Chemicals & Polymers Blog
Explore Gantrade's News & Industry Articles

Caprolactone-Modified (Meth)acrylate Monomers

published on September 18, 2020

At Gantrade, we offer a variety of caprolactone-modified (meth)acrylate monomers. The caprolactone-modified acrylates (FA-series) and methacrylates (FM-series) are reactive oligomeric monomers containing caprolactone chains with a primary hydroxyl end-functionality.  

These unique hydroxyl-terminated caprolactone (meth)acrylate [HCL(M)A] monomers can be incorporated in various acrylic resin systems where they can be subsequently crosslinked.  The primary hydroxyl end-groups react particularly well with conventional melamine-formaldehyde crosslinking agents and multi-functional isocyanates to afford high performance coatings and films. Formulators also use our caprolactone (meth)acrylate monomers in the preparation of UV-curable urethane acrylates and UV-curable acrylate formulations where the wide range of viscosities of the oligomeric monomers provide good formulating latitude.



Attributes of Caprolactone-Modified (Meth)acrylate Monomers

By positioning the primary hydroxyl function away from the main chain in an acrylic copolymer, formulators select these oligomeric caprolactone meth(acrylates) to achieve the following benefits, which also apply to the urethane acrylates:

  • Higher cure speeds with crosslinking agents, higher cure productivity, and efficiencies.
  • Enhanced impact resistance, toughness, and flexibility in the crosslinked product.
  • Improved chemical resistance, especially to fuels, oils and solvents.
  • Increases in the mechanical properties and durability of the cured resins.
  • Balancing hardness and flexibility.
  • Improved abrasion and scratch resistance, adhesion, and better pigment wetting.
  • Weatherability improvements and non-yellowing.

Our customers use crosslinkable HCL(M)A monomers in automotive, coil, plastic and elastomer coatings, cementitious coatings, powder coatings, adhesives, and graphic arts applications.


Acrylic Copolymers Application

Formulators use crosslinkable acrylic and styrenic copolymers based on HCL(M)A monomers in architectural coatings, OEM product finishes, metal coil coatings, and special purpose coatings.  Protective coatings such as fabric and leather finishes, floor polishes, and wood and paper coatings are also based on these modified acrylate monomers.  After copolymerization and film formation, crosslinking is achieved through the primary hydroxy with melamine or multifunctional isocyanate curing agents.  Coating technologies include water-borne and solvent based systems and powder coatings.

The higher reactivity of the hydroxyl function in HCL(M)A versus that based on HEMA is shown in the figure below.  The data is based on measuring the residual NCO content over ten days.  The isocyanate was a HMDI type polyisocyanate, and the more efficient and complete use of this isocyanate is revealed after ten-days.



UV Cure Systems

UV/EB cure is an environmentally friendly technology, since it does not require volatile organic compounds (VOCs), no by-products are eliminated,  and is a low energy, high productivity process.  Recent growth rates in this production area have been in the 10 percent range. The HPC(M)A oligomers offer distinct advantages in UV/EB-cured systems including their inherent low viscosities.   A basic photopolymerizable formulation consists of a polymerizable vehicle (oligomeric acrylate binder) and a light-sensitive compound such as benzophenone or benzoin, capable of initiating a free-radical polymerization through absorbed light energy.

Formulators can use hydroxy-caprolactone (meth)acrylates directly as UV-curable binders or reacted with isocyanates in a ratio of 2:1 to produce urethane acrylates. Preferred isocyanates are the aliphatic IPDI, HDI and H12MDI; also multifunctional isocyanates such as HDI-biuret .  Through the selection of the appropriate HCL(M)A monomer or associated urethane acrylate, coatings and printing inks can be optimized for superior flexibility, hardness, durability, adhesion properties, and specific processing characteristics.  The HCP(M)A series monomers can be formulated with other acrylates and multi-functional acrylates like TMP triacrylate. 

The use of caprolactone acrylates has been growing in all aspects of the UV/EB cure market. The urethane acrylates are ideal for the fast-growing world of 3D printing.  Other applications include coatings, laminating and pressure sensitive adhesives, graphic arts, doming resins, and cure-in-place gasketing systems.  An advantage inherent with the HPC(M)A oligomeric monomers is their low viscosities (the caprolactone chains have low MWDs).  This is seen in the initial viscosity data of the UAs shown in the table below.

The table below compares the mechanical properties of cured urethane acrylate based on an HCL(M)A vs. systems based on HEA (hydroxyethyl acrylate).  The system using FA2D exhibited a lower modulus value, but it also featured a significantly higher degree of compression repair as measured by nanoindentation using a displacement at a maximum load value (Elionics Corp.).  The hardness values can be increased using a tri-isocyanate intermediate in place of the IPDA or a multifunctional acrylate crosslinking monomer.  You can get this result while maintaining the compressive repairability of the HCL(M)A based UAs.


