Well-defined Polyesters Research Articles

Living/Controlled Anionic Polymerization of Glycolide in Fluoroalcohols: Toward Sustainable Bioplastics.

Ring-opening polymerization (ROP) is a promising approach to accessing well-defined polyesters with superior (bio)degradability and recyclability. However, the living/controlled polymerization of glycolide (GL), a well-known sustainable monomer derived from carbon monoxide/dioxide, has never been reported due to the extremely low solubility of its polymer in common solvents. Herein, we report the first living/controlled anionic ROP of GL in strong protic fluoroalcohols (FAs), which are conventionally considered incompatible with anionic polymerization. Well-defined polyglycolide (PGA, Đ < 1.15, Mn up to 55.4 kg mol-1) and various PGA-based macromolecules are obtained at room temperature for the first time. NMR titration and computational studies revealed that FAs simultaneously activate the chain end and monomer without being involved in initiation. Low-boiling-point FAs and PGA can be recycled through simple distillation and sublimation at 220 °C in vacuo, respectively, providing a promising sustainable alternative for tackling plastic pollution problems.

Tunable and recyclable polyesters from CO2 and butadiene.

Carbon dioxide is inexpensive and abundant, and its prevalence as waste makes it attractive as a sustainable chemical feedstock. Although there are examples of copolymerizations of CO2 with high-energy monomers, the direct copolymerization of CO2 with olefins has not been reported. Here an alternative route to functionalizable, recyclable polyesters derived from CO2, butadiene and hydrogen via an intermediary lactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one, is described. Catalytic ring-opening polymerization of the lactone by 1,5,7-triazabicyclo[4.4.0]dec-5-ene yields polyesters with molar masses up to 13.6 kg mol-1 and pendent vinyl side chains that can undergo post-polymerization functionalization. The polymer has a low ceiling temperature of 138 °C, allowing for facile chemical recycling, and is inherently biodegradable under aerobic aqueous conditions (OECD-301B protocol). These results show that a well-defined polyester can be derived from CO2, olefins and hydrogen, expanding access to new polymer feedstocks that were once considered unfeasible.

Accelerating effect of crown ethers on the lactide polymerization catalysed by potassium acetate

Recent advances in catalysis enriched the toolbox to prepare well-defined polyester materials such as polylactide (PLA).

Organomagnesium towards efficient synthesis of recyclable polymers

Recyclable polymers, such as poly(γ-butyrolactone) (PGBL), offer a great opportunity to address the environmental issues of plastics. Herein, we presented an alternative commercial powerful organomagnesium catalysis for ring-opening polymerizations of 3,4-trans six-membered ring-fused γ-butyrolactone (M), enantiomer (R)-M and (S)-M with high conversions (up to 89%). Di-n-butylmagnesium and n-butylethylmagnesium exhibited effective activities for all three kinds of monomers. The polymerization process of (R)-M was systematically investigated with di-n-butylmagnesium as the catalyst. Well-defined polyesters with molecular weights ranging from 4780 to 17420 g/mol were obtained. The commercial organomagnesium catalysis would broaden the applications of recyclable polymers.

Strontium Isopropoxide: A Highly Active Catalyst for the Ring-Opening Polymerization of Lactide and Various Lactones.

Commercially available strontium isopropoxide represents a suitable catalyst/initiator for the ring-opening polymerization (ROP) of lactide (LA), ε-caprolactone, δ-valerolactone, δ-caprolactone, and δ-decalactone. Well-defined polyesters are accessible via the solution polymerization of lactide in toluene with a [LA]:[Sr] ratio of 100:1 at room temperature with or without the addition of dodecanol as coinitiator. Kinetic studies and detailed analysis by means of matrix-assisted laser desorption ionization mass spectrometry reveal pseudo-first-order kinetics of the ROP as well as excellent endgroup fidelity of the polylactide (PLA) with isopropyl and dodecyl α-endgroups. Both isopropanolate moieties as well as the coinitiator each initiate PLA chains, enabling the synthesis of PLA with tailored molar mass. The polymerization of ε-caprolactone and δ-valerolactone confirms the high catalyst activity, which causes quantitative monomer conversion after 1 min polymerization time but broad molar mass distributions. In contrast, the catalyst is well suited for the ROP of the less reactive δ-caprolactone and δ-decalactone. Although kinetic studies reveal initially bimodal molar mass distributions, polyesters with dispersity values Ð < 1.2 and unimodal molar mass distributions can be obtained at moderate to high monomer conversions.

