Silanes for Powerful Connections

Creating tomorrow’s solutions SILANES I ORGANOFUNCTIONAL FOR POWERFUL CONNECTIONS You’ve never worked like this WITH SILANES OUR GENIOSIL® TRADEMARK WACKER organofunctional silanes, WACKER has been actively researching Contents marketed under the trademark and developing organofunctional silanes GENIOSIL®, include our established for decades. Chemically and technologi- The GENIOSIL® Trademark 3 standard silanes as well as numerous cally, they are closely related to silicones, Organofunctional Silanes 4 specialty silanes that will be of use which have always constituted one of Chemical Bonding to in a variety of new application areas. our core businesses. Our experience in Organic Polymers 6 these fields, together with our expertise The “a Effect” 8 We encounter industrial products con- in organic fine chemicals, enables us GENIOSIL® für Adhesives and taining organofunctional silanes every to continuously develop innovative Sealants 12 day, and without them, the world as processes and products in these key Product Overview GENIOSIL® we know it would be hard to imagine. technologies. Organofunctional Silanes 16 As an important component of paints Product Overview and varnishes, organofunctional silanes Today, WACKER produces a broad range Non-functional Silanes 18 ensure that they adhere to a variety of organofunctional silanes and markets WACKER at a Glance 19 of substrates and last for many years. them under the GENIOSIL® trademark. Adhesives containing silanes can replace The product portfolio includes not only rivets and bolts, while silane-modified the established, standard products, but fillers and glass fibers reinforce plastics, also novel molecules with unrivaled prop- thus making them suitable for a huge erties. These open up completely new range of applications. fields of application. This brochure provides an overview of the organofunctional silanes produced by WACKER. Special importance is given to the a-silanes. WACKER and GENIOSIL® are registered trademarks of Wacker Chemie AG. 3 ORGANOFUNCtional silanes – Organofunctional silanes act as Fig. 1: Organofunctional silanes as molecular bridges molecular bridges between organic polymers and inorganic materials. Reactive Hydrolyzable organofunctional alkoxy group group Organic Inorganic polymer X Si OR HO substrate X Si O Organofunctional silanes are hybrid com- Bonding to the inorganic material is pounds that combine the functionality effected by way of the hydrolyzable of a reactive organic group and the inor- functional groups –OR. The most common ganic functionality of an alkyl silicate in of these are the methoxy and ethoxy a single molecule. This special property substituents. The silane’s alkoxy groups means they can be used as molecular hydrolyze in the presence of moisture bridges between organic polymers and to form reactive silanols. These either inorganic materials react with themselves to form oligomeric siloxanes, or else react with the inorganic The choice of functional group X will substrate. Since hydroxyl groups are depend ultimately on the nature of the present on almost all mineral and metallic organic polymer. Commercially avail- surfaces, the silane will generally undergo able silanes contain amino, epoxy and a condensation reaction and bond cova- glycidoxy, mercapto and sulfido, isocya- lently to the inorganic substrate. nate, methacryloxy and vinyl groups. How these functional groups bind to The bridge-building property of organo- the organic polymer is described in functional silanes is particularly important detail on pages 6 and 7. in three application fields: • Adhesion promotion • Surface modification • Polymer crosslinking 4 MOLECULAR BRIDGES FORGE STABLE BONDS Fig. 2: Adhesion promotion Fig. 3: Surface modification Fig. 4: Crosslinking Coating Filler Polymer Polymer R X X X X O O O O O O O Si X Si O O HO Si O Si O Si OH O Si Si O O O O O Si HO Si OR X X X X Substrate Polymer Polymer Adhesion Promotion Surface Modification Crosslinking Organofunctional silanes enhance adhe- Organofunctional silanes improve com- Organofunctional silanes function as sion of coatings, adhesives and sealants patibility and enable inorganic fillers to crosslinkers for organic polymers, e. g. in to a wide variety of substrates. bond chemically to organic resins. moisture-curing adhesives and sealants, in paints and varnishes and in thermo- plastics. 