| Polymers have become the primary materials of mankind since the second half of last century. The annual global production of polymers increases with the increasing world demand, and it has reached to about 200 million metric tons recently. The overwhelming success of polymers is the result of their unique combination of properties, such as light weight, stable, economical, and easy to process. Polyolefins, mainly including polyethylene, polypropylene, and ethylene-α-olefin block and random copolymers, hold more than half of the polymer market due to their versatile applications e.g. packaging films, containers, bags, and molded parts etc. Thus understanding their structure-property relationships is essential for an efficient tailor of polyolefin products to meet specific needs.;Since polyolefins usually can partially crystallize and the crystallization behavior will directly influence the properties of polyolefins in the solid state, studies were carried out using in-situ synchrotron X-ray techniques combined with Linkam shear stage and Instron tensile machine, which were used to observe the structure changes of polyolefins under simulated processing conditions and to evaluate their mechanical performance, respectively. Formation of initial crystallization precursor structure, shish-kebab, and the kinetic and thermodynamic aspects of flow-induced and quiescent crystallization of polyolefins were investigated. This also has many practical implications to industrial polymer processing methods such as extrusion, injection molding and spinning, which involve external flow field. Meanwhile, mechanical properties, such as modulus, strength, elongation, and relaxation, of these polyolefins in the form of films and fibers, crosslinked and non-crosslinked, were obtained as well as the phase behavior and structure development during the uniaxial deformation according to the analysis of wide-angle and small-angle X-ray scattering data. The relationships between different mechanical properties and various structural parameters, for example, chain architecture, block distribution, comonomer content, crystal structure, morphology, and orientation, were revealed. |
