Poly(propylene succinate): A New Polymer Stereocomplex

Ring-Opening Copolymerizaton of Cyclohexene Oxide and Succinic Anhydride by Zinc and Magnesium Schiff-Base Complexes Containing Alkoxy Side Arms

The ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a promising method for the synthesis of new polyesters with various polymer properties. Among previously reported metal catalysts for ROCOP, the Schiff-base complexes have gained significant attention because of their ease of synthesis and modification. In this work, zinc and magnesium complexes containing Schiff-base ligands with different alkoxy side arms [-(CH₂)₂O- and -(CH₂)₃O-] were synthesized and shown to have a cubane metal core by X-ray crystal structures. All complexes were studied in the ROCOP of cyclohexene oxide (CHO) and succinic anhydride (SA) in toluene at 110 °C. The zinc complex having a shorter side arm is the most active catalyst for copolymerization, giving poly(CHO-alt-SA) with narrow dispersity and negligible ether linkage. On the other hand, magnesium complexes were not active because of the formation of stable carboxylate species. The detailed analysis of polyester obtained from zinc complexes unexpectedly revealed three different types of polymer structures occurring at different polymerization times. Cyclic polymer was generated at the beginning by intramolecular transesterification of the alkoxy side arm, giving a low-molecular-weight polyester. At higher conversion, cyclization diminished, giving just a linear polyester but with minor competitive formation of higher-molecular-weight polyester having cyclohexanediol as an end group. On the basis of a thorough understanding of the polymerization mechanism, the desired cyclic poly(CHO-alt-SA) was successfully synthesized using a low monomer/catalyst ratio.

An Investigation of the Organoborane/Lewis Base Pairs on the Copolymerization of Propylene Oxide with Succinic Anhydride

The copolymerization of biorenewable succinic anhydride (SA) with propylene oxide (PO) is a promising way to synthesize biodegradable aliphatic polyesters. However, the catalytic systems for this reaction still deserve to be explored because the catalytic activity of the reported catalysts and the molecular weights of produced polyesters are unsatisfied. Herein, we investigate the copolymerization of SA with PO catalyzed by the organoborane/base pairs. The types of Lewis bases, organoboranes, and their loadings all have a large impact on the activity and selectivity of the copolymerization. High ester content of >99% was achieved when performed the PO/SA copolymerization using triethyl borane (TEB)/phosphazene base P1-t-Bu (t-BuP1) pair with a molar ratio of 1/1 at 30-80 °C. Using TEB/t-BuP1 pair with the molar ratio of 4/1 at 80 °C, the turnover of frequency (TOF) was up to 128 h-1 and clearly higher than the known TOF values (0.5-34 h-1) of the PO/SA copolymerization by previously reported catalysts. The number-average molecular weights (Mns) of the resultant polyesters reached up to 20.4 kg/mol when copolymerization was carried out using TEB/t-BuP1 (1/1, in molar ratio) at 30 °C.

Ring-opening copolymerization of cyclic epoxide and anhydride using a five-coordinate chromium complex with a sterically demanding amino triphenolate ligand

This work describes polyester synthesis via alternating ring-opening copolymerization of epoxides and anhydrides using a trigonal bipyramidal chromium complex containing a sterically demanding ligand.

Reversible Transformation between Amorphous and Crystalline States of Unsaturated Polyesters by Cis-Trans Isomerization

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T_g =18 °C) and crystalline (T_m =124 °C) states through cis-trans isomerization of the C=C bonds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer. A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides, such as epichlorohydrin, phenyl glycidyl ether, and (2,3-epoxypropyl)benzene. These unsaturated polyesters with 100 % E-configuration in the crystalline state were prepared by quantitative isomerization of their Z-configuration analogues in the presence of a catalytic amount of diethylamine, while in the presence of benzophenone, irradiation with 365 nm UV light resulted in the transformation of about 30 % trans-alkene to cis-maleate form, thereby affording amorphous polyesters.

Mechanism-Inspired Design of Bifunctional Catalysts for the Alternating Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides

Advances in catalysis have enabled the ring-opening copolymerization of epoxides and cyclic anhydrides to afford structurally and functionally diverse polyesters with controlled molecular weights and dispersities. However, the most common systems employ binary catalyst/cocatalyst pairs which suffer from slow polymerization rates at low loadings. Inspired by new mechanistic insight into the function of binary metal salen/nucleophilic cocatalyst systems at low concentrations, we report a bifunctional complex in which the salen catalyst and an aminocyclopropenium cocatalyst are covalently tethered. A modular ligand design circumvents the extended linear syntheses typical of bifunctional catalysts, enabling systematic variation to understand and enhance catalytic activity. The optimized bifunctional aluminum salen catalyst maintains excellent activity for the ring-opening copolymerization of epoxides and cyclic anhydrides at low concentrations (≥0.025 mol %), and the aminocyclopropenium cocatalyst suppresses undesirable transesterification and epimerization side reactions, preserving the integrity of the polymer backbone.

