This work discloses a zwitterionic approach for selective copolymerization of carbon dioxide (CO 2 ) and propylene oxide (PO), producing poly(propylene carbonate) (PPC), a biodegradable polymer with broad applications. Small-molecule catalysts composed of triethylamine (TEA) and trialkyl boranes are effective for CO 2 / PO copolymerization with an alternating degree of >99% and a productivity of 171 g PPC/g catalyst. A diamine N,N,N′,N′-tetraethyl ethylenediamine (TEED) paired with trialkyl borane exhibited improved activity and productivity (up to 216 g PPC/g catalyst). By adjusting the Lewis acid−base pair, the PPC selectivity can be regulated to 99%. In addition, PPCs have medium regioregularity with a head-to-tail diad content of 80−82% and number-average molecular weights of up to 56.0 kg/mol with narrow polydispersity (below 1.2). The overall catalytic performance of these readily available simple molecules is better than that of previously reported organic catalysts for CO 2 /PO copolymerization. Successive insertion of PO and CO 2 into the Lewis pair leads to the formation of an end-to-end zwitterion featuring a TEB-masked anion and an onium cation, which is highly selective to the alternating copolymerization, as demonstrated by quantum mechanical calculations.
Novel constrained Schiff-base ligands (inden) were developed based on the well-known salen ligands. Chromium complexes supported by the constrained inden ligands were successfully synthesized and used as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO 2 ). The catalyst having tert-butyl ( t Bu) groups as substituents in combination with tetrabutylammonium bromide (TBAB) as a cocatalyst exhibited very high catalytic activity with a turnover frequency of up to 14800 h −1 for the conversion of CO 2 and propylene oxide into propylene carbonate exclusively at 100 °C and 300 psi of CO 2 under solvent-free conditions. The catalyst was found to be highly active for various epoxide substrates to produce terminal cyclic carbonates in 100% selectivity.
Introducing sulfur atoms into polycarbonate can improve its optical properties, but is limited by the lack of efficient synthetic methods. Here we develop a facile method to achieve the one‐pot/one‐step incorporation of sulfur atoms into polycarbonate chains using raw chemicals of propylene oxide (PO), carbon dioxide (CO2), and carbonyl sulfide (COS). The metal‐free Lewis acid–base pair composed of N, N‐dimethylcyclohexylamine combined with triethyl borane can effectively catalyze the terpolymerization of PO, CO2, and COS, affording a sulfur‐containing polycarbonate with high molecular weight (Mn) up to 58.4 kDa and narrow dispersity (Đ = 1.24–1.56). The obtained terpolymers display gradient sequence with tunable thiocarbonate units (27%–81%) upon simply varying the feed ratio of COS. The refractive indices of the terpolymers can be enhanced up to 1.55 at high thiocarbonate content, suggesting promising applications of the terpolymer in optical materials.
An effective route for ring-opening copolymerization of β-butyrolactone (BBL) with ε-decalactone (ε-DL) is reported. Microstructures of the block copolymers characterized by
13
C NMR spectroscopy revealed syndiotactic-enriched poly(3-hydroxybutyrate) (PHB) blocks. Several di- and triblock copolymers (PDL-
b
-PHB and PDL-
b
-PHB-
b
-PDL, respectively) were successfully synthesized by sequential addition of the monomers using (salan)Y(III) complexes as catalysts. The results from MALDI-ToF mass spectrometry confirmed the presence of the copolymers. Moreover, thermal properties of the block copolymers were also investigated and showed that the microphase separation of PDL-
b
-PHB copolymers into PHB- and PDL-rich domains has an impact on the glass transition temperatures of both blocks.
The copolymerization of carbonyl sulfide (COS) with epoxides has been developed to be a facile method to synthesize well-defined sulfur-containing polymers. This work describes the steric effect of tertiary amines...
Facile construction of sulfur-rich polymers using readily available raw chemicals is an area aggressively pursued but challenging. Herein we use common feedstocks of ethylene oxide (EO), propylene oxide (PO), and carbonyl sulfide (COS) to synthesize copoly(thioether)s which are traditionally produced from unpleasant and difficult to store episulfides. In this protocol, the EO/COS coupling selectively generates a pure poly(ethylene sulfide) (PES) with melting temperature (T m ) values up to 172 C and high yields up to 98%. The EO/PO/COS terpolymerization leads to the incorporation of soft poly(propylene sulfide) (PPS) and hard PES segments together, affording a random PES-co-PPS copoly(thioether) with the complete consumption of EO and PO. Additionally, by simply varying the EO/PO feeding ratio, the obtained copoly(thioether)s possess tunable thermal properties, T m values in the range of 76-144 C, and excellent solubility. These copolymerizations are conducted in one-pot/one-step at industrially favored reaction temperatures of 100-120 C using catalysts of common organic bases, suggesting a facile and practical manner. Especially, the copoly(thioether) exhibits high refractive indices up to 1.68 owing to its high sulfur content, suggesting a broad application prospect in optical materials.
PdII‐bis(triazolyl)phenylmethanol complexes bearing different groups (i. e., H, OMe, OH, COOH) directly attached to the benzyl rings were explored as precatalysts for copper‐free Sonogashira and Suzuki–Miyaura coupling reactions in water. Crystal structures reveal a bidentate N,N binding mode of the bis(triazolyl) ligands affording a distorted square planar PdII complexes. With the exception of the phenol‐substituted bis(triazolyl) ligands, the other three Pd complexes exhibited high activities toward Suzuki–Miyaura coupling reactions. Transmission electron microscopy (TEM) study and PPh3 poisoning experiments confirm that bis(triazoly)‐stabilized Pd nanoparticles (Pd NPs) were generated in situ during the catalytic reactions and involved as one of the active catalytic species in the Suzuki–Miyaura cross coupling.
A series of tin(II) complexes supported by N 2 O 2 bis(phenol)-amine ligands were prepared from the reactions of the corresponding ligands with Sn[N(SiMe 3 ) 2 ] 2 in benzene at room temperature. The ligands were designed to have different substituted group at the ortho-position on the aryl rings (R = t Bu, CH 3 ) and N-containing side arm (E = CH 2 NEt 2 and pyridine) giving a variation of tin(II) complexes (R = t Bu, E = CH 2 NEt 2 , 2a; R = t Bu, E = py, 2b; R = CH 3 , E = CH 2 NEt 2 , 2c; R = CH 3 , E = py, 2d). All complexes were characterized by NMR spectroscopy and single-crystal X-ray analysis. The single-crystal X-ray crystallography revealed that all complexes have a monomeric four-coordinate tin center with a distorted seesaw structure. All complexes are active for solvent-free polymerization of L-lactide at 120 C giving poly(L-lactide) with narrow to moderate dispersity (Ð = 1.12-1.56). In the presence of benzyl alcohol during the polymerization, the resulting polymer was found to be linear having benzyl alcohol as the end group while, in the absence of benzyl alcohol, the polymer was cyclic. The large t Bu group at the ortho-position was found to decrease polymerization activity while the more basic CH 2 NEt 2 group was found to increase the polymerization activity. The polymerization of rac-lactide under a similar condition gave PLA having a slight heterotactic bias for all catalysts.
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