every types of elastomer include this slide

1. 1
Classes of Polymeric Materials
Elastomers
Professor Joe Greene
CSU, CHICO

2. 2
Elastomers
• Elastomers are rubber like polymers that are
thermoset or thermoplastic
– butyl rubber: natural rubber
– thermoset: polyurethane, silicone
– thermoplastic: thermoplastic urethanes (TPU),
thermoplastic elastomers (TPE), thermoplastic olefins
(TPO), thermoplastic rubbers (TPR)
• Elastomers exhibit more elastic properties versus
plastics which plastically deform and have a lower
elastic limit.
• Rubbers have the distinction of being stretched
200% and returned to original shape. Elastic limit is

3. 3
Rubbers
• Rubbers have the distinction of being stretched 200%
and returned to original shape. Elastic limit is 200%
• Natural rubber (isoprene) is produced from gum resin
of certain trees and plants that grow in southeast Asia,
Ceylon, Liberia, and the Congo.
– The sap is an emulsion containing 40% water & 60% rubber particles
• Vulcanization occurs with the addition of sulfur (4%).
– Sulfur produces cross-links to make the rubber stiffer and harder.
– The cross-linkages reduce the slippage between chains and results in
higher elasticity.
– Some of the double covalent bonds between molecules are broken,
allowing the sulfur atoms to form cross-links.
– Soft rubber has 4% sulfur and is 10% cross-linked.
– Hard rubber (ebonite) has 45% sulfur and is highly cross-linked.

4. 4
Rubber Additives and Modifiers
• Fillers can comprise half of the volume of the rubber
– Silica and carbon black.
– Reduce cost of material.
– Increase tensile strength and modulus.
– Improve abrasion resistance.
– Improve tear resistance.
– Improve resistance to light and weathering.
– Example,
• Tires produced from Latex contains 30% carbon black which improves the
body and abrasion resistance in tires.
• Additives
– Antioxidants, antiozonants, oil extenders to reduce cost
and soften rubber, fillers, reinforcement

5. 5
Vulcanizable Elastomeric Compounds
• Rubbers are compounded into practical elastomers
– The rubber (elastomer) is the major component and other
components are given as weight per hundred weight rubber (phr)
• Sulfur is added in less than 10 phr
• Accelerators and activators with the sulfur
– hexamethylene tetramine (HMTA)
– zinc oxide as activators
• Protective agents are used to suppress the effects of oxygen and
ozone
– phenyl betabaphthylamine and alkyl paraphenylene diamine (APPD)
• Reinforcing filler
– carbon black
– silica when light colors are required
– calcium carbonate, clay, kaoilin
• Processing aids which reduce stiffness and cost
– Plasticizers, lubricants, mineral oils, paraffin waxes,

6. 6
Vulcanizable Rubber
• Typical tire tread
– Natural rubber smoked sheet (100),
– sulfur (2.5) sulfenamide (0.5), MBTS (0.1), strearic acid (3), zinc
oxide (3), PNBA (2), HAF carbon black (45), and mineral oil (3)
• Typical shoe sole compound
– SBR (styrene-butadiene-rubber) (100) and clay (90)
• Typical electrical cable cover
– polychloroprene (100), kaolin (120), FEF carbon black (15) and
mineral oil (12), vulcanization agent

7. 7
Synthetic Rubber• Reactive system elastomers
– Low molecular weight monomers are reacted in a polymerization
step with very little cross-linking.
– Reaction is triggered by heat, catalyst, and mixing
• Urethanes processed with Reaction Injection Molding (RIM)
• Silicones processed with injection molding or extrusion
• Thermoplastic Elastomers
– Processing involves melting of polymers, not thermoset reaction
– Processed by injection molding, extrusion, blow molding, film
blowing, or rotational molding.
• Injection molded soles for footwear
– Advantages of thermoplastic elastomers
• Less expensive due to fast cycle times
• More complex designs are possible
• Wider range of properties due to copolymerization
– Disadvantage of thermoplastic elastomers
• Higher creep

8. 8
Thermoplastic Elastomers
• Four types of elastomers
– Olefinics and Styrenics
– Polyurethanes and Polyesters
• Olefinics (TPOs are used for bumper covers on cars)
– Produced by
• Blending copolymers of ethylene and propylene (EPR) or ter polymer of
ethylene-propylene diene (EPDM) with
• PP in ratios that determine the stiffness of the elastomer
– A 80/20 EPDM/PP ratio gives a soft elastomer (TPO)
• Styrenic thermoplastic elastomers (STPE)
– Long triblock copolymer molecules with
• an elastomeric central block (butadiene, isoprene, ethylene-butene, etc.) and
• end blocks (styrene, etc.) which form hard segments
– Other elastomers have varying amounts of soft and hard blocks

9. 9
Thermoplastic Elastomers
• Polyurethanes
– Have a hard block segment and soft block segment
• Soft block corresponds to polyol involved in polymerization in ether based
• Hard blocks involve the isocyanates and chain extenders
• Polyesters are etheresters or copolyester thermoplastic
elastomer
– Soft blocks contain ether groups are amorpous and flexible
– Hard blocks can consist of polybutylene terephthalate (PBT)
• Polyertheramide or polyetherblockamide elastomer
– Hard blocks consits of a crystallizing polyamide
Soft Hard
Hard
Hard
Soft Soft

