No abstract

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.

SynopsisThe cationic polymerization of 3-methylbutene-1 was investigated with the use of aluminum chloride and aluminum bromide initiators in the temperature range of -62 to -102°C. Polymerizations are homogeneous in the presence of pentane, and above -50°C. in methyl chloride. However, the polymer tends to precipitate below -5OOC. in methyl chloride. The molecular weight of poly-3-methylbutene-1 increases with decreasing temperatures a t the same conversion level. Significantly, the molecular weights increase with conversion and seem to reach their maximum a t high conversions. Higher molecular weights were obtained in n-pentane-alkyl chloride mixtures than in methyl chloride solution alone. The molecular weights are independent of catalyst concentrations in the range investigated (31.8-7.97 X loF4 mole/l. AlBr3 and 57.6-28.8 X mole/l. AlC13). The rate of homogeneous polymerization with aluminum bromide in propane solvent was studied. The rate is first order in monomer concentration and catalyst concentration and the rate constant is 0.610 l./mole sec. The apparent activation energy calculated from the Arrhenius plot is 6.57 kcal./mole. In methyl bromide the rate of polymerization increases significantly (effect of the dielectric constant). In toluene the molecular weight as well as the rate is strongly depressed indicating the preponderance of a chain breaking mechanism involving this solvent. 367

The low temperature cationic polymerization of 3‐methylbutene‐1 proceeds by intramolecular hydride shift mechanism. The secondary carbonium ion rearranges to a tertiary one prior to propagation. Thus the repeat unit of cationically obtained poly‐3‐methylbutene‐1 is not the expected or 1,2 structure but an α,α′‐dimethylpropane‐type 1,3 unit, e.g.,

The structures of cationically obtained poly‐3‐methylbutene‐1, isotactic poly‐3‐methylbutene‐, and hydrogenated 3,4‐polyisoprene have been investigated by nuclear magnetic resonance and infrared spectroscopy. These studies corroborate the previously proposed structure of an α,α′‐dimethylpropane repeating unit for the cationic polymer and they confirm the conventional 1,2 head‐to‐tail enchainment for the isotactic polymer and for the hydrogenated 3,4‐polyisoprene. The NMR spectra of cationic poly‐3‐methylbutene‐1 and polyisoprene are very similar and show only two peaks. They are quite different from the spectra of isotactic poly‐3‐methylbutene‐1 and hydrogenated 3,4‐polyisoprene. The isotactic product was solubilized by careful pyrolysis to render it amenable to spectroscopic studies. Unfortunately, present‐day NMR spectroscopy does not possess high enough resolution to be useful in the quantitative investigation of mixtures of 1,3 and 1,2 enchainments. The NMR spectrum of polyisobutylene oxide can be used to distinguish cationic poly‐3‐methylbutene‐1 from the isotactic modification and from the hydrogenated 3,4‐polyisoprene. The more important bands have been analyzed and assigned. Isotactic poly‐3‐methylbutene‐1 and hydrogenated 3,4‐polyisoprene both have a conventional 1,2 structure, and their infrared spectra are essentially identical.