Synthesis and Characterization of Biodegradable Homopolymers and Block Copolymers Based on 1,5-Dioxepan-2-one

Synthesis and Post-Functionalization of Poly(conjugated ester)s Based on 3-Methylene-1,5-dioxepan-2-one

Poly(α-methylene ester)s are an attractive type of functional aliphatic polyesters that represent a platform for the fabrication of various biodegradable and biomedical polymers. Herein, we report the controlled ring-opening polymerization (ROP) of a seven-membered α-methylene lactone (3-methylene-1,5-dioxepan-2-one, MDXO) that was synthesized based on the Baylis-Hillman reaction. The chemoselective ROP of MDXO was catalyzed by diphenyl phosphate (DPP) at 60 °C or stannous octoate (Sn(Oct)₂) at 130 °C, generating α-methylene-containing polyester (PMDXO) with a linear structure and easily tunable molar mass. The ring-opening copolymerization of MDXO with ε-caprolactone or 1,5-dioxepan-2-one was also performed under the catalysis of DPP or Sn(Oct)₂ to afford copolymers with different compositions and sequence structures that are influenced by the kinds of monomers and catalysts. PMDXO is a slowly crystallizable polymer with a glass transition temperature of ca. -33 °C, and its melting temperature and enthalpy are significantly influenced by the thermal history. The thermal properties of the copolymers are dependent on their composition and sequence structure. Finally, the post-modification of PMDXO based on the thiol-Michael addition reaction was briefly explored using triethylamine as a catalyst. Given the optimized condition, PMDXO could be dually modified to afford biodegradable polyesters with different functionalities.

Studying the Ring-Opening Polymerization of 1,5-Dioxepan-2-one with Organocatalysts

Three different organocatalysts, namely, 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris (dimethylamino) phosphoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene) (t-BuP4), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), have been used as 1,5-dioxepan-2-one (DXO) ring-opening polymerization (ROP) catalysts at varied reaction conditions. 1H NMR spectra, size exclusion chromatography (SEC) characterizations, and kinetic studies prove that the (co)polymerizations are proceeded in a controlled manner with the three organocatalysts. It is deduced that t-BuP4 and DBU catalysts are in an initiator/chain end activated ROP mechanism and TBD is in a nucleophilic ROP mechanism.

Strong, Resilient, and Sustainable Aliphatic Polyester Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) composed of ABA block polymers exhibit a wide variety of properties and are easily processable as they contain physical, rather than chemical, cross-links. Poly(γ-methyl-ε-caprolactone) (PγMCL) is an amorphous polymer with a low entanglement molar mass (M_e = 2.9 kg mol^-1), making it a suitable choice for tough elastomers. Incorporating PγMCL as the midblock with polylactide (PLA) end blocks (f_LA = 0.17) results in TPEs with high stresses and elongations at break (σ_B = 24 ± 2 MPa and ε_B = 1029 ± 20%, respectively) and low levels of hysteresis. The use of isotactic PLA as the end blocks (f_LLA = 0.17) increases the strength and toughness of the material (σ_B = 30 ± 4 MPa, ε_B = 988 ± 30%) due to its semicrystalline nature. This study aims to demonstrate how the outstanding properties in these sustainable materials are a result of the entanglements, glass transition temperature, segment-segment interaction parameter, and crystallinