In accordance with the present invention, there are provided 
toughening agents which are useful for improving the performance properties of 
epoxy-based 
adhesive formulations. For example, epoxidized polysulfides have been found to be useful 
toughening agents of component level underfill 
adhesive compositions. Invention materials are liquid rubbers which provide improved 
fracture toughness while maintaining satisfactory capillary flow properties. Invention materials can be synthesized in neat (solventless) reactions from readily available low-cost raw materials and isolated in high yields. They have linear and branched telechelic structures with terminal 
epoxide functional groups, and are prepared without substantially increasing the molecular weight of the starting 
polysulfide materials. Invention materials are compatible with common 
epoxy formulations and may be used without purification. At low levels of incorporation, they provide adhesives that meet the minimum 
fracture toughness (Gq>2.0 lb / in) and capillary flow specifications (
flow time<180 seconds) for many commercial underfill applications. In accordance with a further embodiment of the present invention, there are provided 
adhesive compositions comprising invention compounds and methods for use thereof. In additional embodiments of the present invention, there are provided methods for the preparation of invention 
toughening agents, methods for adhesively attaching a device to a substrate, and assemblies comprising first article(s) adhered to second article(s).