The functionality of a monomer is the number of
Answer: A
A bifunctional monomer gives a linear chain, and a functionality of three or more permits branching and cross-linking into a network. It is the property that decides whether the product will be a thermoplastic or a thermosetting resin.
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The repeat unit of a condensation polymer weighs less than the monomers that formed it because
Answer: B
Water, methanol or hydrogen chloride splits out as each bond forms, so the polyester or polyamide repeat unit is lighter than the diacid and the diol or diamine taken together. In an addition polymer nothing is eliminated and the repeat unit matches the monomer exactly.
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Condensation polymerisation requires monomers that are
Answer: C
Two reactive groups per molecule are the minimum for a chain to grow at both ends, as in a diacid with a diamine. A monofunctional molecule stops the chain, which is how the molecular mass is deliberately controlled in practice.
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In free radical addition polymerisation the initiator's role is to
Answer: D
Benzoyl peroxide or azobisisobutyronitrile decomposes thermally to radicals that attack the monomer's double bond and begin propagation. It is consumed rather than recovered, so it is not a catalyst in the strict sense.
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The steps of a free radical chain polymerisation are initiation, propagation and
Answer: A
Termination occurs when two radicals combine or one abstracts a hydrogen from another chain, killing both growing ends. A chain transfer agent can also end a chain while starting a new one, which lowers the molecular mass without slowing the reaction.
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Ziegler-Natta catalysts are valued because they give polymers of
Answer: B
A titanium halide with an aluminium alkyl orients each monomer as it adds, so isotactic polypropylene can be made at all. High-density polyethylene from the same route is linear and far stronger than the branched free radical product.
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Low-density polyethylene differs from the high-density grade in being
Answer: C
Chain transfer during high-pressure free radical polymerisation produces side branches that stop the chains packing closely. The coordination-catalysed grade is linear, packs well and is stiffer and stronger as a result.
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An isotactic polymer has its substituent groups
Answer: D
Correct answer: all on the same side of the chain
Isotactic means every substituent lies on the same side of the backbone, syndiotactic means they alternate regularly, and atactic means they are randomly placed. Tacticity matters because regularity allows the chains to pack: isotactic polypropylene is crystalline, strong and useful, while the atactic form of the same chemical compound is a soft amorphous material of no structural value.
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Emulsion polymerisation is carried out with the monomer
Answer: A
Reaction occurs in surfactant micelles swollen with monomer, so the heat is easily removed and a high molecular mass is obtained at a high rate. The product is a latex, and removing the surfactant completely is the method's drawback.
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Suspension polymerisation differs from emulsion polymerisation in producing
Answer: B
Monomer droplets held apart by a mechanical stabiliser each polymerise as a small bulk reaction, giving pearls easily separated by filtration. No surfactant contaminates the product, which is why the route suits moulding grades.
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