2-Ethylhexyl Acrylate (2-EHA ) is a highly versatile building block that readily copolymerizes with a wide variety of other acrylic and vinyl monomers to tailor specific high molecular weight copolymer properties for a diverse range of non-rigid applications.
As a higher alkyl acrylate comonomer, 2-EHA imparts a glass transition temperature that is well below room temperature (homopolymer Tg is – 65 °C), flexibility and elasticity, and a hydrophobic nature. Unique features contributed to copolymer compositions include low temperature flexibility, water resistance, good weathering characteristics, and UV (sunlight) resistance. Primary applications that take advantage of these characteristics include multiple adhesives, especially pressure-sensitive adhesives (PSA), paint & coatings, caulks & sealants, textile & paper finishes, and printing inks.
Because 2-EHA contributes to clarity, toughness, light & weather resistance, and chemical resistance, manufacturers can use acrylic copolymers containing 2-EHA in interior, exterior, basecoat and topcoat paint & coating formulations, and other related products.
New areas of technical application for 2-EHA are in the homopolymer, poly(2-ethylhexyl acrylate), used as a plasticizer material for surface coatings, film, sheeting, and pressure-sensitive adhesives and tapes. As a plasticizer incorporated into PSAs, it results in an increase in peel strength, tack, and at the same time can improve removability. 2-EHA is used in superabsorbent copolymers to produce fast swelling and highly porous hydrogels for diapers and hygiene products.
Growth in paints & coatings, adhesives & sealants, printing inks, and superabsorbent polymers are driving the global 2-EHA market.
Attributes of 2-EHA as a comonomer include:
- A low Tg -65 °C and low temperature flexibility
- Facilitates design of softness and tackiness in copolymers
- Excellent copolymerization characteristics
- Entanglement of the C8 side chain facilitates macromolecular entanglement (Me)
- Improves water resistance and weathering; suitable for external applications.
- A low order of toxicity
- Availability and commodity economics
The performance profile of 2-EHA has led to a strong growth rate in commercial applications. 2-EHA homopolymers and copolymers comply with numerous sections of the Code of the Federal Register (21CFR) for adhesives, coatings, and indirect food additives.
The Versatility of 2-EHA
2-Ethylhexyl acrylate is a key monomer in a wide range of copolymer compositions. Free-radical polymerization techniques afford high monomer conversions and very high macromolecule molecular weights (>200,000). The ease of handling and co-polymerization of 2-EHA allow for use in emulsion, solvent, suspension and bulk polymerizations.
The molecular formula of 2-EHA, shown below, illustrates the long-chain branched structure of this unique monomer.
As we describe below, the long C8 chain structure contributes side-chain entanglement, leading to an increase in cohesive strength with increasing 2-EHA contents.
Acrylate esters in general, which include 2-EHA, BA, MMA and GAA, represent a versatile family of building blocks for thousands of copolymer compositions. Copolymerization can lead to well-designed properties required in a broad range of end-use applications. Styrene monomer and the short-chain acrylic monomers like methyl methacrylate produce harder, more brittle polymers, with high cohesion and strength characteristics. The long-chain monomers like 2-EHA and BA enable soft, flexible, tacky polymers with lower strength characteristics.
By managing the comonomer ratios and the glass transition temperatures, the chemist can balance hardness and softness, tackiness and block resistance, adhesive and cohesive properties, low-temperature flexibility, strength and durability, and other key properties to facilitate end-use goals. Functional monomers like diacetone acrylamide, (meth)acrylic acid, glycidyl acrylates and maleic anhydride can be incorporated as crosslinking agents and/or as cure accelerators. Monomers like acrylonitrile and (meth)acrylamide, can improve solvent and oil resistance. See Gantrade’s blog on the technology of DAAM and ADH crosslinking in acrylic polymers.
Pressure Sensitive Adhesives (PSAs) based on 2-EHA
Chemists facilitate the rational design of PSAs by the availability monomers like 2-EHA, which contribute unique properties in adhesive copolymer compositions. The challenge in designing PSAs is to balance properties like adhesion and cohesion, tack, shear, and peel strength, high and low temperature performance, hardness and softness, and removability and permanence. An understanding of the copolymer contributions of 2-EHA and other complimentary monomers can assist in the engineering of copolymer compositions to meet performance profiles required for various end-uses.
In one study, the effect of 2-EHA monomer content on the peel strength and shear strength of an acrylic emulsion PSA prepared from 2-EHA, BA, 2-HEA, and GAA was determined. Peel and shear strength increased with increasing 2-EHA contents. However, the loop tack decreased as the 2-EHA was increased. The 2-EHA content had a strong effect on the flow of the adhesive and substrate wetting characteristics. The shear strength increase was ascribed to chain entanglement of the 2-ethylhexyl side chain, an interesting feature of the long-chain in the 2-EHA acrylate monomer.
