Effects of chlorinated polypropylene on the hydrogen-bond and electric property of polypropylene/chlorinated polypropylene/polyaniline composites: FTIR analysis.

In this article, the volume resistivity of polypropylene (PP)/chlorinated polypropylene (CPP)/polyaniline (PANI) composites was detected. The results show that the volume resistivity of PP/CPP/PANI composites decreases with increasing CPP content, and there exists a minimum volume resistivity. The relationship between volume resistivity of the PP/CPP/PANI composites and CPP content can be explained by Fourier-transform infrared spectra (FTIR). Effects of CPP on the formation of the intermolecular and innermolecular hydrogen-bond in the PP/CPP/PANI composites were carefully investigated by FTIR. An iterative least-squares computer program was adopted to obtain the best FTIR fit curves of the PP/CPP/PANI composites by varying the wavenumber (v), width at half-height ([w.sub.1/2]), and area (S) of several bands. The obtained semiquantitative results illuminate that the intermolecular and innermolecular H-bonded interaction of the PANI-DBSA is weakened by the introduction of CPP; the interactional strength between PANI-DBSA and CPP increases with increasing CPP content, and there exists a maximum, which is favorable to disperse well PANI-DBSA in PP/CPP/PANI composites and improve the conductive property of the PP/CPP/PANI composites. POLYM. ENG. SCI., 49:462-470, 2009. [c] 2008 Society of Plastics Engineers

INTRODUCTION

Conductive polymers are expected to yield attractive combinations of properties, and are getting more and more attention for researchers all over the world. They have been making use of these polymers for production of electrical materials (1-3), especially antistatic materials, sensor materials (4-6), anticorrosive coating (7-9), and so on. Among conductive polymers, polyaniline has the best potential to become economically competitive owning to its cheap materials, simple synthetic method and stability in environment (10).

Although polyaniline has many merits, it is very difficult to be processed like conventional polymers by general means because of its strong intermolecular and inner-molecular interactions (11). For these reasons wide scale industrial application of polyaniline has been strongly impeded over several years. Recently, many new protonating agents such as sulfonic acids, phosphoric acid esters (11), (12), and phosphoric acids (13) have been introduced to improve the processability of polyaniline. It is worthy to note that it was Cao et al. (14) who first introduced sulfonic acid as a protonating agent, and this made polyaniline possible to be processed in solvent. Other method to improve the processability of polyaniline was by blending with thermoplastic polymers because of their good processing properties (13), (15-17). An unique speciality of this method lies in the combination of electric properties of polyaniline and processing properties of thermoplastic polymers.

Although the aforementioned two methods have its own merits, the second method has more advantages than the first one because it does not need much of solvent, and is more convenient and more suitable to wide scale industrial application. During the melt processing of polyaniline, polar polymers such as PVC, poly(methyl methacrylate), polystyrene, cellulose propionate are usually adopted as thermoplastic matrix (15), (16), moreover, the electrical conductivity of the blends reaches the standard of the antistatic materials. However, nonpolar polymer such as polypropylene is not satisfactory for the standard of the antistatic materials. To reach the standard of the antistatic materials, the weight fraction of PANI is very large in the blend. This will certainly weaken the mechanical properties of the blend.

In this article, the possibility of melt processing and the electric property of PP/CPP/PANI composites are investigated, and effects of CPP on the formation of the intermolecular and innermolecular hydrogen-bond in the PP/CPP/PANI composites are carefully analyzed by FTIR. An iterative least-squares computer program was adopted to obtain the best FTIR fit curves of the PP/CPP/PANI composites.

EXPERIMENTAL

Materials

Polyaniline (PANI) protonated with hydrochloric acid (HC1) was supplied by Chengdu Organic Chemicals Co. Ltd. (China) and is synthesized by the method of air oxidation (China patent: CN1626564A). Its electrical conductivity was about 1 S/cm. The granularity of PANI-HCl is about 30 micron.

PP (PPH-XD-045, melt flow index = 3.5 g/10 min) was supplied by PetroChina Co. Ltd. (China).

DBSA (industrial grade) was supplied by Kewei Chemicals Co. Ltd. (China), and its content was about 96% (wt).

CPP was supplied by Sichuan Weiye Chemicals Co. Ltd. (China), and its chlorine content was about 31% (wt).

