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Antimicrobial activity of polysiloxane coatings containing quaternary ammonium-functionalized polyhedral oligomeric silsesquioxane.

Abstract An array of quaternary ammonium functionalized-polyhedral oligomeric silsesquioxane (Q-POSS) compounds with different alkyl chain lengths and counter ions were synthesized using a two-step process. First, octasilane POSS was functionalized with dimethylamino groups by hydrosilylation with allyl-dimethylamine. Next, partial quaternization of the tertiaryamino-functional POSS was achieved using an alkyl halide to produce the Q-POSS. Alkyl chain length of the Q-POSS compounds varied from [-C.sub.12][H.sub.25] to [-C.sub.18][H.sub.37] and the counter ions varied between chlorine, bromine, and iodine. Moisture-cured polysiloxane coatings were prepared by dispersing Q-POSS molecules into a solution blend of silanol-terminated poly-dimethylsiloxane, methylacetoxysilane, and a catalyst. To evaluate the utility of the Q-POSS molecules as a broad-spectrum antimicrobial additive, the antimicrobial activity of the coatings toward the Gram-negative bacterium, Escherichia coli, the Gram-positive bacterium, Staphylococcus aureus, and the opportunistic fungal pathogen, Candida albicans, was determined using an agar plating method. The results obtained showed that both the composition of the Q-POSS and the composition of the polysiloxane matrix affected antimicrobial properties. Compositions were identified that inhibited the growth of all three microorganisms on the coating surface. Surface Raman spectroscopic analysis was performed on selected set of coatings to understand the relative concentration of Q-POSS molecules at the coating surface.

Keywords Polyhedral oligomeric silsesquioxane (POSS), Polydimethylsiloxane, Antimicrobial additive

Introduction

Polyhedral oligomeric silsesquioxane compounds (POSS) continue to be of interest for the production of novel nanocomposites. (1) POSS molecules have a nanosized cage structure with a silica core and organic groups on its surface which provides a high compatibility with polymers and acts as a building block for organic-inorganic hybrid materials. It has been reported that POSS-polymer nanocomposites can result in increased glass transition temperature, (2) enhanced mechanical properties, (3), (4) increased use temperature, (5) lower flammability, and enhanced Theological properties compared to the unmodified polymer. (6) Functionalization of silicon corners of POSS with a variety of organic substituents such as epoxy, (7), (8) amine, (9) and vinyl (10) groups have been successfully achieved.

Quaternary ammonium compounds (QACs) are widely used as disinfectants to control microbial growth. (11-13) Both ionic and hydrophobic interactions between the QAC and bacterial walls or cytoplasmic membranes lead to cell death or malfunction in cellular processes. (14), (15) Various compositional factors such as charge density, amphiphilicity, molecular size, and molecular mobility also determine the ability of a QAC to bind to the bacterium cell wall and/or cell membrane and disrupt its function. Since cell wall/cell membrane composition and structure varies from one microorganism to another, the effectiveness of a given QAC is microorganism dependent. Several investigators have reported the complex relationship between QAC composition, microorganism species, and antimicrobial activity. (16), (17)

Quaternary ammonium salt (QAS) functional polymers with multiple QAS groups have been found to be more effective antimicrobial agents compared to low molecular weight mono- or divalent QACs since they have higher charge densities that provide higher affinities for the negatively charged microorganism cell wall. (18) However, their diffusion through the cell membrane can be inhibited due to the higher molecular weight and higher extent of inter- and intramolecular ionic interactions associated with QAS-functional polymers. As a means to enable high charge densities while maintaining a compact molecular structure, Chen et al. (19) investigated QAS-functional poly(propylene imine) dendrimers as an antimicrobial agent and showed that a dendrimer possessing 16 QAS groups per molecule provided two orders of magnitude greater antimicrobial activity than a monofunctional counterpart.

Since POSS molecules can be readily functionalized to possess multiple functional groups per molecule, it was of interest to synthesize quaternary ammonium functional-POSSs (Q-POSSs) and determine their utility as antimicrobial additives for surface coatings as discussed by Chojnowski et al. (20) POSS molecules have a relatively compact structure with a size of 2-5 nm which allows the POSS-bearing quaternary ammonium compounds to have a charge density similar to dendrimers. Therefore, their ability to destructively interact with negatively charged bacterial walls or cytoplasmic membranes should be pronounced.

