Crown ether complexes of sodium and potassium 2-(benzotriazol-2-yl)phenolates were synthesized and characterized. In the presence of BnOH these complexes are highly active catalysts for the controlled ring-opening polymerization of rac-lactide. The polymerizations are iso-selective and the Pm of polylactide reached 0.77 when the polymerization was performed in toluene at ?60°C; whereas heterorich-polylactide was obtained when the polymerization was carried out in CH2Cl2 or THF. 相似文献
Polyethylenes and highly syndiotactic poly(propylene)s possessing chain end hydroxyl groups were synthesized by living polymerizations using L2TiCl2 [ 1 , L: C6F5NCH(2 O C6H3 3 tBu)]/MAO and functionalized α‐olefins, H2CCH(CH2)n Y [ 2 ; YOAlMe2, n = 4 ( 2a ); YOSiMe3, n = 9 ( 2b )]. Because the primary insertion of 2 to a cationic species L2Ti+ Me ( 3 ) derived from 1 /MAO is much faster than the successive secondary insertion of 2 , addition of an equimolar amount of 2 to 3 resulted in the quantitative formation of L2Ti+ CH2 CH(Me) (CH2)n Y [ 4 ; YOAlMe2, n = 4 ( 4a ); YOSiMe3, n = 9 ( 4b )]. These cationic species 4 served as functionalized initiators for the living polymerization of both ethylene and propylene and afforded polyolefins having extremely narrow molecular weight distributions and a hydroxyl group at the initiating chain end. The terminating chain end of the syndiotactic poly(propylene)s was also functionalized by adding an excess amount of 2b as a chain end capping agent to the living L2Ti–polymeryl species. Due to much slower insertion of the second molecule of 2b relative to the first one, the obtained polymers were end capped quantitatively by a single molecule of 2b . Telechelic syndiotactic poly(propylene)s were successfully synthesized through a living polymerization initiated by 4b and an end capping using 2b .
Phenoxy acid herbicides are widely used herbicides that play an important role in improving the yield and quality of crops. However, some research has shown that this kind of herbicide is poisonous to human and animals. In this study, a rapid and sensitive method was developed for the detection of seven phenoxy acid herbicides in water samples based on magnetic solid‐phase extraction followed by liquid chromatography and tandem mass spectrometry. Magnetic amino‐functionalized multiwalled carbon nanotubes were prepared by mixing bare magnetic Fe3O4 nanoparticles with commercial amino‐functionalized multiwalled carbon nanotubes in water. Then the amino‐functionalized multiwalled carbon nanotubes were used to enrich phenoxy acid herbicides from water samples based on hydrophobic and ionic interactions. The effects of experimental variables on the extraction efficiency have been studied in detail. Under the optimized conditions, the method validation was performed. Good linearities for seven phenoxy acid herbicides were obtained with squared regression coefficients ranging from 0.9971 to 0.9989. The limits of detection ranged from 0.01 to 0.02 μg/L. The method recoveries of seven phenoxy acid herbicides spiked at three concentration levels in a blank sample were from 92.3 to 103.2%, with inter‐ and intraday relative standard deviations less than 12.6%. 相似文献