Question

In: Chemistry

Which of the following step growth polymers represents a homopolymer and is not a polyaddition step-growth...

Which of the following step growth polymers represents a homopolymer and is not a polyaddition step-growth polymer?

Question 1 options:

	a polyurethane
	polyyethylene terephthalate
	polyhexamethylene adipamide
	polycaprolactam
	poly(6-aminocaproic acid)

Expert Solution

According to IUPAC the term step-growth polymerization is used for the term polyaddition, when the propagation steps are addition reactions and no molecules are evolved during these steps and polycondensation is used when the propagation steps are condensation reactions and molecules are evolved during these steps.

Homopolymers :

These are polymers made by joining together monomers of the same chemical composition or structure.

Heteropolymers :

These are polymers composed of more than one kind of monomer.

Polyurethanes :

These are also known as reaction polymers, which include epoxies, phenolics and unsaturated polyesters. Polyurethanes are produced by reacting an isocyanate containing two or more isocyanate groups per molecule (R−(N=C=O)_n with a polyol containing on average two or more hydroxyl groups per molecule (R′−(OH)_n in the presence of a catalyst or by activation with ultraviolet light. It contains two different types of monomers so are heteropolymers or copolymers.Hence not a homopolymer.

Polyethylene terephthalate :

It is the thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins.

Polyethylene terephthalate is synthesized from Ethylene glycol and dimethyl terephthalate(DMT) or terephthalic acid.The former is a transesterification reaction, whereas the latter is an esterification reaction.

Itis also known by other brand names Terylene, Lavsan, Dacron

Dimethyl terephthalate process (DMT):(Polyesterification reaction)

First step

C₆H₄(CO₂CH₃)₂ + 2 HOCH₂CH₂OH → C₆H₄(CO₂CH₂CH₂OH)₂ + 2 CH₃OH

Second step

n C₆H₄(CO₂CH₂CH₂OH)₂ → [(CO)C₆H₄(CO₂CH₂CH₂O)]_n + n HOCH₂CH₂OH

Terephthalic acid process:(Polycondensation reaction)

n C₆H₄(CO₂H)₂ + n HOCH₂CH₂OH → [(CO)C₆H₄(CO₂CH₂CH₂O)]_n + 2n H₂O

.since it contains two different types of monomers so it is a heteropolymer.

Simillarly polyhexamethylene adipamide is also a heteropolymer containing hexamethylene diamine, H₂N(CH₂)₆NH₂, and adipic acid, HOOC(CH₂)₄-COOH.

poly(6-aminocaproic acid):

This is a condensation homopolymer. this is formed by amonomer unt 6-aminocaproic acid which is an intermediate in nylon 6 formation . here during polymerization there is loss of water so it not step growth polymerization according to IUPAC.

polycaprolactam:

Nylon 6 or polycaprolactam is a polymer developed by Paul Schlack at IG Farben to reproduce the properties of nylon 6,6 without violating the patent on its production.

Nylon 6 is synthesized by ring-opening polymerization of caprolactam.

Caprolactam has 6 carbons, hence 'Nylon 6'. When caprolactam is heated at about 533 K in an inert atmosphere of nitrogen for about 4-5 hours, the ring breaks and undergoes polymerization. There is no loss of any water like molecule. therefore according to IUPAC it is a step growth homopolymer.

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