I was using Paraformaldehyde in some of my reactions and its Molecular weight was unknown.
For measuring viscosity average molecular weight different concentrations of paraformaldhyde solution is required. But, paraformaldehyde is insoluble in water at room temperature and dissolves in water at 60 C and we get clear solution after addition of NaOH.
if paraformaldehyde dissolves in water it forms formaldehyde solution instead of paraformaldehyde!!
can any one suggest,
1. How to prepare different concentrations of Paraformaldehyde solution (or) 2. Mark-Houwink constants for paraformaldehyde solution in water
Your question falls apart into 2 parts: 1. Making paraformaldehyde (PF) solutions, 2. Measuring molecular weight (MW).
1. Literature suggests that dimethylsulfoxide (DMSO) is suitable as a solvent for PF, provided that temperature is not too high. See attached file (Johnson et al., 1975).
2. Measuring MW by intrinsic viscosity is only feasible if results can be compared with at least 2 standard PF samples with known MW, which may be problematic. Moreover, MW of PF seems to be rather low, with degrees of polymerization ranging from 8-100 according to Wikipedia. Such low values could also make the use of osmotic pressure and light scattering problematic. Perhaps the best way is to use freezing point depression (FPD) in DMSO, because this quantity only depends on the number of molecules in solution and not on solute type. So you can compare FPD of your sample with FPD of e.g. sucrose, preferably at a range of concentrations. If you have sensitive NMR equipment available, you could also try to estimate MW from the amount of terminal H or C. Please note that DMSO is hygroscopic.
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