There  are  three isomers of phthalic acid: orthophthalic  acid  (1,2-benzenedicarboxylic  acid), isophthalic acid (1,3-), and  terephthalic acid  (1,4-). Each phthalic isomer has particular advantages  and  liabilities  when used in polyester production. Isopolyester resins  are the  products of chemical reactions between isophthalic  acid,  maleic anhydride  and  a  glycol generally diluted with  a  reactive  monomer (styrene). Research indicates that polyesters made from  Isophthalic acid  offer substantially better properties than  equivalent  formulations  made  with  Phthalic anhydride. Isophthalic  acid  reacts  more readily  than terephthalic acid, but its initial rate is  slower  than phthalic  anhydride.  The esterification of isophthalic  acid  can  be catalyzed  to provide reaction times approximating those of  anhydride esterification. Resins based on isophthalic or terephthalic acid  will normally be processed to higher molecular weights and will show higher viscosities  and  lower end group counts (acid  numbers  and  hydroxyl numbers)  than  equivalent  phthalic  anhydride  formulations.  Isopolyesters offer a balance of proeprties. Tensile toughnes, a  multivariate  property, is more than 20 percent better with the  isopolyester. Formulations with a high ratio of aromatic to unsaturated acids amplify  the difference isophthalic acid can make.  At equivalent  ultimate tensile  elongation,  the isopolyesters have 65 to 75  percent  higher tensile  strength.  At a 1:1 ratio of aromatic to  unsaturated  acids, isopolyesters offer 15 to 20 percent better strengths, ultimate  elongation  and  heat  deflection temperature  than  orthopolyesters.  The isopolyesters are more than 40 percent tougher than the ortho  resins.  Isopolyesters  can  endure  substantially higher  load  than  orthopolyesters  in  laminate  flexural fatigue tests  of  medium  reactivity resins.  Isopolyesters  are about 15 percent tougher  than  equivalent terepolyesters.    
       
Isopolyester resins provide the performance requirements you need at a price  you can afford. This combination gives your product the  advantages  of high performance and provides you the opportunity to  remain competitive.  The  high  rate of commercial  success  demonstrated  by isopolyesters over more than 30 years of practical experience and  the extensive laboratory data generated within the industry confirm  their outstanding performance.
        
Some of the applications for which Dipol  Isopolyesters are  used,  are as follows:-
       
        #  ISOPHTHALATES  for      *  Corrosion resistant chemical equipments
                                                  *  Medium reactive Filament winding grade
                                                      for manufacture of Pipes, Tanks, Vessels,
                                                  *  Hightech Neo Pentyl Glycol modified
                                                     Marine grade resin approved by The Indian
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                                                  *  High reactive Sheet Moulding / Dough Moulding compounds
                                                  *  Medium reactive Pultrusion grade
                                                  *  Low viscosity Resin Transfer Moulding and  Spray up resins