Reversible Chain Transfer Catalyzed Polymerization with Alkyl Iodides Generated from Alkyl Bromides by in Situ Halogen Exchange

Reversible chain transfer catalyzed polymerization(RTCP)is a practical and efficient process for the precise synthesis of polymers with special architecture by using simple phenols(2,4,6-trimethylphenol,TMP)or hydrocarbons(xanthene,XT)as efficient organocatalysts.Herein,alkyl iodide(R-1),which was gen erated from in situ bromine-iodine transformation of alkyl bromide(R-Br)with sodium iodide(Nal),was served as initiator to mediate RTCP with TMP or XT.MMA and other functional methacrylates,including GMA,DEAM,DMAEMA and BzMA,were successfully initiated by combining orga no catalysts and azo in itiators to yield polymers with low-polydispersity(M_(w)/M_(n)=1.1-1.5)and ideal mono mer conversions(50%-90%)at moderate temperature.More over,3-armstar polymers were also obtained by this method.The high chain-end fidelity of the obtained poly(methyl methacrylate)with iodine as chain-end group(PMMA-I)was confirmed by chain-extension reaction.The en vironme ntally frie ndly initiators and orga no catalysts exhibit powerful polymerization properties toward RTCP,providing a sign ificant method to synthesize functional polymers.

Polymerization of Butyl Methacrylate Catalyzed by Salicylaldehyde-Imine Zirconium/Al(i-Bu)_3 System

A new kind of zirconium（Zr） complex containing ligand of salicylaldehyde-imine was successfully synthesized with ZrCl_4·2 THF and salicylaldehyde-imine as raw materials. The ligand was characterized by means of ~1HNMR, IR, and GC-MS, and Zr complex was characterized by means of ~1HNMR and IR, respectively. The Zr complex, combined with co-catalyst of Al（i-Bu）_3, was explored to be effective catalytic system for the polymerization of butyl methacrylate（BMA）, to prepare poly-n-butyl methacrylate（PBMA）, which was characterized by IR, ~13C-NMR and GPC. Compared with other double-component（MAO/Cat, AlEt_3/Cat） catalytic systems, catalytic system of Al（i-Bu）_3 and the Zr complex provided the best catalytic activity under the same conditions. The influence of polymerization parameters, such as molar ratio of Al（i-Bu）_3/Cat and BMA/Cat, polymerization temperature and polymerization time, was studied with Zr complex/Al（i-Bu）_3 system. With increasing polymerization time from 4 to 24 hour, the monomer conversion increased from 40.14% to 96.56%. Viscosity-average molecular weight（M_v） of PBMA, detected by the viscosity methodology, increased from 12.67×10~4Da to 44.97×10~4Da and lower molecular weight distribution was obtained. According to these results, the Zr complex contained ligand of salicylaldehyde-imine was a kind of readily, long lifetime and high activity catalyst for BMA polymerization.

Catalytic anode surface enabling in situ polymerization of gel polymer electrolyte for stable Li metal batteries

Employing quasi-solid-state gel polymer electrolyte(GPE)instead of the liquid counterpart has been regarded as a promising strategy for improving the electrochemical performance of Li metal batteries.However,the poor and uneven interfacial contact between Li metal anode and GPE could cause large interfacial resistance and electrochemical Li stripping/plating inhomogeneity,deteriorating the electrochemical performance.Herein,we proposed that the functional component of composite anode could work as the catalyst to promote the in situ polymerization reaction,and we experimentally realized the integration of polymerized-dioxolane electrolyte and Li/Li_(22)Sn_(5)/LiF composite electrode with low interfacial resistance and good stability by in situ catalyzation polymerization.Thus,the reaction kinetics and stability of metallic Li anode were significantly enhanced.As a demonstration,symmetric cell using such a GPE-Li/Li_(22)Sn_(5)/LiF integration achieved stable cycling beyond 250 cycles with small potential hysteresis of 25 mV at 1 mA·cm^(−2)and 1 mAh·cm^(−2),far outperforming the counterpart regular GPE on pure Li.Paired with LiNi0.5Co0.3Mn0.2O2,the full cell with the GPE-Li/Li_(22)Sn_(5)/LiF integration maintained 85.7%of the original capacity after 100 cycles at 0.5 C(1 C=200 mA·g^(−1)).Our research provides a promising strategy for reducing the resistance between GPE and Li metal anode,and realizes Li metal batteries with enhance electrochemical performance.

Highly chemoselective lipase from Candida sp.99-125 catalyzed ring-opening polymerization for direct synthesis of thiol-terminated poly(e-caprolactone)

Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly（e-caprolactone）.Remarkably,high chemoselectivity of lipase from Candida sp.99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved.The tedious protecting/deprotecting steps for thiol and metal residue were avoided.The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 ℃.Number–average molecular weight of resulted polymers ranged from 3000 to4700 Da by changing the feed ratio between monomer and initiator.The structures of obtained thiolterminated poly（e-caprolactone） were demonstrated by combining NMR and SEC analyses.