Chapter 4- Polymer Structures Chapter 4- Polymer Structures ...

Chapter 4- Polymer Structures

Chapter 4- Polymer Structures ISSUES TO ADDRESS... What are the basic • Classification? • Monomers and chemical groups? • Nomenclature? • Polymerization methods? • Molecular Weight and Degree of Polymerization? • Molecular Structures? • Crystallinity? • Microstructural features?

TEM of spherulite structure in natural rubber(x30,000). • Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially.

MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08


Polymer Microstructure

©D.D. Johnson 2004, 2006, 2007-08


• Polymer = many mers • Covalent chain configurations and strength: More rigid

Van der Waals, H Adapted from Fig. 14.2, Callister 6e.

Polyethylene perspective of molecule Direction of increasing strength Adapted from Fig. 14.7, Callister 6e.

A zig-zag backbone structure with covalent bonds MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08


©D.D. Johnson 2004, 2006, 2007-08

1

Common Examples

Common Classification

- Textile fibers: polyester, nylon…

• Thermoplastics: polymers that flow more easily when squeezed, pushed, stretched, etc. by a load (usually at elevated T).

- IC packaging materials.

– Can be reheated to change shape.

- Resists for photolithography/microfabrication.

• Thermosets: polymers that flow and can be molded initially but their shape becomes set upon curing.

- Plastic bottles (polyethylene plastics).

– Reheating will result in irreversible change or decomposition.

- Adhesives and epoxy.

• Other ways to classify polymers. – By chemical functionality (e.g. polyacrylates, polyamides, polyethers, polyeurethanes…). – Vinyl vs. non-vinyl polymers. – By polymerization methods (radical, anionic, cationic…). – Etc…

- High-strength/light-weight fibers: polyamides, polyurethanes, Kevlar… - Biopolymers: DNA, proteins, cellulose… MatSE 280: Introduction to Engineering Materials


©D.D. Johnson 2004, 2006, 2007-08

Common Chemical Functional Groups H

Ethylene (ethene)

Methyl alcohols

C C H

H

H

Propylene (propene)

Common Hydrocarbon Monomers Alcohols

H

©D.D. Johnson 2004, 2006, 2007-08

H

=

C C H

H

Ethers

Dimethyl Ether

Acids

Acetic acid

C H H

1-butene 2-butene trans

cis

Aldehydes Acetylene (ethyne) Saturated hydrocarbons (loose H to add atoms) MatSE 280: Introduction to Engineering Materials

Unsaturated hydrocarbons (double and triple bonds) ©D.D. Johnson 2004, 2006, 2007-08

Formaldehyde

H C C H

Aromatic hydrocarbons MatSE 280: Introduction to Engineering Materials

Phenol ©D.D. Johnson 2004, 2006, 2007-08

2

Nomenclature

Some Common Polymers

Monomer-based naming: poly________

Common backbone with substitutions Polyacrylonitrile (PAN)

H

H

C

C

H

C

Monomer name goes here

e.g. ethylene -> polyethylene

N

Vinyl polymers (one or more H’s of ethylene can be substituted) H

H C C

H

X

H

H

C

C

H

X

if monomer name contains more than one word: poly(_____ ____) Monomer name in parentheses

e.g. acrylic acid -> poly(acrylic acid) Note: this may lead to polymers with different names but same structure. H H H H

…

C C C C

H H H H

…

…

H H H H

polyethylene MatSE 280: Introduction to Engineering Materials

polymethylene


©D.D. Johnson 2004, 2006, 2007-08

Polymerization Methods

…

C C C C

H H H H

©D.D. Johnson 2004, 2006, 2007-08

Polymerization Methods A. Free Radical Polymerization

A. Free Radical Polymerization 1. Initiation H

R

H

R

C C

Free radical initiator (unpaired electron)

H

H

2. Propagation

H

H

H

C

C

H

monomer

Radical transferred

R

H

H

C

C

H

H

H

H

H

R

C C H

H

H C C

H

H

H

H

C

C

C

C

H

H

H

H

H

H

R

H

H

H

H

H

H

C

C

C

C

C

C

H

H

H

H

H

H

H R

H C

R H C

sp2 carbons

C

C

H

H σ bonds π bond


H

H

sp3 carbon

©D.D. Johnson 2004, 2006, 2007-08

H

R

H

H C

H

H C

H H

H

C

C

Both carbon atoms will change from sp 2 to sp 3.

