Synthesis and Characterization of Castor-Oil-Modified Hyperbranched Polyurethanes Niranjan Karak,* Sravendra Rana, Jae Whan Cho Department of Textile Engineering, Konkuk University, Seoul 143-701, Korea Received 14 July 2008; accepted 13 October 2008 DOI 10.1002/app.29468 Published online 13 January 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A series of castor-oil-modified hyperbranched polyurethanes were synthesized via an A 2 þ B 3 approach based on castor oil, macroglycol poly(e-caprolactone)diol or poly(ethylene glycol) (PEG), and diphenyl methane diisocya- nate, with or without a chain extender. The yield of the prod- uct was 95%, and the polymers were soluble in common organic polar solvents. The synthesized polymers were char- acterized with Fourier transform infrared spectroscopy, NMR, wide-angle X-ray diffraction, and gel permeation chromatog- raphy measurements. The degree of branching of the poly- mers was calculated from their respective 1 H-NMR spectra with the help of model compounds and found to be varied from 0.7 to 0.8. The hard-segment content, the nature of the macroglycol, and the composition of the polymers had promi- nent effects on the thermal degradation and crystallization of the hyperbranched polymers. The crystallization of poly(e- caprolactone) and PEG as soft segments occurred well in the hyperbranched polymers. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 736–743, 2009 Key words: hyperbranched; polyurethanes; synthesis; thermal properties INTRODUCTION The study of the structure–property relationships in polyurethanes has gained tremendous importance because of their various applications 1,2 as thermo- plastic elastomers, foams, fibers, adhesives, coating materials, and so forth. The properties of polyur- ethanes can be monitored by the judicious variation of chemical constituents as well as the composition of the soft and hard segments. A large number of reports are available in the literature on the effects of the structures of hard segments and soft segments on the physical, thermal, and chemical properties of these polymers. 3–5 Today, the high price of petroleum raw materials, scarcity of petroleum products, and stringent environ- mental rules and regulations are pressuring synthetic polymer scientists to use natural renewable resources as the feedstocks for the development of many indus- trially important polymers. These feedstocks, espe- cially vegetables, are well accepted by synthetic polymer chemists for social, economic, and environ- mental reasons. Fortunately, many researchers are now using renewable natural resources as their feed- stocks for the development of many polymers. 6–15 Castor oil is one of the most important renewable resources for the production of many industrial poly- mers and is obtained from the castor seed of the cas- tor plant, Ricinus communis. The unusual composition and chemistry of castor oil make it quite valuable for many applications, including the preparation of polyurethane. 16 Approximately 90% of fatty acids in castor oil are ricinoleic acid. Ricinoleic acid, a mono- unsaturated, 18-carbon fatty acid, has a hydroxyl- functional group at the twelfth carbon; this is a very uncommon property for a biological fatty acid and is the main driving point for the direct use of this oil as a hydroxyl-containing trifunctional monomer (A 3 ). The vegetable oil also has other advantages such as (1) renewability, (2) easy availability in a large quan- tity, (3) environmental friendliness, (4) biodegradabil- ity, and (5) overall low cost. Nonlinear highly branched polymers such as den- drimers and hyperbranched polymers have received considerable attention in recent years because of their unique architectural features and unusual properties. 17–19 These macromolecules exhibit many useful properties such as higher solubility and lower melt and solution viscosity in comparison with their linear analogs of the same molar mass because of the highly functionalized, three-dimensional, globular, unentangled structure. 20–22 Journal of Applied Polymer Science, Vol. 112, 736–743 (2009) V V C 2009 Wiley Periodicals, Inc. *Present address: Department of Chemical Sciences, Tezpur University, Tezpur 784028, India. Correspondence to: J. W. Cho (jwcho@konkuk.ac.kr). Contract grant sponsor: Korea Science and Engineering Foundation (funded by the Science Research Center/ Engineering Research Center program of the Ministry of Science and Technology/Korea Science and Engineering Foundation); contract grant number: R11-2005-065. Contract grant sponsor: Tezpur University.