Unity Makes Strength:Constructing Polymeric Catalyst for Selective Synthesis of CO_(2)/Epoxide Copolymer

Catalyst design strategies such as bi-functional and di-nuclear catalysts have been developed based on intramolecular interactions,achieving excellent catalytic performance.However,most of these catalysts work in a state of disunity.To make progress in this direction,we reckoned that enhancing the neglected intermolecular interactions of these catalysts might be a suitable approach.Herein,we report a strategy of constructing homogeneous polymeric catalysts based on the philosophy of“unity makes strength”to convert the intermolecular interactions into stronger intramolecular interactions.We united discrete active centers of aluminum(Al)porphyrin and tertiary amine(methyl methacrylate;MMA)via a random copolymerization process into one polymer chain with the subsequent metallization using low-toxic metal AlEt_(2)Cl,to construct polymeric catalysts for selective copolymerization of CO_(2)/epoxide.The spatial confinement enabled the multiple interactions among the active centers,which was distinct from the“point-to-point”interacting systems such as binary,bi-functional,or di-nuclear complexes.Through detailed tuning of the multiple synergistic effects between porphyrin/porphyrin(metal synergistic effect)and Al porphyrin/tertiary amine(Lewis pair effect),the optimized polymeric catalyst showed significantly boosted catalytic activity of 4300 h^(−1),much higher than their mono-nuclear(∼0 h^(−1))and homo-polymeric(750 h^(−1))counterparts.Our present approach for designing polymeric catalysts based on multiple synergistic effects provides a platform for developing highly active catalysts.

Temperature-responsive Catalyst for the Coupling Reaction of Carbon Dioxide and Propylene Oxide

The selective synthesis of polypropylene carbonate （PPC） and cyclic propylene carbonate （CPC） from coupling reaction of CO_2 and propylene oxide （PO） is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20-tetra（1,2,3,4,5,6, 7,8-octahydro-1,4：5,8-dimethanoanthracen-g-yl）porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or co- polymerization reaction. Only cydoaddition reaction happened at temperature above 75 ℃ to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25℃, and the obtained PPC showed over 99% carbonate linkage and 92% head-to-tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron-donating substituents displayed a significantly reduced toler- ance towards increased temperature with respect to PPC formation. Therefore, temperature-responsive catalyst could be designed by suitable modifica- tion in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.

Synthetic rubbers prepared by lanthanide coordination catalysts

China is rich in rare earth resources. Rare earth elements, also named lanthanides, are number 58 to number 81 elements in the elemental periodic table. They have unique electronic structures and may form various coordination compounds. In the early 1960s, researchers at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CIAC) found the catalytic activities of lanthanide compounds in stereospecific polymerization of conjugated dienes, and published the first paper on this topic in 1964. On the basis of this finding, CIAC launched extensive research activities on lanthanide compounds as diene polymerization catalysts, from a series of fundamental research to the efforts of industrializing the rare earth catalyzed cis-1,4-polybutatine rubber and cis-1,4-polyisoprene rubber. This review aims to summarize the progress in this field in the past half century.

The Influence of Rare Earth Ions on the Rheological Behavior of Polyamide

The polyamide 66 （PA66）/lanthanum acetate blends with small amounts of salt loadings （≤ 1 wt% of PA） have been prepared in a twin-screw extruder. The rheology of PA66 and its blends has been investigated by a rotational rheometer. The results suggested that with the salt loading in excess of 0.2 wt% the typical Newtonian viscosity plateau disappeared and both the low-frequency complex viscosities η^＊ and storage modulus G＇ of blends were much higher than those of neat PA66, the storage modulus was higher than the loss modulus at low frequencies （tanδ〈 1）, i.e., the melt changed from a viscoelastic liquid for unfilled polymer to a viscoelastic solid （G′ 〉 G″）. While the viscosity followed a strong shear thinning with increasing frequency, the η^＊ and G′ decreased significantly even lower than those of neat PA66 at high frequencies. The combination of dynamic mechanical analysis （DMA） and X-ray photoelectron spectroscopy （XPS） analysis has revealed that coordination effect occurred between lanthanum and carbonyl oxygen atoms in amide groups of the polymer to form pseudo- crosslinked network structure, which makes the glass transition temperatures （Tg） and storage modulus （E′） of blends enhanced. The network structure formation-destruction and chains entanglement-disentanglement processes at different frequencies are responsible for the above rheological behaviors of blends.

