Dr. Mark D. Soucek
Professor of Polymer Engineering
Professor of Chemistry
Department of Polymer Engineering
Phone: 330-972-2583
Email: msoucek@uakron.edu
Research Areas
- UV-Curable Coatings
- Ureas, Urethanes, Polyesters
- Waterborne Coatings
- Space Coatings
- Powder Coatings Center
- Dry Oils and Ceramer Coatings
UV-Curable Coatings
Our group studies various aspects of UV-curable coatings including Dark-cure kinetics, preparation of new reactive oligomers/monomers, and development of UV-curable inorganic/organic hybrid coatings. We have studied the curing kinetics via Real-time IR, and Photo-DSC. Most of our past studies have focused on cationic initiated systems, however some of our new work is focused upon free radical photopolymerizations. We found a synergistic effect between polyol and relative humidity for cationic UV-curable coatings. We have prepared new reactive oligomers based on linseed oil, and we have developed inorganic/organic hybrid coatings with nanosized silicon oxides, and titanium-oxo-clusters.
General Overview
Ultraviolet-curable (UV-curable) coatings offer the advantages of fast cure response, high energy efficiency, and low volatile organic contents (VOCs). As the pressure to reduce VOCs continues to mount, the advantages of UV coatings are becoming more attractive. There are two classes of UV-curable coatings, free radical and cationic. In comparison with free radical UV-curing, the cationic initiated UV-curing technology offers the advantages of insensitivity to oxygen and lower film shrinkage. The cationic initiated UV-curable coatings are also particularly useful in a variety of applications, including: paper coatings, wood coatings, plastic substrate coatings, lithographic and screen printing inks, and decorative metal varnishes.
Epoxides are one of the most important and widely used classes of resins in the field of cationic UV-curable coatings. The three major types of epoxides used are glycidyl ether, epoxidized seed oil (soybean or linseed oil), and cycloaliphatic epoxide. Of the three, cycloaliphatic epoxides are the most widely used due to their fast cure response. In addition to the fast cure response, cylcloaliphatic epoxides provide a number of other important advantages in coating applications, including excellent adhesion to a wide variety substrates, flexibility, good color stability, excellent gloss, low potential for skin irritation, low shrinkage, good weathering, and good electrical properties.
The homopolymer of cycloaliphatic epoxide shown in Scheme 1 is usually too brittle to be used as a coating. Typically, flexible crosslinkers such as di- and tri- functional polyols (especially e-caprolactone derived polyols) are added into the formulations to improve the toughness and impact resistance. The super-acid catalyzed crosslinking reaction is shown in Scheme 2. The super-acid catalyzed UV-curing reaction of cycloaliphatic epoxide and polyol consists of four steps (Scheme 3): initiation, propagation, chain transfer, and termination. The initiation step involves two reactions: the formation of super-acid, and the addition of the super-acid to the monomer molecules to produce the chain initiating species M 1 + , and subsequent propagation of successive epoxide molecules to the chain initiated species M 1 +.
If there are nucleophiles present, such as water or alcohol, both chain transfer or termination reaction can occur.
The propagation of cationic UV-curable coatings occur after UV-exposure. This phenomenon is called “dark-cure”. Dark-cure is due to the long-lived initiating species or ‘living’ cationic species. It was found that the dark-cure process represents a significant part of the overall process.
Dark-cure process can improve the coating properties such as adhesion and hardness.
Preparation of New Epoxides
Norbornyl epoxidized linseed oil was synthesized via Diels-Alder reaction of cyclopentadiene with linseed oil at high pressure (~ 200 Psi) and high temperature (240 °), followed by the epoxidation using hydrogen peroxide with a quaternary ammonium tetrakis(diperoxotungsto) phosphate(3-) epoxidation catalyst.Photo-induced curing kinetics of norbornyl epoxidized linseed oil coatings was investigated using real-time FT-IR spectroscopy with a fiber optic UV-curing system. The norbornyl epoxidized linseed oil was formulated with three different divinyl ether reactive diluent. The effect of divinyl ether concentration and types of divinyl ether on the curing reaction was investigated. It was found that the curing rate of norbornyl epoxidized linseed oil was lower than that of cycloaliphatic epoxide, but higher than epoxidized linseed oil. The incorporation of divinyl ether increased the curing rate substantially. Of the three divinyl ether used, coating with triethyleneglycol divinyl ether (TEGDE) showed the highest curing rate and coating with cyclohexane dimethanol divinyl ether (CHDMDE) showed the lowest curing rate.
