Bio-based aromatic diisocyanates for preparation of polyurethanes

Abstract

The present invention provides bio-based aromatic diisocyanate of formula (I). [Formula should be inserted here] wherein X is OCH.sub.3, Y is selected from H or OCH.sub.3, and m=0-12. The present invention further provides a method for preparation of aromatic diisocyanate of formula (I) useful for preparation of polyurethane. ##STR00001##

Claims

1. A bio-based aromatic diisocyanate of formula (I) ##STR00007## wherein X is OCH.sub.3, Y is H or OCH.sub.3, and m=0-12.

2. The aromatic diisocyanate as claimed in claim 1, wherein said diisocyanate is -bis(4-isocyanato-2-methoxyphenoxy)propane ##STR00008## or -bis(4-isocyanato-2,6-dimethoxyphenoxy)propane ##STR00009## wherein m=1 in both 1a and 1b.

3. A process for the preparation of an aromatic diisocyanate of formula (I) ##STR00010## wherein X is OCH.sub.3, Y is H or OCH.sub.3, and m=0-12, comprising the steps of: (a) converting a bio-based phenolic acid to the corresponding methyl ester; (b) converting 2 equivalents of the methyl ester of step (a) to an aromatic diester by etherification with a dihaloalkane; (c) hydrolyzing the aromatic diester of step (b) to the corresponding aromatic diacid; (d) converting the aromatic diacid of step (c) to an aromatic diacyl azide; and (e) converting the aromatic diacyl azide by thermal Curtius rearrangement to obtain the corresponding aromatic diisocyanate of formula (I).

4. The process as claimed in claim 3, wherein the bio-based phenolic acid used in step (a) is selected from the group consisting of syringic acid and vanillic acid.

5. The aromatic diisocyanate as claimed in claim 1, wherein the aromatic diisocyanate of formula (I) is useful for the preparation of a polyurethane, and wherein the process for the preparation of a polyurethane comprises the steps of: a) heating a reaction mixture of a diisocyanate of formula (I), a diol or a polyol and a catalyst in a dry solvent in an inert atmosphere at a temperature in a range of 70 C. to 80 C. for a time period in a range of 10 to 12 h; and b) removing the solvent under a reduced pressure to obtain the polyurethane.

6. The aromatic diisocyanate as claimed in claim 5, wherein said diol is bio-derived and is 1,3-propane diol, 1,10-decanediol, or 1,12-dodecanediol; and said polyol is petroleum based and is polyethylene glycol or poly(tetramethylene ether)glycol.

7. The aromatic diisocyanate as claimed in claim 5, wherein said catalyst is dibutyltin dilaurate (DBTDL).

8. The aromatic diisocyanate as claimed in claim 5, wherein said solvent is toluene, 1,4 dioxane, tetrahydrofuran, N N-dimethylacetamide, N,N-dimethylformamide, or and N-methyl pyrrolidone.

9. The aromatic diisocyanate as claimed in claim 5, wherein the polyurethane obtained has a molecular weight in the range of 3.2110.sup.4 g/mol to 5.8510.sup.4 g/mol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts synthesis of aromatic diisocyanates containing oxyalkylene linkages and alkoxy substituents on aromatic rings.

(2) FIG. 2 depicts synthesis of polyurethanes.

DETAILED DESCRIPTION OF THE INVENTION

(3) The present invention provides novel aromatic diisocyanates of formula (I).

(4) ##STR00006##

(5) wherein

(6) X is OCH.sub.3, Y is selected from H or OCH.sub.3

(7) m=0-12.

(8) A series of bio-based aromatic diisocyanates, namely, bis(4-isocyanato-2-methoxyphenoxy)alkane and bis(4-isocyanato-2,6-dimethoxyphenoxy) alkanes are synthesized from vanillic acid/syringic acid and dihaloalkanes which have their origin in bio-derived alkane diols. Lignin derived aromatic chemicals are used for the first time for synthesis of fully bio-based aromatic diisocyanates.

