Solvent‐ and Halogen‐Free Modification of Biobased Polyphenols to Introduce Vinyl Groups: Versatile Aromatic Building Blocks for Polymer Synthesis

Abstract

Various biobased polyphenols (lignins and condensed tannins) were derivatized with vinyl ethylene carbonate, a functional cyclic carbonate, to obtain multifunctional aromatic polymers bearing vinyl groups. The reaction was optimized on a condensed tannin and soda lignin. In both cases, full conversion of the phenol groups was achieved in only 1 h at 150 °C without solvent and with K CO as a cheap and safe catalyst. This reaction was later applied to other condensed tannins and technical lignins (Kraft and organosolv), showing only little dependence on the chemical structure of the polyphenols. The obtained derivatives were thoroughly characterized by H and P NMR spectroscopy, FTIR spectroscopy, and size-exclusion chromatography. The developed method was compared with previously published protocols for the introduction of vinyl groups on lignin, and shows promising advances toward the modification of biobased polyphenols according to green chemistry principles. The obtained macromolecules show great potential as highly versatile biobased aromatic building blocks for the synthesis of polymers through, for example, radical, metathesis, or thiol-ene reactions.

Mild and controlled lignin methylation with trimethyl phosphate: towards a precise control of lignin functionality

“…Trimethyl phosphate (TMP, 99%) was purchased from Acros Organics and used as received. The yields were calculated taking into account the increase in mass caused by grafting, as previously reported, 31 according to eqn (1):…”

“…In order to avoid such solvents, we have recently developed several reactions with cyclic carbonates, which can act as both solvent and reagent to modify lignins. 31,32,34 Under these conditions, it is possible to quantitatively derivatize lignins without the need for any organic solvents. Following these results, we applied a similar strategy to methylate lignins with TMP as a mild methylating agent.…”

Clicking Biobased Polyphenols: A Sustainable Platform for Aromatic Polymeric Materials

“…However, the reaction still requires a quantitative amount of an organic base (TBAB) as the catalyst and generates toxic byproducts. In recent work, Duval and Averous used VEC; a five‐membered‐ring cyclic carbonate . Beyond solvent‐free conditions, the reaction works with only a catalytic amount of K 2 CO 3 (0.1 equiv) and does not generate toxic byproducts.…”

Palladium-Catalyzed Functionalization of Kraft Lignin: Ether Linkages through the Telomerization Reaction

“…This hasb een achieveds of ar using mainly conventional synthetic methods. [12][13][14] More recently,t he use of catalytic andc lean reactions to allylate the hydroxyl groups in lignins has emerged as an important issue. [9] Lignin ethers can be obtainedf rom aW illiamson reaction with alkyl halides or epichlorhydrine.…”

“…[10,11] More specifically, allyl ethers that introduce CÀCu nsaturations within the biopolymer are interesting for furtherc hemical transformations, and have thus attracted more recent interest. [12][13][14] More recently,t he use of catalytic andc lean reactions to allylate the hydroxyl groups in lignins has emerged as an important issue. Thus, the palladium-catalyzed allylation of organosolv lignin has been recently performed with allylcarbonate, [15] and it is likely that other allylic groups should be readily accessible from metal catalyzed transformations.…”