Synthesis of hyperbranched polymers by free radical addition-coupling polymerization with A3/B2 and A2A′/B2 approaches
Two tribromide compounds, 1,3-(propanoic acid, 2-bromo-)-2-(2-bromo-1-oxopropylamino)propyl ester (A 1 ) and trimethylolpropane tris(2-bromopropionate) (A 2 ), were synthesized. By Cu/ N,N,N′,N′,N″ -pentamethyldiethylenetriamine (PMDETA)-mediated radical addition-coupling polymerization (RACP) of 2-methyl-2-nitrosopropane (MNP) with the tribromide compounds, two types of hyperbranched polymers were synthesized under mild conditions, respectively. Polymerization degrees of the polymers increased with time gradually, which is in line with a step-growth polymerization mechanism. By tracing the polymerization process by gel permeation chromatography and NMR analysis, proper reaction conditions to get hyperbranched polymers was obtained. Based on the results of NMR analysis on the polymer chain structure, mechanism of forming hyperbranched polymer has been proposed, which includes formation of carbon radicals from the tribromo monomer through single electron transfer, their reaction with MNP to form nitroxide radicals, and cross-coupling reaction of the nitroxide radicals with other carbon radicals. The gelation point of the A 2 -MNP system is larger than that of the A 1 -MNP system, indicating that probability of intramolecular cyclization in A 2 -MNP RACP system is higher than the A 1 -MNP system. The reactivity of —NHCOCH(CH 3 )Br group of A 1 is lower than its two —OCOCH(CH 3 )Br groups, and this resulted in longer distance between two adjacent branch points in the hyperbranched polymer of A 1 -MNP than the A 2 -MNP system. It is possible to adjust the chain structure of RACP-based hyperbranched polymer by changing the reactivity of the functional groups in A 3 monomer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 41972.
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