«RATIONAL DESIGN AND SYNTHESIS OF FUNCTIONAL POLYMERS WITH COMPLEX ARCHITECTURES BY LIVING/CONTROLLED POLYMERIZATION A Dissertation Presented to The ...»
RATIONAL DESIGN AND SYNTHESIS OF FUNCTIONAL
POLYMERS WITH COMPLEX ARCHITECTURES BY
The Academic Faculty
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in the
School of Materials Science and Engineering
Georgia Institute of Technology
COPYRIGHT© 2015 BY CHAOWEI FENG
RATIONAL DESIGN AND SYNTHESIS OF FUNCTIONAL
POLYMERS WITH COMPLEX ARCHITECTURES BY
Dr. Zhiqun Lin, Advisor Dr. John Reynolds School of Materials Science and School of Materials Science and Engineering Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Anselm C. Griffin Dr. Vladimir V Tsukruk School of Materials Science and Materials Science and Engineering Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Seth Marder School of Chemistry and Biochemistry Georgia Institute of Technology Date Approved: April 02, 2015 Dedicated to my loving family
My PhD tenure has been a memorable one, only because of the congenial and supportive culture of the NanoFM research group. Particularly, I would like to thank Prof. Xinchang Pang and Dr. Lei Zhao for providing me with tremendous support and guidance on my research in the junior years. I would specially like to thank Yanjie He and Yijie Tao for being kind and supportive companions. I would also like to thank current and former NanoFM lab members, Prof. S. Li, Prof. Y. Yang, Prof. Y. Ren, Prof. H. Ma, Prof. R.
Wu, Prof. D. Yang, Prof. S. Wu, Dr. M. He, Dr. X. Xin, Dr. W. Han, Dr. M. Ye, Dr. Y.
Xu, Dr. S. Wannapop, C. Zhang, C. Wan, B. Li, J. Jung, C. Han, Y. Chen, X. Liu, B.
Jiang, J. Iocozzia, Young J.Yoon, A. Song, Z. Wang, J. Findley, D. Gottschalk, M.
Wang, H. Tang, H. Xu, D. Zheng, W. Liao, and N. Tipcompor for their constant help and support.
constant support, without whom I would not be here. Sincere gratitude goes to all my friends, Rui Ding, Liyi Li, Zhuo Li, Hongzhi Wang, Siyuan Zhang, Zhishuai Geng, Xin Dong, and Pan Zhang for their mental support over the years.
4 DESIGN AND SYNTHESIS OF SPHERICAL STAR BLOCK COPOLYMER
AS TEMPLATE TO DEVELOP UNIMOLECULAR CORE-SHELL AND
HOLLOW POLYMER NANOPARTICLES 55
5 ORGANO-SILICA HYBRID NANOPARTICLES AND NANOCAPSULES
FROM STAR POLYMERS WITH DIFFERENT ARCHITECTURES AS
UNIMOLECULAR NANOREACTORS 87
6.3.1. Synthesis of Cyclic Backbone Bearing Azide Functionalities 117 6.3.2. Synthesis of Conjugated Side Chains Capped with Ethynyl Group
Table 4.2: Structural parameters of polymer precursors and the prepared nanoparticles.
68 Table 5.1: Structural parameters of star-like PTMSPMA homopolymer and the corresponding organo-silica hybrid nanoparticles (NPs). 94
Table 5.3: Structural parameters of star-like PS-b-PTMSPMA diblock copolymers and the corresponding organo-silica hybrid nanocapsules (NCs).
Figure 1.2: Proposed mechanism for a photoredox-mediated ATRP proceeding through an oxidative quenching pathway with alkyl halides (top) and the use of perylene as an organic photocatalyst for the polymerization of methyl methacrylate with alkyl bromide initiators (bottom) and a photograph of this polymerization being mediated by natural sunlight (bottom right).
Figure 1.8: Schematic representation of the basic approach for the formation of SCK’s.
