Effect of adsorbent on the adsorbed structure of poly (methyl methacrylate)

Curt Thies

Polymer Research Section, Materials Research The National Cash Register Company Dayton, Ohio 45409

Abstract

Isotherms and infrared bound fraction values (p) have been obtained for atactic poly-(methyl methacrylate) (PMMA) adsorbed from trichloroethylene (24°C) on four adsorbents: aluminum oxide (-AI₂O₃) formed by flame hydrolysis, micro-fine reprecipi-tated silica, silica formed by flame hydrolysis, and silica formed by flame hydrolysis and then reacted on the surface with dimethyl dichlorosilane. Differences in PMMA adsorbance values obtained with these adsorbents may be attributed in part to differences in surface area available for adsorption per gram adsorbent. However, variations in surface area do not account for variations in adsorbed structure indicated by the infrared bound fraction data. PMMA adsorbed on silica treated with dimethyl dichlorosilane had a value of p 0.10; p increased to 0.32-0.39 when untreated flame hydrolyzed silica was the adsorbent, and ranged from 0.46 to 0.49 for micro-fine reprecipitated silica. PMMA adsorbed on -AI₂O₃ had p = 0.32-0.28. This was the only adsorbent where values of p tended to decrease with increasing surface coverage. The variations in bound fraction data found in this study are interpreted in light of known differences in surface structure of the four adsorbents used. Drying the reprecipitated silica and -AI₂O₃ at 310°C (in vacuo) caused a slight decrease in values of p which can also be explained in terms of known changes in surface structure caused by heat treatments.