Examining the UV-vis absorption of RAFT chain transfer agents and their use for polymer analysis

Abstract

The absorption characteristics of a large set of thiocarbonyl based chain transfer agents (CTAs) were studied by UV-vis spectroscopy in order to identify appropriate conditions for exploiting their absorbance bands in end-group analysis of polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerisation. Substitution pattern and solvent polarity were found to affect notably the wavelengths and intensities of the Pi-Pi*- and n-Pi*-transition of the thiocarbonyl bond of dithioester and trithiocarbonate RAFT agents. Therefore, it is advisable to refer in end group analysis to the spectral parameters of low molar mass analogues of the active polymer chain ends, rather than to rely on the specific RAFT agent engaged in the polymerisation. When using appropriate conditions, the quantification of the thiocarbonyl end-groups via the Pi-Pi* band of the thiocarbonyl moiety around 300-310 nm allows a facile, sensitive and surprisingly precise estimation of the number average molar mass of the polymers produced, without the need of particular end group labels. Moreover, when additional methods for absolute molar mass determination can be applied, the quantification of the thiocarbonyl end-groups by UV-spectroscopy provides a good estimate of the degree of active end group for a given polymer sample

Living Radical Polymerization by the RAFT Process – A Third Update

“…The UV-visible spectra of an extensive series of an RAFT agents (ZC(¼ S)SR) have been examined. [554] The position of the absorbance maxima for the p-p* and n-p* transitions and the molar absorptivities were found to be dependent on both the 'Z' and 'R' substituents. Thus, changes in UV-visible spectra on conversion of an initial RAFT agent to a macro-RAFT agent need to be considered when using spectrophotometry to follow the course of RAFT polymerization.…”

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

“…50 SEC measurements were done with two different systems. The SEC setup for measurements in a mixture of 80% 0.05 M Na 2 SO 4 in de-ionised water and 20% acetonitrile consisted of a four channel degasser SCM 400 from Spectra Physics, an isocratic pump P 1000 from Spectra Physics, a set of TSK-GEL PW columns (7.5 Â 300 mm) from TOSOH Biosep (Guard, 6000, 5000, 4000, 3000), a Dawn DSP MALLS detector from Wyatt, a UV/VIS detector UV 2000 from Spectra Physics and a dual detector for viscosity and refractive index h-1002 from WGE Dr Bures.…”

“…For well-controlled polymerisation this method leads to reliable results. 50 However, any termination event will reduce the number of trithiocarbonate moieties, and consequently, will make the calculated values of M n UV increasingly overestimating the true values of M n . Thus, the comparison of M n UV to M n MALLS (or to M n theo when SEC-MALLS could not be performed) will reveal the degree of end group functionality.…”

“…Cylindrical sample cells were placed in an index matching toluene vat. Intensity correlation functions were recorded under different angles between 50 and 130 . Oscillating rheology measurements used a Bohlin Gemini 150 rheometer equipped with a high-frequency extension with a piezo rotary vibrator.…”

“…50,60,61 Assuming that every polymer holds the same number of trithiocarbonate moieties as the employed CTA, the number average molar mass is calculated using eqn (1). For well-controlled polymerisation this method leads to reliable results.…”