Chain-End Modification: A Starting Point for Controlling Polymer Crystal Nucleation

Abstract

This computational study illustrates how modifying the end groups of polymer chains offers a viable strategy to control polymer crystal nucleation in entangled melts. More specifically, altering chain ends to enhance chain-end aggregation enables crystal nucleation to occur at higher temperatures than with unmodified counterparts. Surprisingly, while chain-end aggregation does enhance crystal nucleation, chain-end clusters do not act as direct nucleating agents. As such, the crystal nucleation enhancement arising from chain-end modification differs from historical models, for example, via epitaxial matching. This study is based on coarse-grain molecular simulations of polyethylene crystallization in which chain-end modifications have been achieved by altering the Lennard–Jones parameters of the terminal coarse-grain beads of the polyethylene chains, thereby varying the size of chain ends and emulating chain termination with polycylic aliphatic moieties (e.g., adamantyl groups). The present approach thus leverages steric mismatch between chain-end and main-chain segments as a strategy to alter polyethylene crystal nucleation rather than relying on the utilization of directional (e.g., hydrogen bonding) or ionic interactions. The present computer simulations demonstrate an up to 20 K increase in the crystal nucleation temperature of entangled melts composed of n-C720H1442 polyethylene-like chains even though chain ends account for a small fraction (<1 mol %) of the sample. Seemingly, low chemical loadings are needed to control nucleation via end-group modification.

Understanding and Modeling Polymers: The Challenge of Multiple Scales

“…Such findings illustrate how mesoscale structure (entanglements) can have a profound effect on local structure (local packing), and vice versa, in polymers. The associated time scales can be very large, which offers unusually versatile opportunities to control local structure by processing (for example, in flow-induced crystallization − ) or by tiny chemical modifications. , On the other hand, the mesoscale structure and dynamics determines the elastic and plastic response of the materials to deformations , and the inhomogeneous stress fields in the materials, which in turn drive the large-scale structure formation and spherulite growth …”

“…The associated time scales can be very large, which offers unusually versatile opportunities to control local structure by processing 35 (for example, in flow-induced crystallization 36−40 ) or by tiny chemical modifications. 41,42 On the other hand, the mesoscale structure and dynamics determines the elastic and plastic response of the materials to deformations 43,44 and the inhomogeneous stress fields in the materials, which in turn drive the large-scale structure formation and spherulite growth. 45 The interplay of multiple scales also determines the structural and dynamic properties of other multiphase polymer materials 46 that are highly heterogeneous and filled by internal interfaces, such as polymer blends, 47,48 block copolymer melts and solutions, 49−52 or foams.…”

Dependence of Crystallization Behavior of Interacting Telechelic Poly(butylene succinate) Oligomer on Molecular Weight

“…Therefore, the development of new strategies for PBS is Crystals 2021, 11, 1530 2 of 12 still desired. Recently, chain-end modification has been proposed to be a viable method for controlling polymer crystal nucleation [15]. Consequently, it is interesting to regulate the crystallization of PBS by forming interacting telechelic chains.…”

Biodegradable membrane of poly(l-lactide acid-dioxanone-glycolide) and stereocomplex poly(lactide) with enhanced crystallization and biocompatibility

“…A series of controlled P/s membranes was prepared using the solution blending methods (Scheme 1). Epitaxial nucleation and chemical mechanisms are often applied to explain the enhancement of nucleating materials (Hall et al, 2014;Xu et al, 2022). The epitaxial crystallization of polymers that grow on organic materials is usually applied to manifest the crystallization behaviors of PLLA (Takenaka et al, 2004).…”