Thermoplastics, thermosets and elastomers are first-generation polymer
s, and fibre-reinforced plastics are second-generation polymers. Molec
ular composites are emerging as the third-generation polymers; they ar
e defined as homogeneous synergistic composites of molecularly dispers
ed intrinsically rigid and flexible coil macromolecules, conceptually
similar to fibre-reinforced plastic, except that the flexible coil pol
ymer is molecularly reinforced by the rigid macromolecule. In this stu
dy, fundamentals and possible applications of these materials for vibr
o-acoustically stable structures and low-Earth-orbit spacecraft are di
scussed. A molecular theory of solid-state thermodynamics and statisti
cal mechanics for molecular composites is also developed.