FEB 26, 202654 MINS READ
The molecular architecture of multifunctional acrylates oligomer is defined by the presence of at least two acrylate functional groups per molecule, with number-average acrylate functionality (fo) typically exceeding 2 and extending up to 10 in highly branched systems 1,7. These oligomers are synthesized through controlled polyaddition reactions, most commonly involving multifunctional amines (A) with N-H functionality (fA ≥ 2) and multifunctional acrylates (B) with acrylate functionality (fB ≥ 2), resulting in branched structures containing aminoacrylate repeat units (-O₂C-CH₂-CH₂-N=) 1,2. The nitrogen content from the amine component is maintained at ≥0.35 mEq/g, and the initial acrylate-to-N-H ratio (r) is precisely controlled between rinf = 0.90×(fA-1)×(fB-1) and 1.1×rsup, where rsup = 2×fA + 2×fB - 6, ensuring controlled molecular mass and preventing gelation 1.
Key structural features include:
The weight-average molecular weight (Mw) of multifunctional acrylate oligomers typically spans 500–50,000 g/mol, with lower-molecular-weight oligomers (500–2,000 g/mol) preferred for low-viscosity formulations and higher-molecular-weight variants (10,000–50,000 g/mol) used to enhance mechanical robustness 6,7,9. The acrylate equivalent weight—defined as the molecular weight per acrylate group—ranges from 100 to 1,000 g/mol, directly influencing crosslink density and cured film properties 7,9.
The synthesis of multifunctional acrylates oligomer employs several distinct reaction pathways, each offering control over functionality, molecular weight, and viscosity.
Polyaddition of multifunctional amines and acrylates: This one-step process involves the Michael addition of primary or secondary amines to the β-carbon of acrylate groups, forming aminoacrylate linkages without the need for catalysts or solvents 1,2. The reaction is conducted at ambient or slightly elevated temperatures (20–60°C), with the acrylate-to-amine ratio (r) carefully controlled to prevent premature gelation. For example, reacting a trifunctional amine (fA = 3) with a difunctional acrylate (fB = 2) at r = 1.8 yields oligomers with nav ≈ 2–3 repeat units and terminal acrylate groups, ensuring high reactivity in subsequent UV curing 1. The nitrogen content (≥0.35 mEq/g) imparts synergistic crosslinking effects, reducing the need for reactive diluents and lowering VOC emissions 2.
Urethane acrylate synthesis via isocyanate-polyol-acrylate reactions: Multifunctional urethane acrylate oligomers are prepared by first reacting diisocyanates (e.g., hexamethylene diisocyanate, isophorone diisocyanate) with polyols (e.g., polyether polyols, polyester polyols, polycarbonate polyols) at 60–80°C under inert atmosphere, forming prepolymers with terminal isocyanate groups 9,16. These prepolymers are then end-capped with hydroxyl-functional acrylate monomers (e.g., 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate) at 40–60°C, yielding oligomers with 2–6 acrylate functionalities and Mw = 500–5,000 g/mol 9,16. The choice of polyol backbone (aliphatic, aromatic, or fluorinated) allows tuning of flexibility, hardness, and chemical resistance 16.
Michael addition of β-dicarbonyl compounds to multifunctional acrylates: This route involves the base-catalyzed addition of β-dicarbonyl donors (e.g., ethyl acetoacetate, diethyl malonate) to multifunctional acrylate acceptors (e.g., trimethylolpropane triacrylate, pentaerythritol tetraacrylate) in the presence of catalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) 3,5. The reaction proceeds at 25–50°C in polar aprotic solvents (e.g., DMSO, DMF) or solvent-free, yielding oligomers with labile ketone groups that dissociate under UV irradiation to initiate free-radical polymerization 5. For instance, reacting trimethylolpropane triacrylate (TMPTA) with ethyl acetoacetate (EAA) in a 2:1 molar ratio produces photoactive oligomers with Mw ≈ 600–1,200 g/mol and viscosity <5,000 cP at 25°C 3,5.
Modification with cyclic carboxylic anhydrides: Multifunctional acrylated oligomers can be synthesized by reacting common polyols (e.g., glycerol, pentaerythritol) with acrylic acid and cyclic carboxylic anhydrides (e.g., succinic anhydride, phthalic anhydride) in controlled proportions, yielding ether-ester structures with high acrylate functionality and low hydrophilicity 13. This process, conducted at 80–120°C with acid catalysts, allows precise control of crosslinking density without excessive shrinkage, achieving acrylate equivalent weights of 200–800 g/mol 13.