H


©D.D. Johnson 2004, 2006, 2007-08

3

Polymerization Methods

Polymerization Methods Loses water (condensation)

B. Stepwise polymerization A. Free Radical Polymerization 3. Termination

O H2N

R

H

H

C

C

H

H

+

R

R

H

H

C

C R

H

H

R

C

O

O

+

H2N

OH

R

C

H2N

OH

R

C

N H

R

C

OH

+

Proteins (polypeptides have similar composition)

R

H

H

C

C

H

H

+

R

H

H

C

C

H

H

R

H

H

H

H

C

C

C

C

H

H

H

H

O H N H C C R

R

Various R groups…

∑N j M j

O

H

€

j

∑N j M j =

Total # of polymer chains

j

∑ N j M€2j

∑W j M j Mw =

j

∑W j

=

j

20 + 16 + 10 M monomer = 15.3M monomer 3

∑N j =

Total weight

Weight average € molecular weight:

€ 10 mers

Mj = jmo mass of polymer chain with length j (mo = monomer molecular weight).

∑N j

j

16 mers

Nj = # of polymer chains with length j

j

=

∑N j j

©D.D. Johnson 2004, 2006, 2007-08

H

n

©D.D. Johnson 2004, 2006, 2007-08

mo ∑ N j j

j

Mn = Note:


+ (n-1)

C

Number average molecular weight:

Not only are there different structures (molecular arrangements) …… but there can also be a distribution of molecular weights (i.e. number of monomers per polymer molecule).

This is what is called number average molecular weight.

O R

n


Molecular Weights

Average molecular weight =

H N

Anionic polymerization, cationic polymerization, coordination polymerization…

©D.D. Johnson 2004, 2006, 2007-08

20 mers

H

C. Other methods

Intentional or unintentional molecules/impurities can also terminate.


O

H

O

In general:

€

j

W j = N jM j

∑N j M j j

+1 ∑ N j M αj €

M=

j

∑ N j M αj

If α = 0 then

Mn

If α = 1 then Mw

j


€©D.D. Johnson 2004, 2006, 2007-08 €

€

4

Molecular Weights

Molecular Weight: Different Notations In Callister Textbook

In Lecture Notes

Mn = ∑ x i Mi

∑N j M j Mn =

j

i

∑N j

Ni xi = ∑N j

j

∑ N j M 2j €

Mw =

j

€

j

∑N j M j

Why do we care about weight average MW? -some properties are dependent on MW (larger MW polymer chains can contribute to overall properties more than smaller ones).

Ni M i wi = ∑N j M j j

Mw = ∑w i Mi

€

€

j


Distribution of polymer weights

i

©D.D. Johnson 2004, 2006, 2007-08

Examples – Light scattering: larger molecules scatter more light than smaller ones. Infrared absorption properties: larger molecules have more side groups and light absorption (due to vibrational modes of side groups) varies linearly with number of side groups. MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08

€

€

Example 1

Polydispersity and Degree of Polymerization Polydispersity:

Mw ≥1 Mn

Compute the number-average degree of polymerization for polypropylene, given that the number-average molecular weight is 1,000,000 g/mol.

When polydispersity = 1, system is monodisperse.

€

Degree of Polymerization:

Mer molecular weight of PP is

Number avg degree of polymerization

Weight avg degree of polymerization

€ MatSE 280: Introduction to Engineering Materials

€

C3H6

What is “mer” of PP?

nn =

Mn mo

M nw = w mo

©D.D. Johnson 2004, 2006, 2007-08

mo=3AC+6AH =3(12.01 g/mol)+6(1.008 g/mol) = 42.08 g/mol

Number avg degree of polymerization

nn =

Mn 106 g / mol = = 23,700 mo 42.08g / mol


©D.D. Johnson 2004, 2006, 2007-08

€

5

Example 2 (a, b, and c)

Example 2 (cont.)

