老虎机永利

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Professor Tu Yingfeng's group at Soochow University makes new progress in cyclic polymer synthesis and performance research
2019-12-25 Source: Polymer Technology

Compared with linear polymers, cyclic polymers generally have lower viscosity, smaller hydrodynamic volume, higher glass transition temperature, and better stability. Therefore, they are used in the fields of chemistry, materials, biology, etc. Widespread concern. In view of the precise control of controllable polymerization on the structure and the efficient reactivity of click chemistry, combining the two with a ring closure method to synthesize a cyclic polymer is currently the most commonly used preparation method. According to Jacobson-Stockmayer theory, in order to suppress the intermolecular reaction, this method requires intramolecular ring formation in a very dilute solution, so the reaction efficiency is very low. In addition, the separation of residual linear and cyclic polymers is also a great challenge. How to efficiently prepare cyclic polymers is still a major problem.

In response to the above problems, Professor Tu Yingfeng's team used ATRP polymerization at a low monomer conversion rate (<20%) to reduce the disproportionation and coupling termination between free radical end groups, and prepared a high degree of terminal functionalization (~ 100% High-purity cyclic polystyrene was synthesized by linear closure of linear polystyrene after terminal functional group conversion. Under the best synthetic conditions, this method can produce cyclic polystyrene with purity> 99% (detected by SEC). The critical liquid chromatography (Liquid Chromatography at Critical Conditions, LCCC) study of linear polystyrene revealed that the purity of the cyclic polystyrene in this sample was> 98%.

Cyclic polystyrene was purified by tandem LCCC under the critical adsorption conditions of cyclic polystyrene and linear polystyrene, and high-purity (> 99.6%) cyclic polystyrene samples with different molecular weights were prepared. Studies of its glass transition temperature have shown that compared with linear precursors, cyclic polystyrene samples exhibit higher glass transition temperatures and weaker molecular weight dependence, and have similar limits to linear polystyrene Glass transition temperature.

-PS- b -PMPCS)。 On the basis of the above work, recently, a linear rigid-flex block copolymer ( l- PS- b- PMPCS) was prepared by using linear polystyrene as a macromolecular initiator to initiate the polymerization of a crust-type liquid crystal polymer monomer MPCS. After conversion of the terminal groups, the traditional dilute solution ring method was used. It was found that a monocyclic rigid-flex block copolymer ( c -PS- b -PMPCS) was obtained at a reaction concentration of 0.14 g / L, and the yield was 90%. (Figure 1A). When the reaction concentration was increased to 0.28 g / L, the side-cycle yield decreased to 80% due to the intermolecular side reactions.

Figure 1. Traditional dilute solution method (A) and new micellar system ring method (B) to prepare cyclic block copolymers.

-5 mol/L),极大的限制了环状聚合物的量化制备。 In order to avoid intermolecular side reactions, ring closure reactions are usually performed at lower concentrations (< 10 -5 mol / L), which greatly limits the quantitative preparation of cyclic polymers. In 2009, Liu Shiyong's group and Chen Daoyong's group reported a method for ring formation in micellar systems (J. Am. Chem. Soc. 2009, 131, 1628? 1629.), which uses block copolymers from The nature of assembly to form micelles isolates reaction sites between the core and shell of the micelles, thereby limiting intermolecular side reactions. When the free unimer concentration is low, a ring closure reaction can occur. Through the dynamic balance between micelles and single chains, cyclic block copolymers (up to 10 g / L) can be synthesized at higher concentrations.

Using the ring-forming method in this micelle system, Tu Yingfeng's group successfully synthesized a rigid-flex block copolymer c- PS- b- PMPCS (Figure 1B), with a concentration of up to 10 g / L and a yield of up to 92%. After the azide resin treatment removes the linear polymer, a pure cyclic rigid and flexible block copolymer can be obtained. 10 4 g/mol),而由动态激光光散射法测得的环状嵌段共聚物的流体力学半径较线性前体明显变小(图2C,3.6 nm 变为2.7 nm),证明了环状刚柔嵌段共聚物的成功合成。 The corresponding molecular weights of the cyclic and linear block copolymers measured by the static laser light scattering method (SLLS) through the Zimm diagram are the same (Figure 2A & B, ~ 3.9 10 4 g / mol), and measured by the dynamic laser light scattering method The hydrodynamic radius of the cyclic block copolymer is significantly smaller than that of the linear precursor (Figure 2C, 3.6 nm becomes 2.7 nm), which proves the successful synthesis of cyclic rigid and flexible block copolymers.

