Self-healing polymers are smart materials that have the capability to repair themselves when they are damaged without the need for detection or repair by manual intervention of any kind.

1. INTRINSIC SELF-HEALING
POLYURETHANES
AKASH RAJ D
2020248026

2. Introduction
Self-healing polymers are smart materials that have
the capability to repair themselves when they are
damaged without the need for detection or repair by
manual intervention of any kind.

3. There are two different types of self-healing
polymers:
• Extrinsic: Polymers that when mixed with an external
agent that’s put inside the matrix, can repair damage.
• Intrinsic: Polymers that don’t need an external agent
to repair damage.

4. Extrinsic self-healing polymers

5. Intrinsic self-healing polymers
Intrinsic self-healing materials can recover their
properties due to the presence of specific reversible
chemical bonds, which is beneficial due to the
possibility of multiple healing steps at the same
location.

6. The self-repair of intrinsic self-healing polymers is
possible due to the reduction of the material viscosity
by applying temperature or internal and external
stimulus, such as pH changes or irradiation.

8. Polyurethanes
Polyurethanes (PUs) are obtained by polyaddition
reactions between polyols and polyisocyanates.
Adjusting parameters such as the
polyol : polyisocyanate ratio, allow readily tuning
their structural, thermal and mechanical properties.

9. Role of isocyanate
The chemical structure of isocyanate plays an
important role in the resulting thermal and mechanical
properties of PUs. Introducing rigid aromatic
diisocyanates will enhance rigidity and tensile strength
but reduce the chain mobility compared to their
flexible aliphatic counterparts.

11. Role of dihydroxy terminated prepolymer
The choice of the diol-terminated prepolymer is crucial
as it dictates parameters such as the
crystallinity/amorphous and the
hydrophobic/hydrophilic composition, the Tg as well as
the molecular weight of the resulting PUs.

12. In the context of self healing, amorphous and flexible
soft segments are preferred over crystalline and rigid
ones.

13. 1. Self-healing polyurethanes
through dynamic covalent chemistry
This category comprises chemistries with reversible
forming and breaking of covalent bonds. A dynamic
dissociation and re-association of stress-bearing bonds
allow for rapid conformational changes that ensure the
healing action as reaction to damage.

14. a. Thermo-responsive self-healing PUs
Temperature is by far one of the most available sources
of energy, along with the electromagnetic radiations, and
has been used extensively to trigger chemical change in
dynamic materials.
It is important to note that in some cases the external
energy used for a material to self-heal is a combination
on both thermal and electromagnetic radiation, making
the differentiation between both contributions difficult.

16. b. Photo-responsive self-healing PUs
Electromagnetic radiation (visible sunlight, UV, infrared)
is a convenient, available and unlimited source of
energy to heal materials when considering applications
as protective coating and outdoor bulk materials.

18. c. Chemo-responsive self-healing PUs
Recently, variation of pH or humidity have attracted the
attention of the self-healing community as new and
convenient ways to activate adaptive responses.
These two triggers are water-based and one can easily
imagine the important potentiality of repairable
materials when exposed to humidity variation or acidic
precipitation.

20. 2. Self-healing polyurethanes
through supramolecular chemistry
Supramolecular interactions impart the capability of
self-assembly or self-organization using highly
directional and reversible non-covalent interactions
that dictate the overall mechanical properties of a
material. These interactions, reversible by definition,
are ideal to create self healing intrinsic polymers.

21. a. Hydrogen bonding
Though, the term “hydrogen bonded supramolecular
self-healing” is ambiguous when PUs are considered.
Due to the presence of hydrogen bonds from urethane
linkages, hydrogen bonded physical networks are
obtained even for linear PUs.

22. PUs can undergo repairing alter damage due to
reassociation of hydrogen bonds. This
reassociation can be triggered, by temperature,
light or physical reattachment (e.g. electrostatc
interaction).

24. Future direction
MECHANOCHROMIC SELF-HEALING PUs
Ideal self-healing materials should have the ability to
manage crack/damage in a real-time response as well
as the possibility to provide visual inspection of
damage when microcracks are not easily visible (i.e. as
a preventive method).

25. Mechanochemistry refers to chemical reactions
induced by the input of mechanical energy (e.g.
grinding, compression, scratch) and mechanochromic
molecules possess the ability to undergo
conformational changes inducing color changes (i.e.
change of conjugation degree) under mechanical
solicitations.

26. Conclusions and challenges
PU materials are highly used in our daily life while
finding approaches to extend their lifetime which
dictate their use in future applications, the big
takeaway is that self-healing polymers have a
tremendous future, driven by economics, sustainability
and green chemistry, self-healing PUs provide
opportunities for designing novel materials with high
performance and lifetime reliability.

27. FACTORS LIMITING THEIR COMMERCIALIZATION ARE
AS FOLLOWS:
(i) No practical up-scaling synthesis: multi-step
synthesis, low yield, production price, use of solvent;
(ii) Limited healing recovery: in terms of reactive
functions (e.g. damage-induced self-healing PUs),
cycles (e.g. hindered urea) or mobility (e.g. self-healing
PU composites);

28. (iii) High energy input required for self healing: thermal
or UV irradiations should be replaced by softer stimuli
as humidity or visible light;
(iv) Healing limited to microscopic damages: limited to
micrometer sized scratch or requiring physical
reattachment of cut material;

29. REFERENCES
• Bertrand Willocq et.al. (2020), Advances in intrinsic self-healing
polyurethanes and related composites, RSC Adv.,Rev.10, 13766–13782.
• JianHua Xu et.al. (2020), Intrinsic self-healing polymers for advanced
lithium-based batteries: Advances and strategies, Appl. Phys. Rev. 7,
031304.
• S.J. Garcia (2014), Effect of polymer architecture on the intrinsic self-
healing character of polymers, European Polymer Journal 53, 118–125.

30. THANK YOU