A pre-polyaddition mediation of castor oil for polyurethane formation Chandan Sharma, 1 Saji S. Edatholath, 1 A. Raman Unni, 2 T. Umasankar Patro, 3 Vinod K. Aswal, 4 Sangram K. Rath, 5 G. Harikrishnan 1 1 Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India 2 Automotive and Flexible Foam Division, Huntsman Polyurethanes, Navi Mumbai, Maharashtra 400710, India 3 Department of Materials Engineering, Defence Institute of Advanced Technology, Pune, Maharashtra 411025, India 4 Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085, India 5 Polymer Division, Naval Materials Research Laboratory, Ambernath, Maharashtra 421506, India Correspondence to: G. Harikrishnan (E - mail: hari@iitkgp.ac.in) ABSTRACT: We report a simple, serendipitous, two step mediation that overcomes the polyaddition threshold of castor oil during pol- yurethane formation. The mediation facilitates formation of polyurethane systems directly from castor oil without triricinolein chain extension or the use of supplementary hydroxyl compounds. The mediation involves refluxing castor oil with n-Butyl lithium in the presence of a solvent followed by water addition. We demonstrate the effectiveness of this mediation by successfully generating two important polyurethane systems (foam and coating) from castor oil. We identify that the mediation introduces two new compounds in castor oil namely, a lithiated diglyceride and a lithium salt of fatty acid. We characterize the new polyurethane synthesized for their hard-soft segmented morphology, glass transition temperature, and thermomechanical properties. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43964. KEYWORDS: biopolymers & renewable polymers; coatings; foams; polyurethanes Received 22 February 2016; accepted 22 May 2016 DOI: 10.1002/app.43964 INTRODUCTION The versatility of segmented polyurethane arises due to tailora- ble nature of polyaddition reaction between hydroxyl and iso- cyanate functionalities. This enables the formation of numerous polyurethane systems such as foams, coatings, adhesives, seal- ants, and biomedical implants. Castor oil is a major renewable hydroxyl component used in polyurethane synthesis. The inher- ent presence of hydroxyl functional groups in its triricinolein fraction makes it an attractive plant derived renewable hydroxyl compound for polyurethane synthesis. 1–24 However, triricinolein has limited reactivity with isocyanate functional groups due to several factors such as secondary functionality of hydroxyl groups, and steric effects of the dangling chain. 1–8 These factors manifest in several ways during polyaddition reaction as slow kinetics, insufficient molecular weight buildup, low rate of cross-linking, and high sol-fraction. It is almost impossible to overcome these deficiencies in pure castor oil generated polyur- ethane systems, even while the reaction is conducted in the presence of significant concentration of urethane catalysts. 24 These deficiencies are generally overcome by employing one or more of the following methods. A common way is to use other highly reactive supplementary compounds along with castor oil. This, however, severely limits the usable volume fraction of cas- tor oil. 7,8,13,17,24 Another way is to chemically modify triricino- lein chains so as to enhance the reactivity. 21–24 This method requires complex and extensive chemical modification process. In this article, we report a simple, serendipitous, two step media- tion that substantially enhanced castor oil reactivity with isocya- nate moieties and successfully generated polyurethane systems. This process involved refluxing pure castor oil with n-Butyl lith- ium in the presence of a solvent, followed by water addition. The reaction mixture is distilled and the residue is used for polymer- ization. We demonstrate that having all other ingredients and procedure remaining the same, while pure castor oil does not react, the new mediation successfully generates stable polyur- ethane foams and free standing films of coating. This indicates a simple pathway to generate various polyurethane systems com- pletely from castor oil without extensive chain modification of triricinolein or using supplementary hydroxyl compounds. EXPERIMENTAL Formulation We used standard formulations of urethane catalysts/surfactants that are employed for polyurethane foam and coating system generation. During both syntheses, we kept the weight fraction of castor oil and mediated castor oil, the same. The mass of V C 2016 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43964 43964 (1 of 9)