Dibutyl phosphate catalyzed commercial relevant ring-opening polymerizations to bio-based polyesters

Organocatalyzed ring-opening polymerization (ROP) of cyclic esters was developed into a stage that demanding translation of the academic success into commercially viable production. An industrial relevant development of the organocatalysis in ROPs required bulk polymerizations at high temperatures up to 180 °C. Organic phosphoric acid was one of the few organocatalysts workable under these conditions that devoid of otherwise commonly appeared transesterification, epimerization, and decarboxylation in the ROPs. A commercial dibutyl phosphate (DBuP), which was inexpensive and available by hundreds of tons as antistatic agent, was firstly evaluated as a catalyst. Well-defined polyesters catalyzed by DBuP were obtained with narrow dispersities (Đm 1.08–1.31) and predicted molecular weights from 2.1 to 55 kg mol−1. Series of homopolymers, diblock copolymers and end-functionalized polymers of ε-caprolactone (CL), δ-valerolactone (VL), trimethylene carbonate (TMC), and l-lactide (LA) were synthesized. 1H NMR, 13C NMR, SEC, and MALDI–ToF MS analyses indicated that the obtained polyesters were exactly the designated ones. NMR titration experiments confirmed that the ROP proceeded a bifunctional activation mechanism. The cytotoxicity test using MTT assay showed biosafety of the polyesters. The experimental results suggested that dibutyl phosphate is a commercial organocatalyst widely useful in all major cyclic ester monomer toward commercial relevant ring-opening polymerizations.

Poly(3-ethylglycolide): a well-defined polyester matching the hydrophilic hydrophobic balance of PLA

The novel lactide isomer 3-ethyl-1,4-dioxane-2,5-dione (3-ethylglycolide, EtGly) represented the basis for the development of polyesters varying crystallinity.

Metal-free, regioselective and stereoregular alternating copolymerization of monosubstituted epoxides and tricyclic anhydrides

A metal-free, highly regioselective and stereoregular ring-opening alternating copolymerization of monosubstituted epoxides with tricyclic anhydrides was achieved to yield well-defined polyesters.

One-step synthesis, biodegradation and biocompatibility of polyesters based on the metabolic synthon, dihydroxyacetone

The one-step synthesis of a polyester family containing dihydroxyacetone is described along with a quantitative analysis of in vitro/in vivo degradation kinetics and initial biocompatibility. Polyesters were synthesized by combining dihydroxyacetone, which is a diol found in the eukaryotic glucose metabolic pathway, with even-carbon aliphatic diacids (adipic, suberic, sebacic) represented in the long-chain alpha carboxylic acid metabolic pathway, by Schӧtten-Baumann acylation. We show that by using a crystalline monomeric form of dihydroxyacetone, well-defined polyesters can be formed in one step without protection and deprotection strategies. Both diacid length and polyester molecular weight were varied to influence polymer physical and thermal properties. Polyesters were generated with number-averaged (Mn) molecular weights ranging from 2200–11,500. Polydispersities were consistent with step-growth polymerization and ranged from 2 to 2.6. The melting (Tm) and recrystallization (Tc) temperatures were impacted in an unpredictable manner. Thermal transitions for the polyesters were highest for the adipic acid followed by suberic acid and sebacic acid, respectively. It was shown that the thermal response of the DHA-based polyesters was influenced by both the diacid length and molecular weight. In vitro degradation studies revealed first-order weight loss kinetics, the molecular weight loss followed first order kinetics with 25%–40% of the original mass remaining after 8 weeks. In vivo testing over 16 weeks highlighted that mass loss ranged from ∼70% to ∼6% depending upon initial molecular weight and diacid length. Histological analysis revealed rapid resolution of both acute and chronic inflammatory responses, normal foreign body responses were observed and no inflammation was present after week 4. This one-step synthesis proved robust with unique copolymers warranting further study as potential biomaterials.

New bio-renewable polyester with rich side amino groups from l-lysine via controlled ring-opening polymerization

Lysine, a renewable resource from biomass fermentation, was converted to pure O-carboxyanhydride monomer, then well-defined polyester with amino groups was prepared via controlled ring-opening polymerization.

Synthesis and characterization of biodegradable-cum-crosslinkable well-defined polyesters via chain-growth polycondensation in solid–liquid phase

Well-defined aliphatic polyesters, polyglycolide (PGA), polylactide (PLA) and their copolymers (PLGA) were prepared by chain-growth polycondensation of potassium 2-bromocarboxylates in solid–liquid phase. The polymerization proceeded in a living fashion without any side reactions. The degrees of polymerization (D p) of polyesters was in agreement with the feed ratio of monomer to initiator. The polymer, which was only composed of heptamer, octamer and nonamer, possessed a narrow molecular weight distribution. Furthermore, the end groups of polymers, such as allyl and phenyl units, were directly yielded during the polymerization for the further modifying and crosslinking. The synthesized polyesters with allyl end groups were successfully crosslinked, and the products possessed biodegradability in phosphate buffer solution at 37 °C.

