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Zwitterionic catalysis is powerful in simultaneously activating electrophiles and nucleophiles in organic transformations; however, its potential in polymerizations remains untapped. Herein, a zwitterionic catalytic model for ring-opening polymerization (ROP) is introduced and a series quaternary ammonium carboxylate zwitterionic catalysts have been designed and evaluated in the ROPs of cyclic esters. Among the zwitterionic catalysts, L -carnitine, a commercially available and inexpensive natural product, showed the optimal catalytic performance. ROPs of L -lactide (L -LA), trimethylene carbonate, δ-valerolactone and ε-caprolactone were successful. PLLA was prepared with controlled molecular weight (1.4 to 21.2 kg mol−1) and narrow dispersion (Đ 1.02 to 1.21). The zwitterionic catalytic mechanism is proposed where quaternary ammonium and hydroxyl cooperatively activated the carbonyl of monomers, while the carboxylic anion activated the chain-end/initiator. NMR titrations validated the bifunctional activation mechanism. Organocatalysts of zwitterionic nature provide a new design tool for wider scope investigation of catalytic polymerizations. [ABSTRACT FROM AUTHOR]

H-bonding has achieved massive advancements by utilizing an H-bond donor (HBD) to interact with the electron-rich site of the substrate, and an H-bond acceptor (HBA) to coordinate with the electron-deficient site. Rapid transformation is often correlated with the acidity of HBD, namely the degree of charge deficiency of the hydrogen proton. In addition, the positive cations were employed to enhance the HBD; the electron-withdrawing groups were also a dissimilar approach for increasing the capability of the H-bond donor. We first introduced the H-bonding organic ion pair tris(phenylamino)cyclopropenium (TPAC·Cl) into the Friedel–Crafts alkylation of indoles with nitroalkenes, which was implemented via vicinal positive charges on the cyclopropenium core. The counter ion chloride anion became a potential HBA to activate the electron-deficient part of the substrate. X-ray analyses of a single crystal of TPAC·Cl described the 3D architecture and the delocalized cationic charge in the solid state. The aromatic cyclopropenium endowed the N–H moieties with the ability of the H-bond donor to activate the nitroalkene; meanwhile, the chloride anion acted as the H-bond acceptor to activate the indole. The amino-cyclopropenium-offered HBD and HBA displayed cooperative organocatalysis in the Friedel–Crafts alkylation of indole with nitroalkene. A new class of hydrogen bonding catalysis and a working mechanism were proposed. [ABSTRACT FROM AUTHOR]

Halogen bonding, parallel to hydrogen bonding, was introduced into the catalytic cycloaddition of carbon dioxide into epoxide (CCE) reactions. A series of halogen‐bond donor (XBD) catalysts of N‐iodopyridinium halide featured with N−I bond were synthesized and evaluated in CCE reactions. The optimal XBD catalyst, 4‐(dimethylamino)‐N‐iodopyridinium bromide ([DMAPI]Br), under screened conditions at 100 °C, ambient pressure, and 1 mol % catalyst loading, realized 93 % conversion of styrene oxide into cyclic carbonate in 6 h. The substrate scope was successfully extended with excellent yields (mostly ≥93 %) and quantitative selectivity (more than 99 %). 1H NMR spectroscopy of the catalyst [DMAPI]Br on substrate epoxide certified that the N−I bond directly coordinated with the epoxide oxygen. A plausible mechanism of halogen‐bonding catalysis was proposed, in which the DMAPI cation functioned as halogen‐bond donor to activate the epoxide, and the counter anion bromide attacked the methylene carbon to initiate the ring‐opening of the epoxide. CCE reactions promoted by N‐iodopyridinium halide, exemplify a first case of halogen‐bonding catalysis in epoxide activation and CO2 transformation. [ABSTRACT FROM AUTHOR]

