Styrene (St, 99%) and methyl methacrylate (MMA, 99%) were obtained from Aldrich company. These monomers were first dried over calcium hydride, were purified by being passed through a column of basic alumina, and were distilled under reduced pressure. Ethyl 2-bromoisobutyrate (EBIB, 98%), copper (I) bromide (CuBr, 99%), copper (I) chloride (CuCl, 99%), and other chemical reagents were procured from Aldrich company and used as received. N-methylbis[2-(dodecylthio)ethyl]amine (SNS) was synthesized following our previously-reported procedure.42
2.2. Equipment
FT-IR spectra (in KBr pellets) were obtained on a Shimadzu IR-460 instrument (USA). The number averaged molecular weight and molecular weight distributions were determined via gel permeation …show more content…
More specifically, styrene (6.1 mL, 53 mmol) was transferred into a deoxygenated Schlenk flask via syringes. After three freeze-pump-thaw cycles, SNS (0.130 g, 0.265 mmol), CuBr (0.039 g, 0.265 mmol), and EBIB (55 µL, 0.265 mmol) were added to the Schlenk flask. After another three freeze-pump-thaw cycles, the Schlenk flask was placed in an oil bath and thermostatted at 90 °C. At timed intervals, a 0.90 mL aliquot of the polymerization solution was taken for analysis. This sample was then filtered through a short alumina column to remove the catalyst for GPC analysis. The conversion of styrene was followed by NMR spectroscopy, and molecular weights and molecular weight distributions were determined using …show more content…
Results and Discussion
3.1. Block copolymer formation using halogen exchange
Normal ATRP of styrene was carried out at 90 °C using SNS as the ligand, Cu-Br as the catalyst, and EBIB as the initiator. The end group of the resulting polystyrene (PS-Br) is a bromine atom. The chain extension of PS-Br as a macroinitiator is usually associated with poor control when MMA monomers are used for the second block. To improve the initiation efficiency, we used the technique of halogen exchange. For this purpose, the end group of the macroinitiator should be a bromine atom, and Cu-Cl should be employed as a catalyst. To further enhance the efficiency of initiation, a small amount (10%) of styrene was used. At the beginning of the reaction, there were two types of chain growth: PS-PMMA-Cl and PS-Br. Since the rate of growth of the PS-Br chain is higher (because the C-Br bond has a lower bond dissociation energy than the C-Cl bond), PS-Br was more consumed and converted into PS-PMMA-Cl. As a result, PS-PMMA-Cl was the only type of chain growth after a while, leading to a low polydispersity. Scheme 2 is a graphical representation of the process described
2.2. Equipment
FT-IR spectra (in KBr pellets) were obtained on a Shimadzu IR-460 instrument (USA). The number averaged molecular weight and molecular weight distributions were determined via gel permeation …show more content…
More specifically, styrene (6.1 mL, 53 mmol) was transferred into a deoxygenated Schlenk flask via syringes. After three freeze-pump-thaw cycles, SNS (0.130 g, 0.265 mmol), CuBr (0.039 g, 0.265 mmol), and EBIB (55 µL, 0.265 mmol) were added to the Schlenk flask. After another three freeze-pump-thaw cycles, the Schlenk flask was placed in an oil bath and thermostatted at 90 °C. At timed intervals, a 0.90 mL aliquot of the polymerization solution was taken for analysis. This sample was then filtered through a short alumina column to remove the catalyst for GPC analysis. The conversion of styrene was followed by NMR spectroscopy, and molecular weights and molecular weight distributions were determined using …show more content…
Results and Discussion
3.1. Block copolymer formation using halogen exchange
Normal ATRP of styrene was carried out at 90 °C using SNS as the ligand, Cu-Br as the catalyst, and EBIB as the initiator. The end group of the resulting polystyrene (PS-Br) is a bromine atom. The chain extension of PS-Br as a macroinitiator is usually associated with poor control when MMA monomers are used for the second block. To improve the initiation efficiency, we used the technique of halogen exchange. For this purpose, the end group of the macroinitiator should be a bromine atom, and Cu-Cl should be employed as a catalyst. To further enhance the efficiency of initiation, a small amount (10%) of styrene was used. At the beginning of the reaction, there were two types of chain growth: PS-PMMA-Cl and PS-Br. Since the rate of growth of the PS-Br chain is higher (because the C-Br bond has a lower bond dissociation energy than the C-Cl bond), PS-Br was more consumed and converted into PS-PMMA-Cl. As a result, PS-PMMA-Cl was the only type of chain growth after a while, leading to a low polydispersity. Scheme 2 is a graphical representation of the process described