Polymer Poly vinylidene chloride

Redox initiator systems are normally used in the emulsion polymerization of VDC to develop high rates at low temperatures. Reactions must be carried out below 80° C to prevent degradation of the polymer. Poly(vinylidene chloride) in emulsion is also attacked by aqueous base. Therefore, reactions should be carried out at low pH. 

There are presently about 100 different plasticizers produced worldwide, although only about 50 of these are classified as commercially important. Of these 50 products, just 7 plasticizers comprise more than 80% of the global plasticizer market. Approximately 90% of all plasticizers are used in the production of plasticized or flexible PVC materials. For this reason, the majority of the information discussed in this chapter will focus on PVC plasticizers. Other polymer systems that use small amounts of plasticizers include poly (vinyl butyral) or PVB, acrylic polymers, poly(vinylidene chloride), nylon, polyolefins, polyurethanes, and certain fluoroplastics. The estimated worldwide production of plasticizers in 2014 was about 14 billion pounds [6] with the majority of the plasticizer consumption taking place in Asia Pacific, predominately China. About 75% of this volume is phthalate ester plasticizers. 

Membranes with pores having pore diameters in the nanometer range ean be obtained by pyrolysis. Molecular sieves can be prepared by controlled pyrolysis of thermoset polymers [poly(vinylidene chloride), poly(furfuryl alcohol), cellulose, cellulose triacetate, polyacrylonitrile (PAN), and phenol formaldehyde] to obtain carbon membranes, or of silicone rubbers to obtain silica filters. For example, carbon molecular sieves can be obtained by pyrolysis of PAN hollow fibers in an inert atmosphere, which leads to dense membranes whose pores are opened by oxidation, initially at 400°-500°C and finished at 700°C [15]. These membranes are used to separate O2 /N2 mixtures. Le Carbone-Lorraine deposits a resin into a tubular macroporous substrate and then by pyrolysis creates a thin (< 1 pm) carbon active layer. Silicon rubber tubes can be pyrolyzed in an inert atmosphere at temperatures around 700°C followed by oxidation in air at temperatures from 500° to 900°C [16]. The membranes are composed almost completely of Si02 with pores having a maximum porosity of 50% and diameters fi om 5 to 10 nm. The permeabilities for He, H2, O2, and Ar range from 0.5 to 5 x 10 m s Pa. 

Vinylidene chloride copolymers were among the first synthetic polymers to be commercialized. Their most valuable property is low permeabiUty to a wide range of gases and vapors. From the beginning in 1939, the word Saran has been used for polymers with high vinylidene chloride content, and it is still a trademark of The Dow Chemical Company in some countries. Sometimes Saran and poly (vinylidene chloride) are used interchangeably in the Hterature. This can lead to confusion because, although Saran includes the homopolymer, only copolymers have commercial importance. The homopolymer, ie, poly (vinylidene chloride), is not commonly used because it is difficult to fabricate. 

Ninety-six percent of the EDC produced in the United States is converted to vinyl chloride for the production of poly(vinyl chloride) (PVC) (1) (see Vinyl polymers). Chloroform and carbon tetrachloride are used as chemical intermediates in the manufacture of chlorofluorocarbons (CECs). Methjiene chloride, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene have wide and varied use as solvents. Methyl chloride is used almost exclusively for the manufacture of silicone. Vinylidene chloride is chiefly used to produce poly (vinylidene chloride) copolymers used in household food wraps (see Vinylidene chloride and poly(vinylidene chloride). Chloroben2enes are important chemical intermediates with end use appHcations including disinfectants, thermoplastics, and room deodorants. 

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

Similarly, oriented crystallisation can be induced by stretching sheets or films of polymers in two directions simultaneously. The resulting materials have biaxially oriented polymer crystals. Typical examples of such materials are biaxially stretched poly(ethylene terephthalate), poly(vinylidene chloride), and poly (propylene). Since the oriented crystals do not interfere with light waves, such films combine good strength with high clarity, which makes them attractive in a number of applications. 

