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Phosphorylating polycondensation using phosgene as a chain extender
Prk
Eur. Polym.J. Vol. 33, No. 10-12, pp. 1583-1586, 1997 0 1997 ElsevicrScienceLtd. All rishts-ed Fvinted in &at Britain s0014-3057(97)ooo55-4 00143057/97 $17.00 + 0.00
PHOSPHORYLATING POLYCONDENSATION USING PHOSGENE AS A CHAIN EXTENDER TIAN-YI
KE,’ REN-XI ZHUO,‘* ZHEN-RONG LU” and HAN-QIAO FENGb *Department of Chemistry, Wuhan University, Wuhan 430072, People’s Republic of China bWuhan Institute of Physics, the Chinese Academy of Science, Wuhan 430071, People’s Republic of China (Received 21 October 1996; accepted in final form 5 November 1996)
Abstract-A novel phosphorylating polycondensation method using phosgene as a chain extender was carried out for the first time. Polymers obtained were characterized by IR, ‘H NMR, the elemental analysis and copolymers 4 and 5 were further characterized by “C and )‘P NMR. The thermal properties, A&, &s, [s]. of polymers were investigated. The introduction of phosgene as a chain extender can increase substantially the molecular weight of poly(phosphoesters) in solution polycondensation. 0 1997 Elsevier Science Ltd IN’IBODUCTION
EXPERIMENTAL
Poly@hosphoesters) have great potential as a novel class of degradable biomedical polymers, which have attracted considerable attention because of their promising applications in tissue engineering and controlled drug release [ 11. The poly(phosphoesters) could be prepared by using interfacial [2], melt [3] or solution [4] polycondensations. Among these methods, the solution polycondensation has advantages of mild reaction conditions, little restrictions to the monomer and structural versatility of poly(phosphoesters). However, it is difficult to obtain high molecular weight poly@hosphoesters) from solution polycondensation. In the previous paper [5], we reported the phosphorylating polycondensation in the presence of 4-dimethylaminopyridine (DMAP) and the presence of DMAP could increase the reaction rate, but has limited effect on the average molecular weight of the poly(phosphoesters). Here, we attempt to use phosgene as a chain extender to increase the molecular weight of poly(phosphoesters) in its solution polycondensation. Two different procedures were employed to prepare phosgene extended bisphenol A poly@hosphoesters) and the average molecular weight of the extended poly(phosphoesters) increased considerably.
Phosgene toluene solution was prepared from the reaction of CCL and concentrated HISO+ and its content was determined by a titrimetry [6]. Ethyl phosphorodichoridate was prepared according to the published procedure [I and always vacuum distilled just prior to reaction. All other reagents and solvents were dried and purified before use. Gel-permeation chromatography (GPC) was performed on a Shimadzu LC-4A high-performance liquid chromatography (HPLC) system with a UV detector at 280 nm, and tetrahydrofuran was used to elute the sample through HSG-20 and HSG-30 polystyrene column successively (1 mljmin, 25’C). The system was calibrated with polystyrene standards. I%?~was measured by a Knauer vapour pressure osmometer. Fourier transform IR spectroscopy (FTIR) was performed on a Nicolet 17OSX spectrometer (KBr plate). ‘H, “P and “C NMR spectra were measured with a Bruker ARX-500 spectrometer. The resonance frequencies were 500.13 MHz for ‘H, 125.72 MHz for ‘% and 202.45 MHz for “P. Elemental analyses were determined on a Carlo Erba 1106 instrument. Polymers were analyzed by differential thermal analysis (DTA) on a Rigaku TAS-100 comprehensive thermal analytical system at lO”C/min. Intrinsic viscosities were measured in chloroform at 30°C with a Ubbelohde viscosimeter. Preparation of polymer 4: 2.28 g (10 mmol) of bisphenol A and 2.8 mL (20 mmol) of triethylamine were dissolved
OH + x C,H,OP(O)Cl,
Polymer:
+ y COCl, -
1 (x = 1, y = 0), 2 (x = 0.97, y = 0.03), 3 (X = 0.94, y = 0.06), 4 (X = 0.91, y = 0.09) (y = O.lO),t
5 (y = 0.25).? *To whom all correspondence should be addressed. tThe value was calculated according to quantitative ‘)C NMR spectra measured by the inverse gated decoupling sequence. 1583
Tian-Yi Ke el al.
