Ring-Opening Polymerization with Lewis Pairs and Subsequent Nucleophilic Substitution: A Promising Strategy to Well-Defined Polyethylene-like Polyesters without Transesterification

Ring-opening polymerization (ROP) of ω-pentadecalactone (PDL) catalyzed by Lewis pairs was thoroughly explored, and a novel approach to well-defined aliphatic long chain polyester with high molecular weight (MW) was developed in the present work. The Zn­(C₆F₅)₂/1,8-diazabicyclo­[5.4.0]­undec-7-ene (DBU) Lewis pair was proved to be a promising catalytic system for ROP of PDL, producing cyclic PPDL with high MW (<i>M</i>_w > 100 kg/mol) and relatively low polydispersity index (<i>M</i>_w/<i>M</i>_n = 1.6–1.9). Strikingly, no transesterification occurred in the ROP of PDL by Zn­(C₆F₅)₂/DBU. The cyclic topology of the polyester could be switched to linear structure in the presence of alcohol. The feeding mode and the structure of alcohol significantly influence the ROP. Compared with mixing alcohol with Zn­(C₆F₅)₂/DBU at first, adding Ph₂CHOH with low nucleophilicity after full monomer conversion could afford linear PPDL without transesterification. It was noted that random chain scission or chain extension was not detected after adding Ph₂CHOH. Well-defined block copolymer containing polyethylene-like segment can be easily prepared by sequential addition of PDL and lactide (LA) or caprolactone (CL). Cyclic block copolyesters <i>c</i>-poly­(PDL-<i>b</i>-CL) and <i>c</i>-poly­(PDL-<i>b</i>-LA) were obtained in the absence of alcohol. The blocky structures can be maintained even when prolonging reaction time after full monomer conversion. Similarly, introducing Ph₂CHOH before quenching the polymerization led to well-defined linear block copolyesters <i>l</i>-poly­(PDL-<i>b</i>-CL) and <i>l</i>-poly­(PDL-<i>b</i>-LA)

Synthesis of Novel Cyclic Olefin Copolymer (COC) with High Performance via Effective Copolymerization of Ethylene with Bulky Cyclic Olefin

Novel cyclic olefin copolymer (COC) with high glass transition temperature, good mechanical performance, high transparency, and excellent film forming ability has been achieved in this work by effective copolymerization of ethylene and exo-1,4,4a,9,9a,10-hexahydro-9,10­(1′,2′)-benzeno-l,4-methanoanthracene (HBMN). This bulky cyclic olefin comonomer can be simply prepared in good yield via Diels–Alder reaction. By utilizing constrained geometry catalyst (CGC) activated with Al­(^<i>i</i>Bu)₃/[Ph₃C]­[B­(C₆F₅)₄], ethylene/HBMN copolymer can be obtained with excellent production, high molecular weight, and a wide range of HBMN incorporation. ¹³C NMR (DEPT) spectra reveal alternating ethylene–HBMN sequence can be detected at high HBMN incorporation. The glass transition temperature (<i>T</i>_g) of resulted copolymer enhances with increasing HBMN incorporation. A high <i>T</i>_g up to 207.0 °C is attainable at low comonomer incorporation of 30.4 mol %, which is 61 °C higher than that of commercial norbornene (NB)-derived COC (54 mol %). The tensile test indicates that the ethylene/HBMN copolymer has good mechanical performance which is more flexible than ethylene/NB copolymer and the previously reported COC even at a higher <i>T</i>_g level

Synthesis and Reaction of Anthracene-Containing Polypropylene: A Promising Strategy for Facile, Efficient Functionalization of Isotactic Polypropylene