Pertinent Publications
1) Dworak, D.P.; Soucek, M.D. (2004) “Synthesis of Cycloaliphatic Substituted Silane Monomers and Polysiloxanes for Photo-Curing” Macromolecules37(25), 9402.
2) Soucek, M.D.; Johnson, A.H.; Wegner, J.M. (2004) “Ternary Evaluation of UV-Curable Seed Oil Inorganic/Organic Hybrid Coatings Using Experimental Design” Prog. Org. Coat. Vol. 5(4), 300.
3) Zou, K; Soucek, M.D. (2004) “UV-Curable Organic-Inorganic Hybrid film Coatings Based on Epoxidized Cyclohexene Derivatized Linseed Oil” Macro. Chem. Phys., 204(15), 2032.
4) Zong, Z.; Soucek, M.D.; Liu, Y.; Hu, J. (2003) “Cationic Photopolymerization of Epoxynorborane Linseed Oils: The Effect of Diluents” J. Poly. Sci:. Part A41, 3440.
5) Chen, J.; Soucek, M. (2003) “UV-Curing Kinetics of Cyclohexyl Epoxides with Real-Time Fourier Transform Infrared Spectroscopy” J. Appl. Poly. Sci, vol. 90, 2485.
6) Chen, J.; Soucek, M. (2003) “Model for the Effects of Water on the Cationic UV-Curing of Cyclohexyl Epoxides” J. Coat. Technol., vol. 75(937), 49.
7) Chen, J.; Soucek, M. (2003) “Photo-initiated Cationic Polymerization of Cycloaliphatic Epoxide with Siloxane or Alkoxylsilane Functionalized Polyol Coatings” Eur. Polym. J, 39(3), 505.
8) Chen, J.; Soucek, M.D.; Simonsick, W.J.; Celikay, R.W. (2002) “Preparation and Photopolymerization of Norbornyl Epoxidized Linseed Oil” Polymer, 40(20), 5379.
9) Wu, S.; Sears, M.T.; Soucek, M.D. (1999) “Siloxane Modified Cycloaliphatic Epoxide UV Coatings” Prog. Org. Coat. Vol. 36, 89.
10) Wu, S.; Sears, M.T.; Soucek, M.D. Simonsick, W.J. (1999) “Synthesis of Reactive Diluents for Cationic Cycloaliphatic Epoxide UV Coatings” Polymer vol. 40, 5675.
11) Wu, S.; Soucek, M.D. (1998) “Effects of Siloxane Functionalized e -Caprolactone Polyols on Photocurable Epoxy Coatings”J. Coat. Tech., vol. 70 , No. 887, 53.
Synthesis of Cycloaliphatic Substituted Silane Monomers and Polysiloxanes for Photo-Curing
D. P. Dworak and M. D. Soucek*
The University of Akron
Department of Polymer Engineering
250 S. Forge Street
Akron, OH 44325-0301
Abstract
A synthetic scheme was developed to prepare cationically polymerizable methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes. Initially, the desired cycloalkene and dichlorosilane were reacted at high pressure (approx. 250 psi) and high temperature (120° C) to yield the desired cycloaliphatic dichlorosilane. The chlorosilane monomers underwent an oligomerization to produce cyclic oligomers of low molecular weight (~2,000 g/mol). Polysiloxanes were produced through the acid catalyzed ring opening polymerization of the cyclic oligomers to yield high molecular weight polysiloxanes (~45,000 g/mol). The polysiloxanes were then functionalized with a cycloaliphatic epoxy and alkoxy silane groups via hydrosilation. Monomers, oligomers, and polymers were characterized by 1H and 29Si NMR, FT-IR, and electrospray ionization mass spectroscopy. The photo-induced curing kinetics and activation energies were investigated using photo-differential scanning calorimetry. Differential scanning calorimetry was used in order to observe any physical changes in the films that are brought about due to the variation of the pendant groups. The cycloaliphatic substituents raised the glass transition temperature and affected the curing kinetics when compared to a methyl substituted polysiloxane. The activation energies were found to be 144.8 ± 8.1 kJ/mol for the methyl substituted and 111.0 ± 9.2 and 125.7 ± 8.5 kJ/mol for the cyclopentyl and cyclohexyl substituted polysiloxanes.
