Difference Between TG and TM Polymers

Tg and Tm are two significant parameters used to understand how polymers behave. Tg stands for glass transition temperature whereas Tm stands for melting temperature. How stretchy and strong it is determined by the property of the polymers. The properties of the polymer are varied by many things such as molecular weight, flexibility, and crystallinity. Understanding these properties will help us to understand how different polymers behave in different situations.

If a polymer has different melting points then it is made up of multiple components with different molecular weights or structures this means Tg is typically lower than Tm and it is rigid at room temperature. If Tg is higher than Tm that means it doesn’t have a distinct melting point and on heating shows a transition from solid to a rubbery state.

What is TG Polymers?

Glass transition temperature (Tg) is an important characteristic that determines the response of the polymer to changes in temperature. The polymers which a glass transition temperature below room temperature are Tg polymers making them elastic in surrounding conditions. At this temperature hard, glassy state converts into a rubbery state.

Polymers can be classified into amorphous or crystalline based on their molecular structure. Amorphous polymers have a randomized arrangement of repetitive units while crystalline polymers have an orderly form. At glass transition temperature amorphous go from being hard and brittle to be softer and more flexible. The Tg of a polymer depends on various factors, including the chemical structure of the polymer, the presence of chemical groups, flexibility, etc. The Tg determines the applications of the polymer, including coatings and stretchy materials called elastomers. 

The properties of Tg polymers can be altered or modified, such as increased strength and resistance to moisture. All this is possible by adding plasticizers, or other chemical agents to the polymer.

What are Tm Polymers?

Tm polymer is the temperature at which a solid plastic material changes into a softer, flexible form or a solid amorphous form. The conversion occurs because the bond holding the plastic due to intermolecular force becomes loose or breaks down. The intermolecular forces in Tm polymers are very strong which helps them withstand high temperatures, and resist chemicals, wear, and tear. They are used in a variety of industries because of these properties.

The value of Tm polymer depends on several factors, including molecular structure, the chemical structure of the polymer, and the crystallinity of the polymer. For example, polymers with long chains and a high degree of crystallinity have higher Tm values because of stronger intermolecular forces and ordered arrangement of molecules in the crystal lattice. They are classified into two categories based on their Tg values i.e. Amorphous Tm polymers ( low Tg values and do not exhibit any crystalline structure) and Semi-Crystalline (high Tg values and exhibit crystalline structure) Tm polymers.

Similarities Between Tg and Tm Polymers

Tg and Tm are two significant parameters that are used to study how polymers respond to changes in temperature. Here are some similarities between Tg and Tm polymers listed below.

• Changes in physical properties occur in both Tg and Tm temperature points.
• Tg and Tm values can be varied on the basis of molecular weights, branching, and monomers of the polymer.
• The rate of heating and cooling affects both Tg and Tm values. Quick heating and cooling can result in differences in Tg and Tm values compared to slow heating or cooling.
• The techniques that are used to measure Tg and Tm values are differential scanning calorimetry (DSC) or thermomechanical analysis (TMA).

Comparison Between Tg and Tm Polymers

S.No	Characteristics	Tg Polymers	Tm Polymers
1.	Definition	Tg of polymers is the glass transition temperature	Tm of polymers is the melting temperature
2.	Temperature	It ranges below Tg to room temperature	It ranges from room temperature to above Tm
3.	Phase of Matter	The matter phase converts from a solid to a rubbery state.	The matter phase converts from solid to liquid/crystalline
4.	Molecular Arrangement	Amorphous	Can be amorphous or semi-crystalline
5.	Properties	Flexible, soft, and ductile	Strong, rigid, and tough
6.	Examples	Polystyrene, polyvinyl chloride, polycarbonate, etc.	Polyethylene, polypropylene, polyamide, etc.

Conclusion

In conclusion, We can say Tg and Tm polymers are the factors that play an important role in the determination of the behavior of the different polymers. Tg and Tm can be used to compare different polymers by some techniques and depends upon factors like the structure of the polymer, the groups attached, and crystallinity degree.

FAQs

Q.1. How do Tg and Tm act as important properties of polymers?

Ans: Glass transition temperature (Tg) is an important property of polymers that determines their thermal stability and flexibility. While on the other hand, the Melting Temperature (Tm) is an important property of polymers as well, because it determines the temperature at which it melts and shows the ability to be molded and shaped. 

Q.2. How are Tg and Tm measured?

Ans: There are different scientific techniques or methods of analysis by which these two factors can be measured. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), or Thermomechanical Analysis (TMA) are some of the commonly adopted techniques to measure Tg. While Tm is measured using Differential Scanning Calorimetry (DSC) or Hot-Stage Microscopy.

Q.3. How do the structures of polymers affect Tg and Tm?

Ans: Tg is influenced by molecular weight, cross-linking, and degree of crystallinity. This is because due to cross-links the polymer becomes rigid and ordered in structure, hence making it more difficult to convert into a rubbery state. The Tm is also influenced by molecular weight and melting behavior. The high value of Tm is due to higher molecular weight and crystallinity. A higher melting point is due to the efficient packing of the ordered lattice.

Q.4. Can Tg and Tm be used to compare different polymers?

Ans: Yes, It can be used to compare different parameters of the polymer. The polymer which has a higher value of Tg is considered as stiffer and their thermal stability is and the polymer with lower Tg values tends to have processing properties.

Q.5. Are there any polymers that do not have a Tg or Tm?

Ans: Elastomers and amorphous polymers fall under this category that does not have a distinct Tm because they do not have a higher melting point due to the efficient packing of the ordered lattice. However, they still have Tg values which signify the temperature at which polymer coverts from a glassy to a rubbery state.