Polymethylpentene

As recently as 1986 almost all addition polymers were excluded from the ranks of engineering plastics. However, progress since then has been made in the development of addition polymeric resins such as polymethylpentene and polycyclopentadiene and its copolymers (see Cyclopentadiene AND DICYCLOPENTAD IENE). 

Fig. 11. Effect of polyolefin primers on bond strength of ethyl cyanoacrylate to plastics. All assemblies tested in accordance with ASTM D 4501 (block shear method). ETFE = ethylene tetrafluoroethylene copolymer LDPE = low-density polyethylene PFA = polyper-fluoroalkoxycthylene PBT = polybutylene terephthalate, PMP = polymethylpentene PPS = polyphenylene sulfide PP = polypropylene PS = polystyrene PTFE = polytetrafluoroethylene PU = polyurethane. From ref. [73].

Materials compatibility. We use scrupulously clean and scratch-free FEP (FEP is the acronym for the copolymer of tetrafluoroethylene and hexafluoropropylene) tubing for handling our mixtures of fluorine and nitrogen at ambient temperature. Corrugated FEP tubing is convenient for making strain-free assemblies. We have found that Monel is excellent for use with dry molten KF-2HF. Mild steel corrodes slowly and stainless steels corrode rapidly. Kel-F polychlorotrifluoroethylene is satisfactory for use with HF and with KF-2HF polypropylene and polymethylpentene are not satisfactory. 

Using Ziegler-Natta polymerization, methylpentene is converted to polymethylpentene (PMP), as shown in Figure 4.17. 

Polymethylpentene is sensitive to pro-oxidant metals such as copper but protective masterbatches are marketed. 

The glass transition temperatures of polymethylpentenes by DSC measurements are generally in the room temperature range, from 20°C up to 30°C. The glass temperatures by DTMA measurements can be higher, depending on the frequency. 

Transparency is one of the main advantages of polymethylpentenes and some grades are especially designed for high light transmission, for example 90-92%. Let us remember that transmission data are of the order of 98% for polystyrene. 

The refractive index varies with the type of polymethylpentene, and can be, for example, about 1.463. 

Thermoplastic neat polymethylpentenes have rather low moduli involving high strains for moderate loading. Consequently ... 

Polymethylpentene resists hydrolysis well but is naturally sensitive to light and UV. It must be protected by addition of specific anti-UV and other protective agents. 

Polymethylpentenes have very weak loss factors, about 2 X 10 , and do not heat up under high-frequency current. They can be used for microwave ovenware but cannot be welded by the high-frequency technique. 

Neat polymethylpentenes absorb little water and are not very sensitive to it. 

Suitable grades are usable in contact with food and are used for food packaging. Chemical resistance is generally good but polymethylpentenes are attacked by oxidizing acids, chlorinated solvents, certain oxidants and aromatic hydrocarbons. Resistance to aliphatic hydrocarbons, ketones, gasoline and kerosene is limited. 

Polymethylpentene is more permeable to gases than some other polyolefins. 

Table 4.12 Polymethylpentenes examples of chemical behaviour at room temperature...

Fire resistance is naturally weak. Standard grades burn easily generating flames, even after the ignition source is removed. Moreover, polymethylpentene drips while burning. 

The opacity of a crystalline polymer may also be reduced by copolymerization. Even so, polymethylpentene (TPX) is transparent because the n values of the amorphous and the crystalline phase are quite similar. Transparency may also be enhanced by copolymerization of the methylpentene with a small amount of another polymerizable olefin with a similar n. 

R. Akki and H. Shin, Flash spinning polymethylpentene process and product, US Patent 6352773, assigned to E. I. du Pont de Nemours and Company (Wilmington, DE), March 5,2002. 

Mitsui Chemicals, Polymethylpentene processing method, [electronic ] http //www.mitsuichemicals.com/tpx proc.htm, 2008. 

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