Question

The following melting temperature data were obtained for a series of polyamides of the type - [-HN-(CH2)x-NH-CO(CH2):CO-]n- Х w N Tm 2 258 3 221 4 240 5 196 6 220

a. Explain the temperature dependence of Tm with x
b. What would be the effect of Tm on replacing the -(CH2)x— groups in the polyamides with a p-phenylene group?

Answer 1

The melting temperature (Tm) of polyamides is influenced by the number of CH2 groups in the polymer chain, with changes in flexibility and chain packing affecting Tm. Replacing the CH2 groups with p-phenylene groups would increase Tm due to increased rigidity and stronger intermolecular interactions.

Step-by-step explanation:

The melting temperature (Tm) of polyamides depends on the length of the methylene (-CH2-) groups within the polymer chain. As x, representing the number of CH2 groups, increases from 2 to 6, the Tm first decreases after x=2, then increases at x=4, and decreases again at x=5.

This could be due to the changing flexibility and packing efficiency of the polymer chains, with shorter chains potentially packing more tightly and longer chains allowing for more flexibility and movement.

Replacing the -(CH2)x— groups with a rigid p-phenylene group, which is a stiff, planar structure, would likely result in an increased Tm due to the enhanced rigidity and reduced flexibility of the polymer chain, leading to stronger intermolecular interactions and a more stable crystalline structure.