Imagine a world where coatings are not just protective layers but smart, eco-friendly, and ultra-efficient materials that transform industries. Enter hyperbranched polymers—the unsung heroes of modern coatings technology. These innovative materials are shaking up the coatings industry, offering solutions that are faster, greener, and more versatile than ever before. Let’s dive into how hyperbranched polymers are making waves in UV curing, powder coatings, and high-solid formulations.
What Are Hyperbranched Polymers?
Hyperbranched polymers are like the Swiss Army knives of the polymer world. Unlike traditional linear polymers, they have a 3D, tree-like structure with tons of reactive end groups. This unique architecture gives them superpowers:
- Low viscosity: They flow like water, making them easy to work with.
- High reactivity: Their abundant end groups make them quick to bond and cure.
- Eco-friendly synthesis: They’re made without nasty byproducts, perfect for sustainable manufacturing.
First discovered in the 1950s, hyperbranched polymers have come a long way. Today, they’re the darlings of researchers, governments, and industries alike.
Hyperbranched Polymers in UV Curing: Speed Meets Sustainability
UV-curable coatings are already a game-changer—they’re fast, energy-efficient, and perfect for heat-sensitive materials. But traditional UV coatings have a problem: high viscosity. To fix this, manufacturers often add solvents, which are bad news for the environment.
Enter hyperbranched polymers. Their 3D structure keeps viscosity low without the need for solvents. Plus, their reactive end groups make them cure faster under UV light, creating coatings that are harder, more durable, and better at sticking to surfaces.
Real-world example: Researchers have developed hyperbranched polyurethane coatings that outperform traditional linear coatings in hardness and adhesion. Another breakthrough? UV-curable hyperbranched polyester coatings that are flexible, water-resistant, and chemical-resistant.
Powder Coatings: The Eco-Friendly Revolution
Powder coatings are the poster child for green technology—they’re solvent-free, produce zero VOCs, and have near-perfect material utilization. But they’re not without challenges: storage stability and flow properties can be tricky.
Hyperbranched polymers are here to save the day. By modifying these polymers, scientists have created coatings that:
- Flow better: Lower melt viscosity means smoother, more even surfaces.
- Store longer: Improved stability ensures coatings stay fresh.
- Perform stronger: Enhanced impact resistance and adhesion make them tougher than ever.
Case in point: Modified hyperbranched polyester coatings have been shown to reduce melt viscosity by up to 50%, while also improving surface smoothness and mechanical properties.
High-Solid Coatings: More Solids, Less Waste
High-solid coatings are all about packing more solids into less liquid, reducing waste and emissions. But high solids often mean high viscosity, which can be a nightmare for application.
Hyperbranched polymers solve this problem with their low viscosity and high reactivity. They allow manufacturers to create coatings with up to 85% solids—without sacrificing flow or performance.
Example: Hyperbranched polyurethane-acrylate resins have been developed for high-solid coatings, offering excellent mechanical properties and chemical resistance. These coatings are perfect for industrial tanks, food packaging, and corrosion protection.
Why This Matters
The coatings industry is at a crossroads. With growing environmental regulations and consumer demand for sustainable products, hyperbranched polymers offer a way forward. They’re not just improving performance—they’re making coatings greener, faster, and smarter.
From UV-curable coatings that cure in seconds to powder coatings that flow like silk, hyperbranched polymers are unlocking new possibilities. And with their simple, scalable synthesis, they’re poised to become a cornerstone of the coatings industry.
The Bottom Line
Hyperbranched polymers are more than just a scientific curiosity—they’re a revolution in materials science. Whether you’re in automotive, construction, or packaging, these polymers are set to transform the way you think about coatings.
So, the next time you see a smooth, durable, eco-friendly coating, remember: it might just be powered by hyperbranched polymers. The future of coatings is here—and it’s hyperbranched.
Hyperbranched polymers have many terminal functional groups, low viscosity, good solubility and other advantages, which can improve the film-forming property and film performance of coatings. At the same time, hyperbranched polymers are simple and easy to operate in the synthesis method, which provides a good foundation for large-scale production and industrialization. This article introduces the synthesis of hyperbranched polymers and some advantages of hyperbranched polymers in UV-curing coatings, high-solid coatings and powder coatings.
