Polyester Block Research Articles

Recent progress of heterocycle ring‐opening (co)polymerization for the synthesis of sequence‐controlled block polyesters and polycarbonates

AbstractAliphatic polyesters and polycarbonates are among the promising sustainable polymers, which exhibit unique degradability and chain‐chain interactions owing to their heterofunctionality. However, monocomponent aliphatic polyesters and polycarbonates usually suffer from inferior properties and functionalities. By contrast, precisely modulated block copolymers composed of polyesters and polycarbonates give rise to sustainable materials with tailored performance. An efficient approach to synthesize the block copolymers is the ring‐opening (co)polymerization of the heterocycle monomers. Herein, this review presents the heterocycle monomer ring‐opening (co)polymerization for the formation of sequence‐controlled block polyesters and polycarbonates. Available synthetic strategies, different monomers, monomer combinations and the catalyst systems for the formation of different block polyesters and polycarbonates are summarized.

Bulky Phosphazenium Salt Controlling Chemoselective Terpolymerization of Epoxide, Anhydride and CO2: From Well‐Defined Block to Truly Random Copolymers

AbstractCopolymers with precise compositions and controlled sequences are great appealing for high‐performance polymeric materials, but their synthesis is very challenging. In this study, tetrakis[tris(dimethylamino)phosphoranylidenamino] phosphonium chloride (P5Cl) and triethylboron (TEB) were chosen as the binary catalyst to synthesize both well‐defined block and truly random poly(ester–carbonate) copolymers via the one‐pot/one‐step terpolymerization of epoxide/anhydride/CO2 under metal‐free conditions. The bulky nature of phosphazenium cation not only led to loose cation–anion pairs and enhanced the reactivity, but also provided the chain‐end an appropriate protection and improved the controllability. In particular, P5Cl/TEB with a molar ratio of 1/0.5 showed an extraordinary chemoselectivity for ring‐opening alternating copolymerization (ROAC) of cyclohexene oxide (CHO) and phthalic anhydride (PA) first and then ROAC of CHO/CO2. Thus, well‐defined block polyester–polycarbonate copolymers were synthesized by CHO/PA/CO2 terpolymerization. The chemoselectivity was easily tuned and the ROAC of CHO/PA and ROAC of CHO/CO2 occurred simultaneously with P5Cl/TEB=1/2, producing truly random poly(ester–carbonate) copolymers from CHO/PA/CO2. In addition, this P5Cl/TEB catalyst and the strategy to regulate its chemoselectivity are versatile for various anhydrides, epoxides and initiators. Thus, poly(ester–carbonate) copolymers with varying sequences, compositions, and topologies are successfully synthesized, making it possible to compare their properties and to expand their applications.

Synthesis of alternating polyesters using a dual catalytic system of alkali metal alkoxides and crown ether

In this study, a dual catalytic system that merges crown ether with alkali metal alkoxides (AMA) is utilized in the ring-opening alternating polymerization (ROAP) of phthalic anhydride (PA) and propylene oxide (PO). This method streamlines the production of polyesters characterized by a fully alternating sequence, a modifiable molar mass (achieving up to 59.3 kg mol−1), and a narrow molar mass distribution (ÐM < 1.26). Analysis of various commercially available AMAs, notably sodium ethoxide (EtONa), sodium methoxide, and lithium ethoxide, in tandem with crown ethers (15-crown-5 and 18-crown-6), underscores the superior catalytic efficacy of the EtONa and 18-crown-6 pairing. This heightened efficiency is attributed to the coordination of crown ether with alkali metal ions, thereby boosting the nucleophilicity of terminal alkoxide anions. The methodology has been successfully deployed in the ROAP of PA, norbornene anhydride, and multiple epoxides, while also simplifying the creation of aliphatic–aromatic block polyesters from a mixture of PA, PO, and lactide. This strategy presents a straightforward approach to polyester production, thus making significant contributions to the evolution of polyester synthesis technology.

Selective Copolymerization from Mixed Monomers of Phthalic Anhydride, Propylene Oxide and Lactide Using Nano-Sized Zinc Glutarate.