1584
in 10 mL methylene chloride. The mixture were stirred in an ice bath under a gentle stream of nitrogen gas and 1.483 g (9.1 mmol) of ethyl phosphorodichloridate, 0.9 mL of phosgene toluene solution (1.OM) and 10 mL of methylene chloride were added with a syringe successively. The reaction was maintained at 3540°C for 24 hr. Then the mixture was filtrated to remove triethylammonium hydrochloride and the filtrate was washed with distilled water three times. The organic phase was dried over anhydrous Na2S04, then concentrated to 5 mL and poured into ethyl ether to precipitate out polymer. The polymer was dissolved in methylene chloride and precipitated with ethyl ether again. The polymer 4 was obtained as a white fluffy compound after drying under vacuum. Yield: 1.9g (61%). IR: 2971, 2935, 1604, 1504, 1231, 1202, 1167, 1041, 1015, 958, 840cm-‘. ‘H NMR (ppm): S 7.tS7.2 (8H, 4-H) 6 4.14.3 (2H, O--CH& 6 I .5-l .6 [6H, -C(CHj)& 6 1.3 (3H, -CH,). ‘C NMR (ppm): 152.8, 149.0-149.5, 147.9, 128.2-128.7, 120.1-120.9, 66.1, 43.0, 31.5, 16.7. “‘P NMR F;$ ; 11.1. Calc: C, 65.26; H, 6.05. Found: C, 64.93; H, The” polymers 1-3 were synthesized according to the same procedure as above and bisphenol A, ethyl phosphorodichloridate and phosgene are abbreviated as BPA. EP and Phosg, respectively. Polymer I (BPA 10 mmol. EP 10 mmol): yield 2.0 g (65%). IR 2974, 2962, 1604, 1503, 1231. 1202, 1167, 1041, 1014, 955, 837 cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H). 6 4.14.3 (2H, O--CH>), 6 1.5-i.6 [6H, -C(CHI)I]. S 1.3 (3H. --CHI). Calc: C. 64.43; H. 5.91. Found: C. 64.14; H, 6.02%. -’ Polymer 2 (BPA lOmmo1, EP 9.7mmo1, Phosg. 0.3mmol): yield 2.2g (70%). IR: 2970, 2935, 1775, 1603, 1503, 1231, 1203, 1170, 1039, 1015, 956, 840cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H), 6 4.143 (2H, 0-CHz), 6 1.5-1.6 [6H, --C(CHJ)~], S 1.3 (3H. -CHI). Calc: C, 64.67; H, 5.91. Found: C, 64.37; H, 5.91%. Polymer 3 (BPA 10 mmol, EP 9.4 mmol, Phosg. 0.6 mmol): yield 1.9 g (62%). IR: 2970, 2935, 1775, 1603, 1503, 1232, 1203, 1170, 1040, 1015, 957, 840cm-‘. ‘H NMR (ppm): 6 7.c7.2 (8H, 4-H). 6 4.14.3 (2H, O-CH>), 6 1.5-1.6 [6H, -C(CH,)& 6 1.3 (3H, -CH,). Calc: C, 64.87; H, 6.17. Found: C, 64.65; H, 5.98%. Preparation of polymer 5: A prepolymer was prepared from 2.28 g (10 mmol), excess bisphenol A and 1.304 g (8 mmol) of ethyl phosphorodichloridate according to the method of preparing polymer 4. Yield 1.2 g. 1.0 g of the prepolymer were dissolved in 15 mL dried
pyridine and phosgene was passed through the solution at room temperature. After -25 min the solution was very viscous and the yellow colour formed did not disappear and then phosgene was stopped. Methanol was then added to the solution to precipitae polymer. The polymer 5 was isolated and dissolved in methylene chloride again, then precipitated in methanol. Yield 0.5 g. IR: 260&3600, 2967. 2932, 1775, 1604, 1505, 1233, 1163, 1120, 1040, 1015. 954. 837 cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H) 6 4.14.3 (2H, O-CHz), 6 1.5-1.6 [6H, --C(CH3)& 6 1.3 (3H. -CH,). “C NMR (ppm): 152.8, 149.Ck149.5, 148.Sl48.2. 126.2-130.4, 120.1-121.0, 66.1. 43.0, 31.6, 16.7. “‘P NMR (ppm): -11.1, -16.9. Found: C, 68.53; H, 6.11%.
