A process of preparing a polymer modified asphalt (PMA) comprising mixing a predetermined amount of a polymer-asphalt master batch with a predetermined amount of an asphalt-cross linking agent blend. The polymer-asphalt master batch comprises at least one polymer and a first asphalt. The asphalt-cross linking agent blend comprises a second asphalt and at least one cross linking agent. A predetermined amount of the polymer-asphalt master batch is blended with a predetermined amount of the asphalt-cross linking agent blend to form a PMA blend. Mixing of the PMA blend is performed without substantial delay following blending of the polymer-asphalt master batch with the asphalt-cross linking agent blend.