Selective polymerization with heterogeneous catalysts from mixed monomers remains a challenge in polymer synthesis. Herein, we describe that nano-sized zinc glutarate (ZnGA) can serve as a catalyst for the selective copolymerization of phthalic anhydride (PA), propylene oxide (PO) and lactide (LA). It was found that the ring-opening copolymerization (ROCOP) of PA with PO occurs firstly in the multicomponent polymerization. After the complete consumption of PA, the ring-opening polymerization (ROP) of LA turns into the formation of block polyester. In the process, the formation of zinc-alkoxide bonds on the surface of ZnGA accounts for the selective copolymerization from ROCOP to ROP. These results facilitate the understanding of the heterogeneous catalytic process and offer a new platform for selective polymerization from monomer mixtures.

Monodomain Liquid Crystal Elastomers Composed of Main‐Chain Type Nematic Polyester Bonded to Rubbery Segments at Both Ends

AbstractMonodomain liquid crystal elastomers (LCEs) are prepared using liquid crystal block copolymers (LCBCPs) comprised of a nematic liquid crystal (NLC) main‐chain polyester linked to cross‐linkable polymethacrylate (PMA) at both ends. LCBCPs at a PMA weight fraction of ≈30% are doped with a tetra‐thiol compound, stretched in one direction, and then illuminated by UV light, yielding LCBCPs that formed microlamellae consisting of alternate stacking crosslinked PMA blocks and NLC polyester blocks. The LC director lay along the stretching direction (SD). Raising the temperature to the NLC isotropization temperature, the crosslinked LCBCP strips fixed at one end contracted reversibly by a factor of 1.2–1.4 along the SD, deforming the microlamellae. The strips fixed at both ends increased the tensile stress to ≈200 kPa while maintaining the microlamellae undeformed. Regardless of strip fixation at one or both ends, the NLC decreased the orientational order. The contraction amounts and the tensile stress of strips are well associated with decreased NLC orientational order.

Six-membered ring-reinforced flexible high-elongation block polyamide as strong and multi-reusable hot melt adhesive

This study presented the synthesis and characterization of polyester block polyamide hot melt adhesives (PPHMAs) with high adhesion strength and toughness. The PPHMAs demonstrated an adhesion strength of 11.04 MPa and toughness of 22.54 MJ·m−3, making them suitable for various substrates such as aluminum, copper, and stainless steel. The polyamide segments synthesized from dimer acid and 2-methyl-1,5-diaminopentane exhibited characteristics of softness and high elongation. Using isophorone diamine as a reinforcing agent introduced a stable six-membered ring structure, which enhanced the polymer's rigidity and strength, thus meeting the requirements for polyamide segments to function as the hard segments in block polymers. A trace amount of Tris (2-aminoethyl) amine provided the cross-linking sites which are similar to those in neuronal structures. The polyester segments, which were synthesized from poly (propylene glycol) diglycidyl ether and sebacic acid, served as the soft segments in the block polymer and were connected to the hard segment via amide bonds. The addition of the polyester segments enhanced the non-covalent molecular interactions within PPHMAs, leading to dynamic crosslinking properties. The adhesive maintained stable adhesion even after six cycles, which showcased its durability. Furthermore, the PPHMAs exhibited notable chemical resistance. It retained over 60 % adhesion strength after exposure to some chemical solvents including artificial seawater, 5 % NaOH solution, 5 % HCl solution, and DMSO for 24 h. These findings offered a novel approach to enhancing the adhesion strength and toughness of conventional thermoplastic hot melt adhesives.

Hybrid Photoiniferter and Ring-Opening Polymerization Yields One-Pot Anisotropic Nanorods.

Polymerization-induced self-assembly (PISA) has emerged as a scalable one-pot technique to prepare block copolymer (BCP) nanoparticles. Recently, a PISA process, that results in poly(l-lactide)-b-poly(ethylene glycol) BCP nanoparticles coined ring-opening polymerization (ROP)-induced crystallization-driven self-assembly (ROPI-CDSA), was developed. The resulting nanorods demonstrate a strong propensity for aggregation, resulting in the formation of 2D sheets and 3D networks. This article reports the synthesis of poly(N,N-dimethyl acrylamide)-b-poly(l)-lactide BCP nanoparticles by ROPI-CDSA, utilizing a two-step, one-pot approach. A dual-functionalized photoiniferter is first used for controlled radical polymerization of the acrylamido-based monomer, and the resulting polymer serves as a macroinitiator for organocatalyzed ROP to form the solvophobic polyester block. The resulting nanorods are highly stable and display anisotropy at higher molecular weights (>12k Da) and concentrations (>20% solids) than the previous report. This development expands the chemical scope of ROPI-CDSA BCPs and provides readily accessible nanorods made with biocompatible materials.

