Catalyst free visible light induced cycloaddition as an avenue for polymer ligation

The current study introduces a tetrazole species able to perform a rapid, visible light induced nitrile imine-mediated tetrazole-ene cycloaddition (NITEC). Full conversion of the tetrazole species under mild, catalyst free conditions is reported. Importantly, the visible light ligation technology is applied as a method for the modification and ligation of polymers featuring the rapid, clean and exclusive formation of the desired cycloadduct

Mechanistic insights into the UV-induced radical copolymerization of 1,3-butadiene with acrylonitrile

An in-depth mechanistic study into the solution based initiator-free UV-induced radical copolymerization of 1,3-butadiene with acrylonitrile is reported. The light induced constant radical flux leads to moderate monomer conversions within 4 to 24 h. The number-average molecular weights of the prepared nitrile butadiene rubber (NBR) range from 2500 to 50 000 g mol -1 (1.7 ≤ PDI ≤ 2.4), while the achievable monomer conversion ranged from close to 7 up to 31% depending on the polymerization temperature, reaction time and UV light intensity. The rate coefficient for the generation of primary radicals, determined as the coupled parameter k1 *k3, showed a dependence on the UV light intensity with values between 6.0 s-2 and 34.6 s-2 deduced for the UV light intensity range of 280 to 700 W. The estimated values of the lower limit average termination rate coefficient displayed no dependence on the UV light intensity, with lower limit values between 2.6 × 108 L mol-1 s-1 and 6.3 × 108 L mol -1 s-1 for the UV light intensity range of 280 to 700 W. The deduced values for the average termination rate coefficient were above the expected values for comparable average termination rate coefficients. © 2013 American Chemical Society

High molecular weight acrylonitrile-butadiene architectures via a combination of RAFT polymerization and orthogonal copper mediated azide-alkyne cycloaddition

α-Functional nitrile butadiene rubber (NBR) building blocks were employed in the copper mediated 1,3-dipolar Huisgen coupling upon addition of 1,4-bis(azidomethyl)benzene (4). Polymer-polymer coupling afforded linear polymers with molecular weights ranging from 2500 g mol -1 to 97000 g mol -1 and polydispersities from 1.1 to 1.6. The α-functional NBR building blocks were obtained via the reversible addition-fragmentation chain transfer (RAFT) copolymerization of acrylonitrile (AN) and 1,3-butadiene (BD) at 100 °C, utilizing the high temperature azo initiator 1,1′-azobis(cyclohexane-1-carbonitrile) and chlorobenzene or acetone as solvents. A novel alkyne-functional trithiocarbonate 2 was synthesized in 64% yield via the N,N′-dicyclohexylcarbodiimide mediated coupling of 2-((dodecylsulfanyl)carbono-thioyl)sulfanyl propanoic acid (DoPAT, 1) and propargyl alcohol. 2 was shown to be an efficient controlling agent for the controlled/living radical copolymerization of acrylonitrile and 1,3-butadiene. The use of copper mediated azide-alkyne cycloaddition was extended towards the side-chain modification of acrylonitrile-butadiene rubbers as well as applied in the synthesis of branched and cross-linked NBR structures. For this purpose an acrylonitrile-1,3-butadiene-propargyl methacrylate (PMA) terpolymer of 3900 g mol -1 with a PDI of 1.3 was synthesized by a DoPAT-mediated RAFT polymerization. Herein, monomers were employed in the ratio of 56:35:9 (BD:AN:PMA). The ability of the terpolymer to undergo side-chain modification was demonstrated upon addition of 1-undecane azide. Cross-links were established via addition of 1,4-bis(azidomethyl)benzene. The current study provides the first successful approach to employ an orthogonal conjugation technique on this technically important class of synthetic rubbers. © 2012 The Royal Society of Chemistry

Reporting pH-sensitive drug release via

We pioneer an approach for the visualization of pH-controlled molecular release of a fluorescent drug from a nitroxide polymer which combined yields a profluorescent system. A methacrylate-based terpolymer, bearing water-solubilizing triethylene-glycol chains, unpaired spins in the form of nitroxide and hydrazone-bound doxorubicin was synthesized to explore the possibilities of release quantification from profluorescent assemblies. Critically, we establish the fluorescence-silencing effect of polymer-bound nitroxides on covalently attached fluorophores and the overall accessibility of such constructs. The facile approach towards a functional assembly shown here provides an easy-to-assemble construct for complex delivery architectures towards applications in theranostics