Polymer Formation Flashcards

9.1 Polymer Formation

• Polymers are often referred to as plastics due to their versatility, low cost, and ease of manufacturing.

• Polymers are used to make items like combs, pen casings, and rulers where special properties aren't required.

• Scientists have developed sophisticated polymers with high-performance properties.

Polymer Structure

• Polymers are covalent molecular substances composed of many small molecules joined together.

• The word polymer comes from Greek words: "poly" meaning 'many' and "mer" meaning 'part'.

• Polymers are formed by joining thousands of smaller molecules called monomers (mono means 'one') through a process called polymerization, see Figure 9.1.2

Plastics

• The term 'plastic' describes a property of a material, indicating it can be molded into different shapes readily.

• A plastic material can be reshaped upon heating (e.g., a plastic basket), while others are hard and brittle and do not melt when heated (e.g., a saucepan handle).

Addition Polymerization

• Addition reactions involve the reaction of an alkene with another molecule; all atoms of both molecules are present in the final molecule.

• Alkenes can undergo an addition reaction with themselves to produce long chains.

• The reaction of ethene monomers to form polyethene is an example of addition polymerization, as shown in Figure 9.1.4.

• Thousands of ethene monomers react to form a polyethene molecule.

• Large square brackets and a subscript n are used to simplify the drawing of long polymer molecules.

• The value of n may vary, and a polymer chain might contain as many as 20,000 carbon atoms.

• The empirical formula of the monomer is the same as that of the polymer in addition polymers.

Ethene Polymerization

• Ethene is an unsaturated molecule because it contains a carbon-carbon double bond.

• During polymerization, the double bonds break, and new covalent bonds form between carbon atoms on nearby monomers.

• The resulting polyethene does not contain any double bonds.

• The name of a polymer formed through addition polymerization often includes the monomer used (Table 9.1.1).

Polymer Properties

• The length of polymer molecules gives them useful properties.

• Polyethene is essentially a long alkane. As molecule size increases, the melting point increases.

• Dispersion forces between long polymer chains are strong enough to make polyethene a solid at room temperature, as shown in Figure 9.1.6.

General Polymer Properties:

• Polymers are generally:

  • Non-conductors of electricity

  • Lightweight

  • Durable

  • Versatile

  • Acid-resistant

  • Flammable

History of Polymers

• Naturally occurring polymers include wool, cellulose, and proteins.

• Most commercial polymers are synthetic; their use has become widespread in the last 100 years.

• Native Americans played with crude rubber balls made from the sap of rubber trees.

• Charles Goodyear introduced large-scale production of rubber in 1839 through vulcanization, involving heating rubber with sulfur.

• The properties of rubber are improved by vulcanization.

• The first completely synthetic polymer, Bakelite, was released in 1909 by Leo Baekeland, made from phenol and formaldehyde. Table 9.1.2 shows significant milestones in the history of polymers.

Discovery of Polyethene

• The first practical method for synthesizing polyethene was discovered accidentally in 1933 at ICI in Cheshire, England.

• Oxygen initiated the polymerization reaction between ethene molecules.

Low-Density Polyethene (LDPE)

• The earliest method of producing polyethene involved high temperatures (around 300°C) and extremely high pressures.

• Under these conditions, the polymer is formed rapidly, resulting in many short branches off the main polymer chain, as shown in Figure 9.1.8.

• The presence of branches prevents molecules from packing closely together, weakening dispersion forces.

• The arrangement of polymer molecules is described as amorphous or non-crystalline, giving the material a relatively low density.

High-Density Polyethene (HDPE)

• A low-pressure method of producing polyethene was developed by Union Carbide in the late 1960s.

• Ziegler-Natta catalysts (transition metal catalysts) are used to avoid high pressures.

• Polymer molecules are produced under milder conditions with very few branches.

• The lack of branches allows molecules to pack tightly, increasing density and hardness, resulting in crystalline sections.

