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Chemical modification of poly(vinyl chloride) by nucleophilic substitution
Polymer Degradation and Stability 94 (2009) 107–112
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Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab
Chemical modification of poly(vinyl chloride) by nucleophilic substitution Tomohito Kameda a, Masahiko Ono b, Guido Grause a, Tadaaki Mizoguchi b, Toshiaki Yoshioka a, * a b
Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Environment Conservation Research Institute, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 July 2008 Received in revised form 2 September 2008 Accepted 7 October 2008 Available online 19 October 2008
The reaction of poly(vinyl chloride) (PVC) in nucleophile (Nu)/ethylene glycol (EG) or Nu/N,N-dimethylformamide (DMF) solution was found to result in the substitution of Cl in PVC with Nu from solution, in addition to the straight elimination of HCl, both of which led to the dechlorination of PVC. Examined Nu were I, SCN, OH, N 3 , and the phthalimide anion. For the Nu/EG solution, elimination was favoured over substitution for all Nu. The ratio of substitution to dechlorination was notable, descending in the order OH > SCN ¼ N 3 > phthalimide anion > I . For the Nu/DMF solution, the ratio of substitution to dechlorination was high, in the order SCN > N3 > I > phthalimide anion. In both cases, the orders of the ratios were similar to those of the nucleophilic reactivity constant, I > SCN > N 3 > phthalimide anion, except for I. The low ratio for I was attributable to the elimination of HI after the substitution of Cl in PVC with I in solution, because I is a strong nucleophile, as well as an excellent leaving group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Poly(vinyl chloride) Chemical modification Nucleophilic substitution Ethylene glycol N,N-Dimethylformamide
1. Introduction Numerous studies have explored the dechlorination of poly(vinyl chloride) (PVC) from the viewpoint of recycling waste plastics. They are based on the phenomenon that the dechlorination of PVC occurs by a radical zipper reaction at 200–250 C [1]. Some studies have examined the dry process for the dechlorination of PVC [2–6]. Thermal degradation of PVC resulted in almost complete dechlorination above 260 C [3], although the degree of dechlorination of poly(vinylidene chloride) (PVDC) was around 60% at 300 C [7]. However, the thermal degradation of PVC also leads to the production of polyenes and their cyclisation. Therefore, this efficient method of dechlorinating PVC is limited to cascade use, such as a blast furnace reductant. Several reports have described wet processes for the dechlorination of PVC [8–11]. We developed a wet treatment process for efficient dechlorination in aqueous NaOH at high temperature and pressure using an autoclave [12–15]. This process has already been put to practical use in Denmark. Recently, we demonstrated the efficient dechlorination of PVC in NaOH/ethylene glycol (EG) solution at atmospheric pressure due primarily to the high boiling point of EG (196 C) [16]. This dechlorination reaction was found to occur by a combination of E2 and SN2 mechanisms, as shown in Scheme 1 [16]. We focused on the SN2 reaction for the dechlorination of PVC in NaOH/EG solution. As shown in Scheme 2, the substitution of Cl in PVC with nucleophile (Nu) * Corresponding author. Tel./fax: þ81 22 795 7211. E-mail address: [email protected] (T. Yoshioka). 0141-3910/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2008.10.006
in solution has the possibility of developing new polymers with new functional groups to ‘‘upgrade’’ PVC during recycling. Such new polymers could be widely and effectively used, depending on the characteristics resulting from the new functional groups. This study examined the substitution of Cl in PVC with Nu in solution. The examined Nu were I, SCN, OH, N 3 , and the phthalimide anion. The polymers developed by the substitutions of Cl in PVC with I and SCN in solution are expected to have conductive properties and antibacterial activity, respectively. The polymer with N 3 can lead to further kinds of functional polymers because the N3 group has high reactivity. For the phthalimide anion, the polymer may be useful as an ion-exchange resin. 2. Experimental 2.1. Materials PVC powder containing 56.7 wt.% Cl and other reagents were purchased from Kanto Chemical (Tokyo, Japan) and Wako Pure Chemical Industries (Osaka, Japan). NaI, KSCN, NaOH, NaN3, and potassium phthalimide were used as Nu reagents. 2.2. Chemical modification of PVC in Nu/EG solution Nu/EG solution was prepared by dissolving Nu in EG solution. Fifty millilitres of a Nu/EG solution was added to a 100 mL flask, and then the flask was heated to 190 C using a silicone oil bath under
108
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100
H CH CH
Elimination (E2)
CH CH
80
Cl CH2 CH
Substitution (SN2)
OH
(a)
HCl n
n
CH2 CH
n
Cl n
OH
Cl
Dechlorination /
OH
60
40
(b)
Scheme 1. Mechanism for the dechlorination of PVC in a NaOH/EG solution.
20
a N2 flow of 200 mL min1. After the temperature reached 190 C, 1.0 g of PVC powder was added to the solution, at a Nu/Cl (in PVC) molar ratio of 4, and was stirred various times. After the flask was cooled with water, the reaction was filtered, washed with deionised water and methanol, and dried under reduced pressure. In the case of OH as the Nu, PVC was added to the OH/EG solution at room temperature (RT), and then the solution was heated to 190 C. This is shown in Fig. 1, which illustrates the effect of adding PVC on the degree of dechlorination of PVC in an OH/EG solution with an OH/Cl (in PVC) molar ratio of 4 at 190 C. When the OH/EG solution containing PVC was heated from RT to 190 C and was then kept standing, the degree of dechlorination was more than 90% at 0.5 h (Fig. 1a). In contrast, the degree of dechlorination was around 50% at 0.5 h when PVC was added to the solution at 190 C (Fig. 1b). This finding was attributable to the formation of double bond and bridge-bond hydrocarbons on the surface of the PVC, caused by the very high dechlorination rate of PVC in the OH/ EG solution. This change on the surface of PVC prevents the OH from penetrating inside the PVC, which inhibits the dechlorination of PVC. 2.3. Chemical modification of PVC in a Nu/DMF solution Nu/DMF solution was prepared by dissolving Nu in DMF solution. One gram of PVC powder was added to 30 mL of a DMF solution in a 100 mL flask with mild agitation. Then, 20 mL of a Nu/ DMF solution was added to the flask and stirred at RT for 5 min. The Nu/Cl (in PVC) molar ratio was 4. The flask was then placed in a silicone oil bath at the required temperature under a N2 flow of 200 mL min1 (this was the reaction start time) and was kept standing for various times. The resulting suspension was added to a mixed solution of methanol and deionised water, with a concentration ratio of 2:1, to obtain a precipitate, which was filtered, washed with deionised water and methanol, and dried under reduced pressure.
