Weights of Linear Condensation Polymers

The requirement that A and B shall be present in equivalent quantities is automatically taken into account in the type (i) polymerization if the monomer is pure and no side reaction occurs. In type (ii) it is also necessary to specify that the reactants are present in equivalent proportions if Eqs. (9) and (10) are to apply. 

The problem of achieving the highest possible molecular weight in a linear condensation polymerization resolves itself into the problem of reducing the number of end groups to the lowest possible value. Just as a chemical reaction cannot be carried to absolute completion, the 

The depression of the molecular weight brought about by nonequivalence of reactants, by monofunctional ingredients, or by unbalance in the stoichiometric proportions may be expressed quantitatively as follows. Suppose that a small amount of a reactant designated by B—I—B is added either to a pure A-------B monomer or to an 

Aa = total number of A groups initially present Ab = total number of B groups initially present t = Na/Nb 

The same equations are applicable to polymers containing small amounts of a monofunctional reactant B— —, provided that r is redefined as follows  

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Fig. 1.11. The molecular weight of linear condensation polymers is generally controlled by the addition of a small percentage of monofunctional molecules.

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