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A Colorless Epoxy Catalysts |
Hycat AO-3
A common problem with various epoxy cures is the tendency for the cured products to be colored due to the components in the formulation, sensitivity to elevated cure temperatures and the chemical interaction of the catalyst during the cure. Combine with this the requirements for catalytic latency and ease of use for component blending only adds to the quest for the ideal cure system. Hycat™ AO-3, produced by Dimension Technology Chemical Systems, Inc., achieves these goals of clear and colorless and fast cures when reacting anhydrides with diglycidyl ether of bisphenol A, diglycidyl ether bisphenol F and cycloaliphatic diepoxides. Other epoxides are expected to behave favorably in similar formulations. Commonly used catalysts do not give these desired results. For example, a large difference in color was observed comparing the use of different cure catalysts. In a typical formulation of diglycidyl ether of bisphenol F (DER 354) and methylhexahydrophthalic anhydride (Lindride 52D) with 2.0 % catalyst loading at 120°C there is a noticeable change in color or uniformity of cure when comparing Hycat™ AO-3 to tetrabutylammonium bromide (TBABr) or 1,8-diaza-bicyclo[5.4.0]undec-7-ene (DBU) and benzyldimethylamine (BDMA).
Additionally, Hycat™ AO-3 gave good cure time and hardness values.
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TBABr
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DBU
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BDMA
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Hycat™ AO-3
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Cure Time (min.)
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8-12
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8-12
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4-8
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12-16
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Hardness Test, Durometer Type D
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86
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88
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86
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89
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Again, when diglycidyl ether of bisphenol A (DER 332) was reacted with MHHPA (Lindride 52D) with 2.0 % Hycat™ AO-3 catalyst loading at 120ºC, a clear and colorless cure resulted. By contrast, using the catalysts TBABr, DBU, and BDMA resulted in highly colored cures or considerable voids throughout the cure.
And as before, the cure time and hardness was favorable.
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TBABr
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DBU
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BDMA
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Hycat™ AO-3
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Cure Time (min.)
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8-12
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8-12
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8-12
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12-16
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Hardness Test, Durometer Type D
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86
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87
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86
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89
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An Excellent Catalyst for High Temperature Epoxy Cures |
Hycat™ SM3
One major problem encountered with some catalysts used in high temperature (>200O C) epoxy cures is the tendency to form a rough surface, bubbles or voids due to the volatilization of low boiling components contained in the catalyst or decomposition of the catalyst. Hycat™ SM3, produced by Dimension Technology Chemical Systems, Inc., has effectively eliminated this problem. For example, in a formulation containing a cycloaliphatic diepoxy (Lindride 190) and MHHPA (Lindride 52D) catalyzed with 4% DBU (1,8-Diazabicyclo [5.4.0] Undec-7-ene) the reaction completely decomposed at 200O C and bubbled over the test pan.
Although using Hycat™ 3000S in the same formulation gave quick cures that were under 3 minutes at 200O C, bubbles were formed on the surface and the weight loss of the cured product was substantial at 2%. But using the newly developed Hycat™ SM3 catalyst these problems were eliminated. As can be seen in the photos below, the cure (<3 minutes) results in a smooth surface and is free of entrapped bubbles. Using Hycat™ SM3 the weight loss of the product was less than 0.2% and gave a Durometer-D hardness of 86.
Hycat™ SM3 is an excellent catalyst where high temperature quick cures are needed.
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Uniform Cross Linking of Aziridine Polymers with Dimer Acids |
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Written by Renato Rindone
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Monday, 28 September 2009 12:10 |
Uniform Cross Linking of Aziridine Polymers with Dimer Acids 
Polyaziridines, such as Xama-2 and Xama-7 are used in a number of applications such as:
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Adhesives
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Varnishes
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Protective Films
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Pressure Sensitive Adhesives
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Wood Coatings
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Photograph Films
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Printing Inks
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Leather and Textile Coatings
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Plastic Films
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Cross linking of an aziridine with a poly functional carboxylic acid (or carboxylic acid anhydride) can be the desired end product.
Use of Hycat™ catalysts eliminates the problem of homopolymerization as shown in the reaction of pentaerythritol-tris-3-(1-aziridinyl)-propionate (Xama-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.
ATTEMPTED HOMOPOLYMERIZATION OF XAMA-7 WITH HYCAT™ CATALYST
To show that Xama-7 does not homopolymerized 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.
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Epoxy Acrylate Resins and Vinyl Hydroxy Esters |
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Written by Renato Rindone
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Monday, 14 September 2009 12:42 |
Improved Reaction Conditions for Epoxy Resin Acrylate Ester Formation.
A better way to Vinyl Hydroxy Esters using Hycat™ Catalysts.
Literature is replete with references on how to prepare epoxy acrylates and epoxy methacrylates.
The reaction of a saturated carboxylic acid with an epoxide is also well known and many different catalysts to accelerate this reaction is also shown in literature and practiced in the industry. But the current catalysts used for the saturated carboxylic acid reaction don’t always work that well when making the acrylate/vinyl ester. For example, when using a trialkyl amine base or an imidazole, usually at an elevated temperature, it is difficult to prevent some polymerization of the acrylate to form the poly-acrylates or homo-polymerization to form the ether. Furthermore, typically with amine catalysts, the conversions generally stop or it significantly slows down after 75-85% conversion due to the formation of an adduct of the hydroxyl group hydrogen and the nitrogen amine. Also, elevated reaction temperature (e.g., 75 to 100 OC) conditions are necessary to achieve these conversions.
Because of the highly active nature of the Hycat™ catalysts and especially Hycat™ 2000S and Hycat™ OA, these synthesis issues are eliminated or significantly reduced. Using the Hycat™ catalysts conversion of over 90% of the predominantly β-hydroxy ester is realized with little or no homopolymerization. As with the amine or imidazole type catalysts, a radical scavenger, like hydroquinone, is still needed to prevent the polymerization of the acrylate group but because the reaction can be conducted at a lower temperature, e.g., 25 to 60 OC, this side-reaction is significantly minimized
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Written by Renato Rindone
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Monday, 31 August 2009 09:42 |
Epoxy Silanes
In a recent Switzerland patent to Sika Technology (Frick, Karsten et. al.; PCT Int. Application WO 2009 65,914; 28 May 2009) a carboxy terminated polybutadiene-acrylonitrile copolymer (CTBN), modified with epoxy functionality and terminated with carboxy end groups was described. It was shown that these polymers were extremely effective as agents for improving the impact strength of epoxy resin compositions. These formulations are especially efficient adhesives for gluing on metal surfaces. It was shown in our labs that the reaction silyl epoxides or silicone diepoxides, such as PC-1000 [bis-2-(3,4-epoxycyclohexylethyl)-1,3-tetramethyldisiloxane] with CTBN could be greatly accelerated using Hycat™ 2000 or Hycat™ OA. Complete reaction was achieved either at elevated (ca. 80 OC) or at ambient temperature giving cured polymers with excellent adhesive attributes. The photo shows typical polymer properties (just taken from the curing oven), at elevated temperature, after ten minutes. These polymers may have beneficial use in armor protection (bullet proof vests).
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