Polymer Synthesis CHEM 421 Poly(arylene ether)s Characteristics –Thermal stability –Hydrolytic stability –Wide range of properties PEEK PES

Polymer SynthesisCHEM 421

Poly(arylene ether)s

O O C

O

n

C O S

O

nO

CH3

CH3

O

• Characteristics

–Thermal stability

–Hydrolytic stability

–Wide range of properties

PEEK

PES


Nucleophilic Aromatic Substitution

C O S

O

nO

CH3

CH3

O PES

C OH S

O

O

CH3

CH3

HO Cl Cl

Weak base (K2CO3)Polar, aprotic solvent (NMP)Azeotropic agent (toluene)


Nucleophilic Aromatic Substitution:Mechanism

X

+ Y

X

Y

X

Y

X

Y

X

YY

+ X

Meisenheimer Complex (an intermediate)

F > NO2 > OTs > SOPh > Cl, Br, I

- Reverse order for aliphatic substitution- NO2 never lost in aliphatic systems- In aliphatic SN2 displacement

R-I > R-Br > R-Cl > R-FFirst step is R.D.S and favored by more electron withdrawing group



• Important features– Activating group and leaving group combinations

Cl

Cl S

O

O

CH3

Cl

Cl S

O

O

CH3

NaOH

350 C

NaOH

150 C



• Important features - Conversion to phenate

PESC O S

O

nO

CH3

CH3

O

C OH S

O

O

CH3

CH3

HO Cl Cl

Weak base (K2CO3)Polar, aprotic solvent (NMP)Azeotropic agent (toluene)

OH + K2CO32

O K + KHCO3+ OH

O K O K + H2CO3+ H2O + CO2



HO S

O

O

• Important features– Conversion to phenate

– Dehydrating agent

» Upset stoichiometry

– Solvent

H2O HOCl S

O

O



• Important features– Activating group and leaving group combinations

X S

O

O

X C

O

Cl S

O

O

F C

O

Cl S

O

O

F C

O



HO OH C

O

O O C

O

n

F F

Ph-SO2-Ph335 CK2CO32-3 h

• $25 lb

• Tg = 144 °C Tm = 335 °C

PEEK



PEK

C

O

OCO

n

PEKK

O C

O

n


Composite Materials

• Composites have been used in airplanessince the 1950s

• Critical applications of composites startedin the early 1980s

• Composite materials have some fundamentallydifferent characteristics from metals

• A composite is defined as two or more materialsthat retain their identities in the combinationwhile yielding properties superior to either

• Common composite types include fibrous, laminate and particulate

– They can employ glass, aramid or carbon fibers

– Various resins are used as the "matrix" bonding individual materials together into the desired form.


Advantages of Composite Construction

• Structural Tailorability– Fibers are able to be oriented in directions that are best for the design.

– Metals have the same properties in all directions.

• Lightweight Strength– The advantage of being lighter than metals is usually misunderstood

– Composites indeed have lower density than most metals

– But for structural stability and with other design reasons, composite airplanes usually weigh the same as metal airplanes

– By using a greater amount of lighter material, structural parts like skins are relatively thicker

– A composite aircraft has the feel of a more sturdy airplane, and also has better dampening (less vibration transmission)


Advantages of Composite Construction

• Better aerodynamics– Composite manufacturing more readily allows complex curved surfaces

with fewer joints, seams and rivets

– Easier to get smooth surfaces for laminar flow designs which contributes to additional speed.

• Stealth Potential– Ability to minimize radar cross section

– Electronic transparency means antennas can be hidden inside for streamlining without loss of reception.

• Simple assembly– Aircraft assembly simplified, since many of the fasteners and small

parts can be replaced with larger, more integrated structures.


General Beliefs…

• Composites are thought to be corrosion and fatigue resistant

– “…Composites are not subject to corrosion from natural or man made elements…”

– “…Certainly with composites, fatigue is less of an issue than with metals"

Scott W. BeckwithTechnical directorSociety for the Advancement of Material &

Process Engineering


General Knowledge about Composites

• Things that mitigate the ESC problem include:–Crystallinity–Filled systems–Crosslinking


Example from the Scientific Literature

• “Environmental Stress Cracking and Solvent Effects in High-Performance Polymeric Composites”

Dillard, Kander, et. alComposite MaterialsASTM, 1996

• ESC of carbon fiber-reinforced thermoplastic and thermoset composite systems were investigated


Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset systemGraphite fiber reinforced, semicrystalline thermoplastic compositeGraphite fiber reinforced, amorphous thermoplastic composite

Three-point Bending Tests

One hour exposure at room temperature,not under any load…


Fracture Mode – Unexposed Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset system

• Matrix enveloping the fibers

• Failure primarily in the matrix (good thing)

• Ductile fracture


Fracture Mode – Solvent Exposed Graphite fiber reinforced, thermoplastic toughened cyanate ester thermoset system

• One hour exposure to solvent

– at room temperature

– not under load…

• Fibers relatively clean

• Brittle, interfacial failure

• Ductile fracture

Polymer SynthesisCHEM 421Conclusions

• “Environmental Stress Cracking and Solvent Effects in High-Performance Polymeric Composites”

• 10 – 30% drop in bending strength under “safe” experimental conditions

• Differences in failure modes upon solvent exposure

• Propensity for interfacial failure


Research Questions

• Are the long-term prospects clear for structural, load-bearing composites immersed in jet fuel in the F-22, JSF and Comanche?

• What are the most appropriate methods for long-term aging studies of environmental stress cracking of composites for such applications?

• Are there effective, easily implementable methods for mitigating solvent-induced ESC in composites?

Documents

Polymer Synthesis CHEM 421 Poly(arylene ether)s Characteristics –Thermal stability –Hydrolytic stability –Wide range of properties PEEK PES