JOURNAL OF MACROMOLECULAR SCIENCEw Part A—Pure and Applied Chemistry Vol. A41, No. 10, pp. 1087–1094, 2004
Nanoporous Crosslinked Copolymers Prepared by Thermal Degradation of Poly(Methacryl-N,N0 -diisopropylureaco-ethylene Glycol Dimethacrylate) Ana Erceg Kuzmic´, Radivoje Vukovic´, Grozdana Bogdanic´, Branka Sˇpehar, and Dragutin Flesˇ* INA—Industrija Nafte d.d., Research and Development Sector, Lovincˇic´eva bb, Zagreb, Croatia
ABSTRACT Copolymers of methacryl-N,N0 -diisopropylurea (MA-DiPrU) with ethylene glycol dimethacrylate (EDMA) at monomer-to-monomer ratios in the feed: 0.3/0.7; 0.5/ 0.5; 0.7/0.3; 0.8/0.2 were prepared in butanone in the presence of 2% of dibenzoyl peroxide (Bz2O2) at 708C for 48 hr. Copolymers regardless of the ratio of comonomers in the feed decompose thermally at 200– 2508C under the separation of isopropylisocyanate (iPrNCO). Residues after the removal of iPrNCO are thermally stable nanoporous crosslinked copolymers of methacryl-isopropylamide (MA-iPrA) with EDMA which decompose by a one-step mechanism between 2808C and 4508C. Nonporous model copolymers poly(MA-iPrA-co-EDMA) of similar composition, prepared by copolymerization of MA-iPrA with EDMA, also decomposed by a one-step mechanism as shown by TGA measurements. Key Words: Methacryl-N,N0 -diisopropylurea; Poly(methacryl-N,N0 -diisopropylureaco-ethylene glycol dimethacrylate); Methacryl-N-isopropylamide; Poly(methacryl-N-
*Correspondence: Dragutin Flesˇ, INA—Industrija Nafte d.d., Research and Development Sector, Lovincˇic´eva bb, P.O. Box 555, 10002 Zagreb, Croatia; Fax: þ385-1-245-2794; E-mail: ana.
[email protected]. 1087 DOI: 10.1081/MA-200026543 Copyright # 2004 by Marcel Dekker, Inc.
1060-1325 (Print); 1520-5738 (Online) www.dekker.com
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isopropylamide-co-ethylene glycol dimethacrylate); Thermal properties; Thermal degradation of poly(methacryl-N,N0 -diisopropylurea-co-ethylene glycol dimethacrylate); Nanoporous poly(methacryl-N-isopropylamide-co-ethylene glycol dimethacrylate); Nonporous poly(methacryl-N-isopropylamide-co-ethylene glycol dimethacrylate).
INTRODUCTION In previously published papers[1 – 3] it was shown that acryl-N,N0 -dicyclohexylurea (A-DCU) and methacryl-N,N0 -dicyclohexylurea (MA-DCU) were readily copolymerized with ethylene glycol dimethacrylate (EDMA) yielding crosslinked copolymers which thermally decompose by a two-step mechanism under the formation of volatile cyclohexylisocyanate and nanoporous crosslinked acryl-N-cyclohexylamide and methacrylN-cyclohexylamide, respectively. In continuation of this work, we wish to describe in the present paper, the preparation of methacryl-N,N0 -diisopropylurea (MA-DiPrU) by condensation of methacrylic acid (MAA) with diisopropylcarbodiimide (DiPrC) in tetrahydrofuran (THF). Copolymerization of MA-DiPrU with EDMA, at a different monomerto-monomer ratio in the feed, gave crosslinked copolymers which by thermal degradation under the separation of isopropylisocyanate (iPrNCO) gave nanoporous poly(MA-iPrAco-EDMA). The corresponding nonporous poly(MA-iPrA-co-EDMA) was prepared by copolymerization of methacryl-isopropylamide (MA-iPrA) with EDMA.
