Open AccessEffects of Network Structures on the Tensile Toughness of Copper-Catalyzed Azide–Alkyne Cycloaddition (CuAAC)-Based Photopolymers
Author(s) -
Songjun Han,
Nancy Sowan,
Austin Baranek,
Jasmine Sinha,
Wayne D. Cook,
Christopher N. Bowman
Publication year - 2021
Publication title -
macromolecules
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.994
H-Index - 313
eISSN - 1520-5835
pISSN - 0024-9297
DOI - 10.1021/acs.macromol.0c02455
Subject(s) - azide , alkyne , monomer , polymer chemistry , cycloaddition , materials science , polymerization , ultimate tensile strength , polymer , glass transition , chemistry , composite material , catalysis , organic chemistry
In the present study, the photo-initiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization was utilized to form structurally diverse glassy polymer networks. Systematic alterations in the monomer backbone rigidity (e.g., cyclic or aliphatic groups with a different length of backbone) and the reactive functional group density (e.g., tetra-, tri-, di-, and mono-functional azide and alkyne monomers) were used to provide readily tailorable network structures with crosslink densities (estimated from the rubbery modulus) varying by a factor of over 20. All eight of the resultant networks exhibited glass transition temperatures (T g ) between 50 and 80 °C with tensile toughness ranging from 28 to 61 MJ m -3 . A nearly linear dependence of yield stress and elongation at break (broadly defined as strength and ductility, respectively) on the T g and rubbery modulus was established in these triazole networks. When a flexible di-alkyne monomer (5 carbon spacing between alkynes) was incorporated in a network composed of a tri-alkyne and di-azide monomer, the elongation at break was improved from 166 to 300 %, while the yield stress was reduced from 36 to 23 MPa. Additionally, the polymer ductility was also varied by incorporating mono-functional azides as chain ends in the network - replacing a sterically hindered stiff mono-azide with a more flexible mono-azide increased the elongation at break from 24 to 185 % and the tensile toughness from 6 to 28 MJ m -3 .