The interactions betweenpoly(methylmethacrylate)(PMMA),poly(vinylalcohol) (PVA) poly(ethylene glycol)(PEG)as industrial biopolymers andchitosan, cellulose, starch as natural biopolymers with iodine(I 2 ) were investigated using diethyl ether as a solvent. 5% of I 2 was added to each polymer and soaked in the solvent. The interactions were investigated using concepts of the activation energy(Ea), Decisivefactor (Df) and the changing in the glass transition temperature (ΔTg , s). Therefore, the differential scanning calorimeter (DSC) was used to monitorthe thermal transitions. The optical microscope(OM) device was used to study the surface morphologies.Resultsshowed a clear depression in the glass transition temperatures (T g , s) for all polymers( as well as new colors appear) except cellulose still unaffected .It appears that cellulose molecules coated with a film prevent iodine to diffuse through the network structure of cellulose thus no effected its color or its Tg which indicates that molecular structure of cellulose quite different from that of starch and for this fact cellulose not soluble by a solvent and undigested in the human body. The depression inTg values of polymers indicate that iodine ruptures the engineering bonds of the polymers. The most effected Tg is of chitosan (lowered by 40.23˚C, this mean that iodine ruptures both hydrogen bonding through nitrogen and oxygen atoms in chitosan molecule.From T g values, it seems that iodine can acts as moderate plasticizer, by diffusing through the net of synthetic and natural biopolymers ruptures their secondary bonds result in depression of their T g except in case of cellulose.