Unraveling Sequence Effect on Glass Transition Temperatures of Discrete Unconjugated Oligomers

Abstract

Sequence plays a critical role in enabling unique properties and functions of natural biomolecules, which has promoted the rapid advancement of synthetic sequence-defined polymers in recent decades. Particularly, investigation of short chain sequence-defined oligomers (also called discrete oligomers) on their properties has become a hot topic. However, most studies have focused on discrete oligomers with conjugated structures. In contrast, unconjugated oligomers remain relatively underexplored. In this study, three pairs of discrete oligomers with the same composition but different sequence for each pair are employed for investigating their glass transition temperatures (T g s). The resultant T g s of sequenced oligomers in each pair are found to be significantly different (up to 11.6 °C), attributable to variations in molecular packing as demonstrated by molecular dynamics and density function theory simulations. Intermolecular interaction is demonstrated to have less impact on T g s than intramolecular interaction. The mechanistic investigation into two model dimers suggests that monomer sequence caused the difference in intramolecular rotational flexibility of the sequenced oligomers. In addition, despite having different monomer sequence and T g s, the oligomers have very similar solubility parameters, which supports their potential use as effective oligomeric plasticizers to tune the T g s of bulk polymer materials.

Discrete oligourethanes of sequence-regulated properties – impact of stereocontrol

“…Sequence-effect on glass transition has been previously observed for oligourethanes 34 and other discrete oligomers. 44 While comparing oligourethanes of the same composition but different monomer order, slight differences in T g (max ΔT g = 1.3 °C) were observed between oligomers Bz-ABBA, Bz-BBAA, and Bz-ABAB. Oligomers, where the B monomer migrates from the first position to the second position, have very close T g values (ΔT g = 0.5 °C).…”

Stereodivergent Synthesis of Enantiopure Oligomers with Tailored Physical Properties

“…53 This type of packing generally requires uniform and straight chain conformations, which result from the balance between the energetic cost for polymer chain bending and increased entropy. [54][55] That is, twisted or non-uniform macromolecular conformations provides loose packing of polymer chains and a low…”

Effect of Monomer Sequence Distribution on the Glass Transition Temperature of Poly(d,l-lactic-co-glycolic acid) (PLGA)

“…In other molecular dynamics simulation studies conducted by Liu et al and Carbone et al, the calculated T g values for various sequential arrangements of cooligomers/ copolymers closely corresponded to experimentally determined T g data. 43,44 For this study, Liu et al synthesized distinct trimers (comprising N-phenyl maleimide, indene, fumaronitrile, and dimethyl fumarate monomers) using the photoinduced Reversible Addition−Fragmentation Chain Transfer (RAFT) single-unit monomer insertion technique, while Carbone et al utilized different catalysts or varied experimental conditions with the same catalyst to produce copolymers (consisting of ethylene and norbornene monomers) with unique sequences. 43,44 While these synthesis approaches served the purposes of these studies, there still is a need for a facile yet systematic synthesis technique to achieve precise monomer sequence control.…”