Chlorotropylium chloride as a catalyst for the transformations of oximes, ketones, and aldehydes to their corresponding amides and nitriles in excellent yields (up to 99 %) and in short reaction times (mostly 10–15 min). Oximes were electrophilically attacked on the hydroxyl oxygen by chlorotropylium. The produced tropylium oxime ethers were the key intermediates, of which the ketoxime ether led to amide through Beckmann rearrangement, and the aldoxime ether led to nitrile by nitrogen base DBU assisted formal dehydration. This chlorotropylium activation protocol offered general, mild, and efficient avenues bifurcately from oximes to both amides and nitriles by one organocatalyst. [ABSTRACT FROM AUTHOR]

The cycloaddition of CO 2 into epoxide (CCE) reaction was the few routes viable industrially in catalytic fixation of carbon dioxide into value-added chemicals in which cocatalyst halide was predominant. To obviate the harmful corrosion of halide anions to steel reactors, and to alleviate the environmental burden of halogen waste, halide-free catalyst was desirable. We propose a category of one-component H-bond donor (HBD) and nucleophilic anion (HBD–anion) bifunctional organocatalyst as representative halide-free catalyst in CCE reactions. Squaramide (Sq) in conjugation with phenolate constitutes a typical HBD–anion catalyst featured with the squaramide as the HBD moiety and the phenolate as the nucleophilic anion moiety. Series of pre-catalyst in structure of squaramide–phenol (Sq–PhOH) was designed and the active catalyst Sq–phenolate (Sq–PhO) was generated from the corresponding Sq–PhOH by deprotonating of the weakly acidic hydroxyl of the phenol by super strong Brønsted base. In an optimal N -benzyl squaramide para -phenol (Sq–PhOH- p) and P2 phosphazene (t -BuP 2) combination, CCE reactions proceed under mild conditions of 120 °C, and atmospheric pressure of 0.1 MPa, by 2.5 mol % loading of catalyst Sq–PhOH- p / t -BuP 2. Terminal epoxides were transformed with excellent conversions (86–99 %) and high selectivity (85–97 %) in 8 h. Bifunctional activations mechanisms were proposed and validated. 1H and 13C NMR titrations certified the coordination of H-bond donor squaramide to epoxide, and FT-IR spectra observed formation of phenyl carbonate anion from phenolate and carbon dioxide, these suggested unprecedent CCE reaction composed capture of CO 2 in carbonate anion followed by its intramolecular nucleophilic attack on the HBD coordinated epoxide as the key catalytic steps. The squaramide–phenolate catalytic dyad exemplified halide-free HBD–anion organocatalyst of wide scope for carbon dioxide activation and fixation. [Display omitted] • One-component H-bond donor and nucleophilic anion (HBD–anion) catalyst for halide-free cycloaddition of CO 2 into epoxides. • Squaramide–phenolate exemplified typical HBD–anion catalyst with squaramide as HBD and phenolate as nucleophilic anion. • Phenolate activated CO 2 in carbonate anion that attacked on HBD coordinated epoxide. [ABSTRACT FROM AUTHOR]

Polylactic acid or polylactide (PLA) is the leading commercialized bio‐based polyester widely used in biomedical apparatus and disposable food packaging materials, among others. Desirable features of green and environmentally friendly ring‐opening polymerization (ROP) of lactide (LA) by organocatalysts were bulk ROP at high temperature; the organocatalyst should be inexpensive, readily available, and biosafe in the produced PLA; and the ROPs should afford PLA of precisely controlled molecular weights with no transesterifications, nor epimerizations. An organocatalyst that met all these desirable merits has, to the best of our knowledge, not been reported to date. We proposed pyridinium saccharinate binary organocatalyst for industrially feasible ROPs of lactide, carbonates, and lactones. Pyridinium saccharinates of three commercial pyridines including 4‐dimethylaminopyridine (DMAP), 4‐pyrrolidinopyridine, and pyridine were prepared in one step by quantitative yields. An optimal DMAP saccharinate (DMAP ⋅ Sac) as the catalyst successfully promoted ROPs of l‐lactide (LLA) and δ‐valerolactone (VL) with benzyl alcohol (BnOH) as an initiator. The bifunctional DMAP ⋅ Sac coordinated to living polymer chain‐end with enolate oxygen to hydrogen of the hydroxyl, and to monomer with pyridinium N−H to oxygen of the carbonyl that successfully catalyzed efficient polymerization of LLA. High relative growth rate (RGR>90%) of the DMAP ⋅ Sac containing poly(l‐lactic acid) (PLLA) ensured the desirable biocompatibility and biosafety. [ABSTRACT FROM AUTHOR]

Tritylium cation-catalyzed interrupted Povarov reactions afforded cis-4-aminobenzodihydropyrans in excellent yields (90 %) within 10 min by low catalyst loadings (1 mol-%). A mechanism involving Lewis acidic catalysis by a carbocation was proposed and validated. Changing a one-pot batch version of the reaction into a two-stage convergent continuous flow procedure led to a 10-fold time reduction (to 1 min) with 88 % yield. [ABSTRACT FROM AUTHOR]

H-bond donor (HBD) and nucleophilic halide cooperating catalysis was well developed in cycloaddition of CO 2 with epoxide (CCE) reactions where common strong HBD was prevalent. Here a type of onium halide organocatalyst featured weak C–H and N–H HBD was proposed, designed and evaluated in CCE reactions. Based on biobased nicotinamide, nicotinamidium halide catalyst was prepared by simple alkylation on pyridyl N and/or on amide NH. A mono-alkylated on pyridyl N, 1-octyl nicotinamidium iodide, was screened an optimal catalyst that achieved 96 % yield of carbonate under 1 mol% catalyst loading, 1 atm pressure of CO 2 , 80 °C, by 24 h. Terminal epoxides were converted successfully into their corresponding cyclic carbonates by 84–99 % yields with 99 % selectivity. Scale-up preparation of styrene carbonate with 100 g of styrene epoxide (by 88 % yield and 98 % selectivity), and preparation of bis(cyclic carbonate) of a commercial diglycidyl ether of bisphenol A (by 79 % yield and 98 % selectivity) showed practical utility. The H-bonding activation between C–H and N–H HBDs with epoxide was validated by 1H NMR titrations. Designed analog catalysts to 1-octyl nicotinamidium iodide with blocked C–H or blocked N–H revealed the bidentate HBDs worked synergistically. The observations of the beneficial outcome of weak pyridium α-C–H and amide N–H H-bond donors proposed a protocol for simple yet efficient biobased H-bond donor organocatalyst development for CCE reactions. [Display omitted] • A bidentate hybrid C–H and N–H H-bond donor onium halide organocatalyst model was proposed. • Nicotinamidium bidentate H-bond donor catalyst was designed and evaluated in CCE reaction. • Activation of epoxide by weak C–H and N–H H-bond donors was validated by 1H NMR titrations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Halogen bonding donor catalyst was introduced in CO 2 epoxide cycloadditions. • A bifunctional mechanism was proposed and validated by NMR titrations. • The cycloadditions of CO 2 , CS 2 , and isocyanates with epoxides were viable. Halogen bonding catalysis was introduced into the [3+2] cycloaddition reactions of epoxides with CO 2 , and other heterocumulenes. Series of 2-iodoimidazolium halides, a typical halogen bond donor (XBD) featured with C–I bond, were synthesized and evaluated in the [3+2] cycloaddition reactions. An optimal XBD catalyst, 1,3-bis-(2,6-diisopropylphenyl)-2-iodoimidazolium bromide, achieved 96 %, 94 %, and 61 % conversions in the cycloadditions of epoxides with CO 2 , isocyanates, and CS 2 , respectively, under 80 °C. Arrays of epoxides were transformed into the corresponding five-membered heterocycles of cyclic carbonates, oxazolidinones, and cyclic dithiocarbonates by high yields and selectivity. 1H NMR and 13C NMR titrations of the XBD catalyst on the styrene oxide indicated that the halogen bond donor coordinated with the substrate through halogen bonding between iodine atom of C–I moiety and oxygen of the epoxide. Possible mechanism was proposed, in which halogen bond donor activated the epoxides by halogen bonding and halide counter anion attacked the carbon of methylene to facilitate the ring-opening of the epoxides. Halogen bonding catalysis was firstly extended to general [3+2] cycloaddition reactions of epoxides with CO 2 , isocyanates, and CS 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metal- and halide-free binary cocatalyst DABCO·HSac was designed for CCE reactions. • The saccharinate played the role similar to halide in the ring-opening of the epoxide of which appropriate nucleophilicity and nucleofugality were determinants. • The plausible cocatalysis mechanism was studied by 1H NMR titrations and counterpart ions exchange experiments. Both saccharinate and DABCO-H+ were indispensable in the catalytic cycle. Metal- and halide-free catalyst DABCO·HSac, i.e., the binary adduct of 1,4-diazabicyclo[2.2.2]octane (DABCO) and saccharin (HSac), in an ionic pair structure of DABCO-H+·Sac- is shown mild and efficient in promoting the cycloaddition of CO 2 into epoxides (CCE) reactions. Under comparatively low temperature of 60 °C, ambient pressure of 0.1 MPa, and 10 mol% catalyst loading, DABCO·HSac catalyzed the cycloaddition of epichlorohydrin into CO 2 with the conversion of 96% in 24 h. Terminal epoxides including epibromohydrin, glycidyl ethers, and alkylene oxides received 83–99% conversions, however, cyclohexene oxide and stilbene oxide were not viable under these mild reaction conditions. A catalytic cycle initiated by the saccharinate anion of its nucleophilic attack on methylene carbon of an epoxide ring with the iminolate oxygen was proposed as the key step, in which the Sac- anion functioned similarly to halide X- in other ring-opening mechanisms. The tertiary amine DABCO was protonated into an onium cation DABCO-H+ that worked as a hydrogen-bond donor in coordinating and activating the epoxide. A cocatalysis mechanism was suggested and validated by NMR titrations. Further control experiments by switch cation or anion of DABCO-H+·Sac- in structural analog cocatalysts certified both the onium DABCO-H+ and the saccharinate Sac- was indispensable in the catalytic cycle. The design of ionic pair organocatalysts illustrated the possibility of non-halide anions as the nucleophiles in wider halide-free catalyst discovery. [ABSTRACT FROM AUTHOR]

• A neutral H-bonding organocatalyst was designed for chiral oxazolidinone. • A synthesis strategy for 4-substituted 2-oxazolidinone from glycidol and isocyanate was developed. • XRD analysis revealed the S N 2-type intramolecular cyclization occurred in the reaction process. We developed a kind of neutral organocatalyst amino-cyclopropenium halide to facilitate the [3 + 2] cycloaddition of glycidol and isocyanate to prepare optical active oxazolidinone. Glycidol coupling with isocyanate followed by 5-exo-tet -type cyclization in the presence of organic ion pair. The mild H-bonding coordination between catalyst and substrate prevented the non-selective ring-opening of glycidols and racemization of products. Rather, the cation and anion species activated the epoxy sites and enhanced the nucleophile ability of amide sites, respectively. NMR titrations and control experiments demonstrated the crucial role of H-bonding in cycloaddition reactions. X-ray diffraction (XRD) verified the configuration of intermediate and product, indicating an S N 2 cyclization occurred in the process. HPLC analysis of the chiral oxazolidinones unveiled a high enantiomeric excess, signifying the ion pair has excellent stereochemical control. This work provided a simple, efficient, and large-scalable approach to synthesizing 4-hydroxymethyl oxazolidinones. [Display omitted] [ABSTRACT FROM AUTHOR]

Polybenzoxazine bearing phosphonium and phenol functions was firstly designed, synthesized, and evaluated for the cycloaddition of CO 2 into epoxide (CCE) reactions. Benzoxazine monomers intrinsically installed with phosphonium halide moiety were thermally polymerized to obtain phenolic-type polybenzoxazines. The bifunctional polybenzoxazine catalyst promoted CCE reactions at 120 °C within 2 h to afford high yields up to 96% under atmospheric pressure. The catalyst was recycled four times and maintained 92% yield. A possible bifunctional catalytic mechanism composed of hydrogen-bonding activation by phenol and co-catalysis by halide was proposed and validated. The easy preparation of the benzoxazine monomers with variety of catalytic moieties, and one-step fabrication of the polybenzoxazines suggest untapped potential of manifold polymeric catalyst design and applications. [Display omitted] • Polybenzoxazine with phenol and phosphonium catalytic groups was designed as bifunctional catalyst in CCE reactions. • A bifunctional catalytic mechanism of hydrogen-bonding activation by phenol and cocatalysis by halide was proposed. • The polybenzoxazine catalyst was recycled four times almost retaining the original activity. [ABSTRACT FROM AUTHOR]

