83 research outputs found
David Sherrington commemorative issue
This themed issue of Polymer Chemistry was commissioned following the passing, in October 2014, of Professor David Colin Sherrington, FRS. It was commissioned as a dedication to the memory of a world-class polymer chemist of international renown, as well as a celebration of a subject area that was very close to Dave's heart and upon which he founded his career and made his name. It is entirely appropriate that this collection of papers is published in a leading international journal that bears the name of the subject field with which Dave's name is synonymous and to which he contributed so much – Polymer Chemistry – and that this collection be published in the UK by his own professional chemical society, the Royal Society of Chemistry
Polymerizable UV absorbers for the UV stabilization of polyesters. I. Design, synthesis and polymerization of a library of UV absorbing monomers
Poly(ethylene terephthalate) (PET) absorbs strongly in the ultraviolet (UV) region of the EM spectrum (Figure 1), and this can lead to photodegradation of the polymer chains and loss of polymer properties. UV stabilizer additives are normally employed to suppress the UV-induced photodegradation of polyester films, especially for those applications where the levels of UV exposure to the polymer film are high, e.g., photovoltaic cells. One limitation concerning the use of UV stabilizers is the loss of additive from the polymers over time by leaching, since UV stabilizers are normally low molar mass organic compounds that can be washed out through weathering actions, and this reduces their effectiveness. One way in which this leaching problem can potentially be circumvented is to lock the UV stabilizers into the polymer chains through covalent bond
Polymerizable UV absorbers for the UV stabilization of polyesters. II. Photodegradation study of UV-stabilized PET copolymers
Polymerizable UV absorbing monomers (UVAMs) were copolymerized with bis(hydroxyethyl) terephthalate to yield copolymers of poly(ethylene terephthalate) (PET). PET copolymer films containing 3-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)-3-hydroxyphenoxy]-1,2-propanediol (UVAM 12) and 6,6’-(6-phenyl-1,3,5-triazine-2,4-diyl)bis(3-(2-hydroxyethoxy)phenol) (UVAM 24) were exposed to UV radiation for 1082 hrs. in a QUV-A accelerated weathering instrument and analyzed periodically using FT-IR spectroscopy and GPC. It was found that PET films containing copolymerized UVAMs outperformed films containing admixed Tinuvin 1577 stabilizer, thereby offering even greater protection to polymer films against UV-induced crosslinking and chain scission
Synthesis of poly(acrylonitrile-co-divinylbenzene-co-vinylbenzyl chloride)-derived hypercrosslinked polymer microspheres and a preliminary evaluation of their potential for the solid-phase capture of pharmaceuticals
Poly[acrylonitrile (AN)‐co‐divinylbenzene (DVB)‐co‐vinylbenzyl chloride (VBC)] terpolymers were synthesized by precipitation polymerization in the form of porous polymer microspheres. The poly(AN‐co‐DVB‐co‐VBC) polymers were then hypercrosslinked, via a Friedel‐Crafts reaction with FeCl3 in nitrobenzene, to provide a significant uplift in the specific surface areas of the polymers. FTIR spectra of the hypercrosslinked poly(AN‐co‐DVB‐co‐VBC)s showed that the chloromethyl groups derived from VBC were consumed by the Friedel‐Crafts reactions, which was consistent with successful hypercrosslinking. Hypercrosslinking installed a number of new, small pores into the polymers, as evidenced by a dramatic increase in the specific surface areas upon hypercrosslinking (from ∼530 to 1080 m2 g−1). The hypercrosslinked polymers are very interesting for a range of applications, not least of all for solid‐phase extraction (SPE) work, where the convenient physical form of the polymers (beaded format), their low mean particle diameters, and narrow particle size distributions, as well as their high specific surface areas and polar character (arising from the AN residues), make them attractive candidates as SPE sorbents. In this regard, in a preliminary study one of the hypercrosslinked polymers was utilized as an SPE sorbent for the capture of the polar pharmaceutical diclofenac from a polar environment
The synthesis and characterisation of porous thioamide-sulfonated-modified poly(acrylonitrile-co-divinylbenzene-80) as a potential sorbent to capture polar analytes
Pharmaceuticals contain biologically active components that can pollute water courses as a result of the excretions from individuals and/or uncontrolled release of residues from chemical plants, and they can pose a hazard to health. Pharmaceutical residues can persist at low concentrations in the environment, and thus may be potentially harmful to aquatic animals and to humans. Controlling and monitoring such residues are therefore a prime interest, for example, a solid-phase extraction uses solid sorbents to purify and preconcentrate the residues prior to their chemical analysis. In the present study, poly (acrylonitrile-co-divinylbenzene-80) sorbents are synthesised by varying the comonomer feed ratios under precipitation polymerisation conditions to deliver a family of porous polymer microspheres. Acrylonitrile confers polar characters onto the sorbents, and the acrylonitrile-derived nitrile groups can be chemically transformed via polymer-analogous reactions into thioamide and sulfonated residues which make the sorbents even more suitable for the capture of polar analytes, including selected pharmaceuticals. The utility of the porous thioamide-sulfonated containing sorbents is demonstrated via the dispersion-solid phase extraction of mefenamic acid from aqueous media; mefenamic acid is an anthranilic acid derivative which is a potent, non-steroidal anti-inflammatory drug which is found in environmental waters at low concentrations
