Molecular weight Polyvinyl chloride

Plasticisers. Plasticisers are low molecular weight materials which alter the properties and forming characteristics of the plastic. An important example is the production of flexible grades of polyvinyl chloride by the use of plasticisers. 

SynChropak CATSEC columns are evaluated similarly using a polyvinyl-pyridine standard of molecular weight 600,000 and cytidine. The mobile phase is 0.1 % trifluoroacetic (TEA) acid containing 0.2 M sodium chloride. Minimum plate counts are listed in Table 10.4. 

Polyvinyl chloride/Polyvinyl acetate Good prevent yellowing. High-molecular-weight organotin stabilizers improve radiation stability color-corrected radiation formulations are available. Less resistant than PVC. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

Thermal Effects in Addition Polymerizations. Table 13.2 shows the heats of reaction (per mole of monomer reacted) and nominal values of the adiabatic temperature rise for complete polymerization. The point made by Table 13.2 is clear even though the calculated values for T dia should not be taken literally for the vinyl addition polymers. All of these pol5Tners have ceiling temperatures where polymerization stops. Some, like polyvinyl chloride, will dramatically decompose, but most will approach equilibrium between monomer and low-molecular-weight polymer. A controlled polymerization yielding high-molecular-weight pol)mier requires substantial removal of heat or operation at low conversions. Both approaches are used industrially. 

The properties of a polymer depend not only on its gross chemical composition but also on its molecular weight distribution, copolymer composition distribution, branch length distribution, and so on. The same monomer(s) can be converted to widely differing polymers depending on the polymerization mechanism and reactor type. This is an example of product by process, and no single product is best for all applications. Thus, there are several commercial varieties each of polyethylene, polystyrene, and polyvinyl chloride that are made by distinctly different processes. 

When many molecules combine the macromolecule is termed a polymer. Polymerization can be initiated by ionic or free-radical mechanisms to produce molecules of very high molecular weight. Examples are the formation of PVC (polyvinyl chloride) from vinyl chloride (the monomer), polyethylene from ethylene, or SBR synthetic rubber from styrene and butadiene. 

Figure 2. Intrinsic viscosity-molecular weight data for polystyrene and polyvinyl chloride measured by osmometry and by SEC using broad MWD standard calibration (polystyrene (m) M = 7,06 X 10 in THF/1% PPG (O) [ ] =...

Figure 3. Molecular weight calibration curves for polyvinyl chloride obtained using universal calibration and one and two broad MWD standards (two broad standard method (0) [rj = 7.06 X 10 single broad standard method ...

A more common decision concerns the production of a material made to different specifications in one plant. In the production of polyvinyl chloride (PVC) there are many different possible products. The average molecular weight may differ, as well as the range of molecular weights. It may be sold in pellets or powder, may or may not be colored, and it may or may not have certain impurities present. The permuta-... 

Addition polymers, which are also known as chain growth polymers, make up the bulk of polymers that we encounter in everyday life. This class includes polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Addition polymers are created by the sequential addition of monomers to an active site, as shown schematically in Fig. 1.7 for polyethylene. In this example, an unpaired electron, which forms the active site at the growing end of the chain, attacks the double bond of an adjacent ethylene monomer. The ethylene unit is added to the end of the chain and a free radical is regenerated. Under the right conditions, chain extension will proceed via hundreds of such steps until the supply of monomers is exhausted, the free radical is transferred to another chain, or the active site is quenched. The products of addition polymerization can have a wide range of molecular weights, the distribution of which depends on the relative rates of chain grcnvth, chain transfer, and chain termination. 

Figure 22.3 Example of weight average molecular weight of polyvinyl chloride as a function of polymerization temperature...

The greater the rate constant for chain transfer, the lower the molecular weight of the polymer. One way to affect the rate constants is by changing the temperature. In general, the chain transfer rate constant is much more sensitive to temperature effects, increasing dramatically as the temperature is increased. For these reasons, there is an inverse correlation between temperature and molecular weight of polyvinyl chloride as shown in Fig. 22.3. 

Vinyl chloride polymerization occurs via an exothermic radical reaction. In fact, the reaction is approximately 25% more exothermic than polyethylene polymerization. The highly exothermic nature of the reaction and the strong molecular weight dependence on temperature make heat transfer, and its control, critical to the manufacture of polyvinyl chloride. 

The plasticizer-range alcohols are largely used as feedstock for production of high molecular weight diesters of phthalic, adipic, azelaic, and sulftiric acids. All these are used primarily in plasticizers for polyvinyl chloride (PVC) and other plastics. The plastics industry also uses them as additives for heat stabilization, to control the viscosity of PVC plastisols, ultraviolet absorbers, flame retardants, and antioxidants. They are also found in synthetic, lubricants, agricultural chemicals, and defoamers. 

Polyvinyl Chloride. The results obtained for a polyvinyl chloride sample are listed in Table 5. It is seen that the measured molecular weight statistics are in reasonable agreement with the nominal values. The Mark-Houwink parameters K and a obtained from the linear plot of log [nl vs. log M are in good agreement with one group of literature values (41-43) while the a value is lower than that of another group. (3,44-46)... 

Although some polymers may be satisfactory when used under the stress of static loads, they may fail when subjected to impact. The impact resistance, or resistance to brittle fracture, is a function of the molecular weight of a polymer. Thus uhmwpe is much more resistant to impact failure than general purpose high-density polyethylene (hdpe). The impact resistance of brittle polymers is also increased by the addition of plasticizers. Thus polyvinyl chloride (PVC), plasticized by relatively large amounts of dioctyl phthalate, is much less brittle than unplasticized rigid PVC. 

Intractable polymers, such as polyvinyl chloride (PVC), may be flexibilized, to some extent, by the formation of copolymers, such as the copolymers of vinyl chloride and vinyl acetate or octyl acrylate, or by the addition of nonvolatile low-molecular-weight compounds (plasticizers) having solubility parameters similar to those of the polymer. Thus PVC is plasticized by the addition of dioctyl phthalate. The flexibility of these products is proportional to the amount of plasticizer added. Copolymers, such as the vinyl chloride-vinyl acetate copolymer, require less plasticizer to obtain the same degree of flexibility. 

Deters, and Huang (129) describe the formation of graft copolymers of cellulose triacetate and vinyl chloride in vibratory mill treatments. Through hydrolytic degradation of the triacetate backbone, they isolated the polyvinyl chloride side chains and characterized them by infrared spectroscopy and cryoscopic molecular weight determination. The length of the side chains has been found to be between 15 and 30 vinyl chloride units. 

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