Alcohol-initiated ring-opening polymerization (ROP) of cyclic esters for synthesizing polyesters was well established, but amine-initiated ROP of cyclic esters was rare. A challenge is slow initiation and fast propagation in the amine-initiated ROPs. To address the difficulties, an ionic H-bond donor (iHBD) and H-bond acceptor (HBA) binary organocatalysis in amine-initiated ROP of lactide (LA) was developed. Guanidinium hexahydro-2 H -pyrimido[1,2- a ] pyrimidin-1-ium [(HppH 2 ) + ] and tertiary amine sparteine (SP), cooperatively played the role of iHBD/HBA binary catalysts, efficiently promoted ROP of LA from amine initiators toward polylactide (PLA) and polysarcosine- block -polylactide diblock copolymer (PSar- b -PLA). Benzyl amine and N -methylbenzylamine initiated ROPs of LA under mild conditions produced PLAs with predictable molecular weights ( M n,NMR  = 2.9–17.1 kg mol −1 ) and narrow dispersities ( Ð M,SEC  = 1.13–1.23). Macroinitiator PSar copolymerized with LA under the iHBD/HBA catalysis, producing PSar- b -PLAs with controlled molecular weights ( M n,NMR  = 5.7–14.8 kg mol −1 ) and low dispersities ( Ð M,SEC  = 1.16–1.21). Kinetics and chain extension experiments confirmed that the amine-initiated ROP of LA in presence of (HppH 2 ) + BF 4 − /SP was in controlled/living manner. 1 H NMR, 13 C NMR, SEC, and MALDI-ToF MS analyses indicated that the obtained PLA was exclusively initiated from the corresponding amine with amide linkage. An iHBD/HBA binary activation mechanism was proposed. [ABSTRACT FROM AUTHOR]

H-bonding organocatalysis using (thio)urea/amine achieved massive success. H-bonding binding with Brønsted acid catalysis, especially in polymerizations, was scarcely explored. Here we disclosed 1,3- bis -(3,5- bis (trifluoromethyl)phenyl)thiourea (TU) as hydrogen bond donor (HBD), combined with trifluoroacetic acid (TFA) as a Brønsted acid (BA), promoted efficient controlled/living ring-opening polymerization (ROP) of δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL) at room temperature. The ROPs of δ-VL and ε-CL with benzyl alcohol (BnOH) as the initiator yielded poly(δ-valerolactone) (PVL, M n, NMR = 1900–9900 g mol −1 , M w / M n = 1.28–1.34) and poly(ε-caprolactone) (PCL, M n, NMR = 2400–11,600 g mol −1 , M w / M n = 1.19–1.35) with predicted molecular weights and narrow dispersities. A plausible mechanism of the ROP promoted by associations of TU with TFA through double hydrogen bonding was suggested, in which stabilizing of the carboxylate anion and enhancing of the Brønsted acidity made the catalytic ROPs by TU–TFA viable. The quantitative incorporation of the initiator into the polymer chains was demonstrated by 1 H NMR and MALDI-ToF MS measurements. The controlled/living fashion of the polymerization was supported by the kinetics and chain extension experiments. Synthesis of well defined block copolymers of PVL- b -PCL and PCL- b -PVL verified again the ROPs were in controlled/living manner, and suggested the hydrogen bond donor binding with Brønsted acid catalysis to be a generally applicable method. [ABSTRACT FROM AUTHOR]

