Polymers, thermoplastic addition

Four thermoplastic addition polymers—polyethylene, poly(vinyl chloride), polypropylene, and polystyrene—comprise the majority of the total amount of polymers manufactured in the United States. In 2002 a total of 33.6 million metric tons of these plastics was produced, distributed as shown in Table 24.1. 

Thermoplastic addition polymers - The common addition polymers are those based on a polyethylene backbone. Their synthesis starts with the catalytic activation of monomers such as ethylene, propylene or vinyl chloride to free radicals. These combine sequentially in an addition or chain reaction. The polyethylene backbone consists of a chain of methylene groups. The other common addition polymers, as illustrated in Figmes 1 and 2, are essentially polyethylenes with one or both of the hydrogens on the methylene group substituted. 

Noryl. Noryl engineering thermoplastics are polymer blends formed by melt-blending DMPPO and HIPS or other polymers such as nylon with proprietary stabilizers, flame retardants, impact modifiers, and other additives (69). Because the mbber characteristics that are required for optimum performance in DMPPO—polystyrene blends are not the same as for polystyrene alone, most of the HIPS that is used in DMPPO blends is designed specifically for this use (70). Noryl is produced as sheet and for vacuum forming, but by far the greatest use is in pellets for injection mol ding. 

Because commercial synthetic thermoplastic polymers are either addition polymers or condensation polymers, depolymerization occurs by different routes. Addition polymers, for which the synthesis reactions are essentially not reversible, depolymerize by pyrolysis or such severe chemical attack that few useful monomers can be practically recovered. With pyrolysis, a wide spectrum of species are created, which offers little in the way of valuable reaction products without costly separation processes. The overall yield to desired products can be unattractively low. 

The lack of mechanical strength for thermoplastic hyperbranched polymers makes them more suitable as additives in thermoplast applications. Hyperbranched polyphenylenes have been shown to act successfully as rheology modifiers when processing linear thermoplastics. A small amount added to polystyrene resulted in reduced melt viscosity [31]. (Sect> 3.1). 

Polybrominated Diphenyl Ethers. PBDEs are used as additive flame retardants in thermoplastics. Additive flame retardants are physically combined with the polymer material being treated rather than chemically combined (as in reactive flame retardants). This means that there is a possibility that the flame retardant may diffuse out of the treated material to some extent. 

In general, any additives that are common in the polyolefin sector can be used to achieve the desired properties. We will summarize additives for thermoplastic metathesis polymers. These include (6) ... 

Cyclic olefin copolymers (COC)s are engineering thermoplastics derived from norbornene. An addition polymer of norbornene was originally described in 1955 (1). 

In Chapter 14 (p. 226) you studied the different addition polymers produced from alkenes. Not all polymers are formed by addition reactions, though. Some are produced as a result of a different type of reaction. In 1935 Wallace Carothers discovered a different sort of plastic when he developed the thermoplastic, nylon. Nylon is made by reacting two different chemicals together, unlike poly(ethene) which is made only from monomer units of ethene. Poly(ethene), formed by addition polymerisation, can be represented by ... 

During the same period, commercialization of thermoplastic starch polymer blends was pursued by Novamont, a division of the Ferruzzi Group of Italy.162-172 Their products, marketed under the trade name Mater-Bi, are typically comprised of at least 60% starch or natural additive and hydrophilic, biodegradable synthetic polymers.64,165 It is stated that these blends form interpenetrated or semi-interpenetrated structures at the molecular level. Properties of typical commercial formulations have properties similar to those in the range of low- and high-density PE. Blends of Mater-Bi products with biodegradable polyesters have been claimed for use as water impervious films.173... 

Ebdon, J. R., Hunt, B. J., Joseph, P., and Konkel, C. S., Flame-retarding thermoplastics Additive versus reactive approach, in Speciality Polymer Additives Principles and Applications, Al-Malaika, S., Golvoy, A., and Wilkie, C. A. (Eds.), 2001, Blackwell Science, Oxford, U.K., pp. 231-257. 

