Formation and Stability of Water-Soluble, Molecular Polyelectrolyte Complexes: Effects of Charge Density, Mixing Ratio, and Polyelectrolyte Concentration

摘要

The formation of complexes with stoichiometric(1:1)as well as nonstoichiometric(2:1)and(1:2)compositions between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights is reported in this contribution.Poly(sodium styrenesulfonate)(NaPSS)was used as polyanion,and a range of copolymers with various molar ratios of the poly(methacryloxyethyltrimethylammonium)chloride,poly(METAC),and the nonionic poly(ethylene oxide) ether methacrylate, poly(PEO(45)MEMA), were used as polycations.Formation and stability of PECs have been investigated by dynamic and static light scattering(LS),turbidity,and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration,charge density of the cationic polyelectrolyte, and mixing ratio.The data obtained demonstrate that in the absence of PEO45 side chains the 100% charged polymer(polyMETAC)formed insoluble PECs with PSS that precipitate from solution when exact stoichiometry is achieved.In nonstoichiometric complexes(1:2)and(2:1)large colloidally stable aggregates were formed.The presence of even a relatively small amount of PEO45 side chains(25%)in the cationic copolymer was sufficient for preventing precipitation of the formed stoichiometric and nonstoichiometric complexes. These PEC's are sterically stabilized by the PEO45 chains.By further increasing the PEO45 side-chain content(50 and 75%)of the cationic copolymer,small, water-soluble molecular complexes could be formed.The data suggest that PSS molecules and the charged backbone of the cationic brush form a compact core,and with sufficiently high PE045 chain density(above 25%) molecular complexes are formed that are stable over prolonged times.