Poly(N-isopropylacrylamide) (PNIPAM)− tannic acid (TA) microgels were successfully prepared via surfactant-free emulsion polymerization (SFEP) at 70 °C in aqueous solution using N-isopropylacrylamide (NIPAM) as the monomer and a natural polyphenol macromolecule, TA, as the sole cross-linker. The cross-linking network of the PNIPAM−TA microgels was confirmed to contain both physical cross-linking structures formed via hydrogen-bonding interactions between TA and PNIPAM chains and chemical cross-linking structures formed via capturing the radicals of propagating polymer chains by catechol and pyrogallol groups of TA. Furthermore, TA was applied to modify the surface of hydrophobic Fe 3 O 4 nanoparticles, leading to hydrophilic Fe 3 O 4 @TA composite nanoparticles, which were successfully used as the cross-linker to fabricate PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels. The obtained PNIPAM−TA and PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels had a uniform spherical shape with a relatively narrow size distribution and exhibited thermosensitive behavior and pH-tunable degradation. The PNIPAM−TA microgels were stable in the pH range of 1.3−11.1 but underwent complete degradation with pH above 11.4. The PNIPAM−Fe 3 O 4 @TA hybrid microgels were partially degraded at pH values of 1.3 and 2.1, stable in the pH range of 3.1−11.1, and underwent complete degradation at pH above 11.4. The partial degradation of PNIPAM−Fe 3 O 4 @TA organic−inorganic hybrid microgels under strong acidic conditions was attributed to the disintegration of Fe 3 O 4 nanoparticles. The complete degradation of both microgels at pH above 11.4 was attributed to the hydrolysis of ester groups of TA under strong alkali conditions.

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Ethylene–propylene (E/P) copolymerization with a TiCl4/Di/MgCl2–TEA/De (Di, internal donor; De, external donor; TEA, triethylaluminum)-type Ziegler–Natta catalyst was conducted at various comonomer feed ratios (E/P ratios). Distribution of active centers among three copolymer fractions (fractions soluble in room-temperature n-octane (C8-sol) and boiling n-heptane (C7-sol) and fraction insoluble in boiling n-heptane (C7-insol)) and their change with the E/P ratio were studied by quench-labeling the copolymerization, fractionating the copolymer, and measuring the labeled group in each fraction. By comparing with the active-center distribution of propylene homopolymerization, active centers in copolymerization were differentiated into three categories having low, medium, and high stereoselectivities. At E/P ≥ 40/60, the category of isospecific active centers produced the majority of the C8-sol fraction composed of the random copolymer (rEP). The majority of the active centers with medium isoselectivity also produced rEP, while a small fraction produced segmented copolymers (sEP) containing crystalline polyethylene (PE) segments. The active-center category of low stereoselectivity produced copolymers with very long PE segments in C7-insol. There is evidence that a small proportion of high isospecific centers produced sEP chains containing long crystallizable polypropylene (PP) segments, which can work as compatibilizers in high-impact polypropylene (PP/EP reactor alloy). Using a De type enabling production of PP with higher isotacticity in homopolymerization, more sEP chains having longer crystallizable PP segments were formed in copolymerization.