Studies on Modulating the Phase Behavior of Polymer Blends via Mediated Hydrogen Bonding

• Main Authors: Chen, Shih-Chien, 陳世堅
• Other Authors: Chang, Feng-Chih
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/95261505677950117410

博士 === 國立交通大學 === 應用化學研究所 === 98 === The miscibility and interaction in polymer blends have been a topic and intense interest in polymer science. The miscibility of an immiscible blend was promoted by introducing one component which can form hydrogen bonded with another component. It is the one of the major achievements during last twenty years in polymer blend. This type of interaction has been widely described in terms of Painter & Coleman association model due to exactly prediction in most systems. We have used anionic polymerization to prepare a series of poly[vinyl phenol-b-2-(dimethylamino)ethyl methacrylate] (PVPh-b-PDMAEMA) block copolymers. These block copolymers are miscible, with strong specific interactions occurring between the OH groups of the PVPh segments and the tertiary ammonium groups of the PDMAEMA segments. These PVPh-b-PDMAEMA diblock copolymers exhibit higher glass transition temperatures than do the corresponding PVPh/partially protonated PDMAEMA blends obtained from DMSO solution, which we suspect exist in the form of separate coils. The blocks of the PVPh-b-PDMAEMA diblock copolymers interact strongly, resulting in polymer complex aggregation similar to the behavior of PVPh/partially protonated PDMAEMA blend complexes obtained in methanol. In addition, these PVPh-b-PDMAEMA diblock copolymers exhibit a novel type of pH-sensitivity: at low pH, compact spherical micelles are formed possessing PDMAEMA coronas and PVPh cores; at medium pH, vesicles are observed, consisting of partially protonated hydrophilic PDMAEMA shells and hydrophobic PVPh cores; at high pH, the spherical micelles that formed comprised ionized PVPh coronas and deprotonated hydrated-PDMAEMA cores, i.e., phase inversion of the micelles formed at pH 2. The self-assembly of block copolymers in solution and solid state is attracting intense current attention as a route to nanostructured and hierarchical materials with variety of potential applications. Block copolymers display interesting self-assembly phenomena and allow the creation of hybrid supramolecular material. Furthermore, it is also interesting to control the morphology of microphase separated block copolymers by adding a homopolymer or other block copolymer. In this thesis, we have investigated the phase behavior of poly(4-vinylphenol-b-styrene) (PVPh-b-PS) when respectively blended with poly(4-vinylpyridine) (P4VP), poly(methyl methacrylate) (PMMA), and PVPh homopolymers, of systematically decreased hydrogen-bonding strengths with the PVPh block of the copolymer. The PVPh-b-PS/P4VP blend has a much higher fraction (fH) of hydrogen bonded PVPh blocks for a significantly higher miscibility, compared to the blends with PMMA and PVPh homopolymers. Consequently, the PVPh-b-PS/P4VP blend, behaving as a neat diblock copolymer, exhibited a series of order-order phase transitions from the lamellar, gyroid, hexagonally packed cylinder, to body-centered cubic structures. In contrast, both the PVPh-b-PS/PMMA and PVPh-b-PS/PVPh blends maintained essentially the lamellar structure; the lamellar structure, depending on the hydrogen bonding strength. The ratio of inter-association equilibrium constant (KA) over self-association equilibrium constant (KB), KA/KB, is introduced as a convenient guide in estimating the phase behavior of similar polymer blends, featuring hydrogen bonding interactions between the homopolymer additive and copolymer: with a KA/KB ratio much larger than unity, the blend system tends to behave as a neat copolymer; with a KA/KB ratio significantly smaller than unity, phase separation instead of order-order phase transitions can be expected for the blend above certain volume fraction of homopolymer additive. In addition, we have investigated the complexation-induced phase behavior of the mixtures of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) and octyl gallate (OG) due to hydrogen bonding in different solvents. For PS-b-P4VP/OG mixture in chloroform, the morphological transitions were induced from the unimer configuration to swollen aggregate and complex-micelles by adding OG. Interestingly, the complex-micelles can lead the formation of the honeycomb structure from chloroform solution. The PS-b-P4VP/OG mixture in THF, behaving an amphiphilic diblock copolymer in solution state, exhibited a series of morphological transitions by increasing the OG content. In contrast, the PS-b-P4VP/OG mixture in DMF maintained the unimer configuration upon adding OG. Therefore, the complexation-induced morphology of the mixtures of PS-b-P4VP and OG can be mediated by adopting different common solvents to affect the self-assembly behavior.