交联聚苯乙烯型多孔吸附剂的中孔性质研究

采用77K温度下的氮气吸附方法,测定了经悬浮聚合制备的不同交联度的交联聚苯乙烯多孔吸附剂的吸附／脱附等温线。根据BET吸附模型计算了比表面,由吸附量计算了总的孔体积,由孔体积和比表面计算出平均孔径,并依据脱附等温线采用BJH方法计算孔径分布。结果表明,交联度对交联聚苯乙烯多孔吸附剂的孔结构均具有显著影响。随着交联聚苯乙烯多孔吸附剂的交联度升高,其孔径变小,比表面增大,而且低交联度吸附剂的中孔接近圆柱形,高交联吸附剂的中孔形状接近“墨水瓶”形。显然,交联度对孔性质的影响与孔结构在交闻聚苯乙烯多烯多孔吸附剂制备和后处理过程中的稳定性密切相关。交联度低时,初期形成的小孔不能保持稳定,在后续聚合及后处理过程中合并为大孔,结果造成低交联吸附剂大孔径、低比表面的现象。通过对孔径分布的研究,揭示了不同吸附剂在中孔范围内的孔特征,并对其形成机制进行了分析。

Mesoporous Properties of Porous Crosslinked Polystyrene Absorbents

The adsorption and desorption isotherms of porous crosslinked polystyrene adsorbents with various contents of divinylbenzene were measured by nitrogen adsorption at 77 K on Quantachrome Autosorb MP 1 System. Their specific surface areas were determined on the basis of BET adsorption model. The total pore volumes and average pore sizes were also calculated according to adsorption isotherms. The pore size distributions in the polymeric adsorbents were statistically obtained by using a Quantachrome software following BJH theory. The results showed that specific surface area was increased and average pore size was declined while crosslinking percentage, i.e . divinylbenzene content in a crosslinked polystyrene adsorbent, became higher. Although a pore size distribution peak in the diameter range of 4-7 nm appeared in all samples, mesopores and macropores were displayed on the pore size distribution patterns of porous crosslinked polystyrenes with crosslinking percentage less than 30%. The pore shapes in lowly crosslinked polystyrene adsorbents seemed cylindrical and "ink bottle" pores existing in highly crosslinked ones as observed from the hysteresis loops in their adsorption/desorption isotherms. Such a phenomenon of porous property should be controlled by the stability of pores in the processes of suspension copolymerization and the post treatment. When crosslinking percentage was low, small pores could be combined together into large ones in the processes owing to re organization of long polymeric chains between crosslinking sites. Otherwise, the re organization of polymeric chains hardly took place in highly crosslinked polystyrenes and the pores were almost kept stable.