Solid state phase change materials can be used as thermal energy storage (TES) for passive heating systems and other thermal applications. Alcohol and amine derivatives of neopentane are attractive for TES as they offer advantages of high enthalpy during solid-solid phase transition. Examples of these organic compounds include: Pentaerythritol [PE:C(CH2OH)4)], Pentaglycerine [PG:(CH3)C(CH2OH)3], Neopentylglycol [NPG:(CH3)2C(CH2OH)2], Neopentylalcohol [NPA:(CH3)3C(CH2OH)] Tris(hydroxymethyl)aminomethane [TRIS:(NH2)C(CH2OH)3], and 2-amino-2-methyl-1,3-propanediol [AMPL:(NH2)(CH3)C(CH2OH)2]. These organic compounds undergo solid-solid phase transitions from low temperature ordered polymorphs (tetragonal, monoclinic, etc.) phase to an orientationally disordered high temperature “Plastic Crystal” modulated cubic phase (FCC or BCC) with unusually high enthalpies of transitions. In this presentation, we will discuss ways to change solid state phase transition temperatures by developing phase diagrams of binary systems. The crystal structure details of binary systems, heat capacities, Debye temperatures of these pure plastic crystals will be presented.