Monitoring Block-Copolymer Crossover-Chemistry in ROMP: Catalyst Evaluation via Mass-Spectrometry (MALDI)

Abstract

We report on the monitoring and evaluation of the crossover reaction in ring-opening metathesis polymerization (ROMP) via MALDI methods. ROMP of various monomers using several catalytic systems (first-generation (I) and third-generation Grubbs-type (III)) was investigated with structurally different norbornene monomers derived from (±)endo,exo-bicyclo[2,2,1]-hept-5-ene-2,3-dicarboxylic acid-bis-O-methyl ester (monomer A), (±)endo,exo-bicyclo[2,2,1]-hept-5-ene-2,3-dicarboxylic acid-bis-O-2,2,6,6-tetramethyl piperidinoxyl-ester (monomer T), (±)exo-N-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)-10-oxa-4-azatricyclodec-8-ene-3,5-dione (monomer D), and the highly strained monomer 2-methyl-2-phenyl-cyclopropene (monomer E). The crossover reactions as well as the polymerization kinetics of the various monomers were studied in detail, in particular, using matrix-assisted laser desorption ionization mass spectrometry (MALDI). Catalyst III offered access to the synthesis of highly defined block copolymers, generating poly(A-b-T), poly(A-b-D), and poly(A-b-E) diblockcopolymers in high precision, whereas catalyst I offered access to the diblockcopolymers poly(A-b-D) and poly(A-b-E). Poly(A) was used as a probe to analyze the crossover reaction, revealing well-defined crossover kinetics in the case of monomers T, D, and E and a subsequent good polymerization after the crossover reaction in the case of monomer E. The presented system allows a simple evaluation and monitoring of crossover reactions in ROMP-based polymerization reactions.

The preparation of well-controlled poly(N-cyclohexyl-exo-norbornene-5,6-dicarboximide) polymers

“…The spectrum of polymer 5a1 was obtained according to the literature procedure. 20 The resulting spectra and expansion can be observed in Figure 4. The complete spectrum in Figure 4a shows that the absolute polymer molecular Abbreviation: MALDI-TOF MS, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry.…”

“…The procedure used was as described in the literature. 20 RIs were measured on a SPA-4000 instrument (Sairon Technology Inc, Tokyo, Japan) using the prism-coupled method at 633, 1310 and 1550 nm. EA was performed on a Yanako (New Science Inc, Kyoto, Japan) CHN corder MT-6.…”

Bioresorbable vascular scaffolds: The shape of things to come?

“…The concept of the presented synthetic approach relies on the use of the bivalent quenching agents 6 , 7 which are prepared by a crossmetathesis reaction of the respective monovalent olefins bearing the respective hydrogen bonding moieties using Grubbs catalyst 2nd‐generation ( 2 ) as catalyst (Scheme ). Monomer 5 was chosen, as it can be polymerized well with the catalysts 1 , 3 9 and 4 and the resulting polymers can be easily analyzed via MALDI‐TOF‐MS methods, as demonstrated by us recently 9, 10…”

“…Among the many supramolecular moieties known, hydrogen bonding moieties have gained special interest since they can be used to transform a random chain assembly into an ordered supramolecular structure 5. Thus, we have accomplished the introduction of complex hydrogen‐bonding moieties via a combination of ROMP with “click”‐chemistry methods,6–8 as the direct copolymerization of many monomers with complex functional groups, such as hydrogen bonds or nitroxide‐moieties often leads to uncontrolled polymerization reactions with sometimes broad molecular weight distributions 9, 10. A still challenging task however, is the introduction of a functionalized end group via ROMP to one or both sides of a polymer chain, which can be achieved with different methods often including the reaction of the respective living chain end with functionalized enolethers5, 11–18 or oxygen 19.…”

“…Conceptually, we needed an attachment of the hydrogen bonding moieties to the polymer via CC‐bonds, which provides a higher thermal stability when compared to the often used ether‐ and ester‐bonds in other synthetic strategies 26–28. Besides the purely synthetic approach, the analysis of the quenching reaction and the evaluation of the quenching efficiency is reported, relying on a previously developed MALDI‐method,9 which enables a relatively precise evaluation of the individual species during and after the quenching reaction.…”