The other standard text is Doi and Edwards, The Theory of Polymer Dynamics . Many problems in Rubinstein are variants of Doi & Edwards. If you find a solution in Doi (whose manual is more accessible), you can adapt it for Rubinstein.
This absence has created a vacuum filled by "unofficial" documents, scanned handwritten notes, and crowd-sourced GitHub repositories. Polymer Physics Rubinstein Solutions Manual
Are you currently working on a specific chapter, such as or Flory-Huggins theory , that you'd like to dive deeper into? The other standard text is Doi and Edwards,