Ternary Evaluation of UV-Curable Seed Oil Inorganic/Organic Hybrid Coatings Using Experimental Design
Mark D. Soucek, 1* Aaron H. Johnson, 2 Jonathan M. Wegner 2
1Department of Polymer Engineering
University of Akron, Akron, OH 44325
2Department of Polymers & Coatings
North Dakota State University
Fargo, ND 58105
Abstract
Inorganic/organic hybrid coatings were prepared using epoxidized linseed oil with combinations of the two sol-gel precursors (titanium (IV) isopropoxide, tetraethyl orthosilicate), and a telechelic silicate based on a modified oligomeric caprolactone. The coatings were UV-cured with sulfonium initiators which concomitantly cured the epoxy functional organic phase and the sol-gel inorganic phase to form a co-continuous inorganic/organic system. A ternary experimental design was employed to elucidate the influence of inorganic modifier on the mechanical properties of the inorganic/organic hybrid coatings. Small angle X-ray scattering (SAXS) was used to evaluate radius of gyration of the metal-oxo-cluster. Various coating properties, such as hardness, impact resistance, adhesion, solvent resistance, and surface energy were investigated as a function of sol-gel precursors. Inorganic/organic hybrid coatings containing both tetraethyl orthosilicate and the modified caprolactone resulted in improved hardness and solvent resistance with no loss of impact strength. The inclusion of titanium (IV) isopropoxide in to the systems resulted in a systematic reduction in the coatings properties. This was attributed to inhibition of the organic crosslinking process as a consequence of absorption of ultraviolet light by the titanium-oxo-clusters.
UV-Curable Organic-Inorganic Hybrid Films Coatings: Based on Epoxidized Cyclohexene Derivitized Linseed Oil
Kunrong Zou and Mark D Soucek *
Department of Polymer Engineering, The University of Akron,
Akron, OH, 44325
Abstract
Organic-inorganic hybrid films based on epoxidized cyclohexene derivitized linseed oil (ECLO) and tetraethylorthosilicate (TEOS) oligomers were prepared via a UV-curing process. The kinetics of the hybrid materials were studied by photo-differential scanning calorimetry (DSC). In addition to the kinetics, the tensile properties, pencil hardness, pull-off adhesion, reverse impact resistance, solvent resistance, and abrasion resistance of the hybrid coatings were evaluated. Both a dynamic mechanical thermal analysis(DMTA) and thermogravimetric analysis (TGA) were used to investigate the viscoelastic and thermal properties of the hybrid films. The morphology of the hybrid film was characterized by atomic force microscope (AFM). Based on the results from the aforementioned evaluations of the coatings, the hybrid films exhibited higher pencil hardness, tensile strength, tensile modulus, fracture toughness, abrasion resistance, cross-link density, and thermal stability compared to the ECLO organic film. The Photo-DSC data showed that photo-curing speed of the hybrid materials increased with TEOS oligomers content. It was postulated that the TEOS oligomers were reactive diluents.
Cationic Photopolymerization of Epoxynorbornane Linseed Oils: Effect of Diluents
Zhengang Zong and Mark D. Soucek*
Department of Polymer Engineering, The University of Akron
Akron, OH 44325
Yubiao Liu and Jun Hu
Department of Chemistry, The University of Akron
Akron, OH 44325
Abstract
New epoxynorbornene linseed oils (ENLO) were prepared as a function of norbornene content. The cationic photopolymerization of the ENLOs was investigated using real-time infrared spectroscopy and photo-DSC. The effect of reactive diluent and non-reactive diluents on the polymerization rate was also studied. The diluents were found to decrease the viscosity of formulation and accelerate markedly the rate of polymerization of ENLO and increase their final conversion. The effected reactive diluent was compared for ENLO and epoxidized linseed oil (ELO). It was observed that the relative reactivity of oxiranes was not as important as the viscosity of the reacting system and proposed that the cationic photopolymerization of ENLO was controlled by diffusion.
