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Composites are well known to combine materials with different properties together in an effort to develop desired properties. Polymer-based composites can provide new materials with improved properties and applications that individual component cannot reach. This work focuses on developing novel polymer/inorganic composite systems with either new developed polymer matrix or new method to fabricate hybrid composite.Poly(ethylene terephthalate-co-4,4' bibenzoate) (PETBB55) is one of 4,4'-biphenyl dicarboxylate modified PET with a higher glass transition temperature, improved mechanical properties and faster crystallization rate . In Part II, glass fiber reinforced PETBB55 composite was produced and analyzed. A novel phenomenon “entropy-driven self-ordering of PETBB55copolyester chains proximate to glass fiber surfaces in composites” is reported in Chapter 2. Such glass fiber reinforced PETBB55 composites possess enhanced mechanical properties and easy processing capability, a unique combination. Mechanical properties of its composites are reported in Chapter 3. Glass fiber distribution and orientation in polymer matrix were studied by (microcomputed tomography) µCT scan and analysis. The glass fiber orientation and molecular orientation both contributed on improving the mechanical properties of the glass fiber filled copolyester.To overcome the difficulty in preparing amorphous PETBB55 film, novel copolyesters were produced by incorporating asymmetric molecular “kinks” dimethyl isophthalate (I) or dimethyl 3,4'-bibenzoate (3,4'BB) into polymer backbone to slow down the crystallization rate. The effect of biaxial orientation of such copolyesters films structure and gas barrier properties are investigated in Chapter 4. The orientated films only have 20-30% of oxygen permeabilities of their unoriented films with improved mechanical properties, which provide new polymer candidates for packaging.Polymer/inorganic nanocomposite aerogels were studied in part III. Aerogels are extremely porous materials formed by replacing the liquid solvent in a gel by air without damaging its three-dimensional network structure. Chapter 5 presents a new method of producing tough aerogels through conformally coating a layer of silica nanoparticles onto an ice-templated microporous polymer scaffold. The nanocomposite aerogels have improved mechanical properties and fire resistance with durable hydrophobicity after coating with fluorocarbon silane. pH value of TESO precursors can influence the morphology of silica nanoparticles. Flammabilities of composite aerogels with different morphologies of silica particles are reported in Chapter 6.