Crosslinking of single linear macromolecules

When a crosslinking agent is added to a very dilute solution of a linear high polymer, there will be practically exclusively a self linking of the individual statistical coils, i.e., the molecules of the crosslinking agent will link different parts of the same macromolecule, transforming the original linear high polymer into a three‐dimensional network, practically without a change of its molecular weight. The process of self‐linking of a single coil is associated with a contraction of its average external dimensions and therefore with a decrease of the intrinsic viscosity. If the crosslinking produced by the action of v molecules of the crosslinking agent on one linear polymer molecules occurs statistically and if the original linear high polymer molecule is made of N m statistical chain elements, a decrease of the intrinsic viscosity should occur from the value [η] open to [η] v crosslinks, statist , where {article}{empty}{document}[η ]_ν crosslinks, statist = [η ]_ open [1 - ν (√ 2 /√Nₘ )]{document} . In order to test the validity of this formula a dilute, slightly acid solution of polyvinyl alcohol with M = 100,000 was crosslinked by means of terephthalaldehyde [CHOC 6 H 4 CHO]. The agreement of the values of [η] observed in very dilute solution with the theoretical value indicates the actual statistical formation of cycles through the reaction of terephthalaldehyde on dissolved solitary linear polyvinyl alcohol molecules.