Monomer Sequence Distribution Monitoring in Living Carbanionic Copolymerization by Real-Time ¹H NMR Spectroscopy

Abstract

Detailed understanding of the monomer sequence distribution in carbanionic copolymerization was achieved by direct online monitoring of copolymerizations in an NMR tube. Obtaining detailed knowledge of the changing monomer concentration in stock during the reaction, this technique permits to determine the incorporation probability for each monomer at every position of the polymer chain. An in situ kinetic study of two different carbanionic copolymerizations has been carried out. On the one hand, the copolymerization of the structurally similar, protected hydroxystyrene derivatives, p-(1-ethoxy ethoxy)styrene (pEES) and 4-tert-butoxystyrene (tBuOS), and on the other hand the copolymerization of the chemically different monomers, styrene (S) and pEES, have been studied. Whereas in the first case a slight deviation from an ideal random copolymerization was observed, the latter copolymerization leads to gradient copolymers. Real-time 1 H NMR spectroscopy gave detailed insight into the reaction behavior at every stage of the copolymerization and leads to precise understanding of the resulting gradient structures.

Capitalizing on Protecting Groups to Influence Vinyl Catechol Monomer Reactivity and Monomer Gradient in Carbanionic Copolymerization

“…The copolymerization kinetics can be investigated with 1 H NMR kinetics experiments. This method, which is well established for epoxide copolymerizations, enables direct monitoring of monomer consumption even for monomers that are very similar in their chemical and electronic structure as is the case for styrene and its derivatives . We introduce several series of novel vinyl catechol monomers that vary in their structure and consequently the steric bulk of the protecting group.…”

Sequence-Controlled Polymers via Simultaneous Living Anionic Copolymerization of Competing Monomers

“…The competing, sequence‐controlled (ionic) copolymerization of several monomers to high molecular (multi)block copolymers is rarely reported. Simultaneous copolymerization of different monomers by anionic polymerization is difficult, as in most cases control over monomer incorporation is lost, mainly due to the different nucleophilicities of the propagating species and had only limited success; the terpolymerization of styrene with diphenylethylene (DPE) derivatives was reported to exhibit sequence‐controlled behavior by tuning of the DPE reactivity …”

“…Infrared or UV spectroscopy was applied to monitor cationic polymerizations at low temperatures and the copolymerization of styrene and isoprene . Real‐time 1 H and/or 13 C nuclear magnetic resonance (NMR) spectroscopy was used for the anionic copolymerization of oxiranes and styrenes …”

Poly(Ethylene Glycol) Dimethacrylates with Cleavable Ketal Sites: Precursors for Cleavable PEG‐Hydrogels

“…To investigate the degradation kinetics of both PEG‐ketal‐diols and PEG‐ketal‐DMA macromonomers, we measured the in situ 1 H NMR kinetics of the degradation of macromonomers dissolved in deuterated phosphate buffer solutions buffered to different pH values (degradation scheme see Scheme S1 in the Supporting Information). In situ 1 H NMR measurements have been extensively used to monitor polymerization reactions online . It is also possible to use this technique to analyze the cleavage of ketal macromonomers by monitoring the changes of typical NMR signals in situ during the hydrolysis reaction.…”

“…In situ 1 H NMR measurements have been extensively used to monitor polymerization reactions online. [56][57][58][59] It is also possible to use this technique to analyze the cleavage of ketal macromonomers by monitoring the changes of typical NMR signals in situ during the hydrolysis reaction.…”