Preparation and surface properties of silicone-modified polyester-based polyurethane coats.

A series of novel silicone-modified polyesters (SPE) were prepared by substituting part of diol with low molecular weight hydroxyl-terminated poly(dimethylsiloxane) (PDMS). Then, isophorone diisocyanate (IPDI) as hard segments and 1,4-butanediol as chain extender were added to SPE to prepare a silicone-modified polyurethane (SPU). The effects of the type of diol, diacid, and hydroxyl-terminated PDMS, and the amount of hydroxyl-terminated PDMS on the preparation and surface properties of SPU were investigated. It was found that the amount of PDMS incorporated into a polyester chain was relatively higher when 1,6-hexanediol (HDO) and 1,10-decandiol (DDO) were used as diol and the PDMS with lower molecular weight was used as organosilicone compound. Consequently, the SPU coats with HDO as diol, adipic acid (AA) as diacid, and short chain PDMS as silicone segment had the lowest surface-free energy since it had the highest and most homogeneous distribution of silicone segments at its top layer surfaces.

Keywords: Hydroxyl-terminated poly(dimethylsiloxane), polyesters, polyurethanes, surface-free energy, coats, silicones, ESCA, XPS, Auger, SIMS, crosslinking, cure, surface analysis, stain resistance

**********

Thermoplastic polyurethanes (TPUs) are a versatile group of multicomponent segmented polymers that have excellent mechanical properties, good hardness, and high abrasion and chemical resistance. (1) They are widely used as melt-spandex, synthetic leather, film, adhesive, tube, and wire and cable materials. They find application in the automobile, health care, footwear, and coating industries. When TPUs are used in the coating industry, enhancement of the hydrophobicity of the surfaces of TPU films is of interest as a means of improving the stain resistance of TPU coats or reducing the wettability of TPU coats.

Modification with organosilicone is one of the ideal methods available for improving the hydrophobicity of the surfaces of TPU coats. The most widely used organosilicone is poly(dimethylsiloxane)s (PDMS). For example, Ho et al. (2-6) synthesized poly(dimethylsiloxane)-urea-urethane copolymers by a two-step polymerization method. Wang et al. (7) prepared PDMS-containing polyurethanes that were derived from a hydroxyl-terminated poly(tetramethylene oxide) (PTMO), secondary aminoalkyd functional PDMS oligomer, 4,4'-methylene diphenyl diisocyanate (MDI), and 1,4-butanediol via solution polymerization in terahy-drofuran (THF)/dimethylacetamide (DMAC). Rochery et al. (8) also incorporated PDMS into PTMO-based polyurethanes by using both hydroxyl-terminated PDMS and IPDI. Mequanint et al. (9) prepared phosphate- and siloxane-containing polyurethane dispersions by a conventional method from hydroxyl-terminated phosphated and siloxane macroglycols. Yen et al. (10) synthesized polyethylene glycol/PDMS mixing soft-segment waterborne polyurethane by a procedure of PU blending or soft-segment copolymerization. All of the above prepared silicone-containing polyurethanes showed a reduction in surface-free energy. The methods of preparation of PDMS-modified TPU were mainly based on mixing polyether/polyester and PDMS.

The objective of this study was to prepare silicone-modified TPU coats based on hydroxyl-terminated PDMS-modified polyester and IPDI, which has been seldom reported. A series of novel silicone-modified polyesters (SPE) were first prepared by substituting part of diol with low molecular weight hydroxyl-terminated PDMS using a method for synthesis of conventional polyester. Then, isophorone diisocyanate (IPDI) as hard segments and 1,4-butanediol (BDO) as chain extender were added to prepare a silicone-modified polyurethane (SPU). The structure and the surface properties of SPU coats were characterized by [.sup.1.H]NMR, optical contact angle system (OCA), X-ray photoelectron spectrometer (XPS), and scanning electron microscope (SEM) with EDX. Effects of the type of diol and diacid and the type and quantity of hydroxyl-terminated PDMS, etc. on the surface properties of the obtained polyurethane coats were investigated in detail.

