Variation with average molecular weights

For polystyrene fractions in diethyl phthalate solution (30000average value of 1.6 x 10 18 ( 50%). In dilute solution e/36M is 1.27 x 10 18 for polystyrene (21). No systematic variations with concentration, molecular weight or temperature were apparent, the scatter of the data being mainly attributable to the experimental difficulties of the diffusion measurements. The value of Drj/cRT for an undiluted tagged fraction of polyfn-butyl acrylate) m pure polymer was found to be 2.8 x 10 18. The value of dilute solution data for other acrylate polymers (34). Thus, transport behavior, like the scattering experiments, supports random coil configuration in concentrated systems, with perhaps some small expansion beyond 6-dimensions. 

Table 4. Variation of Average Molecular Weight With...

Figure 5.18 Complex viscosity versus reduced frequency forthree ethylene-butene copolymers in which the butene level ranged from 11 to 21 % at a single temperature (log-log plot). All had nearly identical polydispersities, but there was a modest variation in average molecular weight, which was accounted for by dividing the complex viscosity by the zero-shear viscosity.The data for the three samples do not superpose perfectly, but there is no trend with regard to butene content, and the authors concluded that the variation was probably due to the differences in MWD rather than the presence of the comonomer. From Wood-Adams etal. [75].

We, therefore, propose an indirect method for obtaining the variation of the intrinsic viscosity and number average molecular weight across the chromatogram. First the intrinsic viscosity-molecular weight relationship for a polymer with long chain branching (LCB) is assumed to be expressable in a form similar to that used by Ram and Milts (6),... 

Polyisobutylene. The solution viscosity of an irradiated polyisobutylene block was measured in CC14 at 30 °C. to determine the degree of degradation (5). The variation of viscosity-average molecular weight, Mv, with the dose, r, is shown in Figure 3. Nitrous oxide reduced the... 

To probe the 1/N dependence in the slope F, experiments were carried out on model end-linked networks with different precursor chain lengths (average molecular weight Mn varying from 3100 to 23000 g.mol 1) [55, 56]. As expected, the slope F decreases when N increases. However, it does not follow a 1/N variation F varies only by a factor of about 3 as N varies by a factor of 7. In an end-linked network, N should not be simply assimilated with the length of precursor chains, since trapped entanglements may play the role of effective crosslinks (often denoted as physical crosslinks), in addition to chemical... 

The enthalpy change for this polymerization is AWp = —6.5 Real mor. The polymerization reaction in this problem is finished at a fixed steam pressure (1 atm). The equilibrium concentration of H2O in the polymer melt varies with temperature and steam pressure in this case. Tlte enthalpy of vaporization of H2O is about 8 Real mol . Compare the limiting values of number average molecular weight of the polyamide produced at 280 and 250°C final polymerization temperatures. Hint Recall that the variation of an equilibrium constant K with temperature is given by r/(ln K)/d /T) = —AH/R, where AH is the enthalpy change of the particular process and R is the universal gas constant. Calculate Ki and the equilibrium concentration of H2O in the melt at 250°C and use Eq.(10-8).]... 

Calculate the variation in entropy corresponding to a polydimethylsiloxane network of mass 6.89 g, with an average molecular weight between crosslinks Me = 8.3 X 10, subjected to a reversible uniaxial extension at 25°C until the length is double its initial length. 

Figure 1 Variation of the number average molecular weight (MW ) with time for the polymerization of PBO. The different curves are for different initial monomer concentrations (Cotts and Berry [27]).

Controlled living radical polymerization of CD-complexed styrene in water can be conducted via the RAFT process, especially at low conversion (<20%). The molecular weight of PS can be controlled by variation of the RAFT agent concentration and the number-average molecular weight increases linearly with conversion (Fig. 29). 

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