When X = Y, as in polyethylene, poly-(tetrafluoroethylene), polyisobutylene, and poly -(vinylidene chloride), the polymers are highly crystalline products with sharply definable melting points (except for polyisobutylene, which crystallizes readily on stretching but with difficulty on cooling). Oriented specimens of high strength may be obtained, exactly as in the crystalline condensation polymers. 

A third factor influencing the value of Tg is backbone symmetry, which affects the shape of the potential wells for bond rotations. This effect is illustrated by the pairs of polymers polypropylene (Tg=10 C) and polyisobutylene (Tg = -70 C), and poly(vinyi chloride) (Tg=87 C) and poly(vinylidene chloride) (Tg =- 19°C). The symmetrical polymers have lower glass transition temperatures than the unsymmetrical polymers despite the extra side group, although polystyrene (100 C) and poly(a-meth-ylstyrene) are illustrative exceptions. However, tacticity plays a very important role (54) in unsymmetrical polymers. Thus syndiotactic and isoitactic poly( methyl methacrylate) have Tg values of 115 and 45 C respectively. 

Dual lifetime referencing (DLR) is another powerful technique that enables referenced measurements in case of fluorescent indicators [23]. In this method, the analyte-dependent signal from an indicator is referenced against the signal from an inert luminophore. This can be realized in both the time domain [24] and in the frequency domain [25]. Often, a luminescent reference dye is embedded into gas blocking nanobeads to avoid oxygen quenching. Polymers with very low gas permeability such as poly(acrylonitrile) [24] or poly(vinylidene chloride-co-acry-lonitrile) [26] are the best choice here. 

Kirkpatrick, D. E., Hyun, K.S., and Chung, C.I., Friction and Its Effect on the Mechanical-to-Thermal Energy Conversion During Extrusion of Poly(Vinylidene Chloride), Polym. Eng. Set, 33, 1261 (1993)... 

Polymers such as polystyrene, poly(vinyl chloride), and poly(methyl methacrylate) show very poor crystallization tendencies. Loss of structural simplicity (compared to polyethylene) results in a marked decrease in the tendency toward crystallization. Fluorocarbon polymers such as poly(vinyl fluoride), poly(vinylidene fluoride), and polytetrafluoroethylene are exceptions. These polymers show considerable crystallinity since the small size of fluorine does not preclude packing into a crystal lattice. Crystallization is also aided by the high secondary attractive forces. High secondary attractive forces coupled with symmetry account for the presence of significant crystallinity in poly(vinylidene chloride). Symmetry alone without significant polarity, as in polyisobutylene, is insufficient for the development of crystallinity. (The effect of stereoregularity of polymer structure on crystallinity is postponed to Sec. 8-2a.)... 

The vinyl family of polymers consists of poly(vinyl chloride), poly(vinylidene chloride), poly(vinyl acetate), and their copolymers and derived polymers. 

More than 500 million pounds of poly(vinyl acetate) (PVAc), poly(vinylidene chloride), and their copolymers and polymers derived from them are produced annually in the United States. PVAc does not have sufficient strength for producing the types of products obtained from polyethylene, polystyrene, and poly(vinyl chloride) since it is noncrystalline and has a Tg of only 28°C. However, poly(vinyl acetate) (XLI) and its copolymers find uses as... 

Dehydrochlorination of poly vinylidene chloride and chlorinated polyvinyl chloride was carried out. High chlorine content in the polymers (more than 60%) provides the formation of chlorinated conjugated polymers, polychlorovinylenes. The reactivity of chlorinated polyvinylenes contributes to the sp carbon material formation during heat treatment. Synthesis of porous carbon has been carried out in three stages low-temperature dehydrohalogenation of the polymer precursor by strong bases, carbonization in the inert atmosphere at 400-600°C and activation up to 950°C. 

