Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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4.4 The Chemistry of Polymer Molecules • 105

Table 4.3 (Continued)

Polymer Repeat Unit

C

H

H

CH 3

C

O

O

C

CH 3

VMSE

Repeat Unit

Structures Poly(methyl methacrylate) (PMMA)

OH

CH 2 CH 2

CH 2

Phenol-formaldehyde (Bakelite)

NNCCCC

H H H

H O H O

6 H 4

Poly(hexamethylene

adipamide) (nylon 6,6)

CCC

O O H

H

C O

H

H

O

b

Poly(ethylene terephthalate)

(PET, a polyester)

C O

O

C

CH 3

CH 3

O

b

Polycarbonate (PC)

bThe symbol in the backbone chain denotes an aromatic ring as C

C C

H

H

C

C C

H

H

When all the repeating units along a chain are of the same type, the resulting

homopolymer polymer is called ahomopolymer. Chains may be composed of two or more different

copolymer repeat units, in what are termedcopolymers(see Section 4.10).

The monomers discussed thus far have an active bond that may react to form two

covalent bonds with other monomers forming a two-dimensional chain-like molecu-

bifunctional lar structure, as indicated above for ethylene. Such a monomer is termedbifunctional.

functionality In general, thefunctionalityis the number of bonds that a given monomer can form.

trifunctional For example, monomers such as phenol–formaldehyde (Table 4.3), aretrifunctional:

they have three active bonds, from which a three-dimensional molecular network

structure results.

Concept Check 4.2

On the basis of the structures presented in the previous section, sketch the repeat

unit structure for poly(vinyl fluoride).

[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]