Our previous work on Q-POSS as an antimicrobial additive in polysiloxane coatings has shown that coatings based on Q-POSSs possessing the lowest extent of quaternization (~40 mol%) displayed antimicrobial activity, whereas analogous coatings produced using Q-POSSs possessing the highest extent of quaternization (~100 mol%) showed no antimicrobial activity. (21) However, counter ion composition was not considered in the previous study. This article describes the synthesis of an array of Q-POSS molecules with low extent of quaternization (~40 mol%) possessing systematic variations in chemical composition (alkyl chain length and counter ion). Antimicrobial activity of Q-POSS compounds in aqueous solution was determined toward the Gram-negative bacterium, Escherichia coli (E. coli), and the Gram-positive bacterium, Staphylococcus aureus (S. aureus), after 15 min of contact time. To evaluate the utility of the QPOSS molecules as a broad-spectrum antimicrobial additive for polysiloxane coatings, the antimicrobial activity of coatings was determined toward E. coli, S. aureus, and the opportunistic fungal pathogen, Candida albicans (C. albicans). Since adhesion and subsequent surface growth of microorganisms (bacteria, fungi, etc.) is the primary cause of infection on biomedical implants and devices such as catheters, (22), (23) these coatings could be used to prevent such occurrences.

Experimental

Materials

Octasilane POSS was purchased from Hybrid Plastics, and allyldimethylamine was purchased from TCI America. Karstedt's catalyst (platinum(0)-1,3-divinyl-l, 1,3,3-tetramethyl disiloxane complex), 1-iodooctadecane, 1-iodohexadecane, 1-iodododecane, 1-bromo-octadecane, 1-bromohexadecane, 1-bromododecane, 1-chlorooctadecane, 1-chlorohexadecane, 1-chlorodode-cane, 1.0 M tetrabutylammonium fluoride (TBAF) in tetrahydrofuran (THF), 4-methyl-2-pentanone, and THF were obtained from Aldrich Chemical. 18,000 and 49,000 g/mol silanol-terminated polydimethylsilox-ane (HO-PDMS-OH) and methyltriacetoxysilane (MeAc) were purchased from Gelest. Intergard 264 epoxy primer was obtained from International Marine and Protective Coatings. Tryptic soy broth (TSB), tryptic soy agar (TSA), Luria-Bertani broth (LBB), Luria-Bertani agar (LBA), Sabouraud's dextrose agar (SDA), yeast nitrogen broth (YNB), triphenyltetrazoli-um chloride, and 10x phosphate-buffered saline were purchased from VWR International. 1x PBS was prepared in deionized water. An 80 wt% solution of the 49,000 g/mol HO-PDMS-OH in toluene and a 50 mmol solution of TBAF in 4-methyl-2-pentanone (Cat soln.) were used for coating solution preparation. All other reagents were used as received.

Q-POSS synthesis

As shown in Fig. 1, Q-POSS compounds were synthesized in two steps. The first step involved hydrosilylation between allyldimethylamine and octasilane POSS using Karstedt's catalyst to generate tertiaryamino-functionalized POSS. The second step involved quaternization of tertiaryamino groups with an alkyl halide. The details of Q-POSS synthesis are provided in Appendix 1.

[FIGURE 1 OMITTED]

Preparation of polysiloxane coatings containing Q-POSS

Coating solutions were prepared by adding HO-PDMS-OH, 50% Q-POSS solution, and toluene to a 20-mL plastic cup and mixing at 2400 rpm for 2 min with a SpeedMixer[TM] DAC 150 FVE-K. Next, MeAc and Cat sol were added to the mixture and the mixture was mixed at 2400 rpm for an additional 2 min. The coating solutions were stirred overnight using magnetic stirring before dispensing over primed aluminum discs for antimicrobial testing. On each disc, 200 [micro]L of coating solution was dispensed using an Eppendorf Repeater[R] plus pipetter. The primer used was Intergard 264 epoxy primer.

Antimicrobial property characterization of Q-POSS solutions

The antimicrobial properties of Q-POSS solutions were determined using a D/E neutralization assay. (21) Stocks of E. coli ATCC 12435 and S. aureus ATCC 25923 were maintained weekly at 4[degrees]C on LBA and TSB, respectively. Broth cultures of E. coli (LBB) and S. aureus (TSB) were prepared by inoculating one colony into 10 mL of broth and incubating at 37[degrees]C with shaking. Overnight cultures were pelleted via centrifugation (10 min at 4500 rpm), washed twice in 0.9% NaCl, and resuspended to a 0.5 McFarland turbidity standard (~[10.sup.8] cells [ml.sup.-1]). Two [mu]L of a 5 wt% Q-POSS solution in THF was added to 1 mL of bacterial suspension previously dispensed into a well of a sterile 24-well polystyrene plate. The plates were placed on an orbital shaker and allowed to incubate for 15 min at room temperature. 0.1 mL of each Q-POSS/ bacterial suspension was immediately transferred to 0.9 mL of D/E neutralization medium in a 1.5-mL microcentrifuge tube and serially diluted (1:10) in D/E medium. 0.2 mL of each dilution was transferred in triplicate to a 96-well plate and incubated statically at 37[degrees]C. After 24 h of incubation, the plates were removed from the incubator and photographed with a digital camera to quantify bacterial growth in solution. Bacterial log reductions were reported as the average of three replicate samples. The bacterial suspensions in 0.9% NaCl (without Q-POSS addition) served as a positive growth control (yellow color). Blank D/E medium served as the negative growth control (purple color). Since THF was used to solubilize Q-POSS molecules for biological evaluations, the antimicrobial activity of THF was also determined. As expected, THF did not inhibit bacterial growth. Thus, variations in antimicrobial activity could be exclusively attributed to the Q-POSS molecules.

