@article{cui_sun_argyropoulos_2014, title={Fractional Precipitation of Softwood Kraft Lignin: Isolation of Narrow Fractions Common to a Variety of Lignins}, volume={2}, ISSN={["2168-0485"]}, DOI={10.1021/sc400545d}, abstractNote={In a manner similar to crude oil, technical lignins need refining if their potential as reactive polyphenols of well-defined molecular weight polymers and oligomers is to be actualized. In this paper, we demonstrate that a continuum of narrow fractions can be isolated by the incremental addition of a nonpolar solvent (hexanes) in a polar (acetone) solution of softwood wood kraft lignin. Three distinct commercial samples of softwood kraft lignin were used to examine the validity of the developed protocol using detailed chromatographic and quantitative functional group analytical methods. It was shown that all samples contain a common relatively monodisperse fraction of a polyphenolic material that can be isolated from the different lignins in yields ranging between 10 and 20% w/w. The versatility of the developed fractional precipitation protocol was further validated by creating artificial physical mixtures of the examined lignins in different proportions and isolating from them precisely calculated fract...}, number={4}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, author={Cui, Chengzhong and Sun, Runkun and Argyropoulos, Dimitris S.}, year={2014}, month={Apr}, pages={959–968} }
 @article{argyropoulos_sadeghifar_cui_sen_2014, title={Synthesis and Characterization of Poly(arylene ether sulfone) Kraft Lignin Heat Stable Copolymers}, volume={2}, ISSN={["2168-0485"]}, DOI={10.1021/sc4002998}, abstractNote={In this effort we aim at documenting our understanding of using the phenolic hydroxyl groups of technical softwood kraft lignin in replacing the multifunctional phenolic component required for the synthesis of poly(arylene ether) sulfones. To do this we use a two-pronged approach that uses fractionated softwood kraft lignin whose phenolic hydroxyl groups have been systematically protected in order to avoid gelation when copolymerized with 4, 4′-diflourodiphenyl sulfone (DFDPS). This has been done by careful 31P NMR profiling of the various hydroxyl groups present in the lignin as a function of the degree of phenolic hydroxyl group protection. For all copolymers, weight average molecular weights (Mw), polydispersity indices (PDI), glass transition temperatures (Tg), and thermal stability profiles (TGA) were obtained, providing an integrated picture of the scientific and technological ramifications of this work. Overall, this effort provides the foundations for creating lignin copolymers of controlled and m...}, number={2}, journal={ACS SUSTAINABLE CHEMISTRY & ENGINEERING}, author={Argyropoulos, Dimitris S. and Sadeghifar, Hasan and Cui, Chengzhong and Sen, Sanghamitra}, year={2014}, month={Feb}, pages={264–271} }
 @article{sadeghifar_cui_argyropoulos_2012, title={Toward Thermoplastic Lignin Polymers. Part 1. Selective Masking of Phenolic Hydroxyl Groups in Kraft Lignins via Methylation and Oxypropylation Chemistries}, volume={51}, ISSN={["0888-5885"]}, DOI={10.1021/ie301848j}, abstractNote={This work offers a comprehensive understanding of the conditions required for the selective masking of the phenolic hydroxyl groups in technical kraft lignins, which is pivotal in determining their subsequent chemical and thermal reactivity. To this effect, we have examined the chemistry and developed the conditions for the facile, mild, and selective masking of the phenolic hydroxyl groups in softwood and hardwood kraft lignins. We have compared two series of methylated softwood kraft lignins synthesized using different methylation chemistries. Our data show that (when used as specified) dimethyl sulfate in aqueous NaOH selectively converts the phenolic hydroxyl groups of kraft lignin to its methylated derivatives without apparent side reactions. In contrast, methyl iodide (in the presence of excess K2CO3 in N,N-dimethylformamide) was found to be rather ineffective and unselective. Various milder methylation conditions were also examined for both softwood and hardwood kraft lignins using dimethyl sulfate...}, number={51}, journal={INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH}, author={Sadeghifar, Hasan and Cui, Chengzhong and Argyropoulos, Dimitris S.}, year={2012}, month={Dec}, pages={16713–16720} }