Novel Surface Modifications of Cellulose Polymer – Click Chemistry on TEMPO Cellulose SurfacesPunnamchandar Ramidi, Narsimha Reddy Penthala, Shobanbabu Bommagani and Peter A. Crooks*

Dept. of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, AR-72205

AbstractCellulose is the most abundant naturally available polymerand consists of repeating anhydroglucose unit (AGU) withequatorial 1 to 4 linkages, and it has many beneficialproperties such as, hydrophilicity, biocompatibility,biodegradability, stereoregularity, multichirality, reactivehydroxyl groups and the ability to form superstructure, all ofwhich make this polymer very promising for variousindustrial and biological applications. Although cellulose hasmany useful applications, it possesses poor processabilityand solubility, which is likely due to the possibility for inter-molecular and intra-molecular hydrogen bonding. In order toutilize cellulose more effectively, the primary hydroxylgroups need to be chemically modified by regioselectivechemical modification. The goal of this project is to developnovel scalable, hierarchical cellulose self-assembly processesfor manufacturing more complex, controlled, and sustainablecellulose-based regulated multifunctional surfaces. This willbe achieved by structural modification of cellulose byinvestigating covalent and ionic attachment of chemicalmoieties onto carboxylated and sulfated cellulose surfaces.We have successfully synthesized carboxylated cellulosepolymers by employing 2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO) in the presence of a primary oxidizing agent suchas sodium hypochlorite (NaOCl). TEMPO catalyzes theconversion of carbohydrate primary alcohols to carboxylate(COO-) functionalities. TEMPO oxidized cellulose represent aunique platform for carrying out a plethora of surfacemodifications and for generating a myriad of functionalmoieties via covalent grafting techniques. We haveperformed novel surface click chemistry reactions on TEMPOcellulose surfaces in order to generate novel cellulose surfacearchitectures.

Cellulose Modifications

References

Summary

1. Tempo oxidation

2. Click chemistry on 1,2-TEMPO Cellulose

4. Cellulose sulfate

3. Ionic attachment on 1,2-TEMPO Cellulose

5. Tosylation and Tritylation

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AcknowledgementsArkansas NSF EPSCoRUniv. of Arkansas for Medical Sciences

1. We have successfully synthesized two forms ofTEMPO cellulose, cellulose-propargylamine, azidopolymers, cellulose quats and cellulose sulfate(Scheme 1-4) polymers

2. In our initial studies the reaction time for theoxidation of α-cellulose to 1,2-TC was around 24 hrs,this was improved considerably to 3-4hrs byincreasing the quantity of NaClO. Carrying out thesynthesis in a microwave reactor unit afforded aneven greater improvement in reaction time to 10min, and a significant increase in yield (50-60%).

3. We have also synthesized trityl and tosyl celluloses(Scheme 5) and these modified polymers are usefulfor the nucleophilic addition of various groups

4. All these modified cellulose polymers weresuccessfully characterized by FTIR and NMR Studies

1. Investigation of surface click chemistrymodifications utilizing nanofibrilated celluloses(NFC’s) materials. These NFC’s will display a highsurface area, which should greatly increase thenumber of surface primary hydroxyl groupsavailable for TEMPO oxidation

2. Preparation of cellulose esters, ethers, andaminocelluloses via tosylation, silylation andtritylation will be perofmred

3. Microscopic analysis of newly modified cellulosepolymers

4. Preparation of novel regioregular nanocellulosederivatives from natural wood cellulose

Future studies