ACSBR Addition Polymerisation - Lesson Package

SYLLABUS RELEVANCE & TEXTBOOK CHAPTERS O-LEVEL PURE (5072) /checkbld/checkbld /checkbld/checkbld Chapter 25 O-LEVEL SCIENCE (5116) /checkbld/checkbld /checkbld/checkbld Chapter 20 Topic 20D: Answers Addition Polymerisation N-LEVEL SCIENCE (5155) /xmarkbld/xmarkbld /xmarkbld/xmarkbld Lesson Package & Accompanying Slides Designed by Alex Lee (2011) Last Modified by Alex Lee (2011) ANGLO-CHINESE SCHOOL (BARKER ROAD) 169 TOPIC 20D: ADDITION POLYMERISATION 1. Addition Polymerisation: Polyethene Under extreme pressure (about 1000 atm), ethene molecules can undergo addition reactions with itself. This is known as addition polymerisation . The product of this reaction is polyethene . Polyethene is commonly found in the household, made into ……………………………… or ……………………………… . ‘Polymerisation ’ refers to ……………………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………… . ‘ Addition polymerisation ’ refers to ………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………… . In the above diagram, we had represent the polymer as a segment showing three repeating units. To represent the polymer in its entirety, we should use brackets as shown: C C H H H H  → ressurep high C C H H H H ethene (monomer) polyethene (polymer) n n n represents a very large integer C C H H H H C C H H H H C C H H H H + +  → ressurep high C C H H H H C C H H H H C C H H H H C C H H H H C C H H H H C C H H H H the double bonds are first broken the molecules then bond on both sides ethene (monomer) polyethene (polymer) to form a macromolecule (known as a polymer). a reaction in which many small organic molecules combine organic molecules combine to form a macromolecule as the only product. a reaction in which many small unsaturated plastic bags clingfilm

ANGLO-CHINESE SCHOOL (BARKER ROAD) 170 TOPIC 20D: ADDITION POLYMERISATION We only consider a molecule to be a polymer when an uncountable number of monomers have been joined together. If only two or three monomers have been joined, we do not consider it to be a polymer. Since the number of monomers (or repeating units) is uncountable, we simply represent this by the letter ‘ n’. We have to be careful of the terminology: “MONOMER” The small organic molecule before polymerisation takes place, i.e. ethene. In the case of addition polymerisation, the C=C bond will still be present. “POLYMER” The macromolecule formed after polymerisation takes place; brackets and ‘n’ are used to represent a very large number of repeating units. THREE “REPEATING UNITS” Represents a segment of the polymer chain; do not draw brackets since this represents a definite number of repeating units. However, ‘continuation lines’ and ‘continuation dots’ must still be shown clearly on each end. A polymer refers to ……………………………………………… consisting of ………………………………………………………………………… formed by the reaction of ………………………………………………………………………………………………………………. A monomer refers to ……………………………………………………………… which is able to ……………………………………………… ……………………………………………………………………………… to form a ……………………………………………. Polymers take on the names of their monomers, with the prefix ‘poly’ in front. As we have seen in the previous page, the polymer of ethene is simply known as polyethene or poly(ethene). (Writing the brackets in the polymer name is optional). C C H H H H n POLYETHENE C C H H H H C C H H H H C C H H H H C C H H H H only one repeating unit can be drawn in the brackets ‘continuation lines’ must exceed the brackets ‘continuation lines’ must be drawn on both ends ‘continuation dots’ must also be drawn on both ends many small molecules joining together a large molecule repeating structural units other small organic molecules macromolecule a small organic molecule join with many

ANGLO-CHINESE SCHOOL (BARKER ROAD) 171 TOPIC 20D: ADDITION POLYMERISATION 2. Drawing Addition Polymers from Given Monomers Like all other unsaturated compounds, propene can also undergo addition polymerisation. (a) Fill in the boxes below with the appropriate full structural formulae. MONOMER POLYMER TWO REPEATING UNITS H C C C H H H H H H C C C H H H H H H C C C H H H H H propene propene propene H C C C H H H H H H C C C H H H H H H C C C H H H H H C C C H H H H H H C C C H H H H H H C C C H H H H H H polypropene Must draw ‘continuation dots’! join monom ers where C=C bonds were rearrange H C C C H H H H H C C C H H H H H H n C C C H H H H H H C C C H H H H H H POLYPROPENE

ANGLO-CHINESE SCHOOL (BARKER ROAD) 172 TOPIC 20D: ADDITION POLYMERISATION To determine the structure of an addition polymer from its monomer, we follow these steps: (b) Draw the structural formula of the polymers formed from the monomers below. n  → polymerize n  → polymerize n  → polymerize C H H 3 n C H COOH C n C2 F H H 5 F C C Cl C C H H H n C C C H C O H H H H O H C C C H C F H H H F H H H C C H Cl H C C C H O H H Cl H H C C C H O H H Cl H H C C C H O H H Cl H H n C C C O H Cl H H3 n C C C H O H H Cl H H identify the C=C bond rearrange molecule such that C=C is in the middle or polymerize full structural formula simplified structural formula Do not draw more than one repeating unit in the brackets. Make sure the lines cross the brackets.

ANGLO-CHINESE SCHOOL (BARKER ROAD) 173 TOPIC 20D: ADDITION POLYMERISATION 3. Drawing Monomers from Given Addition Polymers Since the spine of an addition polymer chain is made from the joining of C=C bonds, each monomer unit will eventually occupy two carbon units on the polymer spine. To identify the monomer, we simply ‘slice up’ the polymer into pairs of carbon atoms, and replace the C=C bond that was originally broken during polymerisation. Number of repeating units represented in this segment: 4 Structural formula of monomer(s): It is not uncommon for an addition polymer to be synthesized from two or more monomers. These polymers, which are made from multiple reactants, are referred to as ‘copolymers’. One such example is the plastic saran : Number of repeating units represented in this segment: 2 Structural formula of monomer(s): However, one special exception is the polymerisation of but-1,3-diene, which forms natural rubber. In this special monomer, two C=C bonds are present in each molecule, with one C–C bond between them. C C H Cl H H C C H Cl H Cl C C H Cl H Cl C C H Cl H H C C H Cl H Cl C C H Cl H H each monomer results in two carbons on the polymer spine C C F F F F C C F F F F C C F F F F C C F F F F C C F F F F each monomer results in two carbons on the polymer spine C C C H C H H H H H C C C H C H H H H H C C C H C H H H H H → → Each monomer contains two C=C bonds, both of which are involved in polymerisation. Each C=C breaks, giving an electron to the next molecule, and an electron to the C–C bond. The C–C bond has become a C=C bond, while the C=C bonds have become C–C bonds. This is unusual as each monomer results in four carbons on the polymer spine, instead of two!

ANGLO-CHINESE SCHOOL (BARKER ROAD) 174 TOPIC 20D: ADDITION POLYMERISATION 4. Review Questions (a) Styrofoam is a useful material in packaging due to its good heat insulation properties, low density and relatively soft texture. It is made from a polymer k