Tham khảo tài liệu 'biomedical engineering trends in materials science part 18', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 502 Biomedical Engineering Trends in Materials Science R2. Cu I catalyst R1----N N N H-------- -------R2 ------------ N X Nx R1 N 1 Fig. 17. Copper I -catalyzed alkyne-azide cycloaddition The use of click chemistry for the functionalization of polyesters has also been reported for block copolymerization and for the synthesis of star-shaped polymers Lecomte et al. 2008 but the most interesting strategies remain the grafting onto and grafting through approaches. The latter will be briefly described in the next paragraph. For the grafting onto strategy cyclic esters bearing an azide or alkyne functional group are synthesized in the first step followed by ring-opening polymerization and the grafting of an azide or alkyne endcapped polymer onto the functionalized polyester backbone. Parrish et al. 2005 pioneered this approach synthesizing a a-propargyl-8-valerolactone that was further copolymerized with g-caprolactone Fig. 18 . The resulting alkyne grafted aliphatic polyester served as backbone for clicking oligopeptide moities and poly ethylene glycol onto the backbone. The synthesis of other monomers of interest such as a-azide-g-caprolactone Riva et al. 2005 and 3 6-dipropargyl-1 4-dioxane-2 5-dione Jiang et al. 2008 and subsequent polymerization and grafting have also been reported in the literature leading notably to poly ethylene glycol -graft-poly g-caprolactone and -polylactides respectively. Note that the reactive groups used for the grafting onto method can also be introduced by post-polymerization modification of a chloro-functionalized polyester backbone Riva et al. 2005 . Grafting through methods In this approach a cyclic ester bearing a pendant macromolecular chain is synthesized and polymerized. Poly ethylene glycol chains end-capped by an g-caprolactone unit have been synthesized by living anionic ring-opening polymerization of ethylene oxide initiated by the potassium alkoxide of 1 4-dioxaspiro 4 5 decan-8-ol followed by derivatization of the .
