Quaternary Pyridinium-Functionalised Polynorbornenes

Polymers exhibiting quaternary nitrogen functionalities have commonly been used as biocidal agents [13-21], A number of polymeric disinfectants containing quaternary pyridinium groups, either in the backbone or as pendent groups, have been prepared and exhibit good antibacterial activity. 

Gao and co-workers investigated the random copolymers of acrylamide and vinyl pyridine, of varying MW and pyridine content, which were subsequently quaternised with dimethyl sulfate [22], Investigations proved that polymers with higher cationic functionality showed stronger antibacterial activity. In addition, depending on their alkyl chain length, methacrylate-based polymers with pendent pyridinium moieties were found to exhibit antibacterial activity [23]. 

Quaternary pyridinium polymers can show biological activity when bound to surfaces, e.g., poly(4-vinyl pyridine)-modified glass surfaces which were modified using different alkyl bromide derivatives. Suitable polymers for antibacterial applications not only exhibit antibacterial activity, but also non-toxicity to human cells (i.e., selectivity). 

The structure-activity importance of synthetic pyridinium-based polymers synthesised via the ring-opening metathesis polymerisation (ROMP) of norbornene has been reported these polymers were expected to directly affect the bacterial membrane [24-26]. The interaction of these polymers with a phospholipid membrane model has been investigated using the fluorescent dye, calcein, embedded in unilamellar vesicles. 

By controlling the hydrophobic/hydrophilic equilibrium of the polymers, their selectivity for bacterial cells over red blood cells (RBC) can be improved. This property is related to the effect that the ionic nature and hydrophobic character of these polymers has on cell membrane activity. The length of the alkyl substituents in the polymer repeat units affects antibacterial effectiveness in more hydrophobic polymers (hexyl and higher alkyl chain lengths in the repeat unit), disruption of the membrane integrity occurs more effectively. ROMP is an attractive method of synthesis which is widely used to prepare well-defined polymers with controlled MW and low polydispersity index values (PDl) [27-30]. 

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