Selective determination of hydroquinone in the presence of catechol based on over-oxidized poly(hydroquinone)

Selective determination of hydroquinone (HQ) in the presence of catechol (CC) was developed at an over-oxidized poly(hydroquinone) (PHQ) electrode. The electrochemical polymerization of HQ was carried out by potentiostatic method on a glassy carbon electrode. The resulting PHQ was over-oxidized in 0.10?mol/L NaOH solution and thus poly(p-benzoquinone) was obtained. Two dihydroxybenzene isomers, HQ and CC, show different voltammetric behavior at the over-oxidized PHQ electrode. The peak current of HQ is much larger than that of CC with the same concentration, which is attributed to the different position of the hydroxyl groups in benzene ring of the two isomers. The results from electrochemical impedance spectroscopy also demonstrates that the over-oxidized PHQ electrode has a stronger affinity for HQ over CC.     

以壳聚糖为模板的对苯二酚氧化聚合反应表观动力学研究

以壳聚糖为模板在酸性溶液中实现了对苯二酚的氧化聚合.该反应必须在氧气存在的条件下才能进行.动力学研究表明该氧化聚合反应是以选取机理进行的模板聚合反应.当壳聚糖残基与对苯二酚的摩尔比小于0.8时,反应速度与壳聚糖浓度成正比.当壳聚糖残基与对苯二酚的摩尔比大于0.8时,反应速度不再随壳聚糖浓度提高而提高.反应对对苯二酚而言是一个一级反应.反应的活化能为71.6kJ/mol.     

Chemical Oxidative Synthesis and Characterization of Poly(8-hydroxyquinoline) Particles

The chemical oxidative polymerization (OP) of 8-hydroxyquinoline (HQ) in an organic medium leaded to the formation of the C-2 and C-4 linking poly (8-hydroxyquinoline) (PHQ). The structure of PHQ was confirmed by UV-Vis, FT-IR, and ¹H-NMR. The characterization of polymer was performed by TG-DTA, differential scanning calorimetry, dynamic mechanical analysis, dynamic light scattering, size exclusion chromatography, X-ray diffraction, cyclic voltammetry, atomic force microscope, photoluminescence and solubility tests. The fluorescence spectrum of PHQ exhibited an emission peak at approximately 525 nm in DMSO. Accordingly, it was found PHQ emitted green light whereas HQ emitted yellow light in DMSO solvent. Optical band gaps (E_g) of PHQ was calculated to be 3.31 eV. The electrical conductivities of iodine doped-PHQ and undoped-PHQ were measured with four-point probe technique. Magnetic particles was prepared by chemical precipitation of mixed Fe(II) and Fe(III) salts and modified with HQ by using an in situ chemical oxidation polymerization method in organic medium.     

Covalently attached graft polymer monolayer on organic polymeric substrate via confined surface inhibition reaction

A grafting technique was proposed for the preparation of polymer monolayer on polymeric substrate. On the basis of our recent work on polymer‐supported inhibitor (PSI), hydroquinone (HQ) was first implanted onto polypropylene (PP) surface through UV‐initiated grafting. The resulting immobilized HQ was used as PSI for the thermal‐induced free radical polymerization (FRP) of acrylic acid (AA). The inhibition mechanism was similar to that of free HQ molecule, that is, polymer chain‐carrying radical or peroxy radical could be deactivated by abstracting hydrogen atom from hydroxyl group of immobilized HQ, and the resulting oxyradical (semiquinone radical) combined with another active chain free radical. According to this mechanism, a devised redox initiator consisting of sodium hydrogen sulfite and ammonium persulfate was used to initiate FRP of AA in water at low temperature (50 °C). High crystalline biaxial oriented PP film with HQ immobilized was deliberately laid in this system as a radical trap to capture poly(acrylic acid) (PAA) short chain radical. Through X‐ray photoelectron spectra (XPS) analysis it was found that the atom ratio of C_HQ (carbon in HQ) to C_COOH (carbon in COOH) decreased with prolonging polymerization time and became stable after about 30 min. The formed PAA short chain on the surface showed a distribution of monolayer, and the saturated thickness was calculated as 5–7 Å. The degree of polymerization of graft chain in PAA monolayer was estimated as 15–20 through three different models. Relating to surface coverage being 100% in ideal densely packed PAA monolayer, real monolayer surface coverage in such reaction system was estimated as 12.3–18.5%. This method was expected to give us a general approach for constructing kinds of graft polymer monolayer on polymeric substrate, because the involved chemistry was only common inhibition reaction between immobilized inhibitor (HQ) and FRP system in solution (herein redox initiating system of AA). We named this grafting chemistry as confined surface inhibition reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 745–755, 2007     

