Makromol. Chem., Rapid Commun. 1,403 - 406 (1980) 403

Polyamides Containing Imido Groups by Low Temperature Polycondensation

Sajal Om, Sukurnar Maiti*

Polymer Materials Laboratory, Materials Science Centre, Indian Institute of Technology, Kharagpur 721 302, India

(Date of receipt: April 29, 1980)

Introduction

Polyamides containing imido groups are well recognized as a class of commercially thermo- stable polymers'-5). There are various methods for their ~ y n t h e s i s ~ - ~ ) : (1) Reaction of a diamine containing an amido group with a dianhydride'), (2) reaction of a low molecular- weight polyimide having amino end groups with a diacid dichloride3), (3) reaction of a diamine with the acid monochloride of trimellitic acid anhydride (TMA)4), (4) reaction of a diacid dichloride containing an imido group with a diamine'), and (5 ) reaction of an amide containing imido groups and amino end groups with a diacid dichloride6).

All known methods of polymerization, except the last two, require high tempera- ture. Recently, Imai et al.9) have reported a facile synthesis of polyamides by a direct polycondensation of dicarboxylic acids with diamines in the presence of thionyl chloride at low temperature via the intermediately formed corresponding diacyl di- chloride. This has prompted us to apply this method for the preparation of poly- amides containing imido groups.

Results and Discussion

The polycondensation of dicarboxylic acids containing cyclic imido groups with aromatic diames was carried out at low temperature (= - 5 "C) in l-methyl-2- pyrrolidone (NMP) in the presence of thionyl chloride.

HOOC QJJNQ -

o coon 1 2

SOCI, - 3

5

404 S. Das, S. Maiti

General characteristics of the resulting polyamides 3 and 5 are shown in Tab. 1. Their structures were confirmed by their nitrogen content and their IR spectra (Fig. 1). The characteristic absorption bands of the imido groups were found at 1 780 (symmetrical carbonyl stretching) at 1 720 (assymmetrical carbonyl stretching) at 720 (possibly due to ring carbonyl deformation) and at 1 650 and 1 540 cm- (amide).

Tab. 1.

Polymer Yield Inherent Density T, b, Nitrogen content

Yield; and characteristic data of polyamides containing imido groups

viscositya) in % in d1.g-l in g . ~ m - ~ in "C Calc. Found

3 73 0,09 1,21 220 10,96 10,68 5 82 0,12 1,23 240 10.96 10,83

a) Measured in DMF at 35 "C (0,5 weight-% solution). b, Calc. from DTA curves (Fig. 2).

I L

4000 3500 3000 2500 2000 1 8 0 0 1600 1400 1200 1000 EOO 600 Wave number in cm-'

Fig. 1 . IR spectra of the polyamides 3 and 5

The molecular weights of the polymers were found to be relatively low (Tab. l), which may be due to some side reactions. Further studies to improve the molecular weight of the polymers in this low temperature polycondensation method are under progress.

The polymers were found to be soluble in highly polar solvents like m-cresol, N,N-di- methylformamide (DMF), N,N-dimethyl acetamide, NMP, and dimethyl sulfoxide, but insoluble in methanol, acetone, chloroform, benzene, toluene, xylene, and nitro- benzene. Similar solubilities have been reported by Kurita et a1.8) for polyamides containing imido groups prepared by another method.

Thermogravimetric determinations (TG) of 3 and 5 indicate a weight loss at 300°C of only 12% and a complete weight loss at 650- 700°C in air (Fig. 2). The glass transition temperatures, T,, for the polymers were calculated from their DTA curves. They were found to be 220°C for 3 and 240°C for 5 (Tab. 1). The degradation of the polymers appears to be a single stage process and the maximum weight loss occurs at 540- 580°C.

Polyamides Containing Imido Groups by Low Temperature Polycondensation 405

100 i+ C

a2 3 U In

.-

.- p! 80 c L cn .- 2

60

40

20

0 100 200 300 400 500 600 700

Fig. 2. Thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) of polymers 3 and 5 in air; heating rate: 6"C/min. (1) : 3, (2)-: 5

Experimental Part

Preparation of the monomers: The dicarboxylic acid, N-(2-~arboxyphenyI)trimellitimide (1) and N-(3-~arboxyphenyl)trimillitimide (4) were prepared from o-aminobenzoic acid or m-aminobenzoic acid, respectively, and trimellitic acid anhydride in N,N-dimethylformamide solution. The details of the experimental procedure are given elsewhere lo).

Polymerization procedure: 3,110 g (10 mmol) of the dicarboxylic acid 1 or 4 were dissolved in 20 ml of 1-methyl-2-pyrrolidone and stirred in a 100 ml three-necked flask fitted with a stirrer, a thermometer, and a calcium chloride tube. The solution was cooled to about - 15 "C when 2,40 g (20 mmol) of thionyl chloride were added to the solution and stirred for 1 - 2 min. Then, 1,081 g (10 mmol) of m-phenylenediamine (2) and 1,580 g (20 mmol) of pyridine were added to the mixture. The reaction mixture was stirred for 8 h at - 5 "C and then it was poured over ice/water. The precipitated polymer was isolated by filtration, washed thoroughly with cold water, and dried. It was purified by reprecipitation from dimethylformamide solution by methanol.

Characterization of the polymers: The IR spectra were recorded with a Perkin-Elmer Model 157G spectrophotometer in KBr pellets. DTA was carried out with a Hungarian Mom Derivato- graph of Paulik Paulik Erdey System.

The authors express their sincere thanks to Dr. D. 0. Shah, Deepak Nitrite Ltd. for taking the IR spectra.

406 S. Das, S. Maiti

‘1 “Amoco Amide-Imide Polymers” Technical Bulletin AM-1, Amoco Chemical Corp., USA *) B. A. Bolton, R. J. Dieterle, Plast. Des. Process. 1967, 13 3, H. Lee, D. Stoffey, K. Neville, “New Linear Polymers”, McGraw-Hill, New York 1967,

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