Preparation of Composites

PANI protonated with HC1 was neutralized with 20% (wt) sodium hydroxide (NaOH) aqueous solution for 48 h [NaOH aqueous solution is abundantly excessive comparing with the amount of PANI-HC1 and the pH value of the blends (i.e., PANI-HC1 and NaOH aqueous solution) is at around 11] and then was filtrated and washed with deionized water until the pH value of percolate was at 6-8. Obtained polyemeraldine base ([PANI.sub.emer]) was dried under vacuum at 60[degrees]C and then was blended with DBSA, and the molar ratio of [PANI.sub.emer] was 0.5. The blend was stirred for 48 h in ambient temperature, and then PANI protonated with DBSA (PANI-DBSA) was gained.

The PP/PANI composites with different CPP contents were prepared on a two-roll mill at about 180[degrees]C for 5 min, and then molded into 1 mm plates. The two-roll mill is an universal blending machine. Compression molding was carried out in the following conditions: preheated at 180[degrees]C for 5 min at low pressure, compressed for 10 min at 13 MPa at the same temperature, and then cooled to ambient temperature with the cooling rate 30[degrees]C/min in the mold at 13 MPa. Specimens with the dimensions of 80 X 80 X 1 [mm.sup.3] for the test of volume resistivity were obtained from the 1 mm plates. The blend compositions with their sample codes were listed in Table 1.

TABLE 1. Formation of PP/PANI composition.

Sample     PP    [PANI.sub.emer]  DBSA (wt%)  CPP (wt%)  Theoretical
code      (wt%)       (wt%)                               degree of
                                                         protonation

PP/PANI1  87.23       4.10           7.79        0.88         0.5
PP/PANI2  83.70       4.10           7.79        4.41         0.5
PP/PANI3  79.30       4.10           7.79        8.81         0.5
PP/PANI4  74.89       4.10           7.79       13.22         0.5
PP/PANI5  70.49       4.10           7.79       17.62         0.5

Measurement of the Volume Resistivity

The volume resistivity of the composites was detected with high resistance meter (ZC46A) produced by Shanghai precision Scientific Instrument Co. Ltd. (China). The result of each sample is the average value of four measurements.

FTIR Measurement

The specimens for FTIR measurement are prepared by two methods. Specimens of the PP/CPP/PANI composites for FTIR measurement were molded into very thin films. Compression molding was carried out in the following conditions: preheated at 180[degrees]C for 5 min at low pressure, compressed for 10 min at 15 MPa at the same temperature, and then cooled to ambient temperature with the cooling rate 30[degrees]C/min in the mold at 15 MPa. Because PANI-DBSA is difficult to be molded into very thin film, PANI-DBSA is blended with potassium bromide (KBr) and molded into thin film for FTIR measurement. KBr and PANI-DBSA were dried under vacuum at 60[degrees]C. The sample was detected immediately after the sample preparation was performed under the irradiation of an infrared lamp. FTIR analysis of specimens was conducted with a Nicolet 170X FTIR spectrometer (Nicolct Co. USA) at a resolution of 2 [cm.sup.-1].

RESULTS AND DISCUSSION

The Volume Resistivity of the PP/CPP/PANI Composites

Figure 1 shows the relationship between the volume resistivity of the PP/CPP/PANI composites and CPP content. There exists an interesting phenomenon that the volume resistivity first decreases with increasing CPP content and reaches a minimum volume resistivity when the CPP content is 13.22%, and then increases with further increase of the CPP content. In the next part, FTIR will be adopted to analyze CPP as a compatibilizer how to weaken the intermolecular and innermolecular H-bonded interaction of the PANI-DBSA in the PP/CPP/PANI composites. These are beneficial to decrease the volume resistivity of the PP/CPP/PANI composites.

[FIGURE 1 OMITTED]

FTIR Spectra of the PP/CPP/PANI Composites

Figure 2 shows FTIR spectra of the PP/CPP/PANI composites. It can be seen that several bands in spectra changed obviously with the CPP content in the composites such as N--H stretching region (3320-3600 [cm.sup.-1], 1530-1630 [cm.sup.-1], 780-856 [cm.sup.-1], and 646-760 [cm.sup.-1]). The variation of these bands indicates that the addition of CPP influences the intermolecular or innermolecular interaction in PP/CPP/PANI composites, which will be discussed in detail by FTIR analysis in the following sections.

