Reactivity of allyl and vinyl pentosides in photo-initiated donor-acceptor copolymerization
The present chapter is an attempt to compile the developments in the chemistry of carbohydrate-based monomers featuring an ethylenic moiety suited for free radical polymerization, in terms of design, reactivity and properties of the resulting polymers. Particularly, the reactivity of vinyl and allyl ethers derived from selected sugars was examined in donor-acceptor copolymerization with butenedioates (diethyl fumarate, DEF, or diethyl maleate, DEM) used as acceptor co-monomers. The reactivity of selected pairs of monomers was studied from the viewpoints of polymerization rates and of copolymerization mechanism. Kinetic studies confirmed the higher reactivity of vinyl ethers with respect to allyl analogs, the latter leading to extensive transfer reactions evidenced by the lower molecular weight of the resulting polymers and by the nature of the end groups. Vinyloxy monomers yield regular alternating copolymers with high molecular weight when copolymerized in undiluted liquid blends. Allyloxy monomers polymerized in the presence of DEF typically undergo random copolymerization with DEF homopropagation, as well as the dominant occurrence of transfer reactions as end of growth mechanism. The influence of structural factors, of dilution and of stoichiometry on the reactivity was examined in details so as to optimize polymerization efficiency. Some examples of possible routes towards pentose-based networks illustrate the approach using allyloxy model derivatives, polymerization of hybrid donor-acceptor monomers as well as the copolymerization of a multifunctional xyloside bearing several electron-donor unsaturations together with an acceptor comonomer. Finally, the influence of monomer composition on the thermo-physical properties of the resulting networks was evaluated.