Antimicrobial characterization of coatings containing Q-POSSs

The antimicrobial properties of the coated aluminum discs were determined using an agar plating method. (24) Stocks of E. coli ATCC 12435, S. aureus ATCC 25923, and C. albicans ATCC 10231 were maintained weekly at 4[degrees]C on LBA, TSB, and SDA, respectively. Broth cultures of E. coli (LBB), S. aureus (TSB), and C. albicans (YNB) were prepared by inoculating one colony into 10 mL of broth and incubating at 37[degrees]C with shaking. Overnight cultures were pelleted via centrifugation (10 min at 4500 rpm), washed twice in PBS, and resuspended to a final cell density of ~[10.sup.8] cells [mL.sup.-1]. A sterile swab was used to inoculate a lawn of each microorganism on their corresponding agar plates. The coated aluminum discs were then placed on the agar plates with the coated side in direct contact with the agar surface. The plates were inverted and incubated for 24 h at 37[degrees]C. Inhibition of microbial growth around and/or directly on the coating surfaces was evaluated visually from digital images taken after 24 h of incubation. A biological activity indicator dye, triphenyltetrazolium chloride, was added to the agar medium (70 mg/L E. coli, 15 mg/L S. aureus, and 500 mg/L C. albicans) to aid in the visualization of microbial growth (i.e., red color).

Instrumentation

[.sup.1]H NMR spectra were recorded in [CDCl.sub.3] using a JEOL 400 MHz spectrometer (Peabody, USA). A sweep width of 7503 Hz was used with 16,000 data points, resulting in an acquisition time of 2.184 s. Sixteen scans were obtained with a relaxation delay of 4 s.

[.sup.29]Si NMR spectra were collected using a JEOL 400 MHz spectrometer operating at 79.43 MHz. Acquisition parameters included a 62.5 kHz sweep width, 16,000 data points, and an acquisition time of 0.21 s. A total of 14,000 scans were collected. The lock solvent was acetone-d6 with chromium tris-acetyl acetonate added as a shiftless relaxation agent.

Raman experiments were performed at room temperature using a JOBIN Yvon Horiba Raman Spectrometer (Edison, USA) model HR800, 47 mW solid-state diode laser at 532 nm filtered by a natural density filter to reduce the laser intensity, and a charge-coupled detector (CCD). The Raman spectra were resolved by a 300 line [mm.sup.-1] grating giving a resolution of 1.5 [cm.sup.-1]. The spectral range investigated was 350-4000 [cm.sup.-1], and data processing was achieved using LabSpec 5.2 (JY Horiba) software.

Results and discussion

Octasilane POSS was selected as the starting compound to generate the Q-POSSs because the eight Si-H groups are a siloxane unit away from the inorganic cage resulting in a reduction in steric hindrance for further chemical modification. (25) As shown in Fig. 1, the first step of the Q-POSS synthesis involved hydrosilylation of octasilane POSS with allyldimethylamine to generate a functionalized POSS containing eight tertiary amino groups. Complete functionalization was confirmed by [.sup.1]H NMR. [.sup.29]Si NMR was used to ensure that the cubic structure of POSS remained intact after the reaction. The tertiar-yamino-functionalized POSS was then used as a precursor to generate Q-POSSs. Quaternization of the tertiaryamino-functionalized POSS was achieved by reacting with alkyl halides of varying chain length (R) and halide composition (X) at 50-110[degrees]C for 48 h. Table 1 lists the composition of the Q-POSSs synthesized. An idealized chemical structure of Q-POSS is shown in Fig. 1.
Table 1: Alkyl halide and counter ion composition of Q-POSSs

Q-POSS            R            X

Q-18-1   [C.sub.18][H.sub.37]  I
Q-16-1   [C.sub.16][H.sub.33]  I
Q-12-1   [C.sub.12][H.sub.25]  I
Q-18-Br  [C.sub.18][H.sub.37]  Br
Q-16-Br  [C.sub.16][H.sub.33]  Br
Q-12-Br  [C.sub.12][H.sub.25]  Br
Q-18-CI  [C.sub.18][H.sub.37]  CI
Q-16-CI  [C.sub.16][H.sub.33]  CI
Q-12-CI  [C.sub.12][H.sub.25]  CI

Repeater[R] plus pipetter. The primer used was Intergard 264 epoxy
primer.


Antimicrobial activity of Q-POSSs in aqueous solution

The antimicrobial activity of the Q-POSSs in aqueous solution was measured using the Gram-negative bacterium, E. coli, and the Gram-positive bacterium, S. aureus. Figures 2 and 3 display antimicrobial activity of Q-POSSs as a function of both the length of the alkyl chain and counter ion of the QAS groups toward E. coli and S. aureus, respectively. Both alkyl chain length and counter ion were found to affect antimicrobial properties. For Q-POSS molecules with the chlorine counter ion, a sharp drop in activity toward E. coli was observed as the alkyl chain length increased from C12 or C16 to C18, whereas for Q-POSS molecules with the iodine counter ion the effect was opposite; a sharp increase in activity toward E. coli was observed as the alkyl chain length increased from C12 to C16 or C18. In general, with S. aureus, the activity of Q-POSS molecules decreased with the increase in the alkyl chain length and was independent of counter ion composition.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Complex QAC chemical structure-antimicrobial activity relationships and variations in activity based on the species of microorganisms have been observed by other investigators. Gilbert et al. (26) and Kourai et al. (27) reported a parabolic relationship between QAC alkyl chain length and antimicrobial activity toward different microorganisms. Several factors such as aggregation of QAC molecules in solution, steric interactions, affinity of the QAC for the microorganism surface, and diffusivity through the cell wall affect the QAC chemical structure-antimicrobial activity relationships. (28), (29)

Q-POSS with C12 alkyl chain length and chlorine as a counter ion provided the highest, broadest-spectrum antimicrobial activity. Thus, the alkyl chain length-counter ion combination for dodecyldimethylammoniumchloride-POSS (Q-12-Cl) provided the best balance of lipophilicity and diffusivity to enable both effective binding to the outer surface of the bacterium cell structure and diffusivity through the cell wall to the cell interior.

Antimicrobial activity of coatings

The Q-POSSs described in Table 1 were incorporated into two different moisture-curable polysiloxane coatings which differed with respect to the molecular weight of the HO-PDMS-OH (49,000 and 18,000 g/mol) used to generate the crosslinked network. Table 2 describes the compositions of the coating solutions prepared. Figure 4 provides a schematic representation of the crosslinked network with dispersed Q-POSS molecules.

[FIGURE 4 OMITTED]
Table 2: Compositions of the coatings produced (all values are in
grams)

  Coating    49,000 g/mol  18,000 g/mol  MeAc  Cat soln.    Q-POSS
              HO-PDMS-OH    HO-PDMS-OH                    composition

49K-PDMS        10.00           0.00     1.50    1.50          -
49K-Q-18-I      10.00           0.00     1.50    1.50       Q-18-1
49K-Q-16-I      10.00           0.00     1.50    1.50       Q-16-1
49K-Q-12-I      10.00           0.00     1.50    1.50       Q-12-1
49K-Q-18-Br     10.00           0.00     1.50    1.50       Q-18-Br
49K-Q-16-Br     10.00           0.00     1.50    1.50       Q-16-Br
49K-Q-12-Br     10.00           0.00     1.50    1.50       Q-12-Br
49K-Q-18-CI     10.00           0.00     1.50    1.50       Q-18-CI
49K-Q-16-CI     10.00           0.00     1.50    1.50       Q-16-CI
49K-Q-12-CI     10.00           0.00     1.50    1.50       Q-12-CI
18K-PDMS         0.00          10.00     1.50    1.50          -
18K-Q-18-I       0.00          10.00     1.50    1.50       Q-18-1
18K-Q-16-I       0.00          10.00     1.50    1.50       Q-16-1
18K-Q-12-I       0.00          10.00     1.50    1.50       Q-12-1
18K-Q-18-Br      0.00          10.00     1.50    1.50       Q-18-Br
18K-Q-16-Br      0.00          10.00     1.50    1.50       Q-16-Br
18K-Q-12-Br      0.00          10.00     1.50    1.50       Q-12-Br
18K-Q-18-CI      0.00          10.00     1.50    1.50       Q-18-CI
18K-Q-16-CI      0.00          10.00     1.50    1.50       Q-16-CI
18K-Q-12-CI      0.00          10.00     1.50    1.50       Q-12-CI

