Polymer Science Quiz

Module 8: Applications of Functional Groups

• This module covers the applications of functional groups in polymers, soaps, and lipids.

Polymers

• Introduction and Nomenclature: Polymers are long-chain molecules created by linking monomers through chemical reactions. Polymer molecular weights vary from 10,000 to 1,000,000 grams per mole. Polymer architecture is diverse, encompassing linear, branched, comb, ladder, star, and cross-linked structures.

• Types of Polymers: Synthetic polymers are the focus. Thermoplastics can be reshaped when heated; thermosetting plastics cannot.

• Structure: Polymer structure is represented by repeating units enclosed in brackets with a subscript. Subscripts denote the average polymerization degree, showing how many times the monomer unit repeats.

• Formation Reactions: Two key types of reactions form synthetic polymers:

  • Condensation: Reactions between two functional groups that release water. Examples include carboxylic acid + alcohol → ester + water and carboxylic acid + amine → amide + water
  • Addition: Alkene functional groups react, joining together in long chains without releasing any other products.

• Condensation Polymerization: Requires di-functional monomers, which have two functional groups each. A-A reacting with B-B monomers or A-A and B-B monomers individually reacting together are common ways to make polymers.

• Addition Polymerization: Involves joining monomer units without losing any atoms. A three-step process called initiation, propagation, and termination. Different monomers give different polymers.

Soaps and Detergents

• Introduction: Saponification reactions (soap making) are among the oldest known organic reactions. Modern processes utilize concentrated NaOH solution mixed with triglycerides (a type of lipid) to form glycerol and fatty acid salts (soap).

• Triglycerides (Fats/Oils): Have ester functional groups. Concentrated NaOH solution breaks the ester bond through a process called hydrolysis. Hydrolysis forms alcohol and carboxylic acid. The carboxylic acid is in the ionic form (carboxylate ion), with the sodium ion attracted to that negatively-charged end.

• Soap Structure: Soap molecules have hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails. The hydrophilic end dissolves easily in water, while the hydrophobic tail does not.

• Hard Water: Hard water contains high concentrations of Ca²⁺, Mg²⁺ or Fe³⁺. These ions react with soaps to form insoluble salts (soap scum) which are often grey, sticky, and unpleasant.

• Detergents: Synthetic detergents are a hard water alternative to soaps. Detergent molecules have similar structures to soaps with a hydrophobic tail (long carbon chain) and a hydrophilic head (benzene sulfonate ion).

Lipids

• Introduction: Lipids are a diverse group of compounds with differing structures but similar properties, including the inability to dissolve in water and solubility in non-polar solvents.

• Lipid Families: Lipids include triglycerides (fats and oils), fatty acids (long-chain carboxylic acids), fat-soluble vitamins, prostaglandins, steroids, and hormones.

• Functions: Lipids have various functions, including storing energy, forming cell membranes, serving as emulsifying agents, and regulating metabolism through hormones.

• Classification: Saponifiable lipids can be hydrolysed in basic conditions (e.g., NaOH solution). Other lipids that can't be hydrolysed are non-saponifiable lipids. Common categories include waxes, triglycerides, phospholipids, prostaglandins, and steroids.

• Fatty Acids: Essential building blocks of many lipids, long-chained carboxylic acids. Can be saturated or unsaturated, with varying properties depending on structure.

• Triglycerides: Triglycerides (tri-acyl-glycerols) are formed from glycerol bonded to three fatty acids (three ester bonds). Fats are solid at room temperature; oils are liquid. Reactions include hydrolysis (acidic conditions), saponification (basic conditions), and hydrogenation.

• Bile Salts: Steroid, emulsifying agent aiding fat digestion.

• Phospholipids: Cell membrane components with a glycerol backbone and two fatty acyl chains. A phosphate group links with an amino alcohol. Key components of cell membranes and important as emulsifying agents.

• Sphingolipids: Complex lipids lacking glycerol backbone, with sphingosine instead, and they also have a phosphate ester group. Found in brain and nervous tissue.

• Steroids: Lipids with a characteristic four-ring structure, crucial in hormone production and controlling lipid membrane fluidity. Examples include cholesterol, testosterone, estradiol, ergosterol.