LASER-LIGHT SCATTERING OF POLY(ACRYLAMIDE) IN 1 M NACL AQUEOUS-SOLUTION

Laser light scattering has been used to study the solution behavior in aqueous NaCl of poly(acrylamide) (PAM), polymerized by using two diff erent polymerization processes: solution(S) and microemulsion(M). Resu lts show that poly(acrylamide) samples polymerized from the microemuls ion polymerization process behave as branched flexible chains, but pol y(acrylamide) samples synthesized from solution polymerization exhibit a fairly expanded flexible coil-chain behavior. By combining the stat ic light scattering results with the characteristic linewidth distribu tion as determined by a Laplace inversion of the intensity-intensity t ime correlation function, the molecular weight distribution (MWD) and the radius of gyration distribution (RGD) could be estimated. The mole cular weight dependence of the z-average diffusion coefficient (D-z) w as determined during this conversion, with D-z(0) = (3.05 x 10(-4)) M( w)(-0.585) cm(2) s(-1) and D-z(0) = (1.52 x 10(-4)) M(w)(-0.518) cm(2) s(-1) for PAM(S) and PAM(M), respectively, with the weight average mo lecular weight M(w) expressed in g mol(-1) and D-z(0) in cm(2) s(-1). The superscript zero denotes the value at infinite dilution. The small er alpha(D) value of 0.52 for PAM(M) suggests that PAM(M) could have a fairly compact, but still soluble, flexible coil-chain structure, pos sibly arising asa result of (apparent) branching. Two different models , polydisperse branched chains and branched soft spheres, were used to fit the particle scattering factor obtained from SLS measurements. Th e results show that the particle scattering factors of:samples PAM(M) (but not of PAM(S)) could be fitted satisfactorily by either model. Co ncentration and angular dependence of the mean characteristic linewidt h, as well as the molecular weight distribution derived by using the C ONTIN analysis, are presented. The origin of the apparent branching in the microemulsion prepared poly(acrylamide) is shown to be a noncoval ent aggregation in 1 M NaCl which is not manifest formamide solutions of the same polymer.