The photo-cross-linkability of a polymer depends not only on its chemical structure, but also on its molecular weight and the ordering of the polymer segments. Vinyl polymers, such as PE, PP, polystyrene, polyacrylates, and PVC, predominantly cross-link, whereas vinylidene polymers (polyisobutylene, poly-2-methylstyrene, polymethacrylates, and poly vinylidene chloride) tend to degrade. Likewise, polymers formed from diene monomers and linear condensation products, such as polyesters and polyamides, cross-link easily, whereas cellulose and cellulose derivatives degrade easily. ... 

Vinylidene chloride and chloroprene (Figures 7 and 8) under the given conditions produce curves which more or less resemble the styrene curve. Vinylidene chloride especially shows a long period of a rather constant reaction rate. By the theory of Harkins and Smith-Ewart this would be interpreted as a period of constant particle number and of constant monomer concentration at the reaction site—i.e., the monomer-polymer particles. The first assumption seems justified (15). The second assumption of constant monomer concentration at the reaction site can be true only in a modified sense because poly (vinylidene chloride) is insoluble in its monomer, and the monomer-polymer particles in this system therefore have a completely different structure as compared with the monomer-polymer particles in the styrene system. 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometallic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinylidene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see VlNYL polymers). 

Many other types of polymer have been prepared which exhibit semiconductivity. All obey the equation a = a0exp — E/kT. These include xanthene polymers (109, 110), polymerized phthalocyanines (111, 112), epoxides and polydiketones (86, 113), polypentadienes (114), polydicyanoacetylenes (115), polyvinylferrocene and substituted ferrocene (116, 117, 118, 119), polymeric complexes of tetracyanoethylene and metals (120), poly(vinyl chloride) and poly(vinylidene chloride) (121), polyvinylene and polyphenylene (122) and poly(Schiff s bases) (123, 124). 

The chemical composition of poly (vinylidene chloride) has been confirmed by various techniques, including elemental analysis, x-ray diffraction analysis, degradation studies, and lr. Raman, and nmr spectroscopy. The polymer chain is made lip of vinylidene chloride units added head-to-tail ... 

Poly( vinylidene chloride) does not dissolve in most common solvents at ambient temperatures. Copolymers, particularly those of low crystallinity, are much more soluble. However, one of the outstanding characteristics of vinylidene chloride polymers is resistance to a wide range of solvents and chemical reagents. The insolubility of PVDC results less from its polarity than from its high melting temperature. It dissolves readily in a wide variety of solvents above 130°C. 

Phthalocyanine complexes, deposited as a film on a metal of the same kind as their central metal ion, appeared to be active for hydrazine decomposition 48)-Wholly organic polymers, prepared by the dechlorination of poly vinylidene chloride 62> were also shown to be active, but the ammonia and hydrogen produced reacted with the catalyst, a problem also encountered with the polychelate catalysts. 

Astafiev, I. V. Catalytic Activity of Organic Polymers. II. Catalytic Proporties of a Polymer Obtained by Dechlorination of Poly(vinylidene Chloride). Kinetika Katal. 3, 364(1962). 

Other Polymers. Various other polymers frequently require stabilization against thermal or thermo-oxidative degradation. Poly(vinylidene chloride) is stabilized by epoxides and sodium pyrophosphate. 

Inherently Stable Structure. Inherent stability of the polymer structure includes resins such as unplasticized poly (vinyl chloride) containing about 56% chlorine which is self-extinguishing and poly(vinylidene) chloride. 

The 1,1-disubstitution of chlorine atoms causes steric interactions in the polymer, as is evident from the heat of polymerization (see Table 1) (24). When corrected for the heat of fusion, it is significantly less than the theoretical value of —83.7 kJ/mol (—20 kcal/mol) for the process of converting a double bond to two single bonds. The steric strain apparendy is not important in the addition step, because VDC polymerizes easily. Nor is it sufficient to favor depolymerization the estimated ceiling temperature for poly(vinylidene chloride) (PVDC) is about 400°C. 

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