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 TiCln(OEt)(4-n) (n = 2-2.4) coinitiator in CH2Cl2/hexanes (60/40 v/v) solvent mixture at 0 degrees C. Sequential block copolymerization of isobutylene (IB) with MeVE has also been accomplished. Well-defined living poly(isobutylene) (PIE) was first prepared at -80 degrees C in the presence of TiCl4, 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 degrees 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 similar to 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 x 10(-5) M), and produced stable emulsions of oil in water (average particle size similar to 200 nm).