Dependence Of Thermal Stability Of RAFT/MADIX Agents On Molecule Structure And Functionalization Graphene Oxide Through Regioselective Addition Of Thiocarbonylthio Anion In Water

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most versatile controlled/"living" radical polymerization techniques. Thiocarbonylthio compounds play the central role in reversible addition-fragmentation chain transfer process (RAFT) and its thermal stability has caused great attention in the recent years. If decomposition occurs during the polymerization, it will cause retardation to polymerization rate through the loss of the living chain end and subsequent radical quenching by the resulting dithiocarboxylic acid and thus result in deviation for the living system. In the present work, a series of RAFT/MADIX agents are subject to thermal decomposition in solution and The relationship between the thermal stabilities and molecular structures of thiocarbonythio compounds are investigated with respect to the reaction mechanism, and discussed in correlation with the chain transfer activity. Therefore, it is possible to balance RAFT/MADIX agents chain transfer activity and thermal stability through our fundamental research work. The main contents are as follows:Dependence of Thermal Stability on Molecular Structure of RAFT/MADIX Agents_A Kinetic and Mechanistic Study. The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-emilination, a-elimination and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z-or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens results in faster decomposition rate or lower decomposition temperature. Thus the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z=phenyl):-CH2Ph (5)>-PS (PS-RAFT15)>-C(Me)HPh (2)>-C(Me)2C(=O)OC2H5(7)>-C(Me)2Ph(1)>-PMMA (PMMA-RAFT16)>-C(Me)2CN (6). For those possessing identical leaving group such as1-phenylethyl, the stability decreases in the order of O-ethyl (11)>-N(CH2CH3)2(13)>-SCH (CH3) Ph (8)>-Ph (2)>-CH2Ph (4)>-PhNO2(3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.Synthesis of graphene oxide based RAFT agents via regioselective addition of thiocarbonylthio anion to epoxide in water. In this work, we present the synthsis of graphene-based RAFT agents via regioselective addition of xanthate, dithiocarbamate and trithiocarbonate anion to epoxide on graphene oxide in water at room temperature. A series of new RAFT agents who possess the graphene as theirs leaving group. A multiple analytical methods have been used to characterize this obtained compounds, such as thermogravimetric analysis (TGA), XPS elemental composition analysis, X-ray diffraction pattern analysis (XRD), FT-IR analysis and Raman spectrum. The solubility of the synthetic dithiocarbomate-graphene compounds were employed to run a switchable test by adding p-toluenesulfonic acid. All of this proved that the dithiocarboxylic groups were efficiently installed on the surface of GO. Current efforts are underway to investigate their potential application in controlled radical polymerization.