   Coating     Weight of     Wt% of Q-POSS     THF (from  Toluene
                Q-POSS      (based on 100 g     Q-POSS
                             of HO-PDMS-OH)    solution)

49K-PDMS          -                -                 -     2.50
49K-Q-18-I       1.82            18.20           1.82      2.50
49K-Q-16-I       1.77            17.70           1.77      2.50
49K-Q-12-I       1.65            16.50           1.65      2.50
49K-Q-18-Br      1.73            17.30           1.73      2.50
49K-Q-16-Br      1.67            16.70           1.67      2.50
49K-Q-12-Br      1.56            15.60           1.56      2.50
49K-Q-18-CI      1.64            16.40           1.64      2.50
49K-Q-16-CI      1.58            15.80           1.58      2.50
49K-Q-12-CI      1.47            14.70           1.47      2.50
18K-PDMS         -                 -              -        0.00
18K-Q-18-I       1.82            18.20           1.82      0.00
18K-Q-16-I       1.77            17.70           1.77      0.00
18K-Q-12-I       1.65            16.50           1.65      0.00
18K-Q-18-Br      1.73            17.30           1.73      0.00
18K-Q-16-Br      1.67            16.70           1.67      0.00
18K-Q-12-Br      1.56            15.60           1.56      0.00
18K-Q-18-CI      1.64            16.40           1.64      0.00
18K-Q-16-CI      1.58            15.80           1.58      0.00
18K-Q-12-CI      1.47            14.70           1.47      0.00


As illustrated in Table 3, three different antimicrobial responses were observed. For some coatings, no microorganism growth was observed on the surface of the coating or in a zone surrounding the coated specimen (zone of inhibition). This type of antimicrobial response was given the designation, "+,+." In addition to this response, coatings were identified that showed no microorganism growth on the coating surface, but no zone of inhibition. This antimicrobial response was given the designation, "+,-." Finally, coatings that showed no microorganism growth inhibition on the coating surface or a zone of inhibition were given the designation, "-,-."

[TABLE 3 OMITTED]

Table 4 provides a summary of the antimicrobial results obtained. Overall, Q-POSS-containing coatings were more active toward S. aureus, followed by C. albicans, and then E. coli. Coatings 18K-Q-12-Br or 18K-Q-12-C1 were found to be active against all three microorganisms. Figure 5 was generated using the data shown in Table 4 to enable visualization of the effects of Q-POSS composition and HO-PDMS-OH molecular weight on antimicrobial activity. Antimicrobial activity was represented as the number of microorganism species that were inhibited from growing on the coating surface. With regard to the effect of HO-PDMS-OH molecular weight on antimicrobial activity, the results shown in Fig. 6 indicate that coatings based on the lower molecular weight HO-PDMS-OH (18,000 g/mol) were more likely to display antimicrobial activity than coatings based on the higher molecular weight HO-PDMS-OH (49,000 g/mol). With regard to the effect of Q-POSS composition, coatings based on a Q-POSS with a chlorine counter ion tended to exhibit broader spectrum antimicrobial activity.

[FIGURE 5 OMITTED]
Table 4: Antimicrobial activity of coatings

Coating      S. aureus  E. coli  C. albicans

49K-Q-18-I      -,-       -,-        -,-
49K-Q-16-I      +,-       -,-        -,-
49K-Q-12-I      -,-       -,-        -,-
49K-Q-18-Br     -,-       -,-        -,-
49K-Q-16-Br     +,-       -,-        +,-
49K-Q-12-Br     -,-       -,-        -,-
49K-Q-18-CI     +,-       -,-        +,-
49K-Q-16-CI     +,+       -,-        +,+
49K-Q-12-CI     +,-       -,-        -,-
18K-Q-18-I      +,-       -,-        +,-
18K-Q-16-I      -,-       -,-        -,-
18K-Q-12-I      +,-       -,-        +,-
18K-Q-18-Br     -,-       -,-        -,-
18K-Q-16-Br     -,-       -,-        -,-
18K-Q-12-Br     +,+       +,-        +,+
18K-Q-18-CI     -,-       -,-        -,-
18K-Q-16-CI     +,+       -,-        +,+
18K-Q-12-CI     +,+       +,-        +,+


