In accordance with the present invention, assemblies have been developed which are useful for a variety of applications, e.g., in RF applications where low electrical loss products are desirable, e.g., in cellular communications, RF antennas, satellite communications, radar, power amplifiers, high speed digital applications, laminate-based chip carriers, and the like. Invention assemblies comprise a combination of a first reinforced thermoplastic-containing layer and a first non-reinforced thermoplastic- containing layer, wherein the reinforced and non-reinforced thermoplastic-containing layers are capable of forming a bond (e.g., a cohesive or adhesive bond) therebetween, thereby providing performance properties (e.g., electrical performance and cladding bond strength) that are superior to the performance properties of either material alone. The reinforced thermoplastic-containing layer can include a porous substrate impregnated with a composition comprising: a first component (i.e., a low loss, low dielectric constant, hydrocarbyl thermoplastic), a second component (i.e., a component able to crosslink and produce a thermoset in the presence of the first component), and a free radical source. Also provided in accordance with the present invention are methods for preparing the above-described assemblies.