Abstract: A polymer composite for preparing a low dielectric resin composition having a dielectric loss tangent (Df) that is less than or equal to 0.00200 is provided. The polymer composite includes a first styrene-based copolymer having a weight average molecular weight that is lower than 20,000 g/mol and a second styrene-based copolymer having a weight average molecular weight that is higher than 20,000 g/mol, wherein the weight ratio of the first styrene-based copolymer to the second styrene-based copolymer is from 5/95 to 95/5.

Abstract: A crosslinkable and foamable composition is provided, which comprises a hydrogenated styrenic diblock copolymer, a free radical initiator and a foaming agent, wherein the hydrogenated styrenic diblock copolymer comprises: a first block comprising an isoprene unit; and a second block comprising a styrene unit, wherein the hydrogenated styrenic diblock copolymer comprises 10 to 60 wt % of the styrene unit, 50 mol % or more of the isoprene unit is hydrogenated, and the hydrogenated styrenic diblock copolymer has a weight average molecular weight of 30000 to 200000. In addition, a foam obtained by crosslinking and foaming the aforesaid crosslinkable and foamable composition is also provided.