0 0
0.5
1.0
1.5
2.0
Time /h Fig. 1. Effect of the method of adding PVC on the degree of dechlorination of PVC in an OH/EG solution with an OH/Cl (in PVC) molar ratio of 4 at 190 C. (a) PVC was added to the solution at RT, and then the solution was heated to 190 C. (b) PVC was added to the solution at 190 C.
3. Results and discussion 3.1. Chemical modification of PVC in a Nu/EG solution Fig. 2 shows the effect of the nucleophile on the degree of dechlorination of PVC in the Nu/EG solution, with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. The degree of dechlorination was calculated as the percentage of the amount of Cl in the filtrate to the amount of Cl contained in PVC. For OH and N 3 , the degree of dechlorination increased rapidly with time, and it was more than 95% within 1 h. For SCN, the degree of dechlorination increased gradually with time and reached 98% at 6 h. For I, the degree of dechlorination increased more gradually with time, but it became almost constant, 60%, even at 8 h. In the case of EG only, the degree of dechlorination hardly increased with time. These results indicate that the dechlorination of PVC in Nu/EG solution was caused by the nucleophile. The behaviours of the dechlorinations with SCN and I showed S-shaped curves, although this was not determined for OH or N 3 due to their rapid dechlorination rates. This finding suggests that the dechlorination of PVC proceeded by an autocatalytic reaction, for two reasons. One is that the acceleration of the SN2 reaction was caused by the effect of neighbouring groups due to
100
2.4. Characterization
80 Dechlorination /
Cl concentrations in the filtrate were determined using a Dionex DX-100 ion chromatograph and a Dionex model AS-16A column (eluent: 35 mM NaOH). The residue was treated at 850 C under an airflow of 100 mL min1, and the evolved gas was taken up by water and hydrogen peroxide water traps. The Cl and I in the residue were determined by analyzing the solutions in the traps by ion chromatography. The contents of C, H, N, and S in the residue were determined by combustion analysis. The residue was also analyzed by Fourier transform infrared (FT-IR) spectroscopy.
60 40
0
CH2
+ n Nu
CH Cl
n
CH2
CH Nu
+ n Cl n
Scheme 2. Reaction formula of substitution of Cl in PVC with Nu in solution.
I SCN OH
20
0
2
4
6
N3 EG only
8
Time /h Fig. 2. Effect of Nu on the degree of dechlorination of PVC in a Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C.
T. Kameda et al. / Polymer Degradation and Stability 94 (2009) 107–112
x
+ + (y + z) Cl + z H
CH CH
Nu y
z
Scheme 3. Reaction formula of substitution of Cl in PVC with Nu in solution and the elimination of HCl for dechlorinating PVC.
the substituent group of the nucleophile, which replaced the Cl in PVC. Another reason is the acceleration of the E2 reaction, which was accompanied by an increase in C]C double bonds during the elimination of HCl. This is supported by a report that the E2 reaction of PVC occurs in solution as well as the dry process proceeding via a zipper reaction [8]. The dechlorination of PVC is caused by the substitution of Cl in PVC with Nu in solution and the elimination of HCl, as shown in Scheme 3. Based on the elemental analysis of the residue, the effect of the nucleophile on the substitution of Cl in PVC with Nu in solution, and the elimination of HCl for dechlorinating PVC in Nu/ EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C was examined (Fig. 3). In this case, the degrees of the substitution and elimination were calculated by the percentages of y and z to n, respectively, according to Scheme 3. The total degrees of substitution and elimination refer to the degree of dechlorination of PVC; this is expressed as the percentages of (y þ z) to n. The degree of the remaining Cl in PVC is expressed as the percentage of x to n. In all cases, the degree of substitution was lower than that of elimination. Elimination was favoured over substitution. For SCN, OH, and N 3, the degrees of substitution were relatively high, about 20% (Fig. 3b– d). For I and the phthalimide anion, it was 1.6 and 6.0%, respectively (Fig. 3a and e). The degree of substitution was high, in the order OH > SCN ¼ N 3 > phthalimide anion > I . This order corresponds well to that of the ratio of substitution to dechlorination (i.e., the total substitution and elimination). The nucleophilic reactivity constant, however, was in the order I > SCN > N 3 > phthalimide anion [17], as shown in Table 1. For SCN, N 3 , and the phthalimide anion, the order in the ratio of substitution to dechlorination was almost the same as that of the nucleophilic reactivity constant. However, the ratio of substitution to dechlorination for I was the lowest among all the nucleophiles, in contrast to the order of the nucleophilic reactivity constant. This was attributable to the elimination of HI after the substitution of Cl
Elimination (z/n × 100 )
Substitution (y/n × 100 ) 100
in PVC with I in solution because I is a strong nucleophile as well as an excellent leaving group. Fig. 4 shows the FT-IR spectra of PVC and the product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. For PVC (Fig. 4a), the FT-IR peak corresponding to the C–Cl stretching vibration was observed at around 650 cm1. For PVC treated in the Nu/EG solution (Fig. 4b–f), the peak corresponding to the C–Cl stretching vibration decreased in intensity, suggesting dechlorination of the PVC. In contrast, the FTIR peak corresponding to the C]C stretching vibration appeared at 1600–1730 cm1. The increasing intensity of the C]C stretching vibration in the treated PVC suggests dechlorination by an E2 mechanism. The C]C stretching vibration due to a non-conjugated double bond appears at a higher wavenumber, and vibration due to a conjugated double bond and a double bond derived from an aromatic ring appears at lower wavenumbers. The C]C stretching vibration for I, SCN, and N 3 appeared at a lower wavenumber (Fig. 4b, c and e), indicating the presence of the longer, conjugated double bond. In contrast, the C]C stretching vibration for OH appeared at a higher wavenumber (Fig. 4d), indicating the presence of a shorter non-conjugated double bond. The increase in the length of the conjugated double bond resulted in the change in colour of the product, from white to yellow, orange, red, brown, and black. This is consistent with the colour of the products for I and N 3 being black; the colour for SCN was brown, although the colour of the PVC was white (Fig. 5a–c, e). In the case of the shorter
(a)
(b)
(c)
(d)
(e)
60
N3 40
(f) C=O
Substitution and elimination /
80
7.42 6.7 5.78 5.4 4.37
C Cl
Cl
CH2 CH
nCH3 I ðCH3 OHÞ
I SCN N 3 Phthalimide anion Cl
C=C
CH2 CH
Nucleophile
SCN
n
Transmittance
Cl
Table 1 Nucleophilic reactivity constant [17].
