However, in order to do so, the calixarene must be able to selectively and specifically react with both PIB-OH and PDMS-SiH. Thus, the calixarene core must carry both --OCH2 COOR', where R' is a methyl or ethyl group, and --CH2 CH???CH2 substituents, or --OCH2 CH???CH2 and CH2 COOR', where R' is a methyl or ethyl group, substituents.