Kinetics of polycondensation of urea with formaldehyde. Molecular weight distribution, average molecular weight, and polydispersity parameters

1981 ◽  
Vol 26 (2) ◽  
pp. 381-394 ◽  
Author(s):  
S. Katuščák ◽  
M. Tomáš ◽  
O. Schiessl
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Kinetics Of

The kinetics of the polymerization of sarcosine carbonic anhydride

1949 ◽  
Vol 199 (1059) ◽  
pp. 499-517 ◽  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Constant ◽  
Intrinsic Viscosity ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Intermediate Compound ◽  
Preparative Method ◽  
Kinetics Of

The polymerization of carbonic anhydrides, a reaction important but>u as a preparative method for the synthesis of polypeptides and as an example of a less familiar type of polymerization, has been studied in detail using sarcosine carbonic anhydride (I). The propagation reaction has been shown to involve a reversibly formed compound between the carbonic anhydride and the polymer; this compound decomposes by both a unimolecular and a bimolecular route. The equilibrium constant for the formation of the intermediate compound, and both velocity constants for its decomposition have been determined in two solvents, and the energies of activation and frequency factors calculated. The molecular weight distribution has been calculated; it is extremely sharp. The viscosities of the polymers prepared by this reaction have been measured, and the relation between the intrinsic viscosity and the molecular weight established.

The impact of ionic strength on the molecular weight distribution (MWD) of lignin dissolved during softwood kraft cooking in a flow-through reactor

Holzforschung ◽  
2016 ◽  
Vol 70 (6) ◽  
pp. 495-501 ◽  
Author(s):  
Binh T.T. Dang ◽  
Harald Brelid ◽  
Hans Theliander
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Ion Concentration ◽  
Small Scale ◽  
Kraft Cooking ◽  
Flow Through ◽  
Cooking Times ◽  
The Impact

Abstract The molecular weight distribution (MWD) of dissolved lignin as a function of time during kraft cooking of Scots pine (Pinus silvestris L) has been investigated, while the influence of sodium ion concentration ([Na+]) on the MWD was in focus. The kraft cooking was performed in a small scale flow-through reactor and the [Na+] was controlled by the addition of either Na2CO3 or NaCl. Fractions of black liquors (BL) were collected at different cooking times and the lignin was separated from the BL by acidification. The MWD of the dissolved lignin was analyzed by GPC. Results show that the weight average molecular weight (Mw) of dissolved lignin increases gradually as function of cooking time. An increase of [Na+] in the cooking liquor leads to Mw decrement. Findings from cooks with constant and varying [Na+] imply that the retarding effect of an increased [Na+] on delignification is related to the decrease in lignin solubility at higher [Na+].

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