| The synthesis of PDMS-b-PS copolymers by anionic and nitroxide-mediated radical polymerization (NMRP) is discussed. PDMS- b-PS copolymers are synthesized by two methods. For the first method, hydride end-capped PDMS is synthesized by ring-opening polymerization (ROP) of hexamethylcyclotrisiloxane (D3). The hydride end-capped polymer is then hydrosilylated with an allylic alkoxyamine to form a TEMPO functional macroinitiator. The macroinitiator is reacted with styrene to form PDMS- b-PS copolymer. Alternatively, PDMS macroinitiator, is synthesized directly by ROP of D3 with a lithium atkoxide derivative of a hydroxyl alkoxyamine, and used to initiate NMRP. The block copolymers synthesized by the second method have a hydrolytically unstable junction. Copolymers synthesized by the first method, yielded di-blocks with molecular weights nearly equal to the theoretical value, and polydispersities between 1.27 and 1.35. Molecular weights of di-blocks synthesized by the second method were not as close to their theoretical values, and were more polydispersed (Mw/M n between 1.34 and 1.65). Microstructure characterization by one (1D) and two (2D) dimensional solution NMR verified the composition of the copolymer end-groups and block junction. LC-NMR analysis showed the amount of homopolymers in the copolymer samples. MALDI-ToF MS was used to characterize homopolymers and copolymers. DSC and solid-state NMR analysis verified phase separated morphologies. Finally, TEM analysis revealed the morphology of the copolymers. |
