Cellulose-graft-polystyrene bottle-brush copolymers by homogeneous RAFT polymerization of soluble cellulose macro-CTAs and “CTA-shuttled” R-group approach

- Cellulose-graft-PS copolymers were prepared by cellulose macro-CTAs and CTA-shuttle approach.
- By pre-modification cellulose macro-CTAs were well soluble in organic solvents and monomers.
- Mn and graft density can be well-controlled for grafts by adjusting reaction conditions.
- Very high grafting efficiencies and graft ratios were obtained as monitored by means of SEC.

In this work we introduce well-defined cellulose-graft-copolymers prepared from CTA-functionalized cellulose and an CTA-shuttled R-approach in solution. Micro-crystalline cellulose was transferred into a cellulose-CTA in a three-step approach with degrees of substitution for CTA, DS(CTA), of about 0.2-0.6. Additional transfer of residual OH-groups with propionic ester groups resulted in cellulose-CTA molecules that were well-soluble in a large number of organic solvents. Model polymerizations using styrene monomer, AIBN as initiator and added free CTA produced well-defined cellulose-graft-PS copolymers. The molar mass of the macromolecules generated on the cellulose backbone were found to be similar as the molar mass of the polymers obtained from the CTA free in solution, which allowed a simple analysis of the graft copolymers. The molar mass of the cellulose-grafted PS could be well-controlled between less than 5000 g/mol to more than 40,000 g/mol by adjusting the reaction conversion through variation of the polymerization time. Analysis of the initiation efficiency showed that by using the CTA-shuttled approach for the generation of cellulose-graft-copolymers one can obtain very high grafting densities (relative amount of grafted chains on the cellulose backbone) as well as grafting ratios (relative mass gain due to grafting of the polymers onto the cellulose backbone). The presented results thus offer a number of possibilities for future design of functional cellulose-based bottle brush architectures.

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