A switch of halide X to saccharinate Sac generated halide-free catalytic manifold for coupling carbon dioxide into epoxides. [Display omitted] • Metal- and halide-free binary cocatalyst PPy·Sac was designed for CCE reactions. • The saccharinate played the role like halide in the ring-opening of the epoxide. • Cocatalysis mechanism validated by 1H NMR titrations and cation and anion switch. Cycloaddition of CO 2 into epoxides (CCE) reaction was the few chemical processes viable commercially in valorizations of carbon dioxide. The produced cyclic carbonate was valuable in electrolyte of lithium batteries and so on, however, halide anion was monopoly as cocatalyst in catalytic CCE reactions. To avoid the harmful halide in corrosion of process equipment, the detrimental halide in electrolytes, and the waste halide as environmental burden, halide-free catalysis for CCE was highly desirable. In design of halide-free catalytic platform, we propose binary adducts of food sweetener saccharin and strong pyridine base in ionic pair pyridinium saccharinate exemplified by PPy·Sac (3). CCE reaction of epichlorohydrin at mild conditions of 40 °C, 0.1 MPa, by 10 mol% loading of catalyst 3 in 24 h were evaluated. Terminal epoxides including glycidyl ethers, alky epoxides, and styrene oxide were transformed into their corresponding cyclic carbonates by excellent yields (80 to 90% up). Internal epoxides of hexene and stilbene were not viable under these mild conditions. The key role of saccharinate anion in cocatalysis in both the nucleophilic attack on epoxide in initiating the ring-opening, and as good leaving group in ring-closure was validated. 1H NMR titration experiment of PPy·Sac on epoxide verified the activation of the substrate by H-bonding, the capture of intermediates in mass spectroscopy certified the ring-opening by Sac, and the control experiment by switching the cation and anion of PPy·Sac supported the indispensable of the cation and anion in the cocatalysis. In view of the wide application of halide anions in nucleophilic catalysis and substitutional reactions, diversity design of anions of appropriate nucleophilicity and nucleofugality would be useful in practical catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polybenzoxazine anchored pyridyl moiety as organocatalyst was firstly proposed. • The polybenzoxazine was evaluated as nucleophilic catalyst in acylation reaction. • The catalyst was comparable to commercial PS-DMAP in catalysis and in recycles. Polybenzoxazine (PBz) anchored with an N -4′-pyridyl group on the backbone was prepared and characterized. Phenolic-type polybenzoxazine was selectively prepared by thermally initiated ring-opening polymerization of N -(4′-pyridyl)benzoxazine (Bz-Py). The loading of the catalytic moiety pyridyl on PBz-Py was 2.7 mmol g−1. The catalytic comparison of the prepared PBz-Py to commercial PS-DMAP in acylation reactions was investigated. The catalytic PBz-Py showed a broad scope of substrates of sterically hindered secondary and tertiary alcohols, aniline, quinoline, and steroid at room temperature within two hours by high yields up to 96%. Further extension to PBz-Py-catalyzed silylation and tritylation reactions resulted in high yields. The catalyst retained 85% activity after 4 recycles. The implementation of a 4-pyridyl group on the PBz backbone as a new type of polymeric catalyst showcased a general manifold to introduce catalytic moieties to designed polybenzoxazine catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • First example of polybenzoxazine installed pyridinium salt as efficient catalyst for CO 2 fixation. • The catalytic cycloadditions featured ambient pressure, high yields, and short reaction time. • A cooperated hydrogen-bonding mechanism was proposed and verified. Polybenzoxazine containing N-methylpyridinium iodide (PBz-[PyMe]I) was first utilized as an efficient catalyst for CO 2 fixation into cyclic carbonates. The polymer structure was determined as a phenolic-type polybenzoxazine characterized by FT-IR, 1H NMR. PBz-[PyMe]I shows a wide scope of substrates for the reaction of cycloaddition of CO 2 with epoxides including aliphatic epoxides, styrene oxide derivatives, glycidyl ethers, and spiro-epoxyoxindole at 120 °C within two hours, and obtains high yields up to 96%. The catalyst was recycled up to four times remaining 82% catalytic activity comparing to the first run. A combined hydrogen-bonding mechanism activated by both phenol and pyridinium salt was proposed and verified. The synthesis and application of PBz-[PyMe]I suggested the viability of other catalytic moieties could be introduced into polybenzoxazine. [ABSTRACT FROM AUTHOR]