[FIGURE 2 OMITTED]

N--H Stretching Region of the FTIR Spectra (3320-3600 [cm.sup.-1]). The region (3320-3600 [cm.sup.-1]) is attributed to PANI's N--H stretching region (18), and no band is founded in this region of the FTIR spectra of PP or CPP. Figure 2 shows, that, in this region, the bands and not extraordinary distinct because that the [PANI.sub.emer] content is only 4.10% (w/w). The amplificatory bands of this region were presented in Fig. 3.

[FIGURE 3 OMITTED]

As it is shown in Fig. 3, there are distinctly at least two bands within the range of CPP content from 0.88% to 17.62%. One band is at around 3330 [cm.sup.-1]; another band is at around 3420 [cm.sup-1]. The band, at around 3330 [cm.sup.1],[cm.sup.-1] is attributed to the hydrogen-bonded N--H......Cl and N--H......N because of the following two reasons. Firstly, in the hydrogen-bonded N--H, the interaction between the chlorine (Cl) or the nitrogen (N) and N--H is smaller than that of between the oxygen (O) and N--H because the value of electro-negativity of the Cl atom or the N atom is smaller than that of the O atom, and the atomic radius of the Cl atom or the N atom is bigger than that of the O atom. Hence, the decreasing wavenumber of the hydrogen bonded N--H......Cl or N is smaller than that of the hydrogen-bonded N--H......O. Secondly, the interaction of the hydrogen-bonded N--H......Cl is very close to that of N--H......N because the value of electro-negativity and the atomic radius of the Cl atom are very close to that of the N atom, the two bands of the hydrogen-bonded N--H......Cl and N--H......N are overlapped. The area of the band, at around 3420 [cm.sup.-1], increases with increasing CPP content.

Two bands can also be seen in spectrum of the N--H stretching region of PANI-DBSA presented in Fig. 4. Once band (at 3260 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H......O (18); another band (at 3439 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H......N and "free" N--H stretching vibration, because the width of the band (at 3439 [cm.sup.-1]) is wide enough to include the two kinds of N--H stretching vibration.

[FIGURE 4 OMITTED]

With the aid of computer analysis, the curve-fitting spectra of the N--H stretching region were executed in the PP/CPP/PANI composites with various CPP content and PANI-DBSA. An iterative least-squares computer program was adopted to obtain the best fit of spectra of the N--H stretching region by varying the wavenumber (v), width at half-height ([w.sub.1/2]), and area (S) of the several bands. There were two or three Gaussian bands in the N--H stretching region to be confirmed by the curve-fitting procedure. Typical examples are displayed in the iconograph of Figs, 3 and 4.

The iconograph of Fig. 4 shows that there are three bands of the N--H stretching region in the FTIR spectrum of PANI-DBSA: the first band (at 3280.3 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H......O stretching vibration; the second band (at 3439.9 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H stretching vibration where N--H is hydrogen bonded with the N atom; and the third band (at 3554.5 [cm.sup.-1]) is attributed to so-called "free" N--H stretching vibration. On the other hand, the iconograph of Fig. 3 shows that there are only two bands of the N--H stretching region in the FTIR spectrum of the PP/PANI 4 composite: the band (at 3331.6 [cm.sub.-1]) is attributed to the hydrogen-bonded N--H......O stretching vibration; another band (at 3394.4 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H stretching vibration between N--H and the N atom and CI atom; and the so-called "free" N--H stretching vibration is disappeared. Why is the band at 3394.4 [cm.sup.-1] attributed to the hydrogen-bonded N--H stretching between N--H and N atom and CI atom? In our opinion, the interaction of the hydrogenbonded N--H......CI is very close to that of N--H......N and the two bands are difficult to be detached in the curve-fitting program.

Table 2 shows the curve-fitting results for spectra of the N--H stretching region. There exists a strange phenomenon that the band of v2 exists only in the samples of PP/PANI 1, 2, and 3, and does not exist in PANI-DBSA and PP/PANI 4,5, and 6. Compared with that of the band of vl and v3, the area (S2) of the band of v2 is small enough to be ignored. The band of "free" N--H stretching vibration merely appears in PANI-DBSA, and does not appear in the PP/CPP/PANI composites. This may mean that all the N--H groups form the H-bond with O, N, and Cl.

Table 2. Curve-fitting results for the N--H stretching region.

