Comparison of one-step and two-step methods of polyimidization and substitution effect in the synthesis of new poly(ester-imide)s with bulky pendent group

doi:10.1016/j.polymdegradstab.2006.05.004

Polymer Degradation and Stability

Volume 91, Issue 11, November 2006, Pages 2622-2631

https://doi.org/10.1016/j.polymdegradstab.2006.05.004 Get rights and content

Abstract

New naphthalene-ring containing ester diamines, as new monomers for the preparation of polyimides were synthesized via two successive reactions. Nucleophilic reaction of 3,5-dinitrobenzoylchloride with 1-naphthol and 2-naphthol in the presence of sodium hydroxide led to the preparation of 1- and 2-(3,5-dinitrobenzoyloxy)naphthalene, respectively. Next step was reduction of them by hydrazine hydrate/Pd–C to produce 1- and 2-(3,5-diaminobenzoyloxy)naphthalene. All the prepared compounds were characterized by common spectroscopic methods. These ester containing aromatic diamines with pendent naphthalene group were used to prepare soluble polyimide copolymers via two different methods: catalyzed one-step high-temperature polycondensation in m-cresol, and two-step polycondensation in NMP and subsequent chemical dehydration. The obtained poly(ester-imide)s were characterized and their properties were studied. One-step and two-step methods for the preparation of five-membered ring polyimides were compared. Polymers prepared through one-step method showed higher yield and inherent viscosities and therefore better physical properties.

Introduction

Wholly aromatic polyimides are engineering plastics with high mechanical properties, good chemical resistance, excellent thermal and oxidative stabilities, and low flammability and are widely used in the semiconductor and electric packaging industry [1], [2]. However, their applications are restricted by their poor processability, limited solubility in common organic solvents and high melting point. These make it impossible for most polyimides to be directly processed in their imidized forms, thus their applications have been restricted in some fields. To overcome these problems, incorporation of bulky pendent groups and aliphatic units, and the disruption of their symmetry have been suggested [3], [4], [5], [6], [7], [8], [9]. Therefore, various efforts have been focused on the preparation of soluble or thermoplastic polyimides, while still maintaining the excellent thermal and mechanical properties [10], [11], [12], [13].

Copolycondensation is one of the possible ways for the modification of polymer properties. Therefore, one useful method to improve the solubility of the polyimides without too much sacrificing of their thermal stability is copolymerization. Poly(ester-imide)s are one of the important copolymers that show good balance between processability and thermal stability. For the preparation of PEIs, either esterification of imide containing material or imidization of ester containing material has been used [14], [15].

Generally, polyimides can be prepared via two different methods. One-step method consists of stirring of a dianhydride and a diamine in a high-boiling solvent at 180–220 °C. Under these conditions chain growth and imidization occur spontaneously. In the two-step method of polyimide synthesis, a dianhydride is added to a solution of diamine in a polar aprotic solvent at ambient temperature. The generated polyamic acid is then cyclodehydrated to the corresponding polyimide by extended heating at elevated temperatures or by treatment with chemical dehydrating agents.

To prepare soluble and thermally stable polyimides, the present study deals with the synthesis and characterization of new diamine monomers containing ester group and related polyimides therefrom. Properties of the prepared polymers including inherent viscosity, thermal behavior, solubility and crystallinity were studied. The structure–property relations of the polyimides based on the structure of diamines and different dianhydrides were investigated and also one-step and two-step methods for the preparation of polyimides were compared.

Section snippets

Materials

All chemicals were purchased either from Merck or Aldrich Chemical Co. Dianhydrides were dried in a vacuum oven at 110 °C for 6 h. N-Methyl-2-pyrrolidone (NMP) and m-cresol were distilled under reduced pressure over CaH₂ and P₂O₅, respectively.

Instruments

Infrared measurements were performed on a Bruker-IFS 48 FTIR spectrometer (Ettlingen, Germany). The H NMR spectra were recorded in DMSO-d₆ solution using a Bruker Avance DPX 250 MHz (GmbH, Germany). Elemental analyses were performed by a CHN-O-Rapid Heraeus

Results and discussion

The main objective of this study was the preparation of diamines with bulky naphthyl group to improve solubility and processability of resulted polyimides without substantial diminution on thermal stability and also investigation of structure–property relation by variation of the substituent position on the naphthyl ring and comparison of one-step and two-step methods of polyimidization.

Accordingly, two aromatic diamines bearing ester and naphthyl units were synthesized. Scheme 1, Scheme 2 show

Conclusion

Two ester diamines with bulky naphthyl unit were prepared via reaction of 3,5-dinitrobenzoyl chloride with 1- and 2-naphthols and subsequent reduction of nitro groups with hydrazine hydrate and Pd–C. Different aromatic poly(ester-imide)s were obtained by reactions of the diamines with dianhydrides through one-step and two-step methods. It was observed that polymers derived from one-step imidization process had higher molecular weight and therefore higher thermal stability than the similar

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Comparison of one-step and two-step methods of polyimidization and substitution effect in the synthesis of new poly(ester-imide)s with bulky pendent group

Abstract

Introduction

Section snippets

Materials

Instruments

Results and discussion

Conclusion

Eur Polym J

Eur Polym J

Eur Polym J

Polymer

Engineering thermoplastics

Thermally stable polymers

J Appl Polym Sci

Macromolecules

Macromolecules

High-performance polymers