Question

Outline all steps in a possible synthesis from non-polymeric starting materials of each of the following polymers. (a) Elastic fibers, used in girdles and bathing suits (Spandex, Lycra). (b) A polyester resin, used in making pipe, boats automobile bodies, etc.

Short answer

(a) Elastic fibers (Spandex, Lycra): Synthesize Spandex by preparing a long-chain diol (e.g., 1,4-butanediol) and a diisocyanate (e.g., 4,4'-methylenebis(phenyl isocyanate)) as starting monomers. Conduct the polymerization reaction in a suitable solvent under controlled temperature conditions using a step-growth mechanism to form an alternating copolymer containing urethane linkages and polyester segments. (b) Polyester Resin: Synthesize polyester resin by preparing a dicarboxylic acid (or its anhydride, e.g., phthalic anhydride) and a diol (e.g., propylene glycol) as starting monomers. Conduct the polymerization reaction in a suitable solvent under controlled temperature through a step-growth mechanism to form an alternating copolymer containing ester linkages and various pendant functional groups.

Step-by-step solution

Identify the Structure of Spandex

Spandex is a copolymer made up of two types of monomers: a long-chain diol and a diisocyanate. The chemical structure of spandex contains repeating units of polyester and urethane groups.

Synthesis of Spandex from Monomers

To synthesize Spandex, we first need to prepare the two starting monomers: a long-chain diol (e.g., 1,4-butanediol) and a diisocyanate (e.g., 4,4'-methylenebis(phenyl isocyanate)). The polymerization process involves the formation of a urethane linkage through a reaction between the-isocyanate groups of the diisocyanate and the hydroxyl groups of the diol.

Polymerization Reaction

The polymerization reaction is conducted in a suitable solvent under controlled temperature conditions. The reaction proceeds through a step-growth polymerization mechanism, in which the growth of the polymer chain happens by the stepwise addition of monomers. The diisocyanate and diol monomers react to form an alternating copolymer containing urethane linkages and polyester segments. (b) Polyester Resin

Identify the Structure of Polyester Resin

Polyester resins are polymers formed by the condensation reaction between diols and dicarboxylic acids or their derivatives. These polymers usually have a linear backbone with ester linkages and various pendant functional groups. The monomers involved are typically an aromatic dicarboxylic acid (e.g., phthalic anhydride) and a diol (e.g., propylene glycol).

Synthesis of Polyester Resin from Monomers

To synthesize a polyester resin, we first need to prepare the starting monomers: a dicarboxylic acid (or its anhydride) and a diol. The polymerization process involves the formation of ester linkages through a condensation reaction between the carboxylic acid groups (or the anhydride) and the hydroxyl groups of the diol.

Polymerization Reaction

The polymerization reaction is conducted in a suitable solvent and under controlled temperature conditions. The reaction proceeds through a step-growth polymerization mechanism in which the growth of the polymer chain happens by the stepwise addition of monomers. The dicarboxylic acid and diol monomers react to form an alternating copolymer containing ester linkages and various pendant functional groups, depending on the specific monomers used.

Key concepts

Step-Growth Polymerization

Step-growth polymerization is a common method used in polymer chemistry to form complex polymers. This process involves monomers reacting together to form polymers through a stepwise growth method. Unlike chain-growth polymerization that only adds one monomer at a time to a growing chain, step-growth polymerization allows monomers to join in any order.

In this reaction mechanism, monomers such as diols and dicarboxylic acids, or diisocyanates, react to form oligomers first and then connect step by step. Each step grows the chain until it reaches high molecular weight or the reaction completes. Since each step involves interactions between functional groups of monomers, every addition increases the polymer chain size gradually.

This mechanism is significant in the synthesis of both Spandex and polyester resin where polymers form through urethane and ester linkages, respectively.

Urethane Linkage

Urethane linkages are a type of chemical bond found in many types of polymeric materials, mainly polyurethanes. They are formed when a diisocyanate group reacts with a diol's hydroxyl group. This reaction produces a urethane bond, linking the two molecules into a polymer structure.

A functional group characteristic of urethanes is \( R_2NCOOR_1 \). These linkages are crucial in Spandex production, a polymer known for its elasticity.

Spandex utilizes the flexibility provided by these urethane bonds to ensure that the polymer can stretch and return to its original form. Urethane linkages provide the unique blend of stretchability and strength required in materials like athletic wear and medical textiles.

Ester Linkage

Ester linkages are bonds formed during the polymerization of polyester resins. These linkages arise when the hydroxyl group of a diol reacts with a carboxylic acid group of a dicarboxylic acid, forming an ester bond.

The process, known as esterification, results in a bulky, stable polymer chain. The structure of this bond is represented by \( RCOOR_1 \).

In polyester synthesis, ester linkages contribute to the durability and strength of the final product. They are pivotal for the creation of materials like fibers, fabrics, bottles, and automobile body panels, showcasing their versatile application in daily life.

Diol and Diisocyanate

Diols and diisocyanates are essential monomers used in producing polyurethanes, such as Spandex. Diols are organic compounds containing two hydroxyl groups, while diisocyanates have two isocyanate functional groups. These chemicals react during polymerization to form polymers.

In particular, the hydroxyl groups of diols form urethane linkages by reacting with the isocyanate groups in diisocyanates.

The diol's size and structure can significantly influence the polymer's flexibility and strength, making it a crucial factor in the design of products like elastic fibers in textiles.

• Common examples of diols include ethylene glycol and 1,4-butanediol.
• Typical diisocyanates are methylene diphenyl diisocyanate and toluene diisocyanate.

Polyester Resin

Polyester resins are synthetic polymers made from the reaction between diols and dicarboxylic acids, often used in manufacturing. The reaction involves condensation between the acid and alcohol groups, resulting in a polymer chain linked by ester bonds.

These resins offer benefits such as rigidity, chemical resistance, and ease of work. They are the backbone for products commonly seen in daily life, like plastic containers, automobile parts, and boat hulls.

Depending on the choice of monomers, polyester resins can vary significantly in properties. This flexibility makes them adaptable to a host of applications, whether in packaging, textiles, or construction materials.

Condensation Reaction

Condensation reactions are chemical processes where two molecules combine to form a larger molecule while releasing a small molecule, such as water, as a by-product.

In polymer chemistry, this type of reaction is crucial for the creation of polymers like polyester and polyamides. For instance, when a diol reacts with a dicarboxylic acid, an ester linkage forms, resulting in the loss of a water molecule.

This step-by-step process gradually builds the polymer chain. Condensation reactions enable the formation of high molecular weight polymers with strong covalent bonds, crucial for the durability of materials like polyester resins used in various commercial products.