Transcript Primer - University of Kentucky College of Engineering Courses

Molecular architecture
Chapter 2.
Effects of chain composition and
morphology on bulk properties
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Outline
• Macromolecule structure – building blocks, arrangement,
interaction with the environment
• Synthetic polymers
–
–
–
–
–
–
Carbon-carbon chains
Carbon-nitrogen chains
Carbon-oxygen chains
Carbon-sulfur chains
Inorganic polymers
Copolymers
• Types of constitutions and configurations
• Conformations of single macromolecules
• Structure/processing/performance
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Macromolecular structure
• Materials engineering is built on structure-processingproperty relationships
• Usually, three factors are used to define the 3-D
structure (which leads to the bulk properties)
– Constitution: the types of atoms in the chain, including side
groups, end groups, and the molecular weight distribution
– Configuration: the arrangement of these atoms in the chain and
branch segments
– Conformation: the 3-D arrangement of the chain in the media
(solvent, polymer, …)
• Constitution and configuration are established during
synthesis, while conformation is affected by the media
and its conditions
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Macromolecular structure polyacrylics
Common name
Monomer
Poly(acrylic acid)
Polymer
OH
O
O
HO
C
CH
CH 2
Polyacrolein
H
C
9003-01-4
C
H2
*
n
*
Variable structure
Polyacrylamide
C
25068-14-8
NH2
O
H2 N
Polyacrylonitrile
CAS Reg
#
O
CH
H
C
*
CH 2
C
H2
9003-05-8
n
*
N
H2 C
CH
C
25014-41-9
H
N
n
*
*
H H
Poly(methyl
methacrylate)
H2 C
Me
C
H H
O
C
n
*
OMe
Me
9011-14-7
*
O
O
OH
Me
H2 C
Poly(2-hydroxyethylmethacrylate)
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O
*
chapter 2
O
H
C
CH2
C
H2
n
25249-16-5
*
4
Polyacrylics - PMMA
• Commercial monomers: methacrylic acid, methyl
methacrylate, ethyl methacrylate, n-butyl methacrylate,
isobutyl methacrylate, 2-hydroxyethyl methacrylate
• Tg related to the size of the –OR group, with larger
groups have higher Tg’s
• Free radical polymerization is typical
• Mw > 100,000: uniform properties
• PMMA has very high light transmission over the visible
range; alternative to glass
• Compatible with human tissue – biomed. Appls.
• Photoresist for ebeam lithography
• Worldwide capacity ~ 1 B tons/yr
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Polyacrylics - PAA
• An example of a commercial nonionic polymer soluble in
water at room temperature
• Water solubility is a results of the high number of polar
and hydrogen-bonding groups per repeating unit
• Free radical polymerization in water or suspension
polymerization in benzene
• Tg ~ 126 C; solid polymer is hard, clear and brittle
• Viscosities of aqueous solutions increase with molecular
weight
• Dispersant for organic pigments, flocculant, adhesive,
thickener
• Worldwide capacity ~ 1 M tons/yr
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Polyacrylics- PAM
• Polymerized via free radical initiators (azo compounds, redox
catalysts, light, radiation)
• Unique among vinyl and acrylic monomers because it will
polymerize to very high molecular weights (~106 +) [high purity
monomer, very high ratio of polymerization to termination rate
constants]
• Polymerizations: solution, inverse emulsion, inverse microemulsion,
precipitation/suspension
• Tg ~ 165 C
• Slow dissolution in water, but suspensions are very stable
• Flocculant [major market in water treatment applications], rheology
control, adhesives
• Worldwide monomer capacity ~ 1.4108 kg/yr
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Polyacrylics - PAN
• Manufactured by the ammoxidation of propylene; route is
low cost and led to high volume applications
• Worldwide capacity ~4 B tons/yr
• Head-to-tail configuration; isotactic and syndiotactic
• Highly crystalline, hard, chemical resistance, low gas
permeability, Tm ~ 317 C but the polymer decomposes
below this temperature; solvents must be strongly
hydrogen bonding with nonpolar segments
• Excellent barrier properties to O2, CO2; monomer is
highly toxic,
• Acrylic fibers (50 % of monomer usage; easy to dye),
copolymers with styrene (SAN) and butadiene + styrene
(ABS)
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Polyacrylics – polyacrolein
Poly(vinyl formaldehyde). Specialty polymer
• Acrolein (2-propenal) is highly toxic and carcinogenic
• Anionic, cationic catalyst lead to irregular structures
• Free radical initiators lead to 1,2 vinyl addition, comb-like structures,
which hydrolyze to ladder-like structures
• A number of copolymers are possible
The reaction product is insoluble;
the tetrahydropyrane rings and
possible interchain hemiacetal
links contribute to its insolubility.
