Force-induced redistribution of a chemical equilibrium.

Spiropyran (SP) mechanophores (mechanochemically reactive units) can impart the unique functionality of visual stress detection to polymers and have potential for use in smart materials with self-sensing capabilities. These color-generating mechanophores were incorporated into polyurethane via step growth polymerization. Polyurethane, which is inherently a versatile engineering polymer, possesses an optimized balance of mechanical toughness and elasticity to allow for investigation of the kinetics of the mechanochemical response of the SP mechanophore in the bulk polymer via fluorescence and absorbance measurements. The stress-induced 6-π electrocyclic ring-opening to the colored merocyanine (MC) form of the mechanophore was quantified by measuring the change in absorbance of the polymer, while it was held at constant strain. The closing kinetics of the mechanophore was also studied by fluorescence imaging. Finally, the effects of mechanical strain on the equilibrium between the SP and MC forms are reported and discussed.

[1]  Mary M. Caruso,et al.  Mechanically-induced chemical changes in polymeric materials. , 2009, Chemical reviews.

[2]  M. Rubner.  Synthesis and characterization of polyurethane-diacetylene segmented copolymers , 1986 .

[3]  R. Koepsel,et al.  Surface dispersion and hardening of self-assembled diacetylene nanotubes. , 2005, Nano letters.

[4]  Kenichiro Iwasaki,et al.  Conformational changes of poly(3-alkylthiophene)s with temperature and pressure , 1994 .

[5]  C. Weder,et al.  Deformation-Induced Color Changes in Melt-Processed Photoluminescent Polymer Blends , 2003 .

[6]  T. Shiga,et al.  Fluorescence from poly(N-vinylcarbazole) in uniaxially stretched polymer films , 1997 .

[7]  C. Weder,et al.  Oligo(p-phenylene vinylene) Excimers as Molecular Probes: Deformation-Induced Color Changes in Photoluminescent Polymer Blends , 2002 .

[8]  R. A. Nallicheri,et al.  An examination of the strain-induced orientation of hard segment domains in 4,4′-methylenebis(phenyl isocyanate)-based polyurethane-diacetylene segmented copolymers , 1990 .

[9]  C. Weder,et al.  Strain sensitive photonic natural rubber , 2008 .

[10]  Hexian Li,et al.  Excimer formation in uniaxially stretched polymer films , 2001 .

[11]  C. Tanford.  Macromolecules , 1994, Nature.

[12]  Michael F. Rubner,et al.  Novel optical properties of polyurethane−diacetylene segmented copolymers , 1986 .

[13]  G. Ruggeri,et al.  Bis(benzoxazolyl)stilbene excimers as temperature and deformation sensors for biodegradable poly(1,4-butylene succinate) films , 2007 .

[14]  Hess,et al.  Photoexcitations in polythiophene at high pressure. , 1993, Physical review. B, Condensed matter.

[15]  Christoph Weder,et al.  Self‐Assembly and Dispersion of Chromogenic Molecules: A Versatile and General Approach for Self‐Assessing Polymers , 2006 .

[16]  R. Simha,et al.  Deformation-Induced Color Changes in Mechanochromic Polyethylene Blends , 2007 .

[17]  Wilhelm T S Huck,et al.  Mechanically induced generation of counterions inside surface-grafted charged macromolecular films: towards enhanced mechanotransduction in artificial systems. , 2006, Angewandte Chemie.

[18]  Timothy A. Whitehead,et al.  Mechanical nanosensor based on FRET within a thermosome: damage-reporting polymeric materials. , 2009, Angewandte Chemie.

[19]  Vladimir I Minkin,et al.  Photo-, thermo-, solvato-, and electrochromic spiroheterocyclic compounds. , 2004, Chemical reviews.

[20]  Christoph Weder,et al.  Polyesters with Built-in Threshold Temperature and Deformation Sensors , 2006 .

[21]  R. A. Nallicheri,et al.  Investigations of the mechanochromic behavior of poly(urethane-diacetylene) segmented copolymers , 1991 .

[22]  G. Ruggeri,et al.  Modulation of the optical response of polyethylene films containing luminescent perylene chromophores. , 2008, The journal of physical chemistry. B.

[23]  James R. McElhanon,et al.  Stress Sensing in Polycaprolactone Films via an Embedded Photochromic Compound , 2010, ACS applied materials & interfaces.

[24]  Mitchell T. Ong,et al.  Force-induced activation of covalent bonds in mechanoresponsive polymeric materials , 2009, Nature.

[25]  A. Pucci,et al.  Luminescent Bis(benzoxazolyl)stilbene as a Molecular Probe for Poly(propylene) Film Deformation , 2005 .

[26]  C. Weder,et al.  Self-assessing photoluminescent polyurethanes , 2006 .