+ y Nu
CH2 CH
109
20 0
(a)
(b)
(c)
(d)
(e)
Fig. 3. Effect of Nu on the substitution of Cl in PVC with Nu in solution and elimination of HCl for dechlorinating PVC in a Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (a) I, (b) SCN, (c) OH, (d) N 3 , (e) phthalimide anion. Time: (c) 1 h, (d) 1.5 h, others 8 h.
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/ cm-1 Fig. 4. FT-IR spectra of (a) PVC, and product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Time: (d) 1 h, (e) 1.5 h, others 8 h.
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Fig. 5. Photographs of (a) PVC, and product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (b) I, (c) SCN, (d) OH, (e) N 3, (f) phthalimide anion. Time: (d) 1 h, (e) 1.5 h, others 8 h.
conjugated double bond, the colours of products for OH and phthalimide anion were red and yellow, respectively (Fig. 5d and f). The products were powders, although the thermal treatment of PVC resulted in char. Note that the wet treatment of PVC does not lead to char. The FT-IR spectra shown in Fig. 4 also confirmed the substitution of Cl in PVC with Nu in solution by an SN2 mechanism. For the product for SCN, the FT-IR peak corresponding to the SCN stretching vibration appeared at around 2050 cm1 (Fig. 4c). For the product with N 3 , the large absorption band centred at around 2000 cm1 corresponds to the N3 stretching vibration (Fig. 4e). For the product with the phthalimide anion, which has a C]O bond, the FT-IR peak corresponding to the C]O stretching vibration was observed at around 1700 cm1 (Fig. 4f). Consequently, the reaction of PVC in the Nu/EG solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl, which led to the dechlorination of PVC. 3.2. Chemical modification of PVC in a Nu/DMF solution The substitution of Cl in PVC with Nu in solution is an SN2 reaction. Generally, the SN2 reaction proceeds in aprotic solvents, such as DMF and DMSO, faster than in protic solvents, such as H2O and alcohol. Therefore, the reaction of PVC in the Nu/DMF solution
Substitution (y/n × 100 )
Elimination (z/n ×100 )
100
Substitution and elimination /
80 60 40 20 0
(a)
(b)
(c)
(d)
(e)
Fig. 6. Effect of Nu on the substitution of Cl in PVC with Nu in solution and the elimination of HCl for the dechlorination of PVC in a Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (a) I, (b) SCN, (c) OH, (d) N 3 , (e) phthalimide anion. Condition: (a) 60 C, 24 h, (b) 100 C, 24 h, (c) RT, 6 h, (d) 100 C, 24 h, (e) 60 C, 12 h.
was examined for the substitution of Cl in PVC with Nu in solution. Fig. 6 shows the effect of the nucleophile on the substitution of Cl in PVC with Nu in solution, and the elimination of HCl for dechlorinating PVC in the Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. In this case, the temperature was 60 C for I and the phthalimide anion, 100 C for SCN and N 3 , and RT for OH to prevent gelation of the PVC with increasing temperature. Although the reaction conditions were different, the degree of substitution was high, in the order N 3 > SCN > phthalimide anion > I . The degree of substitution was 66.1, 18.7, 10.5, 3.6, and 0% for N3 , SCN, the phthalimide anion, I, and OH, respectively. The degree of substitution for N 3 was much higher than that of the other nucleophiles. The ratio of substitution to dechlorination (i.e., the total substitution and elimination) was high, in the order SCN > N 3 > I > phthalimide anion. This order was similar to that of the nucleophilic reactivity constant (Table 1), I > SCN > N 3 > phthalimide anion, except I . The low ratio for I in this study was attributable to the elimination of HI after the substitution of Cl in PVC, with I in solution, because I is strong nucleophile and also an excellent elimination group. Fig. 7 shows photographs of the PVC and of the product obtained by the reaction of PVC in the Nu/DMF solution, with a Nu/Cl (in PVC) molar ratio of 4. The colour of the products for N 3 and the phthalimide anion was black (Fig. 7e and f), suggesting the development of a conjugated double bond in the product. The colours of products for I, SCN, and OH were pale yellow, pale pink, and pale brown, respectively (Fig. 7b–d), suggesting the presence of a short nonconjugated double bond in these products. However, estimating the conjugated double bond was difficult in the product from the C]C stretching vibration in the FT-IR spectra (Fig. 8), unlike the case of the products obtained by the reaction of PVC in the Nu/EG solution. Fig. 8 shows the FT-IR spectra of PVC and the products obtained by the reaction of PVC in the Nu/DMF solution, with a Nu/ Cl (in PVC) molar ratio of 4. For PVC (Fig. 8a), the FT-IR peak corresponding to the C–Cl stretching vibration was observed at around 650 cm1. For PVC treated with I, SCN, and OH (Fig. 8b–d), the peak corresponding to the C–Cl stretching vibration decreased a little in intensity, suggesting slight dechlorination of the PVC. This corresponds to the low degree of dechlorination (i.e., the total substitution and elimination) for I, SCN, and OH, as shown in Fig. 6a–c. For PVC treated with N 3 and the phthalimide anion (Fig. 8e and f), the peak corresponding to the C–Cl stretching vibration decreased considerably in intensity, suggesting some dechlorination of the PVC. This corresponds to a high degree of
T. Kameda et al. / Polymer Degradation and Stability 94 (2009) 107–112
111
Fig. 7. Photographs of (a) PVC, and product obtained by the reaction of PVC in a Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Condition: (b) 60 C, 24 h, (c) 100 C, 24 h, (d) RT, 6 h, (e) 100 C, 24 h, (f) 60 C, 12 h.
