Chapter 26, Problem 26.59P

Interpretation Introduction

Interpretation:

It is to be determined which polymer, Kevlar (in Solved Problem $\text{26}\text{.11}$) or polyphthalamide described in Problem $\text{26}\text{.12 }$, has the higher Tg, and the reason is to be explained.

Concept introduction:

Polymers range from being completely amorphous to being highly crystalline. Polymers can exhibit regions that are crystalline, separate from ones that are amorphous. These types of polymers can therefore have both a ${\text{T}}_{\text{m}}$ that characterizes the crystalline regions and a ${\text{T}}_{\text{g}}$ that characterizes the amorphous regions. The value of ${\text{T}}_{\text{g}}$ increases, moreover, as the crystallinity of the polymer increases. ${\text{T}}_{\text{g}}$ increases with the polymer’s crystallinity because the crystalline regions “anchor” the amorphous regions and impede the movement of the chains in the amorphous regions. The stronger the intermolecular interactions in a substance, the higher the temperature required for a phase transition, either from solid to liquid or from liquid to gas. This is also true for polymers. The stronger the intermolecular interactions between polymer molecules, the higher the ${\text{T}}_{\text{g}}$ or ${\text{T}}_{\text{m}}$.