UV-Curing Kinetics of Cycloaliphatic Epoxide Using Real-Time FT-IR Spectroscopy
Jianxia Chen, and Mark D. Soucek
Department of Polymer Engineering
University of Akron,
Akron, OH 44325-3909
Abstract
Photo-induced curing kinetics of cycloaliphatic epoxide coatings was investigated using real-time FT-IR spectroscopy with an optical fiber UV-curing system. The consumption of epoxy group as a function of time was obtained by monitoring the oxirane absorbance in the 789-746 cm -1 region. The effect of type of epoxide, hydroxyl equivalent weight, R-value (the ratio of oxirane to hydroxyl group), photoinitiator, and exposure time on the curing reaction was investigated. In general, the rate of curing was dependent on hydroxyl equivalent weight, R-value, type of epoxide and photoinitiator. For formulations without polyol, both initiator concentration and exposure time have minimal effect on the curing reaction. However, for formulations with polyol, the curing a reaction was dependent on initiator concentration.
Model for the Effects of Water on the Cationic UV-Curing of Cyclohexyl Epoxides
Mark D. Soucek and Jianxia Chen
Department of Polymer Engineering
University of Akron, OH 44325-0301
Abstract
The effect of relative humidity on the photo-induced curing kinetics of cyclohexyl epoxide and epoxide/polyol coating formulations were investigated in real-time using FT-IR spectroscopy. In total, five formulations were used in this study including a cyclohexyl epoxide without polyol, and four with polyols. The polyol formulations were varied with respect to ratio of epoxide to polyol, and molar functionality of the hydroxyl group. The formulations were exposed to a maximum of seven different relative humidities (6, 16, 20, 30, 51, 62, 75 RH). The curing speed and overall conversion of epoxy group passed through a maxima for all the formulations. The polyol had an effect on the hydrophilicity of the overall formulation. It was also found that water and polyols had synergistic effect on the UV-curing kinetics, in effect lowering the relative humidity to achieve a maxima. A model for UV-curing mechanisms at low, medium, and high relative humidity were proposed for both the systems with and without the polyols .
Photo-initiated Cationic Polymerization of Cycloaliphatic Epoxide/Siloxane Functionalized Polyol Hybrid Coatings
Jianxia Chen and Mark D. Soucek *
Polymers and Coatings Department
North Dakota State University, Fargo, ND 58105
Abstract
Polyols were reacted with tetraethyl orthosilicate (TEOS) and 3-isocyanatopropyltriethoxysilane (IPTES) to form siloxane functionalized polyols. The UV curing of these siloxane functionalized polyols were investigated using real-time FT-IR spectroscopy. The curing of TEOS modified polyols was dependent on the relative humidity. However, for the IPTES functionalized polyols the effect of relative humidity was dependent on the degree of IPTES functionalization. When the polyols were only partially functionalized with IPTES, the effect of relative humidity was minimal. But the curing of the fully functionalized polyol was dependent on relative humidity.
The siloxane functionalized polyols were formulated with a cycloaliphatic epoxide and cationic photoinitiator. The photo-induced curing kinetics of these cycloaliphatic epoxide/siloxane functinalized polyol coatings were also investigated. A maximum consumption of epoxide group was observed for epoxide/TEOS functionalized polyol coatings when the TEOS functionalized polyols increased from 0 to 48 wt%. However, if urethane linkage was incorporated into the siloxane functionalized polyols, the UV-curing speed was lowered due to the inhibition of the urethane linkage on the curing reaction. The effect of relative humidity on the UV-curing reaction of cycloaliphatic epoxide coatings was lowered by the incorporation of the TEOS functionalized polyols.
Synthesis and Photopolymerization of Norbornyl Epoxidized Linseed Oil
Jianxia Chen and Mark D. Soucek
Polymers and Coatings Department
North Dakota State University, Fargo, ND 58105
William J. Simonsick and Recep W. Celikay
Marshall R & D Laboratory
DuPont Automotive, Philadelphia, PA 19146
Abstract
Norbornyl epoxidized linseed oil was synthesized via Diels-Alder reaction of cyclopentadiene with linseed oil at high pressure (~ 200 Psi) and high temperature (240 °C), followed by an epoxidation using hydrogen peroxide with a quaternary ammonium tetrakis(diperoxotungsto) phosphate(3-) epoxidation catalyst.The products were characterized using 1H and 13C NMR, FT-IR, and electrospray ionization (ESI) mass spectroscopy. Photo-induced curing kinetics of norbornyl epoxidized linseed oil coatings was investigated using real-time FT-IR spectroscopy with a fiber optic UV-curing system. The norbornyl epoxidized linseed oil was formulated with three different divinyl ether reactive diluent. The effect of divinyl ether concentration and types of divinyl ether on the curing reaction was investigated. It was found that the curing rate of norbornyl epoxidized linseed oil was lower than that of cycloaliphatic epoxide, but higher than epoxidized linseed oil. The incorporation of divinyl ethers increased the curing rate and overall conversion of the epoxide groups. Of the three divinyl ether used, coating with triethyleneglycol divinyl ether (TEGDE) showed the highest curing rate and coating with cyclohexane dimethanol divinyl ether (CHDMDE) showed the lowest curing rate.
