Preparation of dual stimuli-responsive block copolymers based on different activated esters with distinct reactivities

Synthesis of functional polyacrylamide (co)polymers by organocatalyzed post-polymerization modification of non-activated esters

The broad application of polyacrylamides (PAMs) has greatly promoted the development of new synthetic methods to prepare PAM-based functional (co)polymers regarding their traditional preparation via the direct polymerization of various acrylamide monomers. Herein, we have explored the post-polymerization modification of the poly(2,2,2-trifluoroethyl acrylate) (PTFEA) homopolymer, a typical non-activated ester, and various amines using the organo-catalytic system involving 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,2,4-triazole (TA). The reaction kinetics (e.g., the optimized reaction solvent, temperature, time, initial molar ratio of amines to esters and the molar ratio of DBU to TA) were carefully studied with the modulus substrate of iso-propylamine as the formed poly(iso-propyl acrylamide) (PNIPAM) representing the most investigated PAM. The full and partial amidation of the esters in PTFEA could be precisely regulated just by controlling the kinetic conditions to give (co)polymers with designable compositions and structures. We have demonstrated that the poly(N-acryloyl pyrrolidine) obtained by the post-polymerization modification of non-activated ester and pyrrolidine exhibited a noticeable phase transition, which confirmed the robustness and versatility of the post-polymerization modification. The described method paves the way for the synthesis of various (co)polymers with amide side chains from readily available polymer precursors.

Copolymers Derived from Two Active Esters: Synthesis, Characterization, Thermal Properties, and Reactivity in Post-Modification

Copolymers with two distinguished reactive repeating units are of great interest, as such copolymers might open the possibility of obtaining selective and/or consequent copolymers with different chemical structures and properties. In the present work, copolymers based on two active esters (pentafluorophenyl methacrylate and p-nitrophenyl methacrylate) with varied compositions were synthesized by Cu(0)-mediated reversible deactivation radical polymerization. This polymerization technique allows the preparation of copolymers with high to quantitative conversion of both comonomers, with moderate control over dispersity (Đ = 1.3–1.7). Additionally, by in-depth study on the composition of each copolymer by various techniques including elemental analysis, NMR, FT-IR, and XPS, it was possible to confirm the coherence between expected and obtained composition. Thermal analyses by DSC and TGA were implemented to investigate the relation between copolymers’ composition and their thermal properties. Finally, an evaluation of the difference in reactivity of the two monomer moieties was confirmed by post-modification of copolymers with a primary amine and a primary alcohol as the model.

Modulating the reactivity of polymer with pendant ester groups by methylation reaction for preparing functional polymers

Chemical reaction triggered the reactivity of polymeric esters.

Electrochemically-initiated polymerization of reactive monomers via 4-fluorobenzenediazonium salts

We report on the electrochemically-initiated polymerization of reactive monomers using a fluorine-labelled aromatic diazonium salt in an undivided cell setup with subsequent post-polymerization modifications of the intact reactive moieties.

A synthetic approach toward a pH and sugar-responsive diblock copolymer via post-polymerization modification

A novel pH- and sugar-responsive diblock copolymer containing phenylboronic acid was synthesized by RAFT and a post-polymerization modification strategy.

Dual stimuli-responsive Fe3O4 graft poly(acrylic acid)-block-poly(2-methacryloyloxyethyl ferrocenecarboxylate) copolymer micromicelles: surface RAFT synthesis, self-assembly and drug release applications

BACKGROUND

Stimuli-responsive polymer materials are a new kind of intelligent materials based on the concept of bionics, which exhibits more significant changes in physicochemical properties upon triggered by tiny environment stimuli, hence providing a good carrier platform for antitumor drug delivery.

RESULTS

Dual stimuli-responsive Fe3O4 graft poly(acrylic acid)-block-poly(2-methacryloyloxyethyl ferrocenecarboxylate) block copolymers (Fe3O4-g-PAA-b-PMAEFC) were engineered and synthesized through a two-step sequential reversible addition-fragmentation chain transfer polymerization route. The characterization was performed by FTIR, 1H NMR, SEC, XRD and TGA techniques. The self-assembly behavior in aqueous solution upon triggered by pH, magnetic and redox stimuli was investigated via zeta potentials, vibration sample magnetometer, cyclic voltammetry, fluorescent spectrometry, dynamic light scattering, XPS, TEM and SEM measurements. The experimental results indicated that the Fe3O4-g-PAA-b-PMAEFC copolymer materials could spontaneously assemble into hybrid magnetic copolymer micromicelles with core-shell structure, and exhibited superparamagnetism, redox and pH stimuli-responsive features. The hybrid copolymer micromicelles were stable and nontoxic, and could entrap hydrophobic anticancer drug, which was in turn swiftly and effectively delivered from the drug-loaded micromicelles at special microenvironments such as acidic pH and high reactive oxygen species.

CONCLUSION

This class of stimuli-responsive copolymer materials is expected to find wide applications in medical science and biology, etc., especially in drug delivery system.

Thermoresponsive Gels

Thermoresponsive gelling materials constructed from natural and synthetic polymers can be used to provide triggered action and therefore customised products such as drug delivery and regenerative medicine types as well as for other industries. Some materials give Arrhenius-type viscosity changes based on coil to globule transitions. Others produce more counterintuitive responses to temperature change because of agglomeration induced by enthalpic or entropic drivers. Extensive covalent crosslinking superimposes complexity of response and the upper and lower critical solution temperatures can translate to critical volume temperatures for these swellable but insoluble gels. Their structure and volume response confer advantages for actuation though they lack robustness. Dynamic covalent bonding has created an intermediate category where shape moulding and self-healing variants are useful for several platforms. Developing synthesis methodology-for example, Reversible Addition Fragmentation chain Transfer (RAFT) and Atomic Transfer Radical Polymerisation (ATRP)-provides an almost infinite range of materials that can be used for many of these gelling systems. For those that self-assemble into micelle systems that can gel, the upper and lower critical solution temperatures (UCST and LCST) are analogous to those for simpler dispersible polymers. However, the tuned hydrophobic-hydrophilic balance plus the introduction of additional pH-sensitivity and, for instance, thermochromic response, open the potential for coupled mechanisms to create complex drug targeting effects at the cellular level.

Reversible Regulation of Thermoresponsive Property of Dithiomaleimide-Containing Copolymers via Sequential Thiol Exchange Reactions

The facile and efficient functionalization of thermoresponsive polymers based on sequential, reversible thiol-exchange reactions is reported. Well-defined dithiomaleimide-containing polymers have been synthesized via Cu(0)-mediated SET-LRP and characterized by ¹H NMR and size exclusion chromatography (SEC). The resulting thermosensitive copolymers were subsequently reacted with various thiols to demonstrate the applicability of the strategy, and the thiol-exchange reaction was found to be very fast and efficient. The cloud point of the prepared copolymers can be continually and reversibly tuned, and desirable functionality can be dynamically exchanged upon sequential addition of functional thiol reagents. Through the substitution by thioglucose, an ON-to-OFF switch for fluorescence of the copolymers along with the generation of a glycopolymer was achieved.

One-pot polymer modification of carbon nanotubes through mercaptoacetic acid locking imine reaction and π–π stacking

Mercaptoacetic acid locking imine (MALI) reaction has been reassessed as a tricomponent click reaction to collaborate with supramolecular interaction (π–π stacking) to efficiently and facilely modify carbon nanotube surface with polymers.