A polymerization system

which contains inter- and intramolecular reactions

was designed on the basis of the random coil type morphology of macromolecules in solutions．The polytetramethylene glycol

4

4′-diphenylmethane diisocyanate and hexanediamine were used to synthesize the soluble microgels in concentrated solutions successfully．Through varying the use level of the extender i．e．hexanediamine

a series of samples were obtained

namely 1200H-X

where 1200 stands for the molecular weight of soft segments

H stands for the extender and X is the ratio of the number of hydrogen of hexanediamine and that of end groups of the oligomer (from scheme 1). In our system two kinds of functional groups that can react with each other located in the same macromolecular chain

resulting in the existence of inter- and intramolecular reactions

which were a pair of competitive reactions．In the presence of the intramolecular reaction the intermolecular reaction was prevented from unlimited development

so the cross-linking process was controlled

producing the soluble and fusible microgels i．e．cross-linked macromolecules instead of cross-linked polymer macrogels．By using the technique of dynamic light scattering

the molecular dimensions of the samples in solution were measured at different concentrations

showing a sharp distinction of solution behavior between this kind of cross-linked macromolecules and other macromolecules such as the linear ones．It was found that this kind of macromolecules possessed cross-linked structure

which was affected by the use level of the extender：the less the extender was used

the more compact the cross-linked structure was. In solutions these macromolecules preferred to form molecular clusters. The formation and disassociation of molecular clusters was off balance

and the solution concentration had influence on the size of the molecular clusters.