1234 Macromolecules, Vol. 43, No. 3, 2010
Nese et al.
the 10-arm 10B115-M51 is much higher than that of the
linear and the 3-arm copolymer. As discussed by Shim and
Kennedy,34 this behavior could originate in several effects.
First, in addition to the PMMA glassy domains that act as
physical cross-linkers for the softer PBA matrix in the case of
star copolymers, small permanent cross-linking sites, i.e., the
cores of star blocks, are also dispersed in the rubbery matrix,
helping to distribute the applied stress more evenly to the
hard PMMA domains. Second, the multiarm stars exhibit
higher degree of hard-domain interconnectivity between the
copolymer molecules. The improvement of tensile strength is
less significant when comparing the 10-arm vs the 20-arm
samples, which suggests again a plateau or saturation
point in the enhancement of the tensile properties with respect
to number of arms. This is consistent with earlier studies of
polystyrene-b-polyisobutylene35 and polystyrene-b-polydiene56
starlike copolymers and is related to the fact that the contribu-
tion of the above-described effects saturates with increasing the
number of arms. Furthermore, increasing the number of arms
affects the chain conformation and decreases their mobility
which may influence the phase separation.
(4) Hadjichristidis, N.; Iatrou, H.; Pitsikalis, M.; Mays, J. Prog.
Polym. Sci. 2006, 31, 1068–1132.
(5) Gao, C.; Yan, D. Prog. Polym. Sci. 2004, 29, 183–275.
(6) Gaynor, S. G.; Matyjaszewski, K. Macromolecules 1997, 30, 4241–
4243.
(7) Szwarc, M. Science 1970, 170, 23–31.
(8) Bielawski, C. W.; Grubbs, R. H. Prog. Polym. Sci. 2007, 32, 1–29.
(9) Braunecker, W. A.; Matyjaszewski, K. Prog. Polym. Sci. 2007, 32,
93–146.
(10) Debuigne, A.; Poli, R.; Jerome, C.; Jerome, R.; Detrembleur, C.
Prog. Polym. Sci. 2009, 34, 211–239.
(11) Hawker, C. J.; Bosman, A. W.; Harth, E. Chem. Rev. 2001, 101,
3661.
(12) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2005, 58, 379–
410.
(13) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le,
T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad,
G.; Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559–
5562.
(14) Wang, J. S.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614–
5615.
(15) Tsarevsky, N. V.; Matyjaszewski, K. Chem. Rev. 2007, 107, 2270–
2299.
(16) Matyjaszewski, K.; Xia, J. H. Chem. Rev. 2001, 101, 2921–2990.
(17) Matyjaszewski, K.; Tsarevsky, N. V. Nat. Chem. 2009, 1, 276–288.
(18) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001, 101,
3689–3746.
Conclusions
(19) Gao, H.; Matyjaszewski, K. Macromolecules 2006, 39, 4960–4965.
(20) Matyjaszewski, K. Polym. Int. 2003, 52, 1559–1565.
(21) Zhang, X.; Xia, J.; Matyjaszewski, K. Macromolecules 2000, 33,
2340–2345.
(22) Xia, J.; Zhang, X.; Matyjaszewski, K. Macromolecules 1999, 32,
4482–4484.
(23) Radke, W.; Gerber, J.; Wittmann, G. Polymer 2002, 44, 519–525.
(24) Matyjaszewski, K.; Miller, P. J.; Pyun, J.; Kickelbick, G.; Diamanti,
S. Macromolecules 1999, 32, 6526–6535.
(25) Ueda, J.; Matsuyama, M.; Kamigaito, M.; Sawamoto, M. Macro-
molecules 1998, 31, 557–562.
(26) Angot, S.; Murthy, K. S.; Taton, D.; Gnanou, Y. Macromolecules
1998, 31, 7218–7225.
(27) Hawker, C. J. Angew. Chem., Int. Ed. 1995, 34, 1456–1459.
(28) Danko, M.; Libiszowski, J.; Wolszczak, M.; Racko, D.; Duda, A.
Polymer 2009, 50, 2209–2219.
(29) Hans, M.; Mourran, A.; Henke, A.; Keul, H.; Moeller, M. Macro-
molecules 2009, 42, 1031–1036.
(30) Wang, J.-S.; Greszta, D.; Matyjaszewski, K. Polym. Mater. Sci.
Eng. 1995, 73, 416–417.