EXPERIMENTAL Synthesis of MA-DiPrU A solution of 6.3 g (7.81 mL; 0.05 mol) of DiPrC (Fluka, Buchs, Switzerland; purum) in 10 mL of THF (Fluka; purum; 99%) was added slowly under cooling to a solution of 4.3 g (4.24 mL; 0.05 mol) of MAA (Fluka; purum) and 0.2 g of hydroquinone in 10 mL of THF, and left overnight at room temperature. The white crystalline product was filtered off, washed with 5 mL of THF yielding 3.0 g of DiPrU, which under heating in melting point apparatus partially melts at 130– 1408C and then crystallizes to long needles and melts sharply at 1958C. Analysis of DiPrU: Calcd. for C7H16N2O (144) (%): C, 58.33; H, 11.11; N, 19.44; Found: C, 57.95; H, 10.77; N, 18.92. The mother liquid was evaporated to dryness, treated with 30 mL of petrolether and left overnight in a refrigerator yielding 3.4 g (32.1%) of a white crystalline product, melting at 77 – 788C. Analysis of MA-DiPrU: Calcd. for C11H20N2O2 (212) (%): C, 62.26; H, 9.43; N, 13.21; Found: C, 62.18; H, 9.43; N, 13.06. The monomer structure was determined by NMR spectroscopy measurements.
Synthesis of MA-iPrA To a solution of 5.9 g (0.08 mol) of isopropylamine (Fluka, Buchs, Switzerland; puriss) in 20 mL of ether was added under cooling 15.6 g (0.1 mol) of MA-anhydride
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(Fluka, Buchs, Switzerland; pract.) in 30 mL of ether, which contains 0.2 g of hydroquinone. The reaction mixture was left overnight at room temperature, and the etheral solution was washed with two 10 mL portions of aqueous solution of 10% NaOH, and washed with water. Etheral solution was dried with Na2SO4 and evaporated to dryness. The residue was treated with 20 mL of petrolether and left in deepfreeze overnight. The crystalline product was filtered off, yielding 2.09 g (20.0%) of white crystals melting at 89– 908C. Analysis of MA-iPrA: Calcd. for C7H13NO (127) (%): C, 66.14; H, 10.24; N, 11.02; Found: C, 65.24; H, 10.05; N, 10.59. The monomer structure was determined by NMR spectroscopy measurements.
Copolymerization of MA-DiPrU with EDMA at Molar Ratio of 0.5 : 0.5 in the Feed To a mixture of 0.212 g (0.001 mol) of MA-DiPrU and 0.198 g (0.001 mol) of EDMA (Aldrich, Steinheim, Germany; 98%) was added 2 mL of butanone (Fluka, Buchs, Switzerland; purum) which contains 2% (0.0098 g) of dibenzoyl peroxide (Bz2O2, Fluka; purum) as initiator. The reaction mixture was homogenized under the stream of nitrogen and heated for 48 hr at 708C. After cooling, the copolymer was washed with butanone, followed by methanol yielding 0.259 g (63.2%) of insoluble and unswellable crosslinked copolymer. Under the same experimental conditions, the crosslinked copolymers of MA-DiPrU with EDMA at monomer-to-monomer ratios of 0.3/ 0.7; 0.7/0.3; and 0.8/0.2 in the feed were also prepared. The elemental analyses of all copolymers are presented in Table 1.
Copolymerization of MA-iPrA with EDMA at Molar Ratio of 0.5 : 0.5 in the Feed (Model Copolymer) A mixture of 0.128 g (0.001 mol) of MA-iPrA and 0.198 g (0.001 mol) of EDMA in 2 mL of butanone with 2% Bz2O2 was heated for 48 hr at 708C under a stream of nitrogen. Crude polymer was washed with butanone, yielding 0.295 g (90.67%) of crosslinked polymers. Analysis of crosslinked copolymer (%): C, 59.85; H, 8.12; N, 3.67. Based on the nitrogen content, the copolymer contains of 0.33 molar ratio of MA-iPrA and 0.67 ratio of EDMA (Table 2). Under the same experimental conditions, the crosslinked copolymers of MA-iPrA with EDMA at monomer-to-monomer ratios of 0.3/0.7; 0.7/0.3; and 0.8/0.2 in the feed, were also prepared. The results are presented in Table 2.
Physicochemical Measurements The NMR spectra were recorded on a Bruker Avance 300 FT NMR spectrometer. Elemental analysis data were obtained by using a LECO CHNS-932 automatic analyzer. The thermogravimetric analysis was carried out on a Perkin– Elmer TGS-2 thermogravimetric system in nitrogen stream with heating rate of 108C/min.