                             H-bonded N--H N--H......O

Sample code  v1 ([cm.sup.-1])  [w.sub.1/2] 1 ([cm.sup.-1])    S1

PANI-DSBA         3280.3                251.36              10.49
PP/PANI 1         3338.8                 43.37               0.16
PP/PANI 2         3335.8                 51.03               0.29
PP/PANI 3         3324.4                 57.13               1.36
PP/PANI 4         3331.6                 42.25               0.12
PP/PANI 5         3325.0                 35.31               0.15

Sample code  v2 ([cm.sup.-1])  [w.sub.1/2] 2 ([cm.sup.-1])   S2

PANI-DSBA
PP/PANI 1         3372.9                   10.83            0.006
PP/PANI 2         3372.6                   10.75            0.003
PP/PANI 3         3378.6                   24.82            0.07
PP/PANI 4
PP/PANI 5

                               H-bonded N--H
                                N--H.....N
                               N--H......Cl

Sample code  v3 ([cm.sup.-1])  [w.sub.1/2] 3 ([cm.sup.-1])    S3

PANI-DSBA         3439.9                 140.17             18.57
PP/PANI 1         3414.4                  86.33              0.37
PP/PANI 2         3421.0                  99.59              0.88
PP/PANI 3         3415.0                 123.27              8.16
PP/PANI 4         3394.4                 218.46              6.70
PP/PANI 5         3409.9                 135.54              2.87

                                  "Free" N--H

Sample code  v4 ([cm.sup.-1])  [w.sub.1/2] 4 ([cm.sup.-1])   S4

PANI-DSBA        35554.5                  87.05             3.96
PP/PANI 1
PP/PANI 2
PP/PANI 3
PP/PANI 4
PP/PANI 5

v, wavenumber; [w.sub.1/2], width at half-height; A, intensity.

The data listed in Table 2 show that the N--H band of the H-bonded between N--H and O in PANI-DBSA is distinctly different from that in the PP/CPP/PANI composites. The wavenumber of the H-bonded N--H......O band increases magically, and the width at half-height ([w.sub.1/2]l) decreases heavily in the PP/CPP/PANI composites. These illuminate that the average bond distance of H-bonded N--H decreases and that of the H-bond of N--H......O in the PP/CPP/PANI composites increases. Hence, the average strength of the hydrogen bonds decreases and the H-bonded band shifts to the higher wavenumber (19). The variation of [w.sub.1/2]l can explain that the distribution of the H-bonded strength is disturbed (18) and becomes narrower in the PP/CPP/PANI composites. These results show that the intermolecular and innermolecular H-bonded interaction of PANI-DBSA is influenced by the introduction of CPP.

Similarly, the H-bonded N--H band (v3) of PANI-DBSA is distinctly different from that of the PP/CPP/ PANI composites. The v3 shifts to a lower wavenumber. In the PP/CPP/PANI composites, the [w.sub.1/2]3 first increases with increasing CPP content and reaches a maximum when the CPP content is lower than 13.22%, and then decreases with further the increase of the CPP content. In our opinion, the phenomenon is primarily caused by the introduction of Cl atom and the formation of the H-bonded N--H......Cl. The average distance of the H-bond decreases, the average strength of the H-bond increases, and the distribution of the H-bonded strength is disturbed (18) and becomes broader. In PP/PANI 4 composite, the v3 reaches the minimum and the [w.sub.1/2]3 reaches the maximum. These results illuminate that there exists the interaction between CPP and PANI-DBSA in the composites and the interaction is related to the CPP content.

There exist another interesting phenomenon in the PP/ CPP/PANI composites that both the minimum of the v3 and the maximum of the [w.sub.1/2]3 are corresponding to the minimum volume resistivity in the PP/CPP/PANI composites, i.e., the PP/PANI 4. This was qualitatively interpreted by the formation and the average strength of the H-bonded N--H......CI. In the PP/PANI I, the number and strength of the H-bonded N-H CI is very small because the CPP content is very low. With the increasing CPP content, the number and the average strength of the H-bonded N-H CI increases. Because of the saturation capacity of H-bond, when the H-bonded N--H......Cl is saturated, the number of the H-bonded N--H CI does not increase with further increasing CPP content. The more number of the H-bonded N--H......CI is formed, the stronger is the interaction between CPP and PANI-DBSA, the more homogenous is the dispersion of PANI in the PP/CPP/PANI composite, which results in the lower volume resistivity of the PP/CPP/PANI composites. Hence there exists a minimum volume resistivity in the composites corresponding to the minimum of the v3 and the maximum of the [w.sub.1/2]3. The result will be more clearly illuminated by two following methods.

