Poly ethylene-2,6-naphthalene properties

Blending of poly(ethylene terephthalate) (PET) and poly (ethylene naphthalene-2,6-dicarboxylate) (PEN) has been shown to be an attractive possibility to combine the inherent economics of PET with the superior mechanical, thermal and barrier properties of PEN [24]. The molecular structure of PEN is stiffer than that of PET due to the presence in its main chain of naphthalene instead of benzene rings. The glass-transition temperature, Tg, of PEN is about 50° C higher than that of PET contributing to a better performance in terms of thermal, mechanical, and gas barrier properties [17,24]. PET and... 

Although PET and PBT are widely used, better thermal and mechanical properties are desired for some applications. Higher performance in semiaromatic polyesters was obtained from polyalkene naph-thalates. These semicrystalline polyesters are prepared by the condensation polymerization of naphtha-lene-2,6-dicarboxylic acid and flexible aliphatic diols. The naphthalene moiety imparts stiffness to the linear polymer backbone, leading to improved physical and mechanical, barrier, chemical resistance properties, and UV-ray screening performance. Poly(ethylene naphthalene-2,6-dicarboxylate), PEN, became commercially available from Teijin Ltd. in the early 1970s. PEN has a Tg and of 125 and 268°C, respectively [34]. Its structure appears in Fig. 1.18. 

Properties and Applications of Poly(Ethylene 2,6-Naphthalene), its Copolyesters and Blends... 

Biaxially Oriented Poly(Ethylene 2,6-Naphthalene) Films Manufacture, Properties and Commercial Applications... 

The modification of PET with naphthalene-2,6-dicarboxylic acid and other additional comonomers is a common measure in bottle manufacturing. Copolyesters based on this compound show excellent barrier properties. Such materials can be produced by addition of the desired amount of comonomer during polymer processing or by blending PET with poly(ethylene naphthalate) (PEN). Additionally, PEN can also be modified by other comonomers such as isophthalic acid (IPA) to improve the flow properties and reduce the melting point. The high price of naphthalene dicarboxylic acid is the reason for its limited application. The overall cost may be reduced by using TPA or IPA as comonomers. 

Poly(ethylene naphthalate) (PEN) is also completely analogous to PET except that it incorporates a naphthalene group in its main structure as opposed to a phenyl group. The naphthalene unit stiffens the backbone and gives PEN a higher glass transition temperature and improved mechanical properties when compared to PET (see Chapters 9 and 10). 

Regioselective dialkylation of naphthalene is another reaction of considerable interest as 2,6-dialkylnaphthalenes can be oxidised to naphthalene-2,6-dicarboxylic acid, which is used in the synthesis of the commercially valuable polymer, poly(ethylene naphthalenedicarboxylate) (PEN).22 PEN has properties that are generally superior to those of polyethylene terephthalate) (PET) and has become the polymer of choice for a variety of applications such as in films, industrial fibres, packaging, liquid crystalline polymers, coatings, inks and adhesives. However, the high cost of naphthalenedicarboxylic acid has been a major hindrance to widespread application. 

There have been many efforts to commercialize 2,6-dicarboxynaphthalene for the preparation of poly(ethylene-2,6-naphthalate) due to its favorable thermoplastic properties compared with PET. Therefore, there are numerous patents in which 2,6-alkyl-substituted (alkyl = methyl, ethyl, isopropyl) naphthalenes are oxidized to the corresponding aromatic di-acids, applying mostly Co/Mn/Br catalysts with various co-catalysts such as Zr or Pd in acetic acid as the solvent. The major byproduct is formed by the oxidation of the naphthalene ring to give trimellitic acid (TMA) [5a, 8]. Sumikin Chemical has developed a method to prepare 2,6-naphtha-lenedicarboxylic acid by oxidation of 2,6-diisopropylnaphthalene (2,6-DIPN) in the liquid phase with air in a 500 tpy plant. Sumikin uses a newly developed catalyst based on Co/Mn with an addition of a few ppm of Pd giving advantages such as yields higher than 90 %, suppression of TMA production to around 1 %, and thus better catalyst recovery, and reduced consumption of acetic acid. 

This chapter covers fundamental and applied research on polyester/clay nanocomposites (Section 31.2), which includes polyethylene terephthalate (PET), blends of PET and poly(ethylene 2,6-naphthalene dicarboxy-late) (PEN), and unsaturated polyester resins. Section 31.3 deals with polyethylene (PE) and polypropylene (PP)-montmorillonite (MMT) nanocomposites, including blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and high density polyethylene (HDPE). Section 31.4 analyzes the fire-retardant properties of nanocomposites made of high impact polystyrene (HIPS), layered clays, and nonhalogenated additives. Section 31.5 discusses the conductive properties of blends of PET/PMMA (poly (methyl methacrylate)) and PET/HDPE combined with several types of carbon... 

Poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) is considered as an alternative to PET for packaging applications due to its better barrier properties against gases as CO2 and oxygen. However, the higher price for 2,6-naphthalene dicarboxylic acid prevents the wide range use of this material. 

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