• A bidentate H-bond donor and base successfully catalyzed ROPs without proton abstraction. • Produced PLAs possess broad molecular weight ranges and extremely narrow dispersities. • A strict HBD/base cocatalysis mechanism was validated by NMR titrations. Hydrogen bond donor (HBD) and organic base binary cocatalyst established a gold standard in organocatalytic ring-opening polymerizations (ROPs). In depth probe of the mechanisms revealed that proton abstraction of the acidic H on the HBDs by the bases do occur frequently. A truly simple HBD and Lewis base (LB) cocatalysis, however, was elusive. We proposed genuine HBD/LB cocatalyst for ROPs by introducing 3-amino-1,2,4-benzothiadiazine-1,1-dioxide (ABTD) as a bidentate H-bond donor and triethylamine (TEA) as a mild Lewis base. ROPs of lactide (LA) and trimethylene carbonate (TMC) in solutions at room temperature were success. The mild ROPs produced polylactide (PLA) of predictable molecular weights (from 1.6 to 26.7 kg mol−1) and extremely narrow dispersities (Đ 1.01 to 1.06). Furthermore, well-defined diblock copolymers PTMC-b-PLA were synthesized. NMR titration experiments verified exclusive H-bond donor activation of the monomer and TEA activation of the hydroxyl chain end without trace of proton abstraction. [ABSTRACT FROM AUTHOR]

• Pyridinium hydrohalides catalyzed ROPs of LLA in bulk at elevated temperatures. • Activations in bifunctional mechanism by H-bond donor and acceptor was elucidated. • Biosafety of PLA containing catalyst DMAP hydrochloride was assayed by MTT test. Polyesters produced by ring-opening polymerization (ROP) of cyclic monomers using organocatalysts were well developed in academia. Industrially viable ROPs were polymerizations at elevated temperatures in the bulk, thus desirable features of useful organocatalysts would be thermal stable, reasonably active in fast polymerization but mild enough to avoid transesterification. More importantly, the polyesters containing residue organocatalyst should met biosafety regulations. In these regards, series of pyridinium halides readily prepared by one step from mass-produced pyridines and hydrohalic acids were evaluated in ROPs of l -lactide (LLA), trimethylene carbonate (TMC), δ-valerolactone, and ε-caprolactone in the bulk. An optimal catalyst 4-(N,N -dimethylamino)pyridine hydrochloride (DMAP·HCl) was examined in the catalytic performances in ROPs of LLA, TMC, and diblock copolymerization affording PTMC- b -PLLA. Bulk ROP of LLA at 140 °C produced PLLAs by near quantitative conversions with precise molecular weights (M n,NMR = 3.3–16.6 kg mol−1) and narrow dispersities (Đ = 1.13–1.17). Kinetics data, chain extension experiments, and MALDI-ToF MS analysis all supported the controlled/living nature of the ROPs. A bifunctional activation mechanism in which pyridinium activated the monomer and halide activated the initiator/chain end was proposed and validated by 1H NMR and 13C NMR titrations. Poly (l -lactide) samples prepared by bulk ROPs of LLA that containing residue catalyst DMAP·HCl were tested by MTT assay in L929 mouse fibroblasts in vitro. High level of relative growth rate (RGR 93.6–96.8%) revealed favorable biosafety of the sample PLLAs. [ABSTRACT FROM AUTHOR]

TBD catalyzed continuous flow ring-opening polymerizations of ε-caprolactone and δ-valerolactone were exemplified as the model investigation system of organocatalytic synthesis of polyesters in the simple PTFE tubular microreactor (MR). In contrast to the batch reactor (BR), significant benefits of utilizing continuous flow strategy were achieved including higher level control of molecular weights and molecular weight distributions as well as faster polymerizations ( k app (CL) = 0.00602 (MR) vs 0.00286 min −1 (BR); k app (VL) = 0.159 (MR) vs 0.079 min −1 (BR)). Furthermore, more easily and efficiently block copolymerizations were conducted in the integrated-microreactor by sequential introduction of monomers to well-defined poly(δ-valerolactone)- block -poly(ε-caprolactone) and poly(ε-caprolactone)- block -poly(δ-valerolactone). [ABSTRACT FROM AUTHOR]