Ethoxylation and propoxylation for hydrophilicity control: To enhance water reducibility and compatibility with aqueous formulations, multifunctional acrylate oligomers are ethoxylated or propoxylated by reacting with ethylene oxide or propylene oxide at 100–150°C under basic catalysis 3. For example, ethoxylated bisphenol A diacrylate (with 2–10 ethylene oxide units per molecule) exhibits viscosity <1,000 cP at 25°C and can be diluted with water to achieve spray-application viscosities (50–200 cP) without organic solvents 3.
Multifunctional acrylates oligomer exhibits a broad spectrum of physical and chemical properties, directly influenced by molecular architecture, acrylate functionality, and backbone composition.
Viscosity and rheology: Viscosity is a critical parameter for formulation and application, ranging from <500 cP for low-molecular-weight oligomers (Mw <1,000 g/mol) to >50,000 cP for high-molecular-weight variants (Mw >10,000 g/mol) at 25°C 1,3,7. Branched oligomers synthesized via amine-acrylate polyaddition exhibit 30–50% lower viscosity than linear oligomers of equivalent molecular weight, due to reduced chain entanglement 1,2. Ethoxylated or propoxylated oligomers demonstrate shear-thinning behavior, with viscosity decreasing by 50–70% at shear rates >100 s⁻¹, facilitating spray and roll-coating applications 3.
Acrylate functionality and equivalent weight: The number-average acrylate functionality (fo) ranges from 2 to 10, with higher functionality correlating to increased crosslink density and cured film hardness 1,7,9. Acrylate equivalent weight—calculated as Mw divided by fo—spans 100–1,000 g/mol, with lower values (<300 g/mol) yielding rigid, brittle films and higher values (>500 g/mol) producing flexible, impact-resistant coatings 7,9.
Reactivity and cure speed: Multifunctional acrylates oligomer undergoes rapid free-radical polymerization upon exposure to UV radiation (λ = 254–365 nm) or electron-beam irradiation (dose = 5–50 kGy), achieving >90% conversion of acrylate groups within 0.5–5 seconds under typical curing conditions (intensity = 1–5 W/cm²) 1,2,5. Oligomers containing labile ketone groups (from β-dicarbonyl modification) exhibit self-initiating behavior, eliminating the need for external photoinitiators and reducing formulation complexity 5.
Thermal stability: Thermogravimetric analysis (TGA) reveals that multifunctional acrylates oligomer exhibits onset decomposition temperatures (Td,5%) of 200–350°C, depending on backbone composition 6,13. Urethane acrylate oligomers with aliphatic backbones show Td,5% ≈ 250–300°C, while aromatic urethane acrylates and epoxy acrylates exhibit Td,5% ≈ 300–350°C 6,16. Oligomers modified with cyclic anhydrides demonstrate enhanced thermal stability (Td,5% ≈ 280–320°C) due to ester linkages 13.
Solubility and hydrophilicity: Non-ethoxylated oligomers are hydrophobic, with water solubility <0.1 g/L at 25°C, and are soluble in common organic solvents (e.g., acetone, toluene, ethyl acetate) 1,2. Ethoxylated oligomers (with 2–20 ethylene oxide units) exhibit water solubility of 10–500 g/L, enabling formulation of water-reducible UV-curable coatings with VOC content <50 g/L 3.
Mechanical properties of cured films: Crosslinked films derived from multifunctional acrylates oligomer exhibit tensile strength of 20–80 MPa, elongation at break of 2–150%, and Shore D hardness of 40–85, depending on acrylate functionality and backbone flexibility 1,2,5,13. Oligomers with urethane or ester backbones provide elongation at break >50%, while those with rigid aromatic or isocyanurate rings yield hardness >70 Shore D 8,10,15.
Multifunctional acrylates oligomer serves as the backbone resin in UV-curable formulations, typically comprising 30–70 wt% of the total composition, with the remainder consisting of reactive diluents, photoinitiators, and functional additives 1,2,5.
Reactive diluent selection and viscosity control: To achieve application-suitable viscosities (50–2,000 cP), multifunctional acrylates oligomer is blended with low-viscosity reactive diluents such as hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TRPGDA), or isobornyl acrylate (IBOA) at 10–40 wt% 1,3,5. However, oligomers synthesized via amine-acrylate polyaddition exhibit inherently low viscosity (<5,000 cP at 25°C for Mw ≈ 1,000 g/mol), reducing or eliminating the need for reactive diluents and minimizing worker exposure to volatile monomers 1,2. Water-reducible oligomers (ethoxylated variants) can be diluted with 10–30 wt% water to achieve spray-application viscosities without organic solvents, reducing VOC emissions to <50 g/L 3.
