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Chapter 15: Problem 21

Would you expect the tensile strength of polychlorotrifluoroethylene to be greater than, the same as, or less than that of a polytetrafluoroethylene specimen having the same molecular weight and degree of crystallinity? Why?

Short Answer

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Question: Compare the tensile strength of polychlorotrifluoroethylene (PCTFE) and polytetrafluoroethylene (PTFE) with the same molecular weight and degree of crystallinity. Answer: The tensile strength of PCTFE is expected to be less than that of PTFE with the same molecular weight and degree of crystallinity, due to the weaker C-Cl bonds and less efficient stacking resulting from differing electronegativities between fluorine and chlorine atoms in the polymer structure.

Step by step solution

01

Understanding the basic structures of PCTFE and PTFE

Polychlorotrifluoroethylene (PCTFE) and polytetrafluoroethylene (PTFE) are both fluoropolymers. PTFE is composed of carbon and fluorine atoms, with the formula -(CF2-CF2)n-. PCTFE, on the other hand, contains carbon, fluorine, and chlorine atoms, with the formula -(CF2-CClF)n-.
02

Compare the bond strengths between chlorine and fluorine

The main difference between these two polymers is the presence of chlorine atoms in PCTFE. It results in C-Cl bonds in addition to C-F bonds in the polymer structure. The strength of the C-F bond is more substantial than that of the C-Cl bond. This difference in bond strength might have an impact on the tensile strength of the polymers.
03

Analyze the effect of electronegativity on tensile strength

Fluorine is more electronegative than chlorine, making C-F bonds more polar than C-Cl bonds. This difference could impact the intermolecular forces between the polymer chains, which in turn affects the tensile strength.
04

Examine the molecular structure and van der Waals forces

Both PCTFE and PTFE have highly regular structures that can stack tightly due to van der Waals forces. However, the presence of electronegativity differences between fluorine and chlorine could make stacking slightly less efficient for PCTFE, leading to a decreased tensile strength.
05

Conclude the comparison of tensile strength

Considering the differences in bond strength and electronegativity between PCTFE and PTFE, it is expected that the tensile strength of PCTFE will be less than that of PTFE with the same molecular weight and degree of crystallinity. The weaker C-Cl bonds and less efficient stacking due to differing electronegativities are the primary reasons for this conclusion.

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Most popular questions from this chapter

The vulcanization of polyisoprene is accomplished with sulfur atoms according to Equation 15.4. If \(57 \mathrm{wt} \%\) sulfur is combined with polyisoprene, how many crosslinks will be associated with each isoprene repeat unit if it is assumed that, on the average, six sulfur atoms participate in each crosslink?

In your own words, describe the mechanisms by which semicrystalline polymers (a) elastically deform and (b) plastically deform, and (c) by which elastomers elastically deform.

Ten kilograms of polybutadiene is vulcanized with \(4.8 \mathrm{~kg}\) sulfur. What fraction of the possible crosslink sites is bonded to sulfur crosslinks, assuming that, on the average, \(4.5\) sulfur atoms participate in each crosslink?

(a) Compare the fatigue limits for polystyrene (Figure 15.11) and the cast iron for which fatigue data are given in Problem 8.20. (b) Compare the fatigue strengths at \(10^{6} \mathrm{cy}\) cles for poly(ethylene terephthalate) (PET, Figure 15.11) and red brass (Figure 8.34).

In Figure 15.28, the logarithm of \(E_{r}(t)\) versus the logarithm of time is plotted for polyisobutylene at a variety of temperatures. Make a plot of \(E_{r}(10)\) versus temperature and then estimate its \(T_{g}\).
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