C=O C=C
C Cl
dechlorination (i.e., the total substitution and elimination) for N 3 and the phthalimide anion (Fig. 6d and e). The FT-IR peak corresponding to the C]C stretching vibration appeared at 1600–1700 cm1, suggesting dechlorination by an E2 mechanism. The FT-IR spectra shown in Fig. 8 also confirmed the substitution of Cl in PVC with Nu in solution by an SN2 mechanism. For the product with SCN, the FT-IR peak derived from SCN group appeared at 1950–2150 cm1 (Fig. 8c). For the product with N 3 , the large absorption band centred at around 2100 cm1 corresponded to the –N3 stretching vibration (Fig. 8e). Furthermore, the FT-IR peaks
corresponding to the –NHþ and –NH stretching vibrations appeared at around 2450 and 3300 cm1, respectively (Fig. 8e). The presence of –NHþ and –NH groups in the product was attributable to the reaction of –N3 groups substituted with Cl in PVC because of the –N3 group’s own high reactivity. For the product with the phthalimide anion, the FT-IR peak corresponding to the C]O stretching vibration was observed at around 1750 cm1 (Fig. 8f). Consequently, the reaction of PVC in Nu/DMF solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution from Figs. 3 and 6, the ratio of substitution to dechlorination (i.e., the total substitution and elimination) was higher for I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG.
(a) 4. Conclusions
SCN
(c)
NH+
(d) NH
Transmittance
(b)
N3
(e)
(f)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/ cm-1 Fig. 8. FT-IR spectra of (a) PVC, and product obtained by the reaction of PVC in a Nu/ DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Condition: (b) 60 C, 24 h, (c) 100 C, 24 h, (d) RT, 6 h, (e) 100 C, 24 h, (f) 60 C, 12 h.
The reaction of PVC in Nu/EG or Nu/DMF solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl, leading to the dechlorination of PVC. When PVC was treated in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C, elimination was favoured over substitution. For SCN, OH, and N 3 , the degrees of substitutions were relatively high, about 20%. For I and the phthalimide anion, it was 1.6 and 6.0%, respectively. The ratio of substitution to dechlorination (i.e., the total substitution and elimination) was high, in the order OH > SCN ¼ N 3 > phthalimide anion > I . When PVC was treated in Nu/DMF solution, with a Nu/Cl (in PVC) molar ratio of 4 even though the reaction conditions were different, the degree of > phthalimide substitution was high, in the order N 3 > SCN anion > I. The highest degree of substitution was for N 3 , 66.1%. The ratio of substitution to dechlorination was high, in the order SCN > N 3 > I > phthalimide anion. In both the EG and DMF solutions, the order of the ratio of substitution to dechlorination was similar to that of the nucleophilic reactivity constant, I > SCN > N 3 > phthalimide anion, except for I . The low ratio for I in this study was attributable to the elimination of HI after the substitution of Cl in PVC, with I in solution, because I is strong nucleophile and an excellent elimination group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for
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I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG. References [1] [2] [3] [4]
Winkler DE. J Polym Sci 1959;35:3–16. Yoshioka T, Akama T, Uchida M, Okuwaki A. Chem Lett 2000;29:322–3. Yoshioka T, Saitoh N, Okuwaki A. Chem Lett 2005;34:70–1. Bhaskar T, Sakata Y. In: Scheirs J, Kaminsky W, editors. Feedstock recycling and pyrolysis of waste plastics. London: John Wiley & Sons, Ltd.; 2006. p. 498–502. [5] Montaudo G, Puglisi C. Polym Degrad Stab 1991;33:229–62. [6] Mio H, Saeki S, Kano J, Saito F. Environ Sci Technol 2002;36:1344–8.