formation of a yellowish pyridine phosgene complex. Polymer 1 was simply prepared from bisphenol A and ethyl phosphorodichloridate as a control. All the polymers were obtained in relatively high yields and characterized by C, H elemental analysis, IR spectroscopy, gel permeation chromatography and differential thermal analysis, etc. Polymers 2, 3, 4 and 5 should be a copolymer of polyphosphate and polycarbonate with a large excess of polyphosphate portions. It is found that the elemental analysis data of copolymers 2, 3 and 4 fit the corresponding theoretical data very well, indicating that copolymer compositions (i.e. phosphate vs carbonate moieties) were in good agreement with monomer feed ratios. In copolymer 5, the carbon content is higher than other copolymers, suggesting a higher portion of carbonates in the polymer chain. All four copolymers have C=O absorption at 1774 cm-’ in their IR spectra and all five polymers have the following characteristic absorptions; - 1165, - 1200, - 1230 (three P=O absorption), -955, - 1015, 10.41 cm-’ (three P-O-C absorption). Copolymers 4 and 5 were chosen for further characterization with “C and “P NMR spectroscopy because of their relatively high content of polycarbonate portions. The “C NMR spectra of copolymers 4 and 5 with assignment are shown in Figs 1 and 2, respectively. Both copolymers have the C=O peak at 152.8 ppm, which continned the presence of polycarbonate in the polymer chain. The content of polycarbonate in the copolymer was also estimated from integration of the “C peak of the carbonyl, with Y = 10% in copolymer 4, similar to the stoichiometric data and Y = 25% in copolymer 5. The “C NMR spectroscopy indicated a higher content of polycarbonate in copolymer 5, which is consistent with the results of elemental analysis. The 3’P NMR spectrum of copolymer 4 has a single peak at - 11.1ppm. However, it is interesting to note that the “P NMR spectrum of copolymer 5 has two peaks at - 11.1 and -16.9 ppm with the ratio 1:0.2. It is difficult to assign the “P peak at - 16.9 ppm to unreacted or hydrolyzed phosphorate impurities, because any such impurities should be washed away during the purification of the copolymer. We thought that it might be caused by the hydrolysis of the P-0C2HS bond in the copolymer 0
w++l bH or the formation
of hybrid
anhydride.
RESULTS AND DISCUSSION
Polymers 2, 3 and 4 were prepared by simply mixing the monomers bisphenol A, ethyl phosphorodichloridate and phosgene in the molar ratios 1:0.97:0.03, 1:0.94:0.06 and 1:0.91:0.09, respectively and reacting at 3S4O”C for 24 hr in a sealed flask. Polymer 5 was prepared by passing phosgene through a prepolymer of bisphenol A poly(phosphoesters) and the amount of phosgene was monitored by the
However, the broad absorption in the range 3200-2600 cm-’ in IR spectrum of copolymer 5 suggests the presence of P-OH in the copolymer. Thus, the -“P peak at - 16.9 ppm might be attributed to P-OH in the copolymer, which might be formed
Phosphorylating
polycondensation
1585
7 7’
5 5’
-Jl___ 22
66
8
9
3
1
I
I
I
I
I
160
140
I20
I 100
J
-I
I
I
I
I
80
60
40
20
I
wm Fig. 1. ‘T NMR spectra of copolymer 4.
due to the cleavage of the P-OEt bond by excess COCh, and followed by the hydrolysis of P-Cl. Table 1 lists the number average molecular weights (MJ from VPO, the weight average molecular weight (aW) from GPC, the thermal parameters of the polymers. From the Table 1 we can see that the molecular weights (both M, and M,) of the copolymers prepared by using phosgene as a chain extender increased considerably as compared with those of poly(phosphoester) without the chain extender. It suggests that the introduction of phosgene in the solution polycondensation for synthesizing poly(phosphoesters) could increase the molecular weight. It is also observed that the introduction of phosgene after prepolymerization is
less effective to increase the molecular weight of the copolymer comparing copolymer 5 with copolymer 2, 3, 4.
