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Polypeptide brushes are attractive platforms to generate functional and responsive interfaces that are of potential interest due to their possible biodegradability, biocompatibility and tunable secondary structures. Surface-initiated ringopening polymerization (SI-ROP) of α-amino acid N-carboxyanhydrides represents a powerful and versatile strategy to generate polypeptide brushes. This review is an attempt to capture the state-of-the-art in this field and highlights the latest developments in several selected areas. In addition to presenting an overview of the synthetic methods that have been used to generate polypeptide brushes via SI-ROP, this article will discuss the preparation of patterned polypeptide brushes, the conformational properties of surface-tethered polypeptides, ways to control chain orientation at surfaces as well as properties and applications of these thin polymer films. [ABSTRACT FROM AUTHOR]

Design and synthesis of biodegradable stimuli-responsive polypeptides are important areas considering their promising applications in biomedical fields. This article summarizes the most recent progresses in the development of stimuli-responsive polypeptide materials prepared via ring-opening polymerization of α-amino acid N-carboxyanhydrides. We discuss the design, synthesis and structure-property correlation of emerging materials including thermo-responsive, redox-responsive, photo-responsive and biomolecule responsive polypeptides. Considering the unique structural features of amino acids, we try to emphasize that the thermo-responsive properties not only depend on the amino acid structure but also rely on the secondary structures of polypeptides. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 [ABSTRACT FROM AUTHOR]

Comprehensive Summary Copolymerization as an efficient strategy can provide an opportunity to create new closed‐loop recyclable polymeric materials with tailored properties that are generally inaccessible to the individual homopolymers. In this contribution, the bulk ring‐opening copolymerization of bio‐renewable δ‐caprolactone and trans‐hexahydro‐(4,5)‐benzofuranone was achieved to produce closed‐loop recyclable copolyesters by using an organobase/urea binary catalyst at room temperature. The obtained copolyesters exhibited composition‐dependent thermal properties. Remarkably, the obtained copolyesters were able to depolymerize back to recover the corresponding monomers under mild conditions. The copolyesters with suitable compositions can be directly used as pressure‐sensitive adhesives (PSAs) that possessed comparable peel strength with the commercially available PSA scotch tapes. When the copolyesters were mixed with plasticizers, the as‐prepared PSAs exhibited desirable adhesive failure and can be used as removable post‐it note. [ABSTRACT FROM AUTHOR]

Borane‐based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane‐based LPs are moisture‐ and air‐sensitive. Therefore, development of moisture and air‐stable borane‐based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP‐1B featuring poly(4‐vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP‐1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h−1). Furthermore, it enables generation of well‐defined telechelic poly (CHO‐alt‐CO2) diol (0.6–15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers. [ABSTRACT FROM AUTHOR]

Borane‐based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane‐based LPs are moisture‐ and air‐sensitive. Therefore, development of moisture and air‐stable borane‐based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP‐1B featuring poly(4‐vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP‐1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h−1). Furthermore, it enables generation of well‐defined telechelic poly (CHO‐alt‐CO2) diol (0.6–15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Substantial progresses have been made toward the development of metal‐free catalysts for stereoselective ring‐opening polymerization (ROP) of rac‐lactide. Yet the discovery of organic catalysts effective at ambient temperature remains a major challenge. Here, the bifunctional H‐bonding catalyst SQ‐1 containing a basic tertiary amine and squaramide motif proved to be good candidate for the stereoselective ROP of rac‐lactide at room temperature, yielding stereoregular polylactide with controlled molecular weights (up to 21.1 kg/mol) and high tacticity (PiESC up to 0.88). Furthermore, binary H‐bonding catalytic system consisting of squaramides (SQ‐2 to SQ‐6) and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) could efficiently promote the ROP of rac‐lactide at room temperature within short reaction time. Among them, the most bulky squaramide SQ‐2 exhibited the best steroselectivity towards the ROP of rac‐lactide without transesterification side reactions during the polymerization process. The resulting polylactides were proved to have controlled molecular weights as high as 22.2 kg/mol and narrow distributions (1.10—1.24). [ABSTRACT FROM AUTHOR]

Although great successes have been achieved, the preparation of closed‐loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether‐ester monomers by upcycling of poly(3‐hydroxybutyrate) bioplastic. The "living"/controlled ring‐opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well‐defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi‐crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed‐loop life cycle. [ABSTRACT FROM AUTHOR]

