Precision rheological study of the effectiveness of polymer cold flow improvers for corn oil based biodiesel

Combination of the precision rheology and DSC helps to make an objective assessment of the effectiveness of modified copolymers of maleic anhydride with methylidenealkanes and best known commercial pour point depressants as cold flow improvers for corn oil based biodiesel.     

Development of Amino–Oxazoline and Amino–Thiazoline Organic Catalysts for the Ring‐Opening Polymerisation of Lactide

The ring‐opening polymerisation of lactide by a range of amino–oxazoline and amino–thiazoline catalysts is reported. The more electron‐rich derivatives are demonstrated to be the most highly active and polymerisation is well controlled, as evidenced by the linear relationship between the molecular weight and both the monomer conversion and the monomer‐to‐initiator ratio. Mechanistic studies reveal significant interactions between the monomer, initiator and catalyst and that the polymerisation is first order with respect to each of these components. These observations indicate that the polymerisation operates by a general base/pseudo‐anionic mechanism.     

Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands

By judiciously anchoring functional groups onto chiral ionic liquids, functionalized chiral ionic liquids (FCILs) are emerging as a new type of asymmetric organocatalysts and nonclassical chiral ligands. This Focus Review highlights the applications of FCILs from the viewpoint of asymmetric catalysis. We focus mainly on the de novo designed and synthesized FCILs which likely still maintain the typical ionic liquids properties, and in a few cases relevant ionic liquid immobilized chiral catalysts are briefly discussed.     

The versatile,functional polyether,polyepichlorohydrin: History,synthesis, and applications

Polyepichlorohydrin (PECH) is a functional polyether first synthesized in the 1950's by the catalytic ring opening polymerization of epichlorohydrin (ECH), its inexpensive epoxide pre-cursor. PECH elastomers are used in diverse commercial applications due to their unique combination of properties including low temperature flexibility and heat and oil resistance. PECH holds an interesting place in polymer history as its synthesis led to the discovery of highly effective aluminum-based catalysts for epoxide polymerizations and a new class of high molecular weight polyether elastomers by an exceptional polymer chemist, Edwin J. Vandenberg. ECH is an ideal feedstock for polymer materials as it is functional, inexpensive, and produced through environmentally friendly means. However, due to the alkyl chloride pendant, polymerizations involving ECH are difficult and limited synthetic advancement has occurred until very recently. This focused review will discuss modern polymerization methods involving ECH while giving a historical perspective on the evolution of these techniques. We will also review applications of ECH-based polymers and discuss the future development of these materials. We hope to convince the reader to explore ECH-based materials in their own work.     

Ring‐opening polymerization and copolymerization of cyclic esters catalyzed by amidinate aluminum complexes

A series of new alkyl mono‐ and bimetallic aluminum complexes supported by novel amidinate ligands has been prepared in very high yields. These complexes were fully characterized by spectroscopic methods. Alkyl aluminum complexes 1 – 6 were investigated as catalysts for the ring‐opening polymerization and copolymerization of ε‐caprolactone and L‐lactide. Under the optimal reaction conditions, complex 5 acts as an efficient single‐component initiator for the ring‐opening polymerization and copolymerization of cyclic esters to yield biodegradable polyester materials with narrow polydispersities. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2397–2407     

Progress in Polymerization of Cyclic Esters: Mechanisms and Synthetic Applications

Recent advances in the controlled ring-opening polymerization of aliphatic cyclic esters are briefly reviewed. Particular attention is paid to the high molecular weight linear, branched, and star-shaped poly(lactide)s and poly(ε-caprolactone) synthesis. It is concluded that despite the plethora of initiating and/or catalytic systems applied for this purpose the best results so far were achieved with Al- and Sn(II) derivatives. Analytical methods employed for aliphatic polyesters of various architectures characterization, including SEC-MALLS, LC-CC, and fluorescence spectroscopy, are also discussed.     

戊二酸锌催化环氧丙烷与马来酸酐开环共聚反应

以戊二酸锌为催化剂,在无溶剂条件下催化环氧丙烷与马来酸酐的开环共聚反应;优化了聚合条件,利用红外光谱和核磁共振谱研究了共聚物的结构,利用凝胶渗透色谱测定了其分子量.结果表明,戊二酸锌可以有效地催化马来酸酐与环氧丙烷的开环共聚,从而以较高转化率得到交替度较高的共聚物.     

