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Characterization of commercial aliphatic hyperbranched polyesters
Žagar, Ema ; Žigon, Majda ; Podzimek, Štěpán
Commercially available Boltorn Hx (x=20, 30) hyperbranched (HB) polyesters of different theoretical corežmonomer ratio (1ž12 for H20 and 1ž28 for H30) were characterized with respect to molar mass, ...composition, and structure. The results were compared to those obtained for the Boltorn H40 with a corežmonomer ratio of 1ž60 šZagar E, Zigon M. Macromolecules 2002č35Č9913 š11đđ. The main side reaction in the pseudo one-pot synthesis of Boltorn polymers is a self-condensation of bis-MPA leading to the formation of HB structures without a core molecule. These are actually branches containing an unreacted carboxyl group. The fraction of HB structures without a core molecule increases with decreasing corežmonomer ratio due to the decreasing fraction of HB structures with a core molecule. Since HB structures without a core molecule are of lower molar masses than HB structures with a core molecule, they particularly decrease the number average molar masses of the samples compared to the theoretically calculated ones. The polydispersity of Boltorn Hx increases with decreasing corežmonomer ratio. Some of the hydroxyl groups were found to react intramoleculary forming ether bonds. Boltorn Hx polyesters have low degrees of branching due to the limited carboxyl group conversions, low DPn values, the presence of the core unit, and lower reactivity of hydroxyl groups in linear repeat units compared to those in terminal ones. The degree of branching according to Frey increases with decreasing corežmonomer ratio.
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