Rod-coil block copolymers have received increasing attention over the past decade due not only to their potential technological applications but also to their unique self-assembly behavior that clearly distinguishes from that of the conventional coil-coil block copolymers. Both experimental and theoretical studies have established that composition of the constituting blocks is also a key parameter governing the microphase-separated morphology of rod-coil block copolymers; consequently, it is of interest to inspect if the self-assembled structure of rod-coil block copolymers can be tuned systematically by blending with a coil homopolymer. This thesis undertakes systematic studies of the phase behavior of lamellae-forming Poly(2,5-di(2’-ethylhexyloxy)-1,4-phenylene vinylene)-b-Poly(methyl methcrylate) (DEH-PPV-b-PMMA) with three types of coil homopolymers, namely, PMMA, poly(ethylene oxide) (PEO) and poly(4-vinylphenol) (PVPh), with PEO and PVPh being able to form dipole-dipole interaction and hydrogen bonding with PMMA blocks in the copolymer, respectively.
The blends of DEH-PPV-b-PMMA with PMMA homopolymers (h-PMMA) were found to undergo macrophase separation over the major composition window irrespective of the molecular weight of h-PMMA. The phase separation led to the formation of a copolymer-rich phase and a homopolymer-rich phase, in which microphase transition yielding a well-ordered lamellar structure and a sponge structure occurred, respectively. The phase behavior of the rod-coil diblock/coil homopolymer blends is hence fundamentally different from that of the conventional blends of coil-coil diblocks with the corresponding homopolymer in the sense that microdomain morphology transformation induced by the uniform solublization of the corresponding homopolymer into the selective microdomain was essentially inaccessible.
For DEH-PPV-b-PMMA/PEO blends, it was found that the favorable interaction introduced was still unable to outweigh the strong rod-rod attraction coupled with the small again of entropy of mixing upon mixing with the rod blocks. As a result, blends still exhibited a macrophase separation, generating a diblock-rich phase and a h-PEO-rich phase. Similar to DEH-PPV-b-PMMA/h-PMMA blends, a microphase separation occurred in the diblock-rich phase, yielding a well-ordered lamellar nanostructure but the persistence length of the lamellar microdomains was smaller than that formed in the corresponding h-PMMA blend.
The transformation of the rod microdomain morphology became accessible by blending with PVPh homopolymer. The DEH-PPV-b-PMMA/PVPh blends as cast from THF were found to display a lamellar morphology irrespective of the blend composition owing to the crystallization of DEH-PPV block during the solvent casting process. When the DEH-PPV crystals in the lamellar microdomains were melted upon heating, the PVPh chains were allowed to mix uniformly with the PMMA blocks to form wet-brush mixture. The large swelling of the junction point separation then destabilized the lamellar microdomains and transformed them to DEH-PPV cylinders when the overall coil volume fraction was sufficiently high (> 0.65). Therefore, a sufficiently large reduction of enthalpy of mixing between the diblock and the homopolymer is an essential condition for achieving the morphological control for rod-coil diblock copolymers via homopolymer blending.

Rod-coil block copolymers have received increasing attention over the past decade due not only to their potential technological applications but also to their unique self-assembly behavior that clearly distinguishes from that of the conventional coil-coil block copolymers. Both experimental and theoretical studies have established that composition of the constituting blocks is also a key parameter governing the microphase-separated morphology of rod-coil block copolymers; consequently, it is of interest to inspect if the self-assembled structure of rod-coil block copolymers can be tuned systematically by blending with a coil homopolymer. This thesis undertakes systematic studies of the phase behavior of lamellae-forming Poly(2,5-di(2’-ethylhexyloxy)-1,4-phenylene vinylene)-b-Poly(methyl methcrylate) (DEH-PPV-b-PMMA) with three types of coil homopolymers, namely, PMMA, poly(ethylene oxide) (PEO) and poly(4-vinylphenol) (PVPh), with PEO and PVPh being able to form dipole-dipole interaction and hydrogen bonding with PMMA blocks in the copolymer, respectively.
The blends of DEH-PPV-b-PMMA with PMMA homopolymers (h-PMMA) were found to undergo macrophase separation over the major composition window irrespective of the molecular weight of h-PMMA. The phase separation led to the formation of a copolymer-rich phase and a homopolymer-rich phase, in which microphase transition yielding a well-ordered lamellar structure and a sponge structure occurred, respectively. The phase behavior of the rod-coil diblock/coil homopolymer blends is hence fundamentally different from that of the conventional blends of coil-coil diblocks with the corresponding homopolymer in the sense that microdomain morphology transformation induced by the uniform solublization of the corresponding homopolymer into the selective microdomain was essentially inaccessible.