Functionalized polyesters based on valerolactones and [12]aneN3 as effective non-viral gene vectors in HepG2 cells

Block polyesters with BODIPY and [12]aneN3 moieties showed efficient cell-specific nucleic acid expression and anti-tumor gene therapy in vitro.

A one-pot approach towards polycarbonate-b-polyester block copolymers via chemoselective polymerization catalyzed by a one-component phosphonium borane Lewis pair

Chemoselective polymerization from a mixture of l-LA, CHO and CO2 enables the synthesis of PLLA, PCHC or PCHC-b-PLLA achieved by PBB-Br. The chemoselectivity depends on the nature of the growing polymer chain end.

Iron(III) Triflate as a Green Catalyst for Janus Polymerization to Prepare Block Polyesters

Iron(III) Triflate as a Green Catalyst for Janus Polymerization to Prepare Block Polyesters

Understanding differences in rate versus product determining steps to enhance sequence control in epoxide/cyclic anhydride copolymers

One-pot synthesis of random, gradient, and block polyesters via the ring opening copolymerization of epoxides and cyclic anhydrides is investigated using simple yttrium salt catalysts. Impact of rate versus product determining steps is discussed.

Self-switchable polymerization catalysis with monomer mixtures: using a metal-free commercial thiourea catalyst to deliver block polyesters

An easily accessible and cost-effective catalytic system, TU/PPNCl, was developed to produce sequence-controlled multiblock polyesters by self-switchable polymerization from a monomer mixture of epoxides, anhydrides, and cyclic esters.

End-functionalized diblock copolymers by mix and match of poly(2-oxazoline) and polyester building blocks

2-(4-(Iodomethyl)benzyl)isoindoline-1,3-dione was utilized as a protected amine-functionalized initiator for the cationic ring opening-polymerization (CROP) of 2-ethyl-2-oxazoline. As kinetic studies indicated a well-controlled polymerization, the CROP was terminated with sodium azide. Subsequent deprotection of the α-end group enabled successive attachment of a targeting ligand, e.g., retinoic acid or a proteogenic amino acid as a peptide model at the α-chain end. The heterotelechelic PEtOx were coupled to cyclooctyne end-functionalized polylactide, which was obtained by initiating the ring opening polymerization of l-lactide via a cyclooctyne based alcohol, utilizing strain-promoted azide-alkyne cycloaddidtion. In-depth characterization via mass spectrometry, 1H NMR spectroscopy, size exclusion chromatography, and infrared spectroscopy investigations verified the success of all synthetic steps and the preservation of retinoyl and leucine moieties also in the end-functionalized PEtOx-b-PLA block copolymers. Circumventing potential degradation of the polyester block during ligand attachment, the heterotelechelic PEtOx represents a universal building block useful for modular approaches towards tailored materials for nanomedicine.

Degradable terpolyesters synthesized from a monomer mixture mediated by a heterometallic complex: Defined monomer- and stereo-sequences

Copolymers provide a feasible platform to extend the structures of polymeric material, and the control of architecture (such as monomer sequence and stereo sequence) plays a critical role in tailoring specific properties. Herein, a heterometallic (Salph Zn)2-Ho complex was screened out for the synthesis of architecture-defined block terpolymers from a monomer mixture of epoxide, cyclic anhydride and l-lactide (LLA). The polymerization in one-pot firstly underwent ring-opening copolymerization reaction producing completely alternating ester linkage, and then transformed to LLA polymerization with trace stereoerrors, forming block polyesters with a semicrystalline segment and an amorphous segment. The polymerization was “immortal” with the ability to synthesize sequence-defined multiblock polyesters by sequential monomer addition. Furthermore, DSC traces revealed that the obtained block polyesters exhibited distinct thermal properties stemming from each segment. The melting temperature of block terpolymer was increased to 207.6 °C facilitated by the stereocomplexes of PLA segment.

One-Pot Terpolymerization of Macrolactones with Limonene Oxide and Phtalic Anhydride to Produce di-Block Semi-Aromatic Polyesters.

