ROMP protective groups

Colak and Tew [67] also reported the synthesis of NBE-based polycarboxy- and polysulfo betaines (Figure 7.6c) via ROMP with second-generation Grubbs ruthenium catalysts modified with 3-bromo-pyridine. Utilizing a protecting group in the synthesis allowed them to obtain poly(carboxy betaines) with very narrow polydispersities (PDI = 1.03-1.15). 

Because the conditions for final protecting-group removal can be harsh, eliminating this step allows for the synthesis of materials containing sensitive bioactive epitopes. Consequently, the ability to synthesize substituted polymers utilizing both defined initiators and unprotected monomers constituted a critical advance in the synthesis of bioactive substituted polymeric displays via ROMP. Methods that have been used successfully for the incorporation of polar bioactive ligands are highlighted. 

The living character of the ROMP promoted by the initiator Ru(CHPh)(Cl)2 (PCy3)2 (Cy = cyclohexane) was tested with the synthesis of diblock, triblock, and tetrablock copolymers of norbornene derivatives carrying acetyl-protected glucose, [2,3,4,6-tetra-O-acetyl-glucos-l-O-yl 5-norbornene-2-carboxylate], A or maltose groups, [2,3,6,2/,3/,4/,6/-hepta-0-acetyl-maltos-1-O-yl 5-norbornene-2-carboxylate], B, shown in Scheme 41 [102]. The AB, ABA, and ABAB structures were prepared by sequential addition of monomers with narrow molecular weight distributions to quantitative conversions. 

Al-Badri and co-workers [55] studied the effect of fine-tuning the cationic parameter of synthetic mimics of antimicrobial peptides (SMAMP) on haemolytic and antibacterial activities. A category of novel norbornene monomers that carry one, two or three Boc-protected amine-functionalities was synthesised (Figure 3.8). ROMP of the monomers, followed by deprotection of the amine groups led to cationic antimicrobial polynorbornenes that carry one, two and three charges per monomer repeat unit. It was observed that enhancing the number of amine groups on the most hydrophobic polymer effectively decreased its haemolytic activity. 

In principle the most common types of polyelectolytes like poly acids or polyamins should be accessible via ROMP with the Grubbs-type initiators. It turned out that direct polymerisation is problematic as both functional groups are able to form complexes with the initiator. So we decided to protect the carboxylic acid with a tetrahydropyrane group. After the polymerisation this group was easily hydrolysed and the polyacid or the respective salt was easily accessible [10]. 

Figure 3.9 End-capping of living PNBE prepared via living ROMP using molybdenum carbine with 4-trimethylsilyloxybenzaldehyde to give the tri-methylsilyl-protected alcohol polymer end group [64].

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