Moderately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine-sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high-molecular-weight polypropylenes (Mw ≈10(4) ), and the substituent at the ortho-position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho-position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55-0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X-ray diffraction patterns.

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ABSTRACT:Order-disorder transitions (ODT) of symmetric poly(styrene-b-2-vinylpyridine) in a common good solvent and bulk were determined by dynamic rheological and small-angle neutron scattering measurements. ODT conditions determined by both methods are consistent with each other and the degree of polymerization dependence of critical volume fraction in solution at almost constant temperature agrees with the theoretical prediction for semidilute solutions. However, semidilute behavior persists to a much higher concentration than for ordinary polymer solutions and the crossover from semidilute to concentrated regimes is not clear. KEY WORDSOrder-Disorder Transition / Symmetric Diblock Copolymers / Poly(styrene-b-2-vinylpyridine) / Small-Angle Neutron Scattering/ Semidilute Region/ Block copolymers exhibit a phase transition between ordered (microphase-separated) and disordered (homogeneous) states under certain conditions. The orderdisorder transitions (ODT) of block copolymers have been extensively studied and the results are summarized in the literature. 1 -8 A brief outline of the results is as follows.Theoretically, the phase diagram for diblock copolymers in bulk was first discussed by the mean-field approach,9 and later modified to include fluctuation effects. 10 According to the theory, the ODT of symmetric diblock copolymers occurs at (xN)ooT= 10.5 +41.0. N-113 ( 1) where x is the Flory-Huggins interaction parameter, N is the number of statistical segments (monomers) per copolymer molecule and (2) is a term for fluctuation correction. Here (S 2 ), Mm p, and NA are the mean square radius of gyration, number-average molecular weight, mass density and Avogadro's number, respectively. It was also predicted that eq 1 and 2 can be applied to block copolymer solutions by appropriate replacement of the parameters. 11 • 12 Experimentally, most studies on ODT have been carried out for polystyrene-polydiene diblock copolymers such as poly(styrene-b-isoprene) (SI) and hydrocarbon diblock copolymers such as poly(ethylenepropylene-b-ethylethylene) in bulk. Several experimental methods to determine ODT have been examined. At present, small-angle X-ray scattering, small-angle neutron scattering (SANS), birefringence measurement and dynamic rheological measurements (DRM) are generally used. 1 -s Recently, we studied the viscoelastic properties of SI diblock copolymer solutions near ODT and reported that t To whom correspondence should be addressed. 388the shear rate dependence of the first normal stress difference changes from first order to second order, after shear-induced alignment of the microdomain structure occurs. 13 Generally speaking, systematic studies on viscoelastic properties, especially those under steady shear flow are much easier in solution than in bulk. Difference in viscoelastic properties of block components may affect the shear-induced alignment. For better understanding of the viscoelastic properties and shearinduced alignment of diblock copolymers near ODT, it is essential to study them both ...

The steady shear rate dependence of the structure of two poly(styrene-d8-b-2-vinylpyridine)s in R-chloronaphthalene, a common good solvent, was measured by small-angle neutron scattering (SANS) in a couette flow cell geometry in the ordered state, in which the solutions assume a lamellar structure (randomly oriented grains). SANS measurements revealed that steady shear flow induces macroscopic lamellar orientation at certain characteristic shear rates for the higher molecular weight sample (M w ) 3.6 × 10 5 ). Lamellar normals are preferentially oriented along the vorticity direction at high shear rates. However, no shear effect was observed for the low molecular weight sample (Mw ) 2.0 × 10 5 ).

ABSTRACT:Flow effects on the structure and the related viscoelastic properties of lamellar forming poly(styreneblock-2-vinylpyridine)s (SP) and DP in which S in SP replaced by deutrated chains are studied by small angle neutron scattering (SANS) and viscoelastic measurements under shear flows near the order-disorder transition (ODT). A distinctive feature of this sample is that both components have quite similar viscoelastic properties. In the quiescent ordered states, SANS intensities showed strong anisotropy denoting flow-induced alignment of lamellar structure at high shear rates ( _ ) in a limited range of concentration. When the lamellae are well aligned, first normal stress difference was proportional to _ 2 and reduced steady state compliance J eR became practically the same as those of components. The viscosity behaviors in the quiescent ordered and disordered states were also the same as those of components. In the disordered states, on the other hand, J eR was higher than those of components. Under steady shear flows, however, SANS intensities are isotropic and became lower and J eR became almost the same as those of components denoting the suppression of fluctuation effects. Block copolymers possess different microphaseseparated structure in the ordered states, such as sphere, cylinder, co-continuous and lamella, depending on the molecular structure and compositions of components. In the disordered states but near the order-disorder transition (ODT), there exist composition fluctuations of component polymers in the block copolymer liquids. Both the microphase separated structure and the composition fluctuations affect the rheological properties of block copolymers, therefore, structure and the related viscoelastic properties of the block copolymers have been extensively studied both in the ordered and the disordered states. General results of rheological properties for variety of block copolymers are summarized in review articles.

ABSTRACT:Viscoelastic properties of binary blends of immiscible polymers with almost the same viscosity were studied under steady and transient shear flows in the light of the scaling relations in the constitutive equation of textured materials presented by Doi and Ohta. Samples used were blends of polydimethylsiloxane (PDMS) and polybutadiene (PB) with the composition ratios of 3 : 7, I : I, 7: 3, and 9: 1 for PDMS: PB by weight. It was found that both shear stress rr12 and primary normal stress difference N 1 at steady state are proportional to shear rate j, except N 1 of 9: I blend, and the rescaled transient stresses after stepwise increase of shear rate compose a single line in terms of strains if the step ratios of shear rates are constant, in accordance with the scaling relations. For the 9: I blend, in which the contribution of N 1 of component polymers cannot be neglected because the interface is small, however, the extra primary normal stress difference at steady state after subtracting N 1 of component polymers from the measured one was found to be proportional to y in accordance with the scaling relations.

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