3. Synthesis of random and multiblock copolymers

Multiblock (MB) copolymers attract big attention due to their ability to selforganize and form continuous two-phase morphology with controlled characteristic size of the phase particle in the micro- or nanoscale range. MB copolyimides (MB CPIs) are also known as promising materials for design of gas separation and proton-conductive membranes for fuel cells.

Conventionally, polycondensation-type MB copolymers are synthesized by polycondensation of two preliminary synthesized oligomers containing terminal reactive groups. MB CPIs can also be obtained by transimidization reaction of oligoimides with pyrimidine end groups. The limitation of this approach is the fact that only few oligoimides are soluble in organic solvents.

▬O▬; ▬CH2▬; ▬SO2▬ diamines. So, partial effective reactivity leveling in a row of aromatic diamines (not able to form salt) observed experimentally in one-pot PI synthesis in molten BA at 140°C hardly can be explained by difference in acid–base-

Arrhenius plots (a) and logarithm of the equilibrium constant vs. the reciprocal temperature (b) for the acylation of diamines ODA (1), MDA (2), SDA (3), and HMDA (4) with phthalic anhydride [16, 17].

Acylation kinetics of diamines ODA (I), MDA (II), and SDA (III) with phthalic anhydride in AcOH at 22°C (second-order reaction plot). Starting concentration of amino groups: ODA, 0.005; MDA, 0.01; and SDA,

Alternative explanation of this phenomenon is the change of limiting stage from amic acid moiety formation for amic acid moiety imidization; the latter is much less

From Arrhenius plots (Figure 5a), the values of activation energy (Ea) of acylation in glacial acetic acid (AcOH) were determined (Table 3). At elevated temperatures (50°C and higher), the reversible character of the acylation was established. On the basis of experimentally measured equilibrium amino group concentration, the equilibrium constants (Kp) were determined at different temperatures. In Figure 5b, temperature dependences of equilibrium constants for

From these data, using the vant' Hoff equation, the enthalpy change (ΔH) values for the acylation reaction of diamines in AcOH were determined (Table 2). On the basis of the values of the equilibrium constants and the rate constants for direct reaction (k1), the first-order rate constants for the back-reaction (k<sup>1</sup>) were calculated for each temperature. In Table 4, the values of rate constants at 140°C

type interaction of amino groups with BA.

Figure 4.

Figure 5.

48

0.03 Mol L<sup>1</sup> [16].

Solvents, Ionic Liquids and Solvent Effects

obtained by extrapolation are given.

sensitive to chemical structure of starting reagent.

acylation reaction different diamines with PhA are shown.

Vasnev and Kuchanov [18] investigated theoretically the regularities of copolymer chain microstructure formation in the course of copolycondensation in a system (A2 + B2 + C2). Here A2 and B2 are the same type bifunctional monomers of different reactivities; C2 is bifunctional "intermonomer" which reacts with A2 and B2; monomer A2 does not react to B2. According to this theory, MB copolymer can be formed from the system (A2 + B2 + C2) in a regime of slow loading of intermonomer C2 to the mixture of comonomers A2 + B2, but only in the case if polycondensation process meets the following requirements (so-called "ideal" interbipolycondensation): (1) reaction is irreversible; (2) any difference in reactivity of A2 and B2 occurs; any by-reactions are absent; and (3) reaction system is homogenous.

We synthesized a series of CPI samples from BPADA (intermonomer) and different pairs of diamines (CPI-1 series, Figure 6) in the melt of BA at 140°C with variable order of intermonomer loading [19]. In [20], two more CPI series (CPI-2 and CPI-3) were synthesized using dianhydrides ODPA and RDA as intermonomer and AFL and DDA as comonomers (Figure 7). Starting comonomers in all cases were chosen taking into account the solubility of copolymers in CDCl3.

