Poly ethylene

In this section, selected results for other polymers will be presented. It will be demonstrated that our method is applicable to a wide range of systems belonging to different structural classes, including the simplest polymer poly (ethylene) (PE), a bisubstituted polyolefine (poly (isobutylene), PIB), unsaturated systems (poly(butadiene), PBD and poly(isoprene), PIP), polymers with hetero atoms (poly(vinyl chloride), PVC), and extended sidegroups (poly(methyl methacrylate), PMMA). 

All compounds (including aPP presented in the previous chapter) were used as purchased. For the polymers with a glass transition temperature Tg below room temperature (aPP, PIB, PBD, PIP, PE), the sample was slowly cooled down in the course of the NMR measurement, and the spectra were recorded after the glass transition temperature was reached. If Tg is above room temperature (PVC, PMMA), the samples were measured without prior treatment at ambient temperature. 

If technically possible, all samples were heated and cooled down again. In neither case, the amorphous solid state spectrum changed appreciably after performing these mild temperature programs. No special procedures (like precipitation from solution) were chosen to influence the microstructure of the glassy amorphous state. 

Poly(ethylene) (PE) (Fig. 7) is the simplest polymer and permits the investigation of fundamental questions. PE is a semicrystalline compound, and in a solid state NMR spectrum normally both the crystalline phase (around 33 ppm) and an amorphous contribution 31 ppm) can be observed (Fig. 33.a). At room temperature, the amorphous resonance is motionally averaged. The glass transition temperature in this semicrystalline system is still a matter of some controversy [100, 101, 102], but most likely the calorimetric glass point is somewhat below 200 K, perhaps as low as 150 K. Experimentally, the recording of the solid state NMR spectrum of the amorphous 

In a way, poly(ethylene) is the typical chain molecule and has attracted a lot of theoretical interest. Fortunately, the various model descriptions of the conformational statistics are quite similar [105, 5, 27]. The models assume three rotational isomeric states (t, g ) with slightly different values for the 

This polymer has one of the simplest molecular structures ([CH2CH2— ] ) and is at present the largest toimage plastic material, having first been produced commercially in 1939 for use in electrical insulation. There is a difficulty over the nomenclature of this polymer. The lUPAC recommended name for the monomer is ethene, rather than the older ethylene. Hence the lUPAC name for the polymer is poly (ethene). However, this name is almost never used by chemists working with the material throughout this book, therefore, this polymer will be referred to by its more widespread name, poly(ethylene). 

There are four different industrial routes to the preparation of poly (ethylene), and they yield products having slightly different properties. The four routes are  

Ziegler processes are based on co-ordination reactions catalysed by metal alkyl systems. Such reactions were discovered by Karl Ziegler in Germany and developed by G. Natta at Milan in the early 1950s. 

A typical Ziegler-Natta catalyst is the complex prepared from titanium tetrachloride and triethylaluminium. It is fed into the reaction vessel first, after which ethylene is added. Reaction is carried out at low pressures and low temperatures, typically no more than 70 °C, with rigorous exclusion of air and moisture, which would destroy the catalyst. The poly(ethylenes) produced by such processes are of intermediate density, giving values of about 0.945 g cm. A range of relative molar masses may be obtained for such 

Lastly the Phillips and the Standard Oil (Indiana) Processes both yield high density poly(ethylenes), using relatively low pressures and temperatures. Details of these processes are given in Table 1.1. 

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Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70.

Alexandridis P and Hatton T A 1995 Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) blook oopolymer surfaotants in aqueous solutions and at interfaoes thermodynamios, struoture, dynamios, modeling Colloids Surf. A 96 1-46... 

