The glass-transition temperature refers to the temperature at which polymers will be converted from an elastic state to a glassy state, expressed by Tg. When the temperature is higher than Tg, the material is rubber-like in behavior and generates the elastic deformation under load; when the temperature is lower than Tg, the material is glass-like in behavior and prone to brittle failure. Usually if Tg is high, the hardness after film formation is also high, rigidity good and heat resistance is good; otherwise, if Tg is low, the hardness after film formation decreases, but the elasticity and flexibility are good.

In preparation of dry-mixed mortar, redispersible polymer powders of different Tg values should be selected according to the purpose, operating environment and base material of mortar. For example, in the preparation of tile adhesives and crack-resistant plastering mortar, two main factors should usually be considered. One is high adhesion; the other is sufficient flexibility and capacity of deformation resistance. Therefore, select the polymer powder with low Tg, low temperature and good flexibility.