The synthesis of novel block copolymers, namely poly(limonene-phthalate)-block-poly(pentadecalactone) and poly(limonene-phthalate)-block-poly(pentadecalactone) is here described. To achieve this synthesis, a bimetallic aluminum based complex (1) was used as catalyst in the combination of two distinct processes: the ring-opening polymerization (ROP) of macrolactones such as ω-pentadecalactone (PDL) and ω-6-hexadecenlactone (HDL) and the ring-opening copolymerization (ROCOP) of limonene oxide (LO) and phthalic anhydride (PA). The synthesis of di-block polyesters was performed in a one-pot procedure, where the semi-aromatic polyester block was firstly formed by ROCOP of LO and PA, followed by the polyethylene like portion produced by ROP of macrolactones (PDL or HDL). The obtained di-block semiaromatic polyesters were characterized by NMR and GPC. The structural organization was analyzed through XRD. Thermal properties were evaluated using differential thermal analysis (DSC) and thermogravimetric measurements (TGA) either in air or in nitrogen atmosphere.

Self-Organization of Graft Copolymers and Retortable iPP-Based Nanoporous Films Thereof

Polyolefins might become inexpensive alternatives to the existing membranes based on polyethersulfone. Here, we disclose the production of retortable, well-defined polypropylene (PP)-based nanoporous films derived from amphiphilic graft copolymer precursors. The graft copolymers, containing a polypropylene backbone and polyester grafts, were obtained by grafting lactones, specifically δ-valerolactone and ε-caprolactone, from well-defined randomly functionalized poly(propylene-co-10-undecen-1-ol) as a macroinitiator. Depending on the composition, the graft copolymers self-assemble into droplet, cylindrical, lamellar, or interconnected two-phase morphologies. Functional mesoporous iPP-based films were fabricated by the selective degradation of the polyester blocks of the copolymers. Their structure and morphology were studied using atomic force microscopy (AFM), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and solid-state NMR, while the mesoporosity was assessed by nitrogen sorption experiments. The pore size of the films is strongly influenced not only by the volume fraction of the copolymer blocks but unexpectedly also by the topology (i.e., number of grafts) of the graft copolymer, as was confirmed by computational modeling studies using the dynamic density functional theory (DDFT) engine within the Culgi software. This work provides a conclusive answer on how the morphology of iPP-based graft copolymers is tuned by the copolymer composition and the amount and length of the grafted polyester blocks. Filtration tests and flux determination demonstrated that such structurally well-defined mesoporous products could be considered for the development of ultrafiltration membranes while the chemical resistance and sterilization tests revealed their robust performance and suitability for water purification applications.

A Facile Fabrication of Lysosome-Targeting pH Fluorescent Nanosensor Based on PEGylated Polyester Block Copolymer.

A novel lysosome-targeting PEGylated polyester-based fluorescent pH nanosensor is fabricated by the combination of ring-opening copolymerization (ROCOP), side-group modification and subsequent self-assembly. First, a key target amphiphilic copolymer carrier for rhodamine (Rh) pH indicator is synthesized in a facile manner by the ROCOP of phthalic anhydride with allyl glycidyl ether using mPEG-OH and t-BuP1/Et3B as the macroinitiator and binary catalyst, respectively. Subsequently, Rh moieties are covalently attached on the polymer chain with controllable grafting degree via an efficient thiol-ene click reaction. Concurrently, the effect of catalyst systems and reaction conditions on the catalytic copolymerization performance is presented, and the quantitative introduction of Rh is described in detail. Owing to its amphiphilic characteristics, the rhodamine-functionalized polyester-based block copolymer can self-assemble into micelles. With the covalent incorporation of Rh moieties, the as-formed micelles exhibit excellent absorption and fluorescence-responsive sensitivity and selectivity towards H+ in the presence of various metal cations. Moreover, the as-prepared micelles with favorable water dispersibility, good pH sensitivity and excellent biocompatibility also display appreciable cell-membrane permeability, staining ability and pH detection capability for lysosomes in living cells. This work provides a new strategy for the facile synthesis of novel biocompatible polymeric fluorescent pH nanosensors for the fluorescence imaging of lysosomal pH changes.

Exploiting Sodium Coordination in Alternating Monomer Sequences to Toughen Degradable Block Polyester Thermoplastic Elastomers.

