Polymorphism in polymers: A tool to tailor material's properties

Abstract

In this review, the phenomenon of polymorphism in polymers is discussed on the basis of the thermodynamic stability of different polymorphs that defines the conformations of chains in the crystalline lattice and the packing mode. In particular, we show that the symmetry and energy stability of the chain conformation, the crystal density and entropy of packing, and the presence of defects and disorder in the crystals are the main factors that define the mode of crystallization of polymers and induce polymorphism. How specific polymorphs are selected and the effects of the molecular structure and processing conditions on polymorphism are analyzed. How crystallization of particular polymorphs affects the material's properties and ultimate applications is also discussed. The polymorphic behaviors of isotactic polypropylene and poly(1-butene) are described as examples of how processing and the controlled modification of the molecular structure of polyolefins using methods of controlled synthesis that allow controlled incorporation of configurational and constitutional defects may drive crystallization of a desired polymorph. The possibility to select a particular polymorph using these strategies results in a tool to tailor the physical and mechanical properties of polymers.polymorphism in polymers, principles that define polymorphic behavior, effect of processing and molecular structure on polymorphism, influence of defects, tailoring properties by controlling polymorphism, isotactic polypropylene and poly(1-butene) through stabilization or destabilization of a particular conformation or crystal lattice or increasing crystallization rate. [1,4,5] Even though crystallizability of polymers requires, generally, a regularity in the constitution of the macromolecules, in the configuration of the possibly present stereoisomeric centers and in the conformation of the chains, [1,2,4] defects in the regular constitution and configuration may be in general tolerated in the crystal lattice of polymers and may not prevent crystallization. [1,2,4,5] When the amount of defects and of structural disorder is significant, highly disordered metastable polymorphic forms may crystallize. These metastable forms have been described as solid mesophases and are characterized by different types of structural disorder that do not prevent crystallization. [1,2,[4][5][6] The studies of the crystal structures of the disordered polymorphic forms of many different polymers [1] allowed asserting a new view of the concepts of crystallinity and crystals in polymers, introducing the modern polymer crystallography. [1] The first concept is that crystallinity in polymeric materials is compatible with the absence of true three-dimensional long-range order. Second, in these disordered crystalline polymorphic forms of polymers (solid mesophases), the disorder may be described as a structural feature, using the methods of interpretation of the X-ray scattering and electron diffraction. [1] Since advanced methods of polymer synthesis allow controlling the mol...

Quantitative Disorder Analysis and Particle Removal Efficiency of Polypropylene-Based Masks

“…The results, plotted as a function of temperature in Figure 2b, show a clear linear trend between S 2 and temperatureas predicted by Landau theory for a system undergoing an order-disorder transition. This provides additional evidence that polypropylene polymers can have some degree of disorder somewhere within their structure, as has been previously established using x-ray diffraction [13][14][15]. Figure 2.…”

Constrained Amorphous Interphase in Poly(l-lactic acid): Estimation of the Tensile Elastic Modulus

“… 18 It is known that the possible presence of polymorphism can influence the physical and mechanical properties of semicrystalline polymers because different polymorphic forms of the same polymer may show completely different physical and mechanical properties. 16 , 17 This means that the crystallization conditions can markedly control and tailor the final performance of these materials. Actually, a complete interpretation of the physical properties of semicrystalline polymers must take into account not only the crystal phase and mobile amorphous fraction but also the constrained amorphous interphase or rigid amorphous fraction contribution.…”

Effect of an additive TAB-1 on crystallization behaviors and tensile properties of iPB-1

“…[1][2][3] These excellent properties make iPB-1 suitable for manufacturing pressurized tanks, pipes, films, and thin plates, especially hot water pipes, [1][2][3][4][5][6] and make it very competitive relative to polypropylene or polyethylene. 7,8 It should be noted that iPB-1 is polymorphic and its mechanical properties are heavily dependent on the crystal forms, 9 including forms I, II and III, 10,11 consisting of 3/1, 11/3, and 4/1 helices 12,13 in trigonal, 10 tetragonal, [14][15][16][17] and orthorhombic 18 crystal cells. Among the crystal forms, form I has the highest melting temperature T m of around 130 °C and is the most stable.…”