Average molecular weights of polymers

Optimized molecular weight-conversion relationship is related to the system heat transfer coefficient. The degree of conversion improvement from improved heat transfer depends on the average molecular weights of polymer being produced for a given initiator system. 

Vapor Pressure Osmometry - The number average molecular weights of polymers with Mn < 20,000 were determined using "Model 232A Molecular Weight Apparatus, Wescan Instruments, Inc., 3018 Scott Blvd., Santa Clara, CA 95050". Toluene was used as solvent and the instrument was calibrated using polystyrene of Mn 9,000 and 20,400. 

The properties of solutions of macromolecular substances depend on the solvent, the temperature, and the molecular weight of the chain molecules. Hence, the (average) molecular weight of polymers can be determined by measuring the solution properties such as the viscosity of dilute solutions. However, prior to this, some details have to be known about the solubility of the polymer to be analyzed. When the solubility of a polymer has to be determined, it is important to realize that macromolecules often show behavioral extremes they may be either infinitely soluble in a solvent, completely insoluble, or only swellable to a well-defined extent. Saturated solutions in contact with a nonswollen solid phase, as is normally observed with low-molecular-weight compounds, do not occur in the case of polymeric materials. The suitability of a solvent for a specific polymer, therefore, cannot be quantified in terms of a classic saturated solution. It is much better expressed in terms of the amount of a precipitant that must be added to the polymer solution to initiate precipitation (cloud point). A more exact measure for the quality of a solvent is the second virial coefficient of the osmotic pressure determined for the corresponding solution, or the viscosity numbers in different solvents. 

The number average and weight average molecular weights of polymers, defined ... 

The vaiues in parentheses are yieid of poiymer, conversion, average molecular weight of polymer, and the other properties. 

The amount of excess light scattered by dilute polymer solutions compared with that scattered by the pure solvent is used routinely to determine the weight average molecular weight of polymers, A/, ... 

ASTM D 4001-93, Test Method for Determination of Weight-Average Molecular Weight of Polymers by Light Scattering, ASTM, West Conshohocken, Pennsylvania, 1997. 

Mn = number average molecular weight of prepolymers XN = Nt/Mt = number average degree of polymerization Mr = (Xn)(Mn) = number average molecular weight of polymer in an equivalent random network A = mole fraction of difunctional prepolymer 1 — A = mole fraction of monofunctional prepolymer f = average functionality... 

Fig. 21. Plot of the weight average molecular weight of polymer formed in the interior of the gel as a function of the SDS concentration...

This model, of the Rideal type, is of general applicability and includes and explains the most relevant phenomena involved in Ziegler-Natta polymerization. Mathematical formulation of the proposed reaction scheme led to the following equations for polymerization rate Rp and number average molecular weight of polymer Mn, in the absence of hydrogen ... 

Determination of Viscosity Number and Average Molecular Weight of Polymers. The polymers were dissolved and coagulated several times in order to remove the emulsifier. The intrinsic viscosity was then determined with an (Jbbelohde viscometer. Normally we measured values of 7/ p/c at different concentrations [rj] was then determined by graphical extrapolation at concentration zero. 

Table 16. Average molecular weights of polymers and their methods of determination...

Table 15.9. Calculated and measured number average molecular weight of polymers isolated after first and second stage of sequential polymerization of 1,3-dioxolane and 1,3-dioxepane initiated by triflic anhydride. [M]o (A and B) from 2 to 3 mol I 1, [I]q from 10"3 to 10 2 mol 1 1109>...

The colligative properties of dilute polymer solutions can be used to accurately measure Mn, the number average molecular weight of polymers [524,525]. This class of techniques is... 

---