10. 10
Commercial Elastomers
• Diene C=C double bonds and Related Elastomers
– Polyisoprene- (C5H8)20,000
• Basic structure of natural rubber
• Can be produced as a synthetic polymer
• Capable of very slow crystallization
• Tm = 28°C, Tg = -70°C for cis polyisoprene
• Tm = 68°C, Tg = -70°C for trans polyisoprene
– Trans is major component of gutta percha, the first plastic
– Natural rubber was first crosslinked into highly elastic network by
Charles Goodyear (vulcanization with sulfur in 1837)
• Sulfur crosslinked with the unsaturations C=C
– Natural rubber in unfilled form is widely used for products with
• very large elastic deformations or very high resilience,
• resistance to cold flow (low compression set) and
• resistance to abrasion, wear, and fatigue.
– Natural rubber does not have good intrinsic resistance to sunlight,
oxygen, ozone, heat aging, oils, or fuels.
C
H
C
C
H
H3HH
H
C C ][
C
H
C
H
HH
H
C C ][
CH3
Cis
Trans

11. 11
Commercial Elastomers
• Polybutadiene
– Basis for synthetic rubber as a major component in copolymers
Styrene-Butadiene Rubber (SBR, NBR) or in
– Blends with other rubbers (NR, SBR)
– Can improve low-temperature properties, resilence, and abrasion
or wear resistance
• Tg = -50°C
• Polychloroprene
– Polychloroprene or neoprene was the very first synthetic rubber
– Due to polar nature of molecule from Cl atom it has very good
resistance to oils and is flame resistant (Cl gas coats surface)
– Used for fuel lines, hoses, gaskets, cable covers, protective boots,
bridge pads, roofing materials, fabric coatings, and adhesives
– Tg = -65°C.
H H
C
H
C
H HH
C C ][
H H
C
H
C
Cl HH
C C ][

12. 12
Commercial Elastomers
• Butyl rubber- addition polymer of isobutylene.
– Copolymer with a few isoprene units, Tg =-65°C
– Contains only a few percent double bonds from isoprene
– Small extent of saturation are used for vulcanization
– Good regularity of the polymer chain makes it possible for the
elastomer to crystallize on stretching
– Soft polymer is usually compounded with carbon black to increase
modulus
• Nitrile rubber
– Copolymer of butadiene and acrylonitrile
– Solvent resistant rubber due to nitrile C:::N
– Irregular chain structure will not crystallize on stretching, like
SBR
– vulcanization is achieved with sulfur like SBR and natural rubber
• Thiokol- ethylene dichloride polymerized with sodium
H H3
C
CH3H
C
C
][

13. 13
Thermoplastic Elastomers
• Thermoplastic Elastomers result from copolymerization of
two or more monomers.
– One monomer is used to provide the hard, crystalline features, whereas
the other monomer produces the soft, amorphous features.
– Combined these form a thermoplastic material that exhibits properties
similar to the hard, vulcanized elastomers.
• Thermoplastic Urethanes (TPU)
– The first Thermoplastic Elastomer (TPE) used for seals gaskets,
etc.
• Other TPEs
– Copolyester for hydraulic hoses, couplings, and cable insulation.
– Styrene copolymers are less expensive than TPU with lower strength
– Styrene-butadiene (SBR) for medical products, tubing, packaging, etc.
– Olefins (TPO) for tubing, seals, gaskets, electrical, and automotive.

14. 14
Thermoplastic Elastomers
• Styrene-butadiene rubber (SBR)
– Developed during WWII
• Germany under the name of BUNA-S.
• North America as GR-S,Government rubber-styrene.
– Random copolymer of butadiene (67-85%) and styrene (15-33%)
– Tg of typical 75/25 blend is –60°C
– Not capable of crystallizing under strain and thus requires
reinforcing filler, carbon black, to get good properties.
– One of the least expensive rubbers and generally processes easily.
– Inferior to natural rubber in mechanical properties
– Superior to natural rubber in wear, heat aging, ozone resistance,
and resistance to oils.
– Applications include tires, footwear, wire, cable insulation,
industrial rubber products, adhesives, paints (latex or emulsion)
• More than half of the world’s synthetic rubber is SBR
• World usage of SBR equals natural rubber
C C
H
H H
n
H H
C
H
C
H HH
C C ][

15. 15
Acrylonitrile-butadiene rubber (NBR)
• Also called Nitrile rubber
– Developed as an oil resistant rubber due to
• the polar C:::N polar bond. Resistant to oils, fuels, and solvents.
– Copolymer of acrylonitrile (20-50%) and butadiene(80-50%)
– Moderate cost and a general purpose rubber.
– Excellent properties for heat aging and abrasion resistance
– Poor properties for ozone and weathering resistance.
– Has high dielectric losses and limited low temperature flexibility
– Applications include fuel and oil tubing; hose, gaskets, and seals; conveyer
belts, print rolls, and pads.
– Carboxylated nitrile rubbers (COX-NBR) has carboxyl side groups
(COOH)which improve
• Abrasion and wear resistance; ozone resistance; and low temperature flexibility
– NBR and PVC for miscible, but distinct polymer blend or polyalloy
• 30% addition of PVC improves ozone and fire resistance
H H
C
H
C
H HH
C C ][C C
H C:::N
H H
n
m

