Demetris N. Bikiaris

Chain extension of polyesters PET and PBT with two new diimidodiepoxides. II

Two new diglycidyl ester compounds containing preformed imide rings for better thermal stability were prepared to be used as chain extenders for PET and PBT. The preparation of these compounds was carried out in two steps. In the first step, diimidodiacids were prepared from pyromellitic anhydride and 3-aminopropanoic acid or 4-(aminomethyl)benzoic acid. From these diimidoacids, in a second step, diimidodiepoxides were obtained by reaction with epichlorohydrin. The aforementioned diimidodiepoxides were used as chain extenders for poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) with satisfactory results. The polyester samples obtained from various residence times in the reactor, were characterized by solution viscosity measurements, carboxyl, and hydroxyl end-group determination. Starting from a PET having intrinsic viscosity ([η]) of 0.60 dL/g and carboxyl content (CC) of 42 equiv/106 g, one could obtain PET with [η] of 1.16 and CC below 5 equiv/106 g. The typical reaction condition for the coupling of PET was its heating with the chain extender under argon atmosphere above its melting temperature (280°C) for several minutes. Analogous results were obtained for PBT. The hydroxyl content in all cases was increased.

Thermomechanical Analysis of Chain-Extended PET and PBT

Two series of samples, one of PET and another of PBT, were received after chain extension at different reaction times with two new chain extenders (diimidodiepoxides). These samples showed different intrinsic viscosity and degree of branching or crosslinking. The effect of this differentiation on thermal properties was studied by thermomechanical analysis (TMA). The parameters studied were the glass transition temperature (Tg), melting temperature (Tm), and the linear expansion coefficient (α). It is remarkable that in the case of PET amorphous or semicrystalline samples, two peaks appeared next to the Tg in the TMA thermogram. The first peak appeared at a temperature very close and lower to the Tg, and the other peak, at higher temperature into the “cold crystallization region.” The presence of two such peaks was not detected in the DSC thermogram of PET samples either in the TMS or DSC thermograms of PBT. The Tg values were found to agree to within ±1°C of those obtained from DSC; on the contrary, the Tm values varied significantly from those received from DSC. The linear expansion coefficient of samples was found to increase with the degree of chain extension.

Thermal Behavior and Tensile Properties of Poly(ethylene terephthalate-co-ethylene isophthalate)

Poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI) homopolymers were synthesized by the two-step melt polycondensation process of ethylene glycol (EG) with dimethyl terephthalate (DMT) and/or dimethyl isophthalate (DMI), respectively. Nine copolymers of the above three monomers were also synthe- sized by varying the mole percent of DMI with respect to DMT in the initial monomer feed. The thermal behavior was investigated over the entire range of copolymer com- position by differential scanning calorimetry (DSC). The glass transition (Tg), cold crystallization (Tcc), melting (Tm), and crystallization (Tc) temperatures have been determined. Also, the gradually increasing proportion of ethyleno-isophthalate units in the virgin PET drastically differentiated the tensile mechanical properties, which were determined, and the results are discussed.

Synthesis and thermal behaviour of poly(ethylene-co-butylene naphthalene-2,6-dicarboxylate)s

Abstract Poly(ethylene naphthalene-2,6-dicarboxylate) and poly(1,4-butylene naphthalene-2,6-dicarboxylate) homopolymers were synthesized by the two-step melt polycondensation process of dimethyl naphthalene-2,6-dicarboxylate and ethylene glycol (EG) or 1,4-butanediol (BD) respectively. Eight copolymers of the above three monomers were also synthesized by varying the mol% of BD with respect to EG in the initial monomer feed. The copolymer composition was determined by 1 H n.m.r. spectroscopy. The thermal behaviour was investigated over the entire range of copolymer composition by differential scanning calorimetry and thermomechanical analysis. The glass transition ( T g ), cold crystallization ( T cc ), melting point ( T m ) and crystallization ( T c ) temperatures have been determined. The melting temperature of the above copolymers was depressed gradually at first with the increase of BD in the composition and eutectic behaviour appeared with a minimum at about 40 mol% BD content.

Dynamic thermomechanical and tensile properties of chain‐extended poly(ethylene terephthalate)

A series of chemically modified poly(ethylene terephthalate) (PET) samples was received after chain extension of a virgin sample at different reaction times with a new diepoxide as chain extender. These samples showed different intrinsic viscosity and degrees of branching or crosslinking. The effect of this differentiation on thermal properties was studied by dynamic mechanical thermal analysis and the determined Tg values were found to be in good agreement with those obtained by differential scanning calorimetry and thermomechanical analysis. Also, the branching or crosslinking exhibited significant improvement in tensile mechanical properties, which were studied, and the results are discussed.

Effect of some current antioxidants on the thermo-oxidative stability of poly(ethylene terephthalate)

Abstract Four current commercial antioxidants (Naugard 445, Ethanox 330, Irganox 1098 and a blend of Irganox 1098 and 1019) were added during synthesis of poly(ethylene terephthalate) in order to test their thermo-oxidative stability and eventually to obtain more thermostable products during synthesis and processing. Their stabilization effect was evaluated by DSC analysis in nitrogen and air, using as criteria the stabilization coefficient and the induction period of oxidation. At low concentrations (0·03% and 0·10%), under the conditions used, better results were obtained with Naugard 445 and Ethanox 330, while at higher concentrations (0·5% and 1·0%) Irganox 1098 and the blend of Irganox 1098 and 1019 were better than the others.