Polytetrafluoroethylene molecular weight

Substances other than enzymes can be immobilized. Examples include the fixing of heparin on polytetrafluoroethylene with the aid of PEI (424), the controUed release of pesticides which are bound to PEI (425), and the inhibition of herbicide suspensions by addition of PEI (426). The uptake of anionic dyes by fabric or paper is improved if the paper is first catonized with PEI (427). In addition, PEI is able to absorb odorizing substances such as fatty acids and aldehydes. Because of its high molecular weight, PEI can be used in cosmetics and body care products, as weU as in industrial elimination of odors, such as the improvement of ambient air quaHty in sewage treatment plants (428). 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

Polytetrafluoroethylene (Teflon) (PTFE) is the most corrosion-resistant thermoplastic polymer. This polymer is resistant to practically every known chemical or solvent combination and has the highest useful temperature of commercially available polymers. It retains its properties up to 500°F (260°C). Because of its exceedingly high molecular weight PTFE is processed by sintering. The PTFE resin is compressed into shapes under high pressure at room temperature and then heated to 700°F (371°C) to complete the sintering process. 

Polytetrafluoroethylene Degradation into low-molecular-weight products ("micropowders") used as additives to coatings, lubricants, and inks High-energy irradiation at 200-400 kGy... 

The high-molecular-weight perfluoropolyethers obtained in the first step have excellent thermal stability (TGA initial decomposition >370°C) and chemical resistance and are true fluorocarbon elastomers that are, in contrast to polytetrafluoroethylene, flexible. Other methods for the synthesis of perfluoropolyethers and functionalized perfluoropolyethers are under development in our laboratories. 

Polytetrafluoroethylene is a linear polymer of the general formula -(CF2 CF2) — Its molecular weight (106 to 107) and its melting point (327 °C) are extremely high The usable temperature range of PTFE extends from below... 

Starkweather, H. W. A comparison of the rheological properties of polytetrafluoroethylene below its melting point with certain low-molecular weight smectic states. J. Polymer Sci., Polymer Phys. Ed. 17, 73 (1979)... 

A routine method for determining relative crystallinity based on the amorphous bands in the spectrum has proved more rapid and precise than the x-ray method. In practice, the ratio of the 778 cm-1 (12.85 ft) and 2367 cm-1 (4.22 ft) band intensities is measured. Use of a ratio eliminates the thickness measurement and increases precision to about 1% at 50% crystallinity and considerably better at higher levels. A density measurement and an infrared crystallinity determination when combined give an estimate of the fraction of microvoids which can occur in molded specimens of polytetrafluoroethylene. The density of a sample is predicted on the basis of its crystallinity as measured by the infrared method and the difference between this density and the actual density measured by displacement in water is a measure of the microvoid content. This determination is precise to about 0,2% voids by volume. By the use of confirmatory infrared measurements, it is possible to check the possibility that the presence of a substantial percentage of voids may have led to erroneous indications of the molecular weight in the standard specific gravity test discussed earlier. 

The vacuum pyrolysis of thin samples of polytetrafluoroethylene follows first-order kinetics with monomer as the major decomposition product in the temperature range from 360—510° C (Siegle, Muus, and Lin). The rate constant does not depend on either the molecular weight or the type of polymer and is characterized by an activation enthalpy of 83.0 kcal/mole and a frequency factor of 3 x 1019 sec-1. The melt viscosity decreases during pyrolysis. 

A. C. Knight, J. H. Peterson and C. A. Sperati The molecular weight of polytetrafluoroethylene. Meeting of the American Chemical Society, Atlantic City, September 1956. 

PC PE PES PET PF PFA PI PMMA PP PPO PS PSO PTFE PTMT PU PVA PVAC PVC PVDC PVDF PVF TFE SAN SI TP TPX UF UHMWPE UPVC Polycarbonate Polyethylene Polyether sulfone Polyethylene terephthalate Phenol-formaldehyde Polyfluoro alkoxy Polyimide Polymethyl methacrylate Polypropylene Polyphenylene oxide Polystyrene Polysulfone Polytetrafluoroethylene Polytetramethylene terephthalate (thermoplastic polyester) Polyurethane Polyvinyl alcohol Polyvinyl acetate Polyvinyl chloride Polyvinyl idene chloride Polyvinylidene fluoride Polyvinyl fluoride Polytelrafluoroethylene Styrene-acrylonitrile Silicone Thermoplastic Elastomers Polymethylpentene Urea formaldehyde Ultrahigh-molecular-weight polyethylene Unplasticized polyvinyl chloride... 

Random chain cleavage followed by chain unzipping is characterized by high monomer yields and a slow decrease in the molecular weight of the polymer, for example, exhibited by PMMA, poly(a-methyl styrene), polystyrene polytetrafluoroethylene. 

Title Directly Polymerized Low Molecular Weight Granular Polytetrafluoroethylene... 

TABLE 1. Single-step experimental parameters used in preparing low molecular weight granular polytetrafluoroethylene using either ethane or chloroform as chain transfer agents. 

Perfluoroalkylvinyl ethers form an important class of monomers in that they are used as comonomers for the modihcation of the properties of homofluoropolymers in addition to their broad nse in copolymers with TFE and other monomers. They are capable of snppressing the crystallization of PTFE efficiently, which imparts usefnl mechanical properties to lower molecular weight of polytetrafluoroethylene polymers. Copolymers of PAVEs and tetrafluoroethylene are thermally stable as PTEE homopolymers. Commercially significant monomers are perfluoropropylvinyl ether and perflnoromethylvinyl ether (PMVE), used for the production of a variety of perflnoroalkoxy resins. 

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