Through-space charge transfer blue polymers containing acridan donor and oxygen-bridged triphenylboron acceptor for highly efficient solution-processed organic light-emitting diodes

Three kinds of through-space charge transfer(TSCT)blue polymers containing non-conjugated polystyrene backbone together with spatially-separated acridan donor and oxygen-bridged triphenylboron acceptors having different substituents of tert-butyl,hydrogen and fluorine are designed and synthesized.The designed TSCT blue polymers possess photoluminescence quantum yields up to 70%in solid-state film,single-triplet energy splitting below 0.1 eV,and typical thermally activated delayed fluorescence(TADF)effect.Meanwhile,the resulting polymers exhibit aggregation-induced emission(AIE)effect with emission intensity increased by up to^27 folds from solution to aggregation state.By changing the substituent of acceptors to tune the charge transfer strength,blue emission with peaks from 444 to 480 nm can be realized for the resulting polymers.Solution-processed organic light-emitting diodes based on the polymers exhibit excellent device performance with Commission Internationale de L’Eclairage(CIE)coordinates of(0.16,0.27),together with the maximum luminous efficiency of 30.7 cd A-1 and maximum external quantum efficiency of 15.0%,which is the best device efficiency for blue TADF polymers.

Construction of Self-Reporting Biodegradable CO_(2)-Based Polycarbonates for the Visualization of Thermoresponsive Behavior with Aggregation-Induced Emission Technology

Thermoresponsive polymers with simultaneous biodegradability and signal“self-reporting”outputs that meet for advanced applications are hard to obtain.To address this issue,we developed fluorescence signal“self-reporting”biodegradable thermoresponsive polycarbonates through the immortal copolymerization of CO_(2)and oligoethylene glycol monomethyl ether-functionalized epoxides in the presence of hydroxyl-modified tetraphenylethylene(TPE-OH).TPE-OH was used as chain transfer agent to afford well-defined polycarbonates with controlled molecular weight(6000—17000 g·mol^(–1))and aggregation-induced emission characteristics.Through temperature-dependent fluorescence intensity study,low critical solution transition of TPE-labeled polycarbonates were determined and the fine details of thermal-induced phase transition process were monitored.Further research indicated that temperature-controlled aggregation and dissociation of TPE moieties are the main reason for fluorescence intensity variations.We anticipate that this work could offer a method to visualize the thermal transition process of thermoresponsive polycarbonates and broaden their application fields as smart materials.

Dithienocarbazole- and benzothiadiazole-based donor-acceptor conjugated polymers for bulk heterojunction polymer solar cells

Donor-acceptor(D-A)-conjugated polymers P(BT-C1)and P(BT-C2),with dithieno[2,3-b;7,6-b]carbazole(C1)or dithieno[3,2-b;6,7-b]carbazole(C2)as D-unit and benzothiadiazole(BT)as A-unit,were synthesized.The optical bandgaps of the polymers are similar(1.84 and 1.88 e V,respectively).The structures of donor units noticeably influence the energy levels and backbone curvature of the polymers.P(BT-C1)shows a large backbone curvature;its highest occupied molecular orbital(HOMO)energy level is 5.18 e V,whereas P(BT-C2)displays a pseudo-straight backbone and has a HOMO energy level of 5.37 e V.The hole mobilities of the polymers without thermal annealing are 1.9×10 3 and 2.7×10 3 cm2 V 1 s 1 for P(BT-C1)and P(BT-C2),respectively,as measured by organic thin-film transistors(OTFTs).Polymer solar cells using P(BT-C1)and P(BT-C2)as the donor and phenyl-C71-butyric acid methyl ester(PC71BM)as the acceptor were fabricated.Power conversion efficiencies(PCEs)of 4.9%and 5.0%were achieved for P(BT-C1)and P(BT-C2),respectively.The devices based on P(BT-C2)exhibited a higher Voc due to the deeper HOMO level of the polymer,which led to a slightly higher PCE.

