Tender For supply of chemicals - tris hydroxymethyl aminomethane brand sigma aldrich, cas no 77-86-1 product code 252859 , pyromelitic acid, brand sigma aldrich cas no 89-05-4, produt id b4007 , pyromellitic dianhydride, cas no 89-32-7, product id 412287 , phthalic acid brand sigma aldrich product code 402915 cas no 88-99-3 , isophorone diamine, brand sigma aldrich, product id 8. 14123, cas no 2855-13-2,