I I@,,, AT,,Tg,T,,and
Table
1
3352
2 3 4
6175 6700 9540 6715
5
9200 12,100 14,100 14,300 11,200
their specific viscosities [VI (dJJnY
(2)
0.16 0.20 0.22 0.28 0.17
63.3 66.7 61.3 68.3 71.7
“M. was determined by the VP0 method (CHCh, 35°C). K by GPC. “[q] was measured using a Ubbelodhe viscosimeter (CHCh, 30°C).
7 I’
5 5’
22
l,__-_
I
,
I
.c I
160
I 140
I
120
I 100
I 80
8
66
9
1
296. I 291.2 298. I 300. I 303.7
I 60
ppm
Fig. 2. ‘T NMR spectra of copolymer 5.
I I 40
. I 20
J
1586
Tian-Yi Ke et al.
All the polymers have a glass transition temperature (T8) in the range 60-75”C, and melting temperature (T,) in the range 295-305°C. Both TE and T, of the polymers increased slightly with increase of the content of polycarbonate portions. In conclusion, employing phosgene as a chain extender could increase effectively the molecular weights of poly(phosphoesters) in solution polycondensation. The presence of a small amount of carbonate in the polymer chain did not change much the thermal properties of the bisphenol A poly(phosphoesters).
REFERENCES
1, Leon& K. W., Mao, H. Q. and Zhuo, R. X., Chinese J. Polym. Sci., 1995, 13, 289.
2. Kishore, K. and Kannan, P., J. Polym. Sci., Polym. Chem.,
1990, 28, 3481.
3. Cass, W. F., U.S. Patent 2, 616, 873, 1952. t: Annakuty, K. S. and Kishore, K., Polymer, 1988,29,156.
Mao, H. Q., Zhuo, R. X., Fan, C. L., Jiang, X. S., Liu, W. P. and Yi, H., Macromol. Chem. Phys., 1995, I%, 655. 6, Domb, A. L., Ron, E. and Langer, R., Macromolecules, 1988, 21, 1925. 7. Saunders, B. C., Stacey, F., Wild, F. and Wilding, I. G. E., J. Chem. Sot., 1948, 1, 699.
Eur. Polym.J. Vol. 33, No. 10-12, pp. 1583-1586, 1997 0 1997 ElsevicrScienceLtd. All rishts-ed Fvinted in &at Britain s0014-3057(97)ooo55-4 00143057/97 $17.00 + 0.00
PHOSPHORYLATING POLYCONDENSATION USING PHOSGENE AS A CHAIN EXTENDER TIAN-YI
KE,’ REN-XI ZHUO,‘* ZHEN-RONG LU” and HAN-QIAO FENGb *Department of Chemistry, Wuhan University, Wuhan 430072, People’s Republic of China bWuhan Institute of Physics, the Chinese Academy of Science, Wuhan 430071, People’s Republic of China (Received 21 October 1996; accepted in final form 5 November 1996)
Abstract-A novel phosphorylating polycondensation method using phosgene as a chain extender was carried out for the first time. Polymers obtained were characterized by IR, ‘H NMR, the elemental analysis and copolymers 4 and 5 were further characterized by “C and )‘P NMR. The thermal properties, A&, &s, [s]. of polymers were investigated. The introduction of phosgene as a chain extender can increase substantially the molecular weight of poly(phosphoesters) in solution polycondensation. 0 1997 Elsevier Science Ltd IN’IBODUCTION
EXPERIMENTAL
Poly@hosphoesters) have great potential as a novel class of degradable biomedical polymers, which have attracted considerable attention because of their promising applications in tissue engineering and controlled drug release [ 11. The poly(phosphoesters) could be prepared by using interfacial [2], melt [3] or solution [4] polycondensations. Among these methods, the solution polycondensation has advantages of mild reaction conditions, little restrictions to the monomer and structural versatility of poly(phosphoesters). However, it is difficult to obtain high molecular weight poly@hosphoesters) from solution polycondensation. In the previous paper [5], we reported the phosphorylating polycondensation in the presence of 4-dimethylaminopyridine (DMAP) and the presence of DMAP could increase the reaction rate, but has limited effect on the average molecular weight of the poly(phosphoesters). Here, we attempt to use phosgene as a chain extender to increase the molecular weight of poly(phosphoesters) in its solution polycondensation. Two different procedures were employed to prepare phosgene extended bisphenol A poly@hosphoesters) and the average molecular weight of the extended poly(phosphoesters) increased considerably.
