Synthesis and characterization of polyisobutylene-b-polyamide multi-block copolymer thermoplastic elastomers

A series of polyisobutylene (PIB)-polyamide (PA) multi-block copolymers was synthesized via an amidation reaction to form novel thermoplastic elastomers (TPEs). A two prepolymer approach was taken in which a difunctional primary-amine-terminated polyisobutylene (NH2-PIB-NH2) was synthesized as the soft block and a difunctional carboxylic acid-terminated polyamide (HO2C-PA-CO2H) was synthesized separately as the hard block. The two prepolymers were reacted in the bulk under nitrogen at 220 °C to form the multiblock copolymer TPEs. Various copolymers were synthesized from combinations of two different PIBs (either 1000 or 2000 g/mol), and four different PAs (PA-11 and PA-6, each at either 1000 or 2000 g/mol). 1H and 13C NMR spectroscopies were used to confirm the structure of the individual prepolymers and the copolymers. Prepolymer molecular weights were determined by gel-permeation chromatography (GPC), end-group titration, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS); the latter also provided confirmation of end-group functionality of prepolymers. For GPC of PA homopolymers and PIB-PA copolymers, trifluoroacetylation of the secondary amide groups of the PA blocks was necessary to obtain solubility of the copolymers in the THF mobile phase. Copolymer number–average molecular weights varied from 8100 to 20,630 g/mol.