polymers/nanotechnology

polymers/nanotechnology

1. Alkenes can be used to make polymers

   • ethenePlastic grocery bags poly(ethene) flexible, cheap, electrical insulator plastic bags and bottles, coating on electrical wires
     • Most polymers, including poly(ethene) and poly(propene) are not biodegradable. This means that microorganisms cannot break them down, so they may last for many years in rubbish dumps. However, it is possible to include chemicals that cause the polymer to break down more quickly. Carrier bags and refuse bags made from such degradable polymers are already available.
       • Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules. Fractions containing large hydrocarbon molecules are vaporised and passed over a hot catalyst. This breaks chemical bonds in the molecules, and forms smaller hydrocarbon molecules.
         • Notice that the molecular models on the right show that the bonds are not really at 90º. Alkanes are saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds. This makes them relatively unreactive, apart from their reaction with oxygen in the air, which we call burning or combustion. Boiling point and state at room temperature Hydrocarbons have different boiling points, and can be either solid, liquid or gas at room temperature: Small hydrocarbons with only a few carbon atoms have low boiling points and are gases. Hydrocarbons with between five and 12 carbon atoms are usually liquids. Large hydrocarbons with many carbon atoms have high boiling points and are solids.

2. Polymers are very large molecules made when many smaller molecules join together, end-to-end. The smaller molecules are called monomers. In general

   • Polymers have many different uses. The use of a polymer is related to its properties.
     • Incineration Polymers can be burnt or incinerated. They release a lot of heat energy when they burn and this can be used to heat homes or to generate electricity.
       • Cracking is an example of a thermal decomposition reaction.
   • There are problems with incineration. Carbon dioxide is produced, which adds to global warming. Toxic gases are produced unless the polymers are incinerated at high temperatures.
     • Alkenes are unsaturated hydrocarbons. They contain a double bond, which is shown as two lines between two of the carbon atoms. The presence of this double bond allows alkenes to react in ways that alkanes cannot. They can react with oxygen in the air, so they could be used as fuels. But they are more useful than that. They can be used to make ethanol (alcohol) and polymers (plastics), two crucial products in today's world.

3. lots of monomer molecules → a polymer molecule

   • Recycling Polymers have recycling symbols like this one for PVC to show what they are Many polymers can be recycled. This reduces the disposal problems and the amount of crude oil used. But the different polymers must be separated from each other first, and this can be difficult and expensive to do

4. The animation shows how several chloroethene monomers can join end-to-end to make poly(chloroethene), which is also called PVC.

   • Polymer problems One of the useful properties of polymers is that they are unreactive, so they are suitable for storing food and chemicals safely. Unfortunately, this property makes it difficult to dispose of polymers.
     • Cracking Fuels made from oil mixtures containing large hydrocarbon molecules are not efficient. They do not flow easily and are difficult to ignite. Crude oil often contains too many large hydrocarbon molecules and not enough small hydrocarbon molecules to meet demand - this is where cracking comes in.
       • Some of the smaller molecules formed by cracking are used as fuels, and some of them are used to make polymers in plastics manufacture.

5. Alkenes can act as monomers because they have a double bond

   • propeneBlue plastic crate poly(propene) flexible and strong buckets and crates
   • chloroetheneA window frame made from uPVC poly(chloroethene) or PVC tough, cheap and long lasting window frames

6. Ethene can polymerise to form poly(ethene), which is also called polythene. Propene can polymerise to form poly(propene), which is also called polypropylene.

   • Hydrocarbons and alkanes Hydrocarbons Most of the compounds in crude oil are hydrocarbons. This means that they only contain hydrogen and carbon atoms, joined together by chemical bonds. There are different types of hydrocarbon, but most of the ones in crude oil are alkanes. Alkanes The alkanes are a family of hydrocarbons that share the same general formula. This is: CnH2n+2 The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two. For example, methane is CH4 and ethane is C2H6. Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.

7. Ethene can polymerise to form poly(ethene), which is also called polythene. Propene can polymerise to form poly(propene), which is also called polypropylene.

   • tetrafluoroetheneNon stick pan poly(tetrafluoroethene) or PTFE tough and non-stick non-stick coating on pans
     • Testing for alkenes Bromine water is used to tell the difference between an alkane and an alkene. An alkene will turn brown bromine water colourless as it reacts with the double bond. Bromine water remains brown in the presence of an alkane as there is no double bond.

8. polymer use polyethene plastic bags and bottles polypropene crates and ropes polychloroethene water pipes and insulation on electricity cables

   • Alkenes The products of cracking include alkenes (for example ethene and propene). The alkenes are a family of hydrocarbons that share the same general formula. This is CnH2n. The general formula means that the number of hydrogen atoms in an alkene is double the number of carbon atoms. For example, ethene is C2H4 and propene is C3H6. Alkene molecules can be represented by displayed formulae, in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.
     • Crude oil is a mixture of compounds called hydrocarbons. Many useful materials can be produced from crude oil. It can be separated into different fractions using fractional distillation. Some of these fractions can go through a process called cracking and can then be used as fuels. This process also produces alkanes and alkenes, which can be used to make polymers.