Micellization of amphiphilic 2 is followed by crosslinking through the styrenyl side chains located in the peripheral aqueous layer to yield 1. 16 Figure 1.9: Temperature-responsive micellization of block copolymers comprised of DMA, AAL, and NIPAM and the reversible IPEC micelle formation. 16 Figure 1.10: Schematic illustration of the environment-sensitive stabilization of the PIC micelle through the formation of a disulfide bond in the core. 17
Figure 1.12: Unstained TEM images of calcium phosphate mineralized polymer nanostructures: (a) shell cross-linked PAA-b-PI micelles; (b) cross-linked PAA nanocages.
In both cases, the inorganic shell is ca. 10 nm thick. 20
Figure 1.15: Schematic of the preparation of hybrid nanospheres by the self-assembly of reactive diblock copolymers.
The light gray corona represents the PEO, the dark gray core is the PTMSPMA, and the black core is the hybrid sphere for the polyorganosiloxane from the gelation process. 24
Figure 1.17: Strategy for the synthesis of an organic/inorganic hybrid nanocapsule.
26 Figure 3.1: Guidelines for selection of appropriate RAFT agent for various monomers.48 Figure 4.1: 1H-NMR spectra of star-like homopolymer. (a) star-like PCL, (b) polymeric RAFT agent star-like trithiocarbonate-end-functionalized PCL (i.e., PCL-TC).
Figure 4.2: GPC traces of (a) star-like PCL with different molecular weights as summarized in Table S1, (b) star-like PCL-b-P(S-Cl) with different molecular weights as summarized in Table 1, (c) star-like PCL-b-P(S-Cl) before and after purification (i.
e., sample-c as an example). 66 Figure 4.3: UV-vis spectra for star-like PCL (black curve) and trithiocarbonate-endfunctionalized star-like PCL (i.e., PCL-TC; red curve). 69
Figure 4.6: AFM height image of partially crosslinked core-shell nanoparticles after exposing to UV irradiation for 20 min.
The close-up is shown as an inset. 72 Figure 4.7: FTIR spectra of star-like diblock copolymer template and polymer nanoparticles. (a) star-like PCL-b-P(S-N3) template, (b) core-shell nanoparticles, and (c) hollow nanoparticles. 72
Figure 4.9: AFM height images of star-like PCL-b-P(S-N3) diblock copolymer template.
(a) Top view, and (b) the corresponding 3D profile. 75
Figure 4.11: (a) TEM image of intermediately stained core-shell nanoparticles, and (b) the core and overall size distributions of nanoparticles for TEM image in (a).
(c) TEM image of heavily stained core-shell nanoparticles, and (d) size distribution of nanoparticles for TEM image in (c). 77
Figure 4.13: TEM image of nanocapsules after a long-term storage (heavily stained sample), showing aggregations of nanocapsules.
79 Figure 4.14: Morphologies of hollow polymer nanoparticles. (a) and (c) AFM height images of hollow nanoparticles and core-shell nanoparticles (i.e., prior to degradation of PCL core; fully crosslinked), respectively. (b) Cross-sectional profiles of hollow and core-shell nanoparticles obtained from the corresponding AFM height images in (a) and (c), respectively (i.e., straight lines across nanoparticles in (a) and (c)). (d) TEM image of hollow nanoparticles after staining. (e) Schematic illustration of the transition from core-shell nanocapsule (left) to collapsed hollow nanoparticles (right) on substrate after degradation of PCL blocks. 81
Figure 4.15: Structure of Os-atom containing dye: osmapentalyne. 82
xii Figure 4.16: Encapsulation and release of dyes. (a) UV-Vis spectra of core-shell nanoparticles loaded with two different dyes (i.e., RhB with an absorption maximum of 559 nm (red dash curve) and osmapentalyne with an absorption maximum of 424 nm (black curve)). (b) TEM image of nanoparticles loaded with osmapentalyne. (c) Fluorescence spectra of partially crosslinked nanoparticles loaded with RhB in chloroform, and (d) florescence intensity at the emission of 572 nm as a function of time, showing different release rates of RhB from nanoparticles of different crosslinking density in THF and CHCl3 (i.e., partially crosslinked nanoparticles in CHCl3 (black squares), fully crosslinked nanoparticles in CHCl3 (red circles), and partially crosslinked nanoparticles in THF (blue triangles)). The curves are used for guidance. 84
Figure 5.4: TEM characterizations of organo-silica hybrid nanoparticles and nanocapsules.