In summary, PBiBEA macroinitiators for starlike copolymers
with degrees of polymerizations 10 and 20 were prepared by
ATRP of HEATMS and the subsequent esterification. These
macroinitiators were used for preparation of series of 10- and 20-
arm starlike PBA which were extended with outer hard PMMA
block using ATRP. Halogen exchange strategy was applied
during the ATRP of PMMA to provide at least equal rate of
cross-propagation compared to rate of propagation.52 Partial
star coupling during PBA arms extension with PMMA blocks
was observed, and the coupling increased with number of arms
and arm length. The morphology of solution-cast films of the star
PBA-PMMA block copolymers was studied by AFM and
SAXS. Both techniques revealed a phase-separated morphology
of cylindrical PMMA domains hexagonally arranged in the PBA
matrix. The mechanical and thermal properties of the star block
copolymers have been thoroughly characterized. These materials
possess typical elastomeric behavior in a broad range of service
temperatures up to at least 250 °C. The ultimate tensile strength
and the elastic modulus of the 10- and 20-arm star PBA-PMMA
copolymers are significantly higher than those of their 3-arm
or linear ABA type counterparts with similar composition,
indicating a strong effect of the number of arms on the tensile
properties. This new synthetic approach can be used for the
preparation of star polymers from other acrylates, methacrylates,
and styrene.
(31) Gao, H.; Matyjaszewski, K. Macromolecules 2008, 41, 1118–1125.
(32) Lapienis, G. Prog. Polym. Sci. 2009, 34, 852–892.
(33) Dufour, B.; Koynov, K.; Pakula, T.; Matyjaszewski, K. Macromol.
Chem. Phys. 2008, 209, 1686–1693.
(34) Dufour, B.; Tang, C. B.; Koynov, K.; Zhang, Y.; Pakula, T.;
Matyjaszewski, K. Macromolecules 2008, 41, 2451–2458.
(35) Shim, J. S.; Kennedy, J. P. J. Polym. Sci., Part A: Polym. Chem.
1999, 37, 815–824.
(36) Shim, J. S.; Kennedy, J. P. J. Polym. Sci., Part A: Polym. Chem.
2000, 38, 279–290.
(37) Shim, J. S.; Asthana, S.; Omura, N.; Kennedy, J. P. J. Polym. Sci.,
Part A: Polym. Chem. 1998, 36, 2997–3012.
(38) Storey, R. F.; Chrisholm, B. J.; Choate, K. R. J. Polym. Sci., Part
A: Polym. Chem. 1994, 34, 2003–2017.
(39) Storey, R. F.; Shoemake, K. A. J. Polym. Sci., Part A: Polym.
Chem. 1998, 36, 471–483.
Acknowledgment. The authors thank Andreas Hanewald for
the technical assistance. The financial support from National
Science Foundation (DMR 05-49353 and CBET 06-09087) is
greatly appreciated.
(40) Beers, K. L.; Gaynor, S. G.; Matyjaszewski, K.; Sheiko, S. S.;
Moeller, M. Macromolecules 1998, 31, 9413–9415.
(41) Neugebauer, D.; Zhang, Y.; Pakula, T.; Sheiko, S. S.; Matyjaszewski,
K. Macromolecules 2003, 36, 6746–6755.
(42) Sheiko, S. S.; Prokhorova, S. A.; Beers, K. L.; Matyjaszewski, K.;
Potemkin, I. I.; Khokhlov, A. R.; Moller, M. Macromolecules 2001,
34, 8354–8360.
(43) Sheiko, S. S.; Sun, F. C.; Randall, A.; Shirvanyants, D.; Rubinstein,
M.; Lee, H.; Matyjaszewski, K. Nature 2006, 440, 191–194.
(44) Qin, S.; Matyjaszewski, K.; Xu, H.; Sheiko, S. S. Macromolecules
2003, 36, 605–612.
Supporting Information Available: Dependence of ultimate
tensile strength on PMMA content and NMR and SAXS traces.
This material is available free of charge via the Internet at http://
pubs.acs.org.
References and Notes
(1) Zhang, M.; Mueller, A. H. E. J. Polym. Sci., Part A: Polym. Chem.
2005, 43, 3461–3481.
(2) Sheiko, S. S.; Sumerlin, B. S.; Matyjaszewski, K. Prog. Polym. Sci.
2008, 33, 759–785.
(45) Keller, R. N.; Wycoff, H. D. Inorg. Synth. 1946, 2, 1–4.
(46) Xia, J. H.; Matyjaszewski, K. Macromolecules 1997, 30, 7692–7696.
(47) Pintauer, T.; Matyjaszewski, K. Coord. Chem. Rev. 2005, 249,
1155–1184.
(3) Gao, H.; Matyjaszewski, K. Prog. Polym. Sci. 2009, 34, 317–350;
Oh, J. K.; Drumright, R.; Siegwart, D. J.; Matyjaszewski, K. Prog.
Polym. Sci. 2008, 33, 448–477.