16. 16
Ethylene-propylene rubber (EPR)
• EPR and EPDM
– Form a noncrystallizing copolymer
• with a low Tg.
– The % PP and PE units determines properties
• Tg = -60°C for PE/PP of 67/33 to 50/50
– Unsaturated polymer since PP and PE are saturated
• Resistant to ozone, weathering, and heat aging
• Does not allow for conventional vulcanization
– Terpolymer with addition of small amount of third monomer (Diene D) has
unsaturations referred to as EPDM
• 1,4, hexadiene (HD); 5-ethylidene-2-norbornene (ENB); diclopentadiene (DCPB)
feature unsaturations in a side (pendant) group
• Feature excellent ozone and weathering resistance and good heat aging
– Limitations include poor resistance to oils and fuels, poor adhesion to many
substrates and reinforcements
– Applications include exterior automotive parts (TPO is PP/EPDM), construction
parts, weather strips, wire and cable insulation, hose and belt products, coated
fabrics.
C C
H H
H H
n
C C
H CH3
H H
m
C C
H CH2
H H
mCH
CH
CH3

17. 17
Ethylene Related Elastomers
• Chlorosulfonated Polyethylene (CSPE)
– Moderate random chlorination of PE (24-43%)
– Infrequent chlorosulfonic groups (SO2Cl)
– Sulfur content is 1-1.5%.
– CSPE is noted for excellent weathering resistance
• Good resistance to ozones, heat, chemicals, solvents.
• Good electrical properties, low gas permeability, good adhesion to substrates
– Applications include hose products, roll covers, tank linings, wire and cable
covers, footwear, and building products
• Chlorinated Polyethylene (CPE)
– Moderate random chlorination
• Suppresses crystallinity (rubber)
• Can be crosslinked with peroxides
• Cl range is 36-42% versus 56.8% for PVC
– Properties include good heat, oil, and ozone resistance
– Used as plasticizer for PVC
C C
H H
H H
n
C
Cl
H
m
C
S
H
k
Cl
O O

18. 18
Ethylene Related Elastomers
• Ethylene-vinylacetate Copolymer (EVA)
– Random copolymer of E and VA
• Amorphous and thus elastomeric
• VA range is 40-60%
• Can be crosslinked through organic peroxides
– Properties include
• Good heat, ozone, and weather resistance
• Ethylene-acrylate copolymer (EAR)
– Copolymer of Ethylene and methacrylate
• Contains carboxylic side groups (COOH)
– Properties include
• Excellent resistance to ozone and
• Excellent energy absorbers
– Better than butyl rubbers
C C
H H
H H
n
C C
H O
H H
O=CCH3
m
C C
H H
H H
n
C C
H C
H H
O
OCH3
m

19. 19
FluoroElastomers
• Polyvinylidene fluoride (PVDF)
– Tg = -35°C
• Poly chloro tri fluoro ethylene (PCTFE)
– Tg = 40°C
• Poly hexa fluoro propylene (PHFP)
– Tg = 11°C
• Poly tetra fluoro ethylene (PTFE)
– Tg = - 130°C
• Fluoroelastomers are produced by
– random copolymerization that
– suppresses the crystallinity and
– provides a mechanism for cross linking by terpolymerization
• Monomers include VDF, CTFE, HFP, and TFE
C C
H F
H F
n C C
F Cl
F F
n
C C
F CF3
F F
n
C C
F F
F F
n

20. 20
FluoroElastomers
• Fluoroelastomers are expensive but have outstanding
properties
– Exceptional resistance to chemicals, especially oils, solvents
– High temperature resistance, weathering and ozone resistance.
– Good barrier properties with low permeability to gases and vapors
• Applications
– Mechanical seals, packaging, O-rings, gaskets, diaphrams,
expansion joints, connectors, hose liners, roll covers, wire and
cable insulation.
• Previous fluoroelastomners are referred to as
– Fluorohydrocarbon elastomers since they contain F, H, and C
atoms with O sometimes
• Two other classes of elastomers include fluorinated types
– Fluorosilicone elastomers remain flexible at low temperatures
– Fluorinated polyorganophosphazenes have good fuel resistance

21. 21
Silicone Polymers
• Silicone polymers or polysiloxanes (PDMS)
– Polymeric chains featuring
• Tg = -125°C
• Very stable alternating combination of
• Silicone and oxygen, and a variety of organic side groups attached to Si
– Two methyl, CH3, are very common side group generates
polydimethylsiloxane (PDMS)
• Unmodified PDMS has very flexible chains corresponding to low Tg
• Modified PDMS has substitution of bulky side groups (5-10%)
– Phenylmethlsiloxane or diphenylsiloxane suppress crystallization
• Substituted side groups, e.g., vinyl groups (.5%) featuring double bonds
(unsaturations ) enables crosslinking to form vinylmethylsiloxane (VMS)
• Degree of polymerization, DP, of polysiloxane = 200-1,000 for low
consistency chains to 3,000-10,000 for high consistency resins.
• Mechanism of crosslinking can be from a vinyl unsaturation or reactive end
groups (alkoxy, acetoxy)
Si
CH3
CH3
m
O