EXPERIMENTAL

Materials

Two kinds of hydroxyl-terminated PDMS, namely PDMS550 (chemical purity grade, average molecular weight: 550 g/mol) and PDMS1000 (chemical purity grade, average molecular weight: 1000 g/mol), were obtained from Aldrich and were used without further purification. Diacid: adipic acid (AA, chemical purity grade) and phthalic anhydride (PA, chemical purity grade), diol: 1,4-butandiol (BDO, chemical purity grade), 1,6-hexandiol (HDO, chemical purity grade), and 1,10-decandiol (DDO, chemical purity grade) were provided by Sinopharm Group Chemical Reagent Co., Ltd., and neopentylene glycol (NPG, 99.65%) by Mitsubishi Chemical Company of Japan. Isocyanate: isophorone diisocyanate (IPDI, Desmodur N-3300) was purchased from Bayer. Catalyst: dibutyltin dilaurate (T-12, chemical purity grade) was obtained from Shanghai No. 1 Reagent Factory of China. Solvents: toluene (analytical purity grade), 3-pentanone (analytical purity grade), cyclohexane (analytical purity grade), and ethylene glycol (EG, analytical purity grade) were also obtained from Sinopharm Group Chemical Reagent Co., Ltd.

Preparation of Silicone-Modified Polyesters and Related Thermoplastic Polyurethanes

Diacid, diol, and hydroxyl-terminated PDMS with 1 wt% T-12 based on the total mass of monomers as the catalyst were charged into a 100 ml three-necked flask, equipped with a mechanical stirrer, a nitrogen inlet, a reflux condenser, and a receiver pipe. The flask was first heated to 140[degrees]C, then slowly to 180[degrees]C within four hours, and kept at that temperature until the acid number of the system was less than 3 mgKOH/g. The total reaction time was about 12-16 hr. The codes and molar feeding ratios of the obtained SPEs are given in Table 1. To remove unreacted PDMS, all of the resulting polyesters were purified by extracting with cyclohexane at least three times, and dried under vacuum conditions at 105[degrees]C for 48 hr. Since most of the prepared SPEs were solid at room temperature, all of the purification work was carried out in an oven at 60[degrees]C.

The corresponding polyurethanes (namely SPU polymers) were prepared via solution polymerization described as follows: The mixture of SPE/IPDI/BDO (molar ratio: 1/2/1) was dissolved in the mixture of toluene and 3-pentanone (volume ratio: 2/1) at 20 wt% solid, and added to a two-necked flask equipped with a nitrogen inlet, magnetic stirrer, and a reflux condenser, and was reacted at 80[degrees]C for one hour, and then poured into a mold. The mold was put into a vacuum oven at 105[degrees]C for 24 hr to finish the reaction and evaporate the solvent. The final product, named SPU-a as corresponding to the polyester of SPE-a (where "a" is the sample number), was dissolved in toluene/3-pentanone (volume ratio: 2/1) again at a concentration of 2 wt%. Polymer coats were prepared by casting the above solution on glass panels using a drawdown rod and dried at 70[degrees]C for one hour. The thickness of the resulted coats was about 1-2 [micro]m.

Characterization

[.sup.1.H]-NMR SPECTRA: The [.sup.1.H]-NMR spectra of liquid state polymers were determined by AVANCE DMX500 (Bruker Biospin Gmbh, Germany) at 500 MHz. Deuterated chloroform (CD[Cl.sub.3]) was used as the solvent.

CONTACT ANGLES: The contact angles of liquid on SPU coats were measured by OCA15 (DataPhysics Instruments Company, Germany). The connected software for measurement and calculation were SCA20 and SCA21, respectively. The complete profile of the sessile droplet was fitted by the ellipse method. The contact angle was the average value of five individual test data at different places on the polymer surfaces.

