Viking Longships, Venetian Galleys, and a New Fluoro-Polyphosphazene Architecture
There are two fundamentally different types of polymers 1. Those in which the side groups are already present in the monomer and cannot be changed after polymerization 2. Those in which the side groups can be changed after the polymer has been synthesized Nearly all classical polymers fall into category 1 One of the few systems in category 2 are the polyphosphazenes
Roughly 30-40 different classes of organic polymers Most materials scientists and engineers continue to work on existing polymers. Is there a need for new polymers?
Monomer Polymer R can generally not be changed after polymer synthesis
Secondary reactions of this type are almost impossible with classical organic polymers
Polyphosphazenes are made by starting with a reactive high polymer and introducing the side groups in a postpolymerization step. This means that not only is the backbone different from all other polymers, but also that a much wider range of side groups can be used. As the side groups are changed, the properties and potential uses are also changed. Thus, the potential applications for these polymers are much broader than for classical polymers, and structureproperty tuning is much easier.
All three aspects can be controlled in polyphosphazenes
Origin of Properties in Polyphosphazenes a. From the phosphazene polymer backbone Fire resistance Very high chain flexibility Stability to UV and high energy radiation Optical transparency throughout the visible and near-ultraviolet regions b. From the side groups Rigid bulky side groups increase the chain stiffness and raise the Tg (from -100 o C to ~200 o C) Some side groups sensitize the polymer to hydrolysis and bioerosion Bioactive side groups yield polymeric drugs Other side groups create hydrophobicity and resistance to hydrolysis Hydrophilic side groups generate polymers for membranes and hydrogels Photo-absorptive groups yield optical filters, non-linear optics, polymer dyes,etc. Fluorinated side groups generate high stability to water and to a wide range of reagents Combinations of two or more groups generate elasticity Paddle-shaped side groups can interdigitate and provide non-covalent crosslinks
Single-Substituent Fluorophosphazene Polymers Mixed-Substituent Fluorophosphazene Polymers
Properties associated with fluorinated side groups Hydrophobicity Biomedical compatibility Fire resistance Chemical stability Properties associated with phosphorus and nitrogen in the skeleton Fire resistance Much broader range of side groups than in classical polymer chemistry Side groups can be introduced after the skeleton has been assembled
Hydrophobic and Superhydrophobic Surfaces (Aerospace)
Elastomers 1. Non-crystalline 2. Hydrophobic 3. T g s as low as -60 o C 4. Non-flammable 5. Solvent and oil-resistant 6. Radiation resistance 7. Vibration damping 8. Ice-phobic 9. Biomedically inert Special Properties of Fluorophosphazene Elastomers
The Two Classical Fluorophosphazene Polymers Microcrystalline thermoplastc Rubbery elastomer (after crosslinking via allylaryloxygroups)
Tomasz Modzelewski
Synthesis
Possible Interdigitation that Underlies the Unusual Elastomeric Behavior
Eight Polymers and a Control Synthesized Ratios of bulky cyclotriphosphazene to trifluoroethoxy (TFE) side 0 : 100 mol% 0.6 : 99.4 mol% 1.2 : 98.8 2.3 : 97.7 4.0 : 96.0 5.8 : 94.2 9.3 : 90.7 14.1 : 85.9 20.8 : 79.2 (Control)
Characterization Data With increase in the cyclic trimeric side groups a. The T g rises b. The T 1 disappears c. Elasticity appears
Differential Scanning Calorimetry T 1 T g
X-Ray Diffraction and Detection of Crystallinity [NP(OCH 2 CF 3 ) 2 ] n
Mechanical Properties
Stress-Strain Curves for semi-crystalline 9 (1.2% trimer), mid-range 11 (4% trimer), and non-crystalline 13 (9.4% trimer)
Polymer 12 5.8 mol percent trimer side groups
Resistance to Combustion Both fluorine and phosphorus confer fire resistance on polymers The combination in the new elastomers gives an impressive material Limiting oxygen index = ~65
Penn State Chemistry and Life Sciences Complex
Millenium Science Complex
Experimental details related to this talk are available in a paper scheduled to appear in Macromolecules, October 2014.