We have uncovered a novel polycondensation strategy for the synthesis of well-defined polyamides of narrow molecular weight distributions based on modifications of our sequential self-repetitive reaction (SSRR) previously developed for diisocyanatedicarboxylic acid polymerization. In our newly discovered SSRR polyamide formation mechanism, a small amount of hindered carbodiimide, N,N-bis(2,6-diisopropylphenyl)carbodiimide (iPr-CDI) or a hindered isocyanate such as 2,6-diisopropylphenyl isocyanate (iPr-NCO), was introduced to the polymerization as an initiator, followed by simultaneous addition of diisocyanates and diacids monomers. By using this new reaction mode, the SSRR mechanism produces polyamide products of narrow molecular weight distributions with their dispersities reduced to 1.21.4, which is far lower than a range of >2.5 found in regular SSRR reactions. Significantly different from a conventional step-growth or standard SSRR reaction, the formation of a polymer backbone is preferential when the diacid is added to the requisite iPr-CDI in the first step, followed by a rearrangement to form amide and fragmented components for SSRR. The control of molecular weight is mainly attributed to the acid addition favoring the unhindered poly-CDI intermediates in the middle of the growing chains over the hindered-CDI at the chain terminals. It appears that the formation of a hindered isocyanate and the subsequent formation of a new hindered-CDI at the terminal end of growing amide-chains in each SSRR cycle force the acid again toward the preferred unhindered CDI sites dictating the observed outcome. This simple polyamide synthesis methodology is unique and unconventional, and it could significantly facilitate the development of tailored-made polyamides from a variety of diisocyanates and diacids
Highly luminescent hybrid CdS (diameter ¼ 3-6 nm)/copolymer nanocomposites are prepared by using the soap-free emulsion polymerization with chemical precipitation methods in this investigation. The core/shell type of ZnS/CdS nanoparticle on the shell layer of the copolymer microsphere can be obtained via the ion-exchange method. The luminescent intensity and energy of the hybrid CdS/copolymer nanocomposite not only can be improved by increasing the pH value due to the surface passivated by the iminodiacetic acid sodium salt of the polymer side chain, but also can be enhanced by the higher band gap inorganic materials ZnS shell layer. In addition, the CdS nanoparticle passivated by inorganic shell ZnS is more robust than when organically passivation. Furthermore, these hybrid nanoparticles are easily employed to manufacture the transparent copolymer membrane at the film formation temperature (608C), and they still keep their high luminescent property.
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