A novel anthracene-containing <i>isotactic</i> polypropylene (An-<i>i</i>PP) with high molecular weight (>10 × 10⁴) and satisfying incorporation (5.7 mol %) was synthesized via direct copolymerization of propylene and 9-hexenyl­anthracene. The pendent anthryl group of the resulting An-<i>i</i>PP is quite active, and this provides a facile and efficient avenue to synthesize various functional <i>i</i>PPs. As a typical and important example, maleic anhydride (MA) functionalized polypropylene, was successfully prepared in a highly efficient, catalyst-free, byproduct-free, and controllable way via mild Diels–Alder (D–A) reaction between pendent anthryl groups and MA. More importantly, the D–A functionalization process did not sacrifice the original properties of the An-<i>i</i>PP, as no unfavorable degradation and cross-linking were detected in DSC and GPC analyses. Besides MA, several other dienophiles could also be conveniently used as functional reagents to prepare various functionalized <i>i</i>PPs with distinct properties. The unique fluorescent property of An-<i>i</i>PP was studied and could be used for functionalization process monitoring

Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers

Several nickel complexes bearing sterically bulky phosphino-phenolate ([P,O]) ligands were synthesized and explored as catalysts for olefin (co)­polymerization. In the absence of an activator, the complexes showed very high catalytic activities (up to 10⁷ g mol_Ni^–1 h^–1) for ethylene polymerization even at 90 °C or with the addition of a large amount of a polar additive (such as ethyl alcohol, diethyl ether, acetone, or even water), affording linear polymers with high molecular weights (up to 6.53 × 10⁵). In contrast, most of the previously reported nickel catalysts suffer from severe activity suppression at elevated temperature. It is rare that a catalyst has so many good performances simultaneously, including high catalytic activity, good tolerance for polar groups, strong thermal stability, and yielding high molecular weight linear polyethylene. Most importantly, these bulky nickel complexes used in this study also effectively copolymerized ethylene with challenging polar vinyl monomers, including commercially available acrylates and an acrylamide. As we expected, introducing a bulky substituent group on the phosphorus atom of the complex was vital for enhanced catalytic activity and the formation of high molecular weight linear copolymers. Microstructure analyses revealed that the polar functional units were mainly incorporated into the polymer main chain and also located at the chain end with insertion percentages of up to 7.4 mol %. The bulky [P,O] neutral nickel complexes reported herein are promising alternatives to the well-established palladium catalysts for direct copolymerization of olefins with commercially available polar vinyl comonomers

Transmission pathways of <i>S. japonicum</i> in China.

<p>The oblique lines show the blocking of the bovine to snail pathway employed in the model; this prevents miracidia that hatch from eggs excreted by bovines from infecting oncomelanid snail intermediate hosts.</p

Model predictions of steady-state (continued transmission without intervention) <i>S. japonicum</i> transmission (Blue dotted line) and simulation of the removal of <i>S. japonicum</i> transmission attributable to water buffaloes (Red solid line).

<p>A) Human prevalence and incidence scenario 1 (Yongfu village); B) Human prevalence and incidence scenario 2 (Mengjiang village); C) Human prevalence and incidence scenario 3 (Xindong village); D) Human prevalence and incidence scenario 4 (Yongfu village+hypothetical low <i>S. japonicum</i> prevalence in buffaloes; E) Human prevalence and incidence scenario 5 (Mengjiang village+hypothetical low <i>S. japonicum</i> prevalence in buffaloes); F) Human prevalence and incidence scenario 6 (Xindong village+hypothetical low <i>S. japonicum</i> prevalence in buffaloes.</p

Featured Crystallization Polymorphism and Memory Effect in Novel Butene-1/1,5-Hexadiene Copolymers Synthesized by Post-Metallocene Hafnium Catalyst

