(a)     For two different addition polymers, describe and explain one way in which the properties of addition polymers may be modified.

Polymer one:

Polymer two:

(b)     Describe and explain how the extent of branching affects the properties of poly(ethene).

(c)     Discuss two advantages and two disadvantages of using poly(ethene).

(a)     Accept two of the following four pairs of answers.

plasticizers in polyvinyl chloride;

the more plasticizer the more flexible the plastic;

OR

volatile hydrocarbons in the formation of (expanded) polystyrene;

volatile hydrocarbons vaporize during the formation of the polystyrene and reduce the density of (expanded) polystyrene / improving insulating properties;

OR

sulfur added to diene/2-methyl-1,3-butadiene/rubber (produces cross-link polymer);

maintains its spring/softness (for longer periods of time);

OR

blowing air/steam during the polymerisation to form polyurethane;

reduces density/increases springiness

(b)     high degree of branching produces low density polyethene;

small degree of branching produces high density polyethenes;

HDPE/low branching is stiffer/stronger/more resistant to heat and corrosion/less permeable to gases / LDPE/high branching is more flexible/weaker/less resistant to heat and corrosion/more permeable to gases;

(c)     Advantages:

polymer’s properties can be customized / OWTTE

can be recycled/reused

cheap

chemically inert

transparent

non-toxic

Any two correct answers scores [1].

Disadvantages:

rely on non-renewable energy sources

volume occupied by plastics in landfill

non-biodegradability

burning produces toxic gases

burning produces carbon dioxide (greenhouse gas)

burning printed polyethene can release toxic (heavy) metals/substances

may cause suffocation/death of animals

Any two correct answers scores [1].

The way in which the properties of addition polymers depend on their structure and methods for modifying this appeared to be very poorly understood, with only a handful of candidates scoring well on any parts of this question. In Part (b) many candidates discussed the difference between isotactic and atactic polymers rather than the effects of branching.