Enantioselective Resolution Copolymerization of Racemic Epoxides and Anhydrides: Efficient Approach for Stereoregular Polyesters and Chiral Epoxides

Herein we report an efficient strategy for preparing isotactic polyesters and chiral epoxides via enantioselective resolution copolymerization of racemic terminal epoxides with anhydrides, mediated by enantiopure bimetallic complexes in conjunction with a nucleophilic cocatalyst. The chirality of both the axial linker and the diamine backbones of the ligand are responsible for the chiral induction of this kinetic resolution copolymerization process. The catalyst systems exhibit exceptional levels of enantioselectivity with a kinetic resolution coefficient exceeding 300 for various racemic epoxides, affording highly isotactic copolymers (selectivity factors of more than 300) with a completely alternating structure and low polydispersity index. Most of the produced isotactic polyesters are typical semicrystalline materials with melting temperatures in the range from 77 to 160 °C.

Preparation and Properties of sc-PLA/PMMA Transparent Nanofiber Air Filter

Particulate matter (PM) pollution is a serious concern for the environment and public health. To protect indoor air quality, nanofiber filters have been used to coat window screens due to their high PM removal efficiency, transparency and low air resistance. However, these materials have poor mechanical property. In this study, electrostatic induction-assisted solution blowing was used to fabricate polylactide stereocomplex (sc-PLA), which served as reinforcement to enhance the physical cross-linking point to significantly restrict poly(methyl methacrylate) (PMMA) molecular chain motion and improve the mechanical properties of sc-PLA/PMMA nanofibers. Moreover, the introduction of sc-PLA led to the formation of thick/thin composite nanofiber structure, which is beneficial for the mechanical property. Thus, sc-PLA/PMMA air filters of ~83% transparency with 99.5% PM_2.5 removal and 140% increase in mechanical properties were achieved when 5 wt % sc-PLA was added to PMMA. Hence, the addition of sc-PLA to transparent filters can effectively improve their performance.

The effect of me-substituents of 1,4-butanediol analogues on the thermal properties of biobased polyesters

Biobased 1,4-butanediol analogues are used to tune the glass transition temperature and crystallization in a series of polyesters and allow for the formation of stereocomplexes.

A synthetic polymer system with repeatable chemical recyclability

The development of chemically recyclable polymers offers a solution to the end-of-use issue of polymeric materials and provides a closed-loop approach toward a circular materials economy. However, polymers that can be easily and selectively depolymerized back to monomers typically require low-temperature polymerization methods and also lack physical properties and mechanical strengths required for practical uses. We introduce a polymer system based on γ-butyrolactone (GBL) with a trans-ring fusion at the α and β positions. Such trans-ring fusion renders the commonly considered as nonpolymerizable GBL ring readily polymerizable at room temperature under solvent-free conditions to yield a high-molecular weight polymer. The polymer has enhanced thermostability and can be repeatedly and quantitatively recycled back to its monomer by thermolysis or chemolysis. Mixing of the two enantiomers of the polymer generates a highly crystalline supramolecular stereocomplex.

Lipase-catalyzed synthesis of chiral poly(ester amide)s with an alternating sequence of hydroxy acid and l/d-aspartate units

Alternating poly(hydroxyhexanoic acid-alt-l/d-β-aspartate)s with α-benzyl or α-methyl ester side groups were prepared via the enzymatic polycondensation of N-(6-hydroxyhexanoyl) l/d-aspartate diesters.

Pressure-controlled crystallization of stereocomplex crystals in enantiomeric polylactides with remarkably enhanced hydrolytic degradation

Enantiomeric biopolymers, with improved combinatorial heat resistance, hydrolytic degradation and hydrophilicity, were fabricated by pressure-controlled crystallization of stereocomplex crystals.

Alternating ring-opening copolymerization of phthalic anhydride with epoxides catalysed by salophen chromium(iii) complexes. An effect of substituents in salophen ligands

The effect of a ligand structure on the catalytic activity of salophen chromium(iii) complexes in the ring-opening copolymerization of phthalic anhydride with a series of epoxides was studied.