SURFACE-FREE ENERGY: The surface-free energy of the films was calculated by the Owens-Wendt-Kaelble method. In this experiment, deionized water and ethylene glycol were selected as the probe liquid to determine the surface-free energies of polyester-based polyurethane coats. The values of [[sigma].sub.l.sup.d] (21.80 mN/m) and [[sigma].sub.l.sup.p] (51.00 mN/m) for water and [[sigma].sub.l.sup.d] (30.90 mN/m) and [[sigma].sub.l.sup.p] (16.80 mN/m) for ethylene glycol were used in the calculation by SCA21 software.

XPS SPECTRA: XPS spectra were measured by a PHI 5000C ESCA System (Perkin Elmer Inc., USA) using an Al [K.sub.[alpha]] X-ray source. The X-ray gun was operated at 14.0 KV and 250 W, and the analyzer chamber pressure was less than [10.sup.-6] Pa. Survey scans spectra (0-1200 eV) were recorded at pass energy of 93.9 eV. Narrow scan spectra of [C.sub.1s], [O.sub.1s], [N.sub.1s], and [Si.sub.2p] were collected and peak analysis was carried out using PHI-MATLAB software.

SEM WITH EDX: The surface morphology of polymer coats was determined by a scanning electronic microscope (XL30, Philips Corp., Netherlands) equipped with an EDX accessory. Also used in the measurement were 20-30 kV of beam accelerating voltage and 3.8 nm of resolution factor. The morphology of the cross-section of the corresponding polyurethane coats, prepared by fresh fracture in liquid nitrogen, was also observed with the scanning electronic microscope.

RESULTS AND DISCUSSION

Preparation of Silicone-Modified Polyester-Polyurethane

Hydroxyl-terminated PDMS was incorporated into polyester by substituting part of diol. The reaction is described as follows:

[GRAPHIC OMITTED]

Then SPE was further reacted with IPDI and BDO as follows:

[GRAPHIC OMITTED]

Figure 1 displays the [.sup.1.H]NMR spectra of sample PE-1 and sample SPE-1. A new peak at 0.07 ppm attributed to the proton in the methyl group connected to the silicon element (C[H.sub.3]-Si-) was found in the [.sup.1.H]-NMR spectrum of sample SPE-1, indicating that the hydroxyl-terminated PDMS was successfully incorporated into the polyester main chain. In addition, the peaks at 4.1 ppm and 3.6 ppm corresponded to the proton ([H.sub.[beta]]) in the methylene connected with the ester group (-C[H.sub.2]-O-CO-) and the proton ([H.sub.[alpha]]) in the methylene next to the hydroxyl group (-C[H.sub.2]-OH), respectively. Table 2 lists the calculated actual composition of SPE series based on NMR spectra. Compared to the feeding composition in Table 1, it can be seen that a larger amount of PDMS can be copolymerized using HDO and DDO as diol. Moreover, the larger the amount of PDMS fed in condensation polymerization, the higher the PDMS content contained in SPE. Table 2 also shows that PDMS was more easily added to the polyester main chain with only AA rather than only PA as the diacid monomer. However, for the sample with the mixture of AA and PA, the PDMS content in SPE slightly increased with the increment of the amount of PA. In addition, the amount of PDMS in SPE prepared using the PDMS with high molecular weight (sample SPE-6) was lower than that using PDMS with low molecular weight (sample SPE-2), which may have been caused by the relatively lower activity and lower amount of silanol group for the PDMS with high molecular weight.

The degree of condensation, [d.sub.C], can be calculated from the peak area ratio of [H.sub.[alpha]] and [H.sub.[beta]]. (11)

[d.sub.C] = area ([H.sub.[beta]])/area ([H.sub.[alpha]])

Thus, the average molecular weight (Mn) of the polyester can be calculated by the following equation (11):

Mn = [d.sub.C] [M[W.sub.(diacid)] + M[W.sub.(diol)] - 2M[W.sub.(water)]] + M[W.sub.(diol)]

where M[W.sub.(diacid)], M[W.sub.(diol)], and M[W.sub.(water)] are the molecular weights of diacid, diol, and water, respectively. Table 3 summarizes the average molecular weight of polyester or the polyester segment of SPE.