ETHYLENE We discussed ethylene production in an earlier boxed essay (Section 5 1) where it was pointed out that the output of the U S petrochemi cal industry exceeds 5 x 10 ° Ib/year Approximately 90% of this material is used for the preparation of four compounds (polyethylene ethylene oxide vinyl chloride and styrene) with polymerization to poly ethylene accounting for half the total Both vinyl chloride and styrene are polymerized to give poly(vinyl chloride) and polystyrene respectively (see Table 6 5) Ethylene oxide is a starting material for the preparation of ethylene glycol for use as an an tifreeze in automobile radiators and in the produc tion of polyester fibers (see the boxed essay Condensation Polymers Polyamides and Polyesters in Chapter 20)... 

Polyethylene films as packaging ma terial plastic squeeze bottles are molded from high density poly ethylene... 

Poly(ethylene Terephthalate). Poly(ethylene terephthalate) is prepared by the reaction of either terephthalic acid or dimethyl terephthalate with ethylene glycol, and its repeating unit has the general structure. 

Commonly used isocyanates are toluene dhsocyanate, methylene diphenyl isocyanate, and polymeric isocyanates. Polyols used are macroglycols based on either polyester or polyether. The former [poly(ethylene phthalate) or poly(ethylene 1,6-hexanedioate)] have hydroxyl groups that are free to react with the isocyanate. Most flexible foam is made from 80/20 toluene dhsocyanate (which refers to the ratio of 2,4-toluene dhsocyanate to 2,6-toluene dhsocyanate). High-resilience foam contains about 80% 80/20 toluene dhsocyanate and 20% poly(methylene diphenyl isocyanate), while semi-flexible foam is almost always 100% poly(methylene diphenyl isocyanate). Much of the latter reacts by trimerization to form isocyanurate rings. 

Low viscosity 30% glass-fiber reinforced Poly(butylene terephthalate) Poly(ethylene terephthalate) ... 

Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example, the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly(oxyethylene oxyterphthaloyl) according to the lUPAC system, as well as poly (ethylene terephthalate) or polyethylene terephthalate. 

Nylon-6,6 cord Poly (ethylene terephthalate) cord ... 

Poly(ethylene oxide). Although AH j is more than double that of polyethylene, the effect is offset by an even greater increase for AS j. The latter may be due to increased chain flexibility in the liquid caused by the regular insertion of ether oxygens along the chain backbone. 

Next let us examine an experimental test of the Avrami equation and the assortment of predictions from its various forms as summarized in Table 4.3. Figure 4.9 is a plot of ln[ln(l - 0)" ] versus In t for poly (ethylene terephtha-late) at three different temperatures. According to Eq. (4.35), this type of... 

Figure 4.9 Log-log plot of ln(l - 6) versus time for poly(ethylene tereph-thalate) at three different temperatures. [Reprinted from L. B. Morgan, Philos. Trans. R. Soc. London 247A 13 (1954).]...

The crystallization of poly(ethylene terephthalate) at different temperatures after prior fusion at 294 C has been observed to follow the Avrami equation with the following parameters applying at the indicated temperatures ... 

Poly(ethylene terephthalate) was crystallized at 110°C and the densities were measuredf after the indicated time of crystallization ... 

Ester interchange reactions are valuable, since, say, methyl esters of di-carboxylic acids are often more soluble and easier to purify than the diacid itself. The methanol by-product is easily removed by evaporation. Poly (ethylene terephthalate) is an example of a polymer prepared by double application of reaction 4 in Table 5.3. The first stage of the reaction is conducted at temperatures below 200°C and involves the interchange of dimethyl terephthalate with ethylene glycol... 

The ethylene glycol liberated by reaction (5.L) is removed by lowering the pressure or purging with an inert gas. Because the ethylene glycol produced by reaction (5.L) is removed, proper stoichiometry is assured by proceeding via the intermediate, bis(2-hydroxyethyl) terephthalate otherwise the excess glycol used initially would have a deleterious effect on the degree of polymerization. Poly(ethylene terephthalate) is more familiar by some of its trade names Mylar as a film and Dacron, Kodel, or Terylene as fibers it is also known by the acronym PET. 

The windows of the absorption cell are made from polymer material such as polyethylene, poly(ethylene terephthalate Terylene ) or polystyrene. 

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