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- W2247486762 abstract "Dendrimers are highly branched macromolecules which are prepared by a stepwise procedure. The presence of a well-defined core, discrete generations and a large number of terminal groups in dendrimers make them structurally very interesting and potentially useful for a wide variety of applications.1 Hyperbranched polymers,2 on the other hand, do not possess a unique core or discrete generations and they contain a large number of statistically distributed defects. Despite the presence of structural imperfections, studies have indicated that hyperbranched polymers capture many of the essential features of dendrimers, such as adoption of a compact conformation and the presence of a large number of readily accessible terminal functional groups. The first chapter of this thesis provides a brief introduction to hyperbranched polymers, with an emphasis on different methods for synthesizing them, followed by a discussion of the various approaches to control their molecular structural features, such as molecular weight, polydispersity, degree of branching, branching density, terminal end-groups, etc. One of the main objectives of the present study is to develop a simple synthetic strategy to generate peripherally functionalized (or functionalizable) hyperbranched polymers (HBP) that could potentially exhibit core-shell type behavior; in other words, polymers that carry segments of distinctly different solubility preferences within the core-region and the peripheral shell. To this end, in chapter 2 we describe the use of the melt-transetherification process,3 using an AB2 monomer along with a mono-functional A-R type comonomer, to directly generate core-shell type hyperbranched structures in a single step.4 Given that an AB2 monomer carries one equivalent excess of B functionality, copolymerization with an A-R type molecule bearing a single A functional group, readily permits the decoration of the periphery of the hyperbranched structures with these R-units. Thus, hyperbranched polyethers having polyethylene glycol (PEG) segments at their molecular periphery were prepared by a simple procedure wherein an AB2 type monomer was melt-polycondensed with an A-R type monomer, namely heptaethylene glycol monomethyl ether (HPEG). The presence of a large number of PEG units at the termini rendered a lower critical solution temperature (LCST) to these copolymers, above which they precipitated out of an aqueous solution.5 In an effort to understand the effect of various molecular structural parameters on their LCST, the length of the hydrophobic spacer segment within the hyperbranched core and the extent of PEGylation, were varied. Increase in the size and hydrophobicity of the hyper-core resulted in a continuous lowering of its LCST, while an increase in the level of PEGylation, increases the LCST, for a given size of the hyper-core. Additionally, linear analogues that incorporates pendant PEG segments were also prepared and comparison of their LCST with that of the hyperbranched polymer clearly revealed that the hyperbranched topology…" @default.
- W2247486762 created "2016-06-24" @default.
- W2247486762 creator A5057974991 @default.
- W2247486762 date "2009-03-01" @default.
- W2247486762 modified "2023-09-27" @default.
- W2247486762 title "Functional Hyperbranched Polyethers Via Melt-Transetherification Polymerization" @default.
- W2247486762 hasPublicationYear "2009" @default.
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