Although great successes have been achieved, the preparation of closed‐loop recyclable polyesters with high working temperatures still remains as a big challenge. Herein, we present the syntheses of a series of enantiopure bicyclic ether‐ester monomers by upcycling of poly(3‐hydroxybutyrate) bioplastic. The "living"/controlled ring‐opening polymerizations of these enantiopure monomers to produce stereoregular polyesters with controlled molecular weights and well‐defined chain ends were achieved. The effects of stereoconfiguration and substituent on polymerization kinetics and thermodynamics as well as the thermal properties of resultant polyesters were investigated. Of note, the stereoregular polyesters are semi‐crystalline materials with melting temperatures up to 176 °C, even higher than the commodity polyolefin plastics. These polyesters can be depolymerized back to recover pristine monomers, thus successfully establishing a closed‐loop life cycle. [ABSTRACT FROM AUTHOR]

Smart polymeric materials have received extensive attention for various applications. Here, we reported a facile and efficient approach to prepare a class of pegylated polypeptoids by a combination of ring-opening polymerization (ROP) and post-modification strategy. Three different initiators were involved to mediate the polymerization of the monomers. Unlike the previously reported pegylated polypeptoids, the obtained polypeptoids show completely reversible thermoresponsive behaviors in aqueous solution after 8 heating and cooling cycles. In addition, the phase transition of the polypeptoid solutions can be very sharp (ΔT < 5 °C), which is comparable to poly( N -isopropylacrylamide) (PNIPAM). The influence of temperature on solution properties of the polypeptoids has been systematically studied. The clouding points (CPs) of the polypeptoids are highly tunable depending on the degree of polymerization (DP), the side-chain length, and the polymer concentration. We demonstrate that the thermoresponsive property of the polypeptoid may possibly arise from the incorporation of thioether groups and the branched molecular architecure of side chains. These features enable the pegylated polypeptoids potential candidates for next generation of smart polymeric materials. [ABSTRACT FROM AUTHOR]

The low temperature condition, long reaction time and associated high energy inputs involved in the polymerization process still hampered the scalable production of poly(γ‐butyrolactone) (PγBL) via ring‐opening polymerization (ROP) of low strained γBL due to its unfavorable thermodynamics. In this contribution, we presented the rapid ROP of γBL using a bisurea in combination with an organophosphazene base as the binary catalyst. Well‐defined PγBL samples with various terminal groups were prepared by using different alcohol initiators. The bisurea as a co‐catalyst exhibited much higher catalytic activity even compared to the most active monourea in previous report as supported by the kinetic experiments. A moderate monomer conversion of 61% was achieved within 10 mins, producing high‐molecular‐weight PγBL with Mn up to 37.5 kDa and good mechanical properties. The short polymerization time considerably reduced the energy cost for the ROP of γBL conducted at low temperature condition. This study may clear away obstacles for the scalable production and practical applications for PγBL. [ABSTRACT FROM AUTHOR]

It is a highly attractive strategy to develop chemically recyclable polymers to establish a circular plastic economy. Despite the recent advancements, chemically recyclable polymers still face challenges including high energy cost for polymer preparation or recycling, poor monomer recovery selectivity and efficiency as well as undesired material performance. In this contribution, we present the chemoselective controlled ring‐opening polymerization of bio‐renewable bifunctional α‐methylene‐δ‐valerolactone (MVL) to produce exclusive functionalizable polyester using strong base/urea binary catalysts. The obtained polyester with high molar mass exhibits good tensile strength comparable to that of some commodity plastics. Remarkably, the obtained polyester can be depolymerized to recover pristine monomer with a 96 % yield by thermolysis, thus successfully establishing a closed‐loop life cycle. [ABSTRACT FROM AUTHOR]

It is a highly attractive strategy to develop chemically recyclable polymers to establish a circular plastic economy. Despite the recent advancements, chemically recyclable polymers still face challenges including high energy cost for polymer preparation or recycling, poor monomer recovery selectivity and efficiency as well as undesired material performance. In this contribution, we present the chemoselective controlled ring‐opening polymerization of bio‐renewable bifunctional α‐methylene‐δ‐valerolactone (MVL) to produce exclusive functionalizable polyester using strong base/urea binary catalysts. The obtained polyester with high molar mass exhibits good tensile strength comparable to that of some commodity plastics. Remarkably, the obtained polyester can be depolymerized to recover pristine monomer with a 96 % yield by thermolysis, thus successfully establishing a closed‐loop life cycle. [ABSTRACT FROM AUTHOR]

