Sealants for insulated glass units or solar panels are disclosed. The sealant comprises polyisobutylene and a polymer which is a copolymer obtained from the polymerisation of at least one ethylenically-unsaturated aliphatic hydrocarbon monomer and at least one monomer containing a maleic anhydride moiety. The copolymer comprises at least one amphiphilic polymer side chain. Processes for producing the sealants for insulated glass units or solar panels are also disclosed. Insulted glass units and solar panels comprising the sealant are also disclosed. Processes for producing the insulated glass units and solar panels comprising the sealant are also disclosed.