Question 1

What is step-growth polymerization and how does it differ from other polymerization methods?

Accepted Answer

Step-growth polymerization is a stepwise condensation of monomers to form polymers, where dimers form first, then trimers, tetramers, oligomers, and eventually long-chain polymers. Unlike chain-growth polymerization, step-growth polymerization requires no initiator and has no termination reactions. However, it requires longer reaction times to achieve high molecular weight polymers.

Question 2

Why is step-growth polymerization also called condensation polymerization?

Accepted Answer

Step-growth polymerization is called condensation polymerization because each polymerization step involves the loss of small molecules, typically water or HCl. These byproducts are released as monomers bond together, making the reaction a condensation process where atoms combine while releasing small molecular fragments.

Question 3

What functional group requirements do monomers need for step-growth polymerization?

Accepted Answer

Monomers in step-growth polymerization must have two functional groups for bonding. These can be A-A type, B-B type, or A-B type monomers. A-A and B-B type monomers condense to form (A-A-B-B)n polymers, while A-B type monomers undergo self-condensation to form (A-B)n polymers.

Question 4

How do A-B type monomers differ from A-A and B-B type monomers?

Accepted Answer

A-B type monomers have two different functional groups at each end, allowing them to undergo self-condensation to form (A-B)n polymers. In contrast, A-A and B-B type monomers have identical functional groups at both ends and require pairing with complementary monomers to form (A-A-B-B)n polymers where A groups react exclusively with B groups.

Question 5

What are common examples of polymers produced by step-growth polymerization?

Accepted Answer

Common step-growth polymers include polyesters, polyethers, urethanes, and polyamides. Poly(ethylene terephthalate) or PET is formed from glycol and terephthalic acid monomers. Nylon 6 is produced from 6-aminohexanoic acid, an AB-type monomer with amine and acid functional groups that undergoes self-condensation.

Question 6

Why does step-growth polymerization require longer reaction times than chain-growth methods?

Accepted Answer

Step-growth polymerization requires longer reaction times because all monomers are reactive and most are consumed early to form small chains of reactive oligomers. These oligomers then combine in late stages to form long polymer chains. Extended reaction time is necessary to achieve high conversion degrees and high molecular weights.

Question 7

What advantages does step-growth polymerization offer over chain-growth polymerization?

Accepted Answer

Step-growth polymerization offers key advantages: no initiator is required to start the reaction, and termination reactions are absent. These features simplify the polymerization process compared to chain-growth methods, which require initiators and involve termination steps, though step-growth does demand longer reaction times for high molecular weight achievement.

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