The Growth Process of the Soluble Cross-Linked Macromolecule of PU

TEM pictures that were taken at different polymerization times during the formation process of the in- tramolecularly cross-linked macromolecule (ICM) indicate that ICM growth undergoes three stages. At the first stage, monomers (i.e. prepolymers) react with each other to form small coils, called "dot molecules" (DM), which are shown as small black dots in TEM pictures. At the second phase, the reaction of functional groups on the surface of DMs produces globular intramolecularly cross-linked macromolecules which are called pre-ICMs. At the third stages, the globular pre- ICMs react with each other to form ICMs. As soon as DMs formed, they aggregate into molecular cluster. DMs are re- stricted within the molecular cluster. This state of aggregation is beneficial to reaction between DMs, since a higher fre- quency of collision can occur in the molecular cluster. In fact, the molecular cluster is the key polymerization site in the controllable cross-linking polymerization system.