Even though most formulators consider polymers the most important coating ingredient. Other elements make significant contributions to properties. Oligomers are one of those coatings components which can have an outsized influence. What are oligomers and how can they be used to make better coatings? We will explore these and other aspects of oligomers and how they can be used to formulate successful and innovative coatings, exceeding your customers’ expectations. Like polymers, oligomers are made up of repeating molecular units called monomers. Unlike polymers, oligomers have much lower molecular weights since they are made up of only a few repeating units.
The root of the word oligomer, like oligarch, comes from the term few, as in a small group of monomers or rulers. There is no set number of monomers in an oligomer so the term can be applied to a fairly broad range of molecules. Similar to polymers, oligomers can be made from identical or non-identical monomers. If the same monomer is used to synthesize an oligomer we call it a homo-oligomer, a hetero-oligomer is composed of more than one kind of monomer. Oligomers can be classified by the number of monomers for example, a tetramer is comprised of four monomers.
Most monomers used to make polymers for coatings formulations can also be utilized in oligomers. The reaction mechanisms to join the monomers are the same as for polymerization but reaction conditions are often quite different. The goal of polymer synthesis is to build macromolecules of very high molecular weight. Synthesizing oligomers, on the other hand, requires more control to ensure the target oligomer size is achieved without making the molecule too large. Step polymerizations like those used in polyester synthesis can be controlled fairly easily but in free radical polymerization controlling molecular weight can be a challenge.
Oligomers can be used to add specialized ingredients that enhance the performance of your formulations while using standard coatings polymers as the primary binder system. This can be a cost-effective way to increase key performance metrics like hardness, flexibility, or wet adhesion. Functional groups including epoxy, acrylate, methacrylate, silane, and hydroxyl can be added to a formulation without blending several polymer types. Complications of polymer blending such as incompatibility or surface interactions may be avoided by using oligomers. Incompatible polymer blends can cause problems like low gloss or surface defects in the cured films. Because of their low molecular weights, most oligomers are compatible with a broad range of polymers.
Since they have lower molecular weights, oligomers act like solvents in coatings formulations, lowering viscosity, facilitating flow and leveling. Low-volatility oligomers do not contribute to VOC levels which helps attain regulatory compliance in many applications. In waterborne coatings, oligomers act as plasticizers to reduce the minimum film-forming temperature which improves low-temperature coalescence and increases open time. Longer open time allows the painter to ensure complete coverage of each coat and allows brush and roll blending during painting. Oligomers with reactive groups can crosslink into the primary polymeric binder, preventing the oligomer from softening the applied coating.
In high solids coatings reactive oligomers lower viscosity, raise the percentage of non-volatile materials and can increase the crosslink density leading to better chemical and moisture resistance. UV curing, two-component epoxy and two-component urethane coatings formulations especially benefit from the use of oligomers. Oligomers contribute functional groups at a higher weight ratio than polymers with similar functionality. They can also contain different types of functional groups allowing the formation of interpenetrating polymer networks within the coating film. IPNs can impart unique balances of properties to the cured film. Properties such as hardness and flexibility are often at odds in a coating formulation, an optimum balance can be achieved by using oligomers to develop an IPN.
UV cure coatings make use of a large variety of oligomers. In these formulations, oligomers provide many properties of the cured film. Oligomers make it possible to produce one hundred percent solids UV cure coatings with low application viscosity and high cure rates. Oligomers are also a great way to economically introduce specialized performance aspects into UV cured coatings. Oligomers with a high content of specialized but relatively expensive monomers like IBOMA (isobornyl methacrylate) can improve properties such as film hardness, flexibility, and chemical resistance with the higher cost of specialized polymers.
Epoxy and epoxy silane oligomers can be used in many applications requiring corrosion and chemical resistance. They have synergies with epoxy resins to increase resistance to environmental stressors such as CO2 and steam. Compatible oligomers lower the viscosity of two-component epoxy coatings permitting higher solids and lower VOC content. Dendritic oligomers have well-defined star or comb-shaped morphologies (forms) that can impart unique properties to a formulation. Among the functions dendritic oligomers might provide are enhanced pigment dispersion or a good balance of viscosity, solids content, cure rate and pot life. These enhanced properties are a result of dendritic oligomers defined structures.
Biobased content can be added to coatings by using oligomers. Oligomers with many different functional groups are available with varying percentages of biobased content. Biobased oligomers can be used in two-component, UV-cured, baking enamels, and oxidative cure coating systems. Plant-based raw materials like soya oils, paper mill byproducts, and non-food oil crops can all be converted to oligomers suitable for coatings. Both conventional synthetic chemical facilities and bioreactors can be used to manufacture biobased oligomers for coatings uses. The use of these ingredients doesn’t just add biobased content for its own sake but also brings enhanced performance to the table.
When you’re struggling with a formulation, trying to meet those last few key performance factors to exceed your customers’ expectations, give oligomers a chance. A good material database is the best place to start your search for the right oligomer to bring your formulation across the finish line. There are hundreds of oligomers available for use in coatings and the right ingredients your formulation needs might be waiting for you to find it.
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