The structure of methyl methacrylate is given in Table 23.12...

The structure of methyl methacrylate is given in Table $23.12 .$ Draw the structure of a polymethyl methacrylate (PMMA) polymer that has four monomer units. (PMMA has excellent optical properties and is used to make hard contact lenses.)

Key Concepts

Degree of Polymerization

The degree of polymerization refers to the number of monomer units incorporated into a polymer chain. In this question, the polymer is constructed from four repeating units, indicating a low degree of polymerization. This concept is important because the chain length can affect the physical properties of the polymer, such as its mechanical strength and thermal behavior.

Polymerization Mechanism

This key concept involves understanding the process by which the monomers chemically bond to form a polymer. For methyl methacrylate, the polymerization typically occurs via a free radical mechanism, where a radical initiator opens the double bond of the monomer, allowing successive additions to form a long chain. Recognizing the mechanism is crucial for predicting the structure of the final polymer.

Monomer Structure

This concept refers to the chemical structure of the individual unit – in this case, methyl methacrylate – that can join together to form a polymer. It involves recognizing functional groups, such as the carbon–carbon double bond, which serve as the reactive site during polymerization, as well as other substituents like the ester groups that contribute to the overall chemical and physical properties of the material.

Repeating Unit

The repeating unit is the portion of the polymer chain that is derived directly from the monomer after the polymerization reaction. In the context of PMMA, each repeating unit represents the fragment of the methyl methacrylate that remains in the polymer backbone after the double bonds have reacted. Understanding the repeating unit is essential because it defines the chemical structure and properties of the polymer.

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