22. 22
Silicone Polymers
• Silicone polymers or polysiloxanes (PDMS)
– Properties
• Mediocre tear properties
• High temperature resistance from -90C to 250C.
• Surface properties are characterized by very low surface energy (surface
tension) giving good slip, lubricity, and release properties (antistick) nand
water repellency.
• Excellent adhesion is obtained for curing compounds for caulk.
Si
CH3
CH3
m
O

23. 23
Silicones
• Unmodified PDMS has very flexible chains with a low Tg.
– Regular structure allows for crystallization below Tm
– Addition of small amount of bulky side groups are used to
suppress crystallization
• Trifluoropropyl side groups enhance the resistance to solvent swelling and
are called fluorosilicones
• Linear form (uncrosslinked) polysiloxane corresponds to DP of 200-1000
for low consistency to 3,000-10,000 for high consistency resins
• Mechanism for crosslinking (vulcanization) can be based upon vinyl
unsaturations or reactive end groups (alkoxy)
– Silicone polymers are mostly elastomers with mediocre tear properties,
but with addition of silica can have outstanding properties unaffected by
a wide temp range from –90°C to 250°C
• Surface properties have low surface energy, giving good slip, lubricity,
release properties, water repellency, excellent adhesion for caulks
• Good chemical inertness but sensitive to swelling by hydrocarbons
• Good resistance to oils and solvents, UV radiation, temperature
• Electrical properties are excellent and stable for insulation and dielectric

24. 24
Silicones
• Properties
– Low index of reflection gives silicone contains useful combination
of high transmission and low reflectance
– Can be biologically inert and with low toxicity are well tolerated
by body tissue
– Polymers are normally crosslinked in the vulcanization stage. Four
groups
• Low consistency-room temperature curing resins (RTV)
• Low consistency-high temperature curing resins (LIM,LSR)
• High consistency-high temperature curing resins (HTV, HCE),
• Rigid resins
– RTV elastomers involve low molecular weight polysiloxanes and
rely on reactive end groups for crosslinking at room temperature.
• One component, or one part, packages rely on atmospheric moisture for
curing and are used for thin parts or coatings
• Two component systems have a catalyst and require a mixing stage and
result in a small exotherm where heat is given off.

25. 25
Silicones
• Properties
– LSR elastomers involve low molecular weight polysiloxanes but a
different curing system
• Relatively high temperature (150°C) for a faster cure (10-30s)
• Mixed system is largely unreactive at room temp (long pot life)
• Suitable for high speed liquid injection molding of small parts.
– HTV elastomers contain unsaturations that are suitable for
conventional rubber processing.
• Heat curable elastomers (HCE) are cross linked through high temperature
vulcanization (HTV) with the use of peroxides.
– Rigid silicones are cross linked into tight networks.
• Non-crosslinked systems are stable only in solutions that are limited to
paints, varnishes, coatings, and matrices for laminates
• Cross-linking takes place when the solvent evaporates.
• Post curing is recommended to complete reaction, e.g., silicone-epoxy
systems for electrical encapsulation.

26. 26
Silicones Applications• Most applications involve elastomeric form.
• Flexibility and hardness can be adjusted over a wide range
– Electrical applications high voltage and high or low temperatures
• Power cable insulation, high voltage leads and insulator boots, ignition
cables, spark plug boots, etc..
• Semi-conductors are encapsulated in silicone resins for potting.
– Mechanical applications requiring low and high-temperature
flexibility and chemical inertness
• ‘O-rings’, gaskets, seals for aircraft doors and windows, freezers, ovens, and
appliances, diaphragms flapper valves, protective boots and bellows.
– Casting molds and patterns for polyurethane, polyester, or epoxy
– Sealants and caulking agents
– Shock absorbers and vibration damping characteristics
• “Silly-Putty”: Non-crosslinked, high molecular weight PDMS-based
compound modified with fillers and plasticizers.
– Biomedical field for biological inertness include prosthetic devices

27. 27
Miscellaneous Other Elastomers
• Acrylic Rubber (AR)
– Polyethylacrylate (PEA) copolymerized with a small amount (5%)
of 2-chloro-ethyl-vinyl-ether CEVE, which is a cure site.
– The Tg of PEA is about -27°C and acrylic rubber is not suitable for
low temperature applications.
– Polybutylacrylate (PBR) has a Tg of -45°C.
– Applications
• Resistant to high temperatures, lubricating oils, including
sulfur-bearing oils.
• Include seals, gaskets, and hoses.
• Epichlorohydrin Rubber (ECHR)
– Polymerization of epichlorohydrin with a repeat unit of PECH.
– Excellent resistant to oils, fuels and flame resistance. (Cl presence)
– Copolymer with flexible ethyleneoxide (EO) provides Tg = -40C
– Applications include seals, gaskets, diaphragms, wire covers

28. 28
Miscellaneous Other Elastomers
• Polysulfide Rubbers (SR)
– One of the first synthetic rubbers. Tg =-27°C, PES Thiokol A
– Consists of adjacent ethylene and sulfide units giving a stiff chain.
– Flexibility is increased with addition of ethylene oxide for polyethylene-ether-
sulfide (PEES), Thiokol B
– Mechanical properties are not very good, but are used for outstanding resistance
to many oils, solvents and weathering.
– Applications include caulking, mastics, and putty.
• Propylene rubber (PROR)
– Does not crystallize in its atactic form and has a low Tg = -72°C.
– Has excellent dynamic properties
H
C
H
C
H
S S ][
H
S S
C C
H CH3
H H
n
O

