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SynopsisCellulose fractions of different molecular weights were subjected to dynamic thermogravimetric analysis in a nitrogen atmosphere. From the experimental data, activation energies and reaction orders were obtained following the Freeman-Carroll and Broido methods. The thermal stabilities of the samples were estimated taking into account the values of T,, T,,,, and E,. The results show that thermal stability increases as the molecular weight increases. It was also found that the cellulose pyrolisis process cannot be described as having a single value of E, over the entire pyrolisis range. The dependence of E, on molecular weight is also discussed.

SynopsisThe intended objective of this work was to bring together two immiscible polymers, polyarylate (PAr) and Phenoxy [poly(hydroxy ether of bisphenol-A)], preparing ternary mixtures with a third component, poly(buty1ene terephthalate) (PBT). Experimental results showed that ternary mixtures containing 30% or more PBT gave single glass transition temperatures by DSC. Moreover, the PBT melting point depended on the composition of the mixtures. These results, which could be indicative of the existence of a single amorphous phase in these blends, have been discussed. Nevertheless, results must be considered with caution, given the peculiarities of the T,-composition diagrams for the miscible pairs PAr/PBT and Phenoxy/PBT. Hypothetic interchange reactions during melting have been found to be unimportant.

SynopsisIn order to graft a vinyl acetate-methyl acrylate mixture onto cellulose, an exploration of the way of addition of the reactants has been made. The influence of several factors on the grafting parameters was studied, i.e., the order of addition of the ceric ion initiator and the monomer mixture, the removal of the ceric ion solution after a cellulose-ceric ion contact time, and the delayed addition along the polymerization period of the more reactive monomer (methyl acrylate) towards the cellulosic radicals. Some grafting parameters were determined grafting yield, grafting efficiency, cellulose conversion, molecular weight, ceric ion consumption, grafting frequency, number of grafted chains, and synthetic copolymer composition. After a short period (ca. 15 min) for the ceric adsorption on cellulose, a fast formation of cellulosic radicals arises in the initial stages of the polymerization. These initial cellulosic radicals should be trapped by a sufficiently reactive monomer if high grafting yield and high number of grafted chains are to he reached. A portion of the synthetic polymer chains anchored to cellulose that are formed in the first stages of the polymerization, which are generated from cellulosic hemiacetal groups, should constitute block copolymer.

SynopsisPolymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26-40°C, with the redox initiator system ceric ammonium nitrate-isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3-5) X 10