Synthesis and characterization of polyesters based on tartaric acid derivatives

A series of aliphatic polyesters based on tartaric acid and its derivatives were synthesized starting from naturally occurring L-tartaric acid. The hydroxyl groups of the tartaric acid derivatives were first protected and the polyesters were synthesized by bulk and solution polycondensation methods. Two classes of polyesters were synthesized and characterized, the first by polycondensation of dimethyl 2,3-O-isopropylidene-l-tartrate with various alkanediols, and the second by reaction of 2,3-O-isopropylidene-l-threitol with various diacid chlorides. Acid catalyzed deprotection of isopropylidene groups gave well-defined polyesters having pendant hydroxyl functional groups regularly distributed along the polymer chain. The number average molecular weights (Mn) of the polymers were found to vary in the range of 2.3–15.7 × 103 g mol−1. Differential scanning calorimetry (DSC) analysis showed the glass transition temperatures (Tg) of the polyesters varied from −36.1 °C to 17.9 °C on varying the chain length.

Enzyme-catalysis breathes new life into polyester condensation polymerizations

Traditional chemical catalysts for polyester synthesis have enabled the generation of important commercial products. Undesirable characteristics of chemically catalyzed condensation polymerizations include the need to conduct reactions at high temperatures (150-280 degrees C) with metal catalysts that are toxic and lack selectivity. The latter is limiting when aspiring towards synthesis of increasingly complex and well-defined polyesters. This review describes an exciting technology that makes use of immobilized enzyme-catalysts for condensation polyester synthesis. Unlike chemical catalysts, enzymes function under mild conditions (< or =100 degrees C), which enables structure retention when polymerizing unstable monomers, circumvents the introduction of metals, and also provides selectivity that avoids protection-deprotection steps and presents unique options for structural control. Examples are provided that describe the progress made in enzyme-catalyzed polymerizations, as well as current limitations and future prospects for developing more efficient enzyme-catalysts for industrial processes.

“Click” Reactions: Novel Chemistries for Forming Well-defined Polyester Nanoparticles

We present the synthesis of discrete functionalized polyester nanoparticles in selected nanoscale size dimensions via a controlled intermolecular chain cross-linking process facilitated via “click”-chemistry approaches such as the Cu(I)-catalyzed 1,3-dipolar cycloaddition of azides and thiol−ene reactions. Both “click” reactions led to the formation of well-defined nanoparticles with narrow size distribution and selected nanoscopic size dimensions. The controlled coupling involves the cross-linking of an alkyne functionalized polyester with a bisazide, 1,8-diazide-3,6-dioxaoctane, and an allyl functionalized polyester with 3,6-dioxa-1,8-octanedithiol. The linear functional polyester precursors were synthesized via ring-opening copolymerization of δ-valerolactone and α-propargyl-δ-valerolactone as well as with α-ally-δ-valerolactone, respectively. We found that the nanoparticle formation and the control over the nanoscopic dimension are primarily influenced by the degree of the alkyne or allyl entity implemented in the precursor polymer and the amount of bisazide and dithiol cross-linking reagents. These results underline once more the versatility of the intermolecular chain cross-linking reaction which is not limited to epoxide chemistries but can be extended to “click” reactions to form controlled nanoparticles with comparable efficiencies. This work describes the utilization of alkyne−azide and thiol−ene “click” chemistries to facilitate the controlled assembly and cross-linking of supramolecular 3-D structures in selected nanoscopic ranges.

Chain‐Growth Polycondensation: Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chain-Growth Polycondensation: Living Polymerization Nature in Polycondensation and Approach to Condensation Polymer Architecture