Chain microstructure of CPIs was studied by high-resolution NMR 13C. In Figure 8, selected "sensitive" regions of NMR 13C spectra (134–136 and 161–162 ppm) are shown for samples prepared of CPI-2 series. Designation aa, bb, and ab renders to monomer moiety consequences in chain: ACA, BCB, and ACB, correspondingly.

In Figure 8, curves 3–5 the inner two signals in 134–135 and 160–161 ppm regions correspond to aa and bb triads, and the outer two corresponds to ab triads. In the 113–114-ppm region, only one ab signal is observed. Analogous signal attribution was executed for every other CPI samples. Distribution of comonomer moieties in copolymer chain was characterized quantitatively by the coefficient of chain microheterogeneity (Km; Eq. (1)) introduced by Yamadera and Murano [21]:

Km <sup>¼</sup> Pab

DDA/AFL (0.5/0.5)

(1.0/0.5) to AFL (0.5)

triads was executed by comparison with signals of homopolyimides (Table 6).

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

3 Slow (30 min) addition of ODPA to the mixture

4 Slow (30 min) addition of the mixture ODPA/DDA

of CPI-1–3 are shown in Table 5.

Loading condition and characteristics of CPI-2.

Figure 8.

Table 5.

51

Pab þ 2Paa

þ

where Paa, Pbb, and Pab are the fractions of corresponding aa, bb, and ab triads. The average block length lA, l<sup>B</sup> can be calculated as a unit divided by the first and second term in Eq. (1), correspondingly. In such a description, values Km = 0; lA, l<sup>B</sup> = ∞ correspond to the mixture of two homopolymers; Km = 1; lA, l<sup>B</sup> = 2, for random copolymer, and Km = 2; lA, l<sup>B</sup> = 1, for strict alternation of moieties in copolymer. Km values calculated from experimental NMR 13C data for the samples

NMR 13C spectra of CPI-2 series and corresponding homopolyimides in the structure-sensitive regions. Numbers to the right of curves correspond to the experiment number in Table 5. Signal attribution to the aa, bb, and ab

Experiment Sample (order of loading, mole parts) Triad ratio aa/ab/bb Km 1 Homopolyimide DDA-ODPA 1/0/0/ — 2 Homopolyimide AFL-ODPA 0/0/1 —

5 One-shot loading of DDA/AFL/ODPA (0.5/0.5/1.0) 0.55/1/0.62 0.92

As it is seen from Table 5, at slow addition of intermonomer, in all experiments,

In Figure 9, NMR 13C spectra are given for sample CPI-4 series, in which 1,3-bis (2-aminoethyl)adamantane (ADA) was used as intermonomer, and two anhydrides of different reactivities—BPADA and 6F (Table 1)—as comonomers (Figure 10) [23]. Curves 1 and 2 refer to homopolymers; curves 3 and 4 to the CPI-4 samples, obtained with simultaneously monomers loading and slow intermonomer loading, correspondingly. Attribution to triads is the following (ppm): 46.51 (aa), 46.63 (ab), and 46.71 (bb). The values of Km and average block length calculated from the NMR 13C spectra are Km = 0.91 (lA, l<sup>B</sup> = 2.2) for simultaneous comonomer loading and Km = 0.76 (lA, l<sup>B</sup> = 2.63) for slow loading of intermonomer. This result is

we have obtained block CPIs with five-membered imide cycles. In the case of simultaneous loading, only random CPI was obtained. These results differ from data obtained in a work [22], in which only random CPI with five-membered imide cycles was obtained when conventional high-boiling solvent was used at any char-

acter of intermonomer addition to the mixture of diamines.

Pab Pab þ 2Pbb

(1)

1.7/1/1.6 0.48

2/1/1/1.9 0.39

Figure 6. Chain structure of copolyimides of CPI-1 series.

