The aggregation of poly(1,3-cyclohexadiene) (PCHD), obtained by anionic polymerization with alkyllithium/amine systems, was examined using size exclusion chromatography (SEC) and size exclusion chromatography coupled with a multiangle laser light scattering photometer (SEC-MALS). The PCHD polymer chain has a structure consisting of a main chain formed by 1,2-addition (the 1,2-CHD unit) and 1,4-addition (the 1,4-CHD unit). Mild stirring with relatively low temperature in the polymerization reaction forms an aggregation of PCHD. The molecular weight and molar ratio of 1,2-CHD/1,4-CHD units in the polymer chain strongly influence the aggregation of PCHD. In a high molecular weight PCHD, containing similar to 50% 1,2-CHD units, an aggregation of the polymer was observed in tetrahydrofuran (THF) solution at room temperature. This aggregation of PCHD was soluble in 1,2,4-trichlorobenzene (TCBz) and could be separated into each polymer molecule. In contrast, a polymer chain with a high content of 1,4-CHD units having a relatively low cis-stereospecificity was easily soluble in THF and TCBz without aggregating. A long polymer chain structure with a high content of 1,2-CHD units is considered to be the reason for the generation of strong intermolecular forces contributing to the aggregation of PCHD with the solvophobic interactions. The degree of aggregation could be controlled by the conditions of the PCHD polymer solution. (c) 2006 Wiley Periodicals, Inc.