The key difference between TG and TM polymers is that the TG of polymers describes the conversion of the glassy state into rubbery state whereas the TM of polymers describes the conversion of the crystalline state into an amorphous state.
The terms TG (or Tg) and TM (or Tm) give two important parameters of polymers. These are temperatures at which the texture of polymer changes. These values are characteristic features of polymers. TG refers to the glass transition temperature whereas TM refers to the melting temperature.
CONTENTS
1. Overview and Key Difference
2. What is TG Polymers
3. What is TM Polymers
4. Side by Side Comparison – TG vs TM Polymers in Tabular Form
5. Summary
What is TG of Polymers?
TG of polymers or TG polymers is the glass transition temperature. At this temperature, the hard, glassy state of an amorphous polymer converts into a rubbery state. Specifically, the thermosetting polymers undergo this conversion, while thermoplastic polymers undergo melting rather than converting into a rubbery state.
Thermosetting polymers show a very hard and rigid glassy state. However, the rubbery state is viscous and pliable. Furthermore, pure crystalline polymers do not have this glass transition temperature because they melt rather than converting into a glassy state. Therefore, amorphous and semi-crystalline polymers have glass transition temperatures. There are some factors that affect this conversion; chemical structure of the polymer, molecular weight of the polymer, the presence of plasticizers, flexibility, etc. The TG determines the applications of the polymer; for instance, a rigid polymer with a low TG is suitable for high-temperature applications.
What is TM of Polymers?
TM of polymers or TM polymers is the melting temperature. At this temperature, the crystalline phase of a polymer converts into a solid amorphous phase. Therefore, this is different from the usual melting process of other materials in which sold phase converts into liquid phase. This term applies regarding thermoplastics because thermosets undergo decomposition at high temperatures rather than melting.
Figure 01: Comparison of TG and TM
Moreover, this is a first order reaction and an endothermic reaction as well. We can use the enthalpy of melting of the polymer to calculate the degree of crystallinity.
What is the Difference Between TG and TM Polymers?
TG of polymers is the glass transition temperature of a polymer while TM of polymers is the melting temperature of a polymer. The key difference between TG and TM polymers is that the TG describes the conversion of the glassy state into rubbery state whereas the TM describes the conversion of the crystalline state into an amorphous state. Therefore, as another important difference between TG and TM polymers, we can say that the TG describes the conversion of the phase of matter (solid to rubbery phase) but, the TM does not describe the conversion of the phase of matter (solid to solid).
A further difference between TG and TM polymers is that the TG is applicable for amorphous and semi-crystalline polymers while the TM is applicable for semi-crystalline and crystalline polymers.
Summary – TG vs TM Polymers
The TG and TM are very important temperature parameters of polymers. The key difference between TG and TM polymers is that the TG of polymers describes the conversion of glassy state into rubbery state whereas the TM of polymers describes the conversion of crystalline state into an amorphous state.
Reference:
1. kumar, Amit. “Melting Point of Polymer.” LinkedIn SlideShare, 25 Sept. 2015. Available here
2. Alfred Rudin, Phillip Choi, in The Elements of Polymer Science & Engineering (Third Edition), 2013