212835-16-0Relevant academic research and scientific papers
Hyperbranched copolymers versus linear copolymers: A comparative study of thermal properties
Behera, Girish Ch.,Saha, Animesh,Ramakrishnan
, p. 7695 - 7701 (2005)
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.
Synthesis of polyalkylphenyl prop-2-ynoates and their flash vacuum pyrolysis to polyalkylcyclohepta[b]furan-2(2H)-ones
Nagel, Matthias,Hansen, Hans-Juergen
, p. 1022 - 1048 (2007/10/03)
A new method for the smooth and highly efficient preparation of polyalkylated aryl propiolates has been developed. It is based on the formation of the corresponding aryl carbonochloridates (cf Scheme 1 and Table 1) that react with sodium (or lithium) propiolate in THF at 25-65°, with intermediate generation of the mixed anhydrides of the arylcarbonic acids and prop-2-ynoic acid, which then decompose almost quantitatively into CO2 and the aryl propiolates (cf. Scheme 11). This procedure is superior to the transformation of propynoic acid into its difficult-to-handle acid chloride, which is then reacted with sodium (or lithium) arenolates. A number of the polyalkylated aryl propiolates were subjected to flash vacuum pyrolysis (FVP) at 600-650°and 10-2 Torr which led to the formation of the corresponding cyclohepta[b]furan-2(2H)-ones in average yields of 25-45% (cf. Scheme 14). It has further been found in pilot experiments that the polyalkylated cyclohepta[b]furan-2(2H)-ones react with 1-(pyrrolidin-1-yl)cyclohexene in toluene at 120-130°to yield the corresponding 1,2,3,4- tetrahydrobenz[a]azulenes, which become, with the growing number of Me groups at the seven-membered ring, more and more sensitive to oxidative destruction by air (cf. Scheme 15).