• Figure 9.1.10 summarizes the properties and uses of HDPE.

Comparison of LDPE and HDPE (Table 9.1.3)

• HDPE:

  • Catalysts are used to control the polymerization reaction.

  • Long molecules with few branches.

  • Molecules pack tightly.

  • Stronger dispersion forces.

• LDPE:

  • Formed at high temperature and pressure without controlled polymerization.

  • Molecules contain many branches.

  • Molecules cannot pack tightly.

  • Weaker dispersion forces.

• Amorphous polymers are usually less rigid, weaker, and often transparent.

Other Addition Polymers

• Monomers need to be unsaturated to undergo addition polymerization.

• Figure 9.1.11 shows the reaction between bromoethene monomers to form polybromoethene (a flame-resistant polymer).

• Polypropene (PP) is manufactured in Australia and has a wide range of uses, including synthetic sporting fields, microwave containers, and rope (Figure 9.1.12).

Condensation Polymerization

• Monomers with functional groups on each end of the molecule join when the functional groups react with each other, forming condensation polymers.

• The formation of polyester involves the carboxyl group on one monomer reacting with the hydroxyl group on another to form an ester link, see Figure 9.1.13.

• Water is also formed during this process.

• PET (polyethene terephthalate) is a widely used condensation polymer (Figure 9.1.14), found in polyester fabric (Figure 9.1.15a) and bottled water containers (Figure 9.1.15b).

• Plastic items with recycling code 1 are made from PET.

• The formation of a condensation polymer does not necessarily require two different monomers, as seen in the formation of polylactic acid (PLA) from lactic acid (Figure 9.1.16).

• PLA is increasingly popular due to its biodegradability.

Comparison of Addition and Condensation Polymerization (Table 9.1.4)

• Addition Polymerization:

  • Monomer has a carbon-carbon double bond.

  • Double bond breaks during polymerization.

  • Polymer chain contains single C-C bonds only.

  • No other product is formed.

• Condensation Polymerization:

  • Monomer has a functional group on each end.

  • Functional groups react.

  • Polymer chain contains atoms other than carbon.

  • Smaller molecules, such as water, are formed.

Natural Polymers

• Living organisms create natural polymers, such as chitin, proteins, silk, cellulose, and starch.

• Chitin is found in the cell walls of fungi and the exoskeletons of crustaceans and insects (Figure 9.1.17).

• These are all examples of condensation polymers.

9.1 Polymer Formation

• Polymers, often called plastics, are favored for their adaptability, affordability, and ease of production.

• They're used in everyday items like combs and pen casings where specific properties aren't crucial.

• Advanced polymers are engineered for high-performance applications.

Polymer Structure

• Polymers are substances made of many small molecules linked by covalent bonds.

• The term 'polymer' comes from the Greek words 'poly' (many) and 'mer' (part).

• Polymers form when thousands of monomers (small, single-unit molecules) join in a process called polymerization (Figure 9.1.2).

Plastics

• 'Plastic' refers to a material's ability to be molded into various shapes.

• Some plastics can be reshaped with heat, while others are rigid and don't melt.

Addition Polymerization

• In addition reactions, an alkene reacts with another molecule, incorporating all atoms from both into the final product.

• Alkenes can react with themselves to form long chains.

• Ethene monomers reacting to form polyethene is an example of addition polymerization (Figure 9.1.4).

• Thousands of ethene monomers combine to create a polyethene molecule.

• Large square brackets and a subscript nn denote the repeating monomer unit in the polymer chain.

• The value of nn can vary, with polymer chains containing up to 20,000 carbon atoms.

• Empirical formulas of monomers and addition polymers are identical.

Ethene Polymerization

• Ethene is unsaturated due to its carbon-carbon double bond.

• During polymerization, double bonds break, and new covalent bonds form between carbon atoms.

• Polyethene does not contain any double bonds.

• Polymer names often include the monomer name (Table 9.1.1).

