- Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States
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Thermally rearrangeable aromatic polyamides (TEMPO-PA) and random copolyamides (TEMPO-PA-COOH) incorporating alkoxyamine moieties in the main chain were synthesized, and the effects of thermal reorganization behavior on their solution and solid-state structures were investigated. The hydrodynamic radius in solution decreased as the solution temperature increased because of the dissociation of the alkoxyamine unit. Additionally, the dry density of the thin films decreased as the fabrication temperature increased because of the suppression of polymer aggregation caused by the thermally induced radical crossover reaction. In addition, at the film surface of the random copolyamide containing hydrophobic TEMPO and hydrophilic 3,5-diaminobenzoic acid (DABA) units, the hydrophilicity decreased as the fabrication temperature increased. This is because hydrophobic TEMPO and hydrophilic DABA units tend to be discretely aggregated near the film surface to minimize the surface energy and suppress the hydrogen bonding via a radical crossover reaction during the thin-film fabrication process. The present study clearly shows that both the solution structure and the solid-state molecular aggregation structure of the dynamic covalent polymers can be easily controlled by a thermal trigger, and it provides a new method for controlling the higher-order structure of polymer solutions and solids.
- Aiba, Motohiro,Higashihara, Tomoya,Ashizawa, Minoru,Otsuka, Hideyuki,Matsumoto, Hidetoshi
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- Self-healing of polymers via synchronous covalent bond fission/radical recombination
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The present paper is devoted to preparation of intrinsic self-healing polymeric materials used for structural applications. The authors introduced a novel healing chemistry based on dynamically reversible C-ON bonds, which imitates natural healing in livi
- Yuan, Chane,Rong, Min Zhi,Zhang, Ming Qiu,Zhang, Ze Ping,Yuan, Yan Chao
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p. 5076 - 5081
(2012/03/27)
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- Polyurethane macroinitiator for controlled monomer insertion of styrene
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Polyurethane containing alkoxyamine units in the main chain were prepared by polyaddition of diisocyanate with TEMPO-based diol. Radical polymerization of styrene was carried out in bulk with TEMPO-based polyurethane as macroinitiator. GPC, NMR, and IR data revealed that the insertion reaction was accurately controlled to afford the segmented copolymers composed of both urethane groups and polystyrene segments. From the results of model polymerization, it is inferred that the well-defined polystyrene chains were inserted into the macroinitiator. The obtained polymers showed quite different solubility in solvents compared with the macroinitiator and styrene homopolymer. The solubility in polar solvents decreases gradually with increasing inserted polystyrene chain length.
- Higaki, Yuji,Otsuka, Hideyuki,Endo, Takeshi,Takahara, Atsushi
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p. 1494 - 1499
(2007/10/03)
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- Radical crossover in nitroxide mediated 'living' free radical polymerizations
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The efficiency of exchange between the mediating nitroxide moieties at the termini of growing polymer chains during 'living' free radical polymerizations has been probed by a series of crossover experiments using functionalized unimolecular initiators. The design of appropriately substituted initiators permitted the synthesis of specifically functionalized model polymers which could be readily distinguished using high-performance liquid chromatography (HPLC). Using these models, the mixture of macromolecules obtained from a 1:1 combination of disparate initiators was separated and identified. The results reveal that exchange of the mediating nitroxide free radicals is a facile process and at essentially all stages of the polymerization a nearly statistical mixture of crossover products is obtained. The HPLC techniques developed are also useful in evaluating the extent of chain termination in nitroxide mediated 'living' free radical polymerizations.
- Hawker, Craig J.,Barclay, George G.,Dao, Julian
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p. 11467 - 11471
(2007/10/03)
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