Synthesis And Applications Of The Polymer Microspheres Soley Consisting Of Optically Active Helical Substituted Polyacetylenes

During the last decades, more and more scientists have paid great attention to the optically active helical polymers, owing to their remarkably physical and chemical characteristics compared with other polymers and small molecules, such as chirality amplification and chirality memory effects and so on. The unique orderly secondary structure of the helical polymer chain gave birth to the potential industrial application and theoric investigation, especially in chiral recognition, chiral separation and asymmetric catalysis. Up to now, various kinds of helical polymers have been prepared as biomimetic materials, stimuli responsive materials, photoelectric sensor and liquid crystal materials, so synthesis and application of the helical polymers gradually become one of the hottest researches in the macromolecule science development. Recently, the helical polymer was confirmed to have ability of solely being used as a novel organocatalyst for the asymmetric reaction for the first time. Although some innovative trials have been made, design and synthesis of a new helical polymer as a more effective organocatalyst for asymmetric reaction still can be a big challenge. For synthesis of a new kind of helical polymer, the polymerization process plays a key role in the polymer morphology. As a traditional polymerization process, solution polymerization is a main method to synthesize the helical polyacetylenes. Based on the two points, in the thesis a novel kind of substituted polyacetylene using as an organocatalyst for asymmetric Aldol reaction was synthesized for the first time. Secondly, a new polymerization process-coordination precipitation polymerization, which can be considered as a new method for preparing the polyacetylene microspheres, was deeply investigated. The major contents are shown as follows:1. A new substituted acetylene monomer (M1L, and M1D), containing prolinamide pendant group, was synthesized from Boc-proline via condensation reaction and deprotection reaction. Then the homopolymer poly(1) was prepared by coordination polymerization, catalyzed by Rh catalyst. After characterized by the UV-vis, CD spectra and specific rotation, the poly(1) couldn’t form the helical structure and had no chiral amplication effect. Furthermore, the monomer1and its homopolymer had no ability for catalyzing asymmetric Aldol reaction. Then, monomer1was copolymerized with a chiral monomer13to construct a series of new helical copolymer. With the same characterization, the copolymer presented optical activities and adopted helical conformation with a predominantly one-handed screw sense. The fact that the optical activity increased with increasing the chiral monomer units in the copolymers indicated that the copolymers followed the well-known "Sergeants and Soldiers" rule. Meanwhile, the copolymer was used as an organocatalyst to catalyze the asymmetric Aldol reaction of cyclohexanone and ρ-nitrobenzaldehyde. The copolymer exhibited a remarkable catalytic property, owing to a synergic effect occurring between the helical structures in the polymer main chains and the pendent prolinamide moieties. The role of the helical polymer backbones was further verified by tuning the relative helical structure contents. The present concept would open new approaches for developing artificial enzymes for performing asymmetric catalyses.2. Based on the received experimental conclusion, in order to increase the reutility of the chiral catalyst and meet the requirement of the green chemistry, we developed a novel kind of polymerization process named as "coordination precipitation polymerization" to construct the polymer microsphere organocatalyst. To get the microspheres with excellent morphology, we investigated the some varieties of factors in the polymerization process which had great effects on the morphology of the microspheres, such as the solution system, monomer concentration and Rh catalyst concentration. Finally, we created the best experimental conditions as follows:the solution system was composed of butanone and n-heptane at the ratio of1/7; monomer concentration was0.25mol, and the Rh catalyst concentration was1%of monomer. The size of the microspheres prepared under the best condition was nearly1μm. After characterized by CD, UV spectra and specific rotation, the polymer consisted of the microspheres exhibited optical activities and adopted helical conformation with a predominantly one-handed screw sense. The microspheres catalyst showed great ability of heterogeneously catalyzing the asymmetric Aldol reaction of p-nitrobenzaldehyde and cyclohexanone in aqueous media. Remarkable catalytic efficiency was obtained (yield76%and ee80%). The novel microspheres can be easily recovered and reused with just a simple aftertreatment, such as filtration and washing. The experiment data suggested a slight reduction in catalytic efficiency even even in the third cycle of catalysis. Accordingly, the methodology provides opportunities for developing a novel class of chiral polymer organocatalyst.3. To deeply investigate the coordination precipitation polymerization, we reported a novel type of microspheres (approx.720nm in diameter) prepared via precipitation polymerization and constructed by optically active helical substituted polyacetylene (PSA). The microspheres were obtained in high yield (>80%), with regular morphology and narrow size distribution. PSA forming the microspheres was found to adopt helices with predominant one-handed screw sense, according to circular dichroism and UV-vis absorption spectroscopies and specific optical rotation measurements. The helical conformations of PSA endowed the microspheres thereof with considerable optical activity. The chiral microspheres feature in combining in one entity the advantages of both chiral polymers and the micron-sized particles in scale and spherical morphology, and thus are expected to find some significant applications. This is well exemplified by successful induction of enantioselective crystallization with the chiral microspheres. Such chiral microspheres efficiently induced enantioselective crystallization of alanine enantiomers:(S)-PSA preferably induced L-alanine to form octahedral crystals while (R)-PSA toward D-alanine forming needle-like crystals, with a remarkably high ee (85%). This is the first precipitation polymerization of substituted acetylenes for preparing chiral polymeric microspheres. The present chiral microspheres represent a new type of advanced functional chiral materials.