Phosgene toluene solution was prepared from the reaction of CCL and concentrated HISO+ and its content was determined by a titrimetry [6]. Ethyl phosphorodichoridate was prepared according to the published procedure [I and always vacuum distilled just prior to reaction. All other reagents and solvents were dried and purified before use. Gel-permeation chromatography (GPC) was performed on a Shimadzu LC-4A high-performance liquid chromatography (HPLC) system with a UV detector at 280 nm, and tetrahydrofuran was used to elute the sample through HSG-20 and HSG-30 polystyrene column successively (1 mljmin, 25’C). The system was calibrated with polystyrene standards. I%?~was measured by a Knauer vapour pressure osmometer. Fourier transform IR spectroscopy (FTIR) was performed on a Nicolet 17OSX spectrometer (KBr plate). ‘H, “P and “C NMR spectra were measured with a Bruker ARX-500 spectrometer. The resonance frequencies were 500.13 MHz for ‘H, 125.72 MHz for ‘% and 202.45 MHz for “P. Elemental analyses were determined on a Carlo Erba 1106 instrument. Polymers were analyzed by differential thermal analysis (DTA) on a Rigaku TAS-100 comprehensive thermal analytical system at lO”C/min. Intrinsic viscosities were measured in chloroform at 30°C with a Ubbelohde viscosimeter. Preparation of polymer 4: 2.28 g (10 mmol) of bisphenol A and 2.8 mL (20 mmol) of triethylamine were dissolved
OH + x C,H,OP(O)Cl,
Polymer:
+ y COCl, -
1 (x = 1, y = 0), 2 (x = 0.97, y = 0.03), 3 (X = 0.94, y = 0.06), 4 (X = 0.91, y = 0.09) (y = O.lO),t
5 (y = 0.25).? *To whom all correspondence should be addressed. tThe value was calculated according to quantitative ‘)C NMR spectra measured by the inverse gated decoupling sequence. 1583
Tian-Yi Ke el al.
1584
in 10 mL methylene chloride. The mixture were stirred in an ice bath under a gentle stream of nitrogen gas and 1.483 g (9.1 mmol) of ethyl phosphorodichloridate, 0.9 mL of phosgene toluene solution (1.OM) and 10 mL of methylene chloride were added with a syringe successively. The reaction was maintained at 3540°C for 24 hr. Then the mixture was filtrated to remove triethylammonium hydrochloride and the filtrate was washed with distilled water three times. The organic phase was dried over anhydrous Na2S04, then concentrated to 5 mL and poured into ethyl ether to precipitate out polymer. The polymer was dissolved in methylene chloride and precipitated with ethyl ether again. The polymer 4 was obtained as a white fluffy compound after drying under vacuum. Yield: 1.9g (61%). IR: 2971, 2935, 1604, 1504, 1231, 1202, 1167, 1041, 1015, 958, 840cm-‘. ‘H NMR (ppm): S 7.tS7.2 (8H, 4-H) 6 4.14.3 (2H, O--CH& 6 I .5-l .6 [6H, -C(CHj)& 6 1.3 (3H, -CH,). ‘C NMR (ppm): 152.8, 149.0-149.5, 147.9, 128.2-128.7, 120.1-120.9, 66.1, 43.0, 31.5, 16.7. “‘P NMR F;$ ; 11.1. Calc: C, 65.26; H, 6.05. Found: C, 64.93; H, The” polymers 1-3 were synthesized according to the same procedure as above and bisphenol A, ethyl phosphorodichloridate and phosgene are abbreviated as BPA. EP and Phosg, respectively. Polymer I (BPA 10 mmol. EP 10 mmol): yield 2.0 g (65%). IR 2974, 2962, 1604, 1503, 1231. 1202, 1167, 1041, 1014, 955, 837 cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H). 6 4.14.3 (2H, O--CH>), 6 1.5-i.6 [6H, -C(CHI)I]. S 1.3 (3H. --CHI). Calc: C. 64.43; H. 5.91. Found: C. 64.14; H, 6.02%. -’ Polymer 2 (BPA lOmmo1, EP 9.7mmo1, Phosg. 0.3mmol): yield 2.2g (70%). IR: 2970, 2935, 1775, 1603, 1503, 1231, 1203, 1170, 1039, 1015, 956, 840cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H), 6 4.143 (2H, 0-CHz), 6 1.5-1.6 [6H, --C(CHJ)~], S 1.3 (3H. -CHI). Calc: C, 64.67; H, 5.91. Found: C, 64.37; H, 5.91%. Polymer 3 (BPA 10 mmol, EP 9.4 mmol, Phosg. 