This report presents the findings of a 2-year, multitask study to provide a new generation of Sulphlex binders with enhanced low-temperature fracture resistance. The initial phases of the program dealt with the preparation and base-line characterization of Sulphlex 233 and 198, First and Second Generation Sulphlex, respectively, considered the more promising of a broad series of formulations developed under earlier Federal Highway Administration programs. These binders were prepared individually and blended at ratios of 50/50 and 75/25 (198/233) and designated as Third Generation Sulphlex. The former was prepared by directly blending the two binders as well as by a one-pot synthesis. These binders were subjected to a series of screening tests including (a) Penetration @ 25 deg C, (b) Viscosity @ 135 deg C, (c) Specific Gravity, (d) Solubility in CHCl3, (e) Storage Stability, and (f) Glass Transition temperature. A "new and improved" Sulphlex binder designated as Fourth Generation was formulated utilizing the rationale derived from the earlier systems. Sulphlex mixtures along with a control using an AC-20 asphalt were prepared using a crushed limestone aggregate and tested in accordance with Asphalt Aggregate Mixture Analysis System (AAMAS), American Association of State Highway and Transportation Officials (AASHTO), Strategic Highway Research Program (SHRP or Superpave), and Viscoelastic Systems (VESYS) procedures including (a) Indirect Tension, (b) Diametral Resilient Modulus, (c) IDT Creep, (d) Compressive Creep, (e) Unconfined Compression, (f) Repeated Load Permanent Deformation, and (g) Aging using Resilient Modulus. A set of generic manufacturing plans and procedures were generated for the production of Sulphlex in sufficient quantity to satisfy the requirements of an hypothetical test road section.