Model Branched Polymers: Synthesis and Characterization of Asymmetric H-Shaped Polybutadienes

A new type of model branched polymer, asymmetric H-shaped polybutadienes, consisting of central crossbars having various combinations of short and long arms attached to the ends of the crossbars, was synthesized using living anionic polymerization and chlorosilane linking chemistry. The linking agent 4-(dichloromethylsilyl)­diphenylethylene provides selective reactivity to attach short or long arms on one side or both sides as desired. The samples were characterized thoroughly by size exclusion chromatography with light scattering detection (SEC-LS) and found to exhibit controlled molecular weights, as well as narrow polydispersity indices (PDIs of 1.01–1.06). Temperature gradient interaction chromatography, a method with far superior resolution as compared to SEC, also shows that these materials are well-defined, with minimal and identifiable impurities

In Silico Molecular Design, Synthesis, Characterization, and Rheology of Dendritically Branched Polymers: Closing the Design Loop

It has been a long held ambition of both industry and academia to understand the relationship between the often complex molecular architecture of polymer chains and their melt flow properties, with the goal of building robust theoretical models to predict their rheology. The established key to this is the use of well-defined, model polymers, homogeneous in chain length and architecture. We describe here for the first time, the in silico design, synthesis, and characterization of an architecturally complex, branched polymer with the optimal rheological properties for such structure–property correlation studies. Moreover, we demonstrate unequivocally the need for accurate characterization using temperature gradient interaction chromatography (TGIC), which reveals the presence of heterogeneities in the molecular structure that are undetectable by size exclusion chromatography (SEC). Experimental rheology exposes the rich pattern of relaxation dynamics associated with branched polymers, but the ultimate test is, of course, did the theoretical (design) model accurately predict the rheological properties of the synthesized model branched polymer? Rarely, if ever before, has such a combination of theory, synthesis, characterization, and analysis resulted in a “yes”, expressed without doubt or qualification

Correction to In Silico Molecular Design, Synthesis, Characterization, and Rheology of Dendritically Branched Polymers: Closing the Design Loop

Correction to In Silico Molecular Design, Synthesis, Characterization, and Rheology of Dendritically Branched Polymers: Closing the Design Loo

Viscosity of Ring Polymer Melts

We have measured the linear rheology of critically purified ring polyisoprenes, polystyrenes, and polyethyleneoxides of different molar masses. The ratio of the zero-shear viscosities of linear polymer melts η_0,linear to their ring counterparts η_0,ring at isofrictional conditions is discussed as a function of the number of entanglements <i>Z</i>. In the unentangled regime η_0,linear/η_0,ring is virtually constant, consistent with the earlier data, atomistic simulations, and the theoretical expectation η_0,linear/η_0,ring = 2. In the entanglement regime, the <i>Z</i>-dependence of ring viscosity is much weaker than that of linear polymers, in qualitative agreement with predictions from scaling theory and simulations. The power-law extracted from the available experimental data in the rather limited range 1 < <i>Z</i> < 20, η_0,linear/η_0,ring ∼ <i>Z</i>^1.2±0.3, is weaker than the scaling prediction (η_0,linear/η_0,ring ∼<i> Z</i>^1.6±0.3) and the simulations (η_0,linear/η_0,ring ∼ <i>Z</i>^2.0±0.3). Nevertheless, the present collection of state-of-the-art experimental data unambiguously demonstrates that rings exhibit a universal trend clearly departing from that of their linear counterparts, and hence it represents a major step toward resolving a 30-year-old problem