S. Slomkowski, Prog. Polym. Sci., 23, 815-874 (1998).
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Polyacrylics – polyacrolein
Poly(vinyl formaldehyde). Specialty polymer
Conversion to the polyacrolein hydrate
makes a water-soluble system suitable for
medical applications
S. Slomkowski, Prog. Polym. Sci., 23, 815-874 (1998).
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Polyacrylics – polyacrolein
Poly(vinyl formaldehyde). Specialty polymer
Core-shell particles with reactive
surface groups can be carriers
for covalently immobilized
catalysts, enzymes, drugs and
biopolymers
S. Slomkowski, Prog. Polym. Sci., 23, 815-874 (1998).
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Polyacrylics – polyacrolein
Poly(vinyl formaldehyde). Specialty polymer
Example application.
Diagnostic test to detect
antibodies in blood.
Direct. Antibodies are
attached to the microspheres.
When antigens are present,
the microspheres agglomerate.
Reverse. Antigens are
immobilized to microspheres,
and the presence of antibodies
causes agglomeration.
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Polyacrylics – P(HEMA)
• Synthetic bone
• Interpenetrating polymer networks with
collagen, polycaprolactone, vinyl
pyrrolidone
• Artificial corneas; drug delivery system
• Hydrogels: swell in aqueous media. Dental
cements, controlled drug release,
prostheses, optical lenses
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G.D. Winter and B. J. Simpson, Heterotropic bone formed in a synthetic
sponge in the skin of young pigs, Nature, 223, 88-90 (1969).
Polyacrylics – P(HEMA)
• Monolithic or heterogeneous (microporous or
macroporous) 3-D crosslinked gels or sponges
• Linear or branched polymers
• Poly(HEMA) as bone regeneration medium; however,
the synthetic polymer often is encapsulated, which
precludes hard tissue replacement.
• Poly(HEMA)/collagen composites: no fibrous tissue
capsule, slow biodegradation, phosphatase activity in the
implant fragments, uniform mineralization
• Collagen influences adhesion, spreading, proliferation
and differentiation of cells
• The collagen distribution in the copolymer affects these
results
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Polyacrylics – P(HEMA)
Core(transparent
p(HEMA))-and-skirt
(opaque p(HEMA))
morphology
Attachment of skirt to core via IPN
(interpenetrating polymer network).
Porous hydrogel allows cellular
invasion, production of neocollagen,
vascularization.