Photoinitiator systems and cure efficiency: Multifunctional acrylates oligomer is cured using Type I (cleavage-type) or Type II (hydrogen-abstraction) photoinitiators at 1–5 wt% 1,5. Type I initiators (e.g., 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone) provide rapid surface cure and are preferred for thin films (<50 μm), while Type II initiators (e.g., benzophenone with amine synergists) offer deeper cure penetration for thick coatings (>100 μm) 5. Oligomers containing labile ketone groups (from β-dicarbonyl modification) act as self-initiating resins, achieving >85% acrylate conversion without external photoinitiators under UV irradiation (λ = 365 nm, intensity = 2 W/cm², dose = 1 J/cm²) 5.
Synergistic crosslinking with multifunctional monomers: Blending multifunctional acrylates oligomer with multifunctional monomers (e.g., trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate) at 10–30 wt% enhances crosslink density and cured film hardness 4,7,9. For example, formulations containing 50 wt% urethane acrylate oligomer (fo = 4, Mw = 1,500 g/mol) and 20 wt% pentaerythritol tetraacrylate (PETA) exhibit Shore D hardness of 75–80 and solvent resistance (MEK double rubs >200), compared to 60–65 hardness and <100 MEK rubs for oligomer-only formulations 9.
Additives for performance enhancement: Functional additives—including flow and leveling agents (0.1–1 wt%), defoamers (0.05–0.5 wt%), wetting agents (0.1–2 wt%), and waxes (0.5–3 wt%)—are incorporated to optimize coating appearance, adhesion, and scratch resistance 5. Silane coupling agents (
| Org | Application Scenarios | Product/Project | Technical Outcomes |
|---|---|---|---|
| Arkema France | UV-curable coatings, inks, varnishes, paints, adhesives, gel coats, 3D printing resins requiring rapid cure speed, enhanced flexibility, hardness, and solvent resistance with low viscosity formulations. | Branched Multifunctional Acrylate Oligomers | Achieved controlled branched structure via amine-acrylate polyaddition with acrylate functionality >2, nitrogen content ≥0.35 mEq/g, and 30-50% lower viscosity than linear oligomers, enabling synergistic crosslinking without reactive diluents and reducing VOC emissions. |
| Ashland Licensing and Intellectual Property LLC | Water-reducible UV-curable coatings for spray and roll applications requiring low VOC emissions, enhanced wetting and laydown properties, and reduced worker exposure to volatile monomers. | Water-Reducible Radiation-Curable Acrylate Oligomers | Developed ethoxylated multifunctional acrylate oligomers via Michael addition of β-dicarbonyl compounds to multifunctional acrylates, achieving water solubility of 10-500 g/L, viscosity <5000 cP at 25°C, and VOC content <50 g/L with self-initiating photoactive ketone groups. |
| LG Chem Ltd. | Pressure-sensitive adhesives for flexible displays, polarizing plates, and cover windows requiring controlled elastic modulus gradient, excellent adhesion, dimensional stability, and durability under high temperature and humidity conditions. | Multifunctional Acrylate Adhesives for Display Applications | Formulated multifunctional acrylate oligomers (Mw 500-50,000 g/mol) with 2-10 acrylate functionalities and ring-containing structures (isocyanurate, carbocyclic), achieving Shore D hardness 40-85, tensile strength 20-80 MPa, and >90% acrylate conversion under UV curing (0.5-5 seconds at 1-5 W/cm²). |
| Arkema France | High-performance UV-curable coatings and inks for applications requiring tight dimensional tolerances, superior adhesion, minimal shrinkage, and cost-effective production without expensive specialty materials. | Carboxylic Anhydride-Modified Multifunctional Acrylate Oligomers | Synthesized multifunctional acrylated oligomers by reacting polyols with acrylic acid and cyclic carboxylic anhydrides at 80-120°C, yielding acrylate equivalent weights of 200-800 g/mol with controlled crosslinking density, reduced shrinkage, low hydrophilicity, and balanced hardness-flexibility properties. |
| Arkema France | Photocurable compositions for dental materials, biomedical prostheses, protective coatings, adhesives, and composites requiring rapid UV/EB cure, enhanced mechanical robustness, and tailored physical properties. | Multi(meth)acrylate-Functionalized Urethane Oligomers | Prepared urethane acrylate oligomers (Mw 500-5,000 g/mol) with 2-6 pendant and terminal acrylate groups via diisocyanate-polyol-acrylate reactions at 40-80°C, providing tunable flexibility, hardness, and chemical resistance through backbone selection (aliphatic, aromatic, fluorinated polyols). |