Figure 7. Chain structure of copolyimides of CPI-2 and CPI-3 seria. Synthesis of Polyimides in the Melt of Benzoic Acid DOI: http://dx.doi.org/10.5772/intechopen.87032

#### Figure 8.

Vasnev and Kuchanov [18] investigated theoretically the regularities of copolymer chain microstructure formation in the course of copolycondensation in a system (A2 + B2 + C2). Here A2 and B2 are the same type bifunctional monomers of different reactivities; C2 is bifunctional "intermonomer" which reacts with A2 and B2; monomer A2 does not react to B2. According to this theory, MB copolymer can

be formed from the system (A2 + B2 + C2) in a regime of slow loading of intermonomer C2 to the mixture of comonomers A2 + B2, but only in the case if polycondensation process meets the following requirements (so-called "ideal" interbipolycondensation): (1) reaction is irreversible; (2) any difference in reactivity of A2 and B2 occurs; any by-reactions are absent; and (3) reaction system is

were chosen taking into account the solubility of copolymers in CDCl3. Chain microstructure of CPIs was studied by high-resolution NMR 13C. In Figure 8, selected "sensitive" regions of NMR 13C spectra (134–136 and 161–162 ppm) are shown for samples prepared of CPI-2 series. Designation aa, bb, and ab renders to monomer moiety consequences in chain: ACA, BCB, and ACB, correspondingly. In Figure 8, curves 3–5 the inner two signals in 134–135 and 160–161 ppm regions correspond to aa and bb triads, and the outer two corresponds to ab triads. In the 113–114-ppm region, only one ab signal is observed. Analogous signal attribution was executed for every other CPI samples. Distribution of comonomer moieties in copolymer chain was characterized quantitatively by the coefficient of chain microheterogeneity (Km; Eq. (1)) introduced by Yamadera and Murano [21]:

We synthesized a series of CPI samples from BPADA (intermonomer) and different pairs of diamines (CPI-1 series, Figure 6) in the melt of BA at 140°C with variable order of intermonomer loading [19]. In [20], two more CPI series (CPI-2 and CPI-3) were synthesized using dianhydrides ODPA and RDA as intermonomer and AFL and DDA as comonomers (Figure 7). Starting comonomers in all cases

homogenous.

Solvents, Ionic Liquids and Solvent Effects

Figure 6.

Figure 7.

50

Chain structure of copolyimides of CPI-1 series.

Chain structure of copolyimides of CPI-2 and CPI-3 seria.

NMR 13C spectra of CPI-2 series and corresponding homopolyimides in the structure-sensitive regions. Numbers to the right of curves correspond to the experiment number in Table 5. Signal attribution to the aa, bb, and ab triads was executed by comparison with signals of homopolyimides (Table 6).


#### Table 5.

Loading condition and characteristics of CPI-2.

$$K\_m = \frac{P\_{ab}}{P\_{ab} + 2P\_{aa}} + \frac{P\_{ab}}{P\_{ab} + 2P\_{bb}} \tag{1}$$

where Paa, Pbb, and Pab are the fractions of corresponding aa, bb, and ab triads.

The average block length lA, l<sup>B</sup> can be calculated as a unit divided by the first and second term in Eq. (1), correspondingly. In such a description, values Km = 0; lA, l<sup>B</sup> = ∞ correspond to the mixture of two homopolymers; Km = 1; lA, l<sup>B</sup> = 2, for random copolymer, and Km = 2; lA, l<sup>B</sup> = 1, for strict alternation of moieties in copolymer. Km values calculated from experimental NMR 13C data for the samples of CPI-1–3 are shown in Table 5.

As it is seen from Table 5, at slow addition of intermonomer, in all experiments, we have obtained block CPIs with five-membered imide cycles. In the case of simultaneous loading, only random CPI was obtained. These results differ from data obtained in a work [22], in which only random CPI with five-membered imide cycles was obtained when conventional high-boiling solvent was used at any character of intermonomer addition to the mixture of diamines.