0.6 mmol): yield 1.9 g (62%). IR: 2970, 2935, 1775, 1603, 1503, 1232, 1203, 1170, 1040, 1015, 957, 840cm-‘. ‘H NMR (ppm): 6 7.c7.2 (8H, 4-H). 6 4.14.3 (2H, O-CH>), 6 1.5-1.6 [6H, -C(CH,)& 6 1.3 (3H, -CH,). Calc: C, 64.87; H, 6.17. Found: C, 64.65; H, 5.98%. Preparation of polymer 5: A prepolymer was prepared from 2.28 g (10 mmol), excess bisphenol A and 1.304 g (8 mmol) of ethyl phosphorodichloridate according to the method of preparing polymer 4. Yield 1.2 g. 1.0 g of the prepolymer were dissolved in 15 mL dried
pyridine and phosgene was passed through the solution at room temperature. After -25 min the solution was very viscous and the yellow colour formed did not disappear and then phosgene was stopped. Methanol was then added to the solution to precipitae polymer. The polymer 5 was isolated and dissolved in methylene chloride again, then precipitated in methanol. Yield 0.5 g. IR: 260&3600, 2967. 2932, 1775, 1604, 1505, 1233, 1163, 1120, 1040, 1015. 954. 837 cm-‘. ‘H NMR (ppm): 6 7.0-7.2 (8H, 4-H) 6 4.14.3 (2H, O-CHz), 6 1.5-1.6 [6H, --C(CH3)& 6 1.3 (3H. -CH,). “C NMR (ppm): 152.8, 149.Ck149.5, 148.Sl48.2. 126.2-130.4, 120.1-121.0, 66.1. 43.0, 31.6, 16.7. “‘P NMR (ppm): -11.1, -16.9. Found: C, 68.53; H, 6.11%.
formation of a yellowish pyridine phosgene complex. Polymer 1 was simply prepared from bisphenol A and ethyl phosphorodichloridate as a control. All the polymers were obtained in relatively high yields and characterized by C, H elemental analysis, IR spectroscopy, gel permeation chromatography and differential thermal analysis, etc. Polymers 2, 3, 4 and 5 should be a copolymer of polyphosphate and polycarbonate with a large excess of polyphosphate portions. It is found that the elemental analysis data of copolymers 2, 3 and 4 fit the corresponding theoretical data very well, indicating that copolymer compositions (i.e. phosphate vs carbonate moieties) were in good agreement with monomer feed ratios. In copolymer 5, the carbon content is higher than other copolymers, suggesting a higher portion of carbonates in the polymer chain. All four copolymers have C=O absorption at 1774 cm-’ in their IR spectra and all five polymers have the following characteristic absorptions; - 1165, - 1200, - 1230 (three P=O absorption), -955, - 1015, 10.41 cm-’ (three P-O-C absorption). Copolymers 4 and 5 were chosen for further characterization with “C and “P NMR spectroscopy because of their relatively high content of polycarbonate portions. The “C NMR spectra of copolymers 4 and 5 with assignment are shown in Figs 1 and 2, respectively. Both copolymers have the C=O peak at 152.8 ppm, which continned the presence of polycarbonate in the polymer chain. The content of polycarbonate in the copolymer was also estimated from integration of the “C peak of the carbonyl, with Y = 10% in copolymer 4, similar to the stoichiometric data and Y = 25% in copolymer 5. The “C NMR spectroscopy indicated a higher content of polycarbonate in copolymer 5, which is consistent with the results of elemental analysis. The 3’P NMR spectrum of copolymer 4 has a single peak at - 11.1ppm. However, it is interesting to note that the “P NMR spectrum of copolymer 5 has two peaks at - 11.1 and -16.9 ppm with the ratio 1:0.2. It is difficult to assign the “P peak at - 16.9 ppm to unreacted or hydrolyzed phosphorate impurities, because any such impurities should be washed away during the purification of the copolymer. We thought that it might be caused by the hydrolysis of the P-0C2HS bond in the copolymer 0
w++l bH or the formation
of hybrid
anhydride.
