Progress in Organic Coatings 76 (2013) 157–164 Contents lists available at SciVerse ScienceDirect Progress in Organic Coatings jou rn al h om epage: www.elsevier.com/locate/porgcoat Castor oil-based hyperbranched polyurethanes as advanced surface coating materials Suman Thakur, Niranjan Karak ∗ Advanced Polymer and Nanomaterial Laboratory, Department of Chemical Sciences, Tezpur University, Tezpur 784028, India a r t i c l e i n f o Article history: Received 29 January 2012 Received in revised form 25 July 2012 Accepted 2 September 2012 Available online 25 September 2012 Keywords: Hyperbranched polyurethane Synthesis Castor oil Performance Surface coating a b s t r a c t 21st Century is treated as the century for highly branched macromolecules, because of their unique structural architecture and outstanding performance characteristics, in the field of polymer science. In the present study, castor oil-based two hyperbranched polyurethanes (HBPUs) were synthesized via A 2 + B 3 approach using castor oil or monoglyceride of the castor oil as the hydroxyl containing B 3 reactant and toluene diisocyanate (TDI) as an A 2 reactant along with 1,4-butane diol (BD) as the chain extender and poly(-caprolactone) diol (PCL) as a macroglycol. The adopted ‘high dilution and slow addition’ technique offers hyperbranched polymers with high yield and good solubility in most of the polar apro- tic solvents. Fourier transforms infra-red spectroscopy (FTIR) and nuclear magnetic resonance (NMR) analyses confirmed the chemical structure of synthesized polymers, while wide angle X-ray diffraction (WXRD) and scanning electron microscope (SEM) resulted the insight of their physical structures. The degree of branching was calculated from 1 H NMR and found to be 0.57 for castor oil based hyperbranched polyurethane (CHBPU), while it was 0.8 for monoglyceride based hyperbranched polyurethane (MHBPU). The studies showed that MHBPU and CHBPU exhibited tensile strength 11 MPa and 7 MPa, elongation at break 695% and 791%, scratch hardness 5 kg and 4.5 kg, gloss 84 and 72, respectively. Thermal properties like thermo stability, melting point, enthalpy, degree of crystallinity and glass transition temperature (T g ); and chemical resistance in different chemical media were found to be almost equivalent for both the polyurethanes. The measurements of dielectric constant and lost factor indicated that both the HBPUs behave as dielectric materials. Thus the synthesized HBPUs have the potential to be used as advanced surface coating materials. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Polyurethanes are an important class of polymers that have found many applications starting from coating, paint, foam, ther- mosetting, thermoplastic elastomer to fiber. A wide range of physical and chemical properties can be tailor made just by judi- cious variation of composition and structure of three basic building blocks, viz., macroglycol, diisocyanate, and chain extender of polyurethanes or by physical modification like blending or through interpenetrating network formation with other polymers [1]. So, proper design of polyurethane with appropriate structure and com- position of the components may result unique and useful properties for its different end applications. In the past few years, ecologically safe biodegradable polymeric materials have been the focus of momentous attention in aca- demic as well as industrial research for wide applications from a social, environmental, and energy standpoint, with the increas- ing emphasis on issues concerning waste disposal and depletion ∗ Corresponding author. Tel.: +91 3712267009; fax: +91 3712267006. E-mail addresses: karakniranjan@yahoo.com, nkarak@tezu.ernet.in (N. Karak). of non-renewable resources [2–5]. Vegetable oils are relatively cheap, most abundant, renewable natural resources available in large quantities from various oilseeds, such as castor, palm, lin- seed, soya bean, coconut, sunflower, Mesua ferrea L. seed oil and canola oils [6–10]. Different types of vegetable oils have been successfully utilized to synthesize biodegradable polyurethanes. Among them castor oil is a relatively inexpensive source of sec- ondary hydroxyl groups and a triglyceride of fatty acids with 92–95% ricinoleic acid [11]. This fatty acid contains a hydroxyl group at 12th carbon on the fatty acid chain. In addition to that HBPUs have received considerable attention now a day’s owing to their unique architectural features and unusual prop- erties like higher solubility, lower hydrodynamic diameter and lower melt as well as solution viscosity [12–14] compared to their linear analogs of equivalent mass. However, the synthetic protocol needs to be design carefully to avoid gel formation dur- ing polymerization of such hyperbranched polyurethanes. The use of castor oil or its monoglyceride helps to control such reac- tion due to low reactivity of secondary hydroxyl group present in the fatty acid chain. Thus the synthesis of castor oil-based hyperbranched polyurethane will be attempted in the present investigation. 0300-9440/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.porgcoat.2012.09.001