(A) study of living cationic polymerization of styrene derivative and its block copolymerization

Abstract

To develop new initiating system of living cationic polymerization of styrene derivatives, especially styrene and p-methylstyrene, I attempted several initiating system based on the initiators designed carefully, the strength of Lewis acids, solvent polarity, and temperature. Among them, 1-chloroethylbenzene (1-CEB)/$SnCl_4$ and 1,4-bis-(1-chloroethyl) benzene (BCEB)/$SnCl_4$/2,6-DtBP initiating system for styrene monomer, and 1,4-bis-(1-chloro-1-methylethyl) benzene (BCMEB)/$SnCl_4$/2,6-Di-t-butylpyridine (2,6-D-tBP) initiating system for p-methylstyrene led to living cationic polymerization in $CHCl_3$ at -15℃. The number-average molecular weight ($\bar{M}$n) of the polymers was directly proportional to the ratio of initial monomer concentration to initial initiator concentration. The molecular weight distribution (MWD) of the polymers was very narrow ($\bar{M}w$/$\bar{M}n$ < 1.2). These results of living cationic polymerization of styrene and p-methylstyrene suggested that it was largely governed by the rate of initiation of initiators, polarity of solvent, and temperature. The living polymerization could be achieved in the selection of high reactive carbocationic initiator by careful design compared to propagating carbocationic species of polymer, low solvent polarity, and low temperature. 2,6-DtBP was used as trapping agent of proton produced by impurity moisture with $SnCl_4$. The similar rate of polymerization with or without 2,6-DtBP in this polymerization condition indicate that 2,6-DtBP does not stabilize propagating carbocation like added Lewis base. Based on the our systematic study of the living polymerization of styrene and p-methylstyrene, triblock copolymers were synthesized by sequential living cationic polymerizations from a more reactive monomer(p-methylstyrene), following by further addition of $SnCl_4$ in order to accelerate the subsequent polymerization of the second monomer(styrene) These p-methylstyrene-based ABC triblock copolymers ...