Lignins are produced by all vascular plants and they represent one of the most abundant groups of biopolymers in nature. Lignin chemistry research, which has been of great importance for the progress of pulping technologies, has been plagued by the difficulties of its isolation and characterization. The pioneering work of Karl Freudenberg in the 1950’s with synthetic models of lignin paved the way for a detailed structural characterization of many lignin substructures. His work with the so-called “synthetic lignins” or dehydrogenative polymers (DHP) also laid a foundation for understanding how different lignin substructures are formed, reinforcing the already existing theory of lignin polymerization. However, subsequent structural characterizations of DHPs and lignins have repeatedly put this theory to the test. In the past decade, even a new radically different hypothesis for lignin polymerization has emerged and is sustained by a few researchers in the field. In this work, DHPs were produced from phenolic monomers, mostly coniferyl alcohol, a common lignin monomer, in a variety of reaction conditions. This was done in order to establish how different chemical factors, potentially active in the plant cell wall during lignin polymerization, influence the polymer’s final properties. In the presence of nicotine amide adenine dinucleotide (NADH), a quinone methide model, which is an intermediate formed during lignin polymerization, was effectively reduced. An equivalent reduced structure was produced during DHP synthesis in the presence of NADH. These studies showed that reduction might take place during oxidative polymerization, possibly explaining how reduced lignin structures are formed in the plant cell wall. Another reductive agent, ascorbic acid, was also tested during synthesis of DHPs. It displayed a totally different effect than NADH, probably due to its anti-oxidant nature, by altering the final amounts of certain inter-unit substructures, in favour of β-O-4′ structures, which are so prominent in natural lignins. Furthermore, the new suggested model for lignin polymerization, stating that lignin itself possesses the ability for template replication, was tested by synthesizing DHPs in the presence of a simple β-β′ substructure model. The DHPs produced the same amounts of β-β′ substructures as a control synthesis without the model structure, indicating that no replication had occurred. Finally, the role of the monolignol γ-carbon oxidation state in lignin polymerization, was studied. Hypothetically, lignin- like polymers could be produced by the plant, using monolignol biosynthetic precursors which exhibit γ-carbonyl groups instead of an alcohol group, like the common lignin monomer. Synthetic lignins produced with ferulic acid, coniferaldehyde and the normal monolignol, coniferyl alcohol, displayed important differences in chemical and physical properties. Both the ferulic acid and coniferaldehyde polymers exhibited almost no saturated inter-unit substructures and very few cyclic structures, both of which are very common in coniferyl alcohol dehydrogenative polymers and natural lignins. This could have significant implications for the formation of an important type of lignin carbohydrate complexes (LCC). Also the hydrophobicity of the alcohol-type polymer was lower than the other two. The biological implications of all these findings are discussed and some suggestions are made to explain how all these factors might affect lignin polymerization and structure in nature. / QC 20100811

ABSTRACT HYDROGEL FROM TEMPLATE POLYMERIZATION OF METHACRYLIC ACID AND N-VINYLPYRROLIDONE AND POLYETHYLENEOXIDE Yelda, Erdem Department of Polymer Science and Technology Supervisor : Prof. Dr. Teoman Tin&ccedil / er April 2005, 53 pages This theses covers the preparation and the characterization of a rigid hydrogel from N-Vinyl pyrrolidone-methacrylic acid (VP-MAA) monomers and polyethyleneoxide (PEO) polymer. Hydrogels are hydrophillic natured three dimensional networks which can swell in the presence of water. The VP-MAA-PEO hydrogel was obtained by template polymerization which can be defined as a method of polymer synthesis in which specific interactions consists of the preparation of a polymer (daughter polymer) in the presence of a macromolecular compound (template polymer). The hydrogel of VP-MAA-PEO was synthesized by using azobisisobutyronitrile (AIBN) as the initiator, tetrahydrofurane (THF) as the solvent and the temperature of the system was kept constant at 50&ordm / C. Two kinds of VP-MAA-PEO hydrogels were prepared. The only difference between them were their solubilities in water. This difference is due to different crosslinking agent weight percentages of ethylene glycol dimethacrylic (EGDMA) to make the hydrogel water insoluble. The comparison of two hydrogels were carried by swelling behaviors at different pH values and different temperatures. Thermal stability of these two hydrogels were also examined by differential scanning calorimetry (DSC), spectroscopic properties were compared by using FTIR spectrometer and morphological studies were analyzed by using scanning electron microscope (SEM).

