Di- and Triblock Copolymers Based on Polyethylene and Polyisobutene Blocks. Toward New Thermoplastic Elastomers

Azido end-functionalized polyethylenes (PE-N-3, 2250 or 2500 g mol(-1), D = 1.2, functionality higher than 88%) were reacted with alkyne end-functionalized or telechelic polyisobutenes (PIB-C CH: M-n = 2400 g mol(-1), D = 1.1; HC C-PIB-C CH: M-n = 6900 g mol(-1), D = 1.2, respectively) using the 1,3-dipolar cycloadddition reaction in a mixture of toluene and dimethylformamide at 110 degrees C. The reaction led to the quantitative formation of di- and triblock copolymers (PE-b-PIB and PE-b-PIB-b-PE) that were characterized by size exclusion chromatography and H-1 NMR analyses. The original copolymer PE-b-PIB-b-PE that incorporates hard semicrystalline PE blocks and a soft PIB block was further studied by differential scanning calorimetry, optical microscopy, X-ray scattering, and dynamic mechanical analysis It was shown that the crystallinity of PE segments was not perturbed by the PIB phase and that the T-g of PIB was slightly raised because of chain motion restrictions due to PE crystallites In addition, mechanical analyses showed that PE-b-PIB-b-PE behaved as a thermoplastic elastomer over a broad temperature range (0-110 degrees C) with a tensile strength of 4 MPa and an elongation at break of 16%. The use of blocks of higher molar mass should improve the copolymer nanostructuration.