Macromolecular diffusion and the autoadhesion of polybutadiene

Roland, C. M.; Boehm, Gabriele

doi:10.1021/ma00148a046

Cited by 54 publications

(34 citation statements)

References 4 publications

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“…33 However, the time required for development of adhesion in such experiments has been found to be substantially longer than the time calculated from the linear diffusion constant. 33,34 Another manifestation of retarded reentanglement is the equilibration time after removal of the solvent from polymer solutions. Colby et al 35 reported that a 1,4-polybutadiene with a M w exceeding 16 million dalton, for which the terminal relaxation issue was calculated to be 4.4 days, had not attained an equilibrium state even one month after drying.…”

Section: ■ Discussionmentioning

confidence: 99%

Reentanglement Kinetics in Polyisobutylene

Roy

Roland

2013

Macromolecules

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ABSTRACT:The rheological properties of a polyisobutylene (PIB) having a molecular weight five times its entanglement molecular weight were measured, along with interrupted shear flow experiments to quantify the time required for structural recovery following steady state shearing in the non-Newtonian regime. The reentanglement kinetics was substantially slower (by more than an order of magnitude) than expectations based on the linear relaxation time of the fully entangled material. This result is in accord with published interrupted shear flow results for concentrated polymer solutions. The retarded recovery of entanglements may underlie other anomalies, for example, the delayed development of autoadhesion (tack) in rubber, the behavior of freeze-dried dilute solutions and the limiting behavior of the molecular weight dependence of the viscosity. It also offers a route to more processable polymers and, being reversible, will not affect the ultimate physical properties. ■ INTRODUCTIONWhen a polymer melt or solution is sheared at rates sufficiently low that the perturbation of the chains is slow compared to the rate of Brownian motion, their equilibrium conformation is retained, and the viscosity is Newtonian. Shear rates exceeding the reciprocal of the linear relaxation time, however, induce chain stretching and a reduction of entanglements, causing a decrease of the steady-state viscosity, η ss ("shear-thinning"). 1−3During the initial phase of non-Newtonian flow, the stress and normal force both pass through a maximum versus time, as the chains disentangle prior to attaining steady state; 4 birefringence measurements reveal similar behavior.5 The magnitude of the overshoot peak increases with shear rate, occurring at strains around 2 to 3 2 with some increase at high rates. 4 Such behavior is characteristic of a viscoelastic material with time-dependent structure (entanglements in this case), although unentangled polymers can also exhibit stress overshoots and shear thinning, but the effects are weaker. 6,7Herein we study reentanglement kinetics using interrupted non-Newtonian shear flow experiments, in which after steady state is achieved, the flow is halted and the material held in a quiescent state for some time before resumption of the shearing. Since the flow-induced loss of entanglements is reversible, the magnitude of the stress overshoot during subsequent shearing has an amplitude governed by the time allowed for reentanglement. 4,8−15 The steady-state viscosity is unaffected by interruption of the flow, since it depends only on the shear rate. For rest times exceeding some characteristic time, the entanglements return to their equilibrium concentration, and the magnitude of the overshoot has its maximum (initial) value. For concentrated solutions, the time to recover the fully entangled state has been shown to have the same molecular weight dependence (ca. M 3.4 ) as the viscosity and linear relaxation time. 16 Herein we determine its dependences on temperature and shear rate for a polymer melt.Althou...

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Section: ■ Discussionmentioning

confidence: 99%

Reentanglement Kinetics in Polyisobutylene

Roy

Roland

2013

Macromolecules

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“…Once the reptation time is identified, it is easy to calculate the self-diffusion coefficient (D). Accordingly, at 25 • C the self-diffusion coefficient (D) values of B and BCLNA8 can be calculated from the equation given below [33]:…”

Section: Frequency Sweep Studiesmentioning

confidence: 99%

Efficacy of Novel Nanoclay in Autohesive Tack of Brominated Isobutylene-co-p-Methylstyrene (BIMS) Rubber

Kumar

Tsou

Bhowmick

2010

Journal of Adhesion Science and Technology

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Autohesive tack is the ability of two unvulcanized rubber surfaces to resist separation after they are brought into contact for a short period under light pressure. In this work, the effect of unmodified montmorillonite (MMT) nanoclay on autohesive tack of brominated isobutylene-co-p-methylstyrene (BIMS) rubber was investigated by a 180 • peel test. The nanocomposites were characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM). The autohesive tack strength dramatically increased with nanoclay concentration up to 8 phr, beyond which it reached apparently a plateau at 16 phr of nanoclay concentration. The tack strength of 16 phr of nanoclay loaded sample was nearly 158% higher than the tack strength of neat BIMS rubber. Various tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation time, self-diffusion coefficient, and monomer friction coefficient were analyzed. The addition of nanoclay reduced the extent of molecular diffusion at the tack junction by reducing the chain mobility; however, the diffusion was still sufficient to achieve bond formation. Furthermore, the less diffused chains of the nanocomposite samples showed greater bond breaking resistance due to an increase in cohesive strength, onset of transition zone relaxation time, and monomer friction coefficient value of the BIMS matrix owing to the nanoclay reinforcement. On the other hand, the more diffused chains of the unfilled sample exhibited facile chain separation due to the poor cohesive strength of the BIMS matrix.

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“…For pre-cure times equal to or less than 20 min, the measured strength was roughly equal to the tear strength at the same rate. The failure, even in this case, propagated smoothly at the interface, showing that it remains 14 who studied autohesion of polybutadienes. This evolution can be explained by the decrease of the quantity of peroxide available for co-crosslinking when the precure time becomes longer.…”

Section: Influence Of the Pre-cure Timementioning

confidence: 81%