Effect of Short Chain Branching on the Coil Dimensions of Polyolefins in Dilute Solution

This paper deals with the short branch effect in α -olefin copolymers on radius of gyration R g and intrinsic viscosity [ η ] in trichlorobenzene at 135 °C. 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 [ η ] are accurately described by power laws R g = K s M α s and [η] = K v M α v . The coefficients K s and K v vary with comonomer type and amount, but the same exponents, α s = 0.58 and α 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 = [η]/([η]) PE vary linearly with comonomer weight fraction, with slopes that depend on the comonomer type. Various explanations for the observations are considered.