In Figure 9, NMR 13C spectra are given for sample CPI-4 series, in which 1,3-bis (2-aminoethyl)adamantane (ADA) was used as intermonomer, and two anhydrides of different reactivities—BPADA and 6F (Table 1)—as comonomers (Figure 10) [23]. Curves 1 and 2 refer to homopolymers; curves 3 and 4 to the CPI-4 samples, obtained with simultaneously monomers loading and slow intermonomer loading, correspondingly. Attribution to triads is the following (ppm): 46.51 (aa), 46.63 (ab), and 46.71 (bb). The values of Km and average block length calculated from the NMR 13C spectra are Km = 0.91 (lA, l<sup>B</sup> = 2.2) for simultaneous comonomer loading and Km = 0.76 (lA, l<sup>B</sup> = 2.63) for slow loading of intermonomer. This result is

Figure 9. A structure-sensitive region of the NMR13C spectra of CPI-4 series.

Figure 10. Chain structure of copolyimides of CPI-4.

indicative of trend of formation of a multiblock chain microstructure at slow intermonomer loading.

This trend is not very pronounced in the comonomers chosen and shows rather weak influence of chemical structure of anhydride component on reactivity in molten BA.

In [24, 25], mathematical model has been developed by us for chain microstructure formation in copolyimide (CPI) synthesis (CPI) from two diamines A and B (comonomers) and one dianhydride C (intermonomer) in molten BA different regimes of intermonomer loading. The kinetic scheme was analyzed involving acylation of both diamines with anhydride fragment, decomposition, and imidization of two intermediate amic acid fragments.

Kinetic constants of acylation and imidization stages necessary for calculations were taken from our earlier experiments with model reactions described in Part 2.3 of this review. By numerical solution of the system of kinetic equations for different regimes of intermonomer loading, we calculated dependences of the change in time of the average block length lA, lB, the current concentrations of amino and anhydride groups, amic acid fragments, imide cycles, and triads aa, bb, and ab for CPI-1–3. The calculated values of the average block length and the chain microheterogeneity parameter (Km = 0.5–0.6) for several comonomer pairs at slow intermonomer loading are in good agreement with the experimental values obtained from NMR 13C data.

low, less than 10% of starting amino groups. These fragments react rapidly to give

Typical curves of change in time of the concentration of amino groups of A(1) and B (2), anhydride groups

Typical curve of change in time of the average length of blocks lA (1) and lB (2) in experiment with slow loading

aa ab bb 160.82 160.60; 161.37 161.12 134.96 135.01; 134.51 134.53 113.56 113.77 113.97

Attribution of signals in NMR13C spectra of CPI-1 series to triads.

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

Kinetics of accumulation of imide cycles and different types of triads (aa, bb,

Accumulation of imide cycles and aa triads from the more reactive comonomer occurs faster than that for the less reactive monomer and forms a block consisting of several triads aa. Concentration of imide cycles and triads bb from less reactive comonomer increases with conversion more slowly. So, the model developed by us can be used to predict microstructure of the CPI chains at any conversion and at any loading order of intermonomer and comonomers. Dependence of parameter Km for the final CPI on the duration of intermonomer BPADA loading for system AFL-DDA is presented in Figure 14. It should be noted that the fact of influence of intermonomer loading order on chain microstructure is very important for

imide cycles.

53

Figure 12.

Table 6.

Figure 11.

of the intermonomer (30 min).

and ab) are presented in Figure 13.

C (3), and amic acid fragments (4, 5).

The kinetics of the block length (lA and lB) growth for regime of the slow intermonomer loading (for 30 min) is given in Figure 11. The length of block (lA) containing the moieties of more active comonomer reaches its final value lA = 4 already to the end of intermonomer loading, whereas the block length lB goes on to increase. In the end, block copolymer forms. The difference in times of block formation is the sequence of difference in comonomer reactivity.

Typical consumption kinetics of amino and anhydride groups is presented in Figure 12. Consumption rates of amino groups belonging to the first and the second comonomers differ considerably. Concentration of transient amic acid fragments is Synthesis of Polyimides in the Melt of Benzoic Acid DOI: http://dx.doi.org/10.5772/intechopen.87032


Table 6.

