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More than 23 million tonnes of lignin are produced annually in the US from wood pulping and 98% of this lignin is burnt. Therefore, creating products from lignin, such as plastics, offers an approach for obtaining sustainable materials in a circular economy. Lignin-based copolymers were synthesized using a single pot, solvent free, melt condensation reaction. The synthesis occurred in two stages. In the first stage, a biobased prepolymer consisting of butanediol (BD, 0.8-1 molar content) and a diacid (succinic (SA), adipic (AA) and suberic acids (SuA), with varying amounts of diaminobutane (DAB, 0-0.2 molar content) was heated under vacuum and monitored by Fourier transform infra-red (FTIR) spectroscopy and electrospray ionization-mass spectrometry (ESI-MS). In the second stage, prepolymer was mixed with a softwood kraft lignin (0-50 wt.%) and further reacted under vacuum at elevated temperature. Progression of the polymerization reaction was monitored using FTIR spectroscopy. The lignin-copolyester/amide properties were characterized using tensile testing, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. Lignin co-polymer tensile (strength 0.1-2.1 MPa and modulus 2 to 338 MPa) properties were found to be influenced by the diacid chain length, lignin, and DAB contents. The lignin-copolymers were shown to be semi-crystalline polymer and have thermoplastic behavior. The SA based copolyesters/amides were relatively stiff and brittle materials while the AA based copolyesters/amides were flexible and the SuA based copolyesters/amides fell in-between. Additionally, > 30 wt.% lignin the lignin- copolyesters/amides did not exhibit melt behavior. Lignin-co-polyester/amides can be generated using green synthesis methods from biobased building blocks. The lignin- copolyesters/amides properties could be tuned based on the lignin content, DAB content and diacid chain length. This approach shows that undervalued lignin can be used in as a macromonomer in producing thermoplastic materials.

Abstract: The preparation of hyperbranched polymers from a unique combination of commercially available A2, B3 and CB1 3-type monomers is presented. Direct melt condensation of aliphatic dicarboxylic acid (A2) to compounds having trihydroxy groups ((B3), triethanolamine) and trihydroxy-monoamino groups ((CB1 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 NH2 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 (0.46–0.63) 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. [Copyright &y& Elsevier]