Firstly, in the PP/CPP/PANI composites, the total concentration of N--H groups is constant and equal to [C.sub.v1] + [C.sub.v2] + [C.sub.v3]. In PANI-DBSA, the total concentration of N--H groups is also expressed by [C.sub.v1] + [C.sub.v3] + [C.sub.v4]. The Beer-Lambert law and the reference (19) show that

[SIGMA]S = [S.sub.4] + [[S.sub.1]/K] + [[S.sub.3]/K] (1)

and the mole fraction of each N--H "species" can be calculated by

X1 = [[S.sub.1]/K[SIGMA]S]; X3 = [[S.sub.3]/K[SIGMA]S]; X4 = [[S.sub.4]/[SIGMA]S] (2)

The K was the ratio of the absorption coefficient of v1 to that of v4, and was considered to be independent of the average strength of the H-bond. However a flaw of this hypothesis was pointed out in reference (20), and it did not take into account the dependence of the absorption coefficient ([epsilon]) upon band frequency. Taking one with another, the number of each N--H "species" is very closely dependent on the area (S) of each N--H "species".

In this article, the area percentum was used semi-quantitatively to indicate the variation of function group's concentration with CPP content based on the following deduction.

Because [epsilon] and c changing with the wavenumber (v), [epsilon] and c can be expressed by the functions of v.

[epsilon] = [epsilon](v); c = c(v) (3)

S = [[integral].sub.[v.sub.1].sup.[v.sub.2]] Adv (4)

[[integral].sub.[v.sub.1].sup.[v.sub.2]] Adv [[integral].sub.[v.sub.1].sup.[v.sub.2]] [epsilon] (v) c(v)ldv = l [[integral].sub.[v.sub.1].sup.[v.sub.2]] [epsilon](v)dv [[integral].sub.[v.sub.1].sup.[v.sub.2]] c(v)dv(5)

A percentum of area (X) is adopted to indicate the variation of the molar concentration with the CPP content, for example

X1 = [[S.sub.1]/[S.sub.1] + [S.sub.2] + [S.sub.3] + [S.sub.4]] (6)

According to Eqs. 4 and 6, X1 can be expressed by

X1 = [[[integral].sub.[v.sub.1].sup.[v.sub.2]][A.sub.1]dv/[[integral].sub.[v.sub.1].sup.[v.sub.2]] [A.sub.1]dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [A.sub.2]dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [A.sub.3]dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [A.sub.4] dv] (7)

For the four bands of the same sample, l is a constant. The four bands are obtained through curve-fitting spectra between [v.sub.1] and [v.sub.2]. As it is shown in the iconograph of Figs. 3 and 4, every band lies in the same region. Therefore, although [epsilon] is dependent on the wavenumber, the integral [epsilon](v) of every band is identical in the same integral region. Combining Eqs. 5 and 7, X1 can be expressed by

X1 = [[[integral].sub.[v.sub.1].sup.[v.sub.2]][C.sub.1]dv/[[integral].sub.[v.sub.1].sup.[v.sub.2]] [C.sub.1](v)dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [C.sub.2](v)dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [C.sub.3](v)dv + [[integral].sub.[v.sub.1].sup.[v.sub.2]] [C.sub.4](v) dv] (8)

As shown in the Eqs. 6 and 8, the X1 is capable to reflect the variation of the molar concentration. Therefore X is adopted to denote the variation of a certain N--H "species" concentration with the CPP content. The calculative results are listed in Table 3.

TABLE 3. The calculating results for the N--H stretching region.

                 H-bonded N-H
                  N--H......O

Sample code    S1   X1 (%)  X1' (%)   S2    X2 (%)

PANI-DBSA    10.49  31.76
PP/PANI 1     0.16  29.67    0.24    0.006  1.03
PP/PANI 2     0.29  24.89    0.39    0.003  0.28
PP/PANI 3     1.36  14.22    0.46    0.07   0.75
PP/PANI 4     0.12   1.73    0.23
PP/PANI 5     0.15   4.98    0.23

              H-bonded N--H
              N--H......N
              N--H......Cl       "Free" N--H           C--H

Sample       S3     X3     X3'    S4     X4   [v.sub.C-H]  [S.sub.C-H]
code               (%)    (%)           (%)

PANI-DBSA  18.57  56.25          3.96  11.99
PP/PANI 1   0.37  69.30   0.56                   2955.7        66.29
PP/PANI 2   0.88  74.83   1.18                   2955.7        74.63
PP/PANI 3   8.16  85.03   1.75                   2956.5       297.27
PP/PANI 4   6.70  98.27  12.96                   2957.3        51.72
PP/PANI 5   2.87  95.02   4.31                   2955.7        66.51

Table 3 shows that the band of v2 may be ignored are clearly certified again because X2 is very small. The area percentum (X1) of the H-bonded N--H......O changes with the CPP content, which is consistent with the variety of the volume resistivity with the CPP content in the PP/CPP/PANI composites. However, the area percentum (X3) of the H-bonded N--H......N and N--H......C1 shows the completely inverse change with the CPP content compared with X1The relation between the area percen-tum of the H-bonded N--H and CPP content is presented in Fig. 5.

