Rheology and Structure of Entangled Telechelic Linear and Star Polyisoprene Melts

Abstract

We investigate the linear viscoelastic response of model telechelic linear and star (of varying functionality) polyisoprene melts with different molar masses above the entanglement limit in relation to their structure. We find that these systems self-assemble as a result of the strong dipolar interactions and form clusters that seem to depend primarily on the number of dipolar groups per star. The dynamics is rather complex, but some pertinent features are observed: the segmental dynamics is affected by the telechelic functionalization, especially for short arm lengths; this reflects the change of microstructure (and thus glass-transition temperature) with functionalization. The terminal relaxation is much slower compared to similar nonionic stars, reflecting the relaxation of clusters. Linear semitelechelic polymers (with only one end functionalized) aggregate in a star-like fashion. We further develop a tube model based on the time-marching algorithm for stars and linear chains, where we incorporate the association status of the chains via the dipolar interactions at each time step. The agreement of the predictions with the data, using two adjustable parameters (the average times when two dipolar pair remain associated or free, respectively), is remarkable and suggests design criteria for forming desired supramolecular assemblies.

Stochastic and preaveraged nonlinear rheology models for entangled telechelic star polymers

“…In both linear and non-linear regimes, we explore the parameter space, indicating the parameter values for which qualitative changes in response to the applied flow are predicted. Theory and results in the linear rheology regime are consistent with previous more detailed work of van Ruymbeke and co-workers [2]. Finally, we develop a pre-averaged version of the stochastic equations described above to obtain a set of non-stochastic coupled equations that produces very similar predictions but requires less computing resources.…”

“…We now aim at establishing a non-linear rheology model for entangled telechelic stars, that would, in the limit of the linear regime, be compatible with Ref. [2].…”

“…τ free ≪ τ as , this leads to a fraction of associated arms at equilibrium close to unity [2]. Typical systems called "sticky" or "supramolecular" are usually designed such that most bonds are formed, so φ is close to 1.…”

“…Efficient synthetic routes and unique rheological properties make them promising tools for use in drug delivery, biomedical applications, or thermoplastics, amongst other applications [27,28]. Entangled telechelic star polymers have been the focus of previous work where they successfully established a linear rheology model [2]. We now aim at establishing a non-linear rheology model for entangled telechelic stars, that would, in the limit of the linear regime, be compatible with Ref.…”

Linear shear and nonlinear extensional rheology of unentangled supramolecular side-chain polymers

“…Several theoretical models have been proposed to describe the rheological response of telechelic polymers [77,78] and unentangled [41,[79][80][81][82] or entangled [83][84][85][86][87] supramolecular polymers. For unentangled polymers with supramolecular side-groups, the polymer type relevant to our work, the so-called sticky-Rouse model has been proposed [41,[79][80][81][82].…”