4. Synthesis of (hyper)branched (HB) polyimides

Investigation of hyperbranched (HB) polymers is a new rapidly developing field of polymer chemistry. HB polyimides (HB PIs) are of special interest for development of new functional materials as they can combine unique characteristic properties of polyimides (thermal and chemical stability, photostability barrier properties, etc.) with some common characteristic properties of HB polymers (solubility, possibility of placing many functional groups in one macromolecule, etc.). Examples are described in applying HB PI as proton-conductive or gas separation membranes, photosensible materials, etc. The study of these objects is largely constrained by multistage synthesis and a number of difficulties encountered in the synthesis process. Therefore, the creation of a simple convenient synthesis methodology is an important task.

In our work [26], we used the method of one-pot high-temperature polycondensation in molten BA at 140°C for synthesis of HB PIs with reactive anhydride Synthesis of Polyimides in the Melt of Benzoic Acid DOI: http://dx.doi.org/10.5772/intechopen.87032

groups via scheme A3 + B2, the monomer B2 being AFL, and monomer A3 trianhydride of hexacarboxylic acid prepared by reaction of 1,3,5-triaminotoluene sulfate with excess of BPADA. The A3/B2 ratio was chosen 1:1-mol. HB PI prepared was found to have wide MWD, and the glass temperature was Tg = 235°C, which is 55°C less than that for corresponding linear PI AFL-BPADA. In a frame of A2 + B3 approach, HB PI with terminal amino groups was prepared from 2,4,6-tris-(4 aminophenoxy)toluene and BPADA [27]. New HB polyimide with terminal amino groups was prepared also in molten BA via A2 + B4 scheme by polycondensation of 1,4-bis(3,5-diaminophenoxy) benzene (BDAPB, B4) dialkyl semi-ester derivative of BPADA (precursor of A2) obtained by treatment of BPADA with boiling ethyl alcohol (Figure 15) [28]. Structure of the products was confirmed by IR and NMR spectroscopy.

IR spectrum of synthesized HB PI sample (Figure 16a, curve 2) contains characteristic absorption bands at 1720 and 1780 cm<sup>1</sup> (antisymmetric and symmetric stretch C=O vibrations of imide cycle). The absorption band retains at 3300–3050 cm<sup>1</sup> which is observed also in the spectrum of starting B4 (stretch N-H vibrations of amino groups) (Figure 16a, spectrum 1).

The final polymer product was obtained as beige color powder soluble in THF, DMSO, and amic solvents. Mw of HB PI obtained is of about 2\*104 . In NMR <sup>1</sup> H

Figure 15. Synthesis of hyperbranched polyimide.

Figure 16. Review IR spectra (a) and NMR <sup>1</sup> H spectra (b) of monomer B4 (1), HB PI (2), and HB PIac (3).

understanding the mechanism of PI synthesis in molten BA. The process shows symptoms typical for ideal interbipolycondensation. This means that the basic reaction—imidization—is practically irreversible at these conditions, i.e., the rate of evacuation with inert gas flow of the vapor of water released in the course of imidization is high. Otherwise, formation of long blocks would be impossible.

Dependence of parameter Km for CPI (120 min) on duration of intermonomer loading.

Typical curves of change in time of the concentration of imide cycles (1,2) and triads: aa (3), bb (4), ab (5).

Investigation of hyperbranched (HB) polymers is a new rapidly developing field of polymer chemistry. HB polyimides (HB PIs) are of special interest for development of new functional materials as they can combine unique characteristic prop-

properties, etc.) with some common characteristic properties of HB polymers (solubility, possibility of placing many functional groups in one macromolecule, etc.). Examples are described in applying HB PI as proton-conductive or gas separation membranes, photosensible materials, etc. The study of these objects is largely constrained by multistage synthesis and a number of difficulties encountered in the synthesis process. Therefore, the creation of a simple convenient synthesis meth-

In our work [26], we used the method of one-pot high-temperature polycondensation in molten BA at 140°C for synthesis of HB PIs with reactive anhydride

erties of polyimides (thermal and chemical stability, photostability barrier

4. Synthesis of (hyper)branched (HB) polyimides

odology is an important task.

54

Figure 13.

Solvents, Ionic Liquids and Solvent Effects

Figure 14.