[FIGURE 5 OMITTED]

Table 3 and Fig. 5 show that, in PANI-DBSA, the area percentum of H-bonded N--H......O is very high, however the H-bonded N--H......O is disturbed by the introduction of CPP and is substituted by the H-bonded N--H......Cl, which induces that the intermolecular and innermolecular H-bonded interaction of PANI-DBSA become weak, and the interaction between PANI and CPP become strong. Hence, the dispersion of PANI is more homogeneous in the PP/CPP/PANI composites. To some extent, the volume resistivity of the composite depends on the PANI dispersion in the matrix. In the PP/PANI 4 composite, the number of the H-bonded N--H......Cl is the maximum, the interaction between CPP and PANI is the strongest; the number of the intermolecular and inner-molecular H-bond in PANI-DBSA is the minimum, the intermolecular and innermolecular interaction of PANI-DBSA is the weakest, which indicates that the dispersion of PANI is the best homogeneous in the PP/PANI 4 composite. Hence the volume resistivity of PP/PANI 4 composite is the minimum, as shown in Fig. 1. Because the capability of the formation of H-bond between N--H and the O is stronger than that of between N--H and the C1 atom, the H-bonded N--H......O is impossible to be substituted completely by the H-bonded N--H......CI even if the Cl atom is much more than the O atom in composite. This is why there is an inflexion in Fig. 5.

Secondly, in the PP/CPP/PANI composites, the concentration of C--H is considered as a constant value. Based on this premise, the C--H stretching band can be regarded as an inner standard for calculating the relative mole fraction of the each species of H-bonded N--H. The calculating method is

X3' = [[S.sub.3]/[S.sub.C-H]] (9)

The calculating results are listed in Table 3.

Figure 6 and Table 3 reveal the variety of the relative mole fraction of the H-bonded N--H......N and N--H......Cl (X3') with CPP content is analogous to that of the first method. The variety of X3' with the CPP content is contrary to that of the volume resistivity of PP/CPP/PANI composites. In the PP/PANI 4 composite, X3' is the maximum, which means that the number of the H-bonded N--H......Cl is the maximum, the interaction between CPP and PANI is the strongest, and the dispersion of PANI is the best homogeneous in all the PP/CPP/PANI composites. Hence the PP/PANI 4 composite has a minimum volume resistivity. The mole fraction of the Hbonded N--H......O is changed unobvious because the intensity is too small corresponding to the intensity of the C--H stretching band.

[FIGURE 6 OMITTED]

The Region (1530-1630 [cm.sup.-1]) of the FTIR Spectra. The region (1530-1630 [cm.sup.-1]) of the FTIR spectra presented in Fig. 7 includes --C = N--stretching band, N--H bending band and--C = C--(benzene ring) stretching band (21). Hence, the contribution from different molecular motions makes quantitative analysis difficult. The increased hydrogen bond between the C1 and N--H will cause an intensification of a specific vibration band with increasing CPP content (i.e., Cl content). With the aid of computer analysis, curve-fitting spectra of this region were executed in the PP/CPP/PANI composites with various CPP concentrations. There were two Gaussian bands in this region to be confirmed by the curve-fitting procedure. A typical example (PP/PANI 4 composite) is showed in the iconograph of Fig. 7.

[FIGURE 7 OMITTED]

The iconograph of Fig. 7 shows that there are two bands of the region (1530-1630 [cm.sup.-1]) in FTIR spectra of PP/PANT 4 composite: the band (at 1570.8 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H......O bending vibration and--C = N--stretching vibration; another band at (1604.0 [cm.sup.-1]) is attributed to the hydrogen-bonded N--H......Cl and N bending vibration and--C = C--(benzene ring) stretching vibration (19), (21). Because the concentration of--C = N- and--C = C--is constant and their stretching bands are not influenced by CPP content in the PP/CPP/PANI composites, the two stretching bands would not be considered. The curve-fitting results for the region (1530-1630 [cm.sup.-1]) are listed in Table 4. In Table 4.