In 1952, Flory first discovered the branched structure, and then in 1988, Kim and Webster first synthesized the hyperbranched structure. With the continuous exploration of hyperbranched polymers, hyperbranched polymers have attracted extensive research. To this day, governments, enterprises, universities, etc. have invested in the research of hyperbranched polymers. Its advantages such as simple synthesis and no by-products have laid a good foundation for industrialization.
Hyperbranched polymers have a three-dimensional macromolecular structure. Under conventional reactions, this structure will produce a large number of end groups, making it highly reactive. At the same time, the spherical structure makes it difficult for molecules to entangle and has a very low viscosity. Different core molecules and synthesis methods allow hyperbranched polymers to continuously produce new structures. These new structures can be widely used in pharmaceutical carriers, plastic processing, coating synthesis and other fields.
1 Hyperbranched polymers
As a type of dendritic polymer, hyperbranched polymer has a generally similar structure and is mainly formed by the polymerization of core molecules and ABn monomers. The two monomers A and B need to have functional groups that can react with each other, but cannot undergo self-polymerization. The introduction of core molecules can prevent the self-polymerization of ABn monomers from initiating gelation. In the actual reaction, the two monomers A and B are first reacted through condensation polymerization or ring-opening polymerization.
This reaction process does not form any by-products and is simple to operate and easy to mass produce, so it can be used in industry. At the same time, its unique structure can be applied to other industries by modifying the end groups.
Currently, there are two commonly used methods for synthesizing hyperbranched polymers, namely, a one-step method and a two-step method. The one-step method is to synthesize a hyperbranched polymer in one go without using a solvent, while the two-step method is to first generate an ABn monomer through solution polymerization, then remove the solvent, and then add a catalyst to synthesize the ABn monomer into a hyperbranched polymer. This method can avoid the occurrence of gelation in the ABn monomer during the reaction, but it will complicate the synthesis operation.
Wang Yuling, Li Wusong and others [2] used 1,2,4-trimellitic anhydride and ethanolamine as raw materials and synthesized hyperbranched polyester amide using two different reaction methods. They also proved through nuclear magnetic resonance, differential scanning calorimetry, Ubbelohde viscometer and other means that the two-step method can increase the controllability of the reaction. However, the hyperbranched polyester amide synthesized by the one-step method is superior to the hyperbranched polyester amide synthesized by the two-step method in terms of branching degree and performance.
2 Application of hyperbranched polymers in coatings
With the gradual development of society, various new coatings and environmentally friendly coatings have become new exploration directions for researchers, and the special properties of hyperbranched polymers have also provided more routes for people to develop new coatings. At present, the new coatings that have attracted widespread attention from researchers include UV curing coatings, powder coatings, high solid component coatings and other fields.
2.1 UV curing coating
2.1.1 UV curing coating system
At present, the curing system of UV curing coatings consists of free radical photocuring system, cationic photocuring system, thiol-ene photocuring system, dual curing system and multiple curing system.
The free radical photocuring system is composed of free radical photoinitiator, free radical photocuring resin, reactive diluent, etc., the cationic photocuring system is composed of cationic photoinitiator and cationic photocuring resin, and the thiol-ene photocuring system is composed of free radical photoinitiator system and thiol-ethylene resin. Dual curing system and multi-curing system use two or more curing methods to form the paint film.
The UV curing process of UV-curing coatings is generally divided into three steps, namely the chain initiation stage, the growth stage, the chain termination stage, and finally the curing to form a film.
2.1.2 Characteristics of UV curing coatings
Compared with traditional natural drying or heat curing resins, UV curing resins have the advantages of saving energy, reducing air pollution, fast curing speed, small footprint, and suitability for automated assembly line coating. They are particularly suitable for coating substrates that cannot be exposed to heat .