29. 29
Miscellaneous Other Elastomers
• Polynorborene (PNB)
– Norborene polymerizes into highly molecular weight PNB.
– Tg = 35°C but can be plasticized with oils and vulcanized into an
elastomer with lower Tg = -65°C.
– Excellent damping properties that can be adjusted.
• Polyorgano-phosphazenes (PPZ)
– Form an example of a new class of polymeric materials involving
inorganic chains.
• Atoms of Nitrogen (azo) and Phosphorous form, the chain and a variety of
organic side groups, R1 and R2 can be attached to the phosphorous atom.
• Side groups include halo (Cl or F), amino (NH2 or NHR), alkoxy (methoxy,
ethoxy, etc.) and fluoroalkoxy groups.
• High molecular weight is flexible with a low Tg
• Excellent inherent fire resistance, weatherability, and water & oil repellency
• Applications
– coatings, fibers, and biomedical materials

30. 30
Commercial Elastomers
• Characteristics
Name Chemical Name Vucanization agent
Natural rubber cis polyisoprene sulfur
Polyisoprene cis polyisoprene sulfur
Polybutadiene Polybutadiene sulfur
SBR Polybutadiene-styrene sulfur
Nitrile Polybutadiene-acrylonitrile sulfur
Butyl Poly isobutylene-isoprene sulfur
EPR (EPDM) Poly ethylene propylene- diene Peroxies or sulfur
Neoprene Polychloroprene MgO
Silicone Polydimethylsiloxane peroxides
Thiokol Polyslkylenesulfide ZnO
Urethanes Polyester or polyether urethanes Diisocycanates

31. 31
Commercial Elastomers
• Costs
Name Consumption 1983 (metric tons) $/lb Type
Natural rubber 676,267 $0.44 General Purpose
Polyisoprene $0.72 General Purpose
Polybutadiene 335,541 $0.74 General Purpose
SBR 887,005 $0.66 General Purpose
Nitrile 57,239 $1.10 Solvent Resistant
Butyl $0.76 General Purpose
EPR (EPDM) 141,490 $1.01 General Purpose
Neoprene 85,096 $1.29 Solvent Resistant
Silicone $4.40 Heat Resistant
Thiokol Psulfides $1.83 Solvent Resistant
Urethanes $3.70 Solvent Resistant

32. 32
Polymerization Mechanisms
• Step-wise (Condensation) Polymerization
– Monomers combine to form blocks 2 units long
– 2 unit blocks form 4, which intern form 8 and son on
until the process is terminated.
– Results in by-products (CO2, H2O, Acetic acid, HCl
etc.)
• Chain Growth (Addition) Polymerization
– Polymerization begins at one location on the monomer
by an initiator
– Instantaneously, the polymer chain forms with no by-
products

33. 33
Condensation Polymerization Example
• Polyamides
– Condensation Polymerization
• Nylon 6/6 because both the acid and amine contain
6 carbon atoms
NH2(CH2)6NH2 + COOH(CH2)4COOH
Hexamethylene diamene Adipic acid
n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat)
Nylon salt
[NH(CH2)4NH·CO(CH2)4CO]n + nH2O
Nylon 6,6 polymer chain

34. 34
Condensation Polymerization Example
• Polyurethane
– Reaction of isocyanate and polyether-alcohol (polyol)
• Polyester
– Polymerization of acid and and alcohol
• Polycarbonate
– Polycarbonates are linear, amorphous polyesters
because they contain esters of carbonic acid and an
aromatic bisphenol (C6H5OH)
Phenol + Acetone Bisphenol-A + water
2
OH
+
H2O+
C CH2CH3
O
C
CH2
CH2
OHOH

35. 35
Other Condensation Polymers
• Thermoplastic Polyesters
– Saturated polyesters (Dacron).
• Linear polymers with high MW and no
crosslinking.
• Polyethylene Terephthalate (PET). Controlled
crystallinity.
• Polybutylene Terephthalate (PBT).
– Aromatic polyesters (Mylar) O C
O
R O C
O
R
C
O
C
O
R R

36. 36
Step-Growth Polymerization
Condensation Polymerizatio
• Main feature is that all molecular species in the
system can react with each other to form higher
molecular weight species.
– Step-growth polymerization reactions fall into two
classes
• A-R1-A + B-R2-B => A-R1-R2-B + AB
• A-R1-A + B-R2-B => A-R1-AB-R2-B
– where A and B are repeat polymer groups which react with each other;
» Example, for polyurethanes A = Isocyanate and B = Polyol and the
by-product is water.
– and R1 and R2 are long chain polymers

37. 37
Formation of Polymers
• Condensation Polymerization
– Step-growth polymerization proceeds by several steps which result
in by-products.
• Step-wise (Condensation) Polymerization
– Monomers combine to form blocks 2 units long
– 2 unit blocks form 4, which intern form 8 and son on until the
process is terminated.
– Results in by-products (CO2, H2O, Acetic acid, HCl etc.)

