Molecular weight averages temperature effect

Effects of reaction temperature on PBS molecular weight averages were studied for polymerizations in diphenyl ether. Figure 1 delineates product M as a function of reaction time at different temperatures. In 24 h, the polymerization reaction at 60, 70, 80, and 90 C yielded PBS with values of 2000, 4000, 8000, and 7000, respectively. Further increase in reaction time resulted in little... 

It follows from this treatment that the magnitude of the temperature derivative of fo is smaller for very low molecular weights than for high (when compared at the same temperature), and that the molecular weight average which controls this effect is Jf . Thus, for example, the apparent activation energy for viscoelastic relaxation at a temperature To can be expressed by combining equations 35,56, and 44 ... 

T is the glass-transition temperature at infinite molecular weight and is the number average molecular weight. The value of k for poly(methyl methacrylate) is about 2 x 10 the value for acrylate polymers is approximately the same (9). A detailed discussion on the effect of molecular weight on the properties of a polymer may be found in Reference 17. 

The viscous shear properties at any given shear rate are primarily determined by two factors, the free volume within the molten polymer mass and the amount of entanglement between the molecules. An increase in the former decreases the viscosity whilst an increase in the latter, i.e. the entanglement, increases viscosity. The effects of temperature, pressure, average molecular weight, branching and so on can largely be explained in the these terms. 

The products of the process have a density of about 0.96 g/cm, similar to the Phillips polymers. Another similarity between the processes is the marked effect of temperature on average molecular weight. The process is worked by the Furukawa Company of Japan and the product marketed as Staflen. 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

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