50th Anniversary Perspective: Polymer Crystals and Crystallization: Personal Journeys in a Challenging Research Field

Abstract

Analyzing and understanding the structure and morphology of crystalline polymers has been and remains to be a major challenge. Some of the issues have resisted analyses for decades. The present account illustrates how individual contributions help build a body of knowledge that must cover length scales ranging from submolecular features to morphology and correlates them with bulk properties. Emphasis is put on structures and morphologies as formed spontaneously. Possible extension of the research area to connected fields is illustrated with a development on supramolecular crystals.

Designing polymer crystallinity: An industrial perspective

“…Second, significant progress has been made in the area of polymer crystallization over the last 50 years, resulting from both the development of advanced characterization methods and the enhancement of the respective theories and computational possibilities . It is obvious that modelling and experimental validation need to complement each other and should have a solid physical base.…”

“…For example, PET is obtained as amorphous upon cooling a quiescent melt at 3 Ks −1 , [26] while cooling rates as high as 10 6 Ks −1 [27] would be required to obtain amorphous PE.…”

“…Studies by standard differential scanning calorimetry (DSC) or hot‐stage microscopy with a limited heating and cooling rate range had dominated polymer studies for many years. Meanwhile, creative scientists managed to look far deeper into the process, employing X‐ray methods to get an image of the molecular arrangement in the crystalline structure like Lotz or developing innovative setups for processing‐like deformation and cooling histories like Janeschitz‐Kriegl . One major challenge of early crystallization research resolved by the latter group was a routine for measuring high nucleation densities and spherulitic growth rates, thus assessing processing‐relevant temperature ranges.…”

A few rediscovered and challenging topics in polymer crystals and crystallization

“…Many diverse hypotheses have been proposed to explain this lamellar twisting phenomenon, as recently reviewed by Bart Kahr et al Individual lamellae do indeed twist, as illustrated in Figures A,B . The origin of the twist must lie in the structure of individual lamellae and frequently in their fold surfaces that are structurally different from the crystalline core . The asymmetry of the structure in opposite fold surfaces as postulated for PE may result from different folding conformations, chemical compositions, and/or packing densities or of course from any combination of such differences could be the cause of lamellar twisting.…”

“…The PE decoration technique provided clear evidence that the opposite half lamellae showed very different folded surface topologies (Figure C). Detailed explanations can be found in our most recent publication …”