Self-host yellow iridium dendrimers based on carbazole dendrons: synthesis, characterization and application in solution-processed organic light-emitting diodes

On the basis of different generation carbazole dendrons, a series of self-host yellow Ir dendrimers(Y-G0, Y-G1 and Y-G2)have been successfully synthesized and characterized in detail. It is found that the peripheral dendrons can effectively reduce the intermolecular interactions between emissive Ir cores, as verified by the increased photoluminescence quantum yields and film lifetimes. Among these dendrimers, Y-G2 bearing the second generation dendrons shows the best non-doped device performance,revealing a peak luminous efficiency of 20.2 cd/A. The value is nearly twice that of Y-G0 without any dendrons,which could be further improved to 32.1 cd/A by dispersing Y-G2 into a host matrix. We believe that this work will shed light on the development of highly efficient yellow phosphorescent dendrimers with a self-host strategy.

Controlled synthesis of CO_2-diol from renewable starter by reducing acid value through preactivation approach

Synthesis of polyols from carbon dioxide（CO2） is attractive from the viewpoint of sustainable development of polyurethane industry;it is also interesting to adjust the structure of the CO2-polyols for versatile requirement of polyurethane.However,when renewable malonic acid was used as a starter,the copolymerization reaction of CO2 and propylene oxide（PO） was uncontrollable,since it proceeded slowly（13 h） and produced 40.4 wt%of byproduct propylene carbonate（PC） with a low productivity of 0.34kg/g.A careful analysis disclosed that the acid value of the copolymerization medium was the key factor for controlling the copolymerization reaction.Therefore,a preactivation approach was developed to dramatically reduce the acid value to 0.6mg（KOH）/gby homopolymerization of PO into oligo-ether-diol under the initiation of malonic acid,which ensured the controllable copolymerization,where the copolymerization time could be shortened by 77%from 13 to 3 h,the PC content was reduced by 76%from 40.4 wt%to 9.4 wt%,and the productivity increased by 61%from 0.34 to 0.55 kg/g.Moreover,by means of preactivation approach,the molecular weight as well as the carbonate unit content in the CO2-diol was also controllable.

Novel boron-and sulfur-doped polycyclic aromatic hydrocarbon as multiple resonance emitter for ultrapure blue thermally activated delayed fluorescence polymers

Boron(B)-and sulfur(S)-doped polycyclic aromatic hydrocarbons(PAHs)are developed as a novel kind of multiple resonance emitters for ultrapure blue thermally activated delayed fluorescence(TADF)polymers with narrowband electroluminescence.The combination of electron-deficient B atom and electron-rich S atom in PAH can form an intramolecular push-pull electronic system in a rigid aromatic framework,leading to reduced singlet-triplet energy splitting and limited structure relaxation of excited states.The critical roles of S atom in determining emission properties with respect to the oxygen analogues are in two aspects:(i)reducing energy bandgap to shift emission from human-eye-insensitive ultraviolet zone to blue region,and(ii)promoting reverse intersystem crossing process by heavy-atom effect to activate TADF effect.The resulting polymer containing B,S-doped PAH as emitter and acridan as host exhibits efficient blue electroluminescence at 458 nm with small full-width at halfmaximum of 31 nm,representing the first example for ultrapure TADF polymer with narrowband electroluminescence.

Chain-transfer-catalyst: strategy for construction of site-specific functional CO_(2)-based polycarbonates

Site-specific functional polymers are generally synthesized from functionalized chain transfer agents(CTA)in the presence of catalysts.However,the poor solubility or chemical inertness of CTAs may make polymerizations uncontrollable.Now,this issue is addressed by proposing a strategy of designing chain-transfer-catalyst(CTC)that combines catalyst and CTA into one.The occurrence of catalytic effect naturally triggers the chain transfer process to give catalyst-labeled polymers with well-defined structures.As a proof-of-concept,cobalt(III)porphyrin catalysts with one,two and four hydroxyl groups act as efficient CTCs,giving the corresponding site-specific functional poly(propylene carbonate)s(PPC),diversifying the topology of polymers.Furthermore,porphyrin-capped PPCs with controllable Mn in the range of 1,000–16,800 g mol^(-1)were obtained by using monofunctional CTC(CTCOH).Moreover,different from traditional“catalyst+CTA”systems,a novel dynamic network transfer mechanism of CTCOH was proposed.This study provides a CTC strategy for the synthesis of site-specific functional polymers.