(9) The method of preparation of novel diisocyanate of formula (I) comprising the following steps: (a) Converting the substituted phenolic-acid to the corresponding methyl ester; (b) Converting methyl ester of step (a) to aromatic diester by etherification with dihaloalkane; (c) Hydrolyzing the aromatic diester of step (b) to the corresponding aromatic diacid; (d) Converting the aromatic diacid of step (c) to an aromatic diacyl azide; and (e) Converting the aromatic diacyl azide to obtain corresponding aromatic diisocyanate by thermal Curtius rearrangement.

(10) The above process is shown in FIG. 1.

(11) The method for preparation of polyurethane from bio-based aromatic diisocyanate of formula (I) comprising the following steps: a) Heating a reaction mixture of diisocyanate of formula (I), a diol/polyol and a catalyst in a dry solvent in an inert atmosphere at a temperature in the range of 70 C. to 80 C. for 10 to 12 h; and b) Removing the solvent under reduced pressure to afford the polyurethane.

(12) The diol is selected from the group consisting of 1,3-propane diol, 1,10-decanediol, 1,12-dodecanediol, polyethylene glycol (PEG) and polytetramethylene ether glycol (PTMG).

(13) The catalyst used is dibutyltin dilaurate (DBTDL).

(14) The solvent used is selected from the group consisting of toluene, 1,4 dioxane, tetrahydrofuran, N N-dimethylacetamide, N N-dimethylformamide and N-methylpyrrolidone.

(15) The above process is shown in FIG. 2.

(16) Polyurethane synthesized from aromatic diisocyanate exhibited number average molecular weight in the range of 3.2110.sup.4 to 5.8510.sup.4.

EXAMPLES

(17) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example 1

(18) A. General Procedure for Synthesis of Aromatic Diesters (2)

(19) Into a 250 mL two-necked round bottom flask equipped with a reflux condenser were placed, methyl vanillate/syringate (80 mmol), anhydrous potassium carbonate (44.2 g, 320 mmol) and dry N,N-dimethylformamide (150 mL). The reaction mixture was heated at 100 C. for 1 h and then 1,3-dibromopropane (8.04 g, 40 mmol) was added dropwise. The heating was continued at 100 C. for 11 h. After completion of reaction (TLC), the reaction mixture was poured into ice cold water (500 mL) The solid product was collected by filtration and the solid was dissolved in dichloromethane (300 mL). The dichloromethane solution was washed with water (2100 mL), dried over anhydrous sodium sulfate, filtered, and concentrated in a vacuo. The crude product was purified by silica gel column chromatography.

a) Synthesis of dimethyl 4,4-(propane-1,3-diylbis(oxy))bis(3-methoxybenzoate)

(20) Yield: 80%; M.P.-158 C.; .sup.1H NMR (200 MHz, CDCl.sub.3, /ppm): 2.35-2.48 (m, 2H), 3.90 (s, 6H), 4.30 (t, 2H), 6.94 (d, 2H), 7.54 (d, 2H), 7.64 (dd, 2H). .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 28.9, 52.0, 56.0, 65.4, 111.5, 112.3, 122.8, 123.4, 148.9, 152.2, 166.8

b) Synthesis of dimethyl 4,4-(propane-1,3-diylbis(oxy))bis(3,5-dimethoxybenzoate)

(21) Yield: 76%; M.P.-110 C.; .sup.1H NMR (200 MHz, CDCl.sub.3, /ppm): 2.12-2.24 (m, 2H), 3.83 (s, 12H), 3.91 (s, 6H), 4.30 (t, 4H), 7.27 (s, 4H); .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 31.0, 52.2, 56.1, 70.7, 106.7, 124.9, 141.5, 153.1, 166.8

(22) B. General Procedure for Synthesis of Aromatic Diacids (3)

