Journal of the American Chemical Society
Communication
The use of visible light to “unlock” polymer P1c and control
its ability to act as an adhesive was demonstrated by measuring
the tensile shear strengths of two pieces of plastic glued
together by the polymer at two different temperatures. Three
sets of four transparent noncoated poly(ethylene terephthalate)
(312 nm) to convert the ring-opened isomers P1o to the PSS
containing a mixture of P1o and P1c, the adhesive properties of
the polymer increased, as shown by the observation that the
average shear force was 2.15 times higher than that for P1o at
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room temperature. This difference increased to almost 3.26
times at 90 °C, highlighting the fact that while the ring-opened
isomers of the photoresponsive building blocks in polymer P1o
are able to undergo the reverse Diels−Alder reaction, those in
(
PET) strips were spray-coated with a solution of P1o (32 mg/
mL). The strips were cut in half, and the two halves were glued
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together by pressing them under load at 90 °C (Figure 2).
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P1c cannot. The fact that the polymer containing the ring-
closed isomers had the same adhesion strength at room
temperature and 90 °C shows that the system is effectively
“
locked” in this form. This phenomenon can be reversed by
exposing the orange-red films to visible light (λ > 435 nm),
which triggers the ring-opening reaction, regenerates the ring-
opened isomers and polymer P1o, and lowers the adhesive
properties of the photoresponsive “glue”.
In this work, we have demonstrated how two wavelengths of
light can be used to regulate the adhesive properties of a
photoresponsive polymer by inducing ring-closing and ring-
opening reactions of the polymers’ building blocks. We
anticipate that this proof-of-concept example can be potentially
helpful in the development of future generations of self-healing
polymers.
Figure 2. Photographs of PET strips glued together by polymer P1o
and heated under pressure at 90 °C before irradiation (left), after
irradiation with UV light (middle), and after irradiation with UV light
followed by visible light (right).
ASSOCIATED CONTENT
Supporting Information
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*
S
This temperature was critical to ensure that the Diels−Alder
reaction equilibrium would occur and to soften the polymer
during the sample preparation process. The polymer underwent
the color change from colorless to orange-red in a similar
fashion as observed when solutions of them are exposed to UV
light (Figure 2).
Detailed descriptions of experimental methods, synthetic
procedures, characterization of new compounds, and additional
AUTHOR INFORMATION
Figure 3 shows a summary of all of the shear force
measurements on these plastic strips. The shear force at 90 °C
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This research was supported by the Natural Sciences and
Engineering Research Council (NSERC) of Canada and the
Canada Research Chairs Program. This work made use of 4D
LABS shared facilities supported by the Canada Foundation for
Innovation (CFI), the British Columbia Knowledge Develop-
ment Fund (BCKDF) and Simon Fraser University. The
authors thank Prof. Carlo Menon (SFU Engineering) and Dr.
Saeid Kamal (LASIR) for their help with setting up the high-
temperature tensile shear experiments.
Figure 3. Average shear forces of PET strips glued together using
polymer P1o before irradiation, after irradiation with 312 nm light for
REFERENCES
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(
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(
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dx.doi.org/10.1021/ja500496n | J. Am. Chem. Soc. 2014, 136, 3024−3027