cyclic aryl ester dimer 1: yield, 63%; MS (FAB) (m/z): 717 (M+, 100), 702 (M-CH3, 70); 1H NMR (300 MHz, CDCl3): d 7.98 (m, 1H, J = 5.6 Hz), 7.70 (m, 1H, J = 5.6 Hz), 7.20 (d, 2H, J = 8.8 Hz), 7.08 (d, 2H, J = 8.8 Hz), 1.67 (s, 3H); Tm, 306.0 8C (by DSC). Cyclic aryl ester dimer 2: yield, 55%; MS (MALDI-TOF) (m/z): 935 ([M+H]+, 100), 957 ([M+Na]+, 20); 1H NMR (300 MHz, CDCl3): d 8.02 (m, 1H, J = 5.6 Hz), 7.76 (m, 1H, J = 5.6 Hz), 7.48 (d, 2H, J = 8.8 Hz), 7.30 (d, 2H, J = 8.8 Hz); Tm, 306.2 8C (by DSC). 2.2. General procedure of the measurements of isothermal chemorheology The dimer and 0.1 mol% sodium benzoate as the initiator were mixed and pressed into disks with diameter of about 20 mm and thickness of 0.3 mm at room temperature. Rheological measurements were performed using an MCR 300 type rheometer with 25 mm parallel plates at a constant shear rate of 0.05 rad/s under N2 by the rotation test methods. The gap between the upper and lower plates was set as 0.2 mm and the sample was thus forced to be thinner by the rotating upper plate at the experimental temperature. The viscosity’s change with time during the ROP course at a constant angular frequency was measured. 3. Results and discussion The cyclization reactions were conducted by the interfacial polycondensation of phthaloyl dichloride with bisphenol A or 4, 40 (hexafluoroisopropylidene)diphenol under pseudo-high dilution conditions. The pseudo-high dilution conditions were achieved by slowly adding the solutions of two reactants over 8 h from separate dropping funnels to a large amount of solvent containing phase transfer catalyst. GPC chromatography of the isolated product showed a very narrow single peak suggesting the exclusive
CH3
O C
C
C
CH3
x
+
CH3 C
O
O
O
CH3
CF3
O
O O
O
C
CF3
y
CF3
C
C
O
O
C
O
O
O
CF3 2
1 0.1 mol%
nitrogen
COONa
CH3 O
O O
O
O
O
O
C
C
40 min
CF3 O
O CF3
P 2: x = m = 0;
O
C
C n
m CH3
P1: y = n = 0;
O
P 12: x / y = 1
Scheme 1. Chemical structures and ROP of cyclic aryl ester dimers.
Q.-Z. Guo et al. / Chinese Chemical Letters 24 (2013) 897–900
899
800
dimer 1 mixture of dimers 20
Viscosity (Pas)
Viscosity (Pa S)
600
400
15
10
5
0
200
0
5
10 Time (min)
15
20
0 0
10
20 Time (min)
30
40
Fig. 1. GPC curves of P1, P2, and P12.
Fig. 2. Viscosity profiles for the ROP of dimer 1 and mixture of dimers in the presence of 0.1 mol% sodium benzoate as an initiator at 310 8C, 290 8C, respectively.
obtained by co-ROP of cyclic dimers has greater entropy than the homopolymer, which promotes the chain-ring equilibration toward the formation of linear polymers since the ROP of aromatic cyclic oligomers is driven by entropy changes. DSC analysis (Table 1) shows that the resulting polyesters P1, P2, unlike the corresponding cyclic dimers, are amorphous, showing glass transition at 151.3 8C and 158.8 8C, respectively. The single glass transition of copolymer P12 occurs at 155.1 8C, which indicates that the copolymer is random and the relationship between Tgs of homopolymers and the copolymer is in accordance with the FOX equation. Fig. 2 shows the viscosity profiles for the ROP of cyclic ester dimer 1 and co-ROP mixture of dimers with 0.1 mol % sodium benzoate as an initiator at a constant shear rate of 0.05 rad/s and at 310 8C, 290 8C, respectively. Because of the low viscosity of the molten reactive mixture in the initial stage of ROP, a low shear rate and a gap between the parallel plates of 0.2 mm were selected. The shear viscosity of the molten mixture is lower than 10 Pa S at a constant shear rate of 0.05 rad/s and increases slowly in the initial stage of ROP (inset of Fig. 2). This phenomenon suggests that the molecular weight of the mixture is below the critical molecular weight Mc and there are no entanglements between polymer chains. Furthermore, it may reflect that there are a high proportion of cyclic oligomers still remaining in this period and the cyclic oligomers may act as a kind of ‘‘lubricant’’ or ‘‘plasticizer’’ among high molecular weight linear chains. The initial stages of ROP and co-ROP are 15 and 10 min, which imply that the conversion of cyclic dimers in co-ROP is faster than that of ROP. This maybe attribute to a greater entropy change in the process of co-ROP. With the reaction going on, the molecular weight exceeds Mc and the further increase of molecular weight causes entanglements between polymer chains, which results in a dramatic increase of melt viscosity of the resin. The shear viscosities of the products
obtained by ROP of cyclic dimer 1 and co-ROP of mixture of dimers at 35 min are 433.8 Pa S and 693.6 Pa S, which indicates that the content of cyclic dimers remaining in copolymer is lower than that of the former, consistent with the GPC analysis. The initial slow increase of viscosity during ROP provides a processing timewindow, which allow the resin be processed at a lower shear rate and much lower pressure. This would be a significant advantage for the fabrication of thermoplastic compositions.
Table 1 Physical properties of polymers prepared by ROP or co-ROP.
P1 P2 P12
Mna
Mwa
Mw/Mn
Tgb (8C)
TGAc (8C)
Content of cyclic dimer
66.8 77.0 58.0
94.3 108.8 79.9
1.41 1.41 1.38
152.5 162.4 156.8
371 384 393
13.7% 10.2% 2.9%
a Measured by GPC and calibrated against polystyrene standard, unit in 103 g/ mol. b Measured by DSC under nitrogen atmosphere; heating rate was 10 8C/min. c Temperature at 5% weight loss under nitrogen atmosphere; heating rate was 20 8C/min.
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