Lignin acrylate derivatives and their behaviors in free radical copolymerizations

Guaiacol and hydroxypropyl-guaiacol were taken as model compounds for lignins and hydroxypropyl lignins to study their vinylation and copolymerization behaviors. Lignin model compounds and lignin were subjected to reaction with isocyanatoethyl methacrylate (IEM) using dibutyltin dilaurate as catalyst. The acrylate derivatives were characterized by elemental analysis, UV, IR, ¹H-NMR, and ¹³C-NMR spectroscopy.

The acrylated lignin model compounds, guaiacol-IEM urethane (GIU) and hydroxypropyl-guaiacol-IEM urethane (HPGIU), were copolymerized with methyl methacrylate (MMA) and styrene (St) through free radical mechanism. Solution copolymerizations in 1,2-dichloroethane: ethanol were initiated by benzoyl peroxide. The monomer reactivity ratios were investigated for these copolymerization combinations. The copolymer compositions were analyzed by UV for GIU-co-MMA and HPGIU-co-MMA, while methoxyl content determination by HI-GC was used to determine compositions of styrene-based copolymers. The copolymers were characterized by gel permeation chromatography (GPC), and by IR and NMR spectroscopy. The reactivity ratios were computed by use of the Fineman-Ross linearization method, by the KelenTudos equation and by the Yezrielev-Brokhina-Roskin (YBR) numerical method. A comprehensive analysis with respect to the methods used to derive the ratios has shown that the Kelen-Tudos method and the YBR method produce diagnostic reactivity ratios. A great copolymerization tendency of lignins and hydroxypropylated lignins is predicted from the reactivity ratios of the lignin models. A statistical treatment of the model reactivity ratios lead to prediction for chain sequence length distribution of the copolymers formed.

Hydroxybutyl lignin IEM urethanes (HBLIU's) were copolymerized with a vinyl-terminated poly(butadiene-acrylonitrile) macromer and MMA to study the copolymerization behaviors of macromolecular lignin acrylate derivatives. The crosslinked films with desired properties were cast from methylene chloride, with benzoyl peroxide as an initiator. The copolymerized network polymers were characterized by sol fraction measurements, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and by scanning electron microscopy (SEM). The influences of vinyl content in lignin acrylate derivatives and the ratio of lignin derivatives to vinyl monomer or macromer were studied with respect to structure-property relationship in the copolymers.