Chlorobutyl Covulcanization Chemistry and Interfacial Elastomer Bonding

Abstract A new analytical and diagnostic technique has been developed and applied to covulcanized Chlorobutyl—polydiene rubber blends that indicates the existence or absence of interfacial bonds. This technique of differential solvent swelling is based upon solvent—elastomer interaction parameters and draws upon the analogy to filler-adhesion analysis of vulcanized networks. Interfacial bonds between dispersed Chlorobutyl and polydiene rubber phases are first obtained with very active thiuram and thiuram tetrasulfide curative systems. Subsequently less active curatives utilizing bis-alkylphenol polysulfides as sulfur donors were also found to promote interfacial bonds. By means of mercaptan probes it was established that strong evidence of interfacial bonds in covulcanized networks was associated with a preponderance of monosulfidic crosslinks. Prolonged heating, which matures polysulfidic links to more thermally stable monosulfidic links, did not produce strong interfacial bonds where none existed after the initial vulcanization cycle. Thus, interfacial bonds must be formed with more thermally stable monosulfide links during the initial stages of vulcanization. Reinforcing