Rheological properties of polybutadienes prepared by n‐butyllithium initiation

Abstract

synopsisThe flow behavior of n-butyllithium-polymerized polybutadienee w a investigated aa a function of molecular weight, temperature, and shear rate. At low shear r a h these polymers exhibit Newtonian flow up to molecular weighte of several hundred thousand so that "zero shear" Newtonian viscosities can readily be determined without the risk of long extrapolation. Above 1O.OOO molecular weight the Newtonian viscosities obey the well-known 3.4 power dependence on weight-average molecular weight. The entanglement spacing molecular weight is estimated at 5600. The temperature dependence of viscosity is substantially independent of molecular weight w d shear stress and can be represented analytically by functions propoaed in the literature. The apparent activation energy for viacoua flow ia not constant, but decreases with rising temperature.The flow of the polymers becomes increasingly non-Newtonian with the product of shear rate, molecular weight and Newtonian viscosity. However, the departure from Newtonian behavior is apparently less than for any polymer system whose flow behavior has k e n described in the literature. The indications are, therefore, that sharp molecular weight distribution and freedom from long chain branching favor Newtonian flow and that the n-butyllithium initiated polybutadienea represent some of the most perfectly linear, narrow distribution polymers known.

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

“…Early studies on randomly branched poly(vinyl acetate) (PVA) and polybutadiene (PB) indicated higher melt viscosity than linear polymers of the same M w at sufficient branch lengths M b above the characteristic molecular weight between entanglements M e [64][65][66][67]. Graessley et al [68][69][70] and Raju et al (71) observed viscosity enhancement over that of linear polymers of equivalent molecular size in star and comb polyisoprene (PI), polystyrene (PS) and hydrogenated polybutadiene (HPB).…”

Procedures for homogeneous anionic polymerization

“…In conjunction with this point, it is pertinent to note that a small amount of branched material, in contradistinction to the claims of others [23,24], is formed during the polymerization of butadiene [22,56]. This appears to be due to the susceptibility of the vinyl group to attack by an organolithium.…”

“…At this temperature, at l~ast several days are necessary for complete conver- SIOn. The measurement of viscosity is a convenient mode of determining the molecular weight of polymers prepared by these homogeneous anionic polymerization techniques. Values for K and a for several polymer-solvent pairs have been published; polystyrene [13,14], poly-a-methylstyrene [17], polyisoprene [20,] and polybutadiene [23,24].…”

Melt Flow Properties of Block Copolymers

“…89 ,90 This deviation may be caused by systematic deviations in the M w measurements as a result of different calibration procedures, measuring technique, etc. The master curve relations used above seem to be less vulnerable to this kind of uncertainty if all data used are based on experimental results from the same source.…”