Morphology and Topology of Interfaces During Coarsening Via Nonconserved Dynamics and Conserved Dynamics

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Gradient copolymers are novel materials that possess a gradual variation in composition along the chain, thereby forming an intermediate structure between random and block copolymers. As such, they are a model system to investigate the effect of molecular structure on fundamental properties of copolymers and may be useful in many technological applications. By combining controlled radical polymerization and semi-batch copolymerization, gradient copolymers have been synthesized with various molecular weights (MWs) and compositions in seven different A-B comonomer pairs.< Using glass transition temperature (Tg) analyses, uniquely broad Tgs of gradient copolymers (up to 100°C continuous Tg breadth (DTg)) relative to block copolymers (two separate Tgs, each DTg ~15°C) or random copolymers (a single Tg, DTg ~ 15°C) were characterized, providing the first experimental support for a key difference in the nanophase-separated composition profiles of block and gradient copolymers. While A-B block copolymers typically have nearly pure A or pure B nanophase domains, nanophase-separated A-B gradient copolymers are predicted to exhibit sinusoidal composition profiles across the domains, never reaching pure A or B. In addition, it was shown that gradient copolymers with identical overall composition but different comonomer sequencing along the chain can yield different DTgs, proving the importance of sequence distribution in tuning the amplitude of the composition profile along the gradient copolymer nanophases. Microphase properties of gradient copolymers in solution were also analyzed and compared with random and block copolymers. The critical aggregation concentration (CAC) values of amphiphilic gradient copolymers in selective solvent have been measured via fluorescence; the CACs of gradient copolymers were less than those of random and exceeded those of block copolymers. The first demonstration of application of gradient copolymers as blend compatibilizers was also achieved. When added to immiscible blends, gradient copolymers preferentially locate at the interface, thereby reducing interfacial tension and providing steric hindrance against dispersed domain coalescence regardless of the presence of thermodynamically favorable interactions. The success of gradient copolymers as novel interfacial additives for immiscible blends has potential for industrial application. In addition, production of compatibilized, nanoscale polymer blends were studied along with the influence of nanoscale dispersion on blend properties.

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  • 08/06/2018
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