Molecular weight rubbery plateau

Since pc 1/2, we observe that Me 2Mg, as commonly observed. Mg is determined from the onset of the rubbery plateau by dynamic mechanical spectroscopy and Me is determined at the onset of the highly entangled zero-shear viscosity law, T) M. This provides a new interpretation of the critical entanglement molecular weight Mg, as the molecular weight at which entanglement percolation occurs while the dynamics changes from Rouse to reptation. It also represents the... 

The molecular weight between crosslinks (Me) was determined for each epoxy/amine ratio of the neat resin from the rubbery plateau region of the modulus curve following the Tg region. This can be seen in Figure 13 for several epoxy/amine ratios. The Me values were calculated from the following equation ... 

Figures 1 to 3 also show that the decrease from the rubbery plateau to the rubbery flow is more rapid for plasticized PVC than for the pure polymer. This has been previously observed for polystyrene and plasticized polystyrene (27). Maximum relaxation times have been shown to be shorter for the plasticized sample due to the decrease in T0 as well as to a decrease in apparent average molecular weight (27). A similar interpretation applies in the case of plasticized polyviny. chloride.

Chain entanglements are the cause of rubber-elastic properties in the liquid. Below the "critical" molecular mass (Mc) there are no indications of a rubbery plateau. The length of the latter is strongly dependent on the length of the molecular chains, i.e. on the molar mass of the polymer. From the shear modulus of the pseudo rubber plateau the molecular weight between entanglements may be calculated ... 

The use of monomers that produce amorphous hard segments produces highly compatible systems with poorly defined rubbery plateau and elastomeric behavior. Because no heterogenous conditions develop during the reaction, molecular weight in amorphous polyurethane systems tends to be less affected by reaction rates or polymerization conditions. 

The area above the Tg and below the melt is known as the rubbery plateau, and the length of it as well as its viscosity are dependent on the molecular weight... 

We return now to the difference in behavior between the two types of PMMA with molecular weights of 1.5 x 10 and 3.6 x 10 . We note that the rubbery modulus of the type with the higher molecular weight reaches a plateau at /iR = 3.4 MPa. As we discuss in Chapter 6 on rubber elasticity, the entanglement molecular weight Me can be determined from this modulus through the statistical theory of rubber elasticity (Ferry, 1980) as... 

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