Multiblock copolymers of cis-1,4- and trans-1,4-polybutadiene (PBD) have shown exciting and unique elastic properties. But the catalyst that can steadily regulate the content and the distribution of the stereoselective monomers in the PBD copolymer is full of challenge. We reported here a ternary catalyst of Nd(CF3SO3)3·H2O·3TBP/Mg(n-Bu)2/MMAO (TBP: tributyl phosphate; MMAO: modified methylaluminoxane) that can synthesize such copolymer via chain shuttling polymerization in a highly efficient and tunable way. The stereoselectivity of the cis-1,4 and trans-1,4 monomers in the PBD copolymers can be well regulated through the [MMAO]/[Nd] ratio, the [Mg]/[Nd] ratio, and the delayed feeding time of MMAO. The increase of the [MMAO]/[Nd] ratio and the delayed feeding time of MMAO as well as the reduced [Mg]/[Nd] ratio all result in the increase of the trans-1,4 content in the product from 8.4% to 95.3%. The multiblock rather than the diblock structure for the copolymer is validated by NMR, WAXD, and DSC. Finally, the chain shuttling mechanism is confirmed through the self-consistence in the relationship between the composition of the catalyst and the cis-1,4 and trans-1,4 contents in the PBD copolymer.

How polymers with different architectures respond to shear stress is a key issue to develop a fundamental understanding of their dynamical behaviors. We investigate the conformation, orientation, dynamics, and rheology of individual star polymers in a simple shear flow by multiparticle collision dynamics integrated with molecular dynamics simulations. Our studies reveal that star polymers present a linear transformation from tumbling to tank-treading-like motions as the number of arms increases. In the transformation region, the flow-induced deformation, orientation, frequency of motions, and rheological properties show universal scaling relationships against the reduced Weissenberg number, independent of the number and the length of arms. Further, we make a comprehensive comparison on the flow-induced behaviors between linear, ring, and star polymers. The results indicate that distinct from linear polymers, star and ring polymers present weaker deformation, orientation change, and shear thinning, either contributed by a dense center or without ends.

Exploration of the structure of protein complexes, especially the change in conformation and aggregation behavior of proteins upon ligand binding, is crucial to clarify their bioactivities at the molecular level. We applied solution small-angle X-ray scattering (SAXS) to study the complex structure of bovine serum albumin (BSA) and trypsin binding with tea polyphenols, that is, catechin and epigallocatechin gallate (EGCG). We found that tea polyphenols can steadily promote the aggregation of proteins and protein complexes through their bridging effect. The numbers of proteins in the complexes and in the aggregates of complexes are extracted from SAXS intensity profiles, and their dependences as a function of the molar ratio of polyphenol to protein are discussed. EGCG has stronger capability than catechin to promote complex formation and further aggregation, and the aggregates of complexes have a denser core with a relatively smooth surface. The aggregates induced by catechin are loosely packed with a rough surface. BSA shows higher stability than trypsin in the formation of complex with a well-folded conformation. The synergistic unfolding of trypsin results in larger aggregates in the mixtures with more tea polyphenols. The binding affinity and number of tea polyphenols bound to each protein are further determined using fluorescence spectroscopy. The structure of protein complexes explored in this work is referable in the preparation of protein complex-based particles and the understanding of polyphenol-induced formation and further aggregation of protein complexes.Keywords: aggregation; conformation; protein; solution small-angle X-ray scattering; tea polyphenol;

A ring polymer is a classical model to explore the behaviors of biomacromolecules. Compared with its linear counterpart in shear flow, the ring polymer should be more sensitive to excluded volume and hydrodynamic interaction attributed to the absence of chain ends. We carried out multiparticle collision dynamics combined with molecular dynamics simulation to study the effects of excluded volume and hydrodynamic interaction on the behaviors of ring polymers in shear flow. The results show that in the absence of the strong excluded volume interaction, the ring polymer prefers a two-strand linear conformation with high deformation and orientation in the flow-gradient plane, and the tank-treading motion is nearly negligible. Ring polymers without excluded volume show no significant difference from linear polymers in the scaling exponents for the deformation, orientation and tumbling motion. We also observed that the hydrodynamic interaction could efficiently slow down the relaxation of ring polymers while the scaling exponents against the Weissenberg number have rarely been affected.