In Table 3, it was found that the molecular weight of the polyester segment of SPE was greater than that of the corresponding polyester. It seems that the hydroxyl-terminated PDMS was favored for the polycondensation reaction. The effect of the dosage of silicone on the molecular weight of the polyester segment of SPE is displayed in Figure 2. It shows that the molecular weight of the polyester segment of SPE increased as the amount of silicone increased, further indicating the silicone's "catalysis role" on the polycondensation.

[FIGURE 1 OMITTED]

Surface-Free Energies of Silicone-Modified Polyester-Polyurethane Coats

EFFECTS OF THE TYPE OF DIOL, DIACID, AND HYDROXYL-TERMINATED PDMS: The contact angles of water and ethylene glycol on polyurethane coats and the surface-free energies of the polyurethanes with different types of diol, diacid, and hydroxyl-terminated PDMS are summarized in Table 4. Comparing the data of samples from the SPU series with the corresponding PU series suggests that the surface-free energy obviously decreased after the incorporation of silicone.

Based on the surface-free energy data of samples SPU-1, SPU-2, SPU-3, and SPU-4, it shows that sample SPU-2 with HDO as the diol unit had the lowest surface-free energy (12.59 mN [m.sup.-1]). It may be a result of two factors: (1) SPE-2 used for preparation of SPU-2 had the highest PDMS content (see the data in Table 2); (2) the compatibility of PDMS segment with HDO segment may be more appropriate for the transfer of PDMS segment to the surface and homogenous distribution of PDMS segment at the surface of SPU coats, rather than that with a shorter chain (i.e., BDO) or a longer chain (i.e., DDO and NPG) of diol unit since greater or less compatibility will lead to a difficult transfer of PDMS segment to the surface or uneven distribution of the PDMS segment at the surface.

[FIGURE 2 OMITTED]

The data on samples SPU-2 and SPU-5 show that the surface-free energy of SPU coat with phthalic anhydride was greater than the sample with adipic acid, which may have occurred for two reasons: (1) sample SPU-2 had higher silicone content than sample SPU-5; (2) the benzene ring in the phthalic anhydride molecule weakened the facility of the whole system and consequently limited the transferring towards the surface of silicone segments. Figure 3 shows the effect of the composition of mixed diacids (AA and PA) on the surface-free energy of SPU coats. It can be seen that the surface-free energy of SPU coats increased with the amount of PA in mixed diacids, which further confirms that AA as diacid unit is better than PA at reducing the surface free energy of SPU coats. Since the sample with higher silicone content (see the data of samples SPE-11, SPE-12, and SPE-13 in Table 2) had higher surface-free energy, we can infer that the restraining role of the benzene ring in phthalic anhydride for the transfer of PDMS chain towards the surfaces of SPU coats was mainly responsible for the lower surface-free energy of SPU coats.

From Table 4, it was unexpectedly found that the surface-free energy of sample SPU-6 was higher than that of sample SPU-2, indicating that the efficiency of long chain silicone (PDMS1000) was worse than that of short chain silicone (PDMS550) at reducing the surface-free energy of SPU coats when the same molar feed ratio was used. This should be attributed to the lower reactive activity of PDMS 1000 with diacid monomer and, correspondingly, lower PDMS content in SPU coats.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

EFFECT OF THE DOSAGE OF HYDROXYL-TERMINATED PMS: The effect of the dosage of hydroxyl-terminated PDMS on the surface-free energy of SPU is shown in Table 5. The surface-free energies of the SPUs first decreased then leveled off with increasing PDMS amount in feed composition. However, the change was very consistent with the change of the PDMS content in SPU coats. Namely, the higher the PDMS content in SPU coats, the lower the surface-free energy of SPU coats.