Direct synthesis of terminally “clickable” linear and hyperbranched polyesters

1,3‐Dipolar cycloaddition of an organic azide and an acetylenic unit, often referred to as the “click reaction”, has become an important ligation tool both in the context of materials chemistry and biology. Thus, development of simple approaches to directly generate polymers that bear either an azide or an alkyne unit has gained considerable importance. We describe here a straightforward approach to directly prepare linear and hyperbranched polyesters that carry terminal propargyl groups. To achieve the former, we designed an AB‐type monomer that carries a hydroxyl group and a propargyl ester, which upon self‐condensation under standard transesterification conditions yielded a polyester that carries a single propargyl group at one of its chain‐ends. Similarly, an AB₂ type monomer that carries one hydroxyl group and two propargyl ester groups, when polymerized under the same conditions yielded a hyperbranched polymer with numerous “clickable” propargyl groups at its molecular periphery. These propargyl groups can be readily clicked with different organic azides, such as benzyl azide, ω‐azido heptaethyleneglycol monomethylether or 9‐azidomethyl anthracene. When an anthracene chromophore is clicked, the molecular weight of the linear polyester could be readily estimated using both UV–visible and fluorescence spectroscopic measurements. Furthermore, the reactive propargyl end group could also provide an opportunity to prepare block copolymers in the case of linear polyesters and to generate nanodimensional scaffolds to anchor a variety of functional units, in the case of the hyperbranched polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3200–3208, 2010     

Simple, but challenging: recent developments in the asymmetric synthesis of spiroketals

Impressive and elegant approaches to the enantioselective synthesis of spiroketals starting from achiral substrates have been described recently. These strategies based on transition-metal catalysis and organocatalysis hold great potential for further applications.     

Catalytic non-conventional trans-hydroboration: a theoretical and experimental perspective

We have studied the non-conventional trans-hydroboration reaction of alkynes both experimentally and theoretically. A catalytic system based on the in situ mixture of [{Rh(cod)Cl}(2)]/PCy(3) (cod=1,5-cyclooctadiene, Cy=cyclohexyl) has been able to activate pinacolborane and catecholborane and transfer boryl and hydride groups onto the same unhindered carbon atom of the terminal alkynes. The presence of a base (Et(3)N) favored the non-conventional trans-hydroboration over the traditional cis-hydroboration. Varying the substrate had a significant influence on the reaction, with up to 99% conversion and 94% regioselectivity observed for para-methyl-phenylacetylene. Both DFT and quantum mechanical/molecular mechanical ONIOM calculations were carried out on the [RhCl(PR(3))(2)] system. To explain the selectivity towards the (Z)-alkenylboronate we explored several alternative mechanisms to the traditional cis-hydroboration, using propyne as a model alkyne. The proposed mechanism can be divided into four stages: 1) isomerization of the alkyne into the vinylidene, 2) oxidative addition of the borane reagent, 3) vinylidene insertion into the Rh-H bond, and finally 4) reductive elimination of the C-B bond to yield the 1-alkenylboronate. Calculations indicated that the vinylidene insertion is the selectivity-determining step. This result was consistent with the observed Z selectivity when the sterically demanding phosphine groups, such as PCy(3) and PiPr(3), were introduced. Finally, we theoretically analyzed the effect of the substrate on the selectivity; we identified several factors that contribute to the preference for aryl alkynes over aliphatic alkynes for the Z isomer. The intrinsic electronic properties of aryl substituents favored the Z-pathway over the E-pathway, and the aryl groups containing electron donating substituents favored the occurrence of the vinylidene reaction channel.     

The synthesis and study of the photoinitiated cationic polymerization of novel cycloaliphatic epoxides

The synthesis of a series of difunctional epoxides bearing two epoxycyclohexyl groups linked together by an alkylene ether group has been carried out. Subsequently, the reactivities of these novel monomers was investigated and compared to the reactivity of the cycloali-phatic epoxide, 3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexane carboxylate ( I ) in pho-toinitiated cationic polymerization. It was observed that alkylene oxide linking the two epoxycyclohexyl groups was short and the monomers are more reactive than I . The effects of the photoinitiator structure and the experimental conditions of the cationic photopo-lymerization on the rates was also studied using real-time infrared spectroscopy. © 1995 John Wiley & Sons, Inc.     

(Thio)Amidoindoles and (Thio)Amidobenzimidazoles: An Investigation of Their Hydrogen‐Bonding and Organocatalytic Properties in the Ring‐Opening Polymerization of Lactide

The mechanism of the ring‐opening polymerization (ROP) of lactide catalyzed by two partner hydrogen‐bonding organocatalysts was explored. New amidoindoles 4 a , c , thioamidoindoles 4 b , d , amidobenzimidazoles 5 a , c , and thioamidobenzimidazoles 5 b , c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self‐association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b , which activates the growing polymer chain through hydrogen‐bonding. Reactions were conducted in 2–24 h at 20 °C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4 / 5 + 3 . ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine‐tune the catalytic properties of (thio)amides and organocatalysts, more generally.     