Mechanical Properties of Urethane Acrylates

Properties PCL
Initial Viscosity of UA 1,900 cps, 75°C 6,200 cps, 75°C 4,900 cps, 75°C
Elongation at Break 79% 99% 106%
Film Modulus 9.8 MPa 77 MPa 21 MPa
Coating Hardness 21 N/mm2 80 N/mm2 14.3 N/mm2
Coating Modulus 100 N/mm2 6602 N/mm2 150 N/mm2
Degree of Resotration 80% 31% 58%



Gantrade’s Lineup of Caprolactone Acrylates and (Meth)Acrylates

The table below lists the wide range of options available in the Placcel® caprolactone acrylate and methacrylate series produced by Daicel Corporation.  Daicel is the only producer of the methacrylate (FM) series.  The advantages of the Daicel product line include high purity, low color and odor, very low level of residual catalyst, and a broad spectrum of Tgs (glass transition temperatures).  Levels of di(meth)acrylate in the caprolactone (meth)acrylate monomers are very low (<< 1%) and acrylic polyols prepared from these monomers do not show the presence of gels.

Product MW Appearance OH Value, KOH mg/g M.P., °C Acid Value, KOH mg/g Viscosity,
mPa⋅s ,
25 °C
Placcel FA Series - Acrylates
FA 1 230 Liquid 244 -24 3.48 32
FA 2 344 Liquid 163 -12 2.50 78
FA 3 458 Liquid 118 12 1.75 122
FA 5 686 Wax 81.8 NA 0.94 130/40°C
FA 10L 1258 Solution 31 Toluene 0.67 48
Placcel FA Series - Methacrylates
FM 1 244 Liquid 224.3 -60 3.41 32
FM 2 358 Liquid 154.5 -20 32.44 72
FM 3 473 Liquid 116.2 4 1.95 130
FM 4 586 Paste 93.6 15 1.59 200
FM 5 701 Wax 78.2 21 1.36 121/40°C



The HCL(M)A monomers are available in 200 Kg. and 1 MT IBC totes with MEHQ as the stabilizer.

The following figure shows the relationship between the Tg of the Placcel® acrylate (FA series) and methacrylate (FM series) monomers and the moles of caprolactone added per molecule.  As the content of caprolactone units increase, the contribution Tg of the acrylic monomer decreases, with the acrylates exhibiting a lower Tg versus their methacrylate counterpart.



Reactivity Ratios for the Placcel® FM Series

In an interesting study, Daicel Corporation determined the copolymerization reactivity ratios for the FM monomer series in co-polymerizations with styrene monomer.  The measurements of r1 and r2 were carried out in a solution (toluene) polymerization process using the Fineman-Ross method.  This method provides a good indication of the tendency of monomer pairs to randomly copolymerize versus a preference for homo-polymerization or block polymerization.  The reactivity ratio for a pair of monomers is the reaction rate constant for propagation of the first monomer in a growing polymer chain to itself (r1) versus addition to the second monomer (r2).  When the reactivity ratios of the comonomer pairs are similar, random co-polymerizations are observed.

The free-radical copolymerization reactivity ratios r1 and r2 and the parameter Q and e are shown in the table below.  Q values indicate the degree of stabilization of the growing free radical; Q values > 0.35 indicate good stabilization. The e-value indicates the electronegativity of the double bond.  e Values < 0 show an electron rich double bond.  Data for HEMA (hydroxyethyl methacrylate) and MMA methyl methacrylate) are included as a comparison.


Copolymerization Reactivity of Placcel® FM Monomers

  MW r1 r2 Q e r1 x r2
HEMA 130 0.57 1.53 1.31 -0.43 0.87
MMA 100 0.52 0.46 0.74 0.40 0.24
FM-1 244 0.56 1.49 1.27 -0.38 0.83
FM-2 358 0.62 1.21 1.05 -0.28 0.75
FM-3 472 0.57 0.68 0.80 0.18 0.39
FM-4 586 0.58 0.55 0.73 0.27 0.32
FM-5 701 0.60 0.51 0.70 0.29 0.31
FM-6 814 0.60 0.46 0.69 0.35 0.28
FM-10 1270 0.64 0.61 0.72 0.17 0.39


M1 – Styrene and M2 – Placcel® FM Monomer

The reactivity ratios for the Placcel FM monomers and styrene are indicative of very good random copolymerization kinetics.  As the chain length of the polycaprolactone chain increased the r2 value decreased.  As can be observed with the methacrylic monomers MMA and HEMA, the reactivities of the polycaprolactone methacrylates are very similar to the standard methacrylate monomers.