Surface Compositions of Silicone-Modified Polyester-Polyurethane

The atomic concentration of C, O, Si, and N for the airside surfaces of SPU coats are summarized in Table 6. For the sake of comparison, the theoretical atomic concentration is also calculated in Table 6, based on the feed composition. For all SPUs, the experimentally determined Si contents were higher than their corresponding theoretical values, further validating that the incorporated silicone segments tend to enrich at the top layer surfaces of polymer coats. It can also be seen that the Si concentration of sample SPU-2 with 1,6-hexanediol is the highest, which was consistent with the results of the contact angles and the surface-free energies.

Surface and Cross-Section Morphology Of SPU Coats

The SEM pictures of the surfaces and cross-sections of SPU coats are shown in Figure 4. The surface and cross-section morphology of sample SPU-1 show the existence of micron scale particles, and these particles distribute in the coats uniformly. Figure 5 illustrates the EDX spectrum of the particles in sample SPU-1. The atomic concentrations of C, O, Si, N, and Si/C atom ratios are summarized in Table 7. Since the theoretical Si/C ratios of PDMS and the whole sample SPU-1 coats are 0.5 and 0.004, respectively, 0.27 of the Si/C atom ratio for the particles means that the silicone segments should be the predominant species in the particles. This is probably because the silicone segments were not compatible with other components and tended to aggregate in the SPU-1 sample. However, for sample SPU-2, no obvious microphase separation was found at both the surface and cross-section, suggesting that all components in bulk are compatible with each other. This means that silicone segments can homogeneously distribute and enrich on the surfaces of the SPU coats. Some submicron scale particles were also found in the surface and bulk of sample SPU-3, which suggests that the compatibility of the coats with 1,10-decanediol was worse than with 1,6-hexanediol. The uneven distribution of silicone segments at the top layer surfaces of samples SPU-1 and SPU-3 may be responsible for their high surface-free energies. The morphologies of surfaces and cross-sections of samples SPU-4 and SPU-5 were analogous to sample SPU-2, but their surface-free energies were higher. This is attributed to the reduced mobility imposed by the rigid groups (neo-amyl and benzene ring, respectively) of samples SPU-4 and SPU-5.

[FIGURE 5 OMITTED]

CONCLUSIONS

A series of SPU coats was successfully synthesized by substituting part of diol with low molecular weight hydroxyl-terminated PDMS and using a conventional method for synthesis of the polyester. The amount of PDMS incorporated into the polyester chain was relatively higher when HDO and DDO were used as diol and the PDMS with lower molecular weight as organosilicone compound. The concentration of silicone segments tended to be higher at the polymer/air interface. The higher the amount of hydroxyl-terminated PDMS incorporated, the higher the concentration of silicone segments in the top layer, and the lower the surface-free energy of polyurethane coat. For reducing the surface-free energy of SPU coats, AA as diacid unit was better than PA and long chain silicone was worse than short chain silicone when the same molar feed ratio was used. In addition, it seemed that the components of SPU with 1,6-hexanediol as the diol monomer had the appropriate compatibility, and thus this sample had the lowest surface-free energy and the highest Si content at its surface.

References

(1) Woods, G., The ICI Polyurethane Book, Wiley, New York, p. 2, 1990.

(2) Ho, T., Wynne, K.J., and Nissan, R.A., Macromolecules, 26, 7029-7036 (1993).

(3) Chen, X., Gardella, J.A., Ho, T., and Wynne, K.J., Macromolecules, 28, 1635-1642 (1995).

(4) Cho, G., Natansohn, A., Ho, T., and Wynne, K.J., Macromolecules, 29, 2563-2569 (1996).

(5) Pike, J.K., Ho, T., and Wynne, K.J., Chem. Mater., 8, 856-860 (1996).

(6) Gardella, J.A., Ho, T., Wynne, K.J., and Zhuang, H.Z., J. Colloid Interface Sci., 176, 277-279 (1995).

(7) Wang, L.F., Ji, Q., Glass, T.E., Ward, T.C., McGrath, J.E., Muggli, M., Burns, G., and Sorathia, U., Polymer, 41, 5083-8093 (2000).

