Bio-based aromatic diisocyanates for preparation of polyurethanes

1. A bio-based aromatic diisocyanate of formula (I)

wherein

X is —OCH 3 , Y is —H or —OCH 3 , and

m=0-12.

2. The aromatic diisocyanate as claimed in claim 1 , wherein said diisocyanate is

-bis(4-isocyanato-2-methoxyphenoxy)propane

or

-bis(4-isocyanato-2,6-dimethoxyphenoxy)propane

wherein m=1 in both 1a and 1b.

3. A process for the preparation of an aromatic diisocyanate of formula (I)

wherein

X is —OCH 3 , Y is —H or —OCH 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 3.21×10 4 g/mol to 5.85×10 4 g/mol.