Katja Nilles

Covalently bonded layer-by-layer assembly of multifunctional thin films based on activated esters.

We demonstrate that chemically stable, multifunctional polymer thin films can be obtained using the layer-by-layer (LbL) deposition based on covalent bonds between adsorbing chains. Poly(pentafluorophenyl-4-vinylbenzoate) (P1) or poly(pentafluorophenylacrylate) (P2) polymers were assembled with poly(allyl amine) (PAAm) to yield LbL multilayer films through amide bond formation by the reaction between activated esters of P1 or P2 and amine groups in PAAm, which was quantitatively monitored by Fourier transform infrared spectroscopy (FT-IR). It was found that the difference in the solubility of P1 and P2 against ethanol, which was used as the solvent for PAAm, during the LbL deposition yields different reaction conversion for the activated esters in either P1 or P2: the reaction conversion of P2 is higher than the conversion with P1. In addition, free (or unreacted) activated esters and amine groups remaining in the PAAm/P1 LbL film were further utilized for the incorporation of multiple functional materials (5-((2-aminoethyl)amino)naphthalene-1-sulfonic acid (EDANS) and Rhodamine B dyes in the present case) by post-treatments in order to further tailor the film properties. It was also demonstrated that the surface functional groups (activated esters) in the LbL films can also be utilized for surface patterning with one functional material, followed by functionalization with a second functional material during the post-treatment throughout the whole film. Finally, the PAAm/P1 and PAAm/P2 LbL films were shown to be quite stable in the extreme pH range, and free-standing films can easily be obtained by the treatment of the films with mild acidic conditions. The versatility of incorporating multiple functional materials into a single multilayer film as well as the excellent physicochemical stability of the covalently bonded multilayer free-standing films proves to be quite useful to design flexible and multifunctional thin film structures for many chemical and biological applications.

Polymerization of an activated ester monomer based on 4-vinylsulfonic acid and its polymer analogous reaction

Homopolymers containing sulfonic ester side groups were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization utilizing benzyl dithiobenzoate, cumyl dithiobenzoate, and 4-cyano-4-((thiobenzoyl)sulfanyl)pentanoic acid as chain transfer agents. Likewise diblock copolymers containing poly(styrene), poly(octylstyrene) and poly(pentafluorostyrene) as the second block were synthesized. Additionally, nitroxide mediated polymerization (NMP) was investigated for the synthesis of a homopolymer as well as for a diblock copolymer. Furthermore, the post-polymerization functionalization with various amines to yield the respective sulfonamides was conducted. The conversion was analyzed by 1H NMR spectroscopy, 19F NMR spectroscopy and FT-IR spectroscopy and in many cases a very high conversion (>96%) was observed. In addition the reaction kinetics of the post-polymerization functionalization of poly(pentafluorophenyl 4-vinylbenzene sulfonate) and the corresponding carboxyl ester poly(pentafluorophenyl 4-vinylbenzoate) were compared by analysis of the reactions by time-resolved 19F NMR spectroscopy. It was found that poly(pentafluorophenyl 4-vinylbenzoate) showed a higher stability towards hydrolysis and a significantly higher reactivity, resulting in complete conversions with different amines.

Modular approach towards multi-functional surfaces with adjustable and dual-responsive wettability using a hybrid polymer toolbox

Poly(methylsilsesquioxane)-based hybrid polymers carrying orthogonally reactive moieties demonstrate an effective modular approach to creating multi-reactive surface coatings. By a sequential surface-analogous reaction different functions could be immobilized in a defined ratio, resulting in dual- or triple-functionalized surfaces.

Reactive nanorods based on activated ester polymers: a versatile template-assisted approach for the fabrication of functional nanorods

A new route for the fabrication of polymeric nanorods with functional moieties via post-modification of reactive nanorods is described. To this end reactive nanorods with a homogenous and narrow size distribution were fabricated by utilizing an anodic aluminium oxide (AAO) template-assisted approach. The nanorods are based on activated pentafluorophenyl esters, to enable quantitative post-modification with amines under very mild reaction conditions yielding the corresponding functionalized amide. Post-modification with fluorescent dyes as well as the conversion into well-dispersed rod-shaped poly(N-isopropylacrylamide) (PNIPAM) hydrogels that exhibit a thermal-responsive phase transition was demonstrated. The platform of reactive nanorods provides the fabrication of various functional nanoobjects and may find application in research fields like drug delivery.

Precise structural investigation of symmetric diblock copolymer thin films with resonant soft X-ray reflectivity

Symmetric diblock copolymers are known to form lamellar structures in the bulk of an organic thin film. Polymer/polymer and polymer/substrate interfaces play a critical role in this application. Here, we report the investigation of multiple buried interfaces by using a novel technique resonant soft X-ray reflectivity which benefits from enhanced contrast between different polymers near the carbon K-edge. This allows us to obtain a precise interface structure. We also present an alternative method to determine optical constants of polymers by fitting X-ray reflectivity of polymers with known structural parameters at specific soft X-ray energies. This approach is compared with the way of obtaining β by NEXAFS and calculating δ via the Kramers–Kronig relationship. Finally, by using the determined index of refraction, the precise structure of a multilayer formed by a diblock copolymer is obtained by successfully fitting the resonant soft X-ray reflectivity profile.