2.1.3 Application of hyperbranched polymers in UV-curable coatings
UV curing coatings are usually composed of linear molecules synthesized from oligomers, but linear molecules are prone to entanglement. Once the molecular weight is too high, its viscosity will increase sharply. Therefore, diluents must be added to control its viscosity, but the addition of diluents seriously affects the convenience and environmental protection in actual production. The three-dimensional structure of hyperbranched polymers has good fluidity, which can avoid the inconvenience caused by the viscosity of conventional UV curing coatings. At the same time, the large number of terminal groups of hyperbranched polymers provide high reactivity and can be quickly cured into films under light radiation.
Synthesized hyperbranched polyurethane using toluene-2,4-diisocyanate, 2,2-dihydroxymethylpropionic acid and ethylenediamine as raw materials, and then synthesized a hyperbranched polyurethane that cures under photoinitiator by introducing unsaturated bonds. Test characterization and other means show that the product synthesized in this way has higher film hardness and adhesion, and its comprehensive performance is better than that of traditional linear light-curing coatings. At the same time, the synthesis method is simple and the performance is stable.
Synthesized rosin-based hyperbranched polyester by copolymerizing maleopimaric acid, trimethylolpropane and propylene glycol. The hyperbranched polyester has a large number of terminal groups, which is superior to hyperbranched polymers. HBP was modified with methacrylic acid to obtain UV-curable vinyl-terminated rosin-based hyperbranched polyester. Performance analysis showed that the cured film has good flexibility, water resistance, alcohol resistance, alkali resistance and impact resistance.
2.2 Powder coating
At present, the country’s attention to the environmental protection industry is increasing, and environmentally friendly coatings have also become a research direction. Among them, powder coatings are solvent-free, VOC-free and highly efficient. In the past decade, they have been widely used as a highly efficient environmentally friendly coating. At the same time, in order to solve the problems of storage stability and leveling of powder coatings, the main method is to graft flexible chain segments onto terminal hydroxyl hyperbranched polyester resins to form a semi-crystalline structure, or to use a structure with strong polarity such as polyamide-ester structure to obtain a higher glass transition temperature and melt viscosity.
2.2.1 Development of powder coatings
Powder coating is a pure solid component, and is a powder coating material that is environmentally friendly, energy-saving, and has excellent performance. China’s powder coating industry started in the 1970s. With the exploration of domestic researchers and the introduction of related foreign products, the development of powder coatings has made great progress. After the reform and opening up, the development of powder coatings has maintained a good growth, especially in recent years, the ecological environment has attracted great attention from the country, and the development of powder coatings has once again ushered in a rapid growth situation.
In the past, the application areas of powder coatings had huge limitations. With the development of this field, current powder coatings have undergone tremendous changes in raw materials, production methods, application areas and coating processes.
2.2.2 Powder coating and its coating process
The preparation process of powder coatings includes two types: dry process and wet process. The dry process includes melt extrusion mixing and dry mixing; the wet process includes precipitation, evaporation, spray drying, etc.
In actual production, wet process is rarely used for powder coatings, and it is mainly used in the production of special powder coatings. For example, the preparation of acrylic powder coatings, water-dispersible powder coatings, and solvent-based coatings to manufacture powder coatings. At present, the mainstream production method of powder coatings is dry process, and most of them are produced by melt extrusion mixing in dry process. The melt extrusion process includes material premixing, melt extrusion, tablet crushing, fine grinding and other main parts.
Powder coating is mainly divided into hot coating process and cold coating process, including vacuum suction coating, fluidized bed method, electrostatic fluidized bed method, electrostatic spraying method, etc.
2.2.3 Application of hyperbranched polymers in powder coatings
Used stearic acid to modify the hyperbranched polyester sold on the market to increase its glass transition temperature. At the same time, it was used as an additive to increase the surface tension of the powder coating and reduce the melt viscosity. Compared with the hyperbranched polyester without addition, the melt viscosity was greatly reduced, the surface morphology was smoother, and the physical properties and appearance were improved.
