Cleavage of macromolecular RAFT chain transfer agents by sodium azide during characterization by aqueous GPC

Abstract

Accurate and reliable analysis of polymers by GPC is vital in the field of controlled radical polymerisation. Often, water-soluble polymers are analysed by aqueous gel permeation chromatography (GPC) in a solvent containing dilute sodium azide as an anti-microbial agent. Previous reports have shown that sodium azide at high concentration is able to remove terminal CTA groups from polymer chains, producing thiol-terminated polymers.This study demonstrates that GPC sample preparation of RAFT polymers in aqueous solvents containing dilute (200 ppm) sodium azide can cause significant changes in the measured molecular weight distribution. These changes occur within hours of dissolving the polymer sample and are shown to be due to cleavage of the CTA in the polymer chain together with disulfide coupling of the resulting polymeric thiols. The extent to which this occurs is strongly dependent on the CTA attached to the polymer; an almost 10-fold difference in the rate of CTA removal is observed between different RAFT agents. The by-product of the reaction between sodium azide and RAFT polymers is also investigated and shown to be an unstable thiatriazole-functionalised Z group. The thiatriazole then degrades further to form a nitrile-functionalised Z group, N 2 and elemental sulfur.3

Effect of molecular weight distribution of PSSA on electrical conductivity of PEDOT:PSS

“…(Scheme 1) To check the differences in molecular weight distribution between PSSA obtained by the two processes, GPC measurement was implemented. Before measurement, we calibrated the GPC instrument using standard GPC samples with different molecular weights (Mn ¼ 37 500/60 000/210, 400/740, 500) 19,20 (Fig. 2 and Table 2).…”

Reverse-phase high performance liquid chromatography (RP-HPLC) as a powerful tool to characterise complex water-soluble copolymer architectures

“…20 However, characterisation of water-soluble polymer via SEC in aqueous environment remains challenging due to the necessity to use salts which can interfere with the separation process. 21 This is especially true for highly charged polymers whose separation is prone to a variety of electrostatic interferences. 22,23 Gradient Polymer Elution Chromatography (GPEC), a separation method based on difference in the solubility of copolymers with varying chemical composition, is useful to determine the chemical composition distribution (CCD) of copolymers.…”

Synthesis of Block Copolymer Brush by RAFT and Click Chemistry and Its Self-Assembly as a Thin Film

“…An estimation of M n by 1 H-NMR could not be done because a complete loss of aromatic end groups at 7–7.9 ppm was also observed ( Figure S1 ). Indeed, a cleavage of dithiobenzoate end groups in the presence of azide occurred [ 37 ], which was confirmed by a change of the color of the reaction medium from pink to white.…”