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

Abstract

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.

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

“…Several studies investigated the zero shear viscosity η 0 as a function of total molecular weight for different series of loose and dense bottlebrushes with either short chain branches (SCB) [13,18,19,24,[29][30][31]57] or long chain branches (LCB). [11,30] Within these bottlebrush series, two characteristics out of n sc , n g , and n bb are fixed and one of them is varied in the series.…”

“…Figure 5a presents the reduced η 0 for five bottlebrush series and a linear series at a reference temperature T ref = T g + 34 °C. [31] It was shown that η 0 versus M w has two different scaling regimes 1 and 3, which could be related to Rouse and reptation dynamics, respectively. These bottlebrushes were synthesized via ROMP of ω-norbornenyl polylactide macromonomers.…”

“…In both series, the DP of the backbone was below the entanglement length, n bb < n e,bb , and both series show almost a Rouse relaxation mechanism for η 0 . [31] dimethyl ester (DME) as comonomer to vary the grafting densities, [59] z ≅ 2.68/n g , PLA z -ran(DME) 1−z -NB-SCB.…”

“…In the current paper, we investigate the transitions from comb to bottlebrush behavior; therefore, all of these variables are used for both topologies especially in the transition from comb to bottlebrush conformations. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties.…”

Synthetic Methodologies for Chelating Polymer Ligands: Recent Advances and Future Development

“…The linear viscoelastic behavior of poly(norbornene)‐gr‐PLA obtained by living ROMP was studied, depending on the grafting density and total molar weight (Figure ) . It turned out that resulting polymers demonstrate Rouse and reptation dynamics with a sharp transition in zero‐shear viscosity data, demonstrating that grafting density strongly affects the entanglement molar weight.…”