Styrene-Acrylic Coating Properties

Caprolactone methacrylate-modified styrene-acrylic resins were prepared in solution using the recipe below.  The temperature was held at 120°C during the addition of the monomers. AIBN was added over a period of four hours at 120°C. Thereafter, the polymerization was continued for four hours additional to obtain a transparent solution with the properties shown below, without any appearance of gel content.

Copolymerization Recipe for Caprolactone Methacrylate
Starting Materials, pbw   FM-1 FM-2 HEMA
Butyl Acetate 333 333 333
Toluene 333 333 333
Di-t-Bu Peroxide 10 10 10
Styrene 400 400 400
MMA 100 100 100
Butyl Acrylate 100 100 100
Methacrylic Acid 10 10 10
Caprolactone Methacrylate 400 400  
HEMA     215
AIBN 10 10 10
Acrylic Resin Properties Solids Content, % 61.7 60.7 56.2
Gardner Viscosity Z3-Z4 Z1-Z2  
Acid Value, KOH mg/g 5.28 5.06  
Hydroxy Value, KOH mg/g 53.3 35.4  
Hue, Gardner < 1 < 1 < 1



The above acrylic resins were blended with an HDI-biuret multi-functional isocyanate at a OH/NCO ratio of 1.0 and coated on a steel plate.  Contiguous films were obtained by drying and curing the blend compositions. Film performance designated as “O” indicates an excellent result.  Those designed by a “Δ” indicates poor performance.

Coating Properties
Blend   FM-1 FM-2 HEMA
Acrylic Polyol FM-1 FM-2 HEMA
Curing Agent HDI Biuret HDI Biuret HDI Biuret
Film Properties        
Pencil Hardness HB B HB
Cross-cut Test 100/100 100/100 100/100
Impact Resistance (500g.1")cm ≥ 50 ≥ 50 ≥ 50
Water Resistance (50°C, 48hr)      
Whitening O O Δ
Blister O O Δ
Cross-cut 100/100 100/100 100/100
Alkali Resistance (5%
NaOH, 25°C, 48 hr.)
Acid Resistance (5% HCl,
25°C, 48 hr.)
Solvent Resistance (xylene
rubbing, 100 X)
Bending Test (2 mm) O O Δ
Stain Resistance (black ink,
48 hr.)
Elongation, % 61 77 35


The films obtained using the caprolactone methacrylates exhibited superior chemical, stain and solvent resistance, flex strength, impact properties, elongations, and low temperature bending properties versus the system based on HEMA.


Comb PolymerStructures

“Comb-shaped” polymers are a category of materials consisting of a low density of side chains on a linear polymer-backbone structure. This category of comb polymers can be designed using acrylic and styrene monomers copolymerized with caprolactone acrylate oligomers to create the requisite branches on the high-polymer backbone. The side chains mainly affect the melt and solution rheological properties of polymers, such as the extensional viscosity, shear viscosity and the important polymer strain hardening behavior under extensional deformations. Application areas include foam and film where strain hardening and extensional viscosity behavior are of high importance.

Side chain (the comb teeth) entanglement is required for the enhanced performance associated with comb polymers. Entanglement MWs can be reached at the higher chain lengths of caprolactone (meth)acrylate oligomer monomers. The key parameters affecting performance enhancements include the MW of the side chains and the side chain density on the backbone structure.  Formulators achieve these super-elastomeric properties through optimization of these parameters. Hyperbranched structures have also been synthesized using these caprolactone oligomeric monomers.



Daicel’s product line of hydroxy-functional caprolactone (meth)acrylates expand the options for formulators to design specific attributes into an array of acrylic resins and UV-curable urethane acrylates. By selecting the appropriate degree of caprolactone modification in the (meth)acrylic monomer, these monomers allow optimizations of the following properties within an acrylic polymer or urethane acrylate system.

The advantages associated with the Daicel line of HCP(M)A monomers include high purity, low color and odor, and very low residual catalyst levels. The content of diacrylate monomers is very low, allowing gel-free acrylic polyols to be prepared from these monomers.

  • Cure Efficiency
  • Durability
  • Toughness
  • Chemical Resistance
  • Hardness-Flexibility Balance
  • Adhesion
  • Abrasion Resistance
  • Weatherability

To explore how our range of caprolactone (meth)acrylic oligomer monomers can address your unique polyurethane elastomer application, partner with the expert teams at Gantrade Corporation. Our teams, armed with a wealth of technical knowledge and expertise, can guide you to the best solutions for your applications. Contact Gantrade today to get startedWe offer a wide portfolio of acrylic monomers to achieve your high-performance requirements.

Topics: Vinyl & Acrylic Monomers