Processed the synthesized modified hyperbranched polyester powder with a photoinitiator and a defoamer, obtained a powder coating through crushing and classification, and then sprayed it with an electrostatic spray gun. The resulting coating was tested. The test results showed that the impact strength of the hyperbranched powder coating was nearly doubled, the hardness was reduced, and the adhesion and film appearance were slightly improved.
Prepared hydroxyl-terminated hyperbranched polyesters by using trimethylolpropane as the core and 2,2-dimethylolpropionic acid as the AB2 monomer through a quasi-one-step method. They also prepared carboxyl-terminated hyperbranched polyesters by modifying the end groups of hydroxyl-terminated hyperbranched polyesters with phthalic anhydride. The test results show that carboxyl-terminated hyperbranched polyesters can increase the degree of curing of epoxy-polyester systems, while hydroxyl-terminated hyperbranched polyesters can slightly reduce the degree of curing of epoxy-polyester systems. Due to the presence of a large number of cavities in the hyperbranched polyester molecules, both structures can effectively improve the impact resistance of the coating. Among them, the toughening effect of the carboxyl-terminated hyperbranched polyester is better.
First prepared a prepolymer using poly-ε-caprolactone diol, monoglyceride and toluene diisocyanate (TDI) as raw materials, and then synthesized a hyperbranched polyurethane resin by addition polymerization with glycerol. Glyceride and poly-ε-caprolactone diol are soft segments, and TDI is a hard segment. Due to the long-chain structure of ε-caprolactone diol, the polymer has a certain degree of crystallinity. The synthesized resin has a high glass transition temperature ( Tg ) and can be made into powder coatings. The impact strength and flexibility of the coating film increase with the increase of the soft segment ratio, while the hardness, adhesion and heat resistance increase with the increase of the hard segment ratio. The coating film was immersed in 10% NaCl, 20% ethanol, 5% HCl and distilled water for 7 days, and there was no obvious change in appearance.
Used dimethyltrimethylene carbonate as a monomer and a cationic ring-opening polymerization method to synthesize a long-chain terminal hydroxyl polymer with a branched structure. The synthesized polymer was dissolved in triethylamine, and the terminal hydroxyl group was modified with methacrylic anhydride to obtain a resin with an unsaturated double bond at the end group. The resin can be used for photocurable powder coatings. The prepared powder coating was stored at 45°C for 7 days, and its leveling performance was equivalent to that before the experiment. The melt leveling conditions of the powder coating were 3~4 min@120°C, and the cured coating had good adhesion and chemical resistance.
Used ε-caprolactone to react with the terminal hydroxyl groups of BoltornTM-H30 hyperbranched polyester produced by Perstorp to obtain a long-chain terminal hydroxyl polymer with semi-crystalline properties, and then modified the terminal hydroxyl groups with 2-methylacrylic anhydride to obtain a hyperbranched polymer with unsaturated double bonds at the end. The solvents used in the modification process were dichloromethane and triethylamine. The study found that its crystallinity and melting point depend on the number of grafted ε-caprolactones. When the number of grafted ε-caprolactones reached 50, the crystallinity was 50% and the melting point was 50.2 °C.
Modified the hyperbranched polyester product BoltornTM-H20 of Perstorp with acryloyl chloride and hexadecanoyl chloride or acryloyl chloride and octadecanoic acid, respectively. The study found that the hyperbranched polyester modified with hexadecanoyl chloride or a small amount of octadecanoic acid was a waxy product, and only when a large proportion of the terminal hydroxyl groups were modified with octadecanoic acid could a powdery product be obtained. This hyperbranched polymer with an amorphous “core” and a crystallizable “shell” molecular structure has a high melting point, among which the melting point of the hyperbranched polyester modified with octadecanoic acid and acryloyl chloride is 48~56 ℃. Due to the presence of a large number of UV-curable acrylate end groups, the polymer can be quickly cured when melt irradiated.
