Amphiphilic Block Copolymers by Sequential Living Cationic Polymerization:  Synthesis and Characterization of Poly(isobutylene-b-methyl vinyl ether)

The living polymerization of methyl vinyl ether (MeVE) was achieved using initiators obtained by capping 2,4,4-trimethyl-2-chloropentane (TMPCl) with 1,1-diphenylethylene (DPE), or 1,1-ditolylethylene (DTE) in conjunction with TiCl n (OEt) 4 - n ( n = 2−2.4) coinitiator in CH 2 Cl 2 /hexanes (60/40 v/v) solvent mixture at 0 °C. Sequential block copolymerization of isobutylene (IB) with MeVE has also been accomplished. Well-defined living poly(isobutylene) (PIB) was first prepared at −80 °C in the presence of TiCl 4, followed by capping with DPE or DTE. Then, Ti(OEt) 4 was added to reduce the Lewis acidity followed by the addition of MeVE, and the temperature was raised to 0 °C. Well-defined PIB-PMeVE diblock copolymers with controlled molecular weight and narrow molecular weight distribution ( M w / M n < 1.1) have been obtained, with the virtual absence of homopolymer contaminants. According to differential scanning calorimetry, the diblock copolymers exhibit two T g s, suggesting microphase separation. PIB-PMeVE diblock copolymers with ∼50/50 w/w composition were insoluble in water but soluble in methanol. The diblock copolymer with 80 wt % PMeVE content was soluble in water, exhibited excellent surfactant properties (critical micelle concentration = 2.3 × 10 -5 M), and produced stable emulsions of oil in water (average particle size ∼200 nm).