38. 38
Chain Growth (Addition)
Polymerization
• Chain Growth (Addition) Polymerization by
Free Radical Mechanism
– Involves three primary steps
• Initiation- formation of free radicals through homolytic
dissociation of weak bonds (e.g., peroxides). Results in opening
up unsaturated (C=C) bonds to saturated (C-C) bonds)
• Propagation- formation of long chain polymers of the now free
C-C bonds
• Termination- reactions at the ends of the polymer cause C-C to
terminate with a functional group that does not have any free
electrons to bond with and results in unsaturated end group (C-
C=CX)

39. 39
Chain Growth (Addition)
Polymerization
• Special case of Diene polymerization
– Very important in elastomers- mostly addition
– Polydienes are the backbone of the synthetic
rubber are produced by free radical
polymerization
– Early attempts of polymerization was slow and
produced low molecular weight polymers (oils)
– Emulsion polymerization (1930s) was introduced
to speed up polymerization and higher Molecular
weights

40. 40
Polymerization Methods
• 4 Methods to produce polymers
– Some polymers have been produced by all four methods
• PE, PP and PVC are can be produced by several of these
methods
• The choice of method depends upon the final polymer form, the
intrinsic polymer arrangement (isotactic, atactic, etc), and the
yield and throughput of the polymer desired.
– Bulk Polymerization
– Solution Polymerization
– Suspension Polymerization
– Emulsion Polymerization

41. 41
Formation of Polymers
• Polymers from Addition reaction
– LDPE HDPE PP
– PVC PS
C C
H H
H H
n
C C
H H
H H
n
C C
H CH3
H H
n
C C
H Cl
H H
n
C C
H
H H
n

42. 42
Other Addition Polymers
• Vinyl- Large group of addition
polymers with the formula:
– Radicals (X,Y) may be attached to this
repeating vinyl group as side groups to form
several related polymers.
• Polyvinyls
– Polyvinyl chloride
– Polyvinyl dichloride
(polyvinylidene chloride)
– Polyvinyl Acetate (PVAc)
C C
H X
H Y
or
C C
H X
H H
CC
H Cl
H H
C C
H Cl
H Cl
C C
H OCOCH3
H H

43. 43
Manufacturing of Emulsion SBR
• Free-radical emulsion process
– Developed in 1930s and still in use
– Typical process (Figure)
• Soap stabilized water emulsion of two monomers is converted in a train of
10 continuous reactors (4000 gallons each)
• Water, butadiene, styrene, soaps, initiators, buffers, and modifier are fed
continuously
• Temp is 5 to 10°C and conversion proceeds until 60% of the reactants have
polymerized in the last reactor.
• Shortstop is added in the emulsion to stop the conversion at 60%
• Unreacted butadiene is flashed off with steam and recycled
• Unreacted styrene is stripped off in a distillation column that separates
liquid rubber emulsion from the gas styrene.
• Rubber is recovered from the latex in a series of operations.
– Introduction of antioxidants, blending with oils, dilution with brine,
coagulation, dewatering, drying, and packaging the rubber

44. 44
Manufacturing of Emulsion SBR
• Polymerization
– Cold SBR: at 5 to 10°C is called the cold process,
• Better abrasion resistant, treadwear, and dynamic properties.
– Hot SBR: at about 50°C is called the hot process.
• Conversion is allowed to proceed to 70%
• Higher branching occurs and incipient gelation.
– Typical SBR recipes, Table from Morton’s Rubber
technology

45. 45
Manufacturing of Emulsion SBR
• Compounding and Processing
– Similar to natural rubber
– Materials for large scale use, e.g., tires, based on
• Rubber, fillers (carbon black), extending oils, zinc oxide,
sulfur, accelerators, antioxidants, antiozonants, and waxes.
– Materials are mixed in a mill or twin rollers or calendered
– Processing into smooth compounds that can be quickly
pressed, sheeted, calendered, or extruded
• Recipes
– Large parts, e.g., tires and hoses, are given in Tables 7.6,
7.7, 7.8, and 7.9

46. 46
Polymerization of Elastomers
• Butadiene-Acrylonitrile (Nitrile) Rubber
– Produced by emulsion polymerization
– Nitrile rubbers have nitrile contents from 10 to 40%.
• Chloroprene rubber
– Produced by emulsion polymerization
– Produced as a homopolymer that has a high trans 1,4
chain structure and is susceptible to strain-induced
crystallization, much like natural rubber.
• Leads to high tensile strength
– Does not lead itself to copolymerization

47. 47
Polymerization of Elastomers
• Butyl Rubber-
– Only important commercial rubber prepared by cationic
polymerization
• Processes with AlCl at –98 to –90°C
– Copolymer of isobutene and isoprene with isoprene used
in 1.5 % quantities
• The isoprene is introduced to provide sufficient unsaturations
for sulfur vulcanization.
– MW is in the range of 300,000 to 500,000

48. 48
Processing of Elastomers
• Rubber Products
– 50% of all rubber produced goes into automobile tires;
– 50% goes into mechanical parts such as
• mountings, gaskets, belts, and hoses, as well as
• consumer products such as shoes, clothing, furniture, and toys
• Elastomers and Rubbers
– Thermoset rubbers
• Compounding the ingredients in recipe into the raw rubber with
a mill, calender, or Banbury (internal) mixer
• Compression molding of tires
– Thermoplastic elastomers
• Compression molding, extrusion, injection molding, casting.

