Other polyolefins

Other homopolymers of olefins are used in practice, a larger side chain typically leading to materials adequate to be used in adhesives, wax coatings, and elastomers. More frequently, practical applications are known for the copolymers of these compounds with ethylene or in synthetic rubbers with butadiene or with isoprene. The decomposition products of some of the homopolymeric olefins when heated in an inert atmosphere are indicated in Table 6.1.12. 

Polymers with saturated carbon chain backbone 

An example of a branched polymer used as a synthetic elastomer is poly(4-methyl-1-pentene), CAS 25068-26-2 [134]. The idealized structure of poly(4-methyl-1-pentene) and the formulas of a few molecular fragments found in the pyrolysate of this polymer are shown below  

The compounds identified in the pyrolysate are alkanes, alkenes and alkadienes. However, the distinction based on the mass spectra between the different isomers for hydrocarbons with a larger number of carbon atoms is not simple, and a number of peaks in the chromatogram remained unnamed. The assignment of a given mass spectrum to a specific hydrocarbon can be done in some instances only tentatively. 

The photodegradation of other polyolefins has not been studied extensively but the conclusions drawn from work with polyethylene and polypropylene are likely to be valid in general. ESR investigations of the free radicals produced in the photolysis of poly-l-butene [31], poly-4-methylpentene-1 [31, 40] and poly-1-dodecene [31] have been published. 

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There are three basic types of polyethylene foams of importance (/) extmded foams from low density polyethylene (LPDE) (2) foam products from high density polyethylene (HDPE) and (J) cross-linked polyethylene foams. Other polyolefin foams have an insignificant volume as compared to polyethylene foams and most of their uses are as resia extenders. 

S. Van der Ven, Polypropylene and Other Polyolefins Polymerisation and Characterisation, Elsevier Science PubHsliers, B. V., Amsterdam, the Netherlands, 1990. 

Above 100°C, most polyolefins dissolve in various aHphatic and aromatic hydrocarbons and their halogenated derivatives. For example, polybutene dissolves in benzene, toluene, decalin, tetralin, chloroform, and chlorobenzenes. As with other polyolefins, solubiHty of PB depends on temperature, molecular weight, and crystallinity. 

Electrical Properties. AH polyolefins have low dielectric constants and can be used as insulators in particular, PMP has the lowest dielectric constant among all synthetic resins. As a result, PMP has excellent dielectric properties and alow dielectric loss factor, surpassing those of other polyolefin resins and polytetrafluoroethylene (Teflon). These properties remain nearly constant over a wide temperature range. The dielectric characteristics of poly(vinylcyclohexane) are especially attractive its dielectric loss remains constant between —180 and 160°C, which makes it a prospective high frequency dielectric material of high thermal stabiUty. 

The main interest in polybut-1 -ene is in its use as a piping material, where the ability to use a lower wall thickness for a given pressure requirement than necessary with other polyolefins, together with the low density, can lead in some cases to economic use. The principal application is for small-bore cold and hot water piping (up to 95°C) for domestic plumbing. Current world-wide sales are of the order of 16-20X10 tonnes per annum. 

There are two great families of synthetic polymers, those made by addition methods (notably, polyethylene and other polyolefines), in which successive monomers simply become attached to a long chain, and those made by condensation reactions (polyesters, polyamides, etc.) in which a monomer becomes attached to the end of a chain with the generation of a small by-product molecule, such as water. The first sustained programme of research directed specifically to finding new synthetic macromolecules involved mostly condensation reactions and was master-... 

Brosse et al. [41] modified isotactic polypropylene and other polyolefins by a cold plasma. In isotactic polypropylene, plasma treatment results in a polypropylene crystallization of paracrystalline or smectic form into a a-crystalline form. Further, the active films are susceptible to react with monomers in a postgrafting reaction. 

Other polyolefins A variety of other crystalline polyolefins are available such as polybutene-1 (improved creep resistance over polyethylene), poly-4-methyl pentene-1 (excellent temperature deformation resistance) and ethylene-vinyl acetate (greater flexibility). 

Co-extruded films of polypropylene or other polyolefins and a flexible polyester are solutions for pouches for intravenous drug-delivery systems. 

Chemical resistance is generally good up to 60°C but, as with the other polyolefins, polybutenes are attacked by oxidizing acids, chlorinated solvents, certain oxidants and aromatic hydrocarbons. 

The cost, high for a polyolefin, and the limited number of supply sources curb the development of PMP Impact strength is rather weak versus some other polyolefins. 

Polymethylpentene is more permeable to gases than some other polyolefins. 

As with other polyolefins, upon irradiation the free radicals are formed along with evolution of hydrogen gas. If the radical is formed on the pendant methyl, the resulting reaction is cross-linking. However, if the radical is formed in the main chain, the chain end may react with hydrogen, thus causing an irreversible scission. Although the processes of chain scission and... 

As with other polyolefins, the free radicals are formed upon irradiation, along with evolution of hydrogen gas. If the radical is formed on the pendant methyl, the... 

The first article may be a polymer composition with a COC as basic material. Suitable low crystallinity polymers to fabricate the second article include COCs and blends of COCs with poly(methyl pentene), other polyolefins, and styrenics. 

S. van der Ven, Polypropylene and other Polyolefins. Polymerization and Characterization, Elsevier, Amsterdam, 1990. 

It also has a high melting point, 240°C. excellent electrical properties and higher clarity than any other polyolefin. Its weaknesses are low rigidity and solvent resistance sensitivity to oxidation and high permeability, which can sometimes be converted into a virtue. 

Since ionomers contain polar groups, their adhesion to most polar surfaces is better than that of other polyolefins. Ionomers are also employed as packaging film, golf ball covers and shoe components. 

Table I shows the production of different kinds of polyolefins [high-density polyethylene (HDPE), low-density polyethylene (LDPE), isotactic polypropylene (PP), and linear low-density polyethylene (LLDPE)] (6). Apart from LDPE (discovered by workers at ICI), which has a highly branched structure and is produced in free radical reactions at ethylene pressures of 1000-3000 bar (1 bar = 105 Pa), the other polyolefins are synthesized at far lower pressures and in the presence of catalysts (7).

When other polyolefins (such as high-density polyethylene, polypropylene, and the ethylene copolymers) were introduced into commercial use they also were found to be unreceptive to inks and adhesives, but it became apparent that many of the techniques that were in use for treating low-density polyethylene could be applied also to these newer materials. 

Since the measurement of the partition coefficients for LDPE goes much more rapidly than for the other polyolefins, it is practical to apply the K values obtained for LDPE to other polyolefins. This can be done without any large errors. 

Like other polyolefins, the polyethylenes are chemically inert. Strong oxidizing agents will eventually cause oxidation and embrittlement. They have no known solvent at room temperature. Aggressive solvents will cause softening or swelling, but these effects are normally reversible. 

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