A close look at polymer degree of crystallinity versus polymer crystalline quality

Abstract In the broader polymer field, the term ‘crystallinity’ is often used rather loosely. However, increasingly, it becomes critical to clearly distinguish between degree of crystallinity, which provides the fractional amount of crystalline phase in a polymer, and the crystalline quality, which describes the perfection of the crystalline moieties that may form in a polymer. The reason is that these different structural features dictate important properties of plastic materials, including the mechanical properties of commodity polymers and the behavior of macromolecular ferroelectrics; they also determine which photophysical processes occur in semiconducting polymers. Hence, rigor needs to be applied when establishing structure/processing/property interrelations; and it should become a general practice that specific functions are clearly attributed to the degree of crystallinity, the crystalline quality or a combination of the two. In this perspective, in memoriam of Professor Dick Jones, a long‐time member of IUPAC's Polymer Division, we discuss the challenges of identifying—and distinguishing between—these important structural characteristics when using commonly applied measuring techniques and/or theoretical approaches. This task is often elaborate, as small changes in the chemical nature of the polymer and/or processing conditions selected can have drastic effects on both the crystalline quality and the degree of crystallinity, an issue that combined with the general ambiguity of data obtained with methodologies used to characterize polymer structures, theoretically or experimentally based. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.