Ionomers of copolymers of vinylidene aromatic monomer and unsaturated compounds with acid groups

A composition comprising:

• a) in one part a plurality of chains of a copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids having a weight average molecular weight of from about 100 kg/mole to about 400 kg/mole, the copolymer having about 0.01 to about 15.0 percent by weight of the one or more unsaturated acids wherein the one or more unsaturated acids are pendant from the copolymer;
• and
• b) in a separate part one or more metal salts and/or metal oxides of a metal having a valence of 2 or greater;
• wherein when the one part and the separate part are contacted a portion of the chains of the copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids are crosslinked with other chains of the copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids by i) ionic bonding of anions formed from the one or more pendant unsaturated acids with a metal cation having a valence of 2 or greater or ii) complexation between pendant acid groups and metal oxides of the metal cation having a valence of 2 or greater;
• the crosslinks are reversible and the weight average molecular weight of the copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids is substantially the same after the crosslinking is reversed as it is before crosslinking;
• the melt viscosity at 0.314 s−1 angular frequency of the crosslinked copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids is at least 10 percent higher than the same copolymer without ionic crosslinking when measured at 200° C.;
• and, wherein the solution viscosity, measured at 23° C. at 10 weight percent in toluene, of the crosslinked copolymer of one or more vinylidene aromatic monomers and one or more unsaturated acids is at least 100 percent greater than the solution viscosity of the copolymer after the crosslinking is reversed.