Reversible-deactivation anionic alternating ring-opening copolymerization of epoxides and cyclic anhydrides: access to orthogonally functionalizable multiblock aliphatic polyesters

A versatile catalyst system for the synthesis of narrow dispersity polyesters from readily available epoxides and anhydrides is reported.

The alternating copolymerization of epoxides and cyclic anhydrides is an increasingly popular route to aliphatic polyesters that are of interest as biodegradable replacements for petroleum-based polymers and for use in the biomedical field. However, broad and bimodal molecular weight distributions in these polymerizations continues to be an issue, limiting synthesis of multiblock copolymers. By use of a bifunctional catalytic system, the reversible-deactivation anionic alternating ring-opening copolymerization of epoxides and cyclic anhydrides gives unimodal polymers with Đ values generally less than 1.07. This allowed for the formation of well-defined triblock copolymers. Additionally, by incorporating both aldehyde and alkene functionalities into the polymer, orthogonal post-polymerization modification was achieved, giving access to well-defined highly modifiable aliphatic polyesters.

Substrate-Controlled Product Divergence: Silver-Catalyzed Reaction of Trifluoromethyl Ketones with Terminal Alkynes

A distinct dichotomy in product distribution was initially observed in the silver-catalyzed reaction of trifluoromethyl (CF₃) ketones with terminal alkynes having two different types of electronic natures. The domino reaction smoothly proceeded almost exclusively with high stereoselectivity with terminal alkynes containing ester groups, whereas alkynylation occurred in good yield when terminal alkynes containing aryl or alkyl groups were present. The results indicated that the electronic nature of terminal alkynes can act as a switch that enables either the domino reaction or alkynylation between terminal alkynes and CF₃ ketones.

Zinc versus Magnesium: Orthogonal Catalyst Reactivity in Selective Polymerizations of Epoxides, Bio-derived Anhydrides and Carbon Dioxide

Developing selective polymerizations from complex monomer mixtures is an important challenge. Here, dinuclear catalysts allow selective polymerization from mixtures of sterically hindered tricyclic anhydrides, carbon dioxide and epoxides to yield well-controlled copoly(ester-carbonates). Surprisingly, two very similar homogeneous catalysts differing only in the central metal, zinc versus magnesium, show very high but diametrically opposite monomer selectivity. The selectivity is attributed to different polymerization kinetics and to steric factors associated with the anhydrides.

Configurational Molecular Glue: One Optically Active Polymer Attracts Two Oppositely Configured Optically Active Polymers

D-configured poly(D-lactic acid) (D-PLA) and poly(D-2-hydroxy-3-methylbutanoic acid) (D-P2H3MB) crystallized separately into their homo-crystallites when crystallized by precipitation or solvent evaporation, whereas incorporation of L-configured poly(L-2-hydroxybutanoic acid) (L-P2HB) in D-configured D-PLA and D-P2H3MB induced co-crystallization or ternary stereocomplex formation between D-configured D-PLA and D-P2H3MB and L-configured L-P2HB. However, incorporation of D-configured poly(D-2-hydroxybutanoic acid) (D-P2HB) in D-configured D-PLA and D-P2H3MB did not cause co-crystallization between D-configured D-PLA and D-P2H3MB and D-configured D-P2HB but separate crystallization of each polymer occurred. These findings strongly suggest that an optically active polymer (L-configured or D-configured polymer) like unsubstituted or substituted optically active poly(lactic acid)s can act as "a configurational or helical molecular glue" for two oppositely configured optically active polymers (two D-configured polymers or two L-configured polymers) to allow their co-crystallization. The increased degree of freedom in polymer combination is expected to assist to pave the way for designing polymeric composites having a wide variety of physical properties, biodegradation rate and behavior in the case of biodegradable polymers.

Ring-Opening Copolymerization of Epoxides and Cyclic Anhydrides with Discrete Metal Complexes: Structure-Property Relationships

Polyesters synthesized through the alternating copolymerization of epoxides and cyclic anhydrides compose a growing class of polymers that exhibit an impressive array of chemical and physical properties. Because they are synthesized through the chain-growth polymerization of two variable monomers, their syntheses can be controlled by discrete metal complexes, and the resulting materials vary widely in their functionality and physical properties. This polymer-focused review gives a perspective on the current state of the field of epoxide/anhydride copolymerization mediated by discrete catalysts and the relationships between the structures and properties of these polyesters.