For DEH-PPV-b-PMMA/PEO blends, it was found that the favorable interaction introduced was still unable to outweigh the strong rod-rod attraction coupled with the small again of entropy of mixing upon mixing with the rod blocks. As a result, blends still exhibited a macrophase separation, generating a diblock-rich phase and a h-PEO-rich phase. Similar to DEH-PPV-b-PMMA/h-PMMA blends, a microphase separation occurred in the diblock-rich phase, yielding a well-ordered lamellar nanostructure but the persistence length of the lamellar microdomains was smaller than that formed in the corresponding h-PMMA blend.
The transformation of the rod microdomain morphology became accessible by blending with PVPh homopolymer. The DEH-PPV-b-PMMA/PVPh blends as cast from THF were found to display a lamellar morphology irrespective of the blend composition owing to the crystallization of DEH-PPV block during the solvent casting process. When the DEH-PPV crystals in the lamellar microdomains were melted upon heating, the PVPh chains were allowed to mix uniformly with the PMMA blocks to form wet-brush mixture. The large swelling of the junction point separation then destabilized the lamellar microdomains and transformed them to DEH-PPV cylinders when the overall coil volume fraction was sufficiently high (> 0.65). Therefore, a sufficiently large reduction of enthalpy of mixing between the diblock and the homopolymer is an essential condition for achieving the morphological control for rod-coil diblock copolymers via homopolymer blending.

(1) Bates, F. S.; Fredrickson, G. H. Physics Today 1999, 52, 32-38.
(2) Segalman, R. A. Mater. Sci. Eng. R Rep. 2005, 48, 191-226.
(3) Gennes, P. G. d., Scaling concepts in polymer physics Cornell University Press: Ithaca, N.Y., 1979.
(4) Doi, M.; Edwards, S. F., The theory of polymer dynamics. Clarendon Press: Oxford, 1988.
(5) Flory, P. J., Principles of polymer chemistry. Cornell University Press: Ithaca, NY, 1990.
(6) Cheng, J. Y.; Ross, C. A.; Thomas, E. L.; Smith, H. I.; Vancso, G. J. Adv. Mater. 2003, 15, 1599-1602.
(7) Hamley, I. W., Developments in block copolymer science and technology. J. Wiley: Hoboken, NJ, 2004.
(8) Semenov, A. N.; Vasilenko, S. V. Zh. Eksp. Teor. Fiz. 1986, 90, 124-140.
(9) Matsen, M. W.; Barrett, C. J. Chem. Phys. 1998, 109, 4108-4118.
(10) Pryamitsyn, V.; Ganesan, V. J. Chem. Phys. 2004, 120, 5824-5838.
(11) Godfrey, R. A.; Miller, G. W. J. Polym. Sci. Pol. Chem. 1969, 7, 2387-2404.
(12) Billot, J. P.; Douy, A.; Gallot, B. Makromol. Chem. 1977, 178, 1641-1650.
(13) Hu, D. H.; Yu, J.; Wong, K.; Bagchi, B.; Rossky, P. J.; Barbara, P. F. Nature 2000, 405, 1030-1033.
(14) Radzilowski, L. H.; Wu, J. L.; Stupp, S. I. Macromolecules 1993, 26, 879-882.
(15) Radzilowski, L. H.; Stupp, S. I. Macromolecules 1994, 27, 7747-7753.
(16) Radzilowski, L. H.; Carragher, B. O.; Stupp, S. I. Macromolecules 1997, 30, 2110-2119.
(17) Li, W. J.; Wang, H. B.; Yu, L. P.; Morkved, T. L.; Jaeger, H. M. Macromolecules 1999, 32, 3034-3044.
(18) Lee, M.; Cho, B. K.; Zin, W. C. Chem. Rev. 2001, 101, 3869-3892.
(19) Lee, M.; Oh, N. K.; Zin, W. C. Chem. Commun. 1996, 1787-1788.
(20) Lee, M.; Cho, B. K.; Ihn, K. J.; Lee, W. K.; Oh, N. K.; Zin, W. C. J. Am. Chem. Soc. 2001, 123, 4647-4648.
(21) Lee, M.; Oh, N. K. J. Mater. Chem. 1996, 6, 1079-1086.
(22) Lee, M.; Cho, B. K.; Kim, H.; Zin, W. C. Angew. Chem. Int. Ed. 1998, 37, 638-640.
(23) Lee, M.; Cho, B. K.; Kim, H.; Yoon, J. Y.; Zin, W. C. J. Am. Chem. Soc. 1998, 120, 9168-9179.
