Research On Functionalization Of Polymers Via NHPI-catalyzed C(sp~3)-H Bonds Reaction

The functionalization of polymers has always been one of the most important topics in the field of polymers research,and it plays an important role to broaden the scope of polymer applications.There are many methods have been used to functionalize polymers,such as free radical grafting polymerization,and copolymerization of polymers with functional monomers.However,there are some intrinsic problems in these technologies,for examples,uncontrollable structures of the products,the accompanied side reaction of chain transfer and difficulty in removing catalyst from the system,limiting the application range of polymers in a certain extent.Recently,a method based on N-hydroxyphthalimide(NHPI)catalyzed C(sp³)-H bonds reaction is proposed,and this mild and efficient way has been applied to the functionalization of varied alkane,ethers,and alcohols.In this paper,NHPI catalysis was applied to functionalize polyethylene glycol(PEG)and polypropylene(PP)separator in the presence of azodicarboxylate,thus the conversion of C(sp³)-H to C(sp³)-N bonds was achieved.Then activators regenerated by electron transfer atom transfer radical polymerization(ARGET-ATRP)could be used to conduct grafting modification,the main contents as follows:1.Under the catalysis of NHPI,di-tert-butyl azodicarboxylate(DBAD)was introduced into the PEG chain to generate PEG-g-DBAD.Subsequently,the tert-butoxycarbonyl(-Boc)groups of PEG-g-DBAD were removed by treating with trifluoroacetic acid(TFA)to obtain hydrazino functionalized PEG(PEG-g-NHNH₂).The structure of functionalized PEG was confirmed by Fourier transform infrared spectroscopy(FTIR),¹H nuclear magnetic resonance spectroscopy(¹H NMR)and the PEG was hydrazide successfully.PEG-g-NHNH₂was used to toughen epoxy resin(EP).The results of impact strength testing and SEM images showed that the compatibility of modified PEG and EP has been improved due to the presence of hydrazide groups.In addition,PEG-g-NHNH₂reacted with 2-bromoisobutyryl bromide(BIBB)to get PEG-g-BIBB which initiated the polymerization of methyl methacrylate(MMA)by ARGET-ATRP,and PMMA grafting modified PEG was obtained.2.Bis(2,2,2-trichloroethyl)azodicarboxylate(BTCEAD)was anchored on the surface of PP separators in the presence of NHPI to get PP(s)-g-BTCEAD.Then BTCEAD functionalized PP separator initiated the polymerization of Poly(ethylene glycol)methacrylate(PEGMA)by ARGET-ATRP.Thus,PPEGMA modified separators(PP(s)-g-PPEGMA)were obtained.The results of contact angle and electrolyte uptake showed that the electrolyte wettability of PPEGMA functionalized PP separator has been improved significantly.Electrochemical measurements indicated that discharge capacity retentions of Li||Li Fe PO₄cells assembled with PPEGMA functionalized PP separators were distinctly higher than that of cells with pristine PP separator.3.Under the catalysis of NHPI,BTCEAD was fixed on the surface of PP separator to obtain PP(s)-g-BTCEAD,and then 3-(triethoxysilyl)propyl methacrylate(TEPM)was grafted onto PP separator(PP(s)-g-PTEPM)via ARGET-ATRP.The Si-O-Si cross-linked network with good heat resistance was formed on the surface of PP separator after the PTEPM grafted on the separator was hydrolyzed.And the organic/inorganic modified PP separator(PP(s)-g-Si O₂)was prepared successfully.The thermal shrinkage results showed that the thermal shrinkage ratios of PP(s)-g-Si O₂were lower than that of pristine PP separator.The contact angle and electrolyte uptake tests showed that the electrolyte wettability of the corresponding PP(s)-g-Si O₂separator would enhance with increasing of grafting degree of PTEPM.The results of long cycle performance showed that the discharge capacity retentions of Li||Li Fe PO₄cells with organic/inorganic modified separators were higher than that of cell with pristine PP separator.