Association theory (also aggregate theory) is a discredited theory first advanced by chemist Thomas Graham in 1861 to describe the molecular structure of substances such as cellulose and starch, now understood to be polymers. Association theory postulates that such materials are composed of a collection of smaller molecules bound together by an unknown force. Graham termed these materials colloids. Prior to the development of macromolecular theory by Hermann Staudinger in the 1920s, association theory remained the most prevalent model of polymer structure in the scientific community.
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