Addition polymerisation — practice questions

1. Identify the C=C bond: In propene ($CH_3CH=CH_2$), the double bond is between the second and third carbons if numbered from the left, but it's easier to see it as being between a $CH$ group and a $CH_2$ group.
2. Focus on the double bond carbons: The carbons involved are $C_1$ (with two H atoms) and $C_2$ (with one H and one $CH_3$ group).
3. Open the double bond: The $C=C$ becomes a $C-C$ backbone for the polymer chain.
4. Draw the repeat unit: The two carbons from the double bond form the main chain. The groups attached to them ($H$, $H$, $CH_3$, $H$) are placed on these carbons. We show the chain continuing by drawing bonds through the brackets.

Repeat Unit:

-[-CH($CH_3$)-CH$_2$-]-$_n$

Or displayed as:

  H   H
  |   |

...--[C - C]--... | | CH₃ H

Name: poly(propene)

1. Identify the repeating unit: Look for the shortest section that repeats along the chain. The pattern is [-CF$_2$-CFCl-]. This is the repeat unit.
2. Isolate the two-carbon backbone: The repeat unit has a backbone of -C-C-.
3. Identify the attached groups: The first carbon is attached to two fluorine atoms (-CF$_2$-). The second carbon is attached to one fluorine and one chlorine atom (-CFCl-).
4. Re-form the double bond: To find the monomer, place a double bond between the two carbon atoms of the backbone and remove the bonds that link to other repeat units.

Repeat unit: -[CF$_2$-CFCl]-

Monomer: CF$_2$=CFCl

Name of monomer: 1-chloro-1,2,2-trifluoroethene