49. 49
Processing of Elastomers
• Rubber Processors
– Mills and Banbury mixers

50. 50
Compression Molding Process
• Materials
•Elastomers:
•Thermoplastic
•Thermoplastic Olefin (TPO), Thermoplastic Elastomer (TPE),
Thermoplastic Rubber (TPR)
•Thermoset rubbers
•Styrene Butadiene Rubber, isoprene
Thermoplastic:
Heat Plastic
prior to molding
Thermosets:
Heat Mold
during molding

51. 51
Polyurethane Processing
• Polyurethane can be processed by
– Slow process: Casting or foaming, or
– Fast process: Reaction Injection Molding (RIM)

52. 52
Injection Molding Glass Elastomers
• Plastic pellets with copolymer elastomers.
– Similar processing requirements as with injection
molding of commodity and engineering plastics
• Injection pressures, tonnage, pack pressure, shrinkage

53. 53
Transfer Molding of Rubbers
• Transfer molding is a process by which uncured rubber
compound is transferred from a holding vessel (transfer pot) to
the mold cavities using a hydraulically operated piston.
Transfer molding is especially conducive to multicavity designs
and can produce nearly flashless parts.

54. 54
Calendering of Rubbers
• Calendering is the process for producing long runs of uniform
thickness sheets of rubber either unsupported or on a fabric
backing. A standard 3 or 4 roll calender with linear speed range
of 2 to 10 feet/minute is typical for silicone rubber. Firm
compound with good green strength and resistance to
overmilling works the best for calendering.

55. 55
Curing of Rubbers
• Extruded profile may be cured by hot air vulcanization (HAV),
steam vulcanization (CV) or liquid-medium cure. HAV consists
of a heated tunnel through which the profile is fed continuously
on a moving conveyor. Air temperature reaches 600°F to
1200°F, and cure times are usually short, on the order of 3 to 12
seconds. The recommended curing agents are DCBP-50 or
addition cure, both of which provide rapid cure with no
porosity.
• Steam cure commonly refers to the steam curing systems used
by the wire and cable industry and consists of chambers 4” –
6” in diameter and 100 – 150 feet in length. Steam pressure
varies from 50 psig to 225 psig depending on wall thickness of
the insulation.
• For liquid-medium cure, continuous lengths of extruded profile
are fed into a bath of moltenmaterial (salt or lead) which cures
the extrudate.

56. 56
Polymer Length
• Polymer Length
– Polymer notation represents the repeating group
• Example, -[A]-n where A is the repeating monomer and n represents the
number of repeating units.
• Molecular Weight
– Way to measure the average chain length of the polymer
– Defined as sum of the atomic weights of each of the atoms in the
molecule.
• Example,
– Water (H2O) is 2 H (1g) and one O (16g) = 2*(1) + 1*(16)= 18g/mole
– Methane CH4 is 1 C (12g) and 4 H (1g)= 1*(12) + 4 *(1) = 16g/mole
– Polyethylene -(C2H4)-1000= 2 C (12g) + 4H (1g) = 28g/mole * 1000 = 28,000
g/mole

57. 57
Molecular Weight
• Average Molecular Weight
– Polymers are made up of many molecular weights or a
distribution of chain lengths.
• The polymer is comprised of a bag of worms of the same
repeating unit, ethylene (C2H4) with different lengths; some
longer than others.
• Example,
– Polyethylene -(C2H4)-1000 has some chains (worms) with 1001 repeating
ethylene units, some with 1010 ethylene units, some with 999 repeating
units, and some with 990 repeating units.
– The average number of repeating units or chain length is 1000 repeating
ethylene units for a molecular weight of 28*1000 or 28,000 g/mole .

58. 58
Molecular Weight
• Average Molecular Weight
– Distribution of values is useful statistical way to
characterize polymers.
• For example,
– Value could be the heights of students in a room.
– Distribution is determined by counting the number of students in the
class of each height.
– The distribution can be visualized by plotting the number of students on
the x-axis and the various heights on the y-axis.
Histogram of Heights of Students
0
5
10
15
20
25
60 70 80
Height, inches
Frequency
Series1

59. 59
Molecular Weight
• Molecular Weight Distribution
– Count the number of molecules of each molecular weight
– The molecular weights are counted in values or groups that have similar lengths,
e.g., between 100,000 and 110,000
• For example,
– Group the heights of students between 65 and 70 inches in one group, 70 to 75
inches in another group, 75 and 80 inches in another group.
• The groups are on the x-axis and the frequency on the y-axis.
• The counting cells are rectangles with the width the spread of the cells and
the height is the frequency or number of molecules
• Figure 3.1
• A curve is drawn representing the overall shape of the plot by connecting
the tops of each of the cells at their midpoints.
• The curve is called the Molecular Weight Distribution (MWD)

60. 60
Molecular Weight
• Average Molecular Weight
– Determined by summing the weights of all of the chains
and then dividing by the total number of chains.
– Average molecular weight is an important method of
characterizing polymers.
– 3 ways to represent Average molecular weight
• Number average molecular weight
• Weight average molecular weight
• Z-average molecular weight