Since overall antimicrobial response was dependent on multiple factors, ANOVA was performed over the entire coating data set by considering HO-PDMS-OH molecular weight, Q-POSS alkyl chain length, and Q-POSS counter ion as three categorical variables. Each "+" sign in the antimicrobial response for a particular coating described in Table 4 was assigned a numerical value of 1 and for each "-" sign a numerical value of 0 was assigned. Considering three microorganisms, overall antimicrobial response for a particular coating was given by adding the individual numerical values. For example, for the coating 18K-Q-12-C1, the overall antimicrobial response was given a numerical value of 5 [(S. aureus 1 + 1) + (E. coli 1 + 0) + (C. albicans 1 + 1) = 5]. The ANOVA results are shown in Table 5. The Model F-value of 3.65 implied that the model was significant. There was only a 3.20% chance that a "Model F-value" this large could be due to noise. The interaction term with HO-PDMS-OH molecular weight and Q-POSS alkyl chain length was the most significant contributing factor to the overall antimicrobial response followed by Q-POSS counter ion composition. Figure 6 shows the interaction graph of overall antimicrobial response for the coatings with the chlorine counter ion. The interaction graph indicated that the overall antimicrobial activity decreased with the increase of Q-POSS alkyl chain length when dispersed in the lower molecular weight HO-PDMS-OH (18,000 g/mol), whereas with the higher molecular weight HO-PDMS-OH (49,000 g/mol) the chance of getting maximum activity was associated with Q-POSS having the C16 alkyl chain length.

[FIGURE 6 OMITTED]
Table 5: ANOVA table for overall antimicrobial response

Source                 Sum of   DF   Mean      F    Prob >  Implication
                       squares      squares  value    F

Model                   40.56    7   5.79    3.65   0.032   Significant

HO-PDMS-OH molecular     3.56    1   3.56    2.24   0.166
weight

Alkyl chain length       7.44    2   3.72    2.34   0.146

Counter ion             11.44    2   5.72    3.60   0.066

(HO-PDMS-OH molecular   18.11    2   9.06    5.70   0.022
weight) (Alkyl chain
length)

Residual                15.89   10   1.59

Corrected total         56.44   17


Surface characterization using Raman spectroscopy

To understand the antimicrobial properties, surface Raman spectra were collected on select samples, and the results are shown in Fig. 7. For 18K-PDMS, peaks at 489 and 710 [cm.sup.-1] assigned to the Si-O-Si out of plane bending vibration and Si-C stretching mode, respectively, (30), (31) and two peaks at 2909 and 2967 [cm.sup.-1] assigned to the OH symmetric and asymmetric stretches of the Si-[CH.sub.3] group, (32), (33) respectively, can be observed. Coatings 18K-Q-12-C1 and 18K-Q-12-Br, which were active toward all three microorganisms, showed the appearance of a new peak at 435 [cm.sup.-1] assigned to the symmetric stretching of Si-O-Si from the POSS molecule which involves the motion of the oxygen atom along the line bisecting the Si-O-Si angle. (34-36) The broadening of the peak around 490 [cm.sup.-1] indicated a change in the Si-O-Si angular distribution of PDMS in the presence of Q-POSS. (34), (37) Q-POSS-containing coatings, 18K-Q-18-C1 and 18K-Q-18-Br, which were not active against any of the microorganisms, had a very small peak or no peak at 430 [cm.sup.-1] indicating that these coatings had very low concentrations of Q-POSS at the coating surface.

[FIGURE 7 OMITTED]

Spectral deconvolution was done between 400 and 550 [cm.sup.-1] to find the surface contribution from Q-POSS (area under 430 [cm.sup.-1]) and PDMS (area under 490 [cm.sup.-1]) by dividing its area by the total area. Figure 8 shows a representative deconvoluted spectrum, and Table 6 shows differences in peak areas for select 18K-Q-POSS coatings. As shown in Table 6, a correlation between the relative area of the peak at 430 [cm.sup.-1] and antimicrobial activity was observed. In general, antimicrobial activity increased with increasing relative area of the peak at 430 [cm.sup.-1]. Since the band at 430 [cm.sup.-1] is due to the Q-POSS molecule, the results indicated that antimicrobial activity increased as Q-POSS concentration at the coating surface increased. Several factors such as the thermodynamic driving force for phase separation between Q-POSS molecules and the polysiloxane matrix, intermolecular ionic interactions between Q-POSS molecules, intermolecular Vander Waals interactions associated with the long QAS alkyl chains of Q-POSS molecules, and the rate of crosslinking contribute to the surface concentration of Q-POSS molecules. The results shown in Table 6 suggest that increasing the alkyl chain of Q-POSS groups reduces the concentration of Q-POSS molecules at the coating surface. A reduction of Q-POSS surface concentration with increasing QAS alkyl chain length may be due to an enhancement in Q-POSS compatibility with the polysiloxane matrix. Further work is needed to fully understand the distribution of Q-POSS molecules in the coating matrix.

