Reactivity of allyl and vinyl pentosides in photo-initiated donor-acceptor copolymerization - Carbohydrate Chemistry: Chemical and Biological Approaches - page 271

radical or by metal complexes still is the most used method route for
obtaining industrial synthetic polymers, this major polymerization
mechanism is rarely applied to originally designed bio-based monomers.
Carbohydrates with their numerous hydroxylic functions are good
candidates for achieving easy functionalization by minimal chemical
modification for conferring the desired reactivity in free-radical poly-
merization. In order to comply with the principles of Green Chemistry 3
and therefore to reduce the number of atoms introduced to the parent
bio-based platform molecules, ethylenic functions could be generated by
an elimination reaction 4 (chemical or enzymatic routes 5 ) or alternatively
introduced by minimal functionalization with 2 or 3 C atoms reagents.
Reactive unsaturations under the form of vinyl or allyl ether groups 6 were
preferred to the conversion into acrylic and methacrylic esters, 7 essen-
tially for their better compliance with the atom economy principle.
In the following section, a review of the various attempts reported for
obtaining sugar-based monomers polymerizing via a step-growth or a
chain process is presented. Then, our current activity aiming at the de-
sign and at the study of novel pentose derivatives with vinyloxy and
allyloxy functions for donor-acceptor copolymerization is developed. The
photo-initiated copolymerization of vinyloxy and allyloxy pentose de-
rivatives with butenedioates used as comonomers are discussed in terms
of reactivity and of polymerization mechanism. Finally, this particular
chemistry applied to multifunctional compounds is evaluated for the
formation of original networks.

2 State-of-art for carbohydrate-based monomers
2.1 Available feedstock
Early efforts for the ecient conversion of biomass into monomers were
concentrated on the acidic transformation and on the fermentation of
sugars obtained from sucrose, or from glucose after depolymerization of
starch materials (potato, corn). During the last two decades, however,
more attention has been focused on other constituents of plant materials,
such as cellulose and lignocellulosic residues. The current trend is indeed
to avoid competition with food, offering new routes to C6 and C5 carbo-
hydrates, for further transformation into value-added platformmolecules.

2.2 Typology of carbohydrate-based monomers
A variety of carbohydrate-based monomers well-suited for step-growth or
for chain polymerization have been made commercially available since
decades.
Acid-catalyzed condensation of furfuryl alcohol, furfural and other
carbonyl compounds is a key process affording hard products known for
their high resistance to heat, acids, and alkalis, as well as their high
coking values. Hence, the utilization of furan resins in the metal casting
industry as binder for sand moulds is a major industrial application. 8
Diols (1,3-propanediol, isosorbide) and polyols (xylitol, sorbitol), can
also be obtained by chemical of biotechnological transformation of
sugars for the synthesis of polyesters 9 and polyurethanes. 10 Similarly