Effect of Cross-Linking and Crystallization

Cross-linking decreases the free volume, because parts of the chain are tied more closely together by covalent bonds. Hence T increases with the degree of cross-linking. 

Crystallization works in the same way as cross-linking, raising the 7 The amorphous parts of the sample become tied down in the regions between the crystalline domains 

Poly(methyl methacrylate) T 105°C 8 ch3 Poly (ethyl methacrylate) T 65°C ch3 Poty(propyl methacrylate) T 35 °C 

Poly(butyl methacrylate) T 2G°C g Poly (octyl methacrylate) T —20 °C s Poly(dodecyl methacrylate) T —65 °C 

FIGURE 10-67 The approximate glass transition temperatures of various po y(n-aIkyI methacrylates). 

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