61. 61
Gel Permeation Chromatography
• GPC Used to measure Molecular Weights
– form of size-exclusion chromatography
– smallest molecules pass through bead pores, resulting in
a relatively long flow path
– largest molecules flow around beads, resulting in a
relatively short flow path
– chromatogram obtained shows intensity vs. elution
volume
– correct pore sizes and solvent critical

62. 62
Gel Permeation Chromatography

63. 63
Number Average Molecular Weight, Mn
•
• where Mi is the molecular weight of that species (on the x-axis)
• where Ni is the number of molecules of a particular molecular species I (on
the y-axis).
– Number Average Molecular Weight gives the same weight to all polymer
lengths, long and short.
• Example, What is the molecular weight of a polymer sample in which the polymers
molecules are divided into 5 categories.
– Group Frequency
– 50,000 1
– 100,000 4
– 200,000 5
– 500,000 3
– 700,000 1
...
...
321
332211
+++
+++
==
∑
∑
NNN
MNMNMN
N
MN
M
i
ii
n
000,260
)13541(
)700(1)500(3)200(5)100(4)50(1
...
...
321
332211
=
++++
++++
=
+++
+++
==
∑
∑
n
n
i
ii
n
M
KKKKK
M
NNN
MNMNMN
N
MN
M

64. 64
Molecular Weight
• Number Average Molecular Weight. Figure 3.2
– The data yields a nonsymmetrical curve (common)
– The curve is skewed with a tail towards the high MW
– The Mn is determined experimentally by analyzing the number of
end groups (which permit the determination of the number of
chains)
– The number of repeating units, n, can be found by the ratio of the
Mn and the molecualr weight of the repeating unit, M0, for
example for polyethylene, M0 = 28 g/mole
– The number of repeating units, n, is often called the degree of
polymerization, DP.
– DP relates the amount of
monomer that has been converted to polymer.
0M
M
n n
=

65. 65
Weight Average Molecular Weight, Mw
• Weight Average Molecular Weight, Mw
– Favors large molecules versus small ones
– Useful for understanding polymer properties that relate to
the weight of the polymer, e.g., penetration through a
membrane or light scattering.
– Example,
• Same data as before would give a higher value for the
Molecular Weight. Or, Mw = 420,000 g/mole
...
...
332211
2
33
2
22
2
11
2
+++
+++
==
∑
∑
MNMNMN
MNMNMN
MN
MN
M
ii
ii
w

66. 66
Z- Average Molecular Weight
– Emphasizes large molecules even more than Mw
– Useful for some calculations involving mechanical
properties.
– Method uses a centrifuge to separate the polymer
...
...
2
33
2
22
2
11
3
33
3
22
3
11
2
3
+++
+++
==
∑
∑
MNMNMN
MNMNMN
MN
MN
M
ii
ii
z

67. 67
Molecular Weight Distribution
• Molecular Weight Distribution represents the
frequency of the polymer lengths
• The frequency can be Narrow or Broad, Fig 3.3
• Narrow distribution represents polymers of about
the same length.
• Broad distribution represents polymers with varying
lengths
• MW distribution is controlled by the conditions
during polymerization
• MW distributions can be symmetrical or skewed.

68. 68
Physical and Mechanical Property
Implications of MW and MWD
• Higher MW increases
• Tensile Strength, impact toughness, creep resistance, and
melting temperature.
– Due to entanglement, which is wrapping of polymer
chains around each other.
– Higher MW implies higher entanglement which yields
higher mechanical properties.
– Entanglement results in similar forces as secondary or
hydrogen bonding, which require lower energy to break
than crosslinks.

69. 69
Physical and Mechanical Property Implications
of MW and MWD
• Higher MW increases tensile strength
• Resistance to an applied load pulling in opposite directions
• Tension forces cause the polymers to align and reduce the number of
entanglements. If the polymer has many entanglements, the force would be
greater.
• Broader MW Distribution decreases tensile strength
• Broad MW distribution represents polymer with many shorter molecules
which are not as entangled and slide easily.
• Higher MW increases impact strength
• Impact toughness or impact strength are increased with longer polymer
chains because the energy is transmitted down chain.
• Broader MW Distribution decreases impact strength
• Shorter chains do not transmit as much energy during impact

70. 70
Thermal Property Implications of MW & MWD
• Higher MW increases Melting Point
• Melting point is a measure of the amount of energy necessary
to have molecules slide freely past one another.
• If the polymer has many entanglements, the energy required
would be greater.
• Low molecular weights reduce melting point and increase ease
of processing.
• Broader MW Distribution decreases Melting Point
• Broad MW distribution represents polymer with many shorter
molecules which are not as entangled and melt sooner.
• Broad MW distribution yields an easier processed polymer
Mechanical
Properties
Melting
Point
* Decomposition

71. 71
Example of High Molecular Weight
• Ultra High Molecular Weight Polyethylene (UHWMPE)
• Modifying the MWD of Polyethylene yields a polymer with
– Extremely long polymer chains with narrow distribution
– Excellent strength
– Excellent toughness and high melting point.
• Material works well in injection molding (though high melt T)
• Does not work well in extrusion or blow molding, which
require high melt strength.
• Melt temperature range is narrow and tough to process.
• Properties improved if lower MW polyethylene
– Acts as a low-melting lubricant
– Provides bimodal distributions, Figure 3.5
– Provides a hybrid material with hybrid properties