Tough and Elastic Thermoplastic Organogels and Elastomers Made of Semicrystalline Polyolefin-Based Block Copolymers

Abstract

Development of stereo- and regioselective living alkene polymerization catalysts has led to the capability to produce multiblock copolymers with semicrystalline syndiotactic polypropylene blocks and poly(ethylene-co-propylene) rubbery blocks that have excellent elastomeric properties, both undiluted and as gels with as little as 8 wt % copolymer in mineral oil. During step cycle mechanical processing, the crystals can plastically deform and partially transform from lamellae into rod-like fibrils, which align along the tensile direction, giving rise to very large tangent moduli at large strains. The dimensions of these aligned fibrils can be established from small-angle X-ray scattering and used to construct models of the large strain elasticity, as well as its evolution with plastic strain, based on short fiber composite theory. Wide angle X-ray scattering experiments as well as FTIR measurements suggest that the oriented fibrils have the transplanar (form III) crystal structure. The large toughness of the dilute gels can be attributed to the plastic deformation of the crystalline component, which not only evens out the forces on the rubbery chains running from crystal to crystal but also provides a mechanical hysteresis that is effective in absorbing energy at the tip of a growing crack.

Morphological origins of temperature and rate dependent mechanical properties of model soft thermoplastic elastomers

“…Due to strain the material acts as if it was transitioning from a response dominated by an original, mechanically interlocking and stress‐bearing PBT‐crystal network to a more elastomeric one where the crystals act as isolated cross‐linking points. This rapid drop in modulus with strain has been shown for other multi‐block copolymers with a similar strain‐evolving structure 33–35 . Finally, after experiencing very high strains, a highly oriented system with both small PBT crystals and with amorphous segments aligned along the stretching direction (and possibly crystallized) is obtained.…”

“…Eventually, stretching leads to a very aligned morphology (D) where, if temperature allows strain induced crystallization (SIC) of the poly(tetramethylene oxide) (PTMO) segments dominates the mechanical behavior [Color figure can be viewed at wileyonlinelibrary.com] has been shown for other multi-block copolymers with a similar strain-evolving structure. [33][34][35] Finally, after experiencing very high strains, a highly oriented system with both small PBT crystals and with amorphous segments aligned along the stretching direction (and possibly crystallized) is obtained. The morphology evolution with applied strain is illustrated schematically in Figure 4.…”

Mechanical properties of nanostructured films with an ultralow volume fraction of hard phase

“…To investigate the reversibility of the structural changes upon deformation, load-unload stepcycle tests were carried out, similarly to what is typically done for crosslinked rubbers 25 or semi-crystalline polymers 26,27 . The applied deformation history is shown in the inset of Figure 5b, the stress-stretch curves are reported in Figure 5a and the value of the initial modulus as a function of the applied λ max is shown in Figure 5b.…”

Fully biobased thermoplastic elastomers: synthesis and characterization of poly(l-lactide)-b-polymyrcene-b-poly(l-lactide) triblock copolymers

“…13 Hu et al 14 synthesized a series of crosslinkable linear biobased elastomer composites with high strength and elasticity based on lactic acid, which are promising for engineering and medical applications. 13 Hu et al 14 synthesized a series of crosslinkable linear biobased elastomer composites with high strength and elasticity based on lactic acid, which are promising for engineering and medical applications.…”