In this review article, polycondensation that proceeds in a chain-growth polymerization manner (“chain-growth polycondensation”) for well-defined condensation polymers are described. Our approach to chain-growth polycondensation is (1) activation of polymer end group by substituent effects changed between monomer and polymer and (2) phase-transfer polymerization in biphase composed of monomer store phase and polymerization phase. In the approach (1), a variety of condensation polymers such as aromatic polyamides, aromatic polyesters, aromatic polyethers, poly(ether sulfone), and polythiophene with defined molecular weights and low polydispersities were obtained. Their polycondensations had all of the characteristics of living polymerization: a linear correlation between molecular weights and monomer conversion maintaining low polydispersities, and control over molecular weights by the feed ratio of monomer to initiator. Taking advantage of the nature of living polymerization in this polycondensation, we synthesized diblock copolymers of different kinds of aromatic polyamides and of aromatic polyamide and conventional polymers such as poly(ethylene glycol), polystyrene, and poly(tetrahydrofuran), as well as triblock copolymers and star polymers containing aromatic polyamide units. Some copolymers were arranged in a supramolecular self-assembly. In the approach (2), the polycondensation of solid monomer dispersed in organic solvent with a phase transfer catalyst (PTC) was carried out, where solid monomer did not react with each other, and the monomer transferred to organic solvent with PTC reacted with an initiator and the polymer end group selectively in organic solvent, to yield well-defined polyesters.

Application of ketenes to well-defined polyester synthesis (4): End-capping reactions in living anionic polymerization of ethylphenylketene

End-capping reactions of a living polyester, obtained by anionic polymerization of ethylphenylketene (EPK), were carried out. As end-capping reagents, electrophiles such as alkyl halide and acyl halide were successfully used. Reactivity of the terminal enolate and the resulting terminal structures were elucidated by model reactions, using lithium enolates having low molecular weights, obtained by an equimolar reaction of EPK with butyllithium. Polymerization of EPK by lithium alkoxide and the subsequent end-capping reaction afforded the corresponding polyester having functional groups at both chain ends and a narrow molecular weight distribution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3103–3111, 2002

Chain-Growth Polycondensation in Solid-Liquid Phase with Ammonium Salts for Well-Defined Polyesters

Polycondensation of a potassium 4-bromomethylbenzoate derivative dispersed in organic solvent was carried out with tetrabutylammonium iodide as a phase transfer catalyst (PTC) and a reactive benzyl bromide as an initiator to yield polyesters having a defined molecular weight and a narrow molecular weight distribution (M̄w/M̄n < 1.3). Polymerization involves the transfer of monomer to organic solvent layer with the PTC and the reaction of monomer with the initiator and the polymer end benzyl bromide moiety in a chain polymerization manner, as evidenced by polymerization behavior; increase of the molecular weight in proportion to monomer conversion and equal amount of the initiator unit and the end group in polymer irrespective of monomer conversion. Furthermore, the molecular weight increased in proportion to feed ratio ([monomer]0/[initiator]0), and the polydispersity index M̄w/M̄n stayed less than 1.3 over the whole range of feed ratio.

Application of ketenes to well-defined polyester synthesis. III. Living anionic polymerization of ethyl(4-methoxyphenyl)ketene?Development of polyester having masked phenol side chain

A novel ketene, ethyl(4-methoxyphenyl)ketene (EMPK), was synthesized by the dehydrochlorination of 2-(4-methoxyphenyl)butanoyl chloride. The anionic polymerizations of EMPK by butyllithium in tetrahydrofuran at −20 °C were carried out with a varying feed ratio to give the corresponding polyesters having predictable molecular weights and narrow molecular weight distributions, quantitatively. The selective formation of the polyester was confirmed by IR analysis, and the reductive degradation of the polymer was supported by lithium–aluminium hydride. The second feed of the monomer (after the first stage of polymerization) resulted in the formation of the polymer with the expectedly increased molecular weight and low polydispersity to strongly support the living mechanism of this polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1596–1600, 2001

Living anionic polymerization of ethylphenylketene: A novel approach to well-defined polyester synthesis

A living polymerization of ethylphenylketene (EPK) was accomplished. When polymerization of EPK was carried out with butyllithium as an initiator in tetrahydrofuran (THF) at -20 °C, EPK was completely consumed within 5 min, and the corresponding polyester with narrow molecular weight distribution (M w /M n ∼ 1.1) was obtained almost quantitatively. Kinetic study of the polymerization at -78 °C revealed that conversion of EPK agreed with the first-order kinetic equation, and that M n of the polymer increased in virtually direct proportion to the conversion. Along with these results, successful results in postpolymerization at -20 °C strongly supported living mechanism of the present polymerization. Further, lithium alkoxides having a methoxy group, styryl moiety, and nitroxyl radical, also successfully initiated polymerization of EPK to afford the corresponding polymers having functional initiating ends. In the polymerization with varying feed ratio [EPK] 0 /[initiator] 0 , the linear relationship between the feed ratio and M n of the obtained polymer was observed, while maintaining narrow M w /M n .