Synthesis and Characterization of Block Copolymers Using Polysiloxane Based Macroazoinitiator

摘要

Poly(dimethylsiloxane-b-styrene)(PDMS-6-PSt)and poly(dimethylsiloxane-b-methyl methacrylate)(PDMS-6-PMMA)block copolymers containing siloxane segments were studied by the radical polymerizations of vinyl monomers such as styrene(St)and methyl methacrylate(MMA)using polydimethylsilox-ane based macroazoinitiator(PDM-MAI)in solution.PDM-MAI was synthesized by reacting hydroxy-terminated polydimethylsiloxane(PDMS)and 4,4'-azobis(4-cyanopentanoyl chloride)(ACPC)having a thermodegradable azo-linkage.The polycondensation reaction between PDMS and ACPC(2:1,molar ratio)was carried out at room temperature.The polymerizations of St and MMA initiated by PDM-MAI were investigated using different PDM-MAI concentrations(1,5,10,and 15 wt.%)for various reaction times with a methyl ethyl ketone(MEK)/ dichloromethane(DCM)solvent mixture(3:1,molar ratio)as the reaction medium at 65 deg C.The decomposition temperature of MAI azo groups was determined to be 125 deg C by thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).PDM-MAI was characterized from the 'H-NMR spectrum,where the signals of the -CH2 resonance(2.32-2.71 ppm)and -CHa resonance(1.65-1.70 ppm)of ACPC and the dimethylsiloxane protons(0.072 ppm)in siloxane segments are observed.PDM-MAI was also identified by the peak at 1740 cm~(-1)due to the C=O stretching,proving polyester formation,the peaks at 800 and 1260 cm~(-1)as the Si-CHs deforma-tion bands,and the Si-O-Si asymmetric stretching vibration bands appearing at 1100 cm~(-1)from the FTIR spectrum.The number-average molecular weight(M_n)of PDM-MAI was determined to be 812 g/mol by vapor pressure osmometry(VPO)in chloroform.The number- and weight-average molecular weights(M_n and M_w)of PDMS-6-PSt and PDMS-6-PMMA copolymers determined by gel permeation chromatography(GPC)show a decrease with respect to increasing PDM-MAI initial concentration in the polymerization mixture.In addition,the polymerization yields increase with increasing reaction time for constant PDM-MAI concentrations.