A. Calculate the number and weight average degrees of polymerization and polydispersity for a polymer sample with the following distribution. Avg # of monomers/chain 10 100 500 1000 5000 50,000

nn =

=

j

j

=

j

j

∑ jN ∑N j

j

Relative abundance 5 25 50 30 10 5

Mw if monomer is methylmethacrylate (5C, 2O, and 8H) So m 0= 5(12)+2(16)+8(1)= 100 g/mol

j

2

o

j

j

j

Polydispersity:

2

∑ ( jm ) N ∑ j N = ∑ N ( jm ) ∑ jN j

j

o

j

j

Note: m 0 cancels in all these!

j

©D.D. Johnson 2004, 2006, 2007-08

€ MatSE 280: Introduction to Engineering Materials

Example 2 (cont.) C. If we add polymer chains with avg # of monomers = 10 such that their relative abundance changes from 5 to 10, what are the new number and weight average degrees of polymerization and polydispersity? nn =

Mn = mo =

nw =

∑ jN ∑N j

j

j

Mw 3,580,000 = ~ 12.52 Mn 286,040

€

5 *10 2 + 25 *100 2 + 50 * 500 2 + 30 *1000 2 + 10 * 5000 2 + 5 * 50000 2 = = 35, 800 5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000 MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08

Sequence isomerism For an asymmetric monomer T

Add 5 more monomers of length 10 ….

H

+

T

H

j

10 * 10 + 25 * 100 + 50 * 500 + 30 * 1000 + 10 * 5000 + 5 * 50000 = 2750 10 + 25 + 50 + 30 + 10 + 5

e.g. poly(vinyl fluoride):

2 Mw ∑ j j N j = = 35,800 mo ∑ j jN j

Note: significant change in number average (3.8 %) but no change in weight average!

M w 3, 580, 000 = ~ 13 Mn 275000


©D.D. Johnson 2004, 2006, 2007-08

H

T

H

T

H

H

T

H

T

T

H

e.g. PMMA

F

H

H

F

H

H

H

C

C

C

C C

C

C

C

H

H3C H3C H3C O O O O O O O C H C H C H C

H

H

H

F H

H

H

F

C

C

C

C C

C

H

CH3 H

CH3H

CH3 H

T to T H to H

Polydispersity:

T

H

H to T

€

CH3 | -CH2-C| CO2CH3

Mn = nnmo = 2860.4(100g / mol ) = 286,040g / mol Mw = nw mo = 35,800(100g / mol ) = 3,580,000g / mol

j

5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000 = 2860.4 5 + 25 + 50 + 30 + 10 + 5

Mw 1 = mo mo

nw =

∑ jN ∑N

M n m0 = mo m0

B. If the polymer is PMMA, calculate number and weight average molecular weights.

Random arrangement


H3C

O

H to T

H to T

C

C CH3

H to T

Exclusive H to T arrangement (Why?) ©D.D. Johnson 2004, 2006, 2007-08

6

Polymer Molecular Configurations • Regularity and symmetry of side groups affect properties

Polymer Geometrical Isomerism • Regularity and symmetry of side groups affect properties

Can it crystallize? Melting T?

Polymerize

H

H

• Stereoisomerism: (can add geometric isomerism too) Syndiotactic Alternating sides Atactic Randomly placed

- Conversion from one stereoisomerism to another is not possible by simple rotation about single chain bond; bonds must be severed first, then reformed!

-Conversion from one isomerism to another is not possible by simple rotation about chain bond because double-bond is too rigid! -See Figure 4.8 for taxonomy of polymer structures MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08

Polymer Structural Isomerism 2 1

H2C

C

C H

• Covalent chain configurations and strength:

4

CH3

©D.D. Johnson 2004, 2006, 2007-08


Some polymers contain monomers with more than 1 reactive site e.g. isoprene

trans-structure

with R= CH3 to form rubber Cis-polyisoprene trans-polyisoprene

Isotactic On one side


cis-structure

More rigid

Van der Waals, H

CH2 3

trans-isoprene

Direction of increasing strength trans-1,4-polyisoprene

CH3 C H2

C

C H

trans-1,2-polyisoprene

H2 C

H2 C n

H2 C H C

n

C H3C

Adapted from Fig. 14.7, Callister 6e.

3,4-polyisoprene

CH H2C

C H2C

Short branching n

CH3

Long branching

Note: there are also cis-1,4- and cis-1,2-polyisoprene MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08


Star branching

Dendrimers

©D.D. Johnson 2004, 2006, 2007-08

7

CoPolymers

Molecular Structure

• Random, Alternating, Blocked, and Grafted

How do crosslinking and branching occur in polymerization? 1. Start with or add in monomers that have more than 2 sites that bond with other monomers, e.g. crosslinking polystyrene with divinyl benzene

• Synthetic rubbers are often copolymers.

