Study On Preparation Of Lignin-Based Graft Polymers By Atom Transfer Radical Polymerization

Lignin is abundant and renewable biomass resources.Controllable chemical modification of the lignin structure is an important direction of lignin utilization.Atom transfer radical polymerization?ATRP?method can control polymerization reaction and using different monomers to graft from lignin can produce lignin-based polymers with different properties,which is an important way to realize the high-value utilization of lignin.The hydroxyl content of alkali lignin,acid precipitated lignin,and cellulolytic enzyme lignin was determined by phosphorus-31 nuclear magnetic resonance spectrosocopy(³¹P-NMR).The alkali lignin with a highest hydroxyl content was selected as the raw material for grafting.Varying the added amount of2-bromoisobutyryl bromide?Bi BB?and triethylamine?TEA?can obtain lignin macroinitiator?Lignin-Br?with different bromine content.Acrylamide?AM?was introduced into the lignin structure through ATRP reaction to prepare lignin grafted poly?acrylamide?polymer?L-g-PAM?and its morphology is different from lignin and Lignin-Br.Thermogravimetric analysis?TG?shows that the thermal stability of lignin,Lignin-Br and L-g-PAM decreased in turn.Differential scanning calorimetry?DSC?found that the glass transition temperature?T_g?of L-g-PAM was 191?,which indicates that the presence of lignin core reduced the toughness of L-g-PAM.Through ATRP reaction system,the amount of acrylonitrile monomer was changed to obtain a series of lignin grafted poly?acrylonitrile?polymers?Lg-PANs?.FT-IR shows that the intensity of the C?N absorption peak increased with the increase of the added amount of acrylonitrile in L-g-PANs.X-ray photoelectron spectroscopy?XPS?measured the surface element of L-g-PAN,Lignin-Br,Lignin.Br3d peak in Lignin-Br was obvious,the N1s peak of L-g-PAN was obvious,and the three samples had C1s and O1s peak.A narrow area scan of their C1s peak revealed three types of carbon,which belonged to C-C,C-H and C-OH,C-O-C and O-C=O,but lignin had no O-C=O carbon absorption peak.Series of copolymers have poor solubility due to the introduction of PAN.TG analysis shows that all L-g-PANs had a gentle weight loss curve,the residual carbon decreased with the increase of PAN content,initial thermal decomposition temperature?T_d?of all L-g-PANs were enhanced,and their thermal stability were significantly improved.Through the ATRP method,using butyl acrylate?BA?and vinyl acetate?VAc?as monomers to obtain lignin grafted poly?butyl acrylate?polymer?L-g-PBA?,lignin grafted poly?ethyl acetate?polymer?Lg-PVAc?and lignin grafted poly?butyl acrylate-ethyl acetate?polymer(L-g-P?BA-VAc?.L-g-PBA is used as an initiator to graft PVAc to obtain lignin grafted poly?butyl acrylat?-poly?ethyl acetate??L-g-PBA-PVAc?.Gel permeation chromatography?GPC?shows that the molecular weight of the four grafted polymers was significantly larger than that of lignin and Lignin-Br,but the low monomer conversion rate resulted in generally low molecular weight of lignin-based grafted polymer.TG analysis shows that T_d and T_maxof the four grafted polymers were higher than lignin and Lignin-Br,and their thermal stability was all enhanced to a certain extent.DSC shows that the T_g of L-g-PBA-PVAc was less than Lg-PBA but greater than L-g-PVAc,and the Tg of L-g-P?BA-VAC?was the largest in the series polymers;this reveals that the presence of PBA soft chains can enhance toughness and reduce Tg,the presence of a large number of lignin cores can increase Tg,and the connection sequence of PBA and PVAc can also affect the ability of the side chain to move.After synthesizing the monomer 5-acetylaminopentyl acrylate?AA?,the lignin grafted 5-acetylaminopentyl acrylate polymer?L-g-PAA?was obtained by using Me₆TREN as a ligand through ATRP reaction system.TG analysis shows T_d and T_maxof L-g-PAA were high than lignin and Lignin-Br,the weight loss rate further reduced after 550?,the decomposition degree of L-g-PAA was higher than lignin and Lignin-Br,and its residual carbon content was also the lowest.