Elsevier

Polymer

Volume 40, Issue 6, March 1999, Pages 1473-1480
Polymer

Relationship between sequence distribution and transesterification of PEN/PET random/block copolyesters

https://doi.org/10.1016/S0032-3861(98)00374-7Get rights and content

Abstract

The random and block copolyesters of poly(ethylene 2,6 naphthalate) (PEN) and poly(ethylene terephthalate) (PET) are synthesized and studied by 1H-n.m.r., DSC, X-ray. The block length decreases and the degree of transesterification increases at a similar composition ratio. The melting point depressions occur with increasing the content of the other component, and melting peaks disappear at a similar composition ratio. The results of X-ray diffractograms match well with those of dyads fraction, block length, and DSC. It can be seen that a critical block length is needed for components in order to crystallize.

Introduction

The industrial use of polymer blends was growing rapidly. This growth is largely caused by the unique combination of properties which is sometimes achieved by blending two or more polymers. The polyesters have also been used for many commercial blends.

The occurrence of transesterification reaction in polyesters was known for many years [1]. However, it is only recently that more detailed descriptions of the kinetics of the transesterification and the sequence length distribution in the resulting copolymer were obtained [2], [3], [4]. In addition, extensive investigations relating to the transesterification and crystallization behaviour were performed mainly in blends of polycarbonate and poly(ethylene terephthalate)(PET) [5], [6], [7] or poly(butylene terephthalate)(PBT) [8], [9].

The transesterification plays an important role in the formation of block or random copolyesters. The majority of studies in the literature have qualitatively monitored transesterification through phase changes as measured by DSC, WAXD [10], [11]. These indirect analyses cannot provide quantitative information in regard to the transesterification in the polyester blends. Yamadera and Murano [12] investigated the sequence distribution and randomness of copolyesters using direct measurement and some other studies [13], [14] have employed direct measurements, such as i.r. and n.m.r. to identify the transesterification between two polyesters.

Accordingly, we try to find the relationship between sequence distribution and transesterification of PEN/PET random/block copolyesters including crystallization and thermal behaviour. The degree of transesterification is also confirmed by the observation of the melting point and the crystal pattern.

Section snippets

Synthesis of PEN/PET random copolyesters

PEN/PET cooligomers were synthesized from dimethyl 2,6 naphthalate (DMN), dimethyl terephthalate (DMT) and ethylene glycol (EG) with zinc acetate as a catalyst. The starting materials were of commercial grade and were used without further purification. The synthesis of the cooligomers was carried out with agitating at 230°C for 2 h. The polycondensation reaction was continued at 285°C for 2 h under vacuum using antimony trioxide as a catalyst and trimethylphosphate as a stabilizer. The obtained

Measurements

The inherent viscosity of PEN/PET copolyesters was measured in o-chlorophenol with an Ubbelohde viscometer at 25°C±0.1°C (dl g−1). The density was measured with a gradient density column at 25°C±0.1°C using a mixture of n-heptane and carbon tetrachloride.

The composition determination and the sequence distribution analysis of the copolyesters were conducted on 1H-n.m.r. spectra recorded using a Bruker 500 MHz FT-n.m.r. spectrometer. Samples were dissolved in deuterated trifluoacetic acid.

Thermal

Analysis ofsequence distribution

The PEN/PET random and block copolyesters were almost amorphous. Therefore the PEN/PET copolyesters were isothermally annealed and crystallized at 30°C below melting point (Tm) to attain a high degree of crystallinity. Table 1 and Table 2 show the annealing condition of quenched PEN/PET random and block copolyesters.

The inherent viscosity and the density decrease at a similar composition ratio of PEN and PET in both random and block copolyesters. In the block copolyester, the inherent viscosity

Conclusion

The relationship, between sequence distribution and transesterification of PEN/PET random/block copolyesters including crystallization and thermal behaviour was investigated. At a similar composition ratio and with blending time, the degree of transesterification increases but the block length decreases. The melting peak depressions occur with increasing content of the other component and the melting peaks disappear at a similar composition ratio. Because the crystal peaks of PEN/PET random and

Acknowledgments

This work was supported from the research fund of Lotte scholarship foundation.

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