Implementation and Application of Light Induced Orthogonal Ligation Protocols in Polymer Chemistry

The present thesis introduces the concept of orthogonal light induced ligation protocols demonstrating the generation as well as the modification of polymer architectures. The orthogonality is based either on two reaction paths of o-methyl benzaldehyde to introduce chemical selectivity - for the first time - in a photonic field or on the λ-orthogonal reaction principle featuring the wavelength dependent activation of o-methyl benzaldehyde and tetrazole

Global trends for kp? Expanding the frontier of ester side chain topography in acrylates and methacrylates

The Arrhenius parameters of the propagation rate coefficient for two linear methacrylates, two branched methacrylates, and two branched acrylates are determined via the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) method. The Mark-Houwink-Kuhn-Sakurada parameters of these polymers are additionally determined via multidetector SEC of narrowly distributed polymer samples obtained through fractionation, allowing for a correct SEC calibration in the PLP-SEC experiment. The data obtained for stearyl methacrylate (SMA, A = 3.45 (-1.17 to +4.46) × 106 L·mol-1·s-1; Ea = 21.49 (-1.59 to +1.90) kJ·mol-1) and behenyl methacrylate (BeMA, A = 2.51 (-0.80 to +3.06) × 106 L·mol-1·s -1; Ea = 20.52 (-1.43 to +1.85) kJ·mol -1) underpin the trend of increasing kp with increasing ester side chain length. Propylheptyl methacrylate (PHMA, A = 2.83 (-0.82 to 3.15) × 106 L·mol-1·s-1; Ea = 21.72 (-1.20 to +1.64) kJ·mol-1) and heptadecanyl methacrylate (C17MA, A = 2.04 (-0.66 to +1.71) × 10 6 L·mol-1·s-1; Ea = 20.72 (-1.42 to +1.38) kJ·mol-1) can be described as a family of branched methacrylates jointly with isodecyl methacrylate and ethylhexyl methacrylate (both published previously), resulting in joint Arrhenius parameters of A = 2.39 (-0.51 to +0.84) × 106 L·mol -1·s-1 and Ea = 21.16 (-0.78 to +0.76) kJ·mol-1. In addition, the corresponding branched acrylates are studied applying high-frequency PLP at a 500 Hz laser repetition rate, resulting in Arrhenius parameters of A = 1.05 (-0.42 to +2.81) × 10 7 L·mol-1·s-1 and Ea = 16.41 (-1.99 to +2.42) kJ·mol-1 for propylheptyl acrylate (PHA) and A = 8.15 (-2.83 to +10.3) × 106 L·mol -1·s-1 and Ea = 14.66 (-1.49 to +1.66) kJ·mol-1 for heptadecanyl acrylate (C17A). © 2012 American Chemical Society

λ-orthogonal pericyclic macromolecular photoligation

A photochemical strategy enabling λ-orthogonal reactions is introduced to construct macromolecular architectures and to encode variable functional groups with site-selective precision into a single molecule by the choice of wavelength. λ-Orthogonal pericyclic reactions proceed independently of one another by the selection of functional groups that absorb light of specific wavelengths. The power of the new concept is shown by a one-pot reaction of equimolar quantities of maleimide with two polymers carrying different maleimide-reactive endgroups, that is, a photoactive diene (photoenol) and a nitrile imine (tetrazole). Under selective irradiation at λ=310–350 nm, any maleimide (or activated ene) end-capped compound reacts exclusively with the photoenol functional polymer. After complete conversion of the photoenol, subsequent irradiation at λ=270–310 nm activates the reaction of the tetrazole group with functional enes. The versatility of the approach is shown by λ-orthogonal click reactions of complex maleimides, functional enes, and polymers to the central polymer scaffold

λ-Orthogonale Photochemie: Lichtinduzierte pericyclische Reaktionen an Makromolekülen

Eine photochemische Strategie nutzt λ-orthogonale Reaktionen zum Aufbau makromolekularer Architekturen und zum wellenlängenabhängigen Einbau chemischer Funktionalitäten in ein einzelnes Molekül. λ-Orthogonale pericyclische Reaktionen können unabhängig voneinander durch die spezifische photochemische Aktivierung einer chemischen Funktionalität ablaufen. Die Leistungsfähigkeit dieses neuen Konzeptes wird durch eine Eintopfreaktion belegt, bei der Maleinsäureimid mit zwei Polymeren, die unterschiedliche photoaktive Endgruppen (Photoenol und Tetrazol) tragen, selektiv reagieren. Beliebige aktivierte Doppelbindungen können durch eine gezielte Bestrahlung mit λ=310–350 nm mit einem Photoenol-funktionalisierten Polymer reagieren. Nach vollständigem Photoenolumsatz aktiviert eine Bestrahlung mit λ=270–310 nm die Reaktion des Tetrazols mit Maleimid. Die Vielseitigkeit dieses Ansatzes wird durch die λ-orthogonale Klick-Reaktionen von komplexen Maleimiden, funktionalen Enen und Polymeren an ein zentrales Polymergerüst gezeigt

UV-Triggered End Group Conversion of Photo-Initiated Poly(methyl methacrylate)

The analysis of photo-initiated poly­(methyl methacrylate) via electrospray ionization-mass spectrometry (ESI–MS) (synthesized by pulsed laser polymerization (PLP, at λ = 351 nm) of methyl methacrylate (MMA) and benzoin as photoinitiator at 6 mJ/pulse laser energy) evidences the presence of unidentified species. The determination of the origin of these species requires a detailed investigation via size exclusion chromatography-electrospray ionization-mass spectrometry (SEC/ESI–MS) and chemically induced dynamic nuclear polarization-nuclear magnetic resonance spectroscopy (CIDNP–NMR). It was found that post-irradiation of benzoin-initiated poly­(methyl methacrylate) leads to α-cleavage of the benzoyl fragment leading to a sequence of cascade reactions, including the formation of an additional double bond within the polymer chain as evidenced via ESI–MS. Furthermore, the reaction products of the benzoyl radical post α-cleavage (e.g., benzaldehyde, phenyl methyl ketone, methyl formate, or methane) as well as the formed macroradical can be followed by CIDNP–NMR, which allows establishing a reaction mechanism for the UV-induced cleavage process. The study thus evidence thatif the integrity of UV initiated polymers is to be kept intact during their synthesisvery low irradiation energies need to be employed