acts to miscibilize the polymer blocks within the particle,
whilst simultaneously producing the fluorinated ‘‘halo’’
around the extremity of the sphere. Enhancement of misci-
bility between poorly compatible polymers is a well-known
phenomenon in blends formed in scCO2.9 We are currently
investigating methods of enforced phase separation (i.e. tem-
perature and solvent annealing) in order to further understand
this phenomenon.
We have demonstrated that macro-RAFT agents in scCO2
exhibit exceptionally good control over heterogeneous disper-
sion polymerisation and that well-defined spherical micro-
particles are formed. Furthermore, the particles exhibit a
‘‘core–shell’’ type structure with a fluorine-rich region on the
periphery of the particle. The challenge now is to further
develop this methodology to a wider range of block copoly-
mers and to target specific materials for practical application.
Notes and references
1 J.-S. Wang and K. Matyjaszewski, J. Am. Chem. Soc., 1995, 117,
5614; M. Kato, M. Kamigaito, M. Sawamoto and T. Higashimura,
Macromolecules, 1995, 28, 1721; J. Chiefari, Y. K. Chong, F. Ercole,
J. Krstina, J. Jeffery, T. P. T. Le, R. T. A. Mayadunne,
G. F. Meijs, C. L. Moad, G. Moad, E. Rizzardo and S. H. Thang,
Macromolecules, 1998, 31, 5559; C. J. Hawker, A. W. Bosman and
E. Harth, Chem. Rev., 2001, 101, 3661.
2 S. Perrier and P. Takolpuckdee, J. Polym. Sci., Part A: Polym.
Chem., 2005, 43, 5347.
3 K. J. Thurecht, A. M. Gregory, W. Wang and S. M. Howdle,
Macromolecules, 2007, 40, 2965.
Fig. 4 TEM-EDX element map and image for polymer particles: (a)
cross-sectional map showing fluoropolymer distribution (fluorine
map) across a section of a particle and the subsequent histogram over
the area within the yellow box; (b) showing elemental distribution
around an intact particle (red—carbon, pink—oxygen, and
green—fluorine). The inset shows an SEM image of a single particle
before and after focussed ion beam slicing to yield B300 nm
cross-sectioned slice. The fluorine-rich halo is present in all images.
4 A. M. Gregory, K. J. Thurecht and S. M. Howdle, Macromolecules,
2008, 41, 1215.
5 Z. Ma and P. Lacroix-Desmazes, J. Polym. Sci., Part A: Polym.
Chem., 2004, 42, 2405; Z. Ma and P. Lacroix-Desmazes, Polymer,
2004, 45, 6789.
concentration at the surface of the particle is clearly higher (up
to three times) compared to the centre of the particle where the
fluorine density becomes much more uniform.
A surface coating of fluorine is quite predictable for this
system, since the PFOMA group acts as a stabiliser and is
CO2-philic. Thus, migration of these chains to the outside of
the particle is expected and the large amount of stabiliser used
in this process ensures good surface coverage of fluorinated
species. But what is surprising from these maps, is the appar-
ent lack of phase separation between the PFOMA and PMMA
within the centre of the particles. We believe that scCO2 acts as
a compatibilizer and that under the conditions of this experi-
ment, the PFOMA and PMMA blocks become miscible. Upon
release of the scCO2 at the completion of the reaction, the two
blocks are kinetically trapped in this state. Thus, the scCO2
6 H. M. Woods, M. M. C. G. Silva, C. Nouvel, K. M. Shakesheff and
S. M. Howdle, J. Mater. Chem., 2004, 14, 1663; H. M. Woods, C.
Nouvel, P. Licence, D. J. Irvine and S. M. Howdle, Macromolecules,
2005, 38, 3271.
7 P. J. Saikia, J. M. Lee, B. H. Lee and S. Choe, J. Polym. Sci., Part
A: Polym. Chem., 2006, 45, 348.
8 T. S. Wilkinson, A. Boonstra, A. Montoya-Goni, S. van Es, M. J.
Monteiro and A. L. German, J. Colloid Interface Sci., 2001, 237, 21;
M. J. Monteiro and J. de Barbeyrac, Macromolecules, 2001, 34,
4416; C. J. Ferguson, R. J. Hughes, D. Nguyen, B. T. T. Pham, R.
G. Gilbert, A. K. Serelis, C. H. Such and B. S. Hawkett,
Macromolecules, 2005, 38, 2191.
9 E. Kung, A. J. Lesser and T. J. McCarthy, Macromolecules, 1998,
31, 4160; K. J. Thurecht, D. J. T. Hill, C. M. L. Preston, L. Rintoul,
J. W. White and A. K. Whittaker, Macromolecules, 2004, 37, 6019.
ꢀc
This journal is The Royal Society of Chemistry 2008
5944 | Chem. Commun., 2008, 5942–5944