One of the problems with the use of aziridines is their vulnerability to homo-polymerization initiated by protonation of the aziridine ring.
This problem can interfere with systems where cross linking of an aziridine with a poly functional carboxylic acid (or carboxylic acid anhydride) is the desired end product.
As a result, formulations that involve the cross linking reaction of poly acids with polyaziridines must be carefully controlled to eliminate homopolymerization of the aziridine. The use of Hycat™ catalysts eliminates the problem of homopolymerization and improves the application for these systems. Examples of this benefit are experimentally shown below.
REACTION OF PENTAERYTHRITOL-TRIS-3-(1-AZIRIDINYL)-PROPIONATE (XAMA-7; CAS NUMBER: 57116-45-7) WITH A DIMER ACID
Into a mixing cup were weighed 15.5 grams (100.3 meq) of Xama-7, 27.7 grams (101.6 meq) of Empol 1016 dimer acid and 4.28 grams of Hycat™ 2000/2000S. The mixture was mixed for two minutes with a spatula, and then placed into a Garner wire-stirred gel timer (Model GT-S) at 32 OC. After one minute of stirring the contents of the cup were completely solidified into a uniform, hard rubbery mass. Considerable heat was liberated during this period.
As a control, the reaction was also performed without the use of the Hycat™ catalyst. Into an aluminum pan (60 mm diameter) were weighed1.6 grams (10.36 meq) of Xama-7 and 2.7 grams (9.90 meq) of Empol 1016 dimer acid and mixed for 2 minutes with a spatula then allowed to stand at 32 OC overnight. After 15 minutes the composition was tacky which solidified into a semi-tacky mass on standing overnight.
REACTION OF PENTAERYTHRITOL PENTAERYTHRITOL-TRIS-3-(1-AZIRIDINYL)-PROPIONATE (XAMA-7) WITH METHYLHEXAHYDRO-PHTHALIC ANHYDRIDE (MHHPA)
MHHPA, 4.3 grams (51.1 meq) and Xama-7, 2.5 grams (17.6 meq) were weighed into a 30 ml beaker and thoroughly mixed. A small sample, 0.6 gram, was transferred into a 15 ml beaker for a control. To the larger portion (6.2 grams) was added 0.4 gram of Hycat™ 3000/3000S catalyst. The contents of both flasks were allowed to react at room temperature (22° C). After a 10 minute reaction period the Hycat™ catalyzed material was no longer mobile when the beaker was tipped on its side. The material in the control beaker was still mobile. After a 25 minute reaction period the control reaction was not mobile. Although the Hycat™ catalyzed reaction was complete at least twice as fast as the control reaction, both the control and chromium catalyzed reaction products showed an equal amount of hardness when prodded with a pointed spatula. Both reaction products were insoluble in acetone.
REACTION OF PENTAERYTHRITOL-TRIS-3-(1-AZIRIDINYL)-PROPIONATE (XAMA-7) WITH BICYCLO (2.2.2) OCT-7-ENE-2,3,5,6-TETRACARBOXYLIC DIANHYDRIDE (BTA)
Into an aluminum weighing pan was put 6.6 grams (53.2 meq) of BTA, 7.7 grams (54.1 meq) of Xama-7 and 0.4 grams of Hycat™ 3000/3000S. After 45 minutes at 41° C. the contents of the pan cured to a hard, brittle olive green solid.
ATTEMPTED HOMOPOLYMERIZATION OF XAMA-7 WITH HYCAT™ CATALYST
To show that Xama-7 does not homopolymerize in the presence of Hycat™ catalysts even at elevated temperature, 6.8 grams of Xama-7 and 0.4 grams of Hycat™ 2000/2000S were placed into an aluminum pan, thoroughly mixed with a spatula then heated to 41 OC for 3.25 hours. The contents of the pan were still quite fluid. After 9 days storage at about 20 OC the contents of the pan remained fluid.