Siloxane Modified Cycloaliphatic Epoxide UV Coatings
Shaobing Wu, Matthew T. Sears, and Mark D. Soucek *
Department of Polymers & Coatings, North Dakota State University
Fargo, ND 58105
Abstract
Tetraethyl orthosilicate (TEOS) functionalized caprolactone diol and triol were used to modify cycloaliphatic diepoxide/caprolactone polyol cationic ultraviolet (UV) coatings. Two levels of the cycloaliphatic diepoxide (60 and 70 wt %) were used in the coating formulations. The siloxane functionalized polyols were added to the cycloaliphatic diepoxide/caprolactone polyol coating formulations as a replace of the polyols from 10 to 60 %. The resulting coatings were evaluated in terms of the Tukon hardness, tensile properties, wet pull-off adhesion, glass transition temperature, gloss, and dark cure. In addition, the viscosity of the coating formulations were measured as a function of coating pot-life. The addition of the siloxane functionalized polyols into coating formulations significantly improved the glass transition temperature, Tukon hardness, and tensile modulus. The wet adhesion and gloss were also improved. The addition of the siloxane functionalized polyols, however, resulted in reduction of the potlife of the coatings. It was surmised that the reaction between siloxane functionalized polyols and caprolactone polyols were responsible for the decrease in the potlife.
Synthesis of Reactive Diluents for Cationic Cycloaliphatic
Epoxide UV Coatings
Shaobing Wu, Matthew T. Sears, and Mark D. Soucek *
Department of Polymers & Coatings
North Dakota State University, Fargo, ND 58105
William J. Simonsick, Marshall R & D Laboratory
DuPont Automotive, Philadelphia, PA 19146
Abstract
Reactive diluents for cationic cycloaliphatic epoxide UV coatings were synthesized using caprolactone polyols and tetraethyl orthosilicate (TEOS). The structures of the TEOS functionalized polyols were characterized using IR, 1H-NMR, 29Si-NMR, and ESI-FTMS spectroscopy. The resulting siloxane functionalized polyols were used to formulate cationic UV coatings with 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane carboxylate (a cycloaliphatic diepoxide). The crosslinking reactions were monitored using IR and 29Si-NMR spectroscopy. The cured films were evaluated in terms of tensile properties, glass transition temperature. The resultant coatings showed greater tensile modulus, lower elongation, and higher glass transition temperature. In addition, the siloxane functionalized polyols also effectively reduced the viscosity of the coatings formulations. Based on the curing behaviors and spectroscopic data, possible crosslinking reaction(s) were postulated.
* To whom correspondence should be addressed
Effect of Siloxane Functionalized Caprolactone Polyols on
Photocurable Epoxy Coatings
Shaobing Wu and Mark D. Soucek *
Department of Polymers & Coatings
North Dakota State University, Fargo, ND 58105
* To whom all correspondences should be addressed.
Abstract
Cationic ultraviolet (UV) coatings were formulated using a cycloaliphatic diepoxide (3, 4-epoxycyclohexyl methyl-3’, 4’-epoxycyclohexane carboxylate) with caprolactone polyols. Both di and tri-TEOS (tetraethyl orthosilicate) functionalized caprolactone polyols were used to modify the UV coatings. The resulting coatings were cured, and evaluated in terms of the pencil hardness, MEK double rubs, crosshatch/pull-off adhesion, and the reverse impact resistance. Addition of the siloxane functionalized polyols into the caprolactone polyol/cycloaliphatic diepoxide coating formulations improved pencil hardness, MEK double rubs, and enhanced toughness of the coatings. When the addition of the siloxane functionalized polyols was less than 25 wt %, the resulting coatings showed significantly increased adhesion. In addition, modification of the coatings with the siloxane functionalized polyols also reduced surface tension, and improved film formation with reduced levels of surface wetting agent. Without the modification, the coatings exhibited a poor balance of the hardness and adhesion.