synopsisThe effect of monomer sequence on physical properties was investigated for butadienestyrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glaw transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which compe sition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility a t different temperatures. This indicates a tendency for association between segments of different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to T, for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks. 1581
The introduction of one or two long chain branches into a polybutadiene molecule to form trichain or tetrachain molecules, respectively, leads to profound changes in rheological behavior. At low molecular weights the Newtonian (zero shear) viscosity is decreased relative to a linear polymer of the same molecular weight. At molecular weights exceeding 60,000 (trichain) or 100,000 (tetrachain), the Newtonian viscosity rises rapidly above the corresponding value for a linear polybutadiene. However, non‐Newtonian behavior of the branched polymers becomes more pronounced the higher the molecular weight, so that at moderate to high shear rates the viscosity of the branched polymers is uniformly lower than that of linear polymers of identical molecular weight.
SynopsisThe thermal expansion of a butadiene-styrene copolymer filled with carbon blacks differing tenfold in mean particle size (HAF and MT) was investigated. The glass transition was unaffected by &IT and was raised only 0.2"C for every 10 parts per hundred by weight of polymer of HAF black added. The coefficient of expansion of the polymer component of the composite in the rubbery region was substantially unaffected by either carbon black, but decreased markedly with increasing black loading in the glassy state. These results suggest that free volume is not altered appreciably by the presence of the filler in the rubbery state, but expands with decreasing temperature below T,. The latter effect is explained by dilatation due to stresses set up around filler particles, arising from differences in the expansion coefficients of filler and polymer, which are riot relieved in the glassy state. The near invariability of T , and of the rubbery coefficient of expansion with filler content indicate that segmental motion is little affected by adsorption of polymer segments on the carbon black surface. A conservative rough estimate indicates that restriction of segmental motion is confined to a 30 layer around the particles in which T , is elevated by o~ily 10°C.
where i\ is the volume fraction of the solvent in the ternary system, given by r, = xanj(xan, + xph + xahUh) Then, total polymer concentration at the critical point, C0, is given by C" = 1 -(f3)wi. = (1 + l¡V~ry/(2xpA) (7) Equation 7 may predict the compatibility of the A-Btype block copolymer with the B polymer in a solution of common solvent as a function of the ratio of the degrees of polymerization, r, the composition of the block copolymer, ipA, and the copolymer-homopolymer interaction parameter, .Consequently, one may judge roughly whether the solubilization occurs or not, from the following condition.Macromolecules 2 C* ^(1 + 1/V7)2 (8)These results may be applicable for the system involving multiblock copolymers, such as ABA, BAB, ABAB or (AB)¡, as well as the graft copolymers, so far as the following condition is held.
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.
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