The preparation of isobutylene-based ionomers through displacement of halide from
brominated poly(isobutylene-co-isoprene) (BIIR) by triphenylphosphine (PPh3) and N,N-dimethyloctylamine (DMOA) is demonstrated. While the resulting phosphonium and ammonium bromide salts (IIR-PPh3Br and IIR-NR3Br, respectively) possess dynamic mechanical properties that are comparable to
thermoset vulcanizates, the elastomeric network is the result of ion-pair aggregation. Evidence of intra-
and intermolecular aggregation provided by dynamic mechanical and dilute solution viscosity analyses
is reinforced by studies of 1H NMR spin−spin relaxation, which demonstrate the reduced mobility of
those polymer chain segments proximal to the phosphonium bromide functionality within IIR-PPh3Br.
The principles of phase transfer catalysis (PTC) are adapted to facilitate solvent-free nucleophlic substitution reactions of brominated poly(isobutylene-co-isoprene) (BIIR). Catalytic amounts of tetraalkylammonium halides are shown to activate alkali metal carboxylate salts to generate ester derivatives in moderate to high yields without incurring complications associated with ammonium carboxylate salt instability and BIIR dehydrobromination. The structures of a range of new aliphatic and aromatic allylic esters are characterized unambiguously through comparisons with products derived from brominated 2,2,4,8,8-pentamethyl-4-nonene (BPMN), which serves as a model for the reactive functionality found within BIIR. The dynamics of the intrinsic substitution process are examined along with factors that affect the rate and selectivity of phase-partitioned, solvent-free PTC systems.
Phase-transfer techniques are used to activate carboxylate nucleophiles for the purpose of preparing ester derivatives of brominated poly(isobutylene-co-isoprene) (BIIR). Studies of the dynamics and yields of stearate ester syntheses reveal the dual role of tetrabutylammonium bromide, as it serves as a phase-transfer catalyst and a catalyst for the isomerization of exomethylene allylic bromide functionality to kinetically more reactive E,Z-BrMe isomers. Knowledge of reaction fundamentals are used to prepare copolymers from BIIR and carboxylate-terminated polybutadiene (cBR) that phase-partition in the manner required for blend compatibilization applications.
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