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Light‐Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks
Author(s) -
Sowan Nancy,
Song Han Byul,
Cox Lewis M.,
Patton James R.,
Fairbanks Benjamin D.,
Ding Yifu,
Bowman Christopher N.
Publication year - 2021
Publication title -
advanced materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.707
H-Index - 527
eISSN - 1521-4095
pISSN - 0935-9648
DOI - 10.1002/adma.202007221
Subject(s) - materials science , raft , toughness , glass transition , chain transfer , polymer , azide , reversible addition−fragmentation chain transfer polymerization , stress relaxation , composite material , polymer chemistry , polymerization , creep , radical polymerization , organic chemistry , chemistry
Abstract A covalent adaptable network (CAN) with high glass transition temperature ( T g ), superior mechanical properties including toughness and ductility, and unprecedented spatio‐temporally controlled dynamic behavior is prepared by introducing dynamic moieties capable of reversible addition fragmentation chain transfer (RAFT) into photoinitiated copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC)‐based networks. While the CuAAC polymerization yields glassy polymers composed of rigid triazole linkages with enhanced toughness, the RAFT moieties undergo bond exchange leading to stress relaxation upon light exposure. This unprecedented level of stress relaxation in the glassy state leads to numerous desirable attributes including glassy state photoinduced plasticity, toughness improvement during large deformation, and even photoinduced reversal of the effects of physical aging resulting in the rejuvenation of mechanical and thermodynamic properties in physically aged RAFT‐CuAAC networks that undergo bond exchange in the glassy state. Surprisingly, when an allyl‐sulfide‐containing azide monomer (AS‐N 3 ) is used to form the network, the network exhibits up to 80% stress relaxation in the glassy state ( T g − 45 °C) under fixed displacement. In situ activation of RAFT during mechanical loading results in a 50% improvement in elongation to break and 40% improvement in the toughness when compared to the same network without light‐activation of RAFT during the tensile testing.