Made available in DSpace on 2014-12-17T15:42:31Z (GMT). No. of bitstreams: 1 ClaudioLV.pdf: 1496908 bytes, checksum: 9da02c26d9351b21019488117fc27924 (MD5) Previous issue date: 2007-05-28 / Dispersions composed of polyelectrolyte complexes based on chitosan and poly(methacrylic acid), PMAA, were obtained by the dropping method and template polymerization. The effect of molecular weight of PMAA and ionic strength on the formation of chitosan/poly(methacrylic acid), CS/PMAA, complexes was evaluated using the dropping method. The increase in molecular weight of PMAA inhibited the formation of insoluble complexes, while the increase in ionic strength first favored the formation of the complex followed by inhibiting it at higher concentrations. The polyelectrolyte complexation was strongly dependent on macromolecular dimensions, both in terms of molecular weight and of coil expansion/contraction driven by polyelectrolyte effect. The resultant particles from dropping method and template polymerization were characterized as having regions with different charge densities: chitosan predominating in the core and poly(methacrylic acid) at the surface, the particles being negatively charged, as a consequence. Albumin was adsorbed on templatepolymerized CS/PMAA complexes (after crosslinking with glutardialdehyde) and pH was controlled in order to obtain two conditions: (i) adsorption of positively charged albumin, and (ii) adsorption of albumin at its isoelectric point. Adsorption isotherms and zeta potential measurements showed that albumin adsorption was controlled by hydrogen bonding/van der Waals interactions and that brushlike structures may enhance adsorption of albumin on these particles / Dispers?es formadas a partir de complexos polieletrol?ticos de quitosana e de poli(?cido metacr?lico), PMAA, foram obtidas tanto pelo m?todo de gotejamento, como pelo m?todo de polimeriza??o em molde. O efeito da massa molar do PMAA e da for?a i?nica na forma??o dos complexos de quitosana/poli(?cido metacr?lico), CS/PMAA, foi avaliado usando o m?todo de gotejamento. O aumento da massa molar do PMAA inibiu a forma??o dos complexos insol?veis, enquanto o aumento da for?a i?nica primeiramente favoreceu a forma??o dos complexos, depois a inibiu, em altas concentra??es de eletr?litos de baixa massa molar. A complexa??o dos polieletr?litos foi fortemente dependente das dimens?es macromoleculares, tanto em termos da massa molar quanto do efeito de expans?o/contra??o dos novelos, devido ao efeito polieletrol?tico. As part?culas resultantes tanto do m?todo de gotejamento, como da polimeriza??o em molde foram caracterizadas por apresentarem regi?es com diferentes densidades de carga: a quitosana predominantemente presente na regi?o central e o poli(?cido metacr?lico), na superf?cie, sendo, portanto, as part?culas carregadas negativamente. A albumina foi adsorvida nos complexos de CS/PMAA obtidos por polimeriza??o em molde (depois de sofrerem reticula??o covalente usando glutaralde?do) e o pH foi controlado a fim de se obter duas condi??es: (i) adsor??o de albumina carregada positivamente e (ii) adsor??o de albumina em seu ponto isoel?trico. As isotermas de adsor??o e as medidas de potencial zeta mostraram que a adsor??o da albumina foi controlada por liga??es de hidrog?nio/intera??es de van der Waals e que as estruturas em forma de escova puderam aumentar a adsor??o da albumina nessas part?culas