1. Well-defined Thermoresponsive Polymers as Injectable Gels
Dr Theoni K. Georgiou
Department of Materials, ICL

2. Group Transfer Polymerisation
+ Living polymerisation technique  control of the polymer’s molecular weight, composition and architecture
+ Easy, Fast, Cost effective (RT and higher concentration)
+ Developed by DuPont to produce specialised polymers
- Can only use methacrylate and
acrylate monomers with R
not being an acid or alcohol group
Limitation: degree of polymerisation < 200
(depending on monomer)
Webster, O. W. et al J. Am. Chem. Soc. 1983, 105,
Webster, O.W. Science 1991, 251,
Webster, O. W. Adv. Polym. Sci. 2004, 167, 1-34.

3. GTP: Choice of Monomers
Hydrophobic
Hydrophilic
(some depending on the pH or the T)
Make your own monomers!
Methacryloyl chloride + R-OH 

4. Well-Defined Polymers
Polymers of narrow size distribution with defined composition and architecture
Vary the length
Vary the composition
Vary the architecture
Structure/Activity Relationships
Vary the polymer’s structure

5. Injectable Gels Thermoresponsive Gels for Tissue Engineering 37C
at body temperature the polymer will form a gel
room temperature: polymer + cells in culture medium
the polymer/cell mixture will be injected into a wound

6. Sol-Gel Thermo-transition
elastic modulus (G’)
viscous modulus (G’’)
complex viscosity
Sol – Gel Transition
G’, G’’, Viscosity
Temperature

7. Thermoresponsive Triblock Copolymers
Polymers of different molecular weights, architectures and compositions
ABC triblock
ABA triblock
BAC triblock
ACB triblock
Random terpolymer

8. Synthesis of Triblock Copolymers
THF
TBABB (catalyst)
MTS (initiator)
PEGMA
BuMA
BuMA
All polymers have a molecular weight distributions, dispersity Mw/Mn < 1.19.
During polymerisation the dispersity decreased by increasing the MW as expected for a living polymerisation method.
Aqueous properties, self-assembly, micelle size is affected by the molecular weight, the architecture as well as the composition of the polymer.

9. Effect of MW and Composition
20 wt% BuMA wt% BuMA 40 wt% BMA
Effect of MW and Composition
15000 g/mol g/mol g/mol
solid, dotted, and dashed lines corresponds to elastic modulus G’, viscous modulus G’’ and viscous viscosity
Ward, M. A.; Georgiou, T. K. Soft Matter 2012, 8,

10. Effect of Architecture
ABC
ACB
BAC
cmc
Non-ionic hydrophilic
Non-ionic hydrophobic
Hydrophilic, pH- and thermo-responsive
multicompartment
hydrogel ?

11. Effect of Architecture and Alkyl Side Group
The ABC is the “best” architecture – best sol-gel transition
Increasing the length of the side alkyl group lowers the gel point.
The gel stability is decreased with increasing the length of the side alkyl group.
solid, dotted, and dashed lines corresponds to elastic modulus G’, viscous modulus G’’ and viscous viscosity
Ward, M. A.; Georgiou, T. K. Polym. Chem. 2013, 4(6),

12. Does Asymmetry Matter? Gels point decreases when:
The hydrophobic content increases
The triblock copolymers is more symmetric i.e. when the hydrophobic block ratio approaches one.
Ward, M. A.; Georgiou, T. K. J. Polym. Sci., Part A: Polym. Chem. 2013, 51(13), 2850–2859.

13. Summary of Main Results
Aim: Fabrication of thermo-responsive triblock polymers and investigation of how the different characteristics of the polymer affect the thermoresponsive behaviour.
T-response
molecular weight
7000 g mol-1
30-35 wt%
T-response
↑ length  ↓ gel point & stability
T-response
T-response
composition
wt% hydrophobic
architecture
length of hydrophobic side group
Ward, M. A.; Georgiou, T. K. J. Polym. Sci.: Part A: Polym. Chem. 2010, 48,
Ward, M. A.; Georgiou, T. K. Soft Matter 2012, 8,
Ward, M. A.; Georgiou, T. K. Polym. Chem. 2013, 4(6),
Ward, M. A.; Georgiou, T. K. J. Polym. Sci., Part A: Polym. Chem. 2013, 51(13), 2850–2859.

14. Current Investigations
Studying how the PEG side group can affect the thermoresponsive properties. Increase the side group  the gelation point.
Studying how the number of blocks can affect the physical chemical properties and the thermoresponsive properties.
Investigating if these gels can be used in 3-D printing (both pH and temperature can trigger the gel formation)

15. Acknowledgments Thank you
Funding: University of Hull Engineering and Physical Science Research Council (EPSRC) Royal Society (RS) Department of Materials, Imperial College London Students: Mr Mark Ward Miss Anna Constantinou
Thank you