Alfa grass lignin obtained by the acetic acid/formic acid/water CIMV pulping process was characterized by FTIR and (1)H, (13)C-(1)H 2D HSQC, and (31)P NMR spectroscopies. Lignin samples purified by further dissolution/precipitation or basic hydrolysis steps were also analyzed. The CIMV alfa lignin is a mixture of low molar mass compounds (M(n) = 1500 g/mol) of SGH type with β-O-4 ether bonds as the major interunit linkage. The crude lignin contains fatty acids and residual polysaccharides. It also contains large amounts of acetate and hydroxycinnamates, mostly in the γ-position of β-O-4 interunit linkages. Although partial acetylation induced by the process cannot be excluded, the absence of aromatic acetates and acetylated polysaccharides in crude lignin demonstrates the mildness of the process. By combining smooth alkaline hydrolysis and dissolution/precipitation steps to the CIMV pulping, it is possible to produce a purified lignin with a composition and a structure quite analogous to that of the native polymer in the plant.
Summary: Cyclodi(ethylene succinate) (C2) easily reacts with poly(ethylene terephthalate) (PET) in the melt leading to the formation of high molar mass PET‐Poly(ethylene succinate) copolymers (PET‐PES). Copolyesters with a PET/C2 starting mass ratio of 90/10, 80/20, 70/30 and 50/50 were synthesized and characterized by 1H NMR and MALDI‐TOF MS. The 50/50 copolyester was almost random, while copolyesters with higher ethylene terephthalate contents exhibited some block copolymer character. MALDI‐TOF MS/SEC off‐line coupling was used to determine copolyester absolute average molar masses. The results indicate that the conventional SEC polystyrene calibration strongly overestimates copolyester molar masses. The melting temperatures and crystallinity of the 90/10, 80/20 and 70/30 copolyesters were significantly higher than those of comparable PET‐aliphatic polyester copolymers.
The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3-dialkylimidazolium salts, as reaction media. The 1 H NMR spectra of PGA oligomers were assigned and end-group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200-240 8C, because of monomer evaporation during the reaction. On the other hand, PGAs of DP n up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm þ Tf 2 N À ). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second-order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc) 2 was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn 2þ with ionic liquid anion instead of the polymer carboxylic acid end-groups. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: [3025][3026][3027][3028][3029][3030][3031][3032][3033][3034][3035] 2006
SUMMARY A two-step transesterification procedure was applied to combinations of difuranic diesters and both aliphatic and furanic diols. The reaction parameters (including the nature of the catalyst) were varied in both phases of the process and the results compared with those published for similar systems based on aromatic diesters. The best results related to the first phase of the synthesis were obtained using Zn(Ac0)2, Pb(AcO)2 or Ti(OBu), at 200°C with a large excess of diol. The second phase, which led to the actual polymer at 200-240°C, called upon the catalytic action of SnC204, S b 0 3 and Ti(OBu), and was prolonged until the viscosity of the media ceased to increase. Specific problems, related to some fragile moieties, limited the success of these polymerizations to a number of combinations which gave polyesters bearing regular structures and molecular weights in the tens of thousands.
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