Paradox in Sintering of Nascent Ultrahigh Molecular Weight Polymers in the Solid State

The sintering of ceramics, metals, and polymers has been a subject of intense interest, especially when the materials can be sintered without melting in the solid state. In contrast to inorganic materials, crystallizable polymers have segments of the same chain residing in crystalline and noncrystalline regions. The topological constraints between the chain segments residing in the noncrystalline region are strongly influenced by the crystallization and/or polymerization history. Here, we address the influence of topological constraints on the deformation of crystalline domains to the extent that lattice diffusion and grain boundary diffusion in semicrystalline polymers can be achieved without melting. This allows ease in translation of the macroscopic forces to the molecular length scale in the sintered polymer, facilitating uniaxial and biaxial deformation below the melting temperature. Since solid-state processing circumvents the challenges of melt processing, entropic relaxation of the oriented chains, and thermal degradation of the polymers at high temperatures, unprecedented mechanical properties in the uniaxial and biaxial drawn intractable ultrahigh molar mass polymers have been achieved. Thus, solvent-free sustainable solutions are provided for the processing of the intractable engineering polymers needed for demanding applications. The ease of sintering allows the fabrication of grain-boundary-free products, with advantages in prostheses.