5 CHEMICAL BONDING TO ORGANIC POLYMERS The particular function and the nature Fig. 5: Endcapping of the organic polymer will determine the choice of silane as well as the way in which it bonds chemically to the polymer. Functional silane Functional polymer Fig. 6: Radical grafting Polyolefin + peroxide Vinyl- or methacryloxysilane The mechanisms by which organofunc- Endcapping tional silanes bond to organic polymers are as varied as the polymers themselves. In this case, the silane’s organofunctional The most important mechanisms are: group reacts with a terminal functional • Endcapping group of the precursor by forming a • Radical grafting covalent bond (Fig. 5). • Copolymerization The choice of silane will depend on the All three methods produce silane-modi- polymer. The following combinations are fied polymers. These polymers can then common: form stable siloxane bonds via the cross- • Aminosilanes + NCO-terminated linking of the remaining Si-alkoxy groups. polyurethanes Likewise, they can also bond to fillers or • Aminosilanes + acrylic/methacrylic other inorganic surfaces. polymers • Isocyanatosilanes + OH-polymers Table 1 is a guide showing which silanes (polyethers, polyesters, polyurethanes) produce the best results in the various • Amino- and epoxy/glycidoxysilanes polymer systems. + epoxy resin precursors • Aminosilanes + phenol resin precursors 6 Fig. 7: Copolymerization Table 1: Compatibility of polymers and organofunctional silanes Polymer Organofunctional group on silane Polyacrylate Amino C CH C CH 2 2 Epoxy Methacrylic CO2R Vinyl Butyl rubber, neoprene, phenolic resin, Amino Si Vinyl- or Acrylate/ methacryl- polyamide, polyether, epoxy resin, melamine Epoxy methacrylate oxysilane Polyester Methacrylic Polyolefin Amino Vinyl C CH2 C CH2 Polysulfide Epoxy Vinyl CO2R Polyurethane Amino Epoxy Si Isocyanate EPR, EPDM, SBR Vinyl, Mercapto Radical Grafting Unsaturated silanes, such as vinyl- or methacryloxysilanes, can be made to bond to polymer chains via a radical grafting reaction (Fig. 6): • Vinylsilanes + polyolefines • Methacryloxysilanes + polyolefines • Methacryloxysilanes + unsaturated polyesters Copolymerization The polymerizable organofunctional groups of a silane (e. g. methacryloxy- or vinylsilane) are incorporated into the chain during production of the polymer (Fig. 7): • Methacryloxysilanes + monomeric acrylates/methacrylates or styrene • Vinylsilanes + monomeric acrylates/ methacrylates or ethylene/ vinyl acetate 7 THE LENGTH OF THE BRIDGE DETERMINES THE REACTIVITY – The “a EFFECT“ The nature of the “bridge construction” Fig. 8 Fig. 10 determines the application properties. a-Silanes, that is, silanes with a OR OR methylene bridge instead of the usual Si OR Si OR propylene spacer between the silicon X (CH2)3 X CH2 atom and the functional group, are highly reactive and accordingly have OR OR huge application potential. Fig. 9 Fig. 11 CH 3 CH3 Si OR Si OR X (CH2)3 X CH2 OR OR Most established organofunctional sila- WACKER’s strength is on specialty silanes. nes are trialkoxysilanes with a propylene The name “specialty silane” implies first, spacer between the silicon atom and the a special choice of highly reactive orga- functional group X (Fig. 8). Dialkoxysila- nofunctional groups (e.g. isocyanate) nes (Fig. 9) with a propylene spacer are and second, a relatively novel molecular also available but are of little practical structure, as emphasized by the methyl- importance compared with trialkoxy- ene spacer or bridge that replaces the silanes. familiar propylene bridge. The most important functional groups X These innovative silanes, referred to as are the amino, glycidoxy, sulfur and meth- a-silanes (Figs. 10 and 11), display new acryloxy groups. These standard silanes, properties. Their most important prop- of which the GENIOSIL® product portfolio erty is without doubt the extremely high includes a broad range, dominate today’s reactivity of the Si-alkoxy groups. This market. results from electron interaction of the functional group X with the Si atom, and it can only be observed in the presence of a spacer. The phenomenon is accordingly referred to as the “a effect.” 8 Fig. 12: Schematic diagram of the “a effect” Practical Consequences of the “a Effect” The increased reactivity of the alkoxy groups in a-silanes not only opens up new fields of application for which standard g-silanes are insufficiently reactive (e.g. for fast-curing adhesives), but also renders them interesting building blocks that offer many advantages in established fields of application. For example, the “a effect” reduces the difference in reactivity between methoxy- silyl and ethoxysilyl groups, thus making it possible to replace methoxysilane by ethoxysilane without impairing the appli- Since highly reactive silanes are The “a Effect” cation properties. This is particularly im- needed for a wide variety of applications, portant in applications where the release WACKER has developed a specific An electronegative donor such as nitro- of methanol, which has a higher order of portfolio of organofunctional a-silanes. gen or oxygen that is in the a position toxicity than ethanol, is problematic. Besides aminosilanes,

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