Critical molecular weight for

Ito,Y., Shishida,S. Critical molecular weight for onset of non-newtonian flow and upper newtonian viscosity of polydimethylsiloxane. J. Polymer Sci., Polymer Phys. Ed. 10,2239-2278 (1972). 

The studies of model SBS systems show that the T2L component (corresponding to the PB chain between PS blocks) increases proportionally to the number of mobile protons until the critical molecular weight for the formation of entanglement of the rubber segment (40000) is reached then the two T2s are observed for a linear PB 9S). Calculated and NMR determined mobile proton fractions are in a good agreement, except for the smallest (1-f) values. 

Creton C, Kramer EJ, Hadziioannou G (1991) Critical molecular-weight for block copolymer reinforcement of interfaces in a 2-phase polymer blend. Macromolecules 24 1846-1853... 

Inoue T, Okamoto H, Osaki K (1991) Birefringence of amorphous polymers. 1 Dynamic measurements on polystyrene. Macromolecules 24 5670—5675 Isayev AI (1973) Generalised characterisation of relaxation properties and high elasticity of polymer systems. J Polym Sci A-2 116 2123—2133 Ito Y, Shishido S (1972) Critical molecular weight for onset of non-Newtonian flow and upper Newtonian viscosity of polydimethylsiloxane. J Polym Sci Polym Phys Ed 10 2239— 2248... 

Depending on the material, a critical molecular weight for the observation of a stable craze has been found, for PMMA [29,30] and for PC [42], Below this critical value, crazes are not seen by interferometry and the material is very brittle. The molecular weight has to be sufficiently large (about Mw = 3 x 105 g/mol for PMMA and Mw = 12 x 103 g/mol for PC) for the development of a stable craze. The critical craze thickness and craze length (Acr and Ac) are also temperature dependent [29,30,43,44] and this effect is amplified with increasing molecular weight [29,30]. 

Figure 20.9. Effect of molecular weight (MW) on viscosity of linear and branched polymer melts. Beyond a critical molecular weight for entanglements (MW ) viscosity (r o) increases rapidly for linear polymers as MW. ...

Fig. 37. Effect of the diluent molecular weight in blends with 1,800,000 molecular weight PS (X = 0.3) on craze fibril stability (e — ej. The samples were unfiltered and the strain rate used was 5 X 10 s Mc(as2Me) is the critical molecular weight for entanglement effects on the zero-shear-rate viscosity (From Ref. courtesy Macromolecules (ACS))...

Table V. Critical Molecular Weight for Penetration and Maximum Swelling Capacity of Wood and Derived Materials in Water (FSP)...

The molecular weight of the trapped polyisoprene sequence must be higher than the critical molecular weight for entanglements of polyisoprene. 

Fig. 11 Imposed strain rates plotted against critical molecular weight for chain fracture for PEO. The triangles are for experiments with aqueous PEO solutions performed using the pressure driven flow apparatus and the squares are from experiments carried out in the pump driven flow loop. The circles are for the viscous solvent (water/glycerol 50/50 = 6.4 cP) passed through the flow cell...

Two other noteworthy physical properties result from the examination of the data. These are the critical molecular weight for entanglement and the molecular weight between entanglements. Table 10.2 shows that these values are about 9000 and 4000g/mol, respectively. For linear polymer melts, a factor of about 2 is a usual finding in polymer physics. 

FIGURE 21. The critical energy release rate Gc of PMMA as a function of molecular weight A/z. Mg is the critical molecular weight for entanglement. (From Reference 93.)... 

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