(8) Rochery, M., Vroman, I., and Lam, T.M., J. Macromol. Sci., Pure Appl. Chem., A40, No. 3, 321-333 (2003).

(9) Mequanint, K. and Sanderson, R., J. Appl. Polym. Sci., 88, 893-899 (2003).

(10) Yen, M.S. and Tsai, P.Y., J. Appl. Polym. Sci., 90, 233-243 (2003).

(11) Jones, F.N., Fu, S., Hua, J., and Yuan, X,. U.S. Patent 5,587,428, 1996.

Jun Yang, Shuxue Zhou, Bo You, and Limin Wu ([dagger]) -- Fudan University*

* Dept. of Materials Science, The Advanced Coats Research Center of China Educational Ministry, Shanghai 200433, People's Republic of China.

([dagger]) Author to whom correspondence should be addressed. Email: [e-mail].

Table 1 -- Codes and Molar Feed Ratios of Polyester and
Silicone-Modified Polyester (Unit: %)

Sample No.  AA    PA    BDO   HDO   DDO   NPG   PDMS550

PE-1        41.7  --    58.3  --    --    --    --
PE-2        41.7  --    --    58.3  --    --    --
PE-3        41.7  --    --    --    58.3  --    --
PE-4        41.7  --    --    --    --    58.3  --
PE-5        --    41.7  --    58.3  --    --    --
SPE-1       41.7  --    55.0  --    --    --     3.3
SPE-2       41.7  --    --    55.0  --    --     3.3
SPE-3       41.7  --    --    --    55.0  --     3.3
SPE-4       41.7  --    --    --    --    55.0   3.3
SPE-5       --    41.7  --    55.0  --    --     3.3
SPE-6 (a)   41.7  --    --    55.0  --    --     3.3
SPE-7       41.7  --    --    --    56.6  --     1.7
SPE-8       41.7  --    --    --    53.3  --     5.0
SPE-9       41.7  --    --    --    51.6  --     6.7
SPE-10      41.7  --    --    --    48.3  --    10.0
SPE-11      27.8  13.9  --    55.0  --    --     3.3
SPE-12      20.9  20.8  --    55.0  --    --     3.3
SPE-13      13.9  27.8  --    55.0  --    --     3.3

(a) PDMS1000 was used here.

Table 2 -- Actual Composition of SPE Series Based on [.sup.1.H]NMR

            AA      PA      Diol    Hydroxyl-Terminated PDMS
Sample No.  (mol%)  (mol%)  (mol%)  (mol%)

SPE-1       43.0    --      52.8     4.2
SPE-2       40.2    --      51.0     8.8
SPE-3       41.3    --      50.4     8.3
SPE-4       46.1    --      50.6     3.3
SPE-5       --      42.3    52.6     5.1
SPE-6       44.0    --      53.4     2.6
SPE-7       41.7    --      51.0     7.3
SPE-8       41.3    --      49.3     9.4
SPE-9       40.4    --      48.8    10.8
SPE-10      40.4    --      49.0    10.6
SPE-11      30.3    11.8    51.7     6.2
SPE-12      19.5    22.5    50.9     7.1
SPE-13      12.6    29.7    49.8     7.9

Table 3 -- Molecular Weight of Polyester and the Polyester Part of
Silicone-Modified Polyester

Sample
No.     [d.sub.c]  [M.sub.n] (a)  Sample No.  [d.sub.c]  [M.sub.n] (a)

PE-1    2.8        651            SPE-1       4.1         901
PE-2    2.6        712            SPE-2       3.7         952
PE-3    2.6        900            SPE-3       4.2        1366
PE-4    3.4        722            SPE-4       4.6        1080
PE-5    2.7        735            SPE-5       3.4         897

(a) Calculated from [.sup.1.H]NMR.