6. Synthesis of star-shaped polyimides with narrow molecular weight

polymers. The state of the art in a field of SSP is considered in several excellent reviews [30]. In many papers, SSP with narrow MWR was synthesized using the methods of controlled chain polymerization. Yokozawa et al. [31]were the first to show that the "step growth" processes also can be applied to obtain SSP with narrow MWD. They synthesized SSP using polycondensation by the scheme (Bn + AB), where Bn is a multifunctional core initiator and AB is a low reactive monomer with

Star-shaped polymers (SSP) are of special interest among a variety of branching

Narrow MWD can be achieved by using special AB' monomers, which are not able for auto-polycondensation, but able to react to active B groups of Bn core initiator. When AB' moiety attaches to Bn, terminal B<sup>0</sup> group becomes much more reactive due to the changing mesomeric effect in the course of condensation, and

To synthesize star-shaped oligoimides (SOI), we have used known general reaction scheme B3(B4) + AB, but another principle providing selective star arm growth not requiring special monomers AB [32, 33]. 1,3,5-(4-Aminophenoxy)toluene (TAPT) was used as B3, bis(3,5-diaminophenoxy)benzene (BAPB) as B4, and

In the course of synthesis, APPA was introduced slowly to the reaction mixture containing TAPT and BAPB, providing that the current AB concentration in molten BA always being much less than that of TAPT or BAPB. The reaction scheme is given below (Figure 18). To check the possibility of obtaining stars with different average arm lengths, the overall 3-APPA/TAPT ratio was varied in a row: 10:1, 20:1,

In IR spectra of SOI samples, characteristic absorption bands appear at imide cycle at 1720 and 1780 cm�<sup>1</sup> (symmetric and asymmetric C=O vibrations). With increase in 3-APPA/TAPT ratio, the intensity of N-H vibrations in NMR <sup>1</sup>

model compound obtained by treatment TAPT with excess of phthalic anhydride

pound TAPT-PhA, obtained by treatment of TAPT with phthalic anhydride (PhA) (Figure 19), shows that the replacement of the amino group on phthalimide group results in disappearance of the signal of the amino group protons (5.0 ppm) and the signal shift (from 5.8 to 6.6 ppm) of c, d, e, and f protons (Figure 20) belonging to central aromatic ring. There are new signals in the region of 8.0 ppm, referred to the protons "u, z" of the phthalimide fragment. Similar changes are observed in the spectra of SOI: c, d, e, and f signals are shifted download. From the comparison of NMR spectra of SOI 10 and SOI 40 (Figure 19), it is seen that the intensity of proton signals of terminal amino groups "p" at 5.4 ppm and methyl group of the central fragment (2.08 ppm) decreases with an increase in the APPA/TAPT ratio. Weak signals at 6.2–6.5 ppm are referred to aromatic protons "k, l, n" of the terminal fragment containing amino group. The structure of SOI is confirmed by

H signals.

H spectra of TAPT (Figure 19) and the model com-

(TAPT-PhA) of terminal NH2 group at 3380–3480 cm�<sup>1</sup> decreases.

H of the

distribution

two different functional groups A and B.

Synthesis of Polyimides in the Melt of Benzoic Acid DOI: http://dx.doi.org/10.5772/intechopen.87032

selective arm growth occurs.

3-APPA as latent AB monomer.

Comparison of the NMR <sup>1</sup>

the results of integration of NMR <sup>1</sup>

57

40:1, and 100:1.

Figure 17. Isomeric "linear" fragments in hyperbranched polyimide.

spectra of the starting B4 monomer (Figure 16a, spectrum 1), there are signals of protons of amino groups at 4.8 ppm, two signals of protons of aromatic fragments nearest to amino group at 5.58 and 5.42, and one signal of protons of central aromatic cycle at 6.9 ppm. In a spectrum of HB PI (Figure 16b, spectra 2), the signals of amino groups are shifted to 5.4 and 5.8 ppm due to appearance of imide fragments. Also, new signals of aromatic protons appear at 7–8 ppm belonging to protons of aromatic nuclei of dianhydride fragment as well as signals of isopropylidene fragment at 1.67 ppm.

With the presence of reactive terminal amino groups in HB PI, we carried out its reaction with acetic or phthalic anhydrides (at 25°C in dimethylacetamide and in molten BA, respectively). In IR spectra of the product isolated after treatment with acetic anhydride (HB PIac) (Figure 16a, curve 3), an absorption band at 3300– 3500 cm<sup>1</sup> (NH2 group) disappears, and new bands at 1680 and 1550 cm<sup>1</sup> (deformation N-C vibrations, "amide 1" and "amide 2") appear.

In NMR <sup>1</sup> H spectrum of HB PIac (Figure 16b, spectra 3), the signals at 5.4 and 5.8 ppm (NH2) disappear, and new signals at 10.0 and 10.2 ppm appear related to two isomeric "linear" fragments of HB PIac (Figure 17). From the fact of equal intensity of these signals, it should be concluded that reactivity of all amino groups is about the same.

This observation is of importance because on its basis it can be concluded that all four amino groups of B4 monomer participate in chain growth with nearly the same probability, i.e., the scheme of reaction indeed is A2 + B4 and must result in HB polymer.