…

e.g., automobile tires (SBR)

stryene

…

polystyrene

Styrene-Butadiene Rubber random polymer …

Control degree of + crosslinking by styrene-divinyl styrene benzene ratio divinyl benzene

…

crosslinked polystyrene

Monomers with trifunctional groups lead to network polymers. MatSE 280: Introduction to Engineering Materials


©D.D. Johnson 2004, 2006, 2007-08

Molecular Structure

Example 3 Nitrile rubber copolymer, co-poly(acrylonitrile-butadiene), has

Branching in polyethylene (back-biting) H2C CH2

R

H2 C

C H2

H2 C

Same as

C H2

H2 C

Mn = 106,740g / mol C H

H

R

CH2

Radical moves to a different carbon

C

CH2

(H transfer)

C H H2

€

H

H H

nn = 2000

Calculate the ratio of (# of acrylonitrile) to (# of butadiene).

H

H C

©D.D. Johnson 2004, 2006, 2007-08

C

H

CH2

C

R

C H H2

3 C = 3 x 12.01 g/mol 3 H = 3 x 1.008 g/mol 1 N = 1 x 14.007 g/mol

€

4 C = 4 x 12.01 g/mol 6 H = 6 x 1.008 g/mol m 0= 54.09 g/mol

m 0= 53.06 g/mol

CH2

1,4-addition product

We need to use an avg. monomer MW:

Polymerization continues from this carbon

mo =

Mn 106,740 = = 53.57g / mol nn 2000

mo = f1m 1 + f2m 2 = f1(m 1 − m 2 ) + m 2 Process is difficult to avoid and leads to (highly branched) low-density PE . When there is small degree of branching you get high-density PE.


f1 =

€ m 0 − m 2 53.37 − 54.09 = = 0.7 € − 54.09 m 1 − m 2 53.06


©D.D. Johnson 2004, 2006, 2007-08

€

€

f2 = 1− f1 = 0.3

f2 0.7 = →7 :3 f1 0.3

©D.D. Johnson 2004, 2006, 2007-08

€

8

Vulcanization

Molecular Weight and Crystallinity

See also sect. in Chpt. 8

• Crosslinking in elastomers is called vulcanization, and is achieved by irreversible chemical reaction, usually requiring high temperatures.

• Molecular weight, Mw: Mass of a mole of chains.

• Sulfur compounds are added to form chains that bond adjacent polymer backbone chains and crosslinks them. • Unvulcnaized rubber is soft and tacky an poorly resistant to wear.

• Tensile strength (TS):

e.g., cis-isoprene

Single bonds

--often increases with M w. --Why? Longer chains are entangled (anchored) better.

Stress-strain curves

• % Crystallinity: % of material that is crystalline. Double bonds

+ (m+n) S

--TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.

(S)m (S)n

crystalline region amorphous region

Adapted from Fig. 14.11, Callister 6e. MatSE 280: Introduction to Engineering Materials


©D.D. Johnson 2004, 2006, 2007-08

Polymer Crystallinity polyethylene

Volume fraction of crystalline component.

• Some are amorphous. • Some are partially crystalline (semi-crystalline). • Why is it difficult to have a 100% crystalline polymer?

%crystallinity =

ρc ( ρ s − ρa ) × 100% ρ s ( ρc − ρa )

ρs = density of specimen in question ρa = density of totally amorphous polymer ρc = density of totally crystalline polymer

%crystallinity =

€

Mcrystalline Mtotal

ρ V ρ × 100% = c c × 100% = c fc × 100% ρsVs ρs

Mtotal = Mcrystalline + Mamophous

©D.D. Johnson 2004, 2006, 2007-08

Using definition of volume fractions:

Ms = Mc + Ma ρsVs = ρcVc + ρaVa V V ρs = ρc c + ρa a Vs Vs

V fc = c Vs

V fa = a Vs

= ρc fc + ρa fa = ρc fc + ρa (1− fc ) = fc ( ρc − ρa ) + ρa €

€ ρ − ρa fc = s ρc − ρa

€ Substituting in f c into the original definition:


©D.D. Johnson 2004, 2006, 2007-08


ρ ( ρ − ρa ) %crystallinity = c s × 100% ρ s ( ρc − ρa ) € ©D.D. Johnson 2004, 2006, 2007-08

9

Polymer Crystallinity Degree of crystallinity depends on processing conditions (e.g. cooling rate) and chain configuration.

Semi-Crystalline Polymers Fringed micelle model: crystalline region embedded in amorphous region. A single chain of polymer may pass through several crystalline regions as well as intervening amorphous regions.

