Development of SAXS compatible flow reactors for in situ monitoring of nanoparticle formation during RAFT dispersion polymerisation

Flow platforms for the time-resolved monitoring of molecular structure by small-angle X-ray scattering analysis were developed and applied to study the dispersion polymerisation of poly (dimethyl acrylamide)-(diacetone acrylamide) (PDMAm-PDAAm). via aqueous reversible addition fragmentation chain transfer (RAFT).
In situ small-angle X-ray scattering (SAXS) is a powerful technique for characterizing block copolymer nano-object formation during polymerization-induced self-assembly. To work effectively in situ, it requires high intensity X-rays which enable the short acquisition times required for real-time measurements. However, routine access to synchrotron X-ray sources is expensive or highly competitive. By taking advantage of the principles of flow chemistry with new generation laboratory SAXS instruments this allows for detailed studies to be performed without the need for synchrotron sources. The initial development of a coil reactor system which was suitable for the block copolymer system found that PFA tubing was suitable when using additional thermal initiator to provide excess radicals scavenge oxygen during the reaction. This setup was extended with the addition of a SAXS compatible flow cell allowing for an in situ investigation of the impact of hydrophilic block length during RAFT aqueous dispersion polymerisation of PDMAm-PDAAm upon nanoparticle structure in which it was found that core chain stretching significantly changed. The impact of concentration upon nanoparticle structure during PDMAm-PDAAm RAFT synthesis in flow was performed for a series of hydrophilic block lengths in which transition from spheres to higher order morphologies were observed at higher concentrations.
To achieve higher temporal resolution a custom X-ray compatible flow reactor (XRCFR) was developed for use with laboratory which allowed for multi-location analysis of the reaction significantly reducing experimental cost in material and time. Monomer conversion with residence time within the custom flow reactor was approximated by transient kinetics studies by use of a flow through benchtop NMR. This approximation of monomer conversion allowed for fitting of scattering patterns and for detailed kinetics of structural evolution to be confirmed for all syntheses. A new amphiphilic block copolymer system poly(dimethyl acrylamide)-(ethylene glycol phenyl ether acrylate) which undergoes PISA within an ethanol: water co-solvent, was investigated through the use of the continuous flow and batch studies.