Halogenated polyolefins

Halogenated polyolefins form another class of polymers. Some of the polymers from this class have important practical applications. Among these are poly(vinyl chloride), poly(vinylidene chloride), and polytetrafluoroethylene. Several unusual polymers such as poly(vinyl bromide) also are included in this class. Most halogenated polymers are obtained by the polymerization of a halogenated monomer. However, chemical modification (e.g. chlorination) of a preexistent polymer also can be applied to obtain partially halogenated materials. 

Polymers with saturated carbon chain backbone 

Some of the halogenated polyolefins are vinyl derivatives such as poly(vinyl chloride) and poly(vinyl fluoride), some are vinylidene derivatives, and others are polymers with even higher levels of halogenation. For example, from monomers of fluorinated ethylenes, the following polymers can be obtained  

The polymer is commonly obtained from vinyl chloride with a peroxide initiator such as peroxydicarbonates, fert-butylperpivalate, benzoyl or lauroyl peroxide, acetyl cyclohexylsulfonyl peroxide, or azobis(2,4-dimethylvaleronitrile). The polymerization can be done by suspension, emulsion or solution techniques. Low polymerization temperatures are used when high MW material is required. Suspension polymerization employs water suspension agents, such as poly(vinyl alcohol) or methylcellulose. The resulting polymer Is a partially syndiotactic material but with low crystallinity. The macromolecules typically have head to tail linkages (H-T) and a small proportion (less than 1.5%) of branching. Ziegler-Natta catalysts are not used to produce PVC. 

PVC is relatively unstable to heat, and at temperatures as low as 200° C begins to decompose. The decomposition of PVC has a complex chemical mechanism [1 ] and takes place in two steps, the first being dehydrochlorination, and the second being the 

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Other thermoplastic elastomer combiaations, ia which the elastomer phase may or may not be cross-linked, include blends of polypropylene with nitrile (30,31), butyl (33), and natural (34) mbbers, blends of PVC with nitrile mbber (35,36), and blends of halogenated polyolefins with ethylene interpolymers (29). Collectively, thermoplastic elastomers of this type ate referred to herein as hard polymer/elastomer combinations. Some of the more important examples of the various types are shown in Table 3. 

Radio-chemical graft copolymerization with good efficiency on halogenated polyolefins has been carried out by contacting the substrate with monomer (styrene) vapor [158,159]. Interpenetrating polymer network (IPN) could be made by grafting the monomers on preirradiated substrates... 

Polymers with saturated carbon chain backbone include polyolefins, polystyrenes, halogenated polyolefins, halogenated polystyrenes, polyvinyls substituted with various groups such as -OH, -OR, -0(0)C-R, -C(0)0-R, -C(0)-R, -C5H4N, etc. In this class also are included polyacrylates, polymethacrylates, polymers with ketone groups in the backbone, as well as other polymers with saturated carbon chain backbone. The polymers with a saturated carbon chain backbone form the most important and common class of polymers. 

Another halogenated polyolefin that contains chlorine and fluorine in the molecule is poly(ethylene-a/f-chlorotrifluoroethylene), CAS 25101-45-5. As shown in Section 2.1, the pyrolysis of this polymer takes place with the side chain elimination of FICI and FIF by the following reaction ... 

Halogenated polyolefins obtained from a preexistent polymer... 

An interesting case of halogenated polyolefin is that of halogenated poly(vinyl chloride). After-chlorination of PVC improves thermal stability of the polymer. The distribution of chlorine atoms in chlorinated PVC has been studi successfully using Py-GC [57]. 

Similar to vinyl derivatives, a number of substituted vinylidene polymers are used in practice. Some of these polymers are part of classes of polymers such as halogenated polyolefins and were discussed separately (see Section 6.3 and 7.5). One example of polymer that can be indicated here is poly(vinylidene cyanide). Its pyrolysis generates a high yield of monomer [42],... 

Alcryn (Advanced Polymer Alloys Division of Ferro Corporation) is an example of a melt-processable rubber. These are partially cross-linked halogenated polyolefin MPR blends. The specific gravity ranges from 1.08 to 1.35. 

PVC/nitrile rubber/DOP blends Halogenated polyolefin/ethylene interpolymer blends... 

Behavior of Precision Halogenated Polyolefins 10.4.2.1 Precise Fluorine Placement... 

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