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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Green engineering – polymer examples
J.L. Anthony, Kansas State University
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CARBON-CARBON
BACKBONE
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Polydienes
• Monomers either have two C=C bonds per
unit (butadiene, isoprene, chloroprene) or
one C=C in a ring (norbornene,
pentenamer); stereochemistry controlled
by polymerization conditions
• Tg’s are lower than room temperature,
crosslinking results in 3-D solids
•
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Polydienes - Tg
Polymer name
application
Tg, K
Poly(1,2-butadiene)
Tear-resistant films
293, 273
Poly(1,4-butadiene),cis
Tires
218, 170
Polychloroprene
Neoprene rubber
227
Poly(isoprene), cis
203
Poly(isoprene), trans
266, 215
Poly(isoprene), gutta
percha
311
Poly(norbornene)
Ring-opening
304, 317
Cyclopentene
homopolymer
Ring-opening
159
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Polyhalogens
• The bond strengths of C-X are ordered: C-F > C-Cl > CBr > C-I. The fluorocarbons are most stable
• Teflon = PTFE; high thermal stability, resistant to
corrosive attack
• Kynar = PVDF; good weathering, architectural coatings
• PVC; high volume thermoplastic, easy to compound
• Saran = PVDC; flexible films
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Polyolefins
•
•
•
•
Low cost, high volume thermoplastics
PE; HDPE, LDPE,LLDPE, HMWPE
PP
PS
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Other vinyl polymers
• Monomers: CH2=CHR
• PVAc: poly(vinyl acetate). Adhesives,
glues, emulsions, suspensions
• PVAL: poly(vinyl alcohol). Water-soluble
• Poly(vinyl ethers). Adhesives and
plasticizers
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Aromatic w/C-C backbone
• Poly(p-xylylenes). Specialty coatings
• Phenolic resins.
– Novolacs via acid catalysis. Soluble in
alcohols
– Bakelites via base catalysts. Crosslink with
heat. Early application – distributor cap.
• Pine oils. b-pinene
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CARBON-NITROGEN
BACKBONE
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Polyamides
• [-NH-CO-] in the main chain
• Perlon – repeating unit and the monomer are the same.
“Nylon X”. [-NH-CO-R-]. Example – Nylon 6. poly(ecaprolactam). Ring-opening lactam polymerizations may
have significant monomer levels.
• Nylon – repeating unit is formed with two monomers.
“Nylon X,Y” [-NH-R-NH-CO-R1-CO-]. Example – Nylon
6,6. poly(hexamethylene adipamide). Equilibrium is far to
products.
• Nomex, Kevlar have aromatic “R” groups
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Polyimides
• [-NH-CO-]
• Kapton – very rigid chain
• Nylon 1 – poly(isocyanic acid)
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Polyurethanes
Typical monomer pairs are diols/diisocyanates. Polymers have wide
ranges of stiffness, hardness and densities due to the wide variety of
monomers available; low density flexible foams, soft solid elastomers
and print rollers, and high performance adhesives. Original materials
were developed by Otto Bayer, 1937, I.G. Farben. The monomers
circumvented the patents by W. Carothers (du Pont) for polyesters. A
major commercial product was polyurethane foam based on toluene
diisocyanate and polyester precursors. Foaming occurred due to the
heating of adventitious water in the reaction mixture.
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Polyurethanes - history
• Otto Bayer, 1937, I.G. Farben. Liquid diisocyanates and liquid
polyether or polyester diols (circumventing patents by Carothers (du
Pont) on polyesters)
• TDI + polyester polyols, 1954, flexible foams due to adventitious
water
• Linear fibers from hexamethylene diisocyanate (HDI) and 1,4butanediol
• Poly(tetramethylene glycol), duPont, 1956. 1st polyether diol. Low
cost, ease of handling causes replacement of polyesters. BASF,
Dow have products
• 1960’s: chlorofluoroalkane blowing agents, cheap polyether diols,
methylene diphenyl diisocyanate (MDI) for rigid foams,
polyisocyanurates for better thermal stability. Auto interior safety
components – instrument panels with semi-rigid foams
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Polyurethanes - history
•
•
•
•
•
•
•
Bayer AG introduces RIM (reaction injection molding), 1969, all plastic car
Polyurethane RIM – diamine chain extenders, trimerization; poly(urethane
urea), poly(urethane isocyanurate), polyurea RIM
Fillers ( mica, milled glass, mineral fibers) – RRIM, for improved flex
modulus for stiffness and thermal stability. Leads to the 1st plastic body
auto in US (Pontiac Fiero, 1983). SRIM – structural RIM with glass mats
1980’s – auto market share increased via PVC plastisol replacement
1990’s – Montreal Protocol leads to HCFC’s replacing CFC’s, and then
CO2, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3pentafluoropropane (HFC-245fa)
2-component polyurea spray elastomers for coatings on concrete and steel,
2-component polyurethane and hybrid polyurethane-polyurea elastomers for
spray-in-place bed liners
2004 – polyols derived from vegetable oils
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Polyurethanes - chemistry
•
•
•
•
•
•
•
•
•
Reaction polymers – polyurethanes, epoxies, unsatruated polyesters,
phenolics
Polyaddition of polyisocyanate with a polyol
R1 – N=C=O + R2-O-H
R1-NH-CO-O-R2
Isocyanates react with any active hydrogen; with water, form a urea linkage
and CO2
Commercial products – liquid isocyanate, polyols, catalyst, additives (chain
extenders, crosslinkers, surfactants, flame retardants, blowing agents,
pigments, fillers)
Polymeric MDI (diphenylmethane diisocyanate) – blend of 2, 3, and 4
functional monomers with 2.7 average functionality for crosslinking
Prepolymer – partially reacted isocyante + polyol
Key isocyanate properties – backbone, % NCO, functionality, viscosity
Polyols – polyethers (PO, EO) or polyesters (adipic acid + EG)- backbone,
initiator, MW % primary hydoxyls, functionality viscosity
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Polyurethanes - chemistry
• Polymerization catalyzed by tertiary amines (dimethyl
cyclohexylamine) and organometallic salts (dibutyl tin laurate)
• Gel reaction (urethane), blow reaction (urea), trimerization reaction
(potassium octoate)
• Blowing agents – BP near room temperature, heat of reaction
provides energy to vaporize the agent, bubbles grow at nucleation
sites, polymer must cure prior to bubble aggregation and growth,
surfactants can help control whether closed cell foams or open cell
foams are made
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Polyurethanes - toxicity
• CAS # 9009-54-5: polyurethane is chemically inert, no exposure
limits by OSHA, ACGIH; not regulated for carcinogenicity
• Combustible solid, decomposing to CO, NOx, hydrogen cyanide.
• Dust may irritate the eyes and lungs
• Isocyanates: skin and repiratory sensitizers
• Polyols: may contain regulated compounds
• Info: Polyurethane Manufacturers Association, Center for the
Polyurethane Industry, Code of Federal Regulations Title 21 (Food
and Drugs) and Title 40 (Protection of the Environment)
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Polyurethane – material
properties
http://en.wikipedia.org/wiki/Polyurethanes
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Polyurethanes – structure,
processing, properties
• Diisocyanate, polyol, catalyst, surfactants
• Density: vary the type of monomer
• Cure rate: functional group reactivity, # of functional isocyanate
groups
• Photostability: type of diisocyanate, aromatics yellow with exposure
to light
• Soft, elastic, good flex: linear difunctional PEG segments (Spandex,
soft rubber parts, foam rubber)
• Rigid products: polyfunctional polyols for 3-D crosslinked structure,
trimerization catalysts create cyclic structures high thermal stability
• Memory foam: control of viscoelastic properties via catalysts and
polyols to make the product softer at room temperature
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Polyurethanes - applications
• Varnish: finish coats, hardwood floor sealing, faster and higher film
build, cure occurs after solvent evaporation and with moisture;
exterior varnishes susceptible to UV damage
• Solid elastomer wheels: roller blading and skateboarding, abrasion
resistance
• Furniture: batch processes to make foam cushions, casting soft
edges for table tops and panels, bottoms of mouse pads
• Vehicle seats: seats, headrests, armrests, roof liners, instrument
panels; in-situ foam-in-fabric (direct molding – seat cover on mold
surface, metal framework insert, inject two-part mixture through
mixing head under vacuum)
• Decorative elements for houses: domed ceilings, statues, …
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Polyurethanes - applications
• Watercraft: core foam for surfboards, boat hulls
• Construction sealants: 1,2 and 3 part systems for rapid cure
sealants
• Tennis grips: Yonex Supergrap™,
• Electronic components: “potting” or enclosure material to protect
circuit boards, 121 C is upper temperature limit; two-part cast
urethane
• Adhesives: Gorilla Glue™, excellent water resistance; book binding
adhesive; preferable to hotmelt and cold glue, 0.03 mm thickness, 40 C to 100 C
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CARBON-OXYGEN
BACKBONE
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Polyacetals
• [-CHR-O-]
• Polymerization of aldehydes or cyclic
trimers. Example – poly(oxymethylene)
from formaldehyde or trioxane
• Engineering thermoplastics, good abrasion
and wear characteristics
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Polyethers
• [-R-O-]
• Aliphatic: PEO, water soluble; PPO –
polyurethane intermediates, lubricants,
surfactants; EO/PO copolymer – water
soluble detergents and elastomers;
Poly(tetrahydrofuran) – thermoplastic
elastomers; poly(epichlorohydrin) coatings
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Polyethers
• Aromatic: epoxies based on bisphenol A;
poly(phenylene oxide); PEEK – poly(ether
ether ketone)
• PEEK: E = 3.6 GPa, tensile = 90 MPa, 50%
elongation at break
• Tg’s at ~140 C and ~275 C based on
composition; Tm ~ 350 C
• Bearings, piston parts, pumps, UHV
applications
• Reinforced with carbon fiber for medical
implants, aerospace structural material
• Electronic circuitry (high temperature)
• Resistant to many chemicals and solvents
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Polyesters - aliphatic
• Ester group in the chain + aliphatic group
in repeating unit
• Step polymerization: ring-opening, selfcondensation, transesterifications, diols +
dicarboxylic acids or diacyl chlorides, acid
anhydrides + cyclic ethers, o-carboxylic
anhydrides
• Copolymers of lactic and glycolic acids
make biodegradable polymers for tissue
engineering, drug delivery, and other
biomedical uses
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O
O
O
C
(CH 2 ) 5
n
O
48
Polyesters – PLA, PGA
• Bacterial fermentation of corn starch to lactic acid
• Dimer is catalytically (stannous octoate)
polymerized
• lactic acid is chiral; poly(L-lactic acid) and poly(Dlactic acid) are crystalline; PLLA - Tm ~ 60 C,
Tm ~ 173 C
• tissue engineering scaffolds:
– Molecular self-assembly
– Non-woven technology – PGA
– Solvent casting and particulate leaching - PLA in
dichloromethane + inorganic salts; film casting, leaching
of the salt
– Gas foaming
– Emulsification/freeze drying
– Liquid-liquid phase separation
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Polyesters - crosslinked
• Ester monomers with C=C in the chain
allow polyester polymerization + free
radical crosslinking, leading to 3-D
polymers
• Crosslinked polyesters are the
continuous phase for fiberglass
polymers – boat hulls, vehicle bodies,
etc. – as sheet molding compound
• These systems are usually
manufactured in several steps: 1)
viscous prepolymer is mixed with the
glass fibers to make a sheet, 2) the
sheet is placed in a mold and heated,
increasing the polymerization of the
polyester and permitting free radical
polymerization of the C=Cs chapter 2
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Polyesters - aromatic
O
Me
O
C
O
C
Me
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n
• Polycarbonates – bisphenol A
• Bullet-proof windows, high impact strength
• PET – poly(ethylene terephthalate); polyester
fibers, soda bottles
• PBT – poly(butylene terephthalate); lower Tg
than PET; excellent chemical resistance,
excellent wear resistance; keyboard buttons –
PBT can be dyed for different colors; graphics
are attached by sublimation printing
• Poly(4-hydroxybenzoate):
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CARBON-SULFUR BACKBONE
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Polysulfides
• Ryton – poly(phenylene sulfide) – crystalline,
Tm ~ 285 C, flame-retardant (forms char; U94V)), insoluble below 200 C
• High modulus, low creep, thermally stable, no
flame retardants needed, good dielectric and
insulating properties, chemically resistant, low
thermal expansion coefficient (dimensional
stability)
• Small appliances – electric blanket thermostat,
fry pan handles, coffee warmer rings, toaster
switches, curling iron insulators, steam iron
valves
• automotive – fuel systems, brake systems,
engine heat shield, …
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Thiokol™ rubbers
Registry Number:
34808-18-9
•
Component Registry Number: 12034-39-8
Formula: Na2 S4
Component Registry Number: 111-91-1
Formula: C5 H10 Cl2 O2
Formula:
(C5 H10 Cl2 O2 . Na2 S4)x
•
•
CA Index Name:
Ethane, 1,1'[methylenebis(oxy)]bis[2-chloro-, polymer with sodium
sulfide (Na2(S4)) (9CI)
Other Names:
Sodium sulfide (Na2(S4)),
polymer with 1,1'- [methylenebis(oxy)] bis[2chloroethane] (9CI); Bis(2-chloroethoxy)methanesodium tetrasulfide copolymer; Bis(2-chloroethyl
•
•
•
formal)-sodium tetrasulfide copolymer; Bis(2chloroethyl formal)-sodium tetrasulfide polymer; Di(bChloroethyl) formal-sodium tetrasulfide polymer
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–[(CH2)m-Sx]n– , where x indicates the number
of sulfur atoms (or rank), and n indicates the
number of repeat units
Polymers containing sulfur atoms separated by
hydrocarbon sequences are not polysulfides,
e.g. polyphenylene sulfide (C6H4S)n.
condensation polymerization reactions between
organic dihalides and alkal metal salts of
polysulfide anions:
n Na2S5 + n ClCH2CH2Cl → [CH2CH2S5]n + 2n
insoluble in water, oils, other organic solvents.
sealants to fill the joints in pavement,
automotive window glass, and aircraft
structures.
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Poly(alkylene sulfides)
•
•
•
•
Registry Number: 24936-67-2
Formula: (C2 H4 S)n
CA Index Name: Poly(thio-1,2-ethanediyl) (9CI)
Other Names:
Poly(thioethylene) (8CI); Poly(ethylene
sulfide); Poly(ethylene sulfide), SRU
S
CH 2
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CH 2
S
CH 2
n
n
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Copolymer nomenclature
•
•
•
•
•
•
•
•
-co- : any copolymer
-block- : AAAAABBBBB
-graft-: AAAAAA(BBBB)AAA
-star-blend-: melt or solution blend
-random-: AAABAABBBABABABBAAAB
-cross-: crosslinked
-inter-: interpenetrating
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Configurations
• Linear homopolymers: one type of repeating unit, no branching,
crosslinking
• C-C chains [imagine viewing the polymer along the C-C backbone
– Atactic: substituted group appears randomly on either side of the
chain
– Isotactic: substituted groups appears only on one side of the
chain
– Syndiotactic: substituted groups alternate from one side to the
other
• Elastomers with C=C bonds: cis and trans
• Nonlinear homopolymers (branching architectures): see Table 2.21
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Conformations – single macromolecule
• Random coil: typical polymer molecule
“encloses” a volume shaped as an
oblate spheroid, Dx≠Dy≠Dz, rotation of
an ellipse around its minor axis
• Average ratios: 1.36: 0.78: 0.50.
Globular proteins may have similar
shapes, although they are often
crosslinked
• in dilute solution, or above Tm in a melt,
the coil is constantly changing shape
due to Brownian motion
• Rod-like molecules either are highly
crystalline, or have neighboring groups
that repel each other
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