(23) Into a 250 mL two-necked round bottom flask equipped with a reflux condenser were placed, dimethyl 4,4-(propane-1,3-diylbis(oxy))bis(3-methoxybenzoate)/dimethyl 4,4-(propane-1,3-diylbis(oxy))bis(3,5-dimethoxybenzoate) (30 mmol), sodium hydroxide (12 g, 300 mmol), methanol (100 mL) and water (100 mL). The reaction mixture was refluxed for 12 h. After completion of reaction, the excess methanol was removed under reduced pressure. The solution was diluted with water and acidified with aqueous hydrochloric acid (3M). The precipitated solid was filtered and dried under vacuum at 60 C. for 4 h. The product was recrystallized from aqueous ethanol.

a) Synthesis of 4,4-(propane-1,3-diylbis(oxy))bis(3-methoxybenzoic acid)

(24) Yield=90%; M.P.-259 C.; .sup.1H NMR (200 MHz, DMSO-d.sub.6, /ppm): 7.54 (dd, 2H), 7.44 (d, 2H), 7.08 (d, 2H), 4.19 (t, 4H), 3.79 (s, 6H), 2.19-2.25 (m, 2H); .sup.13C NMR (50 MHz, DMSO-d.sub.6, /ppm) 167.1, 151.8, 148.4, 123.2, 123.1, 112.1, 112.0, 65.0, 55.5, 28.5

b) Synthesis of 4,4-(propane-1,3-diylbis(oxy))bis(3,5-dimethoxybenzoic acid)

(25) Yield=92%; M.P.-266 C.; .sup.1H NMR (200 MHz, DMSO-d.sub.6, /ppm): 12.93 (br.s, 2H), 7.21 (s, 4H), 4.13 (t, 4H), 3.79 (s, 12H), 1.92-2.01 (m, 2H); .sup.13C NMR (50 MHz, DMSO-d.sub.6, /ppm): 167.0, 152.7, 140.5, 125.7, 106.4, 69.8, 55.9, 30.6

(26) C. General Procedure for Synthesis of Aromatic Diacyl Azides (4)

(27) Into a 250 mL two-necked round bottom flask equipped with a reflux condenser, an argon inlet and an addition funnel were charged, aromatic dicarboxylic acids (20 mmol) and a mixture of tetrahydrofuran:water (3:1 v/v) (100 mL). The reaction mixture was cooled to 0 C. and a solution of triethyl amine (12 g, 120 mmol) in tetrahydrofuran (20 mL) was added dropwise over a period of 15 min. To the reaction mixture, ethylchloroformate (12.8 g, 120 mmol) was added dropwise over a period of 10 min and stirred for 2 h. A solution of sodium azide (7.8 g, 160 mmol) in water (30 mL) was added dropwise over a period of 10 min and mixture was stirred for 2 h at 0 C. then for 4 h at room temperature. Ice cold water (250 mL) was added gradually to the reaction mixture and solid was precipitated out. The precipitate was filtered and washed with water. Then the product was dissolved in dichloromethane and washed with water (150 mL), dried over anhydrous sodium sulfate, filtered, and concentrated in under reduced pressure at 25 C. to afford a white product.

a) Synthesis of 4,4-(propane-1,3-diylbis(oxy))bis(3-methoxybenzoyl azide)

(28) Yield=78.2%; M.P.-114 C.; IR (KBr): v=2140, 1680 cm.sup.1; .sup.1H NMR (200 MHz, CDCl.sub.3, /ppm): 7.66 (dd, 2H), 7.51 (d, 2H), 6.93 (d, 2H), 4.31 (t, 2H), 3.90 (s, 6H), 2.36-2.48 (m, 2H); .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 171.6, 153.6, 149.2, 123.9, 123.4, 111.8, 111.7, 65.3, 56.0, 28.8; HRMS (ESI): m/z calculated for C.sub.19H.sub.18N.sub.6O.sub.6 (M+Na), 449.1180; found, 449.1162.

