Thermoplastic elastomers (TPEs) exhibit hybrid behavior of thermoplastics and rubbers. They are processed like thermoplastics and perform like rubber. We have prepared a series of these materials by physically modifying semi-crystalline polymers having high melting point like polyamide, polyvinylidene fluoride etc. with amorphous polymers having low glass transition temperatures like fluorocarbon rubber, hydrogenated nitrile rubber, etc. . The unique feature of these materials is the biphasic morphology, where the soft rubbery phase is dispersed in the plastics. Structure development and interactions were correlated with the properties of these TPEs. Tensile strength and Young’s modulus increased with mixing time and interaction. Significant improvement of tensile properties was observed after micro-injection molding of the sample due to reduction in the domain size. The origin of rubber elasticity in such thermoplastic elastomers was due to the interconnected dispersed rubber phase through the thin rubber ligament of 4–12 nm width in the plastics. Atomistic simulation predictions are in line with the experimental results. Modification of polymers by post reactor chemistries can also generate TPEs with unique features. Metallocene-based poly(ethylene-octene) and poly(ethylene-butene) elastomers (designated as POE and PBE respectively) were modified by acrylic acid grafting, and by sulfonation, and subsequently neutralized by zinc salts. With lower comonomer content, both grafting and gelling reactions occurred to a greater extent due to less steric hindrance. Because of the lower stability of PBE radical, it was also more reactive in the system than POE and hence offered higher level of grafting. The nanometric ionic domains formed strong secondary crosslinks and resulted in significant improvement in mechanical as well as thermal properties compared to the corresponding virgin as well as ionomer precursors. Tensile strength of an ionomeric TPE was 49 MPa compared to 32 and 41 MPa for the respective ionomer precursor and the base elastomer.

Thermoplastic elastomers from physical and chemical modification of polymers

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