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Table 1. Elemental analysis of crosslinked copolymers of MA-DiPrU with EDMA obtained at different monomer-to-monomer ratios in the feed, elemental analysis of thermally treated copolymers, as well as theoretical and measured values of iPrNCO in copolymers. iPrNCO (%)
Molar ratio in feed
Conversion (%)
0.3/0.7
83.75
0.5/0.5
63.20
0.7/0.3
41.45
0.8/0.2
30.95
Elemental analysis of copolymersa (%) C, 57.42 H, 7.70 N, 2.38 C, 57.29 H, 7.75 N, 3.36 C, 58.10 H, 8.15 N, 5.03 C, 57.94 H, 8.27 N, 5.98
Molar ratio in copolymersb 0.18/0.82
0.25/0.75
0.38/0.62
0.45/0.55
Elemental analysis of thermally treated copolymersc (%)
Based on N2 content in copolymers
Based on TGA at 2508C
7.6
7.0
10.8
11.5
15.9
14.0
18.7
19.0
C, 58.90 H, 7.38 N, 1.53 C, 59.12 H, 7.57 N, 2.25 C, 60.14 H, 7.78 N, 3.64 C, 60.78 H, 8.05 N, 4.36
a
708C, 48 hr, 2% Bz2O2; in butanone. Based on nitrogen content of copolymers obtained from elemental analyses. c From thermally treated copolymers at 2508C, 48 hr, 2% Bz2O2; in butanone. b
RESULTS AND DISCUSSION Thermograms of copolymers of MA-DiPrU with EDMA presented in Fig. 1, indicate that regardless of the ratio of repeating units in copolymers, they decompose by a two-step mechanism. The first step starts in all cases at about 2008C, and at 258C the amount of volatile fraction closely corresponds to the theoretical amount of removed iPrNCO as shown in Table 1. Thermal stability of copolymers of MA-DiPrU with EDMA presented at different monomer-to-monomer ratios in the feed, was determined for all four copolymers by heating copolymers for 5 min at 2508C in thermogravimetric analyzer (TGA), in nitrogen, and after removal of iPrNCO, the obtained thermograms of nanoporous copolymers are presented in Fig. 2. Similar to the previously described thermal stability of copolymers of A-CHA with EDMA and MA-CHA with EDMA, in this paper is shown that regardless of the ratio of repeating comonomer units in the crosslinked chains of copolymers of MA-iPrA with EDMA, the thermal stability of all nanoporous copolymers presented in Fig. 2 are not significantly different. Thermograms of nonporous copolymers described in Table 2 are presented in Fig. 3. Although in principle nonporous copolymers decompose by similar mechanism as shown in Fig. 2 for nanoporous copolymers, it is evident that nonporous model compounds,
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Table 2. Elemental analysis of crosslinked model copolymers obtained from MA-iPrA with EDMA at different monomer to monomer ratios in the feed. Conversiona (%)
Ratios of monomers in copolymersb
Elemental analysisa (%)
0.3/0.7
98.08
0.20/0.80
0.5/0.5
90.67
0.33/0.67
0.7/0.3
79.25
0.43/0.57
0.8/0.2
77.14
0.54/0.46
C, 60.56 H, 7.75 N, 2.03 C, 59.85 H, 8.12 N, 3.67 C, 60.35 H, 8.30 N, 4.75 C, 61.64 H, 8.80 N, 5.93
Molar ratio in feed
a
708C; 48 hr; 2% Bz2O2; in butanone. Calculated from the nitrogen content in copolymers.
b
which contain larger amount of EDMA are thermally less stable than those containing larger amount of MA-iPrA. A comparison of thermograms of nanoporous residues MA-iPrA-co-EDMA obtained after removal of iPrNCO and nonporous model compounds MA-iPrA-co-EDMA of
Figure 1. Thermograms of crosslinked copolymers of MA-DiPrU with EDMA at molar ratios in the feed: 0.3/0.7 (1); 0.5/0.5 (2); 0.7/0.3 (3); and 0.8/0.2 (4).