Asymmetric and symmetric L-lysine N-carboxylic anhydrides based on perylene bisimide derivatives were successfully synthesized and grafted onto silicon wafers via surface-initiated ring-opening polymerization. The grafted n-type semiconductor film was flat and compact, and its thickness could be tuned by variation of the polymerization conditions. [ABSTRACT FROM AUTHOR]

The development of chemically recyclable polymers presents the most appealing solution to address the plastics' end‐of‐use problem. Despite the recent advancements, it is highly desirable to develop chemically recyclable polymers from commercially available monomers to avoid the costly and time‐consuming commercialization. In this contribution, we achieve the controlled ring‐opening polymerization (ROP) of bio‐sourced δ‐caprolactone (δCL) using strong base/urea binary catalysts. The obtained PδCL is capable of chemical recycling to δCL in an almost quantitative yield by thermolysis. Sequential ROP of δCL and l‐lactide (l‐LA) affords well‐defined PLLA‐b‐PδCL‐b‐PLLA triblock copolymers, which behave as thermoplastic elastomers with excellent elastic recovery, tensile strength and ultimate elongation. The upcycling of PLLA‐b‐PδCL‐b‐PLLA to recover ethyl lactate and δCL with high yields is achieved by refluxing with ethanol and then distillation under reduced pressure. [ABSTRACT FROM AUTHOR]

The development of chemically recyclable polymers presents the most appealing solution to address the plastics' end‐of‐use problem. Despite the recent advancements, it is highly desirable to develop chemically recyclable polymers from commercially available monomers to avoid the costly and time‐consuming commercialization. In this contribution, we achieve the controlled ring‐opening polymerization (ROP) of bio‐sourced δ‐caprolactone (δCL) using strong base/urea binary catalysts. The obtained PδCL is capable of chemical recycling to δCL in an almost quantitative yield by thermolysis. Sequential ROP of δCL and l‐lactide (l‐LA) affords well‐defined PLLA‐b‐PδCL‐b‐PLLA triblock copolymers, which behave as thermoplastic elastomers with excellent elastic recovery, tensile strength and ultimate elongation. The upcycling of PLLA‐b‐PδCL‐b‐PLLA to recover ethyl lactate and δCL with high yields is achieved by refluxing with ethanol and then distillation under reduced pressure. [ABSTRACT FROM AUTHOR]

We investigated the ring opening polymerization (ROP) of di- and tri-ethylene glycol monomethyl ether functionalized L-glutamate N-carboxyanhydrides (NCAs) using hexamethyldisilazane (HMDS) as primary initiator and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) as co-initiator. The binary initiator system afforded a living ROP for these pegylated NCAs, and a series of homopolypeptides with controlled molecular weight (MW) and low polydispersity were obtained. We then systematically studied the helical content and clouding point (CP) dependence on polypeptide MW using circular dichroism (CD) spectroscopy and turbidity measurements, respectively. We found that the helical content of both homopolypeptides increased with MW, but the triethylene glycol functionalized poly-L-glutamate (poly-L-EGGlu) intended to form more stable α-helical structure than diethylene glycol functionalized counterpart (poly-L-EGGlu) at similar MW. Accordingly, the CP of poly-L-EGGlu with known end group has strong dependence on its helical content, which is essentially determined by MW. Our results suggested that the thermal responsive properties of these unique pegylated poly-L-glutamates not only rely on their chemical structure but also on their secondary structures, which is different from conventional thermal responsive polymers. [ABSTRACT FROM AUTHOR]