Thermoplastic elastomers (TPEs) that are closed-loop recyclable are needed in a circular material economy, but many current materials degrade during recycling, and almost all are pervasive hydrocarbons. Here, well-controlled block polyester TPEs featuring regularly placed sodium/lithium carboxylate side chains are described. They show significantly higher tensile strengths than unfunctionalized analogues, with high elasticity and elastic recovery. The materials are prepared using controlled polymerizations, exploiting a single catalyst that switches between different polymerization cycles. ABA block polyesters of high molar mass (60–100 kg mol–1; 21 wt % A-block) are constructed using the ring-opening polymerization of ε-decalactone (derived from castor oil; B-block), followed by the alternating ring-opening copolymerization of phthalic anhydride with 4-vinyl-cyclohexene oxide (A-blocks). The polyesters undergo efficient functionalization to install regularly placed carboxylic acids onto the A blocks. Reacting the polymers with sodium or lithium hydroxide controls the extent of ionization (0–100%); ionized polymers show a higher tensile strength (20 MPa), elasticity (>2000%), and elastic recovery (>80%). In one case, sodium functionalization results in 35× higher stress at break than the carboxylic acid polymer; in all cases, changing the quantity of sodium tunes the properties. A leading sample, 2-COONa75 (Mn 100 kg mol–1, 75% sodium), shows a wide operating temperature range (−52 to 129 °C) and is recycled (×3) by hot-pressing at 200 °C, without the loss of mechanical properties. Both the efficient synthesis of ABA block polymers and precision ionization in perfectly alternating monomer sequences are concepts that can be generalized to many other monomers, functional groups, and metals. These materials are partly bioderived and have degradable ester backbone chemistries, deliver useful properties, and allow for thermal reprocessing; these features are attractive as future sustainable TPEs.

Controlled, one-pot synthesis of recyclable poly(1,3-diene)-polyester block copolymers, catalyzed by yttrium β-diketiminate complexes.

The one-pot synthesis of well-defined block copolymers of olefins/1,3-dienes and polar monomers, such as cyclic esters and acrylates has long been the focus of intense research. Cationic alkyl rare earth metal catalysts, activated by organoborates, have shown to be promising for the polymerization of isoprene or styrene and ε-caprolactone. In this study, we synthesize a series of yttrium bis(alkyl) complexes supported by simple β-diketiminate ancillary ligands. Subtle changes have been made to the β-diketiminate ligand framework to elucidate the effect of ligand structure on the rate and selectivity of olefin/1,3-diene and cyclic ester polymerization, with small ligand changes having a large impact on the resulting polymerizations. Generation of the active cationic species was easily streamlined by identification of appropriate catalyst : organoborate ratios, allowing for high catalyst efficiencies. Notably, we demonstrate the first cationic rare earth metal alkyl-initiated polymerization of δ-valerolactone and ε-decalactone as well as introduced five new block copolymer morphologies. In addition, selective degradation of the ester block in poly(isoprene-b-caprolactone) enabled recovery of the polyisoprene block with identical spectroscopic and thermal properties. Significantly, recopolymerization of the recovered poly(1,3-diene) with fresh ε-caprolactone reproduced the desired diblocks with nearly identical thermal and physical properties to those of virgin copolymer, illustrating a plausible recycling scheme for these materials.

Switchable Polymerization Catalysis Using a Tin(II) Catalyst and Commercial Monomers to Toughen Poly(l-lactide).

Sustainable plastics sourced without virgin petrochemicals, that are easily recyclable and with potential for degradation at end of life, are urgently needed. Here, copolymersand blends meeting these criteria are efficiently prepared using a single catalyst and existing commercial monomers l-lactide, propylene oxide, and maleic anhydride. The selective, one-reactor polymerization applies an industry-relevant tin(II) catalyst. Tapered, miscible block polyesters are formed with alkene groups which are postfunctionalized to modulate the polymer glass transition temperature. The polymers are blended at desirable low weight fractions (2 wt %) with commercial poly(l-lactide) (PLLA), increasing toughness, and elongation at break without compromising the elastic modulus, tensile strength, or thermal properties. The selective polymerization catalysis, using commercial monomers and catalyst, provides a straightforward means to improve bioplastics performances.