Modification of Kraft Lignin to Expose Diazobenzene Groups: Toward pH- and Light-Responsive Biobased Polymers.
A pH- and light-responsive polymer has been synthesized from softwood kraft lignin by a two-step strategy that aimed to incorporate diazobenzene groups. Initially, styrene oxide was reacted with the phenolic hydroxyl groups in lignin, to offer the attachment of benzene rings, thus creating unhindered reactive sites for further modifications. The use of advanced spectroscopic techniques ((1)H and (31)P NMR, UV and FTIR) demonstrated that the reaction was quantitative and selective toward the phenolic hydroxyl groups. In a second step, the newly incorporated benzene rings were reacted with a diazonium cation to form the target diazobenzene motif, whose formation was again thoroughly verified. As anticipated, the diazobenzene-containing kraft lignin derivatives showed a pH-dependent color change in solution and light-responsive properties resulting from the cis-trans photoisomerization of the diazobenzene group.
Department of Chemical Sciences and Technologies, University of Rome "Tor Vergata" , Via della Ricerca Scientifica 1, 00133 Rome, Italy.|Wallenberg Wood Science Center (WWSC), Department of Fiber and Polymer Technology, KTH Royal Institute of Technology , SE-100 44 Stockholm, Sweden.
Antoine
A
Duval
Department of Chemical Sciences and Technologies, University of Rome "Tor Vergata" , Via della Ricerca Scientifica 1, 00133 Rome, Italy.
Heiko
H
Lange
Wallenberg Wood Science Center (WWSC), Department of Fiber and Polymer Technology, KTH Royal Institute of Technology , SE-100 44 Stockholm, Sweden.
Martin
M
Lawoko
Department of Chemical Sciences and Technologies, University of Rome "Tor Vergata" , Via della Ricerca Scientifica 1, 00133 Rome, Italy.
Claudia
C
Crestini
D001554:Benzene / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008027:Light; D008031:Lignin / Q000737:chemistry*; D055668:Photochemical Processes
C076151:Kraft lignin; D008031:Lignin; D001554:Benzene