Synthesis and Antibacterial Properties of Polysiloxanes-bearing Quaternary Ammonium Salt Groups

Synthesis and Antibacterial Properties of Polysiloxanes-bearing Quaternary Ammonium Salt Groups 

Precursor polysiloxanes containing 3-chloropropyl groups pendent to the siloxane chains were generated via the hydrolytic polycondensation of (3-chloropropyl) methyldichlorosilane. This polymer can be subjected to equilibration or coequilibration with octamethylcyclotrisiloxanes catalysed by trifluoromethanesulfonic acid. A known amount of hexamethyldisiloxane is introduced to control the MW and to terminate the chain by trimethylsilyl groups. This procedure leads to a statistical distribution of units in the case of copolymers. 

QAS- and ImS-substituted polysiloxanes is stronger against Gram-positive bacteria than Gram-negative bacteria, which is related to the difference in the structure of their cell walls. It is generally accepted that the mechanism of the bacteriocidal action of polycationic biocides involves their destructive interaction with the cell wall and/ or cytoplasmic membranes. 

A methanol solution containing poly(3) exhibits abroad absorption band with A,max at 422 nm. In aqueous solution, the absorption maximum red-shifts to 432 nm and the absorption coefficient also decreases. The emission properties are greatly dependent upon the nature of the solvent. In a methanol solution, poly(3) exhibits a narrow emission band with A.max = 475 nm and a vibronic band at A,max = 502 nm. In aqueous solution, the emission band becomes broader and the fluorescence quantum yield (Ofi =0.016) is lower than that in methanol ( fi = 0.045). Interestingly, the emission maximum is at the same position as in methanol (475 nm) with a shoulder at 502 nm. Such behaviour is different from other PPE-based CPE, which exhibit large red-shifts of emission band in a poor solvent. The lack of a spectral shift for poly(3) is likely to be due to the fact that the aggregated state of the polymer has a much lower quantum yield, and therefore its contribution to the total emission spectrum is small. 

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