Cooling rate: during crystallization upon cooling through MP, polymers become highly viscous. Requires sufficient time for random & entangled chains to become ordered in viscous liquid. Chemical groups and chain configuration: More Crystalline

Less Crystalline

Smaller/simper side groups

Larger/complex side groups

Linear

ρ − ρa fc = s ρc − ρa

Highly branched

Crystalline volume fractions Important

Crosslinked, network Isotactic or syndiotactic

Random


©D.D. Johnson 2004, 2006, 2007-08

Semi-Crystalline Polymers Chain-folded model: regularly shaped platelets (~10 – 20 nm thick) sometimes forming multilayers. Average chain length

€


©D.D. Johnson 2004, 2006, 2007-08

Semi-Crystalline Polymers Spherulites: Spherical shape composed of aggregates of chain-folded crystallites.

>> platelet thickness.

Natural rubber

Cross-polarized light through spherulite structure of PE.


©D.D. Johnson 2004, 2006, 2007-08


©D.D. Johnson 2004, 2006, 2007-08

10

Diblock copolymers

Thermoplastics vs Thermosets • Thermoplastics:

T

--little cross linking --ductile --soften w/heating --polyethylene (#2) polypropylene (#5) polycarbonate polystyrene (#6) Representative polymer-polymer phase behavior with different architectures:


Molecular weight


©D.D. Johnson 2004, 2006, 2007-08

What Are Expected Properties?

• Packing of “spherical” atoms as in ionic and metallic crystals led to crystalline structures.

• Would you expect melting of nylon 6,6 to be lower than PE ? O H  O H    ||  |  || |   − N − C  − N −C − C  − N −C −     | | | | | H  H H H  6 H 4

H H −C− C− H H

nylon 6,6 • How polymers pack depend on many factors: • long or short, e.g. long (-CH 2-)n. • stiff or flexible, e.g. bendy C-C sp 3. • smooth or lumpy, e.g., HDPE. • regular or random • single or branched • slippery or sticky, e.g. C-H covalent (nonpolar) joined via vdW.

+ +

+

O H  O H    ||  |  || |     − N − C  − N −C − C  − N −C −     | | | | | H  H H H  6 H 4

€

a) b)

+

polyethylene

+

+ bonds + Waals Van der

+

+ + Hydrogen bonds

€

Analogy: Consider dried (uncooked) spaghetti (crystalline) vs. cooked and buttered spaghetti (amorphous). • pile of long “stiff” spaghetti forms a random arrangement. • cut into short pieces and they align easily.

©D.D. Johnson 2004, 2006, 2007-08

Tg

Tg: from rubbery to rigid as T lowers

Packing of Polymers


Tm

--large cross linking (10 to 50% of mers) Adapted from Fig. 15.18, Callister 6e. --hard and brittle Tm: melting over wide range of T --do NOT soften w/heating depends upon history of sample --vulcanized rubber, epoxies, consequence of lamellar structure thicker lamellae, higher T m. polyester resin, phenolic resin

©D.D. Johnson 2004, 2006, 2007-08

Candle wax more crystalline than PE, even though same chemical nature.

Callister, rubber Fig. 16.9 tough plastic

partially crystalline solid

crystalline solid

• Thermosets:

A) Phase separation with mixed LINEAR homopolymers. B) Mixed LINEAR homopolymers and DIBLOCK copolymer gives surfactant-like stabilized state. C) Covalent bond between blocks in DIBLOCK copolymer give microphase segregation.

F. Bates, Science 1991.

viscous liquid

mobile liquid

€

+

+

H

H

−C− C− H H

€ cohesion in Nylon vs PE? What is the source of intermolecular How does the source of linking affect temperature?

With H-bonds vs vdW bonds, nylon is expected to have (and does) higher melting T. MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08

11



Which polymer more likely to crystallize? Can it be decided?

Which polymer more likely to crystallize? Can it be decided?

Linear syndiotactic polyvinyl chloride

Networked Phenol-Formaldehyde (Bakelite)

Linear isotactic polystyrene

Linear and highly crosslink cis-isoprene

+

H

+ H 20 • For linear polymers, crystallization is more easily accomplished as chain alignment is not prevented. • Crystallization is not favored for polymers that are composed of chemically complex mer structures, e.g. polyisoprene . • Linear and syndiotactic polyvinyl chloride is more likely to crystallize. • The phenyl side-group for PS is bulkier than the Cl side-group for PVC. • Generally, syndiotactic and isotactic isomers are equally likely to crystallize.