[7] Yoshioka T, Imai S, Ieshige M, Okuwaki A. In: Muller-Hagedorn M, Bockhorn H, editors. Feedstock recycling of plastics. Karlsruhe, Germany: Universita¨tsverlag Karlsruhe; 2005. p. 147–52. [8] Behnisch J, Zimmermann H. Int J Polym Mater 1992;16:143–57. [9] Yoshinaga T, Yamaye M, Kito T, Ichiki T, Ogata M, Chen J, et al. Polym Degrad Stab 2004;86:541–7. [10] Kise H. J Polym Sci 1982;20:3189–97. [11] Guo L, Shi G, Liang Y. Polymer 2001;42:5581–7. [12] Shin S-M, Yoshioka T, Okuwaki A. J Appl Polym Sci 1998;67:2171–7. [13] Yoshioka T, Furukawa K, Sato S, Okuwaki A. J Appl Polym Sci 1998;70:129–35. [14] Shin S-M, Yoshioka T, Okuwaki A. Polym Degrad Stab 1998;61:349–53. [15] Yoshioka T, Furukawa K, Okuwaki A. Polym Degrad Stab 2000;67:285–90. [16] Yoshioka T, Kameda T, Imai S, Okuwaki A. Polym Degrad Stab 2008;93: 1138–41. [17] Pearson RG, Sobel H, Songstad J. J Am Chem Soc 1968;90:319–26.
Contents lists available at ScienceDirect
Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab
Chemical modification of poly(vinyl chloride) by nucleophilic substitution Tomohito Kameda a, Masahiko Ono b, Guido Grause a, Tadaaki Mizoguchi b, Toshiaki Yoshioka a, * a b
Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan Environment Conservation Research Institute, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 July 2008 Received in revised form 2 September 2008 Accepted 7 October 2008 Available online 19 October 2008
The reaction of poly(vinyl chloride) (PVC) in nucleophile (Nu)/ethylene glycol (EG) or Nu/N,N-dimethylformamide (DMF) solution was found to result in the substitution of Cl in PVC with Nu from solution, in addition to the straight elimination of HCl, both of which led to the dechlorination of PVC. Examined Nu were I, SCN, OH, N 3 , and the phthalimide anion. For the Nu/EG solution, elimination was favoured over substitution for all Nu. The ratio of substitution to dechlorination was notable, descending in the order OH > SCN ¼ N 3 > phthalimide anion > I . For the Nu/DMF solution, the ratio of substitution to dechlorination was high, in the order SCN > N3 > I > phthalimide anion. In both cases, the orders of the ratios were similar to those of the nucleophilic reactivity constant, I > SCN > N 3 > phthalimide anion, except for I. The low ratio for I was attributable to the elimination of HI after the substitution of Cl in PVC with I in solution, because I is a strong nucleophile, as well as an excellent leaving group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Poly(vinyl chloride) Chemical modification Nucleophilic substitution Ethylene glycol N,N-Dimethylformamide
1. Introduction Numerous studies have explored the dechlorination of poly(vinyl chloride) (PVC) from the viewpoint of recycling waste plastics. They are based on the phenomenon that the dechlorination of PVC occurs by a radical zipper reaction at 200–250 C [1]. Some studies have examined the dry process for the dechlorination of PVC [2–6]. Thermal degradation of PVC resulted in almost complete dechlorination above 260 C [3], although the degree of dechlorination of poly(vinylidene chloride) (PVDC) was around 60% at 300 C [7]. However, the thermal degradation of PVC also leads to the production of polyenes and their cyclisation. Therefore, this efficient method of dechlorinating PVC is limited to cascade use, such as a blast furnace reductant. Several reports have described wet processes for the dechlorination of PVC [8–11]. We developed a wet treatment process for efficient dechlorination in aqueous NaOH at high temperature and pressure using an autoclave [12–15]. This process has already been put to practical use in Denmark. Recently, we demonstrated the efficient dechlorination of PVC in NaOH/ethylene glycol (EG) solution at atmospheric pressure due primarily to the high boiling point of EG (196 C) [16]. This dechlorination reaction was found to occur by a combination of E2 and SN2 mechanisms, as shown in Scheme 1 [16]. We focused on the SN2 reaction for the dechlorination of PVC in NaOH/EG solution. As shown in Scheme 2, the substitution of Cl in PVC with nucleophile (Nu) * Corresponding author. Tel./fax: þ81 22 795 7211. E-mail address: [email protected] (T. Yoshioka). 0141-3910/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2008.10.006
in solution has the possibility of developing new polymers with new functional groups to ‘‘upgrade’’ PVC during recycling. Such new polymers could be widely and effectively used, depending on the characteristics resulting from the new functional groups. This study examined the substitution of Cl in PVC with Nu in solution. The examined Nu were I, SCN, OH, N 3 , and the phthalimide anion. The polymers developed by the substitutions of Cl in PVC with I and SCN in solution are expected to have conductive properties and antibacterial activity, respectively. The polymer with N 3 can lead to further kinds of functional polymers because the N3 group has high reactivity. For the phthalimide anion, the polymer may be useful as an ion-exchange resin. 2. Experimental 2.1. Materials PVC powder containing 56.7 wt.% Cl and other reagents were purchased from Kanto Chemical (Tokyo, Japan) and Wako Pure Chemical Industries (Osaka, Japan). NaI, KSCN, NaOH, NaN3, and potassium phthalimide were used as Nu reagents. 2.2. Chemical modification of PVC in Nu/EG solution Nu/EG solution was prepared by dissolving Nu in EG solution. Fifty millilitres of a Nu/EG solution was added to a 100 mL flask, and then the flask was heated to 190 C using a silicone oil bath under
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100
H CH CH
Elimination (E2)
CH CH
80
Cl CH2 CH
Substitution (SN2)
OH
(a)
HCl n
n
CH2 CH
n
Cl n
OH
Cl
Dechlorination /
OH
60
40
(b)
Scheme 1. Mechanism for the dechlorination of PVC in a NaOH/EG solution.
