Helical Disubstituted Polyacetylene Microspheres Prepared By Precipitation Polymerization

Conjugated polymers have drawn great attention for decades due to their excellent optical and electronic properties.As typical conjugated polymers,polyacetylenes have been intensively investigated.They fall into two major groups:monosubstituted polyacetylenes and disubstituted polyacetylenes.Up to date,a great number of monosubstituted polyacetylenes were prepared using Rh catalysts,among which those being able to form helical structures acquired vast interest from researchers.More noticeably,monosubstituted polyacetylene-based microspheres have attracted special attention in recent years,majorly because of the following two reasons:(1)the exquisite combination of macromolecular helical structures and large specific surface area in one entirety and(2)the great potentials in chiral-related applications like chiral recognition/resolution,asymmetric catalysis,enantioselective crystallization,and enantioselective-controlled release.Meanwhile,various approaches(emulsion,suspension,dispersion,and precipitation polymerizations,among others)have been established so far for fabricating the particles being able to meet different requirements in previous studies.Compared to monosubstituted polyacetylenes,disubstituted polyacetylenes usually demonstrate higher thermal stability,better chemical resistance,and fluorescence emitting capacity.Therefore,they are widely applied in diverse fields such as sensitive chemosensors,solar cells,emission materials,gas separation materials,liquid crystalline materials,and chiral stationary phases for HPLC.However,there has been no report dealing with the preparation of microspheres derived from disubstituted polyacetylenes yet.The key factor leading to this situation should be the fact that polymerizations of disubstituted acetylenics require for metal catalysts which are highly sensitive to water.Accordingly,the fabrication of microspheres consisting of disubstituted polyacetylenes still remains as a big academic challenge,despite the impressive progress made in monosubstituted polyacetylenes.We in this thesis made special efforts to overcome the challenge mentioned above and exciting progress has been achieved.Firstly an achiral disubstituted alkyne was chosen as monomer.By adjusting the solvent composition and the amount of catalyst,we successfully obtained disubstituted polyacetylene microspheres with regular morphology from precipitation polymerization.Referring to our previous study on precipitation polymerization,we proposed a formation mechanism of disubstituted polyacetylene microspheres.Accordingly,we established an effective precipitation polymerization approach for constructing microspheres derived from disubstituted acetylenes.Subsequently,disubstituted acetylene monomers(Ml,(+)or(-))with a chiral substituent and a benzene ring substituent were synthesized according to a well-investigated strategy.(+)-Ml was taken as a model monomer to build up the preparation method.A bifunctional butynyl ester was also prepared and used as crosslinker.The expected monodisperse,cross-linked chiral microspheres(CCPMs)were efficiently prepared by precipitation polymerization using the above synthesized monomer and crosslinker.Through adjusting solvent composition and catalyst amount,the microspheres were further optimized in morphology.Subsequently,the formation mechanism of CCPMs was proposed referring to earlier studies concerning precipitation polymerizations.The present work provides an unprecedented protocol for preparing particles of disubstituted polyacetylenes.