Zhi Ma

A new chromium-based catalyst coated with paraffin for ethylene oligomerization and the effect of chromium state on oligomerization selectivity

Abstract A new method is proposed in which a chromium-based catalyst system containing chromium(III) tris (2-ethylhexanoate) (Cr(EH)3), 2,5-dimethylpyrrole (2,5-DMP), GeCl4 and triethylaluminum (TEA) coated with solid paraffin is used for oligomerization of ethylene. GC-MS and 1 H -NMR analyses show that the coated catalyst system prepared via this approach is air-insensitive so it can be stored under ambient conditions. The selectivity for 1-hexene is up to 97.91xa0wt.%, and only slightly decreases when the catalyst system is exposed in air for 24xa0h; in contrast, the selectivity is only 35.6% for its non-coated counterpart. XPS reveals that an attachment of atmospheric oxygen to catalyst makes the chemical state of chromium change from Cr3+ to Cr6+. Such a change, in turn, reduces remarkably its selectivity for 1-hexene.

New polymethylene-based AB2 star copolymers synthesized via a combination of polyhomologation of ylides and atom transfer radical polymerization

New polymethylene-based AB2 star polymers with well-defined architecture and various components were synthesized using a combination of polyhomologation of ylides and atomic transfer radical polymerization (ATRP). The chain structures of polymethylene-b-(polystyrene)2 (PM-b-(PS)2) and polymethylene-b-(poly(methyl methacrylate))2 (PM-b-(PMMA)2) were characterized through 1H NMR, GPC and FT-IR. The porous films of such star copolymers were fabricated via a static breath-figure (BF) process. The influence of polymer molecular weight, solution concentration and environmental temperature on the morphology of such block copolymer films was investigated. The porous surface of such a film presents hydrophobic behaviour with a static water-droplet contact angle of ca. 108°. The electrospinning of PM-b-(PS)2 was performed using CHCl3 as a solvent and the wrinkle-like polymer particles with nanopores on their surface were obtained.

Synthesis of diverse α,ω-telechelic polystyrenes with di- and tri-functionality via tandem or one-pot strategies combining aminolysis of RAFT-polystyrene and a thiol–ene “click” reaction

A thiol–ene “click” reaction proceeds with facile reaction conditions for complete conversion, and displays a higher tolerance to various backbones and functional groups compared with traditional coupling and functionalization strategies. Herein, well-defined α,ω-telechelic polystyrenes with trithiocarbonate and carboxyl terminal groups (PS-CTA) were firstly synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Then, the terminal thiol group was converted from the thiocarbonylthio end group of PS-CTA and subsequently reacted with n-butyl acrylate and vinyl ferrocene, respectively, through thiol–ene “click” chemistry, to achieve α,ω-telechelic polystyrenes with difunctionality. Alternatively, a facile one-pot simultaneous aminolysis and thiol–ene “click” reaction using PS-CTA and various ene-bearing compounds as reactants was found to have high efficiency in synthesizing diverse α,ω-telechelic polystyrenes with di- and tri-functionality. Various functional groups such as hydroxyl, acrylate, fluorinated acrylate, ferrocene and allyl, etc. can be successfully incorporated as terminal groups of α,ω-telechelic polystyrenes.

New synthetic strategy targeting well-defined α,ω-telechelic polymethylenes with hetero bi-/tri-functionalities via polyhomologation of ylides initiated by new organic boranes based on catecholborane and post functionalization

A series of well-defined α,ω-telechelic polymethylenes with hetero bi-/tri-functionalities were synthesized by a tandem strategy combining polyhomologation of ylides initiated by new organic boranes based on catecholborane with post functionalization using end-capping reagents and esterification. The chain structures of such polymers were attested by 1H NMR spectra, FT-IR and GPC. The functionality can reach up to 100%, and the molecular weights of the obtained polymers showed a range from 870 to 12u2006080 g mol−1 with a narrow distribution (Đ = 1.04–1.12).

Synthesis of well-defined α-fluorinated alkyl ester, ω-carboxyltelechelic polystyrenes and fabrication of their hydrophobic highly ordered porous films and microspheres

Well-defined α-fluorinated alkyl ester, ω-carboxyl telechelic polystyrenes (PS) were synthesized via combining aminolysis of RAFT-polystyrene and thiol–ene “click” reaction simultaneously. The perfluoroalkyl end groups were –CF3, –(CF2)2–CF3 and –(CF2)7–CF3, respectively. Highly ordered porous films of such telechelic PS with an average pore size about 1.00 μm were fabricated via a static breath-figure process. With the content of fluorine on the surface of porous films increasing from 1.04 wt%, to 1.64 wt% and 2.97 wt%, respectively, the water contact angle (WCA) of such porous films increased from 112° to 116° and 121° ± 0.4°, respectively, indicating their hydrophobicity. Interestingly, microspheres with average diameters of ca. 0.30–0.65 μm can be fabricated via a static BF process using methanol instead of water as the vapor atmosphere in the glass vessel.

Synthesis of polymethylene-b-poly(vinyl acetate) block copolymer via visible light induced radical polymerization and its application

New well-defined amphiphilic polymethylene-b-poly(vinyl acetate) (PM-b-PVAc) diblock copolymers were synthesized via a tandem strategy combining polyhomologation of ylides, chain-end functionalization and a visible light induced degenerative iodine transfer polymerization using decacarbonyldimanganese (Mn2(CO)10). Firstly, an iodo terminated polymethylene (PM-I) was prepared by polyhomologation of ylides initiated by a new organic borane based on catecholborane followed by functional group transformation using iodine as the end-capping reagent. Then, a series of amphiphilic PM-b-PVAc diblock copolymers with controlled molecular weight (Mn = 5530–17u2006020 g mol−1) and relatively narrow molecular weight distribution (Đ = 1.31–1.45) were obtained efficiently through a visible light induced degenerative iodine transfer polymerization of vinyl acetate (VAc) using PM-I as macroinitiator in the presence of Mn2(CO)10 under weak visible light irradiation at 40 °C. The micelles of such an amphiphilic diblock copolymer formed in tetrahydrofuran were observed by transmission electron microscopy (TEM). Moreover, the fabrication of porous films using PM-b-PVAc diblock copolymers via a static breath-figure process was investigated.

Synthesis of novel guanidine-based ABA triblock copolymers and their antimicrobial honeycomb films

Novel amphiphilic poly(methacryl guanidine hydrochloride)-block-polystyrene-block-poly(methacryl guanidine hydrochloride) (PMAGH-b-PS-b-PMAGH) ABA triblock copolymers with a controlled molecular weight and composition were synthesized via sequential reversible addition/fragmentation chain transfer (RAFT) polymerization of methacryl guanidine hydrochloride (MAGH) and styrene, using S,S′-bis (α,α′-dimethyl-α′′-acetic acid) trithiocarbonate (BDATC) as the initial chain transfer agent. Highly ordered honeycomb films of PMAGH-b-PS-b-PMAGH were fabricated via a facile and versatile static breath-figure process. PMAGHs and the honeycomb films of PMAGH-b-PS-b-PMAGH showed high antimicrobial activity against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). The minimum MIC values of PMAGHs are 113 μg mL−1 for E.coli and 450 μg mL−1 for B. subtilis. PMAGH-b-PS-b-PMAGH honeycomb films inhibited 61% of E. coli and 92% of B. subtilis.