b) Synthesis of 4,4-(propane-1,3-diylbis(oxy))bis(3,5-dimethoxybenzoyl azide)

(29) Yield=81%; M.P.-110 C.; IR (KBr): v=2146, 1684 cm.sup.1; .sup.1H NMR (200 MHz, CDCl.sub.3, /ppm): 7.25 (s, 4H), 4.32 (t, 4H), 3.83 (s, 12H), 2.11-2.24 (m, 2H); .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 171.8, 153.1, 143.0, 125.3, 106.6, 70.7, 56.1, 31.1; HRMS (ESI): m/z calculated for C.sub.21H.sub.22N.sub.6O.sub.8 (M+Na), 509.1391; found, 509.1393.

(30) D. General Procedure for Synthesis of Aromatic Diisocyanate (5)

(31) Into a 100 mL two-necked round bottom flask equipped with a reflux condenser and a nitrogen inlet were charged, aromatic diacyl azides (4.69 mmol) and dry toluene (25 mL) The reaction mixture was heated at 80 C. for 8 h. The toluene was removed under reduced pressure at 60 C. and white solid compound was obtained.

a) Synthesis of 1,3-bis(4-isocyanato-2-methoxyphenoxy)propane

(32) Yield=83%; M.P.-136 C.; IR (KBr): v=2292 cm.sup.1; .sup.1H NMR (400 MHz, CDCl.sub.3, /ppm): 6.84 (d, 2H), 6.63 (dd, 4H), 4.21 (t, 4H), 3.83 (s, 6H), 2.27-2.39 (m, 2H); .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 150.0, 146.4, 126.5, 124.2, 116.6, 113.9, 108.8, 66.0, 56.0, 29.2; HRMS (ESI): m/z calculated for C.sub.19H.sub.18N.sub.2O.sub.6 (M+H), 371.1238; found, 371.1249.

b) Synthesis of 1,3-bis(4-isocyanato-2,6-dimethoxyphenoxy)propane

(33) Yield=87%; M.P.-105 C.; IR (KBr): v=2268 cm.sup.1; .sup.1H NMR (400 MHz, CDCl.sub.3, /ppm): 6.31 (s, 4H), 4.16 (t, 4H), 3.79 (s, 12H), 2.12-2.19 (m, 2H); .sup.13C NMR (50 MHz, CDCl.sub.3, /ppm): 153.8, 153.4, 128.8, 102.2, 70.9, 56.1, 30.8; HRMS (ESI): m/z calculated for C.sub.21H.sub.22N.sub.2O.sub.8 (M+Na), 453.1268; found, 453.127.

Example 2

(34) General Procedure for Synthesis of Poly(Ether Urethane)s

(35) Into a 100 mL two-necked round bottom flask equipped with a reflux condenser and a nitrogen inlet were charged, aromatic diisocyanate (4.69 mmol), aliphatic diol (4.69 mmol), DBTDL (310.sup.3 mmol) and dry toluene (25 mL). The reaction mixture was heated at 80 C. for 8 h. The toluene was removed under reduced pressure at 60 C. and polymer was obtained. The polymer was dissolved in N,N-dimethylacetamide, precipitated in methanol, filtered and dried in vacuum oven at 40 C. for 12 h.

a) Synthesis of poly(ether urethane)s based on 1,3-bis(4-isocyanato-2-methoxyphenoxy)propane and 1,10-decanediol

(36) IR (KBr): v=3328, 1733, 1700 cm.sup.1; .sup.1H NMR (200 MHz, DMSO-d.sub.6, /ppm): 9.37 (s, 2H), 7.17 (d, 2H), 6.84-6.95 (m, 4H), 4.03 (t, 8H), 3.69 (s, 6H), 1.9-2.13 (m, 2H), 1.52-1.62 (m, 4H), 1.18-1.30 (m, 12H); .sup.13C NMR (50 MHz, DMSO-d.sub.6, /ppm): 153.6, 152.9, 135.2, 131.8, 96.0, 69.9, 64.1, 55.6, 30.4, 28.9, 28.7, 28.5, 25.3.