Polymer Properties

• Polymer length affects their properties.

• Polyethene is a long alkane; melting point increases with molecule size.

• Dispersion forces between polymer chains make polyethene solid at room temperature (Figure 9.1.6).

General Polymer Properties:

• Polymers are generally:

  • Non-conductors of electricity

  • Lightweight

  • Durable

  • Versatile

  • Acid-resistant

  • Flammable

History of Polymers

• Natural polymers include wool, cellulose, and proteins.

• Most commercial polymers are synthetic, with widespread use in the last 100 years.

• Native Americans used crude rubber balls from rubber tree sap.

• Charles Goodyear introduced large-scale rubber production in 1839 via vulcanization, heating rubber with sulfur.

• Vulcanization improves rubber properties.

• The first synthetic polymer, Bakelite, was created in 1909 by Leo Baekeland from phenol and formaldehyde. Significant milestones are in Table 9.1.2.

Discovery of Polyethene

• A practical polyethene synthesis was accidentally discovered in 1933 at ICI in Cheshire, England.

• Oxygen initiated ethene polymerization.

Low-Density Polyethene (LDPE)

• Early polyethene production used high temperatures (around 300°C300°C) and extreme pressures.

• This process forms polymers with short branches off the main chain (Figure 9.1.8).

• Branches prevent close packing, weakening dispersion forces.

• This arrangement is amorphous or non-crystalline, resulting in low density.

High-Density Polyethene (HDPE)

• Union Carbide developed a low-pressure polyethene production method in the late 1960s.

• Ziegler-Natta catalysts (transition metal catalysts) avoid high pressures.

• Milder conditions produce polymer molecules with few branches.

• Lack of branches allows tight packing, increasing density and hardness, forming crystalline sections.

• Figure 9.1.10 summarizes HDPE properties and uses.

Comparison of LDPE and HDPE (Table 9.1.3)

• HDPE:

  • Catalysts control polymerization.

  • Long, unbranched molecules.

  • Tight molecular packing.

  • Stronger dispersion forces.

• LDPE:

  • Formed at high temperature and pressure without controlled polymerization.

  • Branched molecules.

  • Loose molecular packing.

  • Weaker dispersion forces.

• Amorphous polymers are typically less rigid, weaker, and transparent.

Other Addition Polymers

• Unsaturated monomers are required for addition polymerization.

• Figure 9.1.11 shows bromoethene polymerizing to polybromoethene (flame-resistant).

• Polypropene (PP) is manufactured in Australia and used in synthetic sporting fields, microwave containers, and ropes (Figure 9.1.12).

Condensation Polymerization

• Monomers with functional groups at each end react to form condensation polymers.

• Polyester forms when a carboxyl group reacts with a hydroxyl group, creating an ester link (Figure 9.1.13).

• Water is also produced.

• PET (polyethene terephthalate) is a widely used condensation polymer (Figure 9.1.14), found in polyester fabric (Figure 9.1.15a) and bottled water containers (Figure 9.1.15b).

• Plastic items with recycling code 1 are PET.

• Condensation polymer formation doesn't always need two monomers, as seen in polylactic acid (PLA) from lactic acid (Figure 9.1.16).

• PLA is increasingly popular due to its biodegradability and is derived from renewable resources like corn starch or sugarcane.

Comparison of Addition and Condensation Polymerization (Table 9.1.4)

• Addition Polymerization:

  • Monomer has a carbon-carbon double bond.

  • Double bond breaks during polymerization.

  • Polymer chain contains single C-C bonds only.

  • No other product is formed.

• Condensation Polymerization:

  • Monomer has a functional group on each end.

  • Functional groups react.

  • Polymer chain contains atoms other than carbon.

  • Smaller molecules, such as water, are formed.

Natural Polymers

• Living organisms produce natural polymers like chitin, proteins, silk, cellulose, and starch.

• Chitin is in fungal cell walls and the exoskeletons of crustaceans and insects