(24) Chen, J. T.; Thomas, E. L.; Ober, C. K.; Hwang, S. S. Macromolecules 1995, 28,, 1688-1697.
(25) Chen, J. T.; Thomas, E. L.; Ober, C. K.; Mao, G. P. Science 1996, 273, 343-346.
(26) Park, J. W.; Thomas, E. L. Adv. Mater. 2003, 15, 585-588.
(27) Park, J. W.; Thomas, E. L. Macromolecules 2006, 39, 4650-4653.
(28) Ahn, J. H.; Lee, J. S. Macromol. Rapid Commun. 2003, 24, 571-575.
(29) Olsen, B. D.; Segalman, R. A. Macromolecules 2005, 38, 10127-10137.
(30) Olsen, B. D.; Segalman, R. A. Macromolecules 2006, 39, 7078-7083.
(31) Olsen, B. D.; Segalman, R. A. Macromolecules 2007, 40, 6922-6929.
(32) Sary, N.; Rubatat, L.; Brochon, C.; Hadziioannou, G.; Ruokolainen, J.; Mezzenga, R. Macromolecules 2007, 40, 6990-6997.
(33) Vriezema, D. M.; Hoogboom, J.; Velonia, K.; Takazawa, K.; Christianen, P. C. M.; Maan, J. C.; Rowan, A. E.; Nolte, R. J. M. Angew. Chem. Int. Ed. 2003, 42, 772-776.
(34) Checot, F.; Lecommandoux, S.; Gnanou, Y.; Klok, H. A. Angew. Chem. Int. Ed. 2002, 41, 1339-1343.
(35) Checot, F.; Lecommandoux, S.; Klok, H. A.; Gnanou, Y. Eur. Phys. J. E Soft Matter 2003, 10, 25-35.
(36) Checot, F.; Brulet, A.; Oberdisse, J.; Gnanou, Y.; Mondain-Monval, O.; Lecommandoux, S. Langmuir 2005, 21, 4308-4315.
(37) Checot, F.; Rodriguez-Hernandez, J.; Gnanou, Y.; Lecommandoux, S. Biomol. Eng. 2007, 24, 81-85.
(38) Checot, F.; Rodriguez-Hernandez, J.; Gnanou, Y.; Lecommandoux, S. Polym. Adv. Technol. 2006, 17, 782-785.
(39) Babin, J.; Rodriguez-Hernandez, J.; Lecommandoux, S.; Klok, H. A.; Achard, M. F. Faraday Discuss. 2005, 128, 179-192.
(40) Gebhardt, K. E.; Ahn, S.; Venkatachalam, G.; Savin, D. A. Langmuir 2007, 23, 2851-2856.
(41) Rodriguez-Hernandez, J.; Lecommandoux, S. J. Am. Chem. Soc. 2005, 127, 2026-2027.
(42) Tung, Y. C.; Wu, W. C.; Chen, W. C. Macromol. Rapid Commun. 2006, 27, 1838-1844.
(43) Wang, H. B.; Wang, H. H.; Urban, V. S.; Littrell, K. C.; Thiyagarajan, P.; Yu, L. P. J. Am. Chem. Soc. 2000, 122, 6855-6861.
(44) Zhong, X. F.; Francois, B. Synth. Met. 1989, 29, E35-E40.
(45) Francois, B.; Widawski, G.; Rawiso, M.; Cesar, B. Synth. Met. 1995, 69, 463-466.
(46) Zhang, Z. J.; Qiang, L. L.; Liu, B.; Xiao, X. Q.; Wei, W.; Peng, B.; Huang, W. Mater. Lett. 2006, 60, 679-684.
(47) Hashimoto, T.; Tanaka, H.; Hasegawa, H. Macromolecules 1990, 23, 4378-4386.
(48) Tanaka, H.; Hasegawa, H.; Hashimoto, T. Macromolecules 1991, 24, 240-251.
(49) Ji, S. H.; Zin, W. C.; Oh, N. K.; Lee, M. Polymer 1997, 38, 4377-4380.
(50) Tao, Y. F.; Olsen, B. D.; Ganesan, V.; Segalman, R. A. Macromolecules 2007, 40, 3320-3327.
(51) Sary, N.; Mezzenga, R.; Brochon, C.; Hadziioannou, G.; Ruokolainen, J. Macromolecules 2007, 40, 3277-3286.
(52) Gao, L. C.; Yao, J. H.; Shen, Z.; Wu, Y. X.; Chen, X. F.; Fan, X. H.; Zhou, Q. F. Macromolecules 2009, 42, 1047-1050.