[FIGURE 8 OMITTED]
Table 6: A comparison between relative peak areas determined from
deconvoluted IR spectra and the number of microorganism species
inhibited

Coating        Relative area     Relative area       Number of
               under the 430     under the 490     microorganism
             [cm.sup.-1] peak  [cm.sup.-1] peak  species inhibited
                    (%)               (%)

18K-Q-18-Br         0.0              100.0               0

18K-Q-16-Br        23.9               76.1               0

18K-Q-12-Br        50.5               49.5               3

18K-Q-18-CI        18.4               81.6               0

18K-Q-16-CI        31.2               68.8               2

18K-Q-12-CI        43.2               56.8               3


Conclusions

Q-POSS compounds of varying composition were synthesized and investigated as an antimicrobial additive for polysiloxane coatings. The results showed that both the composition of the Q-POSS and the composition of the polysiloxane matrix affected antimicrobial properties. Coatings based on Q-12-Br or Q-12-C1 and 18,000 g/mol HO-PDMS-OH were found to be active against all three microorganisms tested using the agar plating method. ANOVA results for overall antimicrobial response indicated that the interaction between HO-PDMS-OH molecular weight and Q-POSS alkyl chain length was the most significant contributing factor. Surface analysis of select coatings using Raman spectroscopy showed that antimicrobial activity of the Q-POSS-containing coatings was primarily a function of the relative concentration of Q-POSS at the coating surface.

Acknowledgment The authors acknowledge financial support from the Office of Naval Research under grants N00014-05-1-0822 and N00014-06-1-0952.

Appendix 1: Synthesis details for Q-POSS compounds

Synthesis of tertiaryamino-functional POSS

In a 100-mL round-bottom flask equipped with a nitrogen inlet, condenser, and temperature controller, 2.00 g of octasilane POSS (1.96 mmol) and 1.75 g of allyldimethylamine (20.55 mmol) were dissolved in 50 mL of THF. Once dissolved, 180 [micro]L of Karstedt's catalyst was added to the reaction mixture and the reaction mixture was refluxed for 48 h. Completion of the reaction was confirmed using proton nuclear magnetic resonance spectroscopy ([.sup.1]H NMR) by observing the disappearance of the Si-H peak at [delta] 4.7 ppm. After completion of the hydrosilylation reaction, excess allyldimethylamine was removed under reduced pressure. Allydimethylamine removal was confirmed by the absence of the [.sup.1]H NMR (in [CDCl.sub.3]) peaks at [delta] 5.72 ppm (-N-[CH.sub.2]-CH=) and 5.01 ppm (-N-[CH.sub.2]-CH=[CH.sub.2]). [.sup.29]Si NMR displayed a singlet at [delta] 14.9 ppm, corresponding to the M-type silicon, and another singlet at [delta] -107.3 ppm, corresponding to the Q-type silicon of the POSS core. The presence of only two singlets in the [.sup.29]Si NMR spectrum confirmed that the cubic structure of POSS remained intact during the reaction. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.02-0.03 ppm (Si-[CH.sub.3]), [delta] 0.45-0.48 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.88 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.39 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N), and [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]]. The proportion of [alpha]-isomer was 20%.

