The studies described in this papier lead to certain conclusions. The crosslinking reaction of halobutyl with zinc oxide does not give rise to ether crosslinks. All the evidence indicates that the chemistry involves the formation of carbon-carbon bonds by an alkylation type chemistry. The dehydrohalogenation of the halobutyl to form a zinc chloride catalyst is a key feature of the crosslinking chemistry. But conjugated diene butyl and Diels-Alder reactions are not the major reaction pathway for the zinc oxide crosslinking reaction. These conclusions have significance for the zinc oxide cure of CR which has an active allylic halide structure formed by 1,2-monomer enchainment.

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 carbon black has a minimal effect upon the acquisition of interfacial bonds or the sulfur-bond chemistry. The curative formulation remains the factor which governs production of the monosulfidic links required for strong interfacial bonding. A definite correlation was found between interfacial bonding and physical strength of fully compounded Chlorobutyl—SBR covulcanized blends. Carbon-black reinforced systems covulcanized with a sulfur donor, such as bis-alkylphenol polysulfide, as the sole source of sulfur, displayed tensile strengths and rupture energies considerably greater than the equivalent systems containing elemental sulfur.

The reactions of isocyanates with carboxy terminated polyisobutylenes, CTPIB, and with hydroxy terminated polyisobutylenes, HTPIB, have been studied in detail. In the case of HTPIB specific emphasis has been given to an hydroxy-ester functionality prepared by the base catalyzed reaction of CTPIB with propylene oxide. Isocyanate reactions with polymeric carboxyl groups were studied to observe if conditions could be established to remove quickly the undesirable carbon dioxide by-product. A potential advantage of this reaction would be the formation of a more stable amide link compared with that of a urethane linkage. In capping reactions with CTPIB and diisocyanates (where NCO group concentrations are in excess), the course of the reaction essentially follows second order kinetics with respect to carboxyl utilization. Bulk reactions, run under vacuum, facilitated the removal of CO2 and markedly increased the rate of reaction. Even so, the reaction required relatively high concentrations of tertiary amine catalysts suggesting a dual role for the base. Aromatic diisocyanates with chlorine substitution were several fold more reactive with CTPIB than was toluene diisocyanate, and gave indications of a better selectivity. Sulfonyl isocyanates possess still greater reactivity. The selectivity of the isocyanate reaction with polymeric COOH is poor when using common diisocyanates such as TDI. The predominant extension of prepolymers is far less probably than in the case of hydroxyl based systems. However, tough, dense, and flexible networks can be formed from initial products of 2000 number average molecular weight. The reactivity of the secondary hydroxyl ester terminal functionality of polyisobutylene, 2° HTPIB, with diisocyanates was comparable to that of commercial polyether or polyester diols which are largely primary hydroxyl. This comparable activity is explained by the fact that in bulk reactions the hydrocarbon backbone of 2° HTPIB provides a reaction medium with a lower dielectric constant and thus a more advantageous environment. In capping reactions followed by IR monitoring of OH consumption, reaction rates also followed second order kinetics with respect to OH consumption when the NCO concentration was in excess. In contrast to isocyanate-polymeric COOH systems, the reaction with HTPIB required no catalysts for extensive consumption of OH groups at moderate temperatures. The HTPIB-toluene diisocyanate reaction was far more selective, and this resulted in a greater potential for extension with the prepolymer. The physical properties of extended and crosslinked networks reflected this selectivity. For a given molecular weight level, networks with HTPIB-diisocyanate prepolymers were more extensible and had higher strengths than did CTPIB based counter parts. Fractionation of original starting materials into narrower molecular weight ranges with slightly improved degrees of functionality improved tensile strengths and extensibilities of subsequent HTPIB based networks. Interesting blocked polymer networks were formed with HTPIB and polyether diols (for example polytetramethyleneglycol). These two liquids which were immiscible, in the molecular weight range of Mn−2000, formed transparent elastic networks of high strength after mutual capping with TDI and subsequent extension and crosslinking by a combination of aromatic diamines and low molecular weight aliphatic diols.

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Isobutylene and styrene were copolymerized at low temperatures, in methyl chloride solution, in the presence of aluminum chloride. The temperature was varied from −30 to −94°C., and the monomer/solvent ratio, the ratio of monomers, and the catalyst concentration were varied over a considerable range. The copolymerization equation was found to be applicable to the data, and the reactivity ratios were determined for various experimental conditions. For an “open” system in which the volume steadily increases during the course of polymerization, it is shown that the copolymerization equation is formally identical to that of Mayo and Lewis, except that concentrations are replaced by amounts of the reacting species. The temperature coefficients of the reactivity ratios in the present system are compared with those for free‐radical systems; some important differences are noted. The reactivity ratios of isobutylene and styrene in the present system are greatly increased under conditions of turbulent agitation. A procedure for the compositional fractionation of the copolymers is described. The results are interpreted in terms of the copolymer chain structure; they appear to admit the postulate that the reactivity ratios and corresponding propagation rate constants are functions of chain length.