TABLE 4. Curve-fitting results for spectra of the region (1530-1630
[cm.sup.-1]).

                                H-bonded N-H
                               N-H......O

Sample code  v1 ([cm.sup.-1])  [W.sub.1/2]1     S1   X1" (%)
                               ([cm.sup.-1])

PP/PANI 1         1570.8          104.75      15.96   99.22
PP/PANI 2         1572.4           80.74       4.62   97.72
PP/PANI 3         1569.8           57.34       5.34   90.11
PP/PANI 4         1570.8           56.75       1.69   85.94
PP/PANI 5         1572.5           83.48       5.49   98.29

                                H-bonded N-H
                                N-H......N
                                N-H......Cl

Sample code  v2 ([cm.sup.-1])  [w.sub.1/2]2     S2   X2" (%)
                               ([cm.sup.-1])

PP/PANI 1         1608.5           14.63      0.126    0.78
PP/PANI 2         1607.4           16.47      0.108    2.28
PP/PANI 3         1603.1           21.11      0.586    9.89
PP/PANI 4         1604.0           21.48      0.277   14.06
PP/PANI 5         1606.3           16.27      0.095    1.71

X1" = [[S.sub.1]/([S.sub.1] + [S.sub.2])] and X2" = [[S.sub.2]/([S.sub.1] + [S.sub.2])] (10)

X1" and X2" may be considered as the variation of the number of a certain N--H "species" with the CPP content.

The relation between the area percentum of each N--H "species" and CPP content is graphically presented in Fig. 8. Table 4 and Fig. 8 show that the area percentum (X1") of the H-bonded N--H......O first decreases with increasing CPP content and reaches a minimum X1" when the CPP content is lower than 13.22%, and then increases with further increase of the CPP content. Compared to X1", the area percentum (X2") of the H-bonded N--H......N and N--H......Cl shows the completely inverse trend with increasing CPP content. The trend of the mole fraction of each N--H "species" changed with CPP content in this region is same with that in the N--H stretching vibration, and is accordant to that of the volume resistivity changed with CPP content.

[FIGURE 8 OMITTED]

The Region (646-760 [cm.sup.-1]) of the FTIR Spectra. Figure 9 shows the FTIR spectra of the region (646-760 [cm.sup.-1]) in the PP/CPP/PANI composites. The contributions from different groups motions make quantitative analysis very difficult. Although the vibration in this region is complex, the increasing hydrogen bonding between N--H and C1 will cause a variation of a specific vibration band with increasing CPP content (i.e. Cl content). The FTIR spectra of this region are mainly attributed to the C--Cl stretching vibration (22), and are the part contribution from PANI. This can be clearly proved by the following part. With the aid of computer analysis, curve-fitting spectra of this region were executed in the PP/CPP/PANI composites with various CPP concentrations, CPP and PANI-DBSA. There were four Gaussian bands in this region to be confirmed by the curve-fitting procedure in the PP/CPP/PANI composites. A typical example is displayed in the iconograph of Fig. 9. The curve-fitting results for spectra of the region are listed in Table 5.

[FIGURE 9 OMITTED]

TABLE 5. Curve-fitting results for spectra of the region (646-760
[cm.sup.-1]).

                             First band

Sample     v1 ([cm.sup.-1])  [w.sub.1/2]1 ([cm.sup.-1])   S1

PANI-DBSA        667.2                 25.809            0.514
CPP
PP/PANI 1        666.4                 16.765            0.286
PP/PANI 2        666.2                 15.512            0.124
PP/PANI 3        666.8                 13.128            0.276
PP/PANI 4        666.0                 16.070            0.245
PP/PANI 5        667.7                 13.514            0.119

                                Second band

Sample     v2 ([cm.sup.-1])  [w.sub.1/2]2 ([cm.sup.-1])   S2

PANI-DBSA        686.8                 10.042            0.036
CPP              684.5                 16.165            2.698
PP/PANI 1        685.1                 19.623            0.304
PP/PANI 2        684.7                 23.549            0.366
PP/PANI 3        683.1                 19.646            0.904
PP/PANI 4        681.5                 17.189            0.438
PP/PANI 5        684.2                 18.152            0.412

