Stages average molar masses

Figures 2 and 5 show the increase of the mass average molar mass, R i, with conversion for the systems with branched and linear prepolymers, respectively. These results indicate that addition of the branching monomer in the first stage yields much higher values of R, and the gel point is reached at lower conversion than addition in the third stage. Translated into practical properties this means that the processing and application qualities (e.g. flow) of a paint based on formulation F40 will be inferior to those of one on the basis of for-...

The extent of reaction (or conversion) at any stage can be expressed by the fraction of total reactive sites that have been consumed. Reactive sites usually display the same reactivity regardless of the size of the molecule to which they are linked. The polymerization process has the characteristics of a statistical combination of fragments. In this way, a distribution of products from the monomer to a generic n-mer is obtained (Table 2.1), with average molar masses increasing continuously with conversion. 

The mathematical model of network formation in the pregel stage will focus on the prediction of the gel conversion and the evolution of number-and mass-average molar masses, Mn and Mw, respectively. For chainwise polymerizations, calculations will be restricted to the limit of a very low concentration of the polyfunctional monomer (A4 in the previous example). Thus, homogeneous systems will always be considered. 

While the size (mass) of component M remains constant throughout the reaction, the size (mass) of component P increases with conversion. The selection of the average size of P and M is arbitrary. As the analysis is carried out in the pre-gel stage where every species remains finite, number-, mass- or any other average molar masses may be taken to illustrate the major trends involved in the phase separation process. Number-average molar masses will be taken in our analysis. 

The average molar mass of the product also shows a drastic increase with an increase of the fully filled length of the extruder (Fig. 10). When the reaction is in the gel stage in the extruder, an increase of the residence time, due to the increase of the fully filled length, leads to a longer reaction time at this stage. Therefore, the average molar mass of the polymer will increase... 

In all calculations the molar masses given in the top of Table I were used. First of all, the effects of variations in the concentration of trifunctional monomers were determined, as exemplified by the nine formulations of Table I and the resulting prepolymer characteristics after full conversion given in Table II. Formulations FIO to F40 result in branched prepolymers, which are cured in the third stage by difunctional monomers. On the other hand, formulations FOO to F04 result in the same linear prepolymer, which is subsequently cured with various mixtures of di- and trifunctional monomers. The number average functionalities of PI (and P2) and of the mixtures of E and F monomers are varied systematically between 2.0 and 2.4. Therefore, the only difference between formulations FjO and FOj is the stage in which the branching units are added. 

As indicated, molar mass both average and dispersity belong to the most important molecular characteristic of synthetic polymers. Molar mass of macromolecules affects their solubility and size in solution and to some extent also their interactivity. For both the synthesists and the technologists, also chemical stracture and physical architecture of macromolecules are highly important becanse they either confirm successful synthesis or markedly affect the end-nse properties of polymers. Similar to molar mass, the latter molecular characteristics impact the interactivity of macromolecules and partially also their size in solution. Development of methods for assessment of dispersities in chemical stracture and pltysical architecture of macromolecules is still only in a rather initial stage. 

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