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    Home > JACS of Xiayan research group, Stanford University: enol ether romp -- the way of "salvation" of degradable polymer

    JACS of Xiayan research group, Stanford University: enol ether romp -- the way of "salvation" of degradable polymer

    • Last Update: 2020-01-08
    • Source: Internet
    • Author: User
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    1、 Background ring opening metathesis polymerization (ROMP) is a ring opening polymerization of ring like olefins, which is a kind of characteristic polymerization method in the preparation of polymer materials Different from free radical polymerization, ion polymerization and Ziegler Natta coordination polymerization, the double bond in the monomer still remains in the polymer obtained by ring opening metathesis polymerization The catalyst (initiator) used in romp is carbene complex of transition metal elements (such as W, Ta, Ru, Ti, Mo, etc.) In the common romp process, excessive vinyl ethers are usually used to achieve chain termination reactions to obtain electron rich Ru carbene complexes This carbene complex usually has higher thermal stability than Grubbs alkylene carbene complex, which can greatly reduce the catalytic activity of the central metal In view of the strong role of vinyl ether in the termination of romp chain, it seems impossible to realize the romp reaction of cyclic enol ether on the surface, but the result is not 2、 Recently, Xiayan research group of Stanford University successfully realized the romp reaction of cyclic enol ether, and prepared a new kind of polymer with heteroatom on the main chain, and found that this kind of polymer has very good degradability Relevant research work was published in J am Chem SOC (DOI: 10.1021 / JACS 9b11834) (photo source: J am Chem SOC.) 3 The author first selected cheap 2,3-dihydrofuran (DHF) as the monomer for romp reaction, and used the first and second generation Grubbs catalysts (G1 and G2) for research It was found that both G1 and G2 could realize the romp reaction of DHF, and the rubber polymer with TG = - 50.5 ℃ was prepared Especially when G2 catalyst is used, the reaction can even be carried out in the air, and the monomer does not need to be purified The conversion rate can reach 15% in 15 minutes The molecular weight of the polymer is Mn = 309 kDa, and the molecular weight distribution is Ð = 1.4 (photo source: J am Chem SOC.) characterized the polymer pdhf by 1H NMR The results show that the polymer has a perfect head tail connection structure, and the E: Z ratio of the double bond on the main chain of the polymer is between 4:6 and 1:1 The molecular weight of the prepared polymer can be well adjusted by changing the ratio of reactants (photo source: J am Chem SOC.) in particular, the author found that the prepared polymer pdhe has the ability of degradation When pdhe was blended with 0.01% equivalent catalyst at room temperature for 3 h, and then the temperature was raised to 60 ℃ for only 2.5 h, more than 90% pure substrate could be distilled In order to further explore the degradability of pdhe, the author conducted in-depth study Pdhf was treated with H 2O 2 and dissolved in THF solution Then 135 mm of water and 25 mm of different acids were added It is found that the strength of acid has a great influence on the degradation rate of pdhf When HCl was added, the polymer could be reduced to monomer completely in only 10 minutes; when trifluoroacetic acid was added, the degradation time was up to several hours However, for solid polymers, the degradation rate is relatively slow The polymer pdhf with molecular weight of 54 kDa was added into 0.1M HCl aqueous solution After 24 hours, the molecular weight of the polymer decreased to 12 kDa This is because the polymer pdhf has certain hydrophobicity, because the rate of HCl water solution penetrating into the polymer is slow, so its degradation rate is relatively slow (photo source: J am Chem SOC.) 4 Research conclusion Xiayan research group has successfully realized the romp reaction of cyclic enol ether, and prepared a new kind of polymer with heteroatom on the main chain At the same time, it is found that this kind of polymer has good degradability, which provides theoretical basis for future application.
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