Star Polymers and the Failure of Time−Temperature Superposition

Abstract

We model the arm of a star polymer as an anchored random walk in an array of fixed obstacles with the added assumption of an energetic cost associated with the walk retracing its previous step. By including this energetic penalty for such "hairpin" turns on the chain, we are able to account for the thermorheological complexity of long-branched hydrogenated polybutadiene yet not introduce deviations from time-temperature superposition in a melt of the linear chains. We also show that the same assumption leads to a prediction for the thermal expansion coefficient of the linear chains that is in reasonable agreement with the latest data.

Effect of temperature on the terminal relaxation of branched polydimethysiloxane

“…Similar results were reported for PIB [19,20]. This correspondence between the effects of branching on the temperature dependence and on thermorheological complexity is predicted by models [8][9][10]. The idea is that retraction of entangled branches is necessary for terminal relaxation in branched polymers.…”

“…Specifically, a negative j (expanded configuration energetically favored) is predicted for branched polymers showing thermorheological complexity in the terminal zone and an enhanced temperature dependence of viscosity. More recent work similarly invokes an energy barrier due to the configurations required for retraction of a branch, leading to the same qualitative predictions [10].…”

“…Specifically, the prediction is that an increased temperature dependence will only arise in polymers for which j negative [8][9][10]. For PDMS, j ¼ 5:9 Â 10 À4 AE 1:4 Â 10 À4 [17].…”

Characterization of Shape Memory Polymer Estane by Means of Dynamic Mechanical Thermal Analysis Technique

“…In other words, the frequency (or time) and the temperature in viscoelastic data are equivalent, and data at one temperature can be superimposed upon data taken at different temperature merely by shifting the curves. This has been shown to be true for numerous polymeric materials [14,15,[23][24][25].…”

Star Polymers in Good Solvents From Dilute to Concentrated Regimes: Crossover Approach

“…A special place in these studies occupy star polymers at theta conditions [13,[15][16][17]19,26,32,36,[38][39][40][41]43,54,57,63,[67][68][69]. There has also been a large number of studies of the dynamics of star polymers, which include the relations between structure and dynamics [70][71][72][73][74][75][76][77][78], phase separation [79] and self-assembly kinetics [80], relaxation phenomena [81][82][83][84][85], viscosity [86][87][88] and diffusion [89][90][91][92][93], rheological behaviour [94,95], viscoelastic properties [96][97][98], and glass transition …”