Effect of short chain branching on the coil dimensions of polyolefins in dilute solution

This paper deals with the short branch effect in alpha -olefin copolymers on radius of gyration R-g and intrinsic viscosity [eta] in trichlorobenzene at 135 degreesC. A wide range of structurally uniform copolymers of ethylene with propylene, 1-butene, 1-hexene, and 1-octene were analyzed by size exclusion chromatography with on-line refractive index, low-angle and multiangle light-scattering and viscometry detectors. Variation of refractive index increment with composition was determined, and corrections for finite concentration were applied. Both R-g and [eta] are accurately described by power laws R-g = KsMalpha s and [eta] = KvMalpha v. The coefficients K-s and K-v vary with comonomer type and amount, but the same exponents, alpha (s) = 0.58 and alpha (v) = 0.695, apply within the measurement uncertainty to all polymers studied. The ratios g(SCB) = R-g(2)/(R-g(2))(PE) and g'(SCB) = [eta]/([eta])(PE) vary linearly with comonomer weight fraction, with slopes that depend on the comonomer type. Various explanations for the observations are considered.