©D.D. Johnson 2004, 2006, 2007-08

What Are Expected Properties? Which polymer more likely to crystallize? Can it be decided? alternating Poly(Polystyrene-Ethylene) Copolymer

• Networked and highly crosslinked structures are near impossible to reorient to favorable alignment.

• Not possible to decide which might crystallize. Both not likely to do so.


©D.D. Johnson 2004, 2006, 2007-08

Detergents • Soap is a detergent based on animal or vegetable product, some contain petrochemicals

water

random poly(vinyl chloride-tetra-fluoroethylne) copolymer

detergent grease

• What properties of soap molecules do you need to remove grease? • “green” end must be “hydrophilic”. Why? • Opposite end must be hydrocarbon. Why?

• Alternating co-polymer more likely to crystallize than random ones, as they are always more easily crystallized as the chains can align more easily.


©D.D. Johnson 2004, 2006, 2007-08

Water must be like oxygen (hoard electrons and promote H-bonding)

e.g., oxy-clean® MatSE 280: Introduction to Engineering Materials

grease

©D.D. Johnson 2004, 2006, 2007-08

12

Simple polymer: Elmers glue + Borax  SLIME! Chemistry

Elmer’s glue is similar to “poly (vinyl alcohol)” with formula: OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

this is a SHORT, n=15 chain of poly(vinyl alcohol)

Simple polymer: Elmer’s glue + Borax  SLIME! Hydrolyzed molecule acts in a condensation reaction with PVA, crosslinking it. B(OH) 3 + 2H 2O  B(OH) 4- + H 3O+ pH=9.2



Borax is sodium tetraborate decahydrate (B4Na 2O7 • 10 H 2O). The borax actually dissolves to form boric acid, B(OH) 3. This boric acid-borate solution is a buffer with a pH of about 9 (basic). Boric acid will accept a hydroxide OH- from water.

B(OH) 3 + 2H 2O  B(OH) 4- + H 3O+ pH=9.2



Hydrolyzed molecule acts in a condensation reaction with PVA, crosslinking it. MatSE 280: Introduction to Engineering Materials

Crosslinked

©D.D. Johnson 2004, 2006, 2007-08

Range of Bonding and Elastic Properties

Crosslinking ties chains via weak non-covalent (hydrogen) bonds, so it flows slowly. MatSE 280: Introduction to Engineering Materials

©D.D. Johnson 2004, 2006, 2007-08

Summary • Polymers are part crystalline and part amorphous.

Is “slime” a thermoset or thermoplastic, or neither?

Thermoset bonding • Covalent bonds form crosslinks

Slime?

• H-bonds form crosslinks

Thermoplastic bonding • Induced dipolar bonds form crosslinks

Stiffness increases

• The more crosslinking the stiffer the polymer. And, networked polymers are like heavily crosslinked ones. • Many long-chained polymers crystallize with a Spherulite microstructure - radial crystallites separated by amorphous regions. • Optical properties: crystalline -> scatter light (Bragg) amorphous -> transparent. Most covalent molecules absorb light outside visible spectrum , e.g. PMMA (lucite) is a high clarity tranparent materials.

Where is nylon? MatSE 280: Introduction to Engineering Materials

• The more “lumpy” and branched the polymer, the less dense and less crystalline.

©D.D. Johnson 2004, 2006, 2007-08


©D.D. Johnson 2004, 2006, 2007-08

13

Chapter 4- Polymer Structures Chapter 4- Polymer Structures ...

Chapter 4- Polymer Structures Chapter 4- Polymer Structures ...

Suggest Documents

Chapter 14: Polymer Structures

Chapter Outline: Polymer Structures Hydrocarbon and polymer ...

Chapter 4 BUILDINGS, STRUCTURES, AND ...

Chapter 4 BUILDINGS, STRUCTURES, AND ...

Chapter 4 BUILDINGS, STRUCTURES, AND NONSTRUCTURAL ...

Chapter 4:Chapter 4 - MAFIADOC.COM

Chapter 4:Chapter 4

Chapter 19 Data Structures

Chapter 1: Aircraft Structures

Chapter 1: Aircraft Structures

CHAPTER 4

chapter 4

Chapter 4

Chapter 4

Chapter 4

chapter 4

Chapter 4

Chapter 4

Chapter 4

chapter 4

CHAPTER 4

Chapter |4

chapter 4

Chapter 4