Figure 2. Zimm plots (A & B) of linear rigid-flexible block copolymers and cyclic rigid-flexible block copolymers, and their hydrodynamic radius distributions in toluene (C).

By changing the ratio of the mixed solvent, the critical micelle concentration of the linear rigid-flex block copolymer in the mixed solvent was measured by SLLS, which is the single-chain concentration in equilibrium with the micelle. Further research has found that both the single-chain concentration and the micelle concentration (ie, the copolymer concentration) have an effect on the loop formation efficiency. g/L附近达到最大,然后随着浓度的继续增大而下降。 Under the condition of constant copolymer concentration, the yield of cyclic rigid and flexible block copolymers first increases with the increase of the single-chain concentration in the selective solvent, reaches a maximum near 10 -2 g / L, and then increases with the concentration. Continue to increase and decrease. This is because too small a single-chain concentration is not conducive to the balance between the micelles and the single-chain, so the loop formation efficiency is low; while when the single-chain concentration is too large, intermolecular side reactions occur and the yield decreases. In addition, the yield of the cyclic block copolymer also decreased slightly with the increase in the concentration of the reaction solution, which was caused by the reaction of some single chains with micelles.

The above results have important guiding significance for the large-scale preparation of cyclic block copolymers.

The combination of dynamic laser light scattering (DLLS) and static laser light scattering was used to study the self-assembly behavior of linear and cyclic rigid-flex block polymers. 及第二维里系数A 2 。 Unlike normal flexible block copolymers, rigid and flexible block copolymers are very stable in selective solvents. The size of the micelles formed does not change with concentration. Therefore, the true molecular weight can be obtained from the Zimm diagram of the micelles. , The mean square turning radius R g and the second virial coefficient A 2 . Analysis of the micelles combined with the results of DLS found that in a selective solvent, the cyclic rigid and flexible block copolymers formed large and loose micelles with a lower molecular weight (ie, fewer aggregates), and their linear precursors The formation of small and compact micelles with higher molecular weights further reveals the effect of changes in topology on the self-assembly behavior of block polymers.

Figure 3. Micelles formed by linear and cyclic rigid and flexible block copolymers: (a) hydrodynamic radius distribution diagram; (b) transmission electron microscope image; (c) micelles formed by linear block copolymer Zimm diagram; (d) Zimm diagram of micelles formed by cyclic block copolymer.

2的值,环状刚柔嵌段共聚物均比线性嵌段共聚物大(尽管在选择性溶剂中是相应胶束的值,为负数)。 In addition, the cyclic rigid and flexible block copolymers are larger than the linear block copolymers in both good and selective solvents (although in selective solvents) The value of the corresponding micelle is negative). The results show that the cyclic topology increases the interaction between the polymer and the solvent and improves its solubility. Therefore, the introduction of a ring topology will help to improve the solubility of difficult-to-dissolve substances and is of great significance for the design of drug molecules.

The above research work on the synthesis, purification and performance of cyclic polystyrene has been helped and guided by Professor Zhang Taizhang of Pohang University of Science and Technology in Korea and Professor Li Yuren of Puyi University in the United States. The results of the collaborative research were published on Polymer (Polymer 2016, 101, 379-387; 2018, 135, 279-284; 2019, 170, 198-203). The results of cyclic rigid-flex block copolymers were published in ACS Macro Letters (ACS Macro Lett. 2019, 8, 1564-1569). The first author of the thesis is Gao Lingfeng , a PhD student in the Department of Materials and Chemistry and Chemical Engineering of Soochow University. The co-first author is Ji Zhichao , a master student in the Department of Materials and Chemistry and Chemical Engineering of Soochow University, and the corresponding author is Professor Tu Yingfeng .

Paper link:

http://pubs.acs.org/doi/10.1021/acsmacrolett.9b00747

http://www.sciencedirect.com/science/article/pii/S0032386119302320

http://www.sciencedirect.com/science/article/pii/S0032386117311758

http://www.sciencedirect.com/science/article/pii/S0032386116307662

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