Hydrocarbon polymers polymerization

Hydrocarbon Polymers. It is difficult to produce perfluorocarbon polymers by the usual methods. Many monomers, such as hexafluoropropylene, polymerize only slowly because of the steric hindrance of fluorine. Furthermore, some monomers are not very stable and are difficult to synthesize. Direct fluorination can be used for the direct synthesis of fluorocarbon polymers (68—70) and for producing fluorocarbon coatings on the surfaces of hydrocarbon polymers (8,29,44—47,49,68—71). 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Precipitation polymerizations dominated the early work which aimed at preparing industrially important hydrocarbon polymers in C02. In 1968, Hagiwara and coworkers explored the polymerization of ethylene in C02 using both gamma radiation and AIBN as free radical initiators [79]. Reactions were conducted at pressures of 440 bar and over the temperature range of 20-45 °C. 

Polymeric materials are used as binders to hold sohd particles together so as to formulate composite explosives or composite propellants. The polymeric materials also constitute part of the fuel ingredients when the crystalline particles are oxidizer-rich. Various types of hydrocarbon polymers are used as polymeric binders. 

Polymeric materials used as fuel components of pyrolants are classified into two types active polymers and inert polymers. Typical active polymers are nitropoly-mers, composed of nitrate esters containing hydrocarbon and oxidizer structures, and azide polymers, containing azide chemical bonds. Hydrocarbon polymers such as polybutadiene and polyurethane are inert polymers. When both active and inert polymers are mixed with crystalline oxidizers, polymeric pyrolants are formed. 

The polymerization products of propylene have been observed to be saturated hydrocarbon polymers and terpenelike unsaturated hydrocarbons (Kuhn, 64). The condensation of formaldehyde with phenols and cyclohexanols by means of aqueous hydrogen fluoride has also been observed (Badertscher el al., 65). 

This polymerization process involves the reaction between CO and H2 to produce hydrocarbon polymers,... 

Synthesis of well defined functionalized (- telechellc or multifunctional-) macromolecules Is an Important task for polymer chemists. The polymers with P0(0R)2, - Si(0R)3, -OH, - . .. functional groupslrS. are produced In limited quantities. The need for polymeric materials possessing specific properties has led to a renewed Interest Is functional polymers, especially if the initial material Is a common hydrocarbon polymer. One of the techniques that we use in our laboratory to prepare these new molecules Is based on anionic processes. This anionic technique is best suited to control the length of the chains prepared and to obtain samples with low polydlsperslty. Although the functionalization of carbanionic sites with various deactivating reagents Is easier than with other methods because of the long lived species, It Is still necessary to carefully control the deactivation reaction to prevent secondary reactions. 

Siloxane polymerization differs mechanistically from the formation of hydrocarbon polymers in that it is essentially an acid-base process, as might be expected from the strong alternation of electronegativites along the het-eroatomic chain, and the radical initiators that catalyze the homocatenation of alkenes do not work for siloxanes. Long, unbranched polysiloxane chains are favored by higher condensation reaction temperatures and basic catalysts such as alkali metal hydroxides. Acidic condensation catalysts tend to produce polymers of lower molar mass, or cyclic oligomers. 

In 1938, while attempting to prepare fluorocarbon derivatives, Roy J. Plunkett, at DuPont s Jackson Laboratory, discovered that he had prepared a new polymeric material. The discovery was somewhat serendipitous as the TFE that had been produced and stored in cylinders had polymerized into poly(tetra-fluoroethylene) (PTFE), as shown in Eigure 4.2. It did not take long to discover that PTFE possessed properties that were unusual and unlike those of similar hydrocarbon polymers. These properties include (1) low surface tension, (2) high Tm, (3) chemical inertness, and (4) low coefficient of friction. All of these properties have been exploited in the fabrication of engineering materials, wliich explains the huge commercial success of PTFE. 

Pitches can be transformed to a mesophase state by further chemical and physical operations. Heat treatment of conventional pitches results in additional aromatic polymerization and the distillation of low molecular weight components. This results in an increase in size and concentration of large planar aromatic molecular species whereupon the precursor pitch is transformed to a mesophase state exhibiting the characteristics of nematic liquid crystals (1). Additional heat treatment converts the mesophase pitch to an infusible aromatic hydrocarbon polymer designated as coke. 

Because of the (chain-length dependent) restricted solubility of polymers in hydrocarbons, solution polymerization requires higher temperatures and / or higher pressures. Technologically, solution polymerization processes are similar to the high-pressure LDPE process, see chapter 3, and will not be discussed here. 

The quality of the water used in emulsion polymerization affects the manufacture of ESBR. Water hardness and other ionic content can directly affect the chemical and mechanical stability of the polymer emulsion (latex). Solution polymerization can use various solvents, primarily aliphatic and aromatic hydrocarbons, SSBR polymerization depends on recovery and reuse of the solvent for economical operation as well as operation under the air-quality permitting of the local, state, and federal mandates involved,... 

Most types of polymerizations can be performed in liquid and supercritical C02. The two major types of polymerizations, chain-growth and step-growth, have been demonstrated in C02. Reviews in the literature (Canelas and DeSimone, 1997b Kendall et al., 1999) have described numerous polymerizations in C02, many of which will not be discussed in this chapter. Since only amorphous or low-melting fluoropolymers and silicones show appreciable solubility at relatively mild temperatures and pressures (T< 100 °C, P<400 bar), only these two classes of polymers can be synthesized by a homogeneous polymerization in C02. All other types of polymers, including semicrystalline fluoropolymers and lipophilic or hydrophilic polymers, must be made by heterogeneous methods, such as precipitation, dispersion, emulsion, and suspension, since the polymers are insoluble in C02 (when T< 100 °C and P<400 bar). Some semicrystalline fluoropolymers and hydrocarbon polymers can be dissolved at more extreme temperatures and pressures and are discussed in Chapter 7 of this book. 

The second article by Kawahara and his coworkers focuses on polyolefin (PO)-based hybrid materials (POH), in view of their synthesis, structures, and properties. POs are currently the most widely and conveniently used polymeric materials as recognized by the production amount of over one hundred million tons annually in the world, due to the cheap price yet good properties. They are basically hydrocarbon polymers, and hence hydrophobic and less polar. These basic properties are to be modified by introducing a polar function for a wider use in practical applications. Preparation of POHs is one of the best ways to... 

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