1. 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, (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, (2010).
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2. TPE synthesis, properties
SRP slurry casting
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3. TPE synthesis, properties
Ammonium perchlorate
Properties
Molecular formula NH4ClO4
Molar mass g/mol
Appearance white granular
Density g/cm3
Melting point
Exothermic decomposition before Tm at >200 °C
Solubility in water 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
2 NH4ClO4 → Cl2 + N2 + 2 O2 + 4 H2O
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4. TPE synthesis, properties
SRP composite fuel
Heterogeneous mixture of powdered metal, crystalline oxidizer and polymer binder.
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5. TPE synthesis, properties
TPE background
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6. 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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7. TPE synthesis, properties
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-butadiene-styrene 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 synthesis, properties

8. TPE synthesis, properties
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 synthesis, properties

9. TPE synthesis, properties
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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10. TPE synthesis, properties
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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11. Route 1. TPE direct synthesis
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, (2010).
Route 1. TPE direct synthesis
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12. TPE synthesis, properties
BAMO-AMMO copolymer
BAMO: C5H8N6O
AMMO:C5H9N3O
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13. BAMO, AMMO decomposition
Composite: heterogeneous mixture of powdered metal, crystalline oxidizer and polymer binder
70% NH4ClO4, 16% Al, 14% polymer binder
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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14. TPE synthesis, properties
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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15. TPE synthesis, properties
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
Liquid
Physical properties
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16. Storage modulus at crossover G’, Pa Crossover frequency, Hz
BAMO-AMMO copolymers
BAMO:AMMO
Measurement T,
Storage modulus at crossover G’, Pa
Crossover frequency, Hz
Viscosity, cPs
100:0 80 - RT
80:20 75
2.5e02 17
1000 RT)
50:50 50
8.8e03 7
20,000
20:80 30
3.7e03
15,500
0:100
6.5e03 28
10,400
rheological properties
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17. TPE synthesis, properties
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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18. TPE synthesis, properties
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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19. Poly(3,3-bis(azidomethyl) oxetane-co-e-caprolactone)s
Route 2: Copolymer synthesis with azide substitution
J.-J. Jutier, A. de Gunzbourg, R. E. Prud’hommer, Synthesis and characterization of poly(3,3-bis(azidomethyl)oxetane-co-e-caprolactone)s, J. Polym. Sci.: Part A. Polymer Chem., 37, (1999).
Poly(3,3-bis(azidomethyl) oxetane-co-e-caprolactone)s
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20. TPE synthesis, properties
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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21. 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
Reactivity ratios: BCMO=0.26; e-CL=0.47;
Tg < -40 C
Substitution of chlorine via NaN3, DMSO, 110 C
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22. 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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23. TPE synthesis, properties
PCL
PCL. Tg = -60 C; Tm = 60 C
FDA approved for sutures, drug delivery, tissue engineering, adhesion barrier
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24. 3,3-bis(chloromethyl)oxetane
Extremely hazardous substance
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25. TPE synthesis, properties
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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26. TPE synthesis, properties
All solvents and reagents must be dried
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27. 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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28. TPE synthesis, properties
Images from Wikipedia.org
Case study: TNT
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29. TPE synthesis, properties
2,4,6-trinitrotoluene
CAS Reg #
Formula: C7H5N3O6
Fw = kg/kmol
Names: TNT, Trotyl, Triton, …
Density: 1654 kg/m3
Melting point: 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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30. TPE synthesis, properties
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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31. TPE synthesis, properties
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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32. Explosive characteristics
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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33. TPE synthesis, properties
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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34. TPE synthesis, properties
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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