Gradient copolymers can exhibit physical properties that are different than their block polymer analogues. Property variations should depend upon differences in the molecular arrangement of individual comonomers in the polymer chain and in the gradient zone of each chain as well as the morphological arrangement of those chains in space. Here we describe experimental approaches based on fast and slow magic-angle spinning (MAS) NMR, which reveal the amount of rigid and soft phases in styrene− butadiene gradient copolymers with component specific resolution. In addition, we introduce a spin-counting strategy that quantitatively and directly determines the amount of the low-T g , or "soft", butadiene component that is incorporated into the rigid domains and also the amount of high-T g , or "hard", styrene component that is incorporated into the mobile domains. In total, the experiments provide bulk rigidity, amount of polybutadiene partitioned in both soft and hard phases and the amount of polystyrene partitioned in each phase. We show that the synthesis conditions can be changed to vary the partitioning of each gradient copolymer component in a systematic way and propose that the interphase between the hard and soft domains is responsible for differential partitioning.
The metal catalyzed ring-opening polymerization of d,l-lactide monomer inside the nanometer-sized channels of MCM-41 and SBA-15 hosts, creating an organic−inorganic hybrid polymeric material, is described. Detailed characterization of the polylactide/mesoporous silica organic−inorganic composite by multiple spectroscopic, microscopy, and calorimetric methods, as well as solvent extraction, reveals that the resulting in situ synthesized composite is unique relative to physical or solution-cast mixtures of polylactide and the mesoporous host. In this contribution, we focus on the incorporation of the stannous octanoate (Sn2+) catalyst inside the mesoporous host channels prior to monomer introduction and subsequent polymerization and specifically target the differentiation of polymerization chemistry that occurs inside the host channels versus less desirable reactions on the exterior surface of the mesoporous host crystallites.
Synthetic modifications to block-copolymer structure-directing agents lead to polymerizable macromers suitable for templating the growth of mesoporous silica particles, which can subsequently react in situ to form extended nanocomposites and nanocomposite networks. Suitably functionalized triblock polymers can preserve the structure-directing capabilities of the triblock polymer for templating ordered mesoporous silica particle growth and also generate a reactive matrix for subsequent polymer network formation via the reactive end groups. The final self-assembled products are polymer nanocomposites or novel crosslinked nanocomposite networks whose organic/inorganic composition ratios can vary systematically. The novel self-assembly route described here should be generally applicable to the synthesis of intimately mixed nanocomposites and nanocomposite networks, starting from a wide variety of block polymeric template/macromer/ordered silica systems.
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