Table 4 -- Effects of the Type of Diol, Diacid, Hydroxyl-Terminated PDMS
on Contact Angle, and Surface-Free Energy of Polymer Coats

            [[theta].sub.[H.sub.2]O]  [[theta].sub.EG]
Sample No.  ([degrees])               ([degrees])

PU-1         82.1                     61.8
PU-2         78.2                     53.4
PU-3         84.6                     63.2
PU-4         80.5                     60.3
PU-5         84.5                     61.9
SPU-1        99.6                     81.1
SPU-2       101.8                     88.7
SPU-3       102.3                     83.0
SPU-4        98.0                     78.9
SPU-5        95.6                     77.6
SPU-6        94.5                     74.6

            [[sigma].sup.da]  [[sigma].sup.pa]  [[sigma].sub.s]
Sample No.  (mN [m.sup.-1])   (mN [m.sup.-1])   (mN [m.sup.-1])

PU-1        17.82             8.39              26.31
PU-2        25.01             7.19              32.20
PU-3        20.75             5.89              26.64
PU-4        17.27             9.62              26.89
PU-5        23.17             5.03              28.20
SPU-1       17.38             1.76              19.14
SPU-2        8.18             4.42              12.59
SPU-3       19.15             0.86              20.01
SPU-4       18.49             1.89              20.38
SPU-5       16.09             3.28              19.37
SPU-6       19.79             2.52              22.31

(a) [[sigma].sup.d] and [[sigma].sup.p] are the disperse and polar
contribution to the surface energy.

Table 5 -- Effects of the Quantity of Hydroxyl-Terminated PDMS on the
SPUs

            PDMS Content  PDMS Content
            in SPE        in SPU Coats  [[theta].sub.[H.sub.2]O]
Sample No.  (mol%)        (mol%)        ([degrees])

PU-3        --            --             84.6
SPU-7        7.3          1.8            87.8
SPU-3        8.3          2.1           102.3
SPU-8        9.4          2.4           103.0
SPU-9       10.8          2.7           105.1
SPU-10      10.6          2.7           104.8

            [[sigma].sub.EG]  [[sigma].sup.d]  [[sigma].sup.p]
Sample No.  ([degrees])       (mN [m.sup.-1])  (mN [m.sup.-1])

PU-3        63.2              20.75            5.89
SPU-7       67.4              19.59            4.96
SPU-3       83.0              19.15            0.86
SPU-8       83.2              19.81            0.65
SPU-9       86.7              17.30            0.70
SPU-10      86.0              18.13            0.62

            [[sigma].sub.s]
Sample No.  (mN [m.sup.-1])

PU-3        26.64
SPU-7       24.55
SPU-3       20.01
SPU-8       20.46
SPU-9       18.00
SPU-10      18.75

(a) The molar percentage of hydroxyl-terminated PDMS in SPU calculated
on the actual composition of SPE.

Table 6 -- Surface Atomic Concentration and Theoretical Values of SPU
Coats

                    C (mol%)                    O (mol%)
Sample No.  Determined  Calculated (a)  Determined  Calculated (a)

SPU-1       52.3        70.0            29.6        23.5
SPU-2       52.2        70.9            28.1        22.3
SPU-3       51.6        71.9            29.7        21.4
SPU-4       58.8        70.6            27.8        23.0
SPU-5       56.2        72.4            29.9        21.1
SPU-6       63.8        71.1            25.7        22.5

                   Si (mol%)                   N (mol%)
Sample No.  Determined  Calculated (a)  Determined  Calculated (a)

SPU-1       17.4        0.3             0.7         6.2
SPU-2       19.0        0.6             0.7         6.2
SPU-3       17.8        0.5             0.9         6.2
SPU-4        9.6        0.2.            3.8         6.2
SPU-5       12.0        0.3             1.9         6.2
SPU-6        8.1        0.2             2.4         6.2

(a) Based on the actual composition of SPE.

Table 7 -- Atomic Concentration of the Particles in Sample SPU-1

Sample  C (mol%)  O (mol%)  Si (mol%)  N (mol%)  Si/C

SPU-1   54.1      30.1      14.7       1.1       0.27