Synthesis and inhibition performance of a polymer‐supported inhibitor

The synthesis of a polymer‐supported inhibitor (PSI) and its inhibition performance for free‐radical polymerization are reported for the first time. A special method has been devised to synthesize PSI with pure and abundant hydroquinone (HQ) groups anchored onto the polymer surface. A thin HQ/acetone (AC) solution is sandwiched between two polymer films. Under ultraviolet irradiation, AC as an photoinitiator quickly and effectively grafts HQ onto the polymer surface. PSI has been characterized with ultraviolet–visible and attenuated total reflectance/Fourier transform infrared spectroscopy. For potential applications, PSI has been used to inhibit the thermal polymerization of styrene and methyl methacrylate. The corresponding inhibition performance has been investigated through the measurement of the induction period with the dilatometer method. With the same absolute amount, the maximum inhibition ability of PSI approaches half that of a free inhibitor. Increasing the dispersion degree of PSI is favorable for the enhancement of the inhibition ability. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4074–4083, 2004     

Electrochemical sensors based on molecularly imprinted polymers grafted onto gold electrodes using click chemistry

We have developed a three-step method to graft molecularly imprinted polymer (MIP) thin films onto Au electrodes. In the first step, propargyl acrylate is clicked onto an azidoundecanethiol (N(3)(CH(2))(11)SH)/decanethiol mixed self-assembled monolayer (SAM). Then, by applying UV light (365 nm) in the presence of N,N'-methylenebis(acrylamide) (MAAM) and azobisisobutyronitrile (AIBN) as the radical initiator, polymerization was carried out directly on the electrode surface in the presence of an electroactive template molecule, hydroquinone (HQ). Detection of HQ using the clicked-on MIP sensor was studied using chronoamperometry and its behavior was compared to that of a sensor prepared by drop-coating MIPs onto Au. The detection limit of the clicked-on MIP sensor for HQ was found to be 1.21±0.56 μM, about four times lower than what was observed using the coated-on MIP sensor. In addition, the sensitivity of the clicked-on MIP sensor was found to be approximately three times greater than the coated-on MIP sensor. Apparent diffusion coefficients determined using chronoamperometry suggest that the improved performance is likely due to the favorable mass transfer characteristics of the clicked-on MIP sensing membrane.     

Control of surface morphology of polypropylene/polystyrene blend pellets prepared by diffusion and subsequent polymerization of styrene in isotactic polypropylene pellets

Inhibitor hydroquinone (HQ) was added to the reaction system to prepare polypropylene/polystyrene (PP/PS) blend pellets without PS on the surface during diffusion and subsequent polymerization of styrene in isotactic polypropylene pellets. The effects of the amount of HQ on diametrical distribution of PS, surface morphology of the pellets and phase morphology inside the blend pellets were investigated.     

Change in phase transition behavior of an NIPA gel induced by solvent composition: hydrophobic effect

We carried out the measurements of the equilibrium size of N-isopropylacrylamide (NIPA) gel immersed in a dilute aqueous solution of hydroquinone (HQ) as a function of temperature. It was found that, by embedding a small amount of HQ molecules into the gel fluid, volume phase transition behavior of the NIPA gel changed qualitatively depending on the HQ concentration. Moreover, the change in phase transition from continuous to discontinuous was observed without permanent alteration of polymer networks such as hydrolysis. This fact suggests that, by changing HQ concentration, we will be able to find a critical isobar without changing the gel structure.     

Functional monomers and polymers. XXXVIII. Postirradiation polymerization of 2,3-dimethylbutadiene in deoxycholic acid canal complexes

Postirradiation polymerization of 2,3-dimethylbutadiene in deoxycholic acid canal complexes was studied under various reaction conditions. The polymerization was carried out in degassed sealed tubes since the atmosphere had a large effect upon the polymer yield. Addition of 2,3-dimethylbutane led to a sharp drop in polymer yield, while hydroquinone showed little effect on the polymerization. The rate of postirradiation polymerization was found to increase with increase in reaction temperature and irradiation dose. The apparent activation energy was obtained as 13.7 kcal/mole in a temperature range between ?14 and 30°C. Existence of living free radicals having a long lifetime, the gradual change of the monomer into the polymer within the canals, and the effective spatial control in canals are discussed on the basis of the postirradiation polymerization behavior, nature of the adducts, and the structure of the polymers.     

