chemistry

Polyketone

Polyketone is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Polyketone rather than just read about it. In short: Polyketones (POK) are a family of high-performance thermoplastic polymers. The polar ketone groups in the polymer backbone of these materials gives rise to a strong attraction between polymer chains, which increases the material's melting point (255 °C for copolymer (carbon monoxide ethylene), 220 °C for terpolymer (carbon monoxide, ethylene, propylene).

Key takeaways

Polyketone belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polyketone to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polyketone from memory before moving on to harder problems.

Reference excerpt

Polyketones (POK) are a family of high-performance thermoplastic polymers. The polar ketone groups in the polymer backbone of these materials gives rise to a strong attraction between polymer chains, which increases the material's melting point (255 °C for copolymer (carbon monoxide ethylene), 220 °C for terpolymer (carbon monoxide, ethylene, propylene). Trade names include Poketone, Carilon, Karilon, Akrotek, and Schulaketon. Such materials also tend to resist solvents and have good mechanical properties. Unlike many other engineering plastics, aliphatic polyketones such as Shell Chemicals' Carilon are relatively easy to synthesize and can be derived from inexpensive monomers. Carilon is made with a palladium(II) catalyst from ethylene and carbon monoxide. A small fraction of the ethylene is generally replaced with propylene to reduce the melting point somewhat. Shell Chemical commercially launched Carilon thermoplastic polymer in the U.S. in 1996, but discontinued it in 2000. Hyosung announced that they would launch production in 2015. Industrially, the ethylene-carbon monoxide co-polymer is most significant. This polymer is synthesized either as a methanol slurry, or via a gas phase reaction with immobilized catalysts.

Polymerization mechanism

Initiation and termination Where external initiation is not employed for the methanol system, initiation can take place via methanolysis of the palladium(II) precursor, giving either a methoxide or a hydride complex. Termination occurs also by methanolysis. Depending on the end of the growing polymer chain, this results in either an ester or a ketone end group, and regenerating the palladium methoxide or hydride catalysts respectively.

Propagation A mechanism for the propagation of this reaction using a palladium(II)-phenanthroline catalyst has been proposed by Maurice Brookhart:

Polyketones are noted for having extremely low defects (double ethylene insertions or double carbonyl insertions, in red):

The activation barrier to give double carbonyl insertions is very high, so it does not occur. Brookhart's mechanistic studies show that the concentration of the alkyl-ethylene palladium complex required to give double ethylene insertions is very low at any one point:

Additionally, the Gibbs energy of activation of the alkyl-ethylene insertion is ~ 3 kcal/mol higher than the corresponding activation barrier for the alkyl-carbon monoxide insertion. As a result, defects occur at an extremely low rate (~ 1 part per million). The industrially-relevant palladium-dppp catalyst has also been investigated.

Importance of bidentate ligands Where palladium(II) pre-catalysts bearing monodentate phosphine ligands are used in methanol, a relatively high fraction of methyl propionate is produced. In comparison, where chelating diphosphine ligands are used, this side-product is absent. This observation is rationalized: the bis(phosphine) complex can undergo cis-trans isomerization to give the sterically favored trans isomer. The propionyl ligand is now trans- to the open coordination site or ethylene ligand, and is unable to undergo migratory insertion. Instead, solvolysis by methanol occurs, which gives the undesired methyl propionate side-product.

Whereas much effort has involved discrete palladium complexes, an example in the patent literature claims that a combination of Lewis acid (aluminum, iron, or titanium halide) and a source of palladium (as a salt or the metal) is effective for making polyketone.

References

External links Macrogalleria

Illustrations

Worked examples

Example 1 — a first encounter with Polyketone

Start with the simplest possible case. Write down what Polyketone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polyketone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polyketone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polyketone

In research: Polyketone appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polyketone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polyketone is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organic polymers, Thermoplastics, so understanding it makes those chapters shorter.
In everyday life: Look for Polyketone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Polyketone in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polyketone means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polyketone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polyketone in simple terms?

Why does Polyketone matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polyketone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polyketone.