State the type of mechanism occurring in the manufacture of low-density poly(ethene).

Distinguish between addition and condensation polymers in terms of how the monomers react together.

Describe and explain how the properties of condensation polymers depend on three structural features.

(free) radical (addition);

addition polymerization: unsaturated/containing C=C monomers add together without elimination/ removal of any atoms (to form polymer) / OWTTE;

condensation polymerization: monomers have two reactive sites/are bifunctional and produce a larger molecule with elimination/removal of a smaller molecule / OWTTE;

OR

in addition polymerisation unsaturated / containing C=C monomers undergo addition and in condensation polymerisation the monomer molecules have two reactive sites/ functional groups/ are bifunctional;

in the addition polymerisation reaction there are no by-products while in the condensation polymerisation reaction a small molecule is eliminated/ produced as a by-product;

chain length: greater chain length, greater intermolecular forces, higher strength / melting point;

way groups are arranged/orientated: trans-orientation allows close approach between chains giving it greater strength / cis-orientation produces bent chains, does not allow close approach for strong bonding / OWTTE / Kevlar example explained;

cross-linking: stronger covalent bonds in cross-linking lead to stronger / higher melting point / more rigid polymers (than linear or branched polymer) / OWTTE / amount of cross-linking determines how rigid structure becomes / vulcanized rubber example: sulfur atoms create strong covalent links between chains / in phenol-methanal (Bakelite), benzene ring is bonded to CHin three / several positions (to produce rigid plastic); 2

branching: depending on branching, close packing possible or prevented / amylose has a straight chain structure while amylopectin has straight linkages as well as branches;

Need explanation for mark – no marks for branching related to LDPE and HDPE or isotactic and atactic arrangements as question is about condensation, not addition polymerization.

Many were able to state free radical addition as type of mechanism, but some stated only addition or had no idea although they should have been able to deduce from the information given in part (b) of the question.

Distinguishing between addition and condensation polymerization solicited partial answers: candidates need to appreciate that in addition polymerization, unsaturated molecules (containing C=C bonds) add together without the elimination or removal of any atoms. Condensation polymerization, on the other hand involves bifunctional monomers (monomers with two reactive sites) that produce a larger molecule with the elimination of a smaller molecule (such as water).

How the properties of condensation polymers depend on structural features turned out to be a challenging question in which few candidates scored partial marks.