Barner-Kowollik, C.

Blinco, J.P.

Bruns, M.

Gerstel, P.

Glassner, M.

Gliemann, H.

Trouillet, V.

English

Blinco, J. P.

KITopen

KIT – University of the State of Baden‐Württemberg andNational Research Center of the Helmholtz AssociationInstitute for Chemical Technology and Polymer ChemistryPreparative Macromolecular Chemistry, www.macroarc.deHetero‐Diels‐Alder Chemistry for Nano‐Structured Materials Design20 21 22 23 24 25 260.00.20.40.60.81.0I norm. / a.u.Retention Time / min PS PS-b-PEO 4 h 8 h 20 h 30 h400 425 450 475 500 525 550 575 600 625 6500.040.060.080.100.120.140.160.180.20 = 521 nmabsorbance / a.u.wavelength / nm 2 min 10 min 30 min 60 min 120 minDynamic Covalent Chemistry on Surfaces Employing Highly Reactive CyclopentadienylMoietiesbFormation of Nanoporous Materials via Mild Retro‐Diels‐Alder ChemistryaIntroductionReferences and AcknowledgmentsTuning the properties of surfaces and functional polymeric systems is a key focus in materials science. One of the major scientific challenges is toachieve well‐defined properties and structural order on the surface of materials in an efficient and selective fashion. A range of efficient reactions,some of which adhere to the criteria defined for Click chemistries, (e.g. copper catalyzed Huisgen [2+3] cycloadditions, (hetero) Diels‐Alder (HDA)cycloadditions, etc.), fulfill the criterion of reaching (ideally) quantitative conversions, making them particularly attractive reaction classes fororthogonal surface design. The development of such reactions for orthogonal design has been a recent focus of the Macroarc group; in particular thedevelopment of RAFT‐HDA. As well as acting as an (ultra)rapid conjugation technique, the (H)DA reaction sequence also has the advantage ofcontaining a cycloadduct linkage that is completely reversible (via a retro‐Diels‐Alder (rDA) reaction) at elevated temperatures. Below are twoexamples of how the (H)DA/rDA chemistry has been applied to the design of novel structured materials and surfaces.This work was supported by the Karlsruhe Institute of Technology in the context of the Excellence Initiative for leading German universities, the German ResearchCouncil, the Ministry of Science and Arts of the state of Baden-Württemberg and the Alexander von Humboldt Foundation (in the form of a research fellowship for JPB).a) "Formation of Nanoporous Materials via Mild Retro-Diels-Alder Chemistry" Glassner, M.; Blinco, J.; Barner-Kowollik, C. Polym. Chem., 2011, 2(1), 83-87. b) "DynamicCovalent Chemistry on Surfaces Employing Highly Reactive Cyclopentadienyl Moieties" Blinco, J.P.; Trouillet, V.; Bruns, M.; Gerstel, P.; Gliemann, H.; Barner-Kowollik,C. Adv. Mater. 2011 23(38), 4435-4439.James P. Blinco1,2, Michael Bruns3, Peter Gerstel1, Mathias Glassner1, Hartmut Gliemann4, Vanessa Trouillet3 and Christopher Barner‐Kowollik11Preparative Macromolecular Chemistry, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology;2Current Address: ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Queensland University of Technology; 3Institute for Applied Materials, Karlsruhe Institute of Technology; 4Institute of Functional Interfaces, Karlsruhe Institute of Technology Here, using a facile synthetic reaction, silicon substrates coated with a bromide‐terminated silane were able to be transformed into highly reactive,cyclopentadiene covered analogues. The ability of these surfaces to undergorapid cycloaddition reactions with various dienophile‐capped polymers was thendemonstrated.Comparison of XPS N 1s (Left), C 1s (middle) and Br 3d (right) spectra forsubstrates Si‐Br (a), Si‐CP (b) and Si‐PiBA (c). Peak heights have been normalized;the Br 3d intensity in (b) has been halved for a better visualizationHigh resolution XPS of the C 1s region (left) and water contact angle (right) of substrates cycling between poly(ethylene glycol) being attached or removed from the surface functionalized surface.In this example, it was possible to synthesize thermally cleavable PS‐b‐PEO blockcopolymers by RAFT‐HDA click chemistry. The cleavage of PS‐b‐PEO can be carriedout by heating to 90 °C in the solid state or in solution. UV‐Vis analysis confirmedthat the dithioester end‐group of the RAFT polymer is returned to the reformedhomopolymer and that is reasonably stable under these conditions.It was found that mild heating of the substrates envoked the rDA reaction to occur,reforming the reactive cyclopentadiene surface. The exposed surface exhibited noevidence of decrease in reactivity, with a second round of grafting yielding similardensities to the original experiments. Thus, an efficiently switchable surface wasgenerated.Nanoporous PS films were easily prepared by removal of the PEO block by applying asimple heating and washing procedure. The method described here enables an easypreparation of nanoporous films bearing a reactive functional group from blockcopolymer precursors which are accessible in various molecular weight compositionsvia the combination of RAFT polymerization and HDA cycloaddition.SEC monitoring of the retro‐HDA cleavage of PS‐b‐PEO in the solid state in water at 90 °C. UV‐Vis spectra of PS‐b‐PEO in toluene at 90 °C. Due to the rDA reaction the concentration of the dithioester‐capped PS increases with time.SEM images of PS‐b‐PEO after heating to 90 °C in the solid state and then washing with water.

Hetero-Diels-Alder chemistry for nano-structured materials design

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Hetero-Diels-Alder chemistry for nano-structured materials design

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