This part of ISO 1628 specifies conditions for the determination of the reduced viscosity (also known as viscosity
number) and K-value of PVC resins. It is applicable to resins in powder form which consist of homopolymers of the
monomer vinyl chloride and copolymers, terpolymers, etc., of vinyl chloride with one or more other monomers, but
where vinyl chloride is the main constituent. The resins may contain small amounts of unpolymerized substances (e.g.
emulsifying or suspending agents, catalyst residues, etc.) and other substances added during the course of the
polymerization. This part of ISO 1628 is not applicable, however, to resins having a volatile-matter content in excess of
0,5 % ± 0,1 %, when determined in accordance with ISO 1269. In addition to this, it is not applicable to resins which are
not entirely soluble in cyclohexanone.
The reduced viscosity and K-value of a particular resin are related to its molecular mass, but the relationship varies
depending on the concentration and type(s) of other monomer(s) present. Hence homopolymers and copolymers
having the same reduced viscosity or K-value may not have the same molecular mass.
The values determined for reduced viscosity and K-value, for a particular sample of PVC resin, are influenced
differently by the concentration of the solution chosen for the determination. Hence the use of the procedures described
in this part of ISO 1628 will only give values for reduced viscosity and K-value that are comparable when the
concentrations of the solutions used are identical.
Limiting viscosity number is not used for PVC resins.
The experimental procedures described in this part of ISO 1628 can also be used to characterize the polymeric fraction
obtained during the chemical analysis of a PVC composition. However, the values calculated for the reduced viscosity
and K-value in these circumstances may not indicate the actual values for the resin used to produce the composition
because of the impure nature of the recovered polymer fraction.