| Date | May 2013 | Marks available | 2 | Reference code | 13M.3.sl.TZ1.C4 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | C4 | Adapted from | N/A |
Question
Poly(propene) has different forms. Isotactic poly(propene) is tough, while atactic poly(propene) is flexible.
State the difference in the structure of the two polymers.
Isotactic:
Atactic:
Explain how the difference in structure results in the different properties of isotactic and atactic poly(propene).
Markscheme
Isotactic: methyl groups all oriented on same side of polymer chain and
Atactic: methyl groups oriented randomly;
Diagram alone is not sufficient – unless difference stated in words.
closer packing of isotactic chains;
isotactic has stronger van der Waals’/London/dispersion/intermolecular forces (than atactic);
Accept opposite statements for atactic.
Allow vdW as abbreviation for van der Waals’ or FDL for London/dispersion.
Examiners report
The orientations of methyl groups in isotactic and atactic poly(propene) were known by more than half of the candidates, but the explanations of the properties did not involve intermolecular forces for the majority of candidates.
The orientations of methyl groups in isotactic and atactic poly(propene) were known by more than half of the candidates, but the explanations of the properties did not involve intermolecular forces for the majority of candidates.
