Amphiphilic 3-arm star block polymers by living cationic polymerization

Via living cationic polymerization with a trifunctional initiator, amphiphi lic tri-armed star block copolymers were synthesized, where each arm consis ted of an AB-block copolymer with a hydrophobic and soft vinyl ether segmen t and a hydrophilic (amine-containing) and hard styrene segment. The sequen tial living polymerization was initiated first for 2-chloroethyl vinyl ethe r (CEVE) with the trifunctional HCl-adduct (1) of a trivinyl ether in conju nction with SnCl4 in the presence of n-Bu4NCl and 2,6-di-tert-butyl-4-methy l pyridine (DTBMP) in CH2Cl2, at -78 degrees C, followed by block polymeriz ation of p-(phthalimidemethyl)styrene (lmSt). The polymers had 3 arm chains with controlled molecular weights and compositions and with narrow molecul ar weight distributions (M-w/M-n similar to 1.3). Similar star amphiphiles were prepared by "one-shot" living cationic block polymerizations of CEVE a nd lmSt with 1/SnCl4/DTBMP in CH2Cl2 at -15 degrees C. due to the large rea ctivity difference between the two monomers (CEVE >> lmSt). Hydrazinolysis of the imide functions gave tri-armed amphiphilic block copolymers consisti ng of a hydrophobic poly(CEVE) soft segment and a hydrophilic hard polystyr ene segment with pendant primary amino groups, soluble in dimethyl sulfoxid e, methanol, water, and 0.5N HCl. Besides the soft-hard (CEVE-lmSt) version , the soft-soft tri-armed polymers were also prepared, consisting of an ami no-functionalized hydrophilic soft poly(vinyl ether) segment and a hydropho bic poly(CEVE) segment. The surface tension of the tri-armed polymers was s maller than that of the linear block (or arm) polymers. Small angle light s cattering measurement showed that these tri-armed copolymers exit as unimer s in water.