Porous Structure of Hypercrosslinked Alpha-Methylstyrene Polymers

A series of stereoregular linear polymers of alpha-methylstyrene have been synthesized by low-temperature cationic polymerization in solution. Molecular weight distribution functions of the synthesized poly(alpha-methylstyrenes) are determined by gel permeation chromatography. Depending on the synthesis conditions, the average molecular weight of the polymers varies in the range from 140 × 10³ to 490 × 10³. According to X-ray phase analysis, the polymers under study are X-ray amorphous. The syndiotactic structure of polymer chains is established by proton magnetic resonance spectroscopy. Hypercrosslinked alpha-methylstyrene polymers are prepared in a 1% polymer solution in dichloroethane by crosslinking phenyl groups of the polymers with 4,4'-bis(chloromethyl)-1,1'-biphenyl in an amount of 0.5 to 2.0 mol per mol of the monomer unit by the Friedel–Crafts reaction. Low-temperature nitrogen adsorption measurements show that the hypercrosslinked poly(alpha-methylstyrenes) possess a well-developed micro–mesopore system. With increasing the degree of crosslinking of the polymers, the volume of ~2 nm micropores doubles but the average size of mesopores decreases from 8 to 4 nm and their volume fraction decreases from 80 to 60%. The specific pore surface area at the maximum degree of crosslinking is 900 m²/g, and the total volume of pores up to 150 nm is 0.94 cm³/g. Hypercrosslinked alpha-methylstyrene polymers are characterized by a bimodal pore system with predominant micropore fractions of ~2 nm and mesopore fractions of 4–8 nm. The synthesized hypercrosslinked polymers are promising for biomedical applications as adsorbents of toxic organic compounds.