Hybrid sol–gel silica adsorbent materials synthesized by molecular imprinting for tannin removal

Journal of Sol-Gel Science and Technology - This study reports the development of a functional adsorbent synthesized by the molecular imprinting method in a sol–gel matrix. The adsorption...     

Increasing molecular weight parameters of a helical polymer through polymerization in a chiral solvent

In this communication, we will demonstrate that polymerization in a chiral solvent can affect the molecular weight distribution of the product by perturbing the balance of the P and M helical screw senses of the growing chains. Specifically, for the Wurtz-type synthesis of polymethylphenylsilane (PMPS) in either (R) or (S)-limonene, the weight-average molecular weight of the products (average Mw = 80 000) was twice that of PMPS synthesized in (R/S)-limonene (average Mw = 39 200). Peturbation of the helical segmentation along the polymer chains leads to a reduction in the rate of occurrence of a key termination step. This the first time that a chiral solvent has been demonstrated to have such an effect on a polymerization process in affecting molecular weight parameters in contrast to affecting tacticity.     

Synthesis and characterization of well‐defined optically active methacrylic diblock copolymers

A new, simple, and cost‐effective approach toward the development of well‐defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low‐cost optically active (S)‐(?)‐2‐methyl‐1‐butanol, a new optically active methacrylic monomer, namely, (S)‐(+)‐2‐methyl‐1‐butyl methacrylate [(S)‐(+)‐MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well‐defined poly[(S)‐(+)‐MBuMA] homopolymers and water‐soluble diblock copolymers based on [(S)‐(+)‐MBuMA] and the hydrophilic and ionizable monomer 2‐(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and ¹H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)‐(+)‐MBuMA)‐b‐p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)‐(+)‐MBuMA]‐b‐p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(ethylene glycol)‐based amphiphilic model conetworks: Synthesis by RAFT polymerization and characterization

Poly(ethylene glycol) (PEG)‐containing quasi‐model amphiphilic polymer conetworks (APCNs) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using α,ω‐bis(2‐cyanoprop‐2‐yl dithiobenzoate)‐PEG as a bifunctional RAFT macrochain transfer agent (macro‐CTA) and stepwise additions of a hydrophobic monomer and a crosslinker (crosslinker: macro‐CTA = 10:1, reaction time 24 h). Three different types of monomers, methyl methacrylate (MMA), n‐butyl acrylate and styrene, were employed as the hydrophobic monomers, whereas ethylene glycol dimethacrylate, ethylene glycol diacrylate and 1,4‐divinylbenzene served as the respective crosslinkers. PEG homopolymer hydrophilic quasi‐model networks were also prepared by RAFT‐polymerizing the three crosslinkers directly onto the two active ends of the PEG‐based macro‐CTA. From the three ABA triblock copolymers prepared, the MMA‐containing one was obtained at the highest polymerization yields. The crosslinking yields of the three ABA triblock copolymers with the corresponding crosslinkers were higher than those of the PEG‐based macro‐CTA with the same crosslinkers. The degrees of swelling (DSs) of all conetworks were measured in water and in tetrahydrofuran (THF). The DSs of the APCNs in THF were higher than those in water, whereas the reverse was true for the DSs of the hydrophilic homopolymer networks. Finally, the aqueous DSs of the APCNs were lower than those of the corresponding hydrophilic homopolymer networks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7556–7565, 2008     

An oligosilane initiator for the Wurtz-type polymerisation of dichloromethylphenylsilane

1-Chloro-4-methyl-1,1,2,2,3,3,4,4-octaphenyltetrasilane was employed as an initiator in the Wurtz-type reductive coupling polymerisations of dichloromethylphenylsilane with sodium in toluene at 65 °C. Yields of polymethylphenylsilane (PMPS) were in the range 32-35% which was almost double that obtained by otherwise identical reactions in the absence of the initiator (16-19%). Furthermore, higher molecular weight parameters were observed for PMPS synthesised with the initiator. This is believed to be a result of the low reduction potential of the oligosilane allowing for it to compete efficiently in the initiation step with the dichloromethylphenylsilane monomer and inhibit end-biting, which usually occurs in conventional syntheses by reaction of the silyl anion with the terminal silicon-chlorine bond in the early stages of the polymerisation. ²⁹Si NMR spectroscopic analysis of an isolated high molecular weight fraction supported the incorporation of the oligosilane in the PMPS chain. In contrast, the use of the initiator in the Wurtz-reductive coupling of dichloromethylphenylsilane in tetrahydrofuran at room temperature led to no increase in molecular weights or yields of PMPS which confirms that the end-biting reaction is not as significant in polymerisations carried out under these conditions.     

Light-regulated supramolecular engineering of polymeric nanocapsules

This article describes the light-driven supramolecular engineering of water-dispersible nanocapsules (NCPs). The novelty of the method lies in the utilization of an appropriate phototrigger to stimulate spherical polymer brushes, consisting of dual-responsive 2-(dimethylamino)ethyl methacrylate (DMAEMA) and light-sensitive spiropyran (SP) moieties, for the development or disruption of the NCPs in a controlled manner. The fabrication of the nanocarriers is based on the formation of H-type π-π interactions between merocyanine (MC) isomers within the sterically crowded environment of the polymer brushes upon UV irradiation, which enables the SP-to-MC isomerization of the photosensitive species. After HF etching of the inorganic core, dual-responsive polymeric vesicles whose walls' robustness is provided by the MC-MC cross-link points are formed. Disruption of the vesicles can be achieved remotely by applying a harmless trigger such as visible-light irradiation. The hydrophilic nature of the DMAEMA comonomer facilitates the engineering of the vesicles in environmentally benign aqueous media and enables the controlled alteration of the NCPs size upon variation of the solution pH. The inherent ability of the NCPs to fluoresce in water opens new possibilities for the development of addressable nanoscale capsules for biomedical applications.     

Solar Reforming of Biomass with Homogeneous Carbon Dots

A sunlight‐powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H₂ fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2–8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long‐lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD‐based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization.