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Polymer synthesis. Case study of
two synthesis pathways
Solid rocket propellant (SRP)
G. P. Sutton and O. Biblarz, Rocket Propulsion Elements, 8th Ed., John Wiley, 2010.
J.-J. Jutier, A. de Gunzbourg and R. E. Prud’homme, Synthesis and characterization of
poly(3,3-bis(azidomethyl)oxetane-co-e-caprolactone)s, J. Polym. Sci.: Part A: Polymer
Chemistry, 37, 1027-1039 (1999).
T.S. Reddy, J.K. Nair, R. S. Satpute, G. M. Gore, A. K. Sikder, Rheological studies on energetic
thermoplastic elastomers, J. Appl. Polym. Sci. 118, 2365-2368 (2010).
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SRP slurry
casting
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Ammonium perchlorate
Properties
Molecular formula NH4ClO4
Molar mass 117.49 g/mol
Appearance white granular
Density 1.95 g/cm3
Melting point
Exothermic decomposition before Tm at >200 °C
2 NH4ClO4 → Cl2 + N2 + 2 O2 + 4 H2O
Solubility in water 11.56 g/100 mL (0 °C)
20.85 g/100 mL (20 °C)
57.01 g/100 mL (100 °C)
Solubility soluble in methanol
partially soluble in acetone
insoluble in ether
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SRP composite fuel
Heterogeneous mixture of powdered metal,
crystalline oxidizer and polymer binder.
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http://en.wikipedia.org/wiki/Thermoplastic_elastomer
TPE BACKGROUND
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Thermoplastic elastomers
•
•
•
•
•
There are six generic classes of TPEs generally considered to exist commercially. They are styrenic block
copolymers, polyolefin blends EXELAST SX (Shin-Etsu Polymer Europe B.V.), elastomeric alloys (TPE-v or
TPV), thermoplastic polyurethanes EXELAST EC (Shin-Etsu), thermoplastic copolyester and thermoplastic
polyamides. Examples of TPE products that come from block copolymers group are Styroflex (BASF),
Kraton (Shell chemicals), Pellethane, Engage (Dow chemical), Pebax, Arnitel (DSM), Hytrel (Du Pont) and
more. While there are now many commercial products of elastomer alloy, these include: Dryflex,
Mediprene ([ELASTO, a Hexpol Company]), Santoprene (Monsanto Company), Geolast (Monsanto), Sarlink
(DSM), Forprene (So.F.Ter. S.p.a.), Alcryn (Du Pont) and Evoprene ([AlphaGary]).
In order to qualify as a thermoplastic elastomer, a material must have these three essential characteristics:
The ability to be stretched to moderate elongations and, upon the removal of stress, return to something
close to its original shape.
Processable as a melt at elevated temperature.
Absence of significant creep.
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TPE’s
•
•
•
It was not until the 1950s, when thermoplastic polyurethane polymers became available, that TPE became a commercial reality. During
the 1960s styrene block copolymer became available, and in the 1970s a wide range of TPEs came on the scene. The worldwide usage
of TPEs (680,000 tons/year in 1990) is growing at about 9% per year. The styrene-butadiene materials possess a two-phase
microstructure due to incompatibility between the polystyrene and polybutadiene blocks, the former separating into spheres or rods
depending on the exact composition. With low polystyrene content, the material is elastomeric with the properties of the
polybutadiene predominating. Generally they offer a much wider range of properties than conventional cross-linked rubbers because
the composition can varies to suit customer needs.
Block copolymers are interesting because they can "microphase separate" to form periodic nanostructures, as in the styrene-butadienestyrene block copolymer shown at right. The polymer is known as Kraton and is used for shoe soles and adhesives. Owing to the
microfine structure, the transmission electron microscope or TEM was needed to examine the structure. The butadiene matrix was
stained with osmium tetroxide to provide contrast in the image. The material was made by living polymerization so that the blocks are
almost monodisperse, so helping to create a very regular microstructure. The molecular weight of the polystyrene blocks in the main
picture is 102,000; the inset picture has a molecular weight of 91,000, producing slightly smaller domains. The spacing between
domains has been confirmed by small-angle X-ray scattering, a technique which gives information about microstructure. Since most
polymers are incompatible with one another, forming a block polymer will usually result in phase separation, and the principle has been
widely exploited since the introduction of the SBS block polymers, especially where one of the block is highly crystalline. One exception
to the rule of incompatibility is the material Noryl, where polystyrene and polyphenylene oxide or PPO forma continuous blend with
one another.
Other TPE's have crystalline domains where one kind of block co-crystallizes with other block in adjacent chains, such as in copolyester
rubbers, achieving the same effect as in the SBS block polymers. Depending on the block length, the domains are generally more stable
than the latter owing to the higher crystal melting point. That point determines the processing temperatures needed to shape the
material, as well as the ultimate service use temperatures of the product. Such materials include Hytrel, a polyester-polyether
copolymer and Pebax, a nylon or polyamide-polyether copolymer.
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TPE’s
•
•
•
•
•
•
Advantages
TPE materials have the potential to be recyclable since they can be molded, extruded and reused
like plastics, but they have typical elastic properties of rubbers which are not recyclable owing to
their thermosetting characteristics. TPE also require little or no compounding, with no need to add
reinforcing agents, stabilizers or cure systems. Hence, batch-to-batch variations in weighting and
metering components are absent, leading to improved consistency in both raw materials and
fabricated articles. TPEs can be easily colored by most types of dyes. Besides that, it consumes less
energy and closer and more economical control of product quality is possible.
[edit] Disadvantages
The disadvantages of TPEs relative to conventional rubber or thermoset are relatively high cost of
raw materials, general inability to load TPEs with low cost fillers such as carbon black (therefore
preventing TPEs from being used in automobile tires), poor chemical and heat resistance, high
compression set and low thermal stability. TPEs soften or melt at elevated temperature above
which they lose their rubbery behaviour. TPEs show creep behaviour on extended use.
[edit] Processing
The two most important manufacturing methods with TPEs are extrusion and injection molding.
Compression molding is seldom, if ever, used. Fabrication via injection molding is extremely rapid
and highly economical. Both the equipment and methods normally used for the extrusion or
injection molding of a conventional thermoplastic are generally suitable for TPEs. TPEs can also be
processed by blow molding, thermoforming and heat welding.
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TPE applications
• TPE's are used where conventional elastomers cannot provide the range of
physical properties needed in the product. These materials find large
application in the automotive sector and in household appliances sector,
some general examples of object made of TPE are shown in this demo.
Thus copolyester TPE's are used in snowmobile tracks where stiffness and
abrasion resistance is at a premium. They are also widely used for
catheters where nylon block copolymers offer a range of softness ideal for
patients. Thermoplastic Silicon & Olefin blends like Exelast SX are used for
extrusion of glass run and dynamic Weatherstripping car profiles. Styrene
block copolymers are used in shoe soles for their ease of processing, and
widely as adhesives. TPE is commonly used to make suspension bushings
for automotive performance applications because of its greater resistance
to deformation when compared to regular rubber bushings. TPE is also
finding more and more uses as an electrical cable jacket/inner insulation.
• Applications
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Route 1: direct synthesis from monomers. BAMO + AMMO
Route 2: TPE synthesis followed by exchange of chlorine groups with Na
azide
SYNTHESIS OPTIONS
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Route 1. Direct synthesis of TPE containing azide groups
T.S. Reddy, J.K. Nair, R. S. Satpute, G. M. Gore, A. K. Sikder, Rheological studies on energetic thermoplastic
elastomers, J. Appl. Polym. Sci. 118, 2365-2368 (2010).
ROUTE 1. TPE DIRECT SYNTHESIS
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BAMO-AMMO copolymer
BAMO: C5H8N6O
AMMO:C5H9N3O
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BAMO, AMMO decomposition
C 5 H 8 N 6 O 
 3N 2  H 2 O  3 H 2  5C
3
C 5 H 9 N 3 O 
 N 2  H 2 O  4 H 2  5 C
2
Green, recyclable propellants can be
formed in place, and heated (carefully) to
remove/reuse them in new geometries.
Thus, they are not crosslinked in place.
Storage lives may be 5-20 years.
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• Composite:
heterogeneous mixture
of powdered metal,
crystalline oxidizer and
polymer binder
• 70% NH4ClO4, 16% Al,
14% polymer binder
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Polymer binders
• Estane (thermoplastic polyurethane), Hytrel
(thermoplastic polyester elastomer) and EVAc
(ethylene vinyl acetate) have been used for
binders.
• However, binders with azido, nitro or natrato
groups would increase combustion, providing
energetic TPEs
• Typical choices: polyBAMO, polyAMMO
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BAMO-AMMO copolymers
BAMO:AMMO
Mn, Mw
PD
KOH/g
Tg, C
Tm, C
100:0
6250, 18700
2.99
18.6
-30
78
80:20
3430, 5200
1.5
32
-36
56
50:50
1200, 1600
1.3
93
-43
41
20:80
3060, 4480
1.46
36
-51
9
0:100
1000, 1740
1.7
112
-30
Liquid
Physical properties
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BAMO-AMMO copolymers
BAMO:AMMO
Measurement T,
Storage
modulus
at
crossover
G’, Pa
Crossover
frequency,
Hz
Viscosity, cPs
100:0
80
-
-
Solid @ RT
80:20
75
2.5e02
17
1000 (solid @
RT)
50:50
50
8.8e03
7
20,000
20:80
30
3.7e03
17
15,500
0:100
30
6.5e03
28
10,400
rheological properties
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Rheology
• Poly(BAMO): very high elastic modulus (due to
symmetric hard block). Shear thinning at low
frequencies, then dilatant behavior (shear
thickening) at higher frequencies
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BAMO:AMMO 20:80
BAMO:AMMO 80:20
The copolymer with more hard block
segments has an elastic modulus
greater than its viscous modulus at high
frequencies. The behavior is reversed
for the copolymer with more soft block
segments
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Route 2: Copolymer synthesis with azide substitution
J.-J. Jutier, A. de Gunzbourg, R. E. Prud’hommer, Synthesis and characterization of poly(3,3bis(azidomethyl)oxetane-co-e-caprolactone)s, J. Polym. Sci.: Part A. Polymer Chem., 37, 1027-1039 (1999).
Poly(3,3-bis(azidomethyl) oxetaneco-e-caprolactone)s
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Good control of Mw
Mw/Mn close to one for well defined
flow and thermal properties
bifunctionality
Low Tg (< -40 C). It should not be glassy
at launch conditions
SRP REQUIREMENTS
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Poly(BCMO-co-e-CL) pathway
• Quasi-living cationic
copolymerization
• BCME, e-CL in
methylene chloride, 0 C
• Mw/Mn 1.0
• HO-[copolymer-O]-H; f
~ 2.0
• Catalyst is BF3 etherate
+ 1,4-butanediol as
coinitiator
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• Reactivity ratios:
BCMO=0.26; e-CL=0.47;
• Tg < -40 C
• Substitution of chlorine
via NaN3, DMSO, 110 C
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Alternatives to poly(BCMO-co-e-CL)
thermoplastic elastomers
• Homopolymers, multiblock copolymers,
random copolymers based on oxetane and
oxetane derivatives
• Telechelic low Tg prepolymer with
monofunctional high Tg
prepolymer/crystalline prepolymer as the
terminal hard blocks (telechelic = can be
polymerized via its end groups)
• Linear ABA triblock copolymers
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PCL
• PCL. Tg = -60
C; Tm = 60 C
• FDA approved
for sutures,
drug delivery,
tissue
engineering,
adhesion
barrier
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3,3-bis(chloromethyl)oxetane
• Extremely hazardous
substance
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polymerization
• Narrow Mw/Mn suggests using ionic polymerization system
• Cationic polymerization with Lewis acid (BF3) in LMW
alcohol, diethylene glycol or 1,4-butanediol (BF3: OEt2/BDO
in 2:1 ratio)
• Activated monomer mechanism that reduces cyclic
oligomers; dihydroxy-terminated chains
• Pure poly(BAMO) has 50 wt% nitrogen and Tg = -41 C, but
tends to crystallize
• Statistical copolymers should lead to appropriate Tg’s, with
no crystallization.
• Poly(e-CL) also crystallizes, so a statistical copolymer is
needed
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• All solvents and reagents must be dried
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Tg of BCMO/e-CL copolymer
This particular copolymer series has a Tg linear with the
mole fractions of the two component polymer
segments.
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Images from Wikipedia.org
CASE STUDY: TNT
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2,4,6-trinitrotoluene
CAS Reg # 118-96-7
Formula: C7H5N3O6
Fw = 227.13 kg/kmol
Names: TNT, Trotyl, Triton, …
Density: 1654 kg/m3
Melting point: 80.35 C; boiling point: 295 C (decomposition)
Solubility: 0.13g/L in water; soluble in ether, acetone, benzene, pyridine
EU classification: explosive (E), toxic (T), environmental hazard (N)
NFPA 704
TRINITROTOLUENE
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background
• Common explosive with convenient handling
properties
• C6H2(NO2)3CH3
• Standard measure of explosive strength
• Synthesis: multi-step process. Nitration of toluene (nitric + sulfuric
acid) to MNT/separation/nitration to DNT then nitration to TNT in
anhydrous mixtures of nitric acid + oleum. NOX in feed nitric acid must be
controlled to prevent oxidation of methyl group.
• Stabilization: aqeous sodium sulfite to remove less stable isomers
and other byproducts. Rinse water is a significant pollutant.
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applications
• Common explosive for military and industrial
applications
• Low sensitivity to shock & friction; ignition
temperature is well above the melting point
• Does not sorb water, relatively stable.
• Block sizes: 0.25, 0.5 and 1 kg.
• Synergistic blends with other exposives
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
Explosive characteristics
2C 7 H 5 N 3 O 6  3 N 2  5 H 2 O  7 CO  7C
•Explosives decompose to elements, stable molecules (mostly) without the aid of
external oxidizing agents.
•Exothermic, high activation energy
•Carbon is a product, leading to sooty appearance of explosions
•Ignition with a high velociy initiator or by concussion
•Reference point – Figure of Insensitivity

•The Figure of Insensitiveness is determined from impact testing, typically using a drop-weight tower. In this test, a small
sample of the explosive is placed on a small steel anvil which is slotted into a recess in the base of the drop tower. A
cylindrical, 1 kilogram steel weight (mounted inside a tube to accurately guide its descent to the impact point in the centre
of the anvil) is then dropped onto the test specimen from a measured height. The specimen is monitored both during and
after this process to determine whether initiation occurs. This test is repeated many times, varying the drop height
according to a prescribed method. Various heights are used, starting with a small distance (e.g. 10 cm) and then
progressively increasing it to as high as 3 metres. The series of drop heights and whether initiation occurred are analysed
statistically to determine the drop height which has a 50% likelihood of initiating the explosives. The intention of these tests
is to develop safety policies/rules which will govern the design, manufacturing, handling and storage of the explosive and
any munitions containing it.
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Energy content
• 4.6 megajoules/kg (energy density)
– Nuclear weapons are measured in megatons of
TNT
– Gunpowder: 3 MJ/kg
– Dynamite: 7.5 MJ/kg
– Gasoline: 47.2 MJ/kg (gas+O2=10.4 MJ/kg)
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500 ton TNT
explosion,
1965,
wikipedia.org
Note white blast
wave at water
surface and
condensate cloud
caused by shock
wave.
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