Preparation Of Functionalized Polystyrene Porous Microspheres

Polystyrene?PS?microspheres do not only have the characteristics of good sphericity,large specific surface area and controllable particle size of general polymer microspheres,but also uniquely have large rigidity property which reflect an ability of not being dissolved by general solvents and not being biodegradable.These properties has made PS microspheres become a research hotspot in the polymer field.The introduction of functional monomer such as divinylbenzene?DVB?into porous polymer microspheres to form PS-DVB,with styrene?St?being the first functional monomer in such microsphere,also has improved properties of strong adsorption,stable physical and chemical properties,easy modifiable surface,and providing many other advantages.This type of polymer microspheres materials is widely used in efficient chromatographic packing,biomedical,adsorbent and catalyst support.In this study,a two-step seed swelling method was used to prepare functional porous polymer microspheres?PPMs?,which were subsequently used as olefin catalyst support to load Ziegler-Natta catalyst in the polymerization of propylene.The main work and research findings of this study are summarized as follows:1.PS seed microspheres were prepared by dispersion polymerization.By changing the mass ratio of ethanol and ethylene glycol monomethyl ether in the mixed solvent,a series of PS seed microspheres with different particle sizes ranging from 1to 3?m were obtained.Three kinds of functional porous polymer microspheres namely:PPM-AN,PPM-AA and PPM-VC were prepared by introducing the third functional monomers acrylcyanide?AN?,acrylamide?AA?and N-vinylcarbazole?VC?into the classical PS-DVB system by two-step seed swelling method.The holes of the microspheres were all slender-shaped accumulation holes with relatively uneven pore sizes.The order of specific surface area and mesoporous pore sizes of the three PPMs is as follows:PPM-AN<PPM-AA<PPM-VC.The amount of nitrogen in PPMs support determines the loading capacity of Ziegler-Natta catalyst,hence,the order for the percentage of nitrogen is found to be:PPM-AA<PPM-VC<PPM-AN.The difficulty degree of the third functional monomer participating in the copolymerization also follows this sequence:PPM-AA<PPM-VC<PPM-AN.2.The PPM-AN,PPM-AA and PPM-VC were then used as organic polymer support to load Ziegler-Natta catalyst?TiCl₄?.The titanium catalyst was combined with magnesium to give full play of their catalytic activity.In order to improve the efficiency of catalysts,the PPMs were first modified with Grignard reagent and finally loaded as support with TiCl₄ catalyst.The order of the content of magnesium and titanium catalyst on the support catalyst is:PPM-AA<PPM-VC<PPM-AN,this is consistent with the trend of the difficulty degree of the third functional monomer to participate in the copolymerization.This indicates PPM-AN as a relatively good catalyst support than the other PPMs.3.Due to the template effect and limited action during the catalytic polymerization of propylene,most of the obtained polypropylene?PP?retained the microspherical morphology of the support microsphere,and a small amount of PP presented a nanofiber shape.With the increase of the carrier aperture of PPM-AN,the molecular weight,molecular weight distribution and isometric dimension of the product PP showed that PPM-AN has better overall increasing trend.For PPM-AN support with the same pore size,the molecular weight,molecular weight distribution and isometric profile of PP as a whole also show PPM-AN with better increasing trend with increase in polymerization pressure.