RESULTS AND DISCUSSION
Polymers 2, 3 and 4 were prepared by simply mixing the monomers bisphenol A, ethyl phosphorodichloridate and phosgene in the molar ratios 1:0.97:0.03, 1:0.94:0.06 and 1:0.91:0.09, respectively and reacting at 3S4O”C for 24 hr in a sealed flask. Polymer 5 was prepared by passing phosgene through a prepolymer of bisphenol A poly(phosphoesters) and the amount of phosgene was monitored by the
However, the broad absorption in the range 3200-2600 cm-’ in IR spectrum of copolymer 5 suggests the presence of P-OH in the copolymer. Thus, the -“P peak at - 16.9 ppm might be attributed to P-OH in the copolymer, which might be formed
Phosphorylating
polycondensation
1585
7 7’
5 5’
-Jl___ 22
66
8
9
3
1
I
I
I
I
I
160
140
I20
I 100
J
-I
I
I
I
I
80
60
40
20
I
wm Fig. 1. ‘T NMR spectra of copolymer 4.
due to the cleavage of the P-OEt bond by excess COCh, and followed by the hydrolysis of P-Cl. Table 1 lists the number average molecular weights (MJ from VPO, the weight average molecular weight (aW) from GPC, the thermal parameters of the polymers. From the Table 1 we can see that the molecular weights (both M, and M,) of the copolymers prepared by using phosgene as a chain extender increased considerably as compared with those of poly(phosphoester) without the chain extender. It suggests that the introduction of phosgene in the solution polycondensation for synthesizing poly(phosphoesters) could increase the molecular weight. It is also observed that the introduction of phosgene after prepolymerization is
less effective to increase the molecular weight of the copolymer comparing copolymer 5 with copolymer 2, 3, 4.
I I@,,, AT,,Tg,T,,and
Table
1
3352
2 3 4
6175 6700 9540 6715
5
9200 12,100 14,100 14,300 11,200
their specific viscosities [VI (dJJnY
(2)
0.16 0.20 0.22 0.28 0.17
63.3 66.7 61.3 68.3 71.7
“M. was determined by the VP0 method (CHCh, 35°C). K by GPC. “[q] was measured using a Ubbelodhe viscosimeter (CHCh, 30°C).
7 I’
5 5’
22
l,__-_
I
,
I
.c I
160
I 140
I
120
I 100
I 80
8
66
9
1
296. I 291.2 298. I 300. I 303.7
I 60
ppm
Fig. 2. ‘T NMR spectra of copolymer 5.
I I 40
. I 20
J
1586
Tian-Yi Ke et al.
All the polymers have a glass transition temperature (T8) in the range 60-75”C, and melting temperature (T,) in the range 295-305°C. Both TE and T, of the polymers increased slightly with increase of the content of polycarbonate portions. In conclusion, employing phosgene as a chain extender could increase effectively the molecular weights of poly(phosphoesters) in solution polycondensation. The presence of a small amount of carbonate in the polymer chain did not change much the thermal properties of the bisphenol A poly(phosphoesters).
REFERENCES
1, Leon& K. W., Mao, H. Q. and Zhuo, R. X., Chinese J. Polym. Sci., 1995, 13, 289.
2. Kishore, K. and Kannan, P., J. Polym. Sci., Polym. Chem.,
1990, 28, 3481.
3. Cass, W. F., U.S. Patent 2, 616, 873, 1952. t: Annakuty, K. S. and Kishore, K., Polymer, 1988,29,156.
Mao, H. Q., Zhuo, R. X., Fan, C. L., Jiang, X. S., Liu, W. P. and Yi, H., Macromol. Chem. Phys., 1995, I%, 655. 6, Domb, A. L., Ron, E. and Langer, R., Macromolecules, 1988, 21, 1925. 7. Saunders, B. C., Stacey, F., Wild, F. and Wilding, I. G. E., J. Chem. Sot., 1948, 1, 699.