Most addition polymers are thermoplastics that is, they are hard at room temperature but soften and eventually melt as they are heated. At low temperatures there is very little motion of the molecules and the polymer is glasslike and brittle. As the temperature of the polymer is raised, it passes through its glass transition temperature (Tg). Above J , more motion of the chains is possible and the polymer is a rubbery solid. Eventually, the polymer passes through its crystalline melting point (Tm) and melts to form a viscous liquid. Many semicrystalline polymers are most useful at temperatures between Tg and Tm. Both Tg and Tm increase as the crystallinity of the polymer increases and as the strength of the intermolecular forces between the polymer chains increases. The total intermolecular force increases as the length of the polymer chains increases. 

In common with most thermoplastics, ABS polymers are not flame resistant. In principle, a flame-resistant ABS could be made by incorporating halogen- and/or phosphorus-containing structures either by (a) copolymerization of appropriate monomers or (b) addition of small molecules containing these structures as plasticizers. Recognizing that the second approach can involve a serious loss in heat deflection temperature, hardness, and occasionally impact strength (4), we have favored the copolymerization approach in the work described here. 

Acyl cations are involved as propagating species in the synthesis of poly-(ether ketone)s. Poly (ether ketone)s are a class of thermoplastic crystalline polymers that have many desirable properties that make them useful as high-performance engineering materials [153,154]. The poly(ether ke-tone)s with the most useful properties are actually para-linked poly(aryl-ether ketone)s (PAEKs). They have excellent chemical resistance to oxidation and hydrolysis, high thermal stability, and many useful mechanical properties. Unlike some other materials with similar properties they are readily melt processable using conventional equipment. In addition, their mechanical properties are not affected deleteriously by most solvents. These polymers are usually crystalline. PAEKs contain arene groups joined by ether and carbonyl linkages. For example, two commercial poly-(ether ketone)s are PEK and PEEK (Fig. 36). 

The chemist classifies polymers in several ways. There are thermosetting plastics such as Bakelite and melamine and the much larger category of thermoplastic materials, which can be molded, blown, and formed after polymerization. There are the arbitrary distinctions made among plastics, elastomers, and fibers. And there are the two broad categories formed by the polymerization reaction itself (1) addition polymers (e.g., vinyl polymerizations), in which a double bond of a monomer is transformed into a single bond between monomers, (2) condensation poly-... 

In terms of nanocomposite reinforcement of thermoplastic starch polymers there has been many exciting new developments. Dufresne [62] and Angles [63] highlight work on the use of microcrystalline whiskers of starch and cellulose as reinforcement in thermoplastic starch polymer and synthetic polymer nanocomposites. They find excellent enhancement of properties, probably due to transcrystallisation processes at the matrix/fibre interface. McGlashan [64] examine the use of nanoscale montmorillonite into thermoplastic starch/polyester blends and find excellent improvements in film blowability and tensile properties. Perhaps surprisingly McGlashan [64] also found an improvement in the clarity of the thermoplastic starch based blown films with nanocomposite addition which was attributed to disruption of large crystals. 

The protection of polymers against high doses (20 - 1000 kGy) requires efficient additives preventing and/or stopping chain reaction type oxidative degradation. Primary and secondary antioxidants work well here in synergy. Commercial raw materials are available for radiation-sterilizable medical devices made out of polyolefins and other thermoplastics. Similarly, polymer compounds of suitable formulae are offered commercially for high-dose applications of polymers in nuclear installations. 

Thermoplastic additives in SMC and BMC accounted for nearly 8 kton/y consumption in the USA [Skeist, 1992]. A primary requirement for the polymer additive is that it must be amorphous with a low to moderate T and fairly soluble or dispersible in the resin matrix initially, but capable of phase separation during the polymerization. 

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