The polymerization of n-butyl methacrylate was investigated using the Atom Transfer Radical Polymerization technique with CuBr and CuCl/N,N,N‘,N“,N“-pentamethyldiethylenetriamine catalytic systems. Various combinations of catalyst systems and initiators were utilized in order to optimize the polymerization conditions and to obtain well-defined polymers (i.e. controlled molecular weights and low polydispersities). It has been found that the optimal initiator for this system is a chlorine-based initiator, when the catalyst used is a Cu(I) salt in conjunction with the N,N,N‘,N“,N“-pentamethyldiethylenetriamine ligand. Bromine-based initiators tend to result in large amounts of initial termination, leading to polymers with less than ideal chain end functionality, even if CuCI is used as the Cu(I) species to invoke the halogen exchange. Additionally, the effects of the polymerization temperature, copper(I) species and the initiator structure were determined. 相似文献
Summary: The living polymerization of N,N‐dimethylacrylamide was achieved by atom transfer radical polymerization catalyzed by copper chloride complexed with a new ligand, N,N′‐bis(pyridin‐2‐ylmethyl 3‐hexoxo‐3‐oxopropyl)ethane‐1,2‐diamine (BPED). With methyl 2‐chloropropionate as the initiator, the polymerization reached high conversions (> 90%) at 80 °C and 100 °C, producing polymers with very close to theoretical values and low polydispersity. The ligand, temperature, and copper halide strongly affected the activity and control of the polymerization.
PDMA molecular weight and polydispersity dependence on the DMA conversion in the DMA bulk polymerizations at different temperatures: DMA/CuCl/MCP/BPED = 100/1/1/1, 100 °C (♦, ⋄); 80 °C (▴, ▵); 60 °C (▪, □); and DMA/CuCl/MCP/BPED = 100/1/1/2, 80 °C (•, ○). 相似文献
Summary: Bifunctional initiators can produce polymers with higher molecular weight at higher initiator concentrations than monofunctional initiators. In this study, we developed a mathematical model for ATRP with bifunctional initiators. The most important reactions in ATRP were included in the model. The method of moments was used to predict monomer conversion, average molecular weights and polydispersity index as a function of polymerization time in batch reactors. The model was used to understand the mechanism of ATRP and to quantify how polymerization conditions affect monomer conversion and polymer properties by examining the effect of several rate constants (activation, deactivation, propagation and chain termination) and of catalyst and initiator concentration on polymerization kinetics and polymer properties. When compared to monofunctional initiators, bifunctional initiators not only produce polymers with higher molecular weight averages at higher polymerization rates, but also control their molecular weight distributions more effectively.
Effect of initial catalyst concentration on polydispersity index as a function of time. 相似文献
Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (Mw/Mn ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and 1H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group. 相似文献