chemistry

Polystannane

Polystannane 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 Polystannane rather than just read about it. In short: Polystannanes are organotin compounds with the formula (R2Sn)n. These polymers have been of intermittent academic interest; they are unusual because heavy elements comprise the backbone.

Key takeaways

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

Reference excerpt

Polystannanes are organotin compounds with the formula (R2Sn)n. These polymers have been of intermittent academic interest; they are unusual because heavy elements comprise the backbone. Structurally related but better characterized (and more useful) are the polysilanes (R2Si)n.

History and synthesis

Oligo- or polystannanes were first described by Löwig in 1852, only 2 years after Edward Frankland's report on the isolation of the first organotin compounds. Löwig's route involved treating an Sn/K and Sn/Na alloys with iodoethane, in the presence of quartz sand which was used to control the reaction rate. Products with elemental compositions close to those of oligo(diethylstannane)s or poly(diethylstannane) were obtained. Cahours obtained similar products and attributed the formation of the so-called "stannic ethyl" to a reaction of the Wurtz type. Already in 1858, "stannic ethyl" was formulated as a polymeric compound denoted with the composition n(SnC4H5). In 1917, Grüttner, who reinvestigated results on hexaethyl-distannanes(H5C2)3Sn-Sn(C2H5)3 (reported by Ladenburg in 1870), confirmed the presence of Sn-Sn bonds and predicted for the first time that tin could form chain like compounds. In 1943, it was postulated that “diphenyltin” exists as a type of polymeric material because of its yellow color, and indeed a bathochromic shift of the wavelength at maximum absorption with increasing number of Sn atoms was found later in the case of oligo(dibutylstannane)s comprising up to 15 Sn atoms. The Wurtz reaction is still used for the preparation of poly(dialkylstannane)s. Treatment of dialkyltin dichlorides with sodium lead to polystannanes of high molar mass, however, in low yields and with formation of (cyclic) oligomers. Other efforts to prepare high molar mass polystannanes by electrochemical reactions or by catalytic dehydropolymerization of dialkylstannanes (R2SnH2) were also made. Unfortunately, frequently, the polymers prepared by those methods were not isolated and typically contained significant fractions of cyclic oligomers. Alternatively, alkyltin halides react with excess electride in ammonia solutions to give metal alkylstannides. Added alkyltin halides then couple to the stannides to give polystannanes.

Linear polystannanes

Dialkytin dihydrides (R2SnH2) were reported in 2005 to undergo dehydropolymerization in the presence of Wilkinson’s catalyst. This method afforded polystannanes without detectable amounts of "cyclic"-byproducts. The polymers were yellow with number average molar masses of 10 to 70 kg/mol and a polydispersity of 2 – 3. By variation of the catalyst concentration the molar masses of the synthesized polymers could be adjusted. A strong influence of the temperature on the degree of conversion was observed. Determination of the molar mass at different degrees of conversion indicated that polymerization did not proceed according to a statistical condensation mechanism, but, likely, by growth onto the catalyst, e.g. by insertion of SnR2-like units. The poly(dialkylstannane)s were found to be thermotropic and displayed first-order phase transitions from one liquid-crystalline phase into another or directly to the isotropic state, depending on the length of the side groups. More specifically, poly(dibutylstannane) for example showed an endothermic phase transition at ~0 °C from a rectangular to a pure nematic phase, as determined by X-ray diffraction. Like polysilanes, polystannanes are semi-conductive. Temperature-dependent, time-resolved pulse radiolysis microwave conductivity measurements of poly(dibutylstannane) yielded values of charge-carrier mobilities of 0.1 to 0.03 cm2 V−1 s−1, which are similar to those found for pi-bond-conjugated carbon-based polymers. By partial oxidation of the material with SbF5 conductivities of 0.3 S cm−1 could be monitored. The liquid-crystalline characteristics of the poly(dialkylstannane)s permitted facile orientation of these macromolecules, for instance, by mechanical shearing or tensile drawing of blends with poly(ethylene). Poly(dialkylstannane)s with short side groups invariably arranged parallel to the external orientation direction, while the polymers with longer side groups had a tendency to order themselves perpendicular to that axis.

References

External links Fabien Choffat (2007) Polystannane, Doctoral dissertation, Swiss Federal Institute of Technology, Zürich.

Illustrations

Polystannane: Repeating unit of polystannane. — Repeating unit of polystannane.

Polystannane: Optical micrographs (crossed polarizers) of an oriented film of poly(3-metylbutylstannane) produced by shearing the material at room temperature, top at 45° and bottom 90° in respect to the polarizers. — Optical micrographs (crossed polarizers) of an oriented film of poly(3-metylbutylstannane) produced by shearing the material at room temperature, top at 45° and bottom 90° in respect to the polarizers.

Worked examples

Example 1 — a first encounter with Polystannane

Start with the simplest possible case. Write down what Polystannane 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 Polystannane 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 Polystannane 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 Polystannane

In research: Polystannane 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 Polystannane 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: Polystannane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Conductive polymers, Inorganic polymers, Organotin compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Polystannane 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 Polystannane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polystannane 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 Polystannane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polystannane in simple terms?

Polystannanes are organotin compounds with the formula (R2Sn)n. These polymers have been of intermittent academic interest; they are unusual because heavy elements comprise the backbone.

Why does Polystannane 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 Polystannane?

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 Polystannane.