The eco-environmentally PVLs without catalyst-residue have been facilely synthesized using heterogeneous PS- t -BuP 2 catalyst by simple filtration and without tedious purification process. • The heterogeneous catalyst PS- t -BuP 2 was employed for ROP of δ -VL. • PS- t -BuP 2 is easily recovered and reusable for five cycles without deactivation. • PVLs without catalyst-residue are synthesized using PS- t -BuP 2 by simple filtration. We demonstrated that the dimeric 1- tert -butyl-2,2,4,4,4-pentakis(dimethylamino)-2Λ5, 4Λ5-catenadi(phosphazene) supported on polystyrene (PS- t -BuP 2 ) was an efficient and recyclable catalyst for the ring-opening polymerization (ROP) of δ -valerolactone (δ -VL). The heterogeneous catalyst PS- t -BuP 2 could be recycled and reused for five consecutive cycles without significant decrease of catalytic activity. The monomer conversions maintained between 79% and 85% for five cycles. Using BnOH as initiator, the produced polyvalerolactones (PVLs) had controlled molecular weights (MWs) and narrow MW distributions (Đ), and the products were free of catalyst by simple filtration. The 1H NMR and MALDI-TOF characterizations of the obtained PVLs clearly indicated the presence of the initiator residue at the chain end. [ABSTRACT FROM AUTHOR]

Graphical abstract The binary organocatalytic system comprised of CTPB and ureas is developed and shows both of high activity and selectivity for the ROP of cyclic esters. Highlights • A simple and synergetic binary catalytic system containing CTPB and urea has been developed. • The ROP of ε -CL and δ -VL was highly controlled. • The linear and three-arm star block copolymers were readily prepared. • The synergetic bifunctional mechanism was investigated. Abstract Phosphazenes have attracted considerable attention in the field of ring-opening polymerization (ROP) of cyclic esters. However, the application of phosphazenes as catalyst is subject to a trade-off between activity and selectivity (chain propagation versus transesterification/back-biting reaction, e.g., controlled polymerization). Despite extensive research efforts, the development of a new catalytic system having concurrent high activity and selectivity remains a great challenge. In this work, we report that the binary organocatalytic system comprised of cyclic trimeric phosphazene base (CTPB) and ureas shows both of high activity and selectivity for the ROP of ε -caprolactone (ε -CL) and δ -valerolactone (δ -VL) in the presence of alcohol as initiator. It is found that the introduction of ureas would significantly increase the catalytic selectivity during ROP without sacrificing the catalytic activity of CTPB. Moreover, the polymerizations catalyzed by the title catalytic system exhibit immortal characteristics and thus thousands equivalent of monomer could be converted to polymer efficiently with desired MWs and microstructures. Linear diblock copolymer AB and star copolymers (AB) 3 with three identical diblock arms could be readily synthesized by sequential copolymerization using different alcohols as initiators. [ABSTRACT FROM AUTHOR]

Al complexes bearing amino-quinoline ligands rapidly converted hundreds even thousands equiv. of ε-CL into PCLs with high conversions in a living and/or immortal manner. [Display omitted] • A series of Al complexes (Al1 − Al5) bearing N,N-bidentate amino-quinoline ligands were synthesized and fully characterized. • Al complexes Al1 − Al5 could catalyze fast and living ring-opening polymerization (ROP) of ε -caprolactone (ε -CL). • Polycaprolactones (PCLs) with high molecular weights (M n up to 129 kDa) and narrow dispersity (Đ = 1.16) were readily synthesized. • An extremely low loading of Al complex (0.05 mol% to ε -CL monomer) was efficient for ROP of ε -CL to prepare PCL with desired M n and narrow distribution in an immortal manner. Catalysts drive innovation in sustainable polymers because of their reactivity and selectivity. In this context, the synthesis and characterization of a series of Al complexes (Al1 − Al5) bearing N,N-bidentate amino-quinoline ligands are described, as well as their applications in ring-opening polymerization (ROP) of ε -caprolactone (ε -CL). The amido-coordination Al complexes were directly synthesized by reactions of imino-quinoline compounds with AlMe 3 via methyl migration from Al to the carbon atom of imine, as indicated by both NMR spectroscopy and X-ray diffraction. In the presence of BnOH, complexes Al1 − Al5 showed significant reactivity for ROP of ε -CL with good control over molar mass (M n) and dispersity (Đ < 1.2), and polycaprolactones (PCLs) with high molecular weights (M n up to 129 kDa) were readily synthesized. Remarkably, immortal catalysis with excess of BnOH (up to 20 equiv. to Al) was achieved to prepare PCLs with predictable M n s, low dispersities, and end groups using an extremely low loading of Al complex (0.05 mol% to ε -CL monomer). [ABSTRACT FROM AUTHOR]

