Thermoresponsive Dendronized Microgels through In Situ Cross-Linking Polymerization to Exhibit Enhanced Confinement for Solvatochromic Dyes

Abstract

Polymeric microgels form a class of promising materials for various applications based on their highly tunable swelling and cooperative interactions between the cross-linked polymer chains. Here, we report on a convenient route for the fabrication of polymeric microgels through in situ cross-linking polymerization of thermally collapsed macromonomers carrying 3-fold dendritic oligoethylene glycol (OEG) pendants, affording thermoresponsive dendronized microgels with intriguing microconfinement. This methodology has been proven to be versatile and can be used to prepare intelligent microgels through homopolymerization of thermoresponsive dendronized macromonomers, or via copolymerization with either hydrophobic or hydrophilic, and dendronized or nondendronized comonomers. The thermoresponsive microgels of uniform sizes undergo shrinking or swelling by changing the temperature above or below their phase transition temperatures and thus exhibit tunable microconfinement to encapsulated solvatochromic dye molecules. This outstanding capacity for confinement by the microgels is compared to linear copolymers with or without dendritic architectures and is proposed to originate from both dendritic crowding effects and cooperative interactions between polymer chains within the network. This remarkable feature of microconfinement opens a new era for microgels to reversibly encapsulate and protect guest molecules and provides a platform to manipulate the functions of the encapsulated guests through external stimuli.

Thermoresponsive Dendronized Poly(phenylacetylene)s via Dynamic Covalent Chemistry Showing Multiple-Responsive Chirality

“…Therefore, we assume that the presence of abundant charged L -Phe may have intensively interacted with the copolymers to exhibit Hofmeister salt-in effects through either π–π stacking with the polyene backbones or ionic–dipolar interactions with the pendants, affording the copolymers with enhanced hydrophilicity. As we demonstrated previously, phase transition temperatures of OEG-based dendronized polymers were determined mainly by hydrophilicity or hydrophobicity of their peripherals, and changing ethoxyl into methoxyl terminals can lead to their T cp s increased by more than 15 °C. , Furthermore, crowding effects from the densely packed dendritic OEGs also showed influence on their T cp s, which provided shielding (i.e., microconfinement) to either hydrophobic or hydrophilic interiors of the polymers. , That is why the hydrophobic PPA backbones reduced only slightly the T cp s by ∼5–6 °C when compared to their dendronized polymethacrylate analogs. , Therefore, the significant increase of T cp s (Δ T > 12 °C) of these dendronized copoly­(phenylacetylene)­s upon the addition of amino acids should be caused by the strong interactions between the pendants and the additional hydrophilic amino acids.…”

“…This indicates that the copolymers with either amide or ester linkage between the polyene backbone and dendritic OEG pendants showed similar chirality transitions across their thermally mediated phase transitions. These results suggest that thermally induced collapse of dendritic OEGs should have reduced the ordered orientation of the pendants along the polyene backbones and simultaneously provided steric hindrance to release the complexed amino acids at elevated temperature, which weakens the excess one-handed helicity induction efficiency from both chiral pendants and complexed amino acids. These results also encouraged us to investigate the helicity transitions of optically inactive copolymers PN 2.5 Ad 1 and PO 2.7 Ad 1 induced by the addition of amino acids.…”

Dendronization of chitosan to afford unprecedent thermoresponsiveness and tunable microconfinement

“…The advances in understanding of microconfinement from these modified biodegradable biomacromolecules offer new research directions, which can be further explored by using dendritic OEGs with different branching densities, including 2-fold, 3-fold, 4-fold and 6-fold. 12,53 With different packing densities of the OEG chains, crowding should be in different levels around the backbone of the biomacromolecules, which should be important in creating different levels of microconfinement for different application purposes, such as protection of proteins or nucleic acids, as well as drug delivery and drug targeting. We hope that the methodology developed in this perspective can provide some inspiration to functionalize other biomacromolecules, especially those carrying amino pendants, such as hyaluronic acid, gelatin or collagen.…”

“…2,6 The most intriguing example includes crown ether invented by Peterson, which can bind metal ions specifically from the aqueous phase through cooperative ionic-dipole interactions between donors (oxygens from crown ethers) and acceptors (metal ions). 2,7 Recently, synthetic crowders, for example, Ficoll, 8 dextran, 9 polyethylene glycol (PEG) 6,10 or even copolymers 11,12 have been used at high concentrations to mimic in vivo crowding effects and play the role of exerting excluded volume effects, stabilizing proteins, and promoting protein aggregation. 13 However, these synthetic (macro) molecules for creating a confined microenvironment are normally not biocompatible and biodegradable, which makes it difficult to use them for bioapplications such as drug prolonged delivery.…”

“…Dendritic macromolecules possess a branched architecture and multivalency characteristics, which have privilege in the formation of a confined microenvironment and provide cooperative interactions supplying guests with better shielding and protection effect. 2,12,52–57 They have shown intriguing potentials for modification of CS to form a novel class of dendronized CSs (DCSs), which excellently integrate both natural properties from CS and imparted functions from the dendritic units. 53,58–60 The synthetic strategies of DCSs have had significant advances recently, but these modified entities are still short of stimuli-responsive properties, which hinders the widespread application of these promising materials.…”