Fabrication of Defined Polydopamine Nanostructures by DNA Origami‐Templated Polymerization

A versatile, bottom‐up approach allows the controlled fabrication of polydopamine (PD) nanostructures on DNA origami. PD is a biosynthetic polymer that has been investigated as an adhesive and promising surface coating material. However, the control of dopamine polymerization is challenged by the multistage‐mediated reaction mechanism and diverse chemical structures in PD. DNA origami decorated with multiple horseradish peroxidase‐mimicking DNAzyme motifs was used to control the shape and size of PD formation with nanometer resolution. These fabricated PD nanostructures can serve as “supramolecular glue” for controlling DNA origami conformations. Facile liberation of the PD nanostructures from the DNA origami templates has been achieved in acidic medium. This presented DNA origami‐controlled polymerization of a highly crosslinked polymer provides a unique access towards anisotropic PD architectures with distinct shapes that were retained even in the absence of the DNA origami template.     

Functional monomers and polymers. CXXXII. Template polymerization of methacrylamide derivatives containing nucleic acid bases

Free-radical polymerizations of methacrylamide derivatives containing nucleic acid bases were studied in the presence of the polymethacrylamide having complementary nucleic acid bases as template polymers. The rate of the polymerization did not show remarkable difference in the presence or the absence of the template polymer. A stable polymer complex, however, was precipitated from the polymerization system, and was found to be different in a thermal analysis from the polymer complex which was obtained by mixing of the complementary polymers in solution. Free-radical copolymerizations in the presence of the template polymers also supported the template polymerization.     

In Situ Controlled Construction of a Hierarchical Supramolecular Chiral Liquid‐Crystalline Polymer Assembly

Hierarchical supramolecular chiral liquid‐crystalline (LC) polymer assemblies are challenging to construct in situ in a controlled manner. Now, polymerization‐induced chiral self‐assembly (PICSA) is reported. Hierarchical supramolecular chiral azobenzene‐containing block copolymer (Azo‐BCP) assemblies were constructed with π–π stacking interactions occurring in the layered structure of Azo smectic phases. The evolution of chirality from terminal alkyl chain to Azo mesogen building blocks and further induction of supramolecular chirality in LC BCP assemblies during PICSA is achieved. Morphologies such as spheres, worms, helical fibers, lamellae, and vesicles were observed. The morphological transition had a crucial effect on the chiral expression of Azo‐BCP assemblies. The supramolecular chirality of Azo‐BCP assemblies destroyed by 365 nm UV irradiation can be recovered by heating–cooling treatment; this dynamic reversible achiral–chiral switching can be repeated at least five times.     

Polymer catenanes via a supramolecularly templated ATRP initiator

Synthesis of polymer catenanes via a living radical polymerization and supramolecular template approach are demonstrated. The ring closure was performed via atom transfer radical cross coupling (ATRC) to obtain polymer catenanes from the linear polymer metal complex precursor.     

Photo-sensitive self-motion of a BQ disk

The photo-sensitive self-motion of a benzoquinone (BQ) disk was investigated on a hydroquinone (HQ) aqueous solution. The mode-switching of self-motion, i.e., continuous → intermittent → no motion, was observed with an increase in the concentration of HQ. Upon irradiation with UV light (～254 nm), the critical concentrations of HQ that were associated with the three modes of motion shifted to lower values, and the average speed of motion decreased. We discuss the mechanism of the photo-sensitive self-motion in relation to the photochemical reaction from BQ to HQ and the driving force of the disk.     

