r and p required for molecular weight control in peds from route 1 for r 0 9 and 0 6 at p 0 96 x n is 14 and 3 m n 3427 and 1243 gmol u2212 1 respectively x n decreases to 2 and 1 6 respectively at p 0 51 suggesting that x n does not vary significantly with r at low extents of reaction p also to achieve a specific x n higher extents of reaction are required for lower r values the shape of the x n versus r plots fig9 also indicates that r has a very significant effect on the polymer molecular weight x n mn average molecular weight of monomers and that a stricter control of r is required in order to achieve higher degrees of polymerization the polyesterification reaction rate is defined by the rate of disappearance of the diacid eq 2 where cooh and oh are the concentrations at time t of diacid and diol respectively and k is the reaction rate constant in case of catalyzed reactions with non stoichiometric amounts of reactants the stoichiometry is given by equation 3 where cooh 0 and oh 0 are the initial concentrations of the diacid and diol groups respectively the combination of equations 2 and 3 further processed by integration results in equation 4 equation 4 is a function of the stoichiometric imbalance r and assuming the rate of reaction to be second order a plot of 1 n oh cooh.