ABSTRACT: The random copolymers poly(LA‐ran‐CL) have improved properties of degradability, mechanical strength, elasticity, and permeability over the PLA and PCL homopolymers. However, the synthesis of such copolymers is still a great challenge in polymer chemistry. In this contribution, we develop a simple but well‐designed phenoxyimine Al complex (4) with bulky Ph2CH groups, which achieves controlled random copolymerization of rac‐LA and ɛ‐CL in a living manner (Ð = 1.06–1.09). The reactivity ratios of rac‐LA and ɛ‐CL (rLA and rCL) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit (LLA) and the caproyl unit (LCL) are in the range of 1.9–2.0 at different stages of conversion. In marked contrast, Al complexes (1–3) having less bulky substituents on the ligands only produce gradient copolymers. Furthermore, this strategy of catalyst design would be readily extended to other catalytic systems including β‐ketiminato Al complex (5). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 611–617 [ABSTRACT FROM AUTHOR]

A new superbase, the cyclic trimeric phosphazene base (CTPB), was prepared with high yield and purity. In the presence of alcohol, the CTPB serves as a highly efficient organocatalyst for ring-opening polymerization of the 'non-polymerizable' γ-butyrolactone to offer well-defined poly(γ-butyrolactone) with high conversions (up to 98 %) at −60 °C. The produced polymers have high molecular weights (up to 22.9 kg mol−1) and low polydispersity distributions (1.27-1.50). NMR analysis of initiation process and the structural analysis of resulting polymers by MALDI-TOF suggest a mechanism involving an activating initiator which leads only to linear polymers with BnO/H chain ends. [ABSTRACT FROM AUTHOR]

Tough and transparent poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) (PLLA/PDLA-PB-PDLA) film with balanced strength was obtained. The PDLA-PB-PDLA triblock copolymer was firstly synthesized by ring-opening polymerization (ROP) of D-lactide using bihydroyl-terminated polybutadiene as macroinitiator, and then the obtained triblock copolymer was mixed with PLLA in solution. The blended films kept in good transparence even when the loading of PDLA-PB-PDLA reached to 15 wt%. Meanwhile, the elongation at break of the PLLA/PDLA-PB-PDLA film increased by ∼10 times without a significant reduction in tensile strength as compared with that of pure PLLA. The mechanical property was ascribed to the synergetic effect of the flexible PB chains and the stereocomplex crystals formed between PLLA matrix and PDLA chains. "Salami-like" dispersed-phase with nanometer scales was observed, which would contribute to the transparency of the blended film. The tensile fractured morphologies indicated that shear yield of the matrix and cavitation might be the major toughening mechanism of PLLA/PDLA-PB-PDLA film. We prepared tough and transparent poly(L-lactic acid) film with balanced tensile strength by blending with poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) triblock copolymer. [Display omitted] • Tough and transparent poly(L-lactic acid)/poly(D-lactide)-b-poly(butadiene)-b-poly(D-lactide) film with balanced strength. • The mechanical properties were ascribed to the synergetic effect of the flexible PB chains and the stereocomplex crystals. • "Salami-like" dispersed-phase with nanometer scales would contribute to the transparency of the blended film. • Shear yield of the matrix and cavitation might be the major toughening mechanism of PLLA/PDLA-PB-PDLA film. [ABSTRACT FROM AUTHOR]

Self-healing polyester elastomers with good mechanical strength, excellent toughness and rapid self-healing property were obtained by post-functionalized polyester backbone with UPy units through a thiol-ene click reaction. [Display omitted] • Self-healing polyester elastomers were obtained by post-functionalized polyester backbone with UPy units. • Elastomers show good mechanical strength, excellent elongation at break, good toughness and rapid self-healing property. • High polyester molecular weight, moderate UPy content and inhibition of crystallization are helpful to improve the mechanical and self-healing properties of elastomers. It is a desirable to prepare high performance polyester elastomers that possess high strength, good elasticity and efficient self-healing capability. Herein, we report the preparation of such elastomers based on aliphatic polyesters cross-linked by UPy-UPy quadruple hydrogen bonding. A functional monomer α-methylene-γ-butyrolactone (MBL) was copolymerized with ε-caprolactone (ε-CL) to give pendent double bonds functionalized copolyester precursors, which were subject to post-modification with UPy groups via the efficient thiol-ene click reaction. Then, the self-healing polyester elastomers were finally obtained by tuning the molecular weight of precursors, the contents of UPy units and crystallization behaviors. The results show that high polyester molecular weight, moderate UPy content and inhibition of crystallization are helpful to improve the mechanical and self-healing properties of elastomers. The obtained elastomers show good mechanical strength (1.0–1.5 MPa), excellent elongation at break (970–1560 %) and toughness (9.6–11.9 MJ/m3), and have the rapid self-healing property (>70 % after healing at 60 °C for 2 h), displaying great potential in biomedical applications. [ABSTRACT FROM AUTHOR]