(a) Hybrid nanoparticles crafted from sample-1 (i.e., star-like PTMSPMA) with smaller molecular weight; the average diameter of nanoparticle, Dave = 13 ± 2 nm. (b) Hybrid nanoparticles created from sample-2 (i.e., star-like PTMSPMA) with larger molecular weight; the average diameter of nanoparticle, Dave = 38 ± 4 nm. (c) Hybrid nanocapsules produced from sample-a (i.e. star-like PS-b-PTMSPMA) with larger molecular weight of the outer PTMSPMA block; the average diameter of nanocapsule, Dave = 71 ± 5 nm. (d) Hybrid nanocapsules yielded from sample-d, with smaller molecular weight of the outer PTMSPMA block; the average diameter of nanocapsule, Dave = 28 ± 5 nm. 99 Figure 5.5: Size distributions of hybrid nanoparticles and nanocapsules obtained from the TEM image analysis. The average diameters of nanoparticles or nanocapsules are summarized in Table 5.1 and Table 5.3, respectively. (a) Organo-silica hybrid nanoparticles crafted from sample-1 (i.e. star-like PTMSPMA with smaller molecular weight). (b) Organo-silica hybrid nanoparticles crafted from sample-2 (i.e. star-like PTMSPMA with larger molecular weight). (c) Organosilica hybrid nanocapsules created from sample-a (i.e. star-like PS-bPTMSPMA with larger molecular weight of outer PTMSPMA block). (d) Organo-silica hybrid nanocapsules created from sample-d (i.e. star-like PS-bPTMSPMA with smaller molecular weight of outer PTMSPMA block). 100
Significant progress has been made in the field of living/controlled polymerizations over the past decades. The advance in living/controlled polymerizations has enabled the design and tailoring of structurally well-defined macromolecules with complex architectures. Polymers with complex molecular architectures often exhibit properties that are distinct from their linear counterparts. This dissertation aims to exploit the unique properties of rationally designed complex polymer structures to address the challenges related to the preparation of polymeric and hybrid nanostructures, as well as to explore and fundamentally understand the morphology or properties of new macromolecular architecture.
The studies presented in this dissertation addressed the challenges (e.g., poor size uniformity, limited accessible compositions) in the formation of polymeric or hybrid nanostructured materials based on the self-assembled polymer micelle approach via rational design of complex spherical star polymer architectures with tailor-made compositions and functionalities through living/controlled polymerizations, as well as investigated the morphology and self-assembly behavior of a newly designed cyclic brush copolymer grafted with P3HT as the side chains. Specifically, the uniqueness of
this study can be summarized through the following novel and critical findings:
1. Uniform core-shell polymer nanoparticles can be formed by photo-crosslinking the shell layer of a monodisperse core-shell star block copolymer with azide moieties attached in the shell block. The dimensions of nanoparticles including the core size and the overall diameter are governed by the molecular weights of constituent blocks (i.e.
inner and shell block) in the core-shell star diblock copolymer template.
produced by etching the degradable inner core of the unimolecular shell-crosslinked nanoparticles.
3. Organo-silica hybrid nanostructures can be crafted if the sol-gel chemistry of trimethylsilyl groups attached to the star polymer templates is employed as the crosslinking mechanism. Nanoparticles were yielded when the trimethylsilyl groups were incorporated in the inner block of star polymers, while nanocapsules with an interior cavity were produced when trimethylsilyl moieties were integrated in the shell block.
4. The novel cyclic brush copolymer composed of PEG as the backbone and P3HT as the side chains self-assembled into an interesting and unique macro-ring morphology in selective solvent.
The novel and robust star macromolecular templating strategy developed in this study will open the access to a wide range of structurally and functionally well-defined polymeric and hybrid nanostructured materials with tailor-made compositions and shapes. The findings presented in the work will provide fundamental insights or practical strategies for rational design of polymers with complex macromolecular architectures via living/controlled polymerizations.