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Figure 2. Thermograms of nanoporous residues after removal of iPrNCO from copolymers of MA-DiPrU with EDMA at molar ratios of: 0.3/0.7 (1); 0.5/0.5 (2); 0.7/0.3 (3); and 0.8/0.2 (4).
Figure 3. Thermograms of nonporous copolymers of MA-iPrA with EDMA at different monomerto-monomer ratio in the feed: 0.3/0.7 (1); 0.5/0.5 (2); 0.7/0.3 (3); and 0.8/0.2 (4).
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Figure 4. Thermograms of nanoporous poly(MA-iPrA-co-EDMA): (1) 0.7/0.3 in feed; (2) 0.8/0.2 in feed and nonporous poly(MA-iPrA-co-EDMA); (3) 0.7/0.3 in feed; and (4) 0.8/0.2 in feed.
similar composition is presented in Fig. 4. It is evident that both copolymers, which contains high molar ratio of MA-iPrA have nearly the same thermal stability, thus indicating that nanopores have no significant influence on the thermal stability of crosslinked copolymers. The possible mechanism of the thermal degradation of crosslinked copolymers of MA-DiPrU with EDMA is illustrated in the Sch. 1. It is of importance to emphasize
Scheme 1. Mechanism of thermal degradation of crosslinked copolymers of MA-DiPrU with EDMA.
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that after the removal of iPrNCO (c) in the Sch. 1, nanopores contain the recognition groups –CO –NH – , thus indicating that obtained nanoporous copolymers could be of interest in various practical applications.[4,5] CONCLUSION MA-DiPrU was copolymerized with EDMA to a high conversion under the formation of crosslinked copolymers at molar ratio of comonomers in the feed: 0.3/0.7 (83.75%); 0.5/0.5 (63.20%); 0.7/0.3 (41.45%); 0.8/0.2 (30.95%). In the thermogravimetric analysis all prepared copolymers decompose by a two-step mechanism under the separation of almost quantitative yield of iPrNCO at a temperature of 2508C. Thermograms of model nonporous copolymers which contain high ratio of MA-iPrA to EDMA (0.7/0.3 and 0.8/0.2) are practically identical with the thermograms of nanoporous copolymers of the same composition. After the removal of iPrNCO from the crosslinked copolymers, recognition groups – CO – NH – remain as reactive groups in nanoporous copolymers. ACKNOWLEDGMENT The Ministry of Science and Technology of Croatia supported this work. REFERENCES 1. Erceg Kuzmic´, A.; Vukovic´, R.; Bogdanic´, G.; Flesˇ, D. Separation of cyclohexylisocyanate from the crosslinked copolymers of N-acryl-dicyclohexylurea with ethylene glycol dimethacrylate or divinyl benzene. J. Macromol. Sci., Pure Appl. Chem. 2003, A40 (1), 81 – 85. 2. Erceg Kuzmic´, A.; Vukovic´, R.; Bogdanic´, G.; Flesˇ, D. Synthesis of nanoporous crosslinked poly(acryl-N-cyclohexylamide-co-ethylene glycol dimethacrylate) by thermal degradation of poly(acryl-N,N 0 -dicyclohexylurea-co-ethylene glycol dimethacrylate). J. Macromol. Sci., Pure Appl. Chem. 2003, 40 (8), 747– 754. 3. Erceg Kuzmic´, A.; Vukovic´, R.; Bogdanic´, G.; Pilizˇota, V.; Flesˇ, D. Preparation of nanoporous crosslinked poly(methacryl-N-cyclohexylamide-co-ethylene glycol dimethacrylate) by thermal degradation of poly(methacryl-N,N 0 -dicyclohexylurea-coethylene glycol dimethacrylate). J. Macromol. Sci., Pure Appl. Chem. 2004, A41, in press. 4. Kriz, D.; Kriz, C.B.; Anderrson, L.I.; Mosbach, K. Thin-layer chromatography based on the molecular imprinting technique. Anal. Chem. 1994, 66 (17), 2636 –2639. 5. Kempe, M.; Mosbach, K. Molecular imprinting used for chiral separations. J. Chromatogr. 1995, A694, 3– 13. Received March 2004 Accepted April 2004
