3238-38-8Relevant articles and documents
Hyperbranched copolymers versus linear copolymers: A comparative study of thermal properties
Behera, Girish Ch.,Saha, Animesh,Ramakrishnan
, p. 7695 - 7701 (2008/02/02)
Copolymerization of two AB2-type monomers that incorporate spacer segments of similar lengths but different flexibility permitted, for the first time, the preparation of a range of hyperbranched copolymers, wherein the backbone rigidity was varied while maintaining similar branching densities. The copolymers were prepared via a recently developed melt transetherification methodology to yield moderately high molecular weight polymers, with molecular weights ranging from 20 000 to 50 000. 1H NMR spectroscopic studies revealed that the composition of the copolymers varied linearly with monomer composition, confirming the formation of truly random copolymers. Analogous linear copolymers based on suitably designed AB-type monomers, containing the same two spacers, were also prepared for comparison. Thermal analysis of these copolymers using DSC indicated that the Tg's of both linear copolymers and hyperbranched copolymers varied with composition in a manner that was in complete accordance with the Fox equation, although all the linear copolymers exhibited significantly higher Tg values than their hyperbranched counterparts. It is interesting that, despite their very different topology and the presence of large number of chain ends, hyperbranched copolymers exhibit a similar Tg variation as their linear analogues. The generality of this observation in the broader context of hyperbranched copolymers, such as those possessing different branching densities and terminal functionalities, remains to be tested.
Ortho-alkylation of phenol with methanol using Pb-Cr promoted magnesium oxide catalysts
Ke, Jyh-Harng,Zena, Jyh-Myng,Wang, Fey-Long
, p. 1407 - 1410 (2007/10/03)
In this study, Pb-Cr promoted magnesium oxide catalysts were used to catalyze the ortho-alkylation of phenol in the presence of excess methanol. The Cr/MgO catalyst exhibited a high conversion of phenol and a relatively high selectivity for the ortho-alkylation of phenol. The catalytic activity and the stability of Cr/MgO were improved by the addition of a fairly small amount of Pb. The Pb-Cr/MgO catalyst showed specificity for the ortho-alkylation of phenol, which was proved by a series of phenol derivative reactions with methanol.
The Baeyer-Villiger Oxidation of Aromatic Aldehydes and Ketones with Hydrogen Peroxide Catalyzed by Selenium Compounds
Syper, Ludwik
, p. 167 - 172 (2007/10/02)
A series of organoselenium compounds was investigated as activators of hydrogen peroxide in the Baeyer-Villiger oxidation.As a result, a convenient and cheap method for transformation of aromatic aldehydes, having polycondensed ring systems or electron-donating substituents, and polymethoxy derivatives of acetophenone, into phenols was elaborated.This method utilizes hydrogen peroxide activated by areneseleninic acids, as oxidizing agent.