Synthesis and Solution Properties of Hydrophobically Associative Polyacrylamides by Microemulsion Polymerization

A series of hydrophobic associative copolymers using acrylamide (AM), sodium 4-styrenesulfonate (SSS) and hydrophobic stearyl methylacrylate (SMA) as co-monomers were prepared by microemulsion polymerization. Factors affecting the rheological properties of the aqueous copolymer solutions, such as the content of hydrophobic monomer, amount of SSS, amount of initiator, amount of sodium dodecyl sulfate, the copolymer concentration and the addition of salt, were investigated. The hydrophobic associative copolymers show good temperature-, shear-, and salt-resistance with the critical aggregation concentration of the copolymers being around 0.4 g·dL−1. The apparent viscosities of hydrophobic associative copolymer solutions increase as SMA content is increased from 8 to 12 %. The apparent viscosity and temperature resistance of the hydrophobic associative copolymers are enhanced by incorporation of a suitable amount of SSS segments into the polymeric chains. In addition, the apparent viscosities of hydrophobic associative copolymer solutions are increased by the addition of a small amount of NaCl and CaCl2. Both the storage modulus and loss modulus of the hydrophobic associative copolymers increase with angular frequency ω and were well fitted by the Maxwell model in the low-frequency region. FTIR and 1H NMR spectra indicate the structure of hydrophobic associative copolymers. AFM indicated that some aggregates and small network connections between polymeric chains were present.