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Polymers by 1,3‐dipolar cycloaddition reactions: the “criss‐cross” cycloaddition
Author(s) -
Maier Gerhard
Publication year - 1996
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1996.021971002
Subject(s) - cycloaddition , 1,3 dipolar cycloaddition , polymer chemistry , monomer , polymer , reactivity (psychology) , copolymer , chemistry , materials science , organic chemistry , catalysis , medicine , alternative medicine , pathology
1,3‐Dipolar cycloaddition reactions have been used to prepare a large number of different heterocyclic and heteroaromatic polymers. Most of this work has been done in the 60's and 70's. Since then, interest in this field has vanished almost completely. While the number of polymer structures accessible by 1,3‐dipolar cycloaddition is very large, the high reactivity and tendency of the 1,3‐dipoles to undergo side reactions limits the successful applications in step growth polymer synthesis considerably. The “criss‐cross” cycloaddition reaction also proceeds via two consecutive 1,3‐dipolar cycloaddition steps. Its starting compounds, azines and diolefins or diisocyanates, are stable, can be purified easily, and do not undergo side reactions if the reaction conditions are chosen properly. Initially, the reaction between hexafluoroacetone azine and various diolefins was studied. This work was aimed at the preparation and structural characterization of soluble polymers. Later on, the “criss‐cross” cycloaddition between aromatic aldazines and diisocyanates was included in this research. Different azines and diisocyanates were studied to find the best compromise between reactivity of the monomers and solubility and glass transition temperature of the products. Due to the special reaction mechanism, the polymers have exclusively isocyanate end groups, independent of stoichiometry of the monomers and the conversion. Thus, this reaction is ideally suited for the preparation of telechelics. Prepolymers obtained by “criss‐cross” cycloaddition between 4‐methoxybenzaldazine and 4,4′‐diisocyanatodiphenyl ether were used as hard segments in segmented block copolymers. Those block copolymers with a hard segment content below 36% showed elastomeric behavior with ultimate elongations above 700% and tensile strengths between 2 and 6 MPa.