Can anybody suggest how hydroxyl value of polyesters can be determined.why the standard titration methods are showing inconsistent results.

What r the reliable methods of determining molecular weight of polyesters ?

re molecular weights: GPC and light scattering techniques are used often. I think each method is based on comparisons to known standards though rather than direct calculation, so 'reliable' is debatable depending on how accurate your reading needs to be. You can use calibration standards similar to your sample, so, use polystyrene standards for styrene like polymers and so on. If you can get polyester standards then calibrate with those before running your polyesters.

 

You can calculate theoretical MWs from your reaction data.... this will be based on the yield, the MW of the monomer, the concentration and efficiency of the initiator and the like. But this doesn't take into account the many and sometimes unknown, side reactions that can take place during polymerization. (I think statistical terminations of chains can also effect the MW and certainly the polydispersites of reactions)

 

re hydroxyl value: I do not know how they measure that. Could it be done by comparing peak heights on an NMR spectra? I'll leave that to someone else.