b) Synthesis of poly(ether urethane)s based on 1,3-bis(4-isocyanato-2-methoxyphenoxy)propane and 1,12-dodecanediol

(37) IR (KBr): v=3331, 1732, 1609 cm.sup.1; .sup.1H NMR (200 MHz, DMSO-d.sub.6, /ppm): 9.37 (s, 2H), 7.16 (d 2H), 6.88 (dd, 4H), 4.02 (t, 8H), 3.68 (s, 6H), 2.0-2.10 (m, 2H), 1.20-1.58 (m, 20H); .sup.13C NMR (100 MHz, DMSO-d.sub.6, /ppm): 153.7, 149.1, 143.3, 133.1, 114.2, 110.1, 103.8, 65.6, 64.0, 55.4, 29.0, 28.7, 25.4

c) Synthesis of poly(ether urethane)s based on 1,3-bis(4-isocyanato-2,6-dimethoxyphenoxy)propane and 1,10-decanediol

(38) IR (KBr): v=3335, 1730, 1705 cm.sup.1; .sup.1H NMR (500 MHz, DMSO-d.sub.6, /ppm): 9.45 (s, 2H), 6.82 (s, 4H), 4.04 (t, 4H), 3.93 (t, 4H), 3.67 (s, 12H), 1.86-1.91 (m, 2H), 1.56-1.61 (m, 4H), 1.25-1.33 (m, 12H); .sup.13C NMR (125 MHz, DMSO-d.sub.6, /ppm): 153.7, 152.9, 135.2, 131.8, 96.0, 69.9, 64.1, 55.6, 30.4, 28.9, 28.7, 28.5, 25.4

d) Synthesis of poly(ether urethane)s based on 1,3-bis(4-isocyanato-2,6-dimethoxyphenoxy)propane and 1,12-dodecanediol

(39) IR (KBr): v=3332, 1733, 1702 cm.sup.1; .sup.1H NMR (400 MHz, DMSO-d.sub.6, /ppm): 9.44 (s, 2H), 6.82 (s, 4H), 4.03 (t, 4H), 3.93 (t, 4H), 3.67 (s, 12H), 1.86-1.90 (m, 2H), 1.54-1.60 (m, 4H), 1.21-1.29 (m, 18H); .sup.13C NMR (100 MHz, DMSO-d.sub.6, /ppm): 153.6, 152.9, 135.2, 131.7, 96.0, 69.9, 64.1, 55.6, 29.0, 28.7, 28.6, 25.4

(40) TABLE-US-00001 TABLE 1 Inherent viscosity, molecular weight and thermal properties of polyurethanes. .sub.inh GPC.sup.b Tg T.sub.10 Polyurethane (dL/g).sup.a M.sub.n M.sub.w M.sub.w/M.sub.n ( C.).sup.c ( C.).sup.d PU-1 0.60 36100 62500 1.7 55 304 PU-2 0.65 45500 88200 1.9 49 304 PU-3 0.58 32100 51800 1.6 74 308 PU-4 0.68 58500 100300 1.7 66 306 .sup.a= .sub.inh was measured with 0.5% (w/v) solution of poly(ether urethane)s in CHCl.sub.3 at 30 0.1 C. .sup.b= Measured by GPC in DMF, polystyrene was used as the calibration standard. .sup.c= Measured by DSC on second heating scan with heating rate at 10 C. min.sup.1 under nitrogen atmosphere .sup.d= Temperature at which 10% weight loss was observed under nitrogen atmospheres.

Advantages of Invention

(41) Aromatic diisocyanates derived from bio-based starting materials

(42) Bio-based polyurethanes obtained