Attribution of signals in NMR13C spectra of CPI-1 series to triads.

Figure 11.

indicative of trend of formation of a multiblock chain microstructure at slow

weak influence of chemical structure of anhydride component on reactivity in

imidization of two intermediate amic acid fragments.

A structure-sensitive region of the NMR13C spectra of CPI-4 series.

This trend is not very pronounced in the comonomers chosen and shows rather

In [24, 25], mathematical model has been developed by us for chain microstructure formation in copolyimide (CPI) synthesis (CPI) from two diamines A and B (comonomers) and one dianhydride C (intermonomer) in molten BA different regimes of intermonomer loading. The kinetic scheme was analyzed involving acylation of both diamines with anhydride fragment, decomposition, and

Kinetic constants of acylation and imidization stages necessary for calculations were taken from our earlier experiments with model reactions described in Part 2.3 of this review. By numerical solution of the system of kinetic equations for different regimes of intermonomer loading, we calculated dependences of the change in time of the average block length lA, lB, the current concentrations of amino and anhydride groups, amic acid fragments, imide cycles, and triads aa, bb, and ab for CPI-1–3. The calculated values of the average block length and the chain

microheterogeneity parameter (Km = 0.5–0.6) for several comonomer pairs at slow

The kinetics of the block length (lA and lB) growth for regime of the slow intermonomer loading (for 30 min) is given in Figure 11. The length of block (lA) containing the moieties of more active comonomer reaches its final value lA = 4 already to the end of intermonomer loading, whereas the block length lB goes on to increase. In the end, block copolymer forms. The difference in times of block

Typical consumption kinetics of amino and anhydride groups is presented in Figure 12. Consumption rates of amino groups belonging to the first and the second comonomers differ considerably. Concentration of transient amic acid fragments is

intermonomer loading are in good agreement with the experimental values

formation is the sequence of difference in comonomer reactivity.

intermonomer loading.

Chain structure of copolyimides of CPI-4.

Solvents, Ionic Liquids and Solvent Effects

obtained from NMR 13C data.

molten BA.

52

Figure 10.

Figure 9.

Typical curve of change in time of the average length of blocks lA (1) and lB (2) in experiment with slow loading of the intermonomer (30 min).

#### Figure 12.

Typical curves of change in time of the concentration of amino groups of A(1) and B (2), anhydride groups C (3), and amic acid fragments (4, 5).

low, less than 10% of starting amino groups. These fragments react rapidly to give imide cycles.

Kinetics of accumulation of imide cycles and different types of triads (aa, bb, and ab) are presented in Figure 13.

Accumulation of imide cycles and aa triads from the more reactive comonomer occurs faster than that for the less reactive monomer and forms a block consisting of several triads aa. Concentration of imide cycles and triads bb from less reactive comonomer increases with conversion more slowly. So, the model developed by us can be used to predict microstructure of the CPI chains at any conversion and at any loading order of intermonomer and comonomers. Dependence of parameter Km for the final CPI on the duration of intermonomer BPADA loading for system AFL-DDA is presented in Figure 14. It should be noted that the fact of influence of intermonomer loading order on chain microstructure is very important for

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

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

3300–3050 cm<sup>1</sup> which is observed also in the spectrum of starting B4 (stretch N-H

The final polymer product was obtained as beige color powder soluble in THF,

H spectra (b) of monomer B4 (1), HB PI (2), and HB PIac (3).

. In NMR <sup>1</sup>

H

stretch C=O vibrations of imide cycle). The absorption band retains at

DMSO, and amic solvents. Mw of HB PI obtained is of about 2\*104

vibrations of amino groups) (Figure 16a, spectrum 1).

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

spectroscopy.

Figure 15.

Figure 16.

55

Review IR spectra (a) and NMR <sup>1</sup>

Synthesis of hyperbranched polyimide.

Figure 13.

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

Figure 14. Dependence of parameter Km for CPI (120 min) on duration of intermonomer loading.

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.