In another study, investigators looked at the effect of varying the n‐butyl acrylate/2-EHA ratio in the monomer feed on copolymer PSA characteristics . These compositions also contained a low constant level of acrylic acid. The results showed that increasing the amount of 2-EHA reduced the glass‐transition temperature and decrease the gel content of the copolymer, up to 50 % 2-EHA; thereafter, gel content increased They observed a synergistic effect leading to increased shear resistance at 25 wt. % 2-EHA without a significant trade‐off in the peel and tack properties. The investigators attributed this behavior to the cooperative entanglement of the 2-EHA units in the free copolymer chains and with the microgel particles.
Cooperation between various levels of 2-EHA in the copolymer structure simultaneously changed the crosslink molecular weight (Mc) of the microgels and the entanglement molecular weight (Me) of the free chains in the network morphology. The adhesive performance of the PSAs correlated with their Mc/Me values as the 2-EHA proportion was varied. Other observations included an increase in tack strength and a decrease in peel strength with increased 2-EHA levels. Increasing 2-EHA in the feed reduced the polymerizations rates vs. butyl acrylate.
Paint and Coating Applications of 2-EHA
When used in paint and coating formulations, 2-EHA copolymers exhibit good water resistance, low temperature flexibility, durability, and good weathering and sunlight resistance.
Acrylic based coatings can be classified into all-acrylic formulations in which the building blocks are exclusively acrylic and methacrylic ester types; styrene-acrylic formulations, which also contain styrene; and vinyl-acrylic formulations which also contain vinyl acetate monomer (VAM).
The various monomers used in the copolymers can differ widely in glass transition temperature (Tg); copolymer hydrophobic-hydrophilic balance; hardness and flexibility; and weathering and sunlight resistance. Even with a fixed Tg, copolymers with different monomer combinations vary significantly in the properties of the final paint and coatings. The most common paint formulations are copolymers of BA and 2-EHA with MMA or BA and 2-EHA with VAM.
Acrylic copolymer formulations often contain four or more different monomers. The glass transition temperature of a random copolymer can be estimated by using the weight fraction of the different monomers and their Tg values for the homopolymer. This method assumes that the repeat unit of the copolymer can be divided into weighted additive contributions to the Tg that are independent of their neighbors. Reference Tg values for several key monomers are shown below:
For a discussion on estimating the Tg of random copolymers please see this article: https://www.highbeam.com/doc/1G1-17351275.html
In the important area of weatherability and sunlight resistance, BA copolymers exhibit the greatest photostability, while styrene and VAM lower the photostability. 2-EHAs is slightly more photosensitive than BA but much superior to styrene and VAM. 2-EHA copolymers are hydrophobic and show the least amount of dirt pick-up in exterior coatings or staining with hydrophilic substances.
Other Application Areas
We can apply the formulating principles delineated above to the other major application areas for copolymers using 2-EHA in the co-monomer compositions. Additional end-uses for 2-EHA copolymers include printing inks, non-woven fabrics, textiles and paper coatings, leather finishing, caulks and sealants, and additives for example in lubricant oils and fuels.
Gantrade’s Sales Specifications for 2-EHA are shown below:
|Color (APHA)||10 maximum||ASTM D1209|
|Purity||99.5 % minimum||GC|
|Specific Gravity, 20°/20°C||0.8820-0.8920||ASTM D4052|
|Water content, Wt. %||0.05 % maximum||ASTM D1364|
|Acidity (expressed as acrylic acid), Wt. %||0.01 % maximum||ASTM D1613|
|Inhibitor content (MEHQ)||10 - 20 ppm||ASTM D3125|
2-EHA is available from Gantrade Corporation in rail tank car and road tank trucks. 2-EHA should be stored at temperatures below ~ 25 °C (<80 °F). With MEHQ inhibitor, the product must be stored under an air atmosphere since the presence of oxygen is required with this stabilizer.
2-EHA is one of the major base monomers used in the manufacture of copolymers for adhesives & sealants, paint & coatings, printing inks, superabsorbent polymers, and a myriad of other application areas. 2-EHA is a unique building block for copolymers, contributing low temperature flexibility and performance, hydrophobicity and water resistance, good weathering characteristics and UV (sunlight) resistance.
For more information on how 2-EHA can work for you, contact Gantrade Corporation today.
A recent study with 2-ethylhexanoic acid (2-EHA) did not indicate any adverse effects regarding reproduction at the highest dose tested. As a result, ECHA has finalized the Community Rolling Action Plan (CoRAP) evaluation, and 2-EHA is no longer under consideration for additional classification. The product is considered safe with risk mitigation measures in place.