20
a N2 flow of 200 mL min1. After the temperature reached 190 C, 1.0 g of PVC powder was added to the solution, at a Nu/Cl (in PVC) molar ratio of 4, and was stirred various times. After the flask was cooled with water, the reaction was filtered, washed with deionised water and methanol, and dried under reduced pressure. In the case of OH as the Nu, PVC was added to the OH/EG solution at room temperature (RT), and then the solution was heated to 190 C. This is shown in Fig. 1, which illustrates the effect of adding PVC on the degree of dechlorination of PVC in an OH/EG solution with an OH/Cl (in PVC) molar ratio of 4 at 190 C. When the OH/EG solution containing PVC was heated from RT to 190 C and was then kept standing, the degree of dechlorination was more than 90% at 0.5 h (Fig. 1a). In contrast, the degree of dechlorination was around 50% at 0.5 h when PVC was added to the solution at 190 C (Fig. 1b). This finding was attributable to the formation of double bond and bridge-bond hydrocarbons on the surface of the PVC, caused by the very high dechlorination rate of PVC in the OH/ EG solution. This change on the surface of PVC prevents the OH from penetrating inside the PVC, which inhibits the dechlorination of PVC. 2.3. Chemical modification of PVC in a Nu/DMF solution Nu/DMF solution was prepared by dissolving Nu in DMF solution. One gram of PVC powder was added to 30 mL of a DMF solution in a 100 mL flask with mild agitation. Then, 20 mL of a Nu/ DMF solution was added to the flask and stirred at RT for 5 min. The Nu/Cl (in PVC) molar ratio was 4. The flask was then placed in a silicone oil bath at the required temperature under a N2 flow of 200 mL min1 (this was the reaction start time) and was kept standing for various times. The resulting suspension was added to a mixed solution of methanol and deionised water, with a concentration ratio of 2:1, to obtain a precipitate, which was filtered, washed with deionised water and methanol, and dried under reduced pressure.
0 0
0.5
1.0
1.5
2.0
Time /h Fig. 1. Effect of the method of adding PVC on the degree of dechlorination of PVC in an OH/EG solution with an OH/Cl (in PVC) molar ratio of 4 at 190 C. (a) PVC was added to the solution at RT, and then the solution was heated to 190 C. (b) PVC was added to the solution at 190 C.
3. Results and discussion 3.1. Chemical modification of PVC in a Nu/EG solution Fig. 2 shows the effect of the nucleophile on the degree of dechlorination of PVC in the Nu/EG solution, with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. The degree of dechlorination was calculated as the percentage of the amount of Cl in the filtrate to the amount of Cl contained in PVC. For OH and N 3 , the degree of dechlorination increased rapidly with time, and it was more than 95% within 1 h. For SCN, the degree of dechlorination increased gradually with time and reached 98% at 6 h. For I, the degree of dechlorination increased more gradually with time, but it became almost constant, 60%, even at 8 h. In the case of EG only, the degree of dechlorination hardly increased with time. These results indicate that the dechlorination of PVC in Nu/EG solution was caused by the nucleophile. The behaviours of the dechlorinations with SCN and I showed S-shaped curves, although this was not determined for OH or N 3 due to their rapid dechlorination rates. This finding suggests that the dechlorination of PVC proceeded by an autocatalytic reaction, for two reasons. One is that the acceleration of the SN2 reaction was caused by the effect of neighbouring groups due to
100
2.4. Characterization
80 Dechlorination /
Cl concentrations in the filtrate were determined using a Dionex DX-100 ion chromatograph and a Dionex model AS-16A column (eluent: 35 mM NaOH). The residue was treated at 850 C under an airflow of 100 mL min1, and the evolved gas was taken up by water and hydrogen peroxide water traps. The Cl and I in the residue were determined by analyzing the solutions in the traps by ion chromatography. The contents of C, H, N, and S in the residue were determined by combustion analysis. The residue was also analyzed by Fourier transform infrared (FT-IR) spectroscopy.
60 40
0
CH2
+ n Nu
CH Cl
n
CH2
CH Nu
+ n Cl n
Scheme 2. Reaction formula of substitution of Cl in PVC with Nu in solution.
I SCN OH
20
0
2
4
6
N3 EG only
8
Time /h Fig. 2. Effect of Nu on the degree of dechlorination of PVC in a Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C.
T. Kameda et al. / Polymer Degradation and Stability 94 (2009) 107–112
x
+ + (y + z) Cl + z H
CH CH
Nu y
z
Scheme 3. Reaction formula of substitution of Cl in PVC with Nu in solution and the elimination of HCl for dechlorinating PVC.
