A low symmetry structure of isotactic poly(4-methyl-pentene-1), Form II. An illustration of the impact of chain folding on polymer crystal structure and unit-cell symmetry

Coherent crystal branches: the impact of tetragonal symmetry on the 2D confined polymer nanostructure

The symmetry of polymer crystals greatly affects the optical, thermal con-ductivity and mechanical properties of the materials. Past studies have shown that the two-dimensional (2D) confined crystallization of polymer nanorods could produce anisotropic structures. However, few researchers have focused on understanding confined nanostructures from the perspective of crystal sym-metry. In this research, we demonstrate the molecular chain self-assembly of tetragonal crystals under cylindrical confinement. We specifically selected poly(4-methyl-1-pentene) (P4MP1) with a 41 or 72 helical conformation (usually crystallizing with a tetragonal lattice) as the model polymer. We found a coherent crystal branching of the tetragonal crystal in the P4MP1 nanorods. The unusual 45°- and 135°-{200} diffractions and the meridional 220 diffraction (from 45°-tilted crystals) have shown a uniform crystal branching between the a 1-axis crystals and the 45°-tilted crystals in the rod long axis, which originates from a structural defect associated with tetragonal symmetry. Surprisingly, this chain packing defect in the tetragonal cell can be controlled to develop along the rod long axis in 2D confinement.

Poly(4-methyl-1-pentene)/alkylated graphene oxide nanocomposites: the emergence of a new crystal structure

Modified graphene oxide (GO) not only offers a wrinkled structure but may also transform the crystal structure, giving it a potential application in high performance polymer/filler composites.

Aerogels and polymorphism of isotactic poly(4-methyl-pentene-1)

Monolithic and highly crystalline aerogels of isotactic poly(4-methyl-pentene-1) (i-P4MP1) have been prepared by sudden solvent extraction with supercritical carbon dioxide from thermoreversible gels. The cross-link junctions of i-P4MP1 gels, depending on the solvent, can be constituted by pure polymer crystalline phases (I or III or IV) or by polymer-solvent cocrystalline phases (for cyclohexane and carbon tetrachloride gels). Gels with cocrystalline phases lead to aerogels exhibiting the denser crystalline form II, whereas all the other considered gels lead to aerogels exhibiting the thermodynamically stable form I. Aerogels obtained from form I gels, which do not undergo a crystalline phase transition during the CO(2) extraction process present the high structural stability most suitable for the preparation of porous membranes. The effect of solvents on the aerogel pore structure and morphology has been also investigated by scanning electron microscopy and N(2) sorption measurements. In all cases, the aerogels present highly porous interconnected structures with macropores and mesopores presenting a large size distribution and a vanishing presence of micropores.