Amphiphilic Graft Copolymers for Time-Delayed Release of Hydrophobic Fragrances

When a controlled or retarded release of perfumes is required such as in cosmetics or cleaning products, polymers can be applied as encapsulation agents. With regard to such applications, we investigated two amphiphilic graft copolymers featuring a polydehydroalanine (PDha) backbone and different hydrophobic side chains. Hereby, grafting of aliphatic octyl side chains (PDha-g-EOct) enabled the adsorption of the aliphatic fragrance tetrahydrolinalool with moderate loads, whereas benzyl side chains (PDha-g-BGE) allowed taking up aromatic fragrances, for example, amylsalicylate-n with exceptionally high loads of up to 8 g g^-1. The side-chain density was studied as well but had no significant influence on the loading. In addition, the characterization and quantification of the load by NMR and thermogravimetric analysis were compared, and it was also possible to load the aromatic model fragrance into the graft copolymer with aliphatic side chains. After 3 months, the load had decreased by 40-50% and, hence, such systems are of interest for a long-term release of perfumes over months. Although this study is a proof-of-concept, we foresee that such polyampholytic graft copolymers can be tailored for the adsorption of a variety of hydrophobic perfumes simply by altering polarity and chemistry of the side chain.

Facile Synthesis of CO2 -Responsive Nano-Objects: Batch versus Semi-Batch RAFT Copolymerization

Precise polymer architecture and self-assembled morphological control are attractive due to their promising applications, such as drug delivery, biosensors, tissue engineering and "smart" optical systems. Herein, starting from the same hydrophilic units poly(ethylene glycol) (PEG), using CO₂ -sensitive monomer N, N-diethylaminoethyl methacrylate (DEAEMA) and hydrophobic monomer benzyl methacrylate (BzMA), a series of well-defined statistical, block, and gradient copolymers is designed and synthesized with similar degree of polymerization but different monomer sequences by batch and semi-batch RAFT polymerization process and their CO₂ -responsive behaviors of these nano-objects is systematically studied. The gradient copolymers are generated by using semi-batch methods with programmed monomer feed rate controlled by syringe pumps, achieving precise control over desired gradient copolymer composition distribution. In aqueous solution, the copolymers could self-assemble into various aggregates before CO₂ stimulus. Upon bubbling CO₂ , the gradient copolymers preferred to form nanosheet-like structures, while the block and statistical copolymers with similar molar mass could only form larger vesicles with thinner membrane thickness or disassemble. The semi-batch strategy to precisely control over the desired composition distribution of the gradient segment presents an emerging trend for the fabrication and application of stimuli-responsive polymers.

Preparation of Gas-Responsive Imprinting Hydrogel and Their Gas-Driven Switchable Affinity for Target Protein Recognition

Novel gas-responsive imprinting hydrogels were fabricated by combining N,N'-dimethylaminoethyl methacrylate gas-sensitive monomers, N,N'-methylenebis(acrylamide) cross-linkers, and human serum albumin (HSA) template proteins via a free radical polymerization. The hydrogel exhibited a reversible gas-responsive property upon N₂/CO₂ exchange. This result was supported by the evidences from hydrogen nuclear magnetic resonance spectroscopy and scanning electron microscopy. By applying this property to sensing application, a CO₂-responsive imprinted biosensor was originally designed on the surface of a glassy carbon electrode. The biosensor exhibited unique self-clean and self-recognition properties toward HSA proteins based on reversible conformational changes driven by N₂/CO₂ stimuli. Moreover, the proposed imprinted biosensor favored HSA proteins by showing satisfactory sensitivity and selectivity and a wider detection range with a low detection limit. As a rare example in imprint sensing, the biosensor was successfully applied to the HSA extraction from complex serum samples. With gas stimuli, the whole process was efficient, controllable, and harmless to the proteins. Thus, the developed biosensor may provide a new prospect in molecularly imprinted sensing applications.

Synthesis of CO2-responsive gradient copolymers by switchable RAFT polymerization and their controlled self-assembly

Switchable RAFT agents, so-called because they can be reversibly switched by an acid/base stimulus to offer very good control over polymerization of both MAMs and LAMs, provide a route to prepare well-defined polyMAM-block-polyLAM copolymers.

CO2-Responsive polymer materials

This paper reviews the chemical fundamentals of CO₂-responsive polymers as well as the latest reported “smart” material systems switched by CO₂.

A CO2-switchable amidine monomer: synthesis and characterization

Smart system employed CO2 gas as new trigger has been attracting enormous attention in recent years, but few monomers that are capable of switching their hydrophobicity/hydrophility upon CO2 stimulation have been reported. A novel CO2 responsive monomer, 4-vinylbenzyl amidine, is designed and synthesized in this work with N,N-dimethylacetamide dimethyl acetal and 4-vinylbenzyl amine that is prepared through the Gabriel reaction. In bi-phase solvent of n-hexane and water, the monomer dissolves in n-hexane first and then transforms into water upon the CO2 treatment, indicating a hydrophobic to hydrophilic transition. This transformation is demonstrated as reversible by monitoring the conductivity variation of its wet dimethyl formamide solution during alternate bubbling/removing CO2. The protonation of 4-vinylbenzyl amidine upon CO2 treatment is demonstrated by 1H NMR which also accounts for the dissolubility change. The reversible addition-fragmentation chain-transfer polymerization of this monomer is also performed, finding the reaction only occurs in glacial acetic acid. The reason can be ascribed to the different radical structure produced in different solvent.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications

CO2 is an ideal trigger for switchable or stimuli-responsive materials because it is benign, inexpensive, green, abundant, and does not accumulate in the system. Many different CO2-responsive materials including polymers, latexes, solvents, solutes, gels, surfactants, and catalysts have been prepared. This review focuses on the preparation, self-assembly, and functional applications of CO2-responsive polymers. Detailed discussion is provided on the synthesis of CO2-responsive polymers, in particular using reversible deactivation radical polymerization (RDRP), formerly known as controlled/living radical polymerization (CLRP), a powerful technique for the preparation of well-defined (co)polymers with precise control over molecular weight distribution, chain-end functional groups, and polymer architectural design. Self-assembly in aqueous dispersed media is highlighted as well as emerging potential applications.

Amphiphilic block copolymer terminated with pyrene group: from switchable CO2-temperature dual responses to tunable fluorescence

Py-PCL-b-P(NIPAM-co-DMAEMA) micelles can present switchable CO₂-temperature dual responses and tunable fluorescence properties.