Smart protein-mimetic materials have received increasing interest for many applications. Here, we reported a facile and efficient approach to prepare a class of dual-responsive copoly( l -glutamate)s by ring-opening polymerization (ROP) and post-modification strategy. Both the oligo(ethylene glycol) (OEG) and glutamic acid residues were incorporated to offer thermal- and pH-responsive property simultaneously. We present a systematic study of the influence of both temperature and pH on the solution properties of the copolypeptides. The copolypeptides show entirely reversible pH-dependent thermal-responsive behaviors with tunable phase transition temperatures. It is demonstrated that the sequence of the polymer units can also influence the solution behavior. The α-helix conformation appears to be the dominant secondary conformation, which shows the pH dependence, but generally irrespective of the temperature. We further verify that the reduced circular dichroism (CD) signal upon heating above the clouding point (CP) is entirely due to the aggregation of the polymer chains. All these features make the obtained polypeptides potential candidates for next generation of smart protein-mimetic materials. [ABSTRACT FROM AUTHOR]

High molecular weights polydiethylsiloxanes and random poly(dimethylsiloxane-co-diethylsiloxane) copolysiloxanes were synthesized via cyclic trimeric phosphazene base catalyzed ring-opening (co)polymerization at room temperature. [Display omitted] • PDES homopolymers, with molecular weight up to 404.0 kg/mol, were conveniently synthesized at room temperature within 4 hrs using CTPB as catalyst. • High molecular weight random copolymers of diethylsiloxane with different dimethylsiloxane contents were successfully prepared within 5 min at room temperature in high yields. • Reactivity ratio determination experiments suggested that the ROCP of D 3 Et with D 4 mediated by CTPB proceeded in a fully random manner, demonstrating the high catalytic activity of CTPB. Polysiloxanes containing diethylsiloxane units with unique low temperature flexibility have been widely applied under extreme conditions in many fields. However, the synthesis of polydiethylsiloxane (PDES) and its copolymers was challenging due to the easy accessible polymerization-depolymerization equilibrium between linear propagating chains and cyclosiloxane byproducts in the ring-opening polymerization (ROP) of hexaethylcyclotrisiloxane (D 3 Et) and the large reactivity gaps among different cyclosiloxanes in the copolymerization. In this work, PDESs were successfully prepared via cyclic trimeric phosphazene base (CTPB) catalyzed ROP at room temperature in high yields. The ROP of D 3 Et proceeded efficiently with low CTPB loading (low to 0.01 mol%) and the resulting PDES homopolymers had high molecular weights (up to 404.0 kg/mol). Moreover, poly(dimethylsiloxane- co -diethylsiloxane) (PMES) random copolymers with tunable diethylsiloxane contents (20 ∼ 87 mol%) can be directly prepared via ring-opening copolymerization (ROCP) of D 3 Et and octamethylcyclotetrasiloxane (D 4) using CTPB as catalyst within 5 min at ambient temperature. The reactivity ratio of D 3 Et (r = 1.04) and D 4 (r = 0.89) suggested the comparable reactivity between D 3 Et and D 4 to ensure their random copolymerization characteristics, thus proving the unique high efficiency of CTPB catalyst applied here. Microstructure characterizations of the PMES copolymers by 1H and 29Si NMR verified the controlled copolymer composition and the random distribution of diethylsiloxane and dimethylsiloxane units. The thermal property investigations by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated the good low-temperature flexibility and thermal stability of PMES copolymers, displaying great potential in extreme environmental applications. [ABSTRACT FROM AUTHOR]

