Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers

The linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0 to 100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed, while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data, demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (G_e) scales with inverse grafting density (n_g) as G_e ∼ n_g^(1.2) and G_e ∼ n_g^0 in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin flexible chains at low grafting density and thick semiflexible chains at high grafting density anticipates the sharp transition between the limiting dynamical regimes

Supporting data for Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers

The folder below include the NMR, SEC, DSC, SAXS, and rheology data for all reported samples. The zipped folder contains each series of data in a subfolder, and the readme file further describes the individual files.These files contain data along with associated output from instrumentation supporting all results reported in Haugan et. al. "Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers." In Haugan et. al. we found: The linear viscoelastic behavior of poly(norbornene)-graft-poly(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0–100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (Ge) scales with inverse grafting density (ng) as Ge ~ ng1.2 and Ge ~ ng0 in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin flexible chains at low grafting density and thick semiflexible chains at high grafting density anticipates the sharp transition between the limiting dynamical regimes.NSF CHE-141386

Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers

The linear viscoelastic behavior of poly­(norbornene)-<i>graft</i>-poly­(±-lactide) was investigated as a function of grafting density and overall molar mass. Eight sets of polymers with grafting densities ranging from 0 to 100% were synthesized by living ring-opening metathesis copolymerization. Within each set, the graft chain molar mass and spacing between grafts were fixed, while the total backbone length was varied. Dynamic master curves reveal that these polymers display Rouse and reptation dynamics with a sharp transition in the zero-shear viscosity data, demonstrating that grafting density strongly impacts the entanglement molar mass. The entanglement modulus (<i>G</i>_e) scales with inverse grafting density (<i>n</i>_g) as <i>G</i>_e ∼ <i>n</i>_g^1.2 and <i>G</i>_e ∼ <i>n</i>_g⁰ in accordance with scaling theory in the high and low grafting density limits, respectively. However, a sharp transition between these limiting behaviors occurs, which does not conform to existing theoretical models for graft polymers. A molecular interpretation based on thin flexible chains at low grafting density and thick semiflexible chains at high grafting density anticipates the sharp transition between the limiting dynamical regimes