Capa® Polycaprolactones: Versatile Raw Materials for Coatings
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Capa® polycaprolactones: versatile raw materials for coatings Technical Information Leaflet 1600 Revised: 03/18/2019 -Caprolactone monomer has been produced in Warrington, England, since 1974. The monomer is used to produce speciality polyester polyols which are sold under the Capa® trade name. These products are used in a variety of demanding applications, particularly in performance polyurethane (PU) markets, including surface coatings where Capa monomer is used to modify hydroxy acrylates, epoxy resins and as a component in co-polyesters. Capa monomer is made by the Bayer-Villager oxidation of cyclohexanone with peracetic acid (Figure 1). Figure 1 H2O2 +C H3COOH CH3COOOH +H 2O Peracetic acid ! ! ! CH COOH + CH3COOOH + 3 Cyclohexanone Caprolactone The single grade of high purity monomer produced will react with a range of active hydrogen compounds in a ring-opening reaction. Typically this function is carried out by a hydroxyl-containing group, although other functional groups such as amino, thiol and carboxyl could be used. The reaction with the hydroxyl group initiates a ring opening addition polymerization of the Capa monomer to produce a linear ester of hydroxy caproic acid with no byproducts. The new primary hydroxyl function formed can react further with other molecules of Capa monomer to build up polymer chains (Figure 2). Figure 2 ! ! HOROH Catalyst ! ! #! " !# ! ! Ingevity distributed by: 5255 Virginia Ave. North Charleston, SC 29406 844 643 8489 ingevity.com Request Quote or Samples In the schematic representation above, a difunctional alcohol is shown, and in practice this would normally be the case. However, one of the characteristics of caprolactone polymerization is that the functionality of the initiator is repeated exactly in the resultant polyol. For example, if we use trimethylolpropane (TMP), we get a trifunctional polyol; If we use pentaerythritol, we get a tetrol; and so on. In some cases the initiating glycol can itself be polymeric. For example, PTMEG giving rise to a block ether/ester copolymer. The reaction is a ring-opening addition polymerization in contrast with the condensation reaction used to make conventional adipate polyesters. This means that the reaction temperatures used are lower, as no water needs to be eliminated and less catalyst is used. This results in a clean reaction, giving a narrower molecular weight distribution, and lower viscosity with a well- defined functionality, as there are no side reactions. One of the major advantages of the use of Capa in surface coatings has been the production of higher-solids coating formulations while maintaining or improving performance, particularly low temperature flexibility of the coating. One of the early applications of Capa was in the modification of epoxy resins either by monomer or by polyols, and this is used extensively today in electro-coat primers. In both 2K PU and 1K (based on melamine cross-linkers or blocked isocyanates) coatings, there is value in the ability to produce highly functional polyols with low viscosity and high reactivity. Some typical examples are listed in Table 1. Table 1 MW OH AV Viscosity Grade Func. OH % Recommended (g/mol) (mg KOH/g) (mg KOH/g) mPas@ 23 °C Capa 2043 2.0 400 280 8.5 <0.25 240 2K Capa 2054 2.0 550 204 6.2 <0.25 340 2K Capa 2085 2.0 830 135 4.1 <0.25 330 (@35 °C) 1K Capa 3031 3.0 300 560 17 <1.0 170 2K Capa 3050 3.0 540 310 9.4 <1.0 1190 2K Capa 3091 3.0 900 183 5.5 <1.0 1250 1K & 2K Capa 4101 4.0 1000 218 6.6 <1.0 1850 2K The use of Capa polyesters as soft segment components in speciality cast elastomer, adhesives and thermoplastic urethane systems are well established using linear diols. For surface coating applications, a higher variety of functionality and liquid systems is required. As shown earlier, the versatile nature of caprolactone chemistry means that manufacturing liquid with functionality of two, three, four or higher can readily be achieved. Caprolactone has utilized this innovative approach to design polyols with unique properties. These products are aimed at the highly demanding requirement of today’s coatings, particularly where high cross-link density, high solids, and water-borne systems are needed. One of these materials is a product called Capa 4101. This material is a tetra-functional polycaprolactone with a molecular weight of 1000. It is a clear, free-flowing liquid with all hydroxyl groups being primary (Figure 3). It is a 100 percent polycaprolactone material, has a low acid number, and no ether functionality, which provides excellent UV stability and is used to formulate coatings with high cross-link density, and high solids. Ingevity distributed by: 5255 Virginia Ave. North Charleston, SC 29406 800 458 4034 ingevity.com Request Quote or Samples Figure 3 Capa 4101 ! ! ! "#$ %&' !$ n $ ! "$ %#&' ! n ! ! ! "#$ %&' !$ n $ ! "$ %#&' ! n Capa 4101 is extensively used in highly demanding applications for both original equipment manufacturers and refinishing in the aerospace and automotive markets. Ingevity has an active development program looking at introducing new products. Currently the range of Capa polyols stands in excess of 30 commercial grades, with numerous new grades under development to meet customers’ needs. Caprolactone chemistry combined with the production facilities operated by Ingevity enables the production of polymers with many different combinations of functionality and molecular weight. Every endeavor has been made to ensure that the information given herein is true and reliable but it is given only for the guidance of our customers without any warranty and with reservation of all patent rights. Users are advised to confirm the suitability of our recommendations by their own tests. Ingevity distributed by: 5255 Virginia Ave. North Charleston, SC 29406 800 458 4034 ingevity.com Request Quote or Samples.