Semiconductors Surface ‐ grafted π ‐ conjugated organic semiconductor layers are attractive for organic electronics and surface nanotechnologies. Zhibo Li and co ‐ workers from the Institute of Chemistry, Chinese Academy of Sciences (ICCAS) developed a simple and universal method to construct compact polymeric n ‐ type semiconductor films via surface ‐ initiated ring ‐ opening polymerization (SI ‐ ROP) of functional lysine N ‐ carboxylic anhydride (NCA) monomers. In their Communication on page 2036   ff., highlighted on the Inside Cover, the research group from ICCAS reports on the preparation of asymmetric and symmetric perylene bisimide (PBI) ‐ functionalized L ‐ lysine NCAs (PBI ‐ NCAs). Using silicon wafers functionalized with a primary amine as substrate, they successfully grated a layer of semiconductors by this method. Their study holds promise for large ‐ area surface modifications for electronic devices directly from organic semiconductor ‐ functionalized monomers. [ABSTRACT FROM AUTHOR]

Three alkyl-polypeptide (AP) amphiphileswere prepared using ring-openingpolymerization of α-amino acid N-carboxyanhydride.The polypeptide segment was composed of diethylene-glycol-monomethyl-ether-functionalizedpoly-l-glutamate (poly-l-EG2Glu). TheseAP amphiphiles can spontaneously self-assemble into transparent hydrogelsin water. These hydrogels showed shear thinning properties, and theirstrength can be modulated by hydrophobic alkyl tails. CryoTEM andAFM characterizations suggested that these hydrogels were formed bynanoribbons arising from intermolecular interactions between nonionicpoly-l-EG2Glu segments. [ABSTRACT FROM AUTHOR]

A new polystyrene supported cyclic trimeric phosphazene base (PS-CTPB) was designed and synthesized. It was demonstrated that hypotoxic poly (ε -caprolactone) (PCL) can be directly prepared via ring-opening polymerization (ROP) by using PS-CTPB as catalyst. The PS-CTPB catalyst was prepared via immobilization of cyclic trimeric phosphazene base (CTPB) moiety on polystyrene microspheres to obtain a heterogeneous organocatalyst. The composition and chemical structure of the heterogeneous PS-CTPB was systematically characterized using solid-state 13C and 31P MAS NMR, FTIR, SEM and element analysis. It was found that immobilization of CTPB on PS microsphere maintained its excellent catalytic activity for ROP of ε -CL, δ -valerolactone (δ -VL), rac -lactide (rac -LA). Moreover, the heterogeneous PS-CTPB could be easily separated or recycled via simple filtration. Given that, the obtained polyesters contained negligible catalyst residual, so the obtained PCL samples have low cytotoxicity indicated from MTT assay. It was worth noting that the recycled PS-CTPB catalyst could be reused for another six consecutive cycles without significant decrease of catalytic activity. Image 1 • PS-CTPB is prepared via immobilization of cyclic trimeric phosphazene base moiety on polystyrene microspheres. • PS-CTPB exhibits highly efficient for ring-opening polymerization of cyclic esters. • PS-CTPB is easily recovered and reusable for six consecutive cycles without obvious deactivation. • The PCLs without catalyst-residue have been facilely synthesized using PS-CTPB by simple filtration. • MTT assay indicates that the resulting PCLs have low cytotoxicity. [ABSTRACT FROM AUTHOR]

Over the past several years, organocatalyzed polymerization reactions have attracted considerable attention, and these efforts have led to major advances. A large number of organic compounds have been proven active for the polymerization of a large variety of monomers. In particular, phosphazene bases (PBs) are a family of extremely strong, non‐nucleophilic, and uncharged auxiliary bases, and have shown their remarkable potential as organocatalysts for the ring‐opening polymerization (ROP) of cyclic monomers. By deprotonation of weak acids or in combination with lithium cation, PBs significantly enhance the nucleophilicity of the initiator/chain‐end, thus allowing fast and usually controlled anionic polymerization. In this feature article, the recent advances in phosphazene‐catalyzed ROP of cyclic esters are summarized. This review is divided into three sections, including general features, design and synthesis, and catalytic applications. It aims to provide a critical analysis of PB‐mediated ROP systems and a useful guide for the further design of organocatalysts applied to polymer synthesis. An outlook is given at the end. Phosphazene bases (PBs) are a family of extremely strong and non‐nucleophilic bases having remarkable potential as organocatalysts for different types of polymerization reactions. This feature article emphasizes the general features and synthetic methods of PBs and focuses on their applications in the ring‐opening polymerization of cyclic ester monomers. [ABSTRACT FROM AUTHOR]