SYNTHESIS AND CHARACTERIZATION OF POLYSTYRENE- BLOCK-POLYLACTIDE BY COMBINATION OF ATRP AND ROP USING TRIBROMOETHANOL AS INITIATOR: PRECURSORS TO ORDERED NANOPOROUS MATERIALS

5. The dual initiator contains a bromide group for the ATRP of styrene and an hydroxyl function for the initiation of the ROP of D,L-lactide. 6 The block copolymers are prepared by a two-step approach: hydroxyl-terminated polystyrene (PS-OH) is firstly obtained by ATRP and then used as a macroinitiator to initiate the ROP of D,L-lactide. Experimental Section Materials. Styrene (Acros, 99%) was vacuum distilled. CuBr (Acros, 98%) was purified by stirring in glacial acetic acid, washed with ethanol and dried in vacuum. 3,6-dimethyl-1,4-dioxane-2,5-dione (D,L-lactide, Acros) was recrystallized from ethyl acetate. CuBr2 (Acros, 99+%), 1,1,4,7,10,10hexamethyl-triethylenetetramine (HMTETA, Acros, 97%), 2,2,2tribromoethanol (Acros, 99%), triethylaluminum (Acros, 1.3M solution in heptane), dichlorodimethylsilane (Acros, 99+%) were used as received. Characterization. The molecular weights and polydispersity index (PDI) of polymers were determined with a steric exclusion chromatography (SEC) system composed of a Waters 610 unit, a Waters 486 tunable UV detector and a Styragel® HT6E column calibrated with polystyrene standards, using THF as the mobile phase at 25°C with a flow rate of 1 mL/min. 1 H NMR spectra of the polymers were obtained with a Bruker 400 MHz using CDCl3 as solvent. AFM characterizations were performed with a Nanoscope III from Digital Instrument Corporation, in tapping mode. Synthesis of Hydroxyl-Terminated Polystyrene (PS-OH) by ATRP. In a typical procedure, a 50 mL round-bottomed flask was charged with styrene (7.2 g, 69.2 mmol), CuBr (0.055 g, 0.384 mmol), CuBr2 (0.004 g, 0.018 mmol), and HMTETA (0.095 g, 0.410 mmol). After the mixture was stirred for 15 min and the organometallic complex was formed (mixture turned green), 2,2,2-tribromoethanol (0.11 g, 0.389 mmol) was added and the reaction mixture was de-oxygenated by bubbling with nitrogen for 30 min. The flask was placed and stirred in an oil bath at 100 °C. After 6 h (conversion = 62 % calculated from 1 H NMR), the flask was removed from the oil bath and the reaction mixture was diluted with toluene and passed through a neutral alumina column to remove the catalyst. The obtained polymer (PS-OH) was precipitated into cold methanol and dried in vacuum at 50 °C for 24 h. PS-OH was characterized by SEC (Mn = 26 000 g/mol, PDI= 1.1) and