New butene-1/1,5-hexadiene copolymers with 0–2.15 mol % methylene-1,3-cyclopentane (MCP) co-units were synthesized by dimethyl­pyridylamido­hafnium/organoboron catalyst, which for the first time introduces structural unit of five-carbon ring type into the polybutene-1 main chain. The effects of these novel co-units on the crystallization polymorphism, and the featured memory effect that often appears above the equilibrium melting point in copolymers, were investigated with differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. First of all, it was found that the hexagonal form I′ can directly crystallize from the melt in the copolymers possessing the two highest co-unit concentrations of 0.65 and 2.15 mol %. With just 2.15 mol % co-unit, pure form I′ crystallites were obtained by the isothermal crystallization at 65 °C, whereas pure form II appeared at 25 °C and a crystallite mixture of form I′ and form II was generated in the intermediate temperature region. Such dependence in butene-1/1,5-hexadiene copolymer that high temperature favors form I′ formation is opposite to the case of butene-1/propylene copolymer, where low temperature induces more form I′. Second, the crystallization kinetics depends on the temperature of initial melt, referred to a memory effect due to the local segregation of long crystallizable segments in the heterogeneous melt. The critical temperature for observing this memory effect decreases with increasing the incorporation. Interestingly, this memory effect has no influence on the modification of the formed crystallites, though the crystallization kinetics is significantly accelerated

Model parameters and predictions after removal of water buffalo transmission of <i>S. japonicum</i> for different endemic scenarios using field epidemiological data from villages in the Dongting (Hunan Province) and Poyang (Jiangxi Province) Lake Areas of Southern China.

<p>R₀ = Reproductive Rate (before removal of water buffalo transmission); R₁ = Reproductive Rate (after removal of water buffalo transmission).</p><p>B_Tx = Contribution of buffaloes to human <i>S. japonicum</i> transmission.</p><p><i>S.j</i> = <i>S. japonicum</i>.</p>a<p>Hypothetical value.</p

Syntheses of Well-Defined Functional Isotactic Polypropylenes via Efficient Copolymerization of Propylene with ω‑Halo-α-alkenes by Post-metallocene Hafnium Catalyst

Catalyzed by the (pyridylamido)­hafnium/organoboron system, a series of halogen-functionalized isotactic polypropylenes were synthesized via the stereospecific copolymerization of propylene with ω-halo-α-alkenes. The (pyridylamido)­hafnium/organoboron system has been proved to be a potent catalyst for propylene/ω-iodo-α-alkenes copolymerization, producing well-defined poly­(propylene-<i>co</i>-ω-iodo-α-undecene)­s with outstanding properties. The high molecular weight (<i>M</i>_w > 100 kg mol^–1) functional <i>i</i>PPs possessing abundant iodoalkene units (up to 11.7 mol %) and unimodal molecular weight distributions (<i>M</i>_w/<i>M</i>_n ≈ 2) could be easily obtained under mild conditions with excellent catalytic activity. High isotactic selectivity of monomers, including propylene and polar comonomer, was unexpectedly observed ([mmmm] > 99%). Moreover, based on the unique copolymerization process and the highly reactive sites on the copolymers, the halogen groups of the resultant copolymers could be easily transformed into other polar groups via click chemistry, and the new functional <i>i</i>PPs with high molecular weights and abundant polar groups could be efficiently obtained

Modulating Polymerization Behaviors of Ether–Ester Monomers and Physicochemical Properties of Poly(ether-<i>alt</i>-ester)s by Heteroatom Substitutions

The design of cyclic monomers is crucial for the development of polymers with ideal thermal and mechanical properties by ring-opening polymerization. Herein, we provide a systematic investigation into the thio-modification effects on the polymerization behavior of cyclic ether–ester monomers and the final properties of the corresponding poly(ether-alt-ester)s. The position of thio-modification significantly affected the polymerization thermodynamics and thus could regulate the ceiling temperature (Tc). O-to-S substitutions in the monomer′s ether/ester sites would increase the monomer′s α-H acidity, and the catalytic system strictly determined the chain initiation process as well as the chain-end groups. Density functional theory calculations and experimental studies revealed that O-to-S substitutions at the ester site would significantly accelerate the polymerization under the same conditions, thanks to the high reactivity of the thioester group and strong nucleophilicity of the chain end. The resulting poly(ether-alt-ester)s exhibited crystallinity, precisely tunable physicochemical properties, high recyclability, and high-density polyethylene-like mechanical properties, which exemplifies the potential of heteroatom modification in modulating the poly(ether-alt-ester)′s properties. This detailed investigation of structure–(de)polymerizability and structure–property relationships will inspire future monomer design toward poly(ether-alt-ester)s with high performance