Hypercrosslinked polystyrenes, synthesized by reaction of linear or lightly crosslinked polystyrene with chloromethyl methyl ether(CME) and a Lewis acid in a good solvent, swell even in nonsolvents for polystyrene. Structures and dynamics of hypercrosslinked polystyrenes in both dry solid and solvent-swollen gel states have been determined by C-13-NMR spectroscopy. Deconvolution of C-13 solid-state CP/MAS spectra gave the relative numbers of quaternary carbon atoms in monosubstituted and disubstituted benzenes. A typical sample, crosslinked by reaction of a mixture containing 0.5 mol of CME per mol of repeat units, contains 35% of unreacted and 65% of crosslinked aromatic rings, and no residual chloromethyl groups. Gels swollen in CDCl3 and in CH3OH have residual static dipolar interactions enabling crosspolarization and require magic angle spinning (MAS) and high power H-1 decoupling to reduce chemical shift anisotropy from similar to 10(4) Hz to similar to 10(3) Hz. A single proton spin-lattice relaxation time in the rotating frame measured from all peaks in the C-13 spectra of dry samples indicates homogeneity on a nanometer scale. Proton NMR line widths indicate no substantial molecular motions in a dry hypercrosslinked polystyrene up to at least 200 degrees C.