0000000000555370
AUTHOR
Johannes Klos
Automated Large-Scale Synthesis of Supramolecular Oligo(p-benzamide) Block Copolymers
A fully automated large-scale synthesis procedure has been developed that allows the preparation of supramolecular rod−coil copolymers on a 100 g scale. The new reaction cycle allows the stepwise growth of oligo(p-benzamide)s onto the chain end of amine-terminated polymers. Amine-terminated poly(ethylene glycol) (PEG, Mn = 5000 g mol-1) and poly(styrene) (PS, Mn = 2950 g mol-1) were prepared, and an octa(p-benzamide) oligomer block was grown from the chain end in an automated computer-controlled reaction cycle. Plotting the apparent molecular weight of the PEG copolymer against the number of reaction cycles revealed a linear relationship, which emphasized the high level of control this meth…
Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor
The paper describes the living anionic polymerization of styrenes to homo- and diblock copolymers in continuous flow, using a microstructured mixing set-up ("microreactor"). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by "break-seal" and "high vacuum" techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g.h -1 . Facile molecular weight adjustment is achieved by variation of the flow rates of initiato…
Ionic Liquids on Demand in Continuous Flow
We report on the development of an alternative protocol for the facile, solvent-free synthesis of various novel imidazolium-based ionic liquids (ILs) that affords highly pure products without the necessity of subsequent purification steps. The continuous approach is based on the combination of HPLC pumps with a micromixer and a capillary residence tube. Our system provides a high degree of control over the alkylation reactions due to a high surface-to-volume ratio and superior heat and mass transport. Within the scope of our studies, we focused on ionic liquids containing differently substituted phenyl rings and characterized these compounds with respect to further use for direct applicatio…
Microstructured Reactors for Polymer Synthesis: A Renaissance of Continuous Flow Processes for Tailor-Made Macromolecules?
Organic synthesis in microfluidic devices has attracted increasing interest in recent years. However, little efforts had been undertaken to exploit this novel technology for polymer chemistry until several recent studies demonstrated the interesting potential of microreactors for the synthesis and modification of polymers. In fact, anionic polymerizations in continuous capillary flow-tube systems were established already in 1962 in pioneering work by Szwarc. Subsequent work focused on detailed kinetic analyses in such reactors. The present article explores different current strategies developed by several research groups to realize bulk and solution polymerizations using continuous flow mic…
Synthesis of Hyperbranched Polyglycerol in a Continuous Flow Microreactor
Hyperbranched polymers have been synthesized in a microreactor for the first time, employing the known ring-opening multibranching polymerization of glycidol. Microreactors are well-known to be beneficial for highly exothermic reactions because of their capability to enhance mass and heat transfer due to short diffusion pathways and large interfacial areas per volume. The characteristics of the microstructured reaction system were utilized to engineer a continuous flow process for the preparation of well-defined hyperbranched polyglycerols with molecular weights up to 1,000 g/mol. Increased flow rates, as well as the use of highly polar solvents, led to the partial formation of very narrowl…
Polymerizable Well-Defined Oligo(thiophene amide)s and their ROMP Block Copolymers
We report the synthesis of conjugated thiophene amide oligomers that constitute a new class of chromophores with potential for optoelectronic applications. The synthesis of defined norbornene-substituted oligothiophene amides using conventional coupling chemistry is described. Their electronic properties depend on the degree of oligomerization as UV/Vis and fluorescence spectroscopy demonstrate. A significant red shift in the spectra upon an increase in the oligomer length evidences conjugation of the thiophene rings via the amide linkages. ROMP of the norbornene-substituted oligomers gives homopolymers and block-copolymers with a solubilizing second block. The amphiphilic character of the …
Synthesis and noncovalent protein conjugation of linear-hyperbranched PEG-poly(glycerol) alpha,omega(n)-telechelics.
Linear-hyperbranched, heterobifunctional alpha,omega(n) telechelic block copolymers consisting of a linear poly(ethylene glycol) (PEG) chain and a hyperbranched polyglycerol (PG) block have been prepared in five steps, using a protected amino-functional initiator. The polyfunctionality omega(n) (OH groups) can be adjusted by the degree of polymerization (DP(n)) of the polyglycerol block. Subsequent introduction of a single biotin unit by amidation in alpha-position permitted noncovalent bioconjugation with avidin.