ar(--L--ar--)w wherein w is an integer of 1 to about 20, each ar is a single ring or a fused ring aromatic nucleus of 4 to about 12 carbon atoms and each L is independently selected from the group consisting of carbon-to-carbon single bonds between ar nuclei, ether linkages (e.g. --O--), keto linkages (e.g., ##STR3## sulfide linkages (e.g., --S--), polysulfide linkages of 2 to 6 sulfur atoms (e.g.