Synthesis of Q-POSS (octadecyldimethyl-ammoniumiodide-POSS, Q-18-I)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.43 g of 1-iodooctadecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.53 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.27 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.01-0.09 ppm (Si-[CH.sub.3]), [delta] 0.45-0.55 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.86 ppm [-[([CH.sub.2]).sub.17]-[CH.sub.3]], [delta] 0.93 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.22 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 1.38 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.71 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.27 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.53 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 34.3 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (hexadecyldimethyl-ammoniumiodide-POSS, Q-16-I)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.32 g of 1-iodohexadecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.54 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.28 ppm [(-[N.sup.+]-([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.11 ppm (Si-[CH.sub.3]), [delta] 0.44-0.56 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.85 ppm [-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 0.93 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.23 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 1.38 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.72 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.28 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.54 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 37.3 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (dodecyldimethylammoniumiodide-POSS, Q-12-I)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.11 g of 1-iodododecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.51 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.25 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.08 ppm (Si-[CH.sub.3]), [delta] 0.44-0.53 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.82 ppm [-[([CH.sub.2]).sub.11]-[CH.sub.3]], [delta] 0.93 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.20 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.9]-[CH.sub.3]], [delta] 1.38 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.69 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.25 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.51 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 34.3 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (octadecyldimethyl-ammoniumbromide-POSS Q-18-Br)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.26 g of 1-bromooctadecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.53 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.30 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.11 ppm (Si-[CH.sub.3]), [delta] 0.45-0.56 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.85 ppm [-[([CH.sub.2]).sub.17]-[CH.sub.3]], [delta] 0.96 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.23 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 1.45 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.68 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.30 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.53 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 27.2 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (hexadecyldimethyl-ammoniumbromide-POSS, Q-16-Br)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.15 g of 1-bromohexadecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.52 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.28 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.10 ppm (Si-[CH.sub.3]), [delta] 0.44-0.55 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.84 ppm [-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 0.95 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.21 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 1.45 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.68 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.28 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.52 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 34.5 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (dodecyldimethylammoniumbromide-POSS Q-12-Br)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 0.94 g of 1-bromododecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 50[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.51 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.28 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.09 ppm (Si-[CH.sub.3]), [delta] 0.44-0.54 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.83 ppm [-[([CH.sub.2]).sub.11]-[CH.sub.3]], [delta] 0.94 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.21 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.9]-[CH.sub.3]], [delta] 1.45 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.68 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.09-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.28 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.51 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 34.4 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (octadecyldimethyl-ammoniumchloride-POSS, Q-18-Cl)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 1.09 g of 1-chlorooctadccane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 110[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.31 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.09 ppm (Si-[CH.sub.3]), [delta] 0.45-0.54 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.84 ppm [-[([CH.sub.2]).sub.17]-[CH.sub.3]], [delta] 0.95 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.22 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 1.45 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.67 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 2.13-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.31 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 27.2 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (hexadecyldimethyl-ammoniumchloride-POSS, Q-16-Cl)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 0.98 g of 1-chlorohexadecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 110[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.32 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.09 ppm (Si-[CH.sub.3]), [delta] 0.44-0.53 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.84 ppm [-[([CH.sub.2]).sub.15]-[CH.sub.3]], [delta] 0.95 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.22 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 1.44 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.67 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.13-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.32 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 28.4 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

Synthesis of Q-POSS (dodecyldimethylammoniumchloride-POSS, Q-12-Cl)

In a 20-mL glass vial containing a magnetic stir bar, 2.00 g of the tertiaryamino-functional POSS (9.4 x [10.sup.-3] moles of tertiary amine functional groups) was mixed with 0.94 g of 1-bromododecane (3.76 x [10.sup.-3] moles) and the quaternization reaction was carried out at 110[degrees]C for 48 h. A substantial increase in viscosity was observed as a result of the reaction. Using [.sup.1]H NMR (in [CDCl.sub.3]), new peaks appeared at [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-) and 3.32 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]] due to quaternization. [.sup.1]H NMR (in [CDCl.sub.3]) peaks are: [delta] 0.03-0.11 ppm (Si-[CH.sub.3]), [delta] 0.44-0.56 ppm [Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+], Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+], Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N, and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 0.85 ppm [-[([CH.sub.2]).sub.11]-[CH.sub.3]], [delta] 0.96 ppm [Si-CH([CH.sub.3])-[CH.sub.2]-[N.sup.+] and Si-CH([CH.sub.3])-[CH.sub.2]-N], [delta] 1.22 ppm [-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.9]-[CH.sub.3]], [delta] 1.43 ppm (Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-N and Si-[CH.sub.2]-[CH.sub.2]-[CH.sub.2]-[N.sup.+]), [delta] 1.68 ppm [[N.sup.+]-[CH.sub.2]-[CH.sub.2]-[([CH.sub.2]).sub.13]-[CH.sub.3]], [delta] 2.14-2.22 ppm [-[CH.sub.2]-N[([CH.sub.3]).sub.2]], [delta] 3.32 ppm [(-[N.sup.+]-[([CH.sub.3]).sub.2]], and [delta] 3.40 ppm (-[N.sup.+]-[CH.sub.2]-). The extent of quaternization was 28.9 mol%. The Q-POSS was diluted with THF to produce 5 and 50 wt% solution.

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This paper was presented at the 2009 CoatingsTech Conference, sponsored by NPCA/FSCT, April 28-29, 2009, in Indianapolis, IN.

P. Majumdar ([??]), J. He, E. Lee, A. Kallam, N. Gubbins, S. J. Stafslien, J. Daniels, B. J. Chisholm

The Center for Nanoscale Science and Engineering, North Dakota State University, 1805 Research Park Drive, Fargo, ND 58102, USA

e-mail: partha.majumdar@ndsu.edu

B. J. Chisholm

Department of Coatings and Polymeric Materials, North Dakota State University, 1735 Research Park Drive, Fargo, ND 58102, USA

[C] FSCT and OCCA 2009

DOI 10.1007/s11998-009-9197-x
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Author:Majumdar, Partha; He, Jie; Lee, Elizabeth; Kallam, Alekhya; Gubbins, Nathan; Stafslien, Shane J.; Da
Publication:JCT Research
Date:Jul 1, 2010
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