Elastomers 02/13/20 1 Elastomers Definition- materials capable of

Elastomers 02/13/20 1 Elastomers  Definition- materials capable of

Elastomers 02/13/20 1 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 02/13/20 2

Types Natural and synthetic rubber-Thiokol, Buna, Neoprene Polyurethanes Silicone-polysiloxanes Natural proteins-elastin 02/13/20

3 Mechanical Properties 10 Fibre Rigid Plastic 5

10 4 Stress Flexible Plastic N/cm2 10 B

Elastomer A 0 02/13/20 1 Strain L/ L 5 10

6 3 2 Elastomers have properties that can be explained by a model that shares characteristics of thermosets and thermoplastics -have all of the domains shown below 02/13/20 5

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 02/13/20 6 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). 02/13/20 7 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. 02/13/20 8 Intermolecular Bonds in Polymers

02/13/20 9 The more nucleophilic primary and secondary amines react much more vigorously with isocyanates. In this reaction, ureas are formed (11). 02/13/20 10

Important Building Blocks for Polyurethanes- Isocyanates OCN CH2 MDI or aromatic polyisocyanate NCO CH3 NCO OCN

CH3 NCO TDI-80 NCO OCN 02/13/20 20%

80% CH2 OCN(CH2)6NCO NCO H12MDI HDI 11

Polyols HO(CH2CH2CH2CH2O)nH PTMO HO(CH2CH2O)nH PEO CH3 HO(CHCH2O)nH CH3

HO(CH2)x Si O CH3 O HO 02/13/20 R OC PPG

CH3 Si (CH2)xOH y CH3 O (CH2)x CO y R OH PSX

Synthetic Scheme of Polyurethanes 02/13/20 13 Typical Chain-extenders HOCH2CH2OH CH2 OH

HOCH2CHOH CH OH CH3 CH2 OH HO(CH2)4OH HO(CH2)6OH H2N(CH2)2-6NH2 02/13/20

02/13/20 15 Polyurethane Structural Model 02/13/20 16 Schematic Model Domain Sturcture

02/13/20 17 Hard Segment Interactions affect Mechanical Performance 02/13/20 18 02/13/20

19 02/13/20 20 02/13/20 21 02/13/20 22

Effect of Polyurethane MW on Mechanical Properties 02/13/20 23

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