CELLULOSE-BASED POLYMERIC MATERIALS
Vladimír Raus
Cellulose is the most abundant organic polymer on Earth. Besides having a unique role
in biological systems, cellulose plays an important part in a number of industrial applications.
To date, cellulose has been prevalently utilized in its native form or in the form of simple
derivatives, such as esters or ethers. However, environmental concerns and economical
factors have recently led to the renewal of interest in cellulose-based products. This also
provided a strong incentive for development of more sophisticated cellulose-derived
materials.
Grafting copolymerization, where cellulose serves as a backbone for attachment of
synthetic polymeric grafts, represents a straightforward way to confer new properties to the
biopolymer and thus extend its functionality and scope of use. Unlike older heterogeneous
approaches, modification of cellulose in solution, employing new methods of controlled
radical polymerization (CRP), allows for a precise control of copolymers architecture. This
synthetic approach can be divided into three basic steps: i) cellulose dissolution, ii) cellulose
acylation to introduce initiation sites, and iii) grafting from the initiation sites via controlled
radical polymerization.
The first part of this work deals with cellulose dissolution in the N,Ndimethylacetamide/lithium
chloride (DMAc/LiCl) solvent system, which is followed by
acylation of cellulose with 2-bromoisobutyryl bromide in order to prepare polyfunctional
macroinitiators for grafting polymerization. It was found that cellulose activation, a process
facilitating cellulose dissolution in DMAc/LiCl, has a pronounced effect on the efficiency of
the following acylation reaction. The current methods of cellulose activation, as well as a
newly developed procedure utilizing 1,4-dioxane as an activating agent, were assessed in this
regard. Moreover, universality of the dioxane activation scheme was studied in detail using
different cellulose samples.
In the central part of the work, atom transfer radical polymerization (ATRP) and
single-electron transfer living radical polymerization (SET-LRP) techniques were used for
grafting of various monomers from the prepared cellulose-based macroinitators. The research
was focused on optimizing polymerization conditions in order to achieve well controlled
processes with good initiation efficiency. Copolymers with diverse composition and
architecture were synthesized, and their behavior in both the solid state and solution was
studied.
Finally, the preparation of (nano)composites based on cellulose graft copolymers will
be briefly mentioned to envisage the application potential of the prepared materials.