Lignin valorization by forming toughened lignin-co-polymers: Development of hyperbranched prepolymers for cross-linking Gopakumar Sivasankarapillai, Armando G. McDonald*, Hui Li Renewable Materials Program, Department of Forest, Rangeland and Fire Sciences, University of Idaho, PO Box 441132, Moscow, ID 83844-1132, USA article info Article history: Received 25 October 2011 Received in revised form 13 September 2012 Accepted 20 September 2012 Available online 18 October 2012 Keywords: Hyperbranched Polyesters Polyamines Polyamides Esterification Lignin abstract The preparation of hyperbranched polymers from a unique combination of commercially available A 2 ,B 3 and CB 1 3 -type monomers is presented. Direct melt condensation of aliphatic dicarboxylic acid (A 2 ) to compounds having trihydroxy groups ((B 3 ), triethanol- amine) and trihydroxy-monoamino groups ((CB 1 3 ), tris(hydroxymethyl)aminomethane) led to a series of hyperbranched polyesters with amine cores and amide linkages. Because of the monomers availability and simplicity of the synthetic process, hyperbranched poly(ester-amine-amide) (HBPEAA) materials can be readily scaled up. This approach was used to synthesize series of prepolymers with varying degree of branching (DB) and distance between branching points. Taking the advantage of reactivity differences of COOH with the NH 2 and OH groups, the hyperbranched polymer with different arrangement of amide linkage along the network was synthesized. The influence of reaction conditions such as monomer compositions, temperature and mode of mixing on the polymerization was examined. The DB of the HBPEAA (0.46e0.63) was dependant on the synthetic route. The HBPEAA exhibited moderate molecular weights as determined by NMR and ESI-MS. Thermogravimetric analysis revealed that the prepolymers exhibit reasonable thermal stability. The synthesized prepolymer was successfully utilized to copolymerize with 40% lignin to form toughened elastomeric materials with tensile strength of 12 MPa, Young’s modulus of 33 MPa and 149% elongation. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction Hyperbranched polymers (HBPs) are an attractive type of polymer due to its structure and functionality and have been much explored in recent years [1e4]. Owing to their highly branched polar structure and tailorable properties, HBPs are promising for future applications in many areas, for instance as biodegradable additives [5], tougheners [6], commercial coatings and resin application [7], biomedical applications [8]. Polyesters are a dominating this class of materials in the field of HBP [9] because of commercial availability of its monomers and, the relative ease of synthesis. In addition, polyesters have in general a high level of commercial impor- tance, and a variety of well known processing technologies are available. Thus, aliphatic, lower molar mass polyesters can be used very effectively in coatings and resins, and the combi- nation of the property profile of polyesters with high func- tionality, low viscosity, and improved miscibility make the hyperbranched products in these fields very attractive. Branched polyesters have been extensively reviewed recently and have been proved that its application for making useful material properties by our own recent work [10]. Some of the * Corresponding author. Tel.: þ1 208 885 9454; fax: þ1 208 885 6226. E-mail address: armandm@uidaho.edu (A.G. McDonald). Available online at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 47 (2012) 99 e108 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biombioe.2012.09.057