the substituent group of the nucleophile, which replaced the Cl in PVC. Another reason is the acceleration of the E2 reaction, which was accompanied by an increase in C]C double bonds during the elimination of HCl. This is supported by a report that the E2 reaction of PVC occurs in solution as well as the dry process proceeding via a zipper reaction [8]. The dechlorination of PVC is caused by the substitution of Cl in PVC with Nu in solution and the elimination of HCl, as shown in Scheme 3. Based on the elemental analysis of the residue, the effect of the nucleophile on the substitution of Cl in PVC with Nu in solution, and the elimination of HCl for dechlorinating PVC in Nu/ EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C was examined (Fig. 3). In this case, the degrees of the substitution and elimination were calculated by the percentages of y and z to n, respectively, according to Scheme 3. The total degrees of substitution and elimination refer to the degree of dechlorination of PVC; this is expressed as the percentages of (y þ z) to n. The degree of the remaining Cl in PVC is expressed as the percentage of x to n. In all cases, the degree of substitution was lower than that of elimination. Elimination was favoured over substitution. For SCN, OH, and N 3, the degrees of substitution were relatively high, about 20% (Fig. 3b– d). For I and the phthalimide anion, it was 1.6 and 6.0%, respectively (Fig. 3a and e). The degree of substitution was high, in the order OH > SCN ¼ N 3 > phthalimide anion > I . This order corresponds well to that of the ratio of substitution to dechlorination (i.e., the total substitution and elimination). The nucleophilic reactivity constant, however, was in the order I > SCN > N 3 > phthalimide anion [17], as shown in Table 1. For SCN, N 3 , and the phthalimide anion, the order in the ratio of substitution to dechlorination was almost the same as that of the nucleophilic reactivity constant. However, the ratio of substitution to dechlorination for I was the lowest among all the nucleophiles, in contrast to the order of the nucleophilic reactivity constant. This was attributable to the elimination of HI after the substitution of Cl
Elimination (z/n × 100 )
Substitution (y/n × 100 ) 100
in PVC with I in solution because I is a strong nucleophile as well as an excellent leaving group. Fig. 4 shows the FT-IR spectra of PVC and the product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. For PVC (Fig. 4a), the FT-IR peak corresponding to the C–Cl stretching vibration was observed at around 650 cm1. For PVC treated in the Nu/EG solution (Fig. 4b–f), the peak corresponding to the C–Cl stretching vibration decreased in intensity, suggesting dechlorination of the PVC. In contrast, the FTIR peak corresponding to the C]C stretching vibration appeared at 1600–1730 cm1. The increasing intensity of the C]C stretching vibration in the treated PVC suggests dechlorination by an E2 mechanism. The C]C stretching vibration due to a non-conjugated double bond appears at a higher wavenumber, and vibration due to a conjugated double bond and a double bond derived from an aromatic ring appears at lower wavenumbers. The C]C stretching vibration for I, SCN, and N 3 appeared at a lower wavenumber (Fig. 4b, c and e), indicating the presence of the longer, conjugated double bond. In contrast, the C]C stretching vibration for OH appeared at a higher wavenumber (Fig. 4d), indicating the presence of a shorter non-conjugated double bond. The increase in the length of the conjugated double bond resulted in the change in colour of the product, from white to yellow, orange, red, brown, and black. This is consistent with the colour of the products for I and N 3 being black; the colour for SCN was brown, although the colour of the PVC was white (Fig. 5a–c, e). In the case of the shorter
(a)
(b)
(c)
(d)
(e)
60
N3 40
(f) C=O
Substitution and elimination /
80
7.42 6.7 5.78 5.4 4.37
C Cl
Cl
CH2 CH
nCH3 I ðCH3 OHÞ
I SCN N 3 Phthalimide anion Cl
C=C
CH2 CH
Nucleophile
SCN
n
Transmittance
Cl
Table 1 Nucleophilic reactivity constant [17].
+ y Nu
CH2 CH
109
20 0
(a)
(b)
(c)
(d)
(e)
Fig. 3. Effect of Nu on the substitution of Cl in PVC with Nu in solution and elimination of HCl for dechlorinating PVC in a Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (a) I, (b) SCN, (c) OH, (d) N 3 , (e) phthalimide anion. Time: (c) 1 h, (d) 1.5 h, others 8 h.
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/ cm-1 Fig. 4. FT-IR spectra of (a) PVC, and product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Time: (d) 1 h, (e) 1.5 h, others 8 h.
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Fig. 5. Photographs of (a) PVC, and product obtained by the reaction of PVC in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C. Nu: (b) I, (c) SCN, (d) OH, (e) N 3, (f) phthalimide anion. Time: (d) 1 h, (e) 1.5 h, others 8 h.
conjugated double bond, the colours of products for OH and phthalimide anion were red and yellow, respectively (Fig. 5d and f). The products were powders, although the thermal treatment of PVC resulted in char. Note that the wet treatment of PVC does not lead to char. The FT-IR spectra shown in Fig. 4 also confirmed the substitution of Cl in PVC with Nu in solution by an SN2 mechanism. For the product for SCN, the FT-IR peak corresponding to the SCN stretching vibration appeared at around 2050 cm1 (Fig. 4c). For the product with N 3 , the large absorption band centred at around 2000 cm1 corresponds to the N3 stretching vibration (Fig. 4e). For the product with the phthalimide anion, which has a C]O bond, the FT-IR peak corresponding to the C]O stretching vibration was observed at around 1700 cm1 (Fig. 4f). Consequently, the reaction of PVC in the Nu/EG solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl, which led to the dechlorination of PVC. 3.2. Chemical modification of PVC in a Nu/DMF solution The substitution of Cl in PVC with Nu in solution is an SN2 reaction. Generally, the SN2 reaction proceeds in aprotic solvents, such as DMF and DMSO, faster than in protic solvents, such as H2O and alcohol. Therefore, the reaction of PVC in the Nu/DMF solution
Substitution (y/n × 100 )
Elimination (z/n ×100 )
100
Substitution and elimination /
80 60 40 20 0
(a)
(b)
(c)
(d)
(e)
Fig. 6. Effect of Nu on the substitution of Cl in PVC with Nu in solution and the elimination of HCl for the dechlorination of PVC in a Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (a) I, (b) SCN, (c) OH, (d) N 3 , (e) phthalimide anion. Condition: (a) 60 C, 24 h, (b) 100 C, 24 h, (c) RT, 6 h, (d) 100 C, 24 h, (e) 60 C, 12 h.
