New methods to synthesize and functionalize polymers are of constant interest to the polymer scientist. The 1,3-dipolar cycloaddition between an azide and terminal alkyne has received much attention since the reports that copper(i) provides high yields and regioselective synthesis of 1,4-substituted 1,2,3-triazoles. This coupling chemistry has been rapidly adopted by polymer scientists in the synthesis and post-polymerization modification of polymers. This Review will provide the historical context of the recent development of the copper-mediated azide–alkyne cycloaddition and its use in polymer science, particularly in dendrimer synthesis/functionalization, surface immobilization/modification, orthogonally functionalizing polymers, and its integration with ATRP (atom transfer radical polymerization).

The Rise of Azide–Alkyne 1,3-Dipolar ‘Click’ Cycloaddition and its Application to Polymer Science and Surface Modification

Cycloaddition reactions have been employed in polymer synthesis since the mid-nineteen sixties. This critical review will highlight recent notable advances in this field. For example, [2 + 2] cycloaddition reactions have been utilized in numerous polymerizations to enable the construction of strained polymer systems such as poly(2-azetidinone)s that can, in turn, afford polyfunctional β-amino acid derived polymers. Polymers have also been synthesized successfully via (3 + 2) cycloaddition methods utilizing both thermal and high-pressure conditions. ‘Click chemistry’
				– a process involving the reaction of azides with olefins, has also been adopted to generate linear and hyperbranched polymer architectures in a very efficient manner. [4 + 2] Cycloadditions have also been utilized under thermal and high-pressure conditions to produce rigid polymers such as polyimides and polyphenylenes. These cycloaddition polymerization methods afford polymers with potential for use in high performance polymers applications such as high temperature resistant coatings and polymeric organic light emitting diodes.

Advances in cycloaddition polymerizations

Publisher Summary This chapter focuses on the chemistry of monocyclic1,2,3-triazoles as much of the chemistry of benzotriazoles and other fused systems has little in common with monocyclic triazole chemistry and provides a broad survey of methods of synthesis and reactions of triazoles. There has been considerable interest in 1,2,3-triazoles as light stabilizers and as optical brightening agents. They are also used as precursors for azapurines and similar heterocyclic systems that are potential carcinostatic agents. Three recognized classes of 1,2,3-triazoles are 1 H -, 2 H -, and 4 H -1,2,3-triazoles. Triazoles unsubstituted on nitrogen can be regarded either as 1 H - or as 2 H -derivatives, depending upon what tautomer is preferred. The first two classes can be regarded as aromatic systems whereas the third, the 4 H -system, cannot. This is reflected in the abundance of examples of 1 H - and 2 H -triazoles and the rarity of 4 H -triazoles. The thermal cycloaddition of azides to acetylenes is the most versatile route to 1 H -1,2,3-triazoles because of the wide range of substituents that can be incorporated into the acetylene and azide components. The base-catalyzed condensation of azides with activated methylene compounds is a well-established route to 1 H -triazoles and is the best route to triazoles bearing a 5-amino or hydroxy substituent and an aryl or carbonyl-containing function in the 4-position. The structure and spectroscopic and physical properties of triazole are discussed in the chapter.

1,2,3-Triazoles

Copper-Catalyzed vs Thermal Step Growth Polymerization of Starch-Derived α-Azide−ω-Alkyne Dianhydrohexitol Stereoisomers: To Click or Not To Click?

Cycloaddition (CA) reactions have attracted recently strong interest not only for the preparation of linear polymers but also for the synthesis and modification of dendritic architectures. This review focuses mainly on the potential of various cycloaddition reactions in the field of dendrimers and especially hyperbranched polymers. The [4 + 2] Diels–Alder cycloaddition, [2 + 2 + 2] CA as well as 1,3-dipolar CA reactions including “click chemistry” will be addressed, and advantages of these reactions will be highlighted. High selectivity, thus high tolerance towards additional functionalities, high yields and often moderate to mild reaction conditions distinguish CA reactions from the often applied classical high-temperature polycondensation type reactions used mainly to synthesize hyperbranched polymers. Thus, besides the high potential in the synthesis and modification of perfectly branched dendrimers, cycloaddition reactions proved also very suited to prepare new types of hyperbranched structures.

M. G. Baldwin

Papers

1,3‐Dipolar cycloaddition polymerization of compounds containing both azido and acetylene groups

1,3‐Dipolar cycloaddition polymerization of 4‐azido‐1‐butyne