Dynamics of Disordered Diblocks of Polyisoprene and Polyvinylethylene

Abstract

The apparent thermorheological simplicity of disordered diblocks is reconciled with the failure of time−temperature superposition of corresponding miscible blends by examining the relaxation of the constituent blocks using rheo-optical techniques. Diblocks of 1,4-polyisoprene (PIP) and polyvinylethylene (PVE) are examined over a range of temperatures for two compositions (φPIP = 0.25 and 0.75). Unlike blends of PIP and PVE, the block copolymers appear to obey time−temperature superposition on the basis of their viscoelastic properties. However, departure from thermorheological simplicity is exposed in their stress−optical behavior. In particular, the copolymer rich in the high T g component (φPIP = 0.25) shows distinct temperature dependencies for the individual blocks, in accord with the behavior of PIP/PVE blends. The block copolymer rich in the low T g component (φPIP = 0.75) is thermorheologically simple because both blocks have similar monomeric friction coefficients ζo, PVE ≈ ζo,PIP, again in accord with prior results on PIP/PVE blends. The failure of time−temperature superposition in these diblocks was not previously observed because the change in ζo,PVE/ζo,PIP with temperature produces subtle changes in the overall relaxation spectrum relative to a linear chain of uniform friction.

Dynamical mechanical behavior of copolymers made of styrene and methyl methacrylate: Random, alternate and diblock copolymers

“…The complex behaviour of the random and alternate copolymers is similar to the one found for blends of miscible homopolymers [17,22]. While the failure of the time-temperature superposition principle for the D2 and D3 samples is the expected behaviour for diblock copolymers in the ordered state, the behaviour of the D3 sample is in agreement with the behaviour described for block copolymers in the disordered state [17,18].…”

“…Similar conclusions were reached at by Ruzette et al for diblock copolymers of styrene and n-alkyl methacrylates in the disordered state, for temperatures well separated from the order-disorder one [5]. However, Arendt et al showed that the 1,4-poly(isoprene-b-vinylethylene) copolymers were thermorheologically complex materials when their rheo-optical properties were analyzed [18]. Thermorheologically complexity was also found when the copolymers approached the order-disorder transition from the disordered phase [5].…”

Dynamic heterogeneity in a miscible poly(vinyl acetate)/poly(ethylene oxide) blend

“…The terminal relaxation times of the two components also depend on temperature differently with each other [6][7][8][9][10]. Consequently time-temperature superposition principle does not hold.…”

Dynamics in disordered block copolymers and miscible blends composed of poly(vinyl ethylene) and polyisoprene

“…Furthermore, the effect of the chemical linkage between different polymer chains on the dynamics of disordered diblock copolymers (BCPs) also needs to be clarified. Many studies of dynamics in miscible blends1–24 and disordered block copolymers12, 25–30 have been performed thus far. Blends commonly exhibit broader relaxation spectra than those of the components.…”