was examined for the substitution of Cl in PVC with Nu in solution. Fig. 6 shows the effect of the nucleophile on the substitution of Cl in PVC with Nu in solution, and the elimination of HCl for dechlorinating PVC in the Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. In this case, the temperature was 60 C for I and the phthalimide anion, 100 C for SCN and N 3 , and RT for OH to prevent gelation of the PVC with increasing temperature. Although the reaction conditions were different, the degree of substitution was high, in the order N 3 > SCN > phthalimide anion > I . The degree of substitution was 66.1, 18.7, 10.5, 3.6, and 0% for N3 , SCN, the phthalimide anion, I, and OH, respectively. The degree of substitution for N 3 was much higher than that of the other nucleophiles. The ratio of substitution to dechlorination (i.e., the total substitution and elimination) was high, in the order SCN > N 3 > I > phthalimide anion. This order was similar to that of the nucleophilic reactivity constant (Table 1), I > SCN > N 3 > phthalimide anion, except I . The low ratio for I in this study was attributable to the elimination of HI after the substitution of Cl in PVC, with I in solution, because I is strong nucleophile and also an excellent elimination group. Fig. 7 shows photographs of the PVC and of the product obtained by the reaction of PVC in the Nu/DMF solution, with a Nu/Cl (in PVC) molar ratio of 4. The colour of the products for N 3 and the phthalimide anion was black (Fig. 7e and f), suggesting the development of a conjugated double bond in the product. The colours of products for I, SCN, and OH were pale yellow, pale pink, and pale brown, respectively (Fig. 7b–d), suggesting the presence of a short nonconjugated double bond in these products. However, estimating the conjugated double bond was difficult in the product from the C]C stretching vibration in the FT-IR spectra (Fig. 8), unlike the case of the products obtained by the reaction of PVC in the Nu/EG solution. Fig. 8 shows the FT-IR spectra of PVC and the products obtained by the reaction of PVC in the Nu/DMF solution, with a Nu/ Cl (in PVC) molar ratio of 4. For PVC (Fig. 8a), the FT-IR peak corresponding to the C–Cl stretching vibration was observed at around 650 cm1. For PVC treated with I, SCN, and OH (Fig. 8b–d), the peak corresponding to the C–Cl stretching vibration decreased a little in intensity, suggesting slight dechlorination of the PVC. This corresponds to the low degree of dechlorination (i.e., the total substitution and elimination) for I, SCN, and OH, as shown in Fig. 6a–c. For PVC treated with N 3 and the phthalimide anion (Fig. 8e and f), the peak corresponding to the C–Cl stretching vibration decreased considerably in intensity, suggesting some dechlorination of the PVC. This corresponds to a high degree of
T. Kameda et al. / Polymer Degradation and Stability 94 (2009) 107–112
111
Fig. 7. Photographs of (a) PVC, and product obtained by the reaction of PVC in a Nu/DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Condition: (b) 60 C, 24 h, (c) 100 C, 24 h, (d) RT, 6 h, (e) 100 C, 24 h, (f) 60 C, 12 h.
C=O C=C
C Cl
dechlorination (i.e., the total substitution and elimination) for N 3 and the phthalimide anion (Fig. 6d and e). The FT-IR peak corresponding to the C]C stretching vibration appeared at 1600–1700 cm1, suggesting dechlorination by an E2 mechanism. The FT-IR spectra shown in Fig. 8 also confirmed the substitution of Cl in PVC with Nu in solution by an SN2 mechanism. For the product with SCN, the FT-IR peak derived from SCN group appeared at 1950–2150 cm1 (Fig. 8c). For the product with N 3 , the large absorption band centred at around 2100 cm1 corresponded to the –N3 stretching vibration (Fig. 8e). Furthermore, the FT-IR peaks
corresponding to the –NHþ and –NH stretching vibrations appeared at around 2450 and 3300 cm1, respectively (Fig. 8e). The presence of –NHþ and –NH groups in the product was attributable to the reaction of –N3 groups substituted with Cl in PVC because of the –N3 group’s own high reactivity. For the product with the phthalimide anion, the FT-IR peak corresponding to the C]O stretching vibration was observed at around 1750 cm1 (Fig. 8f). Consequently, the reaction of PVC in Nu/DMF solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution from Figs. 3 and 6, the ratio of substitution to dechlorination (i.e., the total substitution and elimination) was higher for I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG.
(a) 4. Conclusions
SCN
(c)
NH+
(d) NH
Transmittance
(b)
N3
(e)
(f)
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/ cm-1 Fig. 8. FT-IR spectra of (a) PVC, and product obtained by the reaction of PVC in a Nu/ DMF solution with a Nu/Cl (in PVC) molar ratio of 4. Nu: (b) I, (c) SCN, (d) OH, (e) N 3 , (f) phthalimide anion. Condition: (b) 60 C, 24 h, (c) 100 C, 24 h, (d) RT, 6 h, (e) 100 C, 24 h, (f) 60 C, 12 h.
The reaction of PVC in Nu/EG or Nu/DMF solution was found to result in the substitution of Cl in PVC with Nu in solution, in addition to the elimination of HCl, leading to the dechlorination of PVC. When PVC was treated in Nu/EG solution with a Nu/Cl (in PVC) molar ratio of 4 at 190 C, elimination was favoured over substitution. For SCN, OH, and N 3 , the degrees of substitutions were relatively high, about 20%. For I and the phthalimide anion, it was 1.6 and 6.0%, respectively. The ratio of substitution to dechlorination (i.e., the total substitution and elimination) was high, in the order OH > SCN ¼ N 3 > phthalimide anion > I . When PVC was treated in Nu/DMF solution, with a Nu/Cl (in PVC) molar ratio of 4 even though the reaction conditions were different, the degree of > phthalimide substitution was high, in the order N 3 > SCN anion > I. The highest degree of substitution was for N 3 , 66.1%. The ratio of substitution to dechlorination was high, in the order SCN > N 3 > I > phthalimide anion. In both the EG and DMF solutions, the order of the ratio of substitution to dechlorination was similar to that of the nucleophilic reactivity constant, I > SCN > N 3 > phthalimide anion, except for I . The low ratio for I in this study was attributable to the elimination of HI after the substitution of Cl in PVC, with I in solution, because I is strong nucleophile and an excellent elimination group. Comparing the effect of EG and DMF on the substitution of Cl in PVC with Nu in solution, the ratio of substitution to dechlorination was higher for
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I, SCN, N 3 , and the phthalimide anion in DMF than in EG. The substitution of Cl in PVC with Nu in solution was found to occur preferentially in DMF versus EG. References [1] [2] [3] [4]
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