We synthesized the alternating copolymers of 1,3-diene monomers with sulfur dioxide (SO 2 ) as a new class of thermally stable polymers by the radical copolymerization process and the subsequent hydrogenation. The copolymerizations of 2,4-hexadiene (HD), 1,3-butadiene (BD), and isoprene (IP) with SO 2 were carried out at -78 to 0 °C in toluene in the presence of tert-butyl hydroperoxide, which acts as one component in the redox initiating system in combination with SO 2 . The resulting poly(diene-alt-SO 2 )s were found to consist of highly controlled repeating units, that is, an alternating and 1,4-regiospecific repeating structure. Poly(HD-alt-SO 2 ) was soluble in several organic solvents, such as chloroform, nitromethane, tetrahydrofuran, acetone, and dimethyl sulfoxide. In contrast, poly(IP-alt-SO 2 ) was soluble only in dimethyl sulfoxide, whereas poly(BD-alt-SO 2 ) was insoluble in all of the solvents. The poly(diene-alt-SO 2 )s readily degraded upon heating because of the expected fast depolymerization. We have demonstrated that the thermal stability of the poly(diene-alt-SO 2 )s is modified by the hydrogenation of the double bond in the polymer main chain. The hydrogenation of poly(HD-alt-SO 2 ) resulted in a drastic increase in the 5% weightloss temperature from 135 to 317 °C.
A comprehensive understanding of the structure and properties of gramineous lignocelluloses is needed to facilitate their uses in biorefinery. In this study, lignocelluloses from fractionated internode tissues of two taxonomically close species, Erianthus arundinaceus and sugarcane (Saccharum spp.), were characterized. Our analyses determined that syringyl (S) lignins were predominant over guaiacyl (G) or p-hydroxyphenyl (H) lignins in sugarcane tissues; on the other hand, S lignin levels were similar to those of G lignin in Erianthus tissues. In addition, tricin units were detected in sugarcane tissues, but not in Erianthus tissues. Distributions of lignin inter-monomeric linkage types were also different in Erianthus and sugarcane tissues. Alkaline treatment removed lignins from sugarcane tissues more efficiently than Erianthus tissues, resulting in a higher enzymatic digestibility of sugarcane tissues compared with Erianthus tissues. Our data indicate that Erianthus biomass displayed resistance to alkaline delignification and enzymatic digestion.
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