Degradation of RAFT polymers in a cyclic ether studied via high resolution ESI‐MS: Implications for synthesis, storage, and end‐group modification

Abstract

We report on the detailed mass spectrometric analysis of the degradation products generated during storage of poly(methyl methacrylate) (pMMA) and polystyrene (pSty) carrying cumyldithiobenzoate (CDB) endgroups. Samples were stored in either a cyclic ether (tetrahydrofuran) (THF) or an inert solvent (dichloromethane). The degradation process was followed over a period of 4‐weeks. Degradation rate of the reversible addition fragmentation (RAFT) polymer strongly depends on the hydroperoxide‐content of the solvent. Mass spectrometric evidence supports an unexpected radical degradation mechanism for the pMMA macroRAFT agent. Hydroperoxide functional pMMA was the single product after less than 7 days in high purity THF. No formation of the sulfine/thioester was observed. The identity of the hydroperoxide was unambiguously assigned using accurate mass measurements by Fourier‐Transform ion‐cyclotron‐resonance mass spectrometry together with chemical identification reactions. The hydroperoxide end group formation proceeds efficiently as well as in high yields and thus constitutes a powerful method for end group modification. The degradation pathways of the CDB functional pSty in THF include mainly oxidation towards the sulfine/thioester, with little degradation via thermal elimination of dithiobenzoic acid and subsequent epoxidation. The shelf life of CDB functional polymers is limited even in inert solvent because of this inherent but slow thermal elimination reaction. Because of the short period necessary for the transformation of the functional dithiobenzyl endgroups, substitution of cyclic ethers as solvents for RAFT polymers in synthesis and analysis is strongly suggested. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7447–7461, 2008

Thermo-responsive block copolymers with multiple phase transition temperatures in aqueous solutions

“…The presence of unprotected primary or secondary amine groups may lead to the aminolysis of the CTA and loss of control during the polymerization in aqueous medium, although this can be minimized at acidic pH [56]. Loss of chain end functionality may also occur because of degradation during the polymerization, workup, and storage steps, for example due to the presence of peroxides in the solvent (such as in the case of cyclic ethers) or due to slow thermal elimination [57].The stoichiometric ratios of monomer, chain transfer agent and initiator concentrations determine the theoretical molar mass, the chain end functionalities (dormant vs. dead chains), and the rate of polymerization [58], and allow the design of polymers with desired block lengths. [63].…”

Living Radical Polymerization by the RAFT Process - A Second Update

“…[428] Thus PMMA-dithiobenzoate was converted into PMMAhydroperoxide within 7 days. PSt-dithiobenzoate was more slowly converted into a mixture of products in which the dithiobenzoate end-group had been converted into the corresponding sulfine or thionoester end-groups or was lost and the polymer left with epoxy and unsaturated end-groups.…”

A Perfect Couple: PLP/SEC/ESI‐MS for the Accurate Determination of Propagation Rate Coefficients in Free Radical Polymerization

“…Using common quadrupole ion trap mass spectrometry, molecular weights of up to 15 kg Á mol À1 are accessible with the current method and analysis of a number of poly(acrylates), poly(methacrylates), poly(vinyl acetate) and even polystyrene has been demonstrated. [57,58] We have recently extended the method to provide molecular weight analysis in mixtures of polymers, making use of the potential of soft ionization mass spectrometry to distinguish polymers differing in their endgroups. [59] In the current manuscript we report the application of SEC/ESI-MS for the determination of highly accurate MWD in PLP.…”