Step‐Growth Copolymerization Between an Immobilized Monomer and a Mobile Monomer in Metal–Organic Frameworks

The A–A/B–B step‐growth copolymerization between a monomer immobilized in the crystalline state and a monomer mobile in the solution state is demonstrated. One of the two monomers was immobilized as organic ligands of the metal–organic framework (MOF) and polymerized with the mobile guest monomer, resulting in the formation of linear polymers. The polymerization behavior was completely different from that of the solution polymerizations. In particular, the degrees of polymerization (DP) converged to a specific value depending on the MOF structures. The inevitable termination is caused not by imperfectness of the polymerization reaction, but by the selection of the two polymerization partners among the several adjacent immobilized monomers. This is fully supported by the Monte Carlo simulation on the basis of the polymerization mechanism. Precise immobilization of monomers in the supramolecular assemblies is a promising way for the controlled A–A/B–B step‐growth polymerization.     

阻聚剂对MMA原子转移自由基聚合的影响

Effect of a series of inhibitors as additives on atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with FeCl2/PPh3 as catalyst system was studied, including 2,4,6-trinitrophenol (TNP), 4-methoxyphenol (4-MP), hydroquinone (HQ) and nitrobenzene (NB). It was found that TNP was the only. efficient additive for ATRP among these inhibitors. In the presence of small amounts of TNP, the polymerization proceeded rapidly after induction period to yield the polymers with controlled molecular weights and narrow molecular weight distributions (MWD). The initiating efficiency of the modified catalyst system with TNP was increased. The mechanism was proposed and confirmed by the end group analysis of the polymer.     

Simultaneous determination of hydroquinone and catechol based on three-dimensionally ordered macroporous polycysteine film modified electrode

A three-dimensionally ordered macroporous (3DOM) polycysteine (PCE) film was electropolymerized on the glassy carbon electrode (GCE) using polystyrene spheres as template. The electrochemical behaviors of hydroquinone (HQ) and catechol (CC) were studied, and two independent oxidation peaks were observed. Compared with the bare GCE and GCE modified with PCE without using template, this electrode displays larger peak currents which may be attributed to the structure of PCE and the large surface area of the nanopore array structure. As a result, a novel electrochemical method was developed for the simultaneous determination of HQ and CC. Under the optimized conditions, the peak currents were linear to concentrations in the wider ranges of 9 to 700 μM for HQ and from 3 to 700 μM for CC. The method was successfully applied to the simultaneous determination of HQ and CC in spiked water samples, and the results are satisfactory.     

Thermotropic liquid-crystalline copolyesters containing substituted phenylene terephthalate and ethylene terephthalate units

Three series of aromatic, thermotropic copolyesters, based on terephthalic acid (TA), ethylene glycol (EG), and another diol were prepared. The third monomer was selected from three different hydroquinones including, ethoxyhydroquinone (EHQ), phenylhydroquinone (PHQ), and hydroquinone itself (HQ). The amounts of the different hydroquinone terephthalate units were varied while the amounts of ethylene terephthalate units remained constant. The copolymers and terpolymers were characterized for solubility, for morphology by polarized light microscopy (PLM), for molecular weight by solution viscometry, and by NMR, DSC, and TGA. At elevated temperatures all samples, when observed by PLM, displayed the characteristic texture of a nematic phase. The melting transition temperatures, T_m, were found to vary from 255 to 325°C, while the 5 wt % loss temperatures, T_d, were found to vary from 330 to 440°C. The inherent viscosities varied from 0.6 to 1.9 dL/g. Increases in the HQ monomer content caused a decreased solubility and an increase in melting point. Copolymer compositions determined by NMR showed that only about one-half of the EG added was incorporated into the copolymers. © 1997 John Wiley & Sons, Inc.     

L-Proline Functionalized Polymers Prepared by RAFT Polymerization and Their Assemblies as Supported Organocatalysts

We have prepared a range of well-defined copolymers of styrene and L-proline functionalized styrene (5-11 kDa) using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques and explored their use in supported catalysis. Upon deprotection of the L-proline functionalities, the solution self-assembly of these copolymers was investigated in mixed solvent systems. The resulting assemblies were characterized by dynamic light scattering, transmission electron microscopy (on graphene oxide substrates, along with cryo-TEM and tomography), and scanning electron microscopy. The application of these functional assemblies as supported catalysts for the aldol condensation reaction was explored using cyclohexanone and 4-nitrobenzaldehyde. The rate and selectivity of solution catalysis in our self-assembled system were comparable to those of L-proline, and a significant advantage of our system was that the polymer support could be utilized at lower catalyst loadings with comparable activity and also could be recycled a number of times while maintaining activity and selectivity.