                                     Third band

Sample     v3 ([cm.sup.-1])  [w.sub.1/2]3 ([cm.sup.-1])    S3

PANI-DBSA
CPP              702.0                 12.364            0.688
PP/PANI 1        704.6                  9.335            0.027
PP/PANI 2        701.7                 12.260            0.055
PP/PANI 3        701.3                  9.037            0.041
PP/PANI 4        693.9                 13.888            0.124
PP/PANI 5        700.0                  9.602            0.023

                                      Fourth band

Sample     v4 ([cm.sup.-1])  [w.sub.1/2]4 ([cm.sup.-1])    S4

PANI-DBSA
CPP              727.4                 42.240           11.719
PP/PANI 1        728.1                 23.901            0.376
PP/PANI 2        729.8                 30.187            0.431
PP/PANI 3        729.4                 32.785            1.069
PP/PANI 4        729.4                 47.429            1.024
PP/PANI 5        729.0                 34.184            0.686

Table 5 shows that there are only two bands for PANI-DBSA: one occurs at 667.2 [cm.sup.-1], another occurs at 686.8 [cm.sup.-1], and there are three bands for CPP: the first occurs at 684.5 [cm.sup-1], the second occurs at 702.0 [cm.sup.-1], the third occurs at 727.4 [cm.sup.-1]. In spectra of the PP/CPP/PANI composites, the first band at around 666 [cm.sup.-1] is brought by PANI-DBSA, the second band at around 683 [cm.sup.-1] is the mixed contribution of PANI-DBSA and CPP, and last two bands are attributed to the C--C1 stretching vibration. Here, we mainly review the last two bands. Because of hydrogen-bonded C--C1......H--N, the C--C1 stretching band shifts to the lower wavenumber. Hence the band at around 700 [cm.sup.-1] is attributed to the H-bonded C--C1 stretching vibration between N--H and C1--C; another band at around 729 [cm.sup.-1] is attributed to the so-called "free" C--C1 stretching vibration.

Table 5 shows the [upsilon]4 of "free" C--C1 stretching band changes slightly with increasing CPP content. However the [upsilon]3 of H-bonded C--C1 stretching band is evidently influenced by the CPP content. The relation between [upsilon]3 and the volume resistivity and CPP content is graphically presented in Fig. 10. It can be seen from Fig. 10 that there exists a minimum [upsilon]3 among the composites (i.e. 693.9 [cm.sup.-1]). This means that the interaction of the H-bond between C--C1 and N--H in the PP/PANI 4 composite is the strongest among the PP/CPP/PANI composites. This also proves that the dispersion of PANI-DBSA in the PP/PANI composite is the most homogenous among the PP/CPP/PANI composites. Therefore the PP/PANI 4 composite has the minimum volume resistivity. This is coincident with the results obtained from the investigation of the N--H stretching region.

[FIGURE 10 OMITTED]

CONCLUSIONS

In this article, the volume resistivity of PP/CPP/PANI composites was investigated. FTIR was adopted to analyze and explain the effects of CPP on the formation of the intermolecular and innermolecular hydrogen-bond in the composites. The N--H stretching region (3320-3600 [cm.sup.-1], 1530-1630 [cm.sup.-1], and 646-760 [cm.sup.-1]) of the FTIR spectra have been carefully analyzed. The obtained results from the N--H stretching region and the region (1530-1630 [cm.sup.-1]) show the H-bonded N--H......O is disturbed by the introduction of CPP and is substituted by the H-bonded N--H......Cl; the mole fraction of the H-bonded N--H......Cl first increases with the increasing CPP content and reaches a maximum when the CPP content is lower than 13.22%, and then decreases with further increase of the CPP content. The addition of CPP weakens the intermolecular and innermolecular H-bonded interaction of the PANI-DBSA, and is beneficial to the dispersion of PANI-DBSA and the decrement of the volume resistivity in the composites. The intensity of the H-bond between C--Cl and N--H in PP/CPP/PANI composites and the intermolecular interaction between PANI-DBSA and CPP is closely correlated to the CPP content.

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Lin Yang, Jinyao Chen, Huilin Li

State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu, Sichuan 610065, China

Correspondence to: Huilin Li; e-mail: [e-mail]

Contract grant sponsor: National Nature Science Foundation of China; contract grant number: 50233010: contract grant sponsor: National Basic Research Program of China: contract grant number: 200CB623800.

DOI. 10.1002/pen.21307

Published online in Wiley InterScience (www.interscience.wiley.com).

[c] 2008 Society of Plastics Engineers