Used cyclic carboxylic acid anhydride and diisopropanolamine as raw materials, synthesized AB2 monomers through the reaction of anhydride and amine, and then esterified and condensed to form a hyperbranched polymer with a polyamide-ester structure. When the anhydride used is tetrahydrophthalic anhydride or hexahydrophthalic anhydride, its Tg temperature can reach 70°C; if phthalic anhydride is used as the anhydride, the Tg temperature can reach 100°C. When it is used as a curing agent for carboxyl-containing polyester powder coatings, its functionality is much higher than that of the curing agents currently used (the functionality of the commonly used terminal hydroxyl curing agent XL-552 is 4, and the functionality of polyamide-ester can reach 10), it can still obtain a coating with suitable gel time, good appearance leveling and good mechanical properties.
Used glycerol as the core, isophorone diisocyanate and diethanolamine as raw materials to synthesize a core-added hyperbranched polyurethane (HBPU-OH) containing 6 terminal hydroxyl groups. It was modified with the semi-addition product isophorone diisocyanate-hydroxyethyl acrylate to prepare HPUA (hyperbranched polyurethane acrylic resin) with adjustable double bond number, and its Tg was 67.8℃, which was lower than the Tg of core-added hyperbranched polyurethane (HBUA-OH) (110.0℃).
2.3 High solids coatings
People call coatings whose solid components account for 65% to 85% of the total material mass high-solid content coatings. Currently, common coatings with this solid content include high-solid content epoxy resin coatings, high-solid content acrylic resin coatings, high-solid content alkyd resin coatings, and high-solid content polyester resin coatings.
2.3.1 High solids coating system
High-solid epoxy resin coatings have excellent chemical resistance and good mechanical properties, and are often used for industrial tank coatings, food packaging coatings, and industrial anti-corrosion coatings. The curing conditions are simple, and the film can be cured at room temperature. This feature allows it to be used on a large scale in industry. At the same time, the low viscosity can even further increase its solid content in actual construction [11] , reducing pollution. High-solid acrylic resin coatings are mainly used in the fields of automobiles and decorations because of their good fullness and gloss. As one of the most widely used coatings, a large number of researchers have been exploring its optimization process. The introduction of hyperbranching can achieve better gloss and reduce damage caused by harsh environments. The characteristics of high-solid polyester resin coatings are that compared with traditional polyester resins, they can effectively reduce the number of construction times and the consumption of manpower and material resources. At the same time, they have good mechanical properties and are widely used in the appearance and protection of metal plastics and other products.
2.3.2 Application of hyperbranched polymers in high-solids coatings
Used TDI/TMP adduct G21 as curing agent and a self-made star-shaped hydroxyl polyester according to the NCO/OH molar ratio of 1.05 to prepare a high solid content two-component polyurethane coating, and tested the film performance on wood, glass and tinplate. The test results showed that the coating prepared in the experiment not only had a great advantage in construction VOC, but also had a significant advantage in film hardness.
Used ethyl butyl propanediol, alkoxy-modified trimethylolpropane, polycaprolactone polyol as the core and dimethylol propionic acid AB2 monomer to synthesize a hyperbranched polymer, which was then modified with benzoic acid and lauric acid. After testing, it was found that the resulting coating had good gloss, adhesion and flexibility, but the viscosity was too high. Under the action of caprolactone and fatty acid, the viscosity was greatly reduced, while the hardness, adhesion, flexibility and impact resistance were excellent.
In recent years, hyperbranched polymers have been one of the hot topics of research. Their three-dimensional spherical macromolecular structure brings them advantages such as low viscosity, good solubility, strong terminal group activity, and compatibility with inorganic materials, making them a new research object in the field of coatings. Especially in recent years, with the gradual development of the environmental protection industry, more and more people are aware of the importance of environmental protection, and hyperbranched polymers can meet people’s needs in terms of both synthesis process and application direction. However, due to the uncontrollability of the structure of hyperbranched polymers, we cannot design product formulas through accurate predictions, which requires further exploration and discovery. At present, the application of hyperbranched polymers in coatings is mainly UV curing coatings, powder coatings and high solid component coatings. In addition, there are also applications in water-based coatings, flame retardant coatings and stain-resistant coatings. With the deepening of research, hyperbranched polymers have certain application prospects in dispersants, adhesives, pigment dispersants and printing ink bases.