Structural Organizations of a Mesogen-Terminated Semicrystalline Polymer: Chain Termini Ordering between Polymer Crystal Lamellae

In polymer crystallization, the chain end groups are generally excluded into the nanoscaled amorphous regions confined between crystal lamellae. Understanding the structural characteristic and evolution of interlamellar end groups is of great importance to control the macroscopic properties of polymers. However, the structural evolution of those confined end groups and related physical evidence remain unclear. Herein, we synthesized the end-functionalized poly(lactic acid)s with a self-assemblable mesogenic termini (4-hexyloxy-4'-cyanobiphenyl) and investigated the structural evolution of mesogenic termini between crystal lamellae. Intriguingly, the mesogenic termini can organize into an ordered layer structure between polymer crystal lamellae; such a process strongly depends upon the interlamellar spacing. A higher crystallization temperature (T_c) of the polymer allows for a larger interlamellar region, favoring the formation of an ordered mesogenic layer. However, a lower T_c results in a restricted interlamellar region, in which the end groups are strongly confined without sufficient mobility to undergo structural ordering. This study provides evidence for the structural ordering of chain termini confined between polymer crystal lamellae.

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

A large spherulite structure deteriorates the mechanical properties of crystalline polymers, and therefore various methods have been explored to increase primary nucleation density. Recently, chain-end modification has been proposed as an effective approach for regulating polymer crystal nucleation. However, the relevant nucleation mechanism still requires investigation. Therefore, in this work, 2-ureido-4[1H]-pyrimidinone (UPy) units, which can form stacks via quadruple hydrogen bonds with each other, are introduced as end groups for the preparation of interacting telechelic poly(butylene succinate) (PBS-UPy) oligomers with different molecular weights (Mns). The crystallization, especially the nucleation behavior of PBS-UPy, is studied in detail by comparing with the corresponding pre-polymer, the hydroxyl-terminal PBS (PBS-OH). The thermal properties of PBS-UPy exhibit similar Mn-dependent tendency to those of PBS-OH, but with weaker total crystallization rate. The spherulite growth rate is significantly reduced, whereas the primary nucleation density is highly promoted, after introducing UPy groups. Further investigation reveals that the mechanism of UPy stacks’ influence on nucleation ability changes from inhibition to promotion with respect to Mn. Even under an inhibition of nucleation ability, the final nucleation density is obviously increased because of a significant decline of the growth rate. In addition, the change in the impact of UPy stacks on nucleation ability is speculated to originate from the memory expression feasibility of ordered conformation in the melt during crystallization.

Fabrication of High χ-Low N Block Copolymers with Thermally Stable Sub-5 nm Microdomains Using Polyzwitterion as a Constituent Block

In this work, we used zwitterionic poly(4-vinylpyridine) propane-1-sulfonate (PVPS) as a constituent block to construct high χ-low N block copolymers (BCPs) with different neutral polymers as the other block, including polystyrene (PS), poly(ethylene oxide) (PEO), and poly(l-lactide) (PLLA). Lamellar structures with sub-5 nm microdomains were observed in all three types of BCPs. Due to the tendency of self-aggregation induced by electrostatic interaction in polyzwitterion, the Flory-Huggins parameters (χ) between PVPS and most neutral polymers are relatively high, which provides a facile and efficient way to fabricate high χ-low N BCPs. In addition, the dimension of the sub-5 nm structures formed in PVPS-containing BCPs showed high thermal stability with a small fluctuation (±0.1 nm) of domain spacings upon heating.