Synthesis and characterization of amphiphilic cationic symmetrical ABCBA pentablock terpolymer networks: Effect of hydrophobic content

Group transfer polymerization was employed for the preparation of six amphiphilic terpolymer networks comprising the hydrophilic, pH-responsive 2-(dimethylamino)ethyl methacrylate (DMAEMA), the neutral hydrophilic methoxy hexa (ethylene glycol) methacrylate (HEGMA), and the hydrophobic n-butyl methacrylate (BuMA). 1,4-Bis(methoxytrimethylsiloxymethylene)cyclohexane was used as a bifunctional initiator, whereas ethylene glycol dimethacrylate served as the crosslinker to interconnect the linear terpolymer precursors to three-dimensional terpolymer network structures. Five of the terpolymer networks were model, with linear chains between crosslinks of precise length. Four of the five model networks were based on ABCBA pentablock terpolymers with theoretical structure DMAEMA(5)-b-BuMA(n/2)-bHEGMA(10)-b-BuMA(n/2)-b-DMAEMA(5) with n values equal to 5, 10, 20, and 30. The model network based on the equimolar statistical terpolymer and the nonmodel randomly crosslinked terpolymer network were also prepared. The molecular weights and compositions of the linear pentablock terpolymer precursors to the networks were found to be close to the theoretically expected, while the network Sol fractions were found to be relatively low. The degrees of swelling of the networks in water were found to decrease with increasing the hydrophobic content, whereas those in THF exhibited the opposite trend. Small-angle neutron scattering in deuterium oxide indicated structural organization in the most hydrophobic pentablock terpolymer networks. (c) 2008 Wiley Periodicals, Inc.