Reversibly collapsible macroporous poly(styrene-divinylbenzene) resins

A series of poly(styrene-divinylbenzene) (poly(PS-DVB)) resins have been prepared by suspension polymerisation of styrene-DVB mixtures with DVB contents of 1-12 mol%. In each case 2-ethyl-hexan-1-ol was used as a porogen. Those resins prepared with <10 mol% DVB collapsed to clear glassy particles on drying from dichloromethane or toluene. However, on drying these resins from acetone, methanol and scCO(2) some opacity was retained. The surface area of each dried species was measured by applying the BET theory to N-2 sorption isotherms. Those resins containing less than or equal to 6 mol% DVB and dried from the former two solvents indeed have negligible surface area and superficially are very like gel-type resins. All the resins dried from the latter group of solvents have significant surface area which decreases systematically with fall in DVB mol%. The resin with less than or equal to 6 mol% DVB and negligible surface area dried from toluene was re-swollen in acetone and re-dried. This process re-established the pore structure and surface area. Using inverse size exclusion chromatography the porosity of all the resins was investigated when swollen in tetrahydrofuran. In all cases significant surface area (110-250 m(2) g(-1)) was detected. This group of resins are therefore macroporous but, depending on the solvent and drying procedure, the porous morphology can be collapsed reversibly to form dry resins superficially similar to gel-type species. However, in practice these novel resins retain a latent pore structure which is readily re-established on treatment with suitable solvents. (C) 2000 Elsevier Science Ltd. All rights reserved.