I need to preserve the shared boundary between polygons but make them a multipart polygon. Dissolve with the multipart polygon checked still dissolves the shared boundary, and only makes one multipart polygon with separate polygons if they are not adjacent and sharing a boundary. Union also dissolves the shared boundary. The attributes for the adjacent polygons are the same. There are 100s of polygons in this layer so I don't want to use editing tools. I am hoping there is a Toolbox tool that will do this. Any help is appreciated. Thank you!