Self-assisted stereospecific polymerization of unmasked polar 4-methylthio-1-butene

Stereospecific polymerization of polar olefins has always been an attractive but challenging project because the Lewis basic polar groups of monomers are usually poisonous to the Lewis acidic metal centers of the catalysts. In this contribution,thiophene-fused cyclopentadienyl scandium complexes 1-3 were successfully synthesized. Combined with alkylaluminium and organoborate, these complexes showed extremely low activity and no selectivity for 1-hexene polymerization. Surprisingly,highly stereo-selective coordination polymerization of unprotected polar 4-methylthio-1-butene has been achieved in high activity for the first time under the same polymerization conditions. High-molecular-weight(M_n=110×10~3) and perfectly syndiotactic(rrrr>99%) poly(4-methylthio-1-butene)(P(MTB)) was afforded. Thus the methylthio-group-assisted mechanism that the unmasked methylthio group promoted the polymerization through σ-π chelation to the active scandium center together with the vinyl group was proposed. Moreover, the methylsulfonyl functionalized syndiotactic poly(1-butene) was also easily prepared by the oxidation of P(MTB). These results provided a new route for the synthesis of functionalized stereo-regular polyolefins.

Study on the crystal morphology and melting behavior of isothermally crystallized composites of short carbon fiber and poly(trimethylene terephthalate)

The spherulites of the short carbon fiber(SCF)/poly(trimethyleneterephthalate)(PTT)compositesformedin limited space at designed temperatures,and their melting behaviors were studied by the polarized optical microscopy,atomic force microscopy(AFM),and scanning electron microscopy(SEM),respectively.The results suggest that SCF content,isothermal crystallization temperatures,and the film thicknesses influence the crystal morphology of the composites.The dimension of the spherulites is decreased with increasing SCF content,but whether banded or nonbanded spherulites will form in the composites is not dependent on SCF content.However,the crystal morphology of the composites depends strongly on the temperature.When the isothermal crystallization temperatures increase from 180℃ to 230℃,the crystal morphology of SCF/PTT composites continuously changes in the following order:nonbanded→banded→nonbanded spherulites.Disconti-nuous circle lines form in the film when the film thickness increases from 30 to 60μm.Basing on the SEM observation,it is found that these circle lines are cracks formed due to the constriction difference of the different parts of the spherulites.These cracks are formed when the film is cooled from the isothermal crystallization temperature to the room tempera-ture at a slow cooling rate;while they will disappear gradually at different temperatures in the heating process.The crack will appear/disappear first around the center of the spherulite when the film was cooled/heated.The nontwisted or slightly twisted lamellas will reorganize to form highly twisted lamellas inducing apparent banded texture of the spherulites.

Photo-responsive nanoparticles for β-lapachone delivery in vitro

Drug efficiency delivery and release to target site play an important role in the treatment of cancer. To achieve these goals, developing drug delivery systems is the key step. The common materials used for drug delivery like liposomes, micelles, dendrimers cannot control the delivery and releasing by spatial and temporal. In this paper, we design a photoresponsive drug delivery system to reduce the side effects of traditional chemotherapy on normal cells and improve therapeutic efficacy in treating cancers. We synthesized two kinds of photo-responsive polymers using two different monomers containing two photoresponsive groups. The two monomers were crosslinked by poly （ethylene glycol） dimethacrylate to form polymers and then encapsulated β-lapachone into the nanoparticles, after UV irradiation, the particle will degrade and release the drug. This method may provide new strategies for the photoresponsive nanomaterials.