Controllable crystallization and lamellar organization in nucleobase-functionalized supramolecular poly(lactic acid)s: Role of poly(lactic acid) stereostructure

Abstract

Supramolecular polymers can be conveniently prepared by end-functionalization of oligomers with multiple H-bonding units. Crystallization of H-bonding units and polymer blocks can drive supramolecular polymers to form long-range structural organization. Herein, we studied the crystallization kinetics and crystallization-induced lamellar structure in poly(lactic acid) (PLA)-based supramolecular polymers end-functionalized by thymine (PLA-Thy). Tuning stereoregularity of PLA chains (atactic, isotactic, stereocomplexed) results in various crystallization and self-assembling pathways of this crystallizable supramolecular polymer, giving access to controllable lamellar structure. The thickness of organized lamellae grows steadily with greater PLA block length. Increasing PLA block length and crystallization temperature can enhance the crystallizability of isotactic or stereocomplexed PLA chains, and either the generated homo or stereocomplex (SC) crystallization suppresses the crystallizability of thymine unit. Meanwhile, the formation of PLA crystals depresses the regularity of lamellar ordering and decreases the lamellar thickness. These effects are more significant when PLA block undergoes SC crystallization, due to the more compact chain packing in SC crystals compared to the homocrystals. On contrary, atactic PLA block-based supramolecular polymer processes a high value of lamellar thickness due to the looser packing of amorphous chains.