The polymorphism of 4-cyano-4'-pentylbiphenyl (5CB) was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and proton nuclear magnetic resonance (NMR) experiments. Three new phases has been identified and characterized structurally and dynamically. By a slow cooling at a rate less than or equal to 0.2 K/min, the nematic phase crystallizes into a phase noted C1. Upon a fastest cooling (greater than or equal to 5 K/min) a glassy liquid crystal (GLC) phase with a glass transition temperature T(g) = 208 K, is formed. Upon heating up both the solid state C1 and the GLC phase, a second crystalline phase C2 (DeltaH = 49 J/g.K) which is more stable than C1 (DeltaH = 36 J/g.K) can be obtained. The proposed phase diagram has been investigated by proton NMR lineshape analysis. The motional correlation time of end-chain methyl group motion was determined by means of spin-lattice relaxation time (T(1)) analysis.