Adamantane Functionalized Poly(2-oxazoline)s with Broadly Tunable LCST-Behavior by Molecular Recognition

Abstract

Smart or adaptive materials often utilize stimuli-responsive polymers, which undergo a phase transition in response to a given stimulus. So far, various stimuli have been used to enable the modulation of drug release profiles, cell-interactive behavior, and optical and mechanical properties. In this respect, molecular recognition is a powerful tool to fine-tune the stimuli-responsive behavior due to its high specificity. Within this contribution, a poly(2-oxazoline) copolymer bearing adamantane side chains was synthesized via triazabicyclodecene-catalyzed amidation of the ester side chains of a poly(2-ethyl-2-oxazoline-stat-2-methoxycarbonylpropyl-2-oxazoline) statistical copolymer. Subsequent complexation of the pendant adamantane groups with sub-stoichiometric amounts (0–1 equivalents) of hydroxypropyl β-cyclodextrin or β-cyclodextrin enabled accurate tuning of its lower critical solution temperature (LCST) over an exceptionally wide temperature range, spanning from 30 °C to 56 °C. Furthermore, the sharp thermal transitions display minimal hysteresis, suggesting a reversible phase transition of the complexed polymer chains (i.e., the β-cyclodextrin host collapses together with the polymers) and a minimal influence by the temperature on the supramolecular association. Analysis of the association constant of the polymer with hydroxypropyl β-cyclodextrin via 1H NMR spectroscopy suggests that the selection of the macrocyclic host and rational polymer design can have a profound influence on the observed thermal transitions.

Poly(2-oxazoline)s as Stimuli-Responsive Materials for Biomedical Applications: Recent Developments of Polish Scientists

“…By varying the concentration of the solute, it is possible to tune the temperature at which phase separation occurs. In the following paper [ 86 ], the authors exploited this mechanism by modifying poly(2-oxazolines) with an adamantane group. The adamantane moiety formed inclusion complexes with β-cyclodextrin based on the guest–host interactions.…”

Accelerated Post‐Polymerization Amidation of Polymers with Side‐Chain Ester Groups by Intramolecular Activation

“…Hence unlocking suitable strategies for non-activated ester modification is extremely valuable for the synthetic diversification, upcycling or recycling of both commodity and more specialized polymers. Although the modification of ester groups is typically avoided in post-polymerization modifications due to their poor reactivity, [7,8] several research groups have recently shown the successful transesterification and amidation of polymeric ester groups, as found in polyesters, [9][10][11][12] polyacrylates, [13][14][15][16] polymethacrylates, [17][18][19] and more specialized polypeptides, [1,2] and poly(2-oxazoline)s. [20][21][22][23][24][25] Particularly the use catalysts has flourished, enabling smooth transesterification of various ester substrates. In contrast, amidation of esters suffers from poor reaction kinetics, often requiring long reaction times at elevated temperatures, even in the presence of catalysts.…”

Mechanism insights in controlling host–guest (de)complexation by thermoresponsive polymer phase transitions

“…12 This observed heating-induced decomplexation is an intriguing, † Electronic supplementary information (ESI) available. See DOI: https://doi.org/ 10.1039/d2py00219a a School of Chemical Engineering and Technology, Sun Yat-sen University, Zhuhai 519082, China b but rather specific phenomenon as most other kinds of hostguest complexes attached to a thermoresponsive polymer have been reported to retain in the complexed state upon crossing the T cp (e.g., cyclodextrins, [14][15][16] pillararene 17 hosts or terpyridine ligands 18 ). Benefiting from this LCST-induced decomplexation process that is accompanied by the loss of the characteristic color of the donor-acceptor host-guest complex, this reversible temperature-controlled host-guest interaction can serve as an ideal platform for various potential applications, such as targeted molecular release, or thermoresponsive sensors.…”