Anionic alternating copolymerization of 3,4‐dihydrocoumarin and glycidyl ethers: A new approach to polyester synthesis

Anionic copolymerizations of 3,4‐dihydrocoumarin (DHCM) and a series of glycidyl ethers (n‐butyl glycidyl ether, tert‐butyl glycidyl ether, and allyl glycidyl ether) with 2‐ethyl‐4‐methylimidazole as an initiator proceeded in a 1:1 alternating manner to give the corresponding polyesters, whose structures were confirmed by spectroscopic analyses and reductive scission of the ester bonds in the main chain with lithium aluminum hydride, followed by detailed analyses of the resulting fragments. The polyester obtained by the copolymerization of DHCM and allyl glycidyl ether inherited the allyl groups in the side chain, whose applicability to chemical modifications of the polyester was successfully demonstrated by a platinum‐catalyzed hydrosilylation reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4092–4102, 2008     

Recent Advances in Metal-Mediated Stereoselective Ring-Opening Polymerization of Functional Cyclic Esters towards Well-Defined Poly(hydroxy acid)s: From Stereoselectivity to Sequence-Control

Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring-opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side-chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico–chemical properties, and ultimately, widening their range of uses. Here, we highlight a few important advances in metal-mediated stereoselective ROP of cyclic esters towards the synthesis of (functional) stereoregular poly(hydroxy acid)s that have recently been disclosed, emphasizing on (functional) β- and γ-lactones, diolide and O-carboxyanhydride (OCA) monomers and yttrium-based catalysis. Fine-tuning of the substituents flanked on the catalyst ligand enables reaching poly(hydroxy acid)s with syndiotactic and also isotactic microstructures. The stereocontrol mechanisms at work and their probable origin, relying on steric but also electronic factors imparted in particular by the ligand substituents, are discussed. Taking advantage of such stereoselective ROPs, original copoly(hydroxy acid)s with gradient or alternated patterns then become accessible from the use of mixtures of chemically different, oppositely configured enantiopure monomers.     

The incorporation of rigid diol monomers into poly(butylene terephthalate) via solid‐state copolymerization and melt copolymerization

Incorporation of 2,2‐bis[4‐(2‐hydroxyethoxy)phenyl]propane (Dianol 220®) into poly(butylene terephthalate) (PBT) via solid‐state copolymerization (SSP) showed that Dianol, besides being the reactant, also acts as a swelling agent for rigid amorphous PBT chain segments. Being swollen, these amorphous chain segments become sufficiently mobile to contribute to the SSP process. The thermal behavior of the resulting copolyesters is comparable with melt copolymerized copolymers, although having a different chemical microstructure. The main reason is a full miscibility in the melt of unmodified PBT chain segments and modified chain segments, which eliminates the advantages of a blocky microstructure for the SSP copolyesters. However, incorporation of 2,2′‐biphenyldimethanol (BDM) into PBT resulted in a higher crystallization temperature compared with PBT–Dianol copolymers of equal composition. Preordering of polymer chains in the melt by incorporating rigid, phase separating BDM‐moieties, preferably via SSP to obtain a non‐random distribution, may be the origin of the enhanced crystallization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1203–1217, 2008     

Regioselective lithiation of benzyl imidazole: Synthesis and evaluation of new organocatalysts for trans-diol functionalization.

Abstract

Benzyl imidazole was successfully lithiated using n-BuLi at ?78?°C and verified by deuterium incorporation. The chemical reaction of the lithiated benzimidazole was explored with a series of different electrophiles. This approach was utilized to synthesize new anti and syn diphenyl organocatalysts for trans-diol functionalization.     

Cooperative Activation with Chiral Nucleophilic Catalysts and N‐Haloimides: Enantioselective Iodolactonization of 4‐Arylmethyl‐4‐pentenoic Acids

Chiral triaryl phosphates promote the enantioselective iodolactonization of 4‐substituted 4‐pentenoic acids to give the corresponding iodolactones in high yields with high enantioselectivity. N‐Chlorophthalimide (NCP) is employed as a Lewis acidic activator and oxidant of I₂ for the present iodolactonization. In combination with 1.5 equivalents of NCP, only 0.5 equivalents of I₂ are sufficient to generate the iodinating reagent.