Synthesis of phosphorus-containing polyurethanes and poly(urethane-acrylate)s

Turk J Chem (2017) 41: 630 – 647 Turkish Journal of Chemistry http://journals.tubitak.gov.tr/chem/ c TÜBİTAK ⃝ doi:10.3906/kim-1610-33 Research Article Synthesis of phosphorus-containing polyurethanes and poly(urethane-acrylate)s Mahir Burak SÜDEMEN1,∗, Hacer Ayşen ÖNEN2 Department of Polymer Science and Technology, Institute of Sciences and Technology, İstanbul Technical University, İstanbul, Turkey 2 Department of Chemistry, Faculty of Sciences and Letters, İstanbul Technical University, İstanbul, Turkey 1 Received: 14.10.2016 • Accepted/Published Online: 03.02.2017 • Final Version: 10.11.2017 Abstract: Solvent-based polyurethanes and poly(urethane-acrylate)s were synthesized using phosphorus-containing polyester polyols in order to compare the thermal properties of different polymer types. Since the location of the phosphorus group might have vital importance when comparing the thermal properties, phosphorus groups were kept on the pendant chains in poly(urethane-acrylate)s using phosphorus-containing urethane macromonomers while they were kept on the backbone in polyurethanes. The effect of molar mass of polyurethanes and pendant urethane chains of poly(urethane-acrylate)s on thermal properties was also investigated. Characterization of the synthesized polymers was carried out using FT-IR, GPC, NMR, and DSC followed by evaluation of the thermal properties. Key words: Polyurethane, poly(urethane-acrylate), phosphorus flame retardant 1. Introduction Research on high performance coating polymers has long been an interest for both the academic and industrial communities. In the last few decades, researchers have systematically created new approaches for coating polymers to meet the requirements of the application areas. One of the coating polymers that has gained importance in the last few decades in the industry is polyurethane. Polyurethane coatings find applications in many industries such as textile, leather, paint, aerospace, and metal coating in an increasing trend due to their advantageous properties such as mechanical durability, chemical resistance, and low temperature curing along with their highly elastomeric properties. 1−5 On the other hand, the main disadvantage of polyurethanes is their high price in the market due to expensive raw materials such as di-isocyanates. In addition to the high cost, the production of polyurethanes is more problematic compared to the other polymerization systems due to the high reactivity of isocyanates with impurities such as water. 6 Another important polymer type used in the coating industry is acrylic polymer. While the mechanical properties and chemical resistances of acrylic polymers are inferior compared to polyurethanes, their cost efficiency is making them the choice for low cost applications. The ability to tailor the required properties using the wide selection of commercially available acrylic monomers also makes this polymer type useful for coating industries such as paint, garment, furniture, and textile. The disadvantages of both polyurethane and polyacrylate coatings are somewhat overcome by hybrid coatings. One of the methods for obtaining optimized properties is through physical blending of the polyurethane and polyacrylate. 7 While higher mechanical properties, solvent and chemical resistances, and toughness are ∗ Correspondence: 630 SÜDEMEN and ÖNEN/Turk J Chem gained by polyurethanes, lower cost and outdoor resistance are provided by polyacrylates. Although it is a simple and effective way to achieve some of the hybrid properties, physical blending fails to provide the desired properties in performance coatings. 8 Another method researchers focus on is emulsion acrylic polymerization using polyurethane dispersions as the emulsifier. 9−12 In this case, the resulting polymer network generates more durable polymers compared to a simple blending system. However, this system fails to overcome the shortcomings of blending technology. For this reason, research on covalently bonded hybrid systems is recently attracting a lot of attention using urethane and acrylate chemistry. Covalent hybrid systems focus on the polymerization of acrylic terminated urethane macromonomers with acrylic monomers. 13−18 One of the distinct advantages of this method in performance coating development is the ability to combine different monomer types of the two different polymer technologies in order to obtain the desired properties from the coated substrate. In addition to the benefits gained by chemical versatility, the structural differences offered by urethaneacrylate polymers might provide interesting properties compared to linear polyurethanes or polyacrylates. Even though there are a variety of studies on the polymerization of urethane macromonomers with acrylic monomers, there are no reports that compare the final properties of poly(urethane-acrylate)s with those of linear polyurethanes. Therefore, in order to understand the effect of structural differences between linear polyurethanes and poly(urethane-acrylate)s on the final properties of polymers, we designed and synthesized phosphorus-containing polyurethanes and poly(urethane-acrylate)s. Phosphorus is kept on the backbone of polyurethanes and on the pendant urethane macromonomers of poly(urethane-acrylate)s in order to compare the efficiency of pendant chains of poly(urethane-acrylate)s with linear polyurethanes on thermal properties. After the polymerizations, the effect of phosphorus content and molar mass on the thermal properties of poly(urethaneacrylate)s and linear polyurethanes were discussed. 2. Results and discussion 2.1. Synthesis of polyester polyols Polyester polyols (PEPs) with two different molar masses were synthesized using adipic acid, 1,6-hexanediol, and neopentyl glycol via an esterification reaction as shown in Figure 1. The synthesized polyester polyols were designated as PEP-L and PEP-H, with “L” and “H” indicating low and high molar masses, respectively. Figure 1. Synthesis of polyester polyols. FT-IR spectra of the polyester polyols showed major polyester bands at 1729 cm −1 , 2866/2936 cm −1 , and 1371 cm −1 arising from carbonyl stretching vibration, CH 2 symmetric and asymmetric stretching vibrations, 631 SÜDEMEN and ÖNEN/Turk J Chem and gem-dimethyl stretching vibration of neopentyl glycol, respectively, as shown in Figure 2. The free hydroxyl group appeared as a broad band around 3500 cm −1 . Figure 2. FT-IR spectrum of polyester polyol. Phosphorus-containing polyester polyols (PPEPs) with varying phosphorus contents were synthesized as shown in Figure 3. In order to adjust the phosphorus contents, the molar ratio of phenyl dichlorophosphate and PEP-L/PEP-H was changed. While two of the PPEPs, PPEP-LP and PPEP-HP, were synthesized using PEP-H to be used in the synthesis of polyurethanes, the other two PPEPs, PPEP-LM and PPEP-HM, were synthesized using PEP-L to be used in the synthesis of macromonomers. Figure 3. Synthesis (...truncated)