Donor-acceptor Stenhouse adduct functionalised polymer microspheres
Polymers that carry donor-acceptor Stenhouse adducts (DASAs) are a very relevant class of light-responsive materials. Capable of undergoing reversible, photoinduced isomerisations under irradiation with visible light, DASAs allow for on-demand property changes to be performed in a non-invasive fashion. Applications include photothermal actuation, wavelength-selective biocatalysis, molecular capture and lithography. Typically, such functional materials incorporate DASAs either as dopants or as pendent functional groups on linear polymer chains. By contrast, the covalent incorporation of DASAs into crosslinked polymer networks is under-explored. Herein, we report DASA-functionalised crosslinked styrene-divinylbenzene-based polymer microspheres and investigate their light-induced property changes. This presents the opportunity to expand DASA-material applications into microflow assays, polymer-supported reactions and separation science. Poly(divinylbenzene-co-4-vinylbenzyl chloride-co-styrene) microspheres were prepared by precipitation polymerisation and functionalised via post-polymerisation chemical modification reactions with 3rd generation trifluoromethyl-pyrazolone DASAs to varying extents. The DASA content was verified via 19F solid-state NMR (ssNMR), and DASA switching timescales were probed by integrated sphere UV-Vis spectroscopy. Irradiation of DASA functionalised microspheres led to significant changes in their properties, notably improving their swelling in organic and aqueous environments, dispersibility in water and increasing mean particle size. This work sets the stage for future developments of light-responsive polymer supports in solid-phase extraction or phase transfer catalysis
Polymer-Supported Photosensitizers for Oxidative Organic Transformations in Flow and under Visible Light Irradiation
A 2,1,3-benzothiadiazole (BTZ)–based vinyl crosslinker was synthesized and copolymerized with large excesses of styrene using free radical polymerization to deliver heterogeneous triplet photosensitizers in three distinct physical formats: gels, beads and monoliths. These photosensitizers were employed for the production of singlet oxygen (1O2) and for the aerobic hydroxylation of aryl boronic acids via superoxide radical anion (O2˙-) whereby the materials demonstrated good chemical and photo stability. BTZ-containing beads and monoliths were exploited as photosensitizers in a commercial flow reactor, and 1O2 production was also demonstrated using direct sunlight irradiation, with a conversion rate comparable to the rates achieved when using a 420 nm LED module as the source of photons
Affinity chromatography in dynamic combinatorial libraries: one-pot amplification and isolation of a strongly binding receptor
We report the one-pot amplification and isolation of a nanomolar receptor in a multibuilding block aqueous dynamic combinatorial library using a polymer-bound template. By appropriate choice of a poly(N,N-dimethylacrylamide)-based support, unselective ion-exchange type behaviour between the oppositely charged cationic guest and polyanionic hosts was overcome, such that the selective molecular recognition arising in aqueous solution reactions is manifest also in the analogous templated solid phase DCL syntheses. The ability of a polymer bound template to identify and isolate a synthetic receptor via dynamic combinatorial chemistry was not compromised by the large size of the library, consisting of well over 140 theoretical members, demonstrating the practical advantages of a polymer-supported DCL methodology
Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant
Jet event rates in deep inelastic ep scattering at HERA are investigated
applying the modified JADE jet algorithm. The analysis uses data taken with the
H1 detector in 1994 and 1995. The data are corrected for detector and
hadronization effects and then compared with perturbative QCD predictions using
next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2)
is determined evaluating the jet event rates. Values of alpha_S(Q^2) are
extracted in four different bins of the negative squared momentum
transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the
renormalization group equation to these several alpha_S(Q^2) values results in
alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys.
J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4
Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA
Deep--inelastic scattering events with a leading baryon have been detected by
the H1 experiment at HERA using a forward proton spectrometer and a forward
neutron calorimeter. Semi--inclusive cross sections have been measured in the
kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T
<= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV,
or a neutron with energy E' >= 160 GeV. The measurements are used to test
production models and factorization hypotheses. A Regge model of leading baryon
production which consists of pion, pomeron and secondary reggeon exchanges
gives an acceptable description of both semi-inclusive cross sections in the
region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading
neutron data are used to estimate for the first time the structure function of
the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.
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