The mechanical properties of an amorphous polymer are a consequence of the inter-and intramolecular interactions which are typically similar. Yet, polymers can be made with covalent intramolecular cross-links, leading to stronger intramolecular interactions. Here, a study on the effect of this intramolecular cross-linking on the mechanical properties of a glassy polymer is shown. A linear poly(methyl methacrylate) with defined size was cross-linked at different ratios and assembled into solid samples by solvent casting. Mechanical testing indicates that intramolecular cross-linking does not affect the mechanical properties at the elastic region but does influence these properties at the plastic region. Interestingly, intramolecular cross-linking leads to different effects than "regular" interchain cross-linking. The, results are consistent with a reduction in chain entanglement, reducing toughness and to a lesser extent strength.