Effect of Butadiene End-Capping of Arms in a Star Polystyrene on Solution Properties, Bulk Dynamics, and Bulk Thermodynamic Interactions in Binary Blends

Surface tension of linear-linear and star/linear polystyrene blends were measured using a modified Wilhelmy method. Our results show that for both polystyrene blend systems, the surface tension-composition profile is convex, indicating a strong surface excess of the component with lower surface energy. Star/linear blends display more convex surface tension profiles than their linear-linear counterparts, indicative of stronger surface segregation of the branched-component relative to linear chains. As a first step toward understanding the physical origin of enhancedsurface segregation of star polymers, self-consistent field (SCF) lattice simulations (both incompressible and compressible models) and Cahn-Hilliard theory were used to predict surface tension-composition profiles. Results from the lattice simulations indicate that the highly convex surface tension profiles observed in the star/linear blend systems are only possible if an architecture-dependent, Flory interaction parameter (v ¼ 0.004) is assumed. This conclusion is inconsistent with results from bulk differential scanning calorimetry (DSC) measurements, which indicate sharp glass transitions in both the star/linear and linear/linear homopolymer blends and a simple linear relationship between the bulk glass transition temperature and blend composition. To implement the Cahn-Hilliard theory, pressure-volume-temperature (PVT) data for each of the pure components in the blends were first measured and the data used as input for the theory. Consistent with the experimental data, Cahn-Hilliard theory predicts a larger surface excess of star molecules in linear hosts over a wide composition range. Significantly, this result is obtained assuming a nearly neutral interaction parameter between the linear and star components, indicating that the surface enrichment of the stars is not a consequence of complex phase behavior in the bulk.

Section: Simulations and Theorymentioning

confidence: 79%

Surface tension of polystyrene blends: Theory and experiment

Qian

Minnikanti

Sauer

et al. 2009

“…Finally, even in the most carefully synthesized star/linear blend systems, chemical differences between the chain ends, midsections, and branch point are possible. These effects introduce additional energetic contributions to the surface free energy of the blend, which have been reported to enhance the surface concentration of chain ends 12–18. Jalbert et al,13 for example, preformed incompressible lattice simulations for polymer chains with heterogeneous end segments and found that surface composition of the end groups increases as the energy difference(χ s ) between the end and middle segments is increased.…”

Section: Introductionmentioning

confidence: 99%

Surface segregation of highly branched polymer additives in linear hosts

Qian

Minnikanti

Archer

2008

Entropy-driven segregation of various branched and hyperbranched polymeric additives in chemically similar linear polymer hosts is studied using self-consistent (SCF) mean-field lattice simulations. The simulations account for the effect of molecular architecture on local configurational entropy in the blends, but ignores the effect of architecture on local density and blend compressibility. Star, dendrimer, and comb-like additives are all found to be enriched at the surface of chemically identical linear host polymers. The magnitude of their surface excess increases with increased number of chain ends and decreases with increased segmental crowding near the branch point. Provided the number of arms and molecular weight of the branched additives are maintained constant, we find that the simplest branched architecture, the symmetric star, exhibits the strongest preference for the surface of binary polymer blends. We show that a single variable, here termed the ''entropic driving force density,'' controls the relative surface affinities of branched additives possessing a wide range of architectures.

“…In the case of polymer blends, the topological architecture of star polymers could exert significant influence on intermolecular interaction parameters (χ 12 ). Some recent theoretical frameworks have rationalized the contribution of branched and star topologies to the properties of chemically identical polymer blends in terms of intermolecular interactions parameters 3–14. These theoretical works predicted that the blends containing star analogues have the larger χ 12 (absolute value) than those containing linear chains 10, 14.…”

Section: Introductionmentioning

confidence: 99%

“…These theoretical works predicted that the blends containing star analogues have the larger χ 12 (absolute value) than those containing linear chains 10, 14. Using small‐angle neutron scattering technique, Greenberg and coworkers3–9 measured the thermodynamic interactions in the blends of star‐shaped and linear polystyrene (PS), polybutadiene, and poly(methyl methacrylate) (PMMA). It was observed that in linear–star PS (or PMMA) blends, thermodynamic interactions always increase with increase in the number of arms; nonetheless, this change was not monotonic in PB‐containing blends.…”

Section: Introductionmentioning

confidence: 99%

“…Although extensive literature is available on the chemically identical linear polymer blends with star (or hyperbranched) polymers with moderate number of arms,3–14 the miscibility and phase behavior of chemically unlike linear/star polymer blends remain largely unexplored. Recently, Huang et al15 reported a comparative study on linear and star‐shaped PMMA blends with phenolic resin.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Comparative studies on miscibility and phase behavior of linear and star poly(2‐methyl‐2‐oxazoline) blends with poly(vinylidene fluoride)

Shen

Zheng

2006

The comparative studies on the miscibility and phase behavior between the blends of linear and star‐shaped poly(2‐methyl‐2‐oxazoline) with poly(vinylidene fluoride) (PVDF) were carried out in this work. The linear poly(2‐methyl‐2‐oxazoline) was synthesized by the ring opening polymerization of 2‐methyl‐2‐oxazoline in the presence of methyl p‐toluenesulfonate (MeOTs) whereas the star‐shaped poly(2‐methyl‐2‐oxazoline) was synthesized with octa(3‐iodopropyl) polyhedral oligomeric silsesquioxane [(IC3H6)8Si8O12, OipPOSS] as an octafunctional initiator. The polymers with different topological structures were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the star‐shaped poly(2‐methyl‐2‐oxazoline) was miscible with poly(vinylidene fluoride) (PVDF), which was evidenced by single glass‐transition temperature behavior and the equilibrium melting‐point depression. Nonetheless, the blends of linear poly(2‐methyl‐2‐oxazoline) with PVDF were phase‐separated. The difference in miscibility was ascribed to the topological effect of PMOx macromolecules on the miscibility. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 942–952, 2006