| Summary: | 博士 === 國立中興大學 === 土木工程學系所 === 96 === The reaction of aromatic carbodiimides and carboxylic acids produced aryl N-acylureas in high yields under mild conditions. Thermolysis of N-acylureas at greater than 140 ℃ gave amides and isocyanates readily, the latter could undergo the repetitive reaction sequences in the presence of carbodiimide catalyst. Based on this unique pattern, the sequential self-repetitive reactions (SSRR) is developed in a versatile manner for converting aryl isocyanates into amides, amide-imide and imide. Furthermore, the SSRR reaction has also been successfully applied into poly(amide-imide) and polyimide synthesis. In addition, one-pot synthesis of poly(amide-imide) and polyimide was demonstrated have excellent thermal properties demonstrated by their TGA and DSC measurements.
We have developed a novel poly-condensation for the synthesis of well-defined polyamides by the SSRR reaction. The new polymerization mechanism involved a three-step sequence of carboxylic acid addition to carbodiimide, fragmentation of N-acylurea into amide and isocyanate and isocyanate condense to carbodiimide. The new polymerization technique was demonstrated by using a hindered carbodiimide, N,N’-bis(2,6-diisopropylphenyl)carbodiimide (iPr-CDI) as an initiator, followed by slow but simultaneous addition of diacids and diisocyanates monomers to ultimately generate a polyamide with precisely controlled molecular-weight distributions. Significantly different from the conventional step-growth and chain-growth types, the formation of polymer backbone is through the monomer addition to the requisite initiator, and followed by a rearrangement to amide and fragmented component for SSRR.
The mechanism of monomer addition, fragmentation and SSRR condensation in a sequential order is unique with respect to the way of forming polyamide backbone. Furthermore, the precise control of molecular weight is mainly attributed to the relative rate of sequential acid-addition and CDI-formation. At the end of each reaction cycle, a “hindered CDI” was created at the terminal of the growing amide-chain setting up for the next sequence. This new SSRR method allows the synthesis of precisely controlled polyamides that can not be obtained from the conventional poly-condensation.
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