Conformational Characteristics of Some Model Polydienes and Polyolefins

The conformational behavior of model polydienes and their saturated polyolefinic analogues has been studied. The polymers were based on 1,3-butadiene, 2,3-dimethylbutadiene, 2-ethyl-1,3-butadiene, and 3-methylene-7-methyl-1,6-octadiene (β-myrcene). The unperturbed chain dimensions of these near-monodisperse polymers were evaluated under θ or near-θ conditions via intrinsic viscosity measurements. Consequently, information was obtained regarding the influence of side-chain length on chain dimensions as well as the influence of head-to-head structures in polypropylene. The temperature coefficient (d In 〈R²〉₀/dT) for chain dimensions of alternating poly(ethylene-butene) was determined. Its value of −0.9 × 10⁻³ K⁻¹ is in consonance with the values for polyethylene and alternating poly(ethylene-propylene). The temperature coefficients for poly(vinylethylene), a butene-rich poly(ethylene-butene) material, and poly-(ethylethylene) were also measured. The value for the latter polymer is notably larger (−2.3 × 10⁻³ K⁻¹) than that predicted (−0.1 × 10⁻³ K⁻¹) from the five-state rotational isomeric state model. A value of −1.7 × 10⁻³ K⁻¹ was measured for poly(vinylethylene), while −1.4 × 10⁻³ K⁻¹ was found for a butene-rich poly(ethylene-butene) copolymer (40 ethyl branches per 100 backbone carbons).