Elastomers Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.   Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion. Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience. 9/18/2018

Elastomers Definition- materials capable of reversible change in length at operating temperatures, that is, once a load is removed the material returns to its original dimensions; a rubbery compound; Generally amorphous thermosets with Tg below room temperature to allow full chain mobility- the restoring force in entropic; referred to as “memory” 9/18/2018

Types Natural and synthetic rubber-Thiokol, Buna, Neoprene Polyurethanes Silicone-polysiloxanes Natural proteins-elastin 9/18/2018

Mechanical Properties F i b r e R g d P l a s t c x E o m S N / 2 Strain L D 1 3 4 5 6 B A

Elastomers have properties that can be explained by a model that shares characteristics of thermosets and thermoplastics -have all of the domains shown below 9/18/2018

Principles of Polyurethane Chemistry High molecular weight polymers based isocyanate chemistry Polyisocyanates have the following general formula: R-(N=C=O)n, n= 2-4 9/18/2018

Addition of Nucleophilic Reactants The most important reactions of isocyanates is the formation of carbamic acid derivatives (7) by the addition of components with an acidic H-atom (6) across the C=N double bond (1). 9/18/2018

OH group-containing compounds (8) are by far the most important reactants for isocyanates. They are added under mild conditions, forming carbamic esters (9). Primary alcohols, secondary alcohols, and phenols show decreasing reactivity in that order. The trivial name urethane which is used for the compound ethyl carbamate, gave the whole polyurethane chemistry its name: polyisocyanates and polyols form polyurethanes. 9/18/2018

Intermolecular Bonds in Polymers 9/18/2018

The more nucleophilic primary and secondary amines react much more vigorously with isocyanates. In this reaction, ureas are formed (11). 9/18/2018

Important Building Blocks for Polyurethanes- Isocyanates MDI or aromatic polyisocyanate O C N C H N C O 2 C H 3 C H 3 N C O O C N N C O TDI-80 N C O 2 % 8 % H12MDI O C N C H N C O 2 HDI 9/18/2018 O C N ( C H ) N C O 2 6

Polyols

Synthetic Scheme of Polyurethanes 9/18/2018

Typical Chain-extenders

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Polyurethane Structural Model 9/18/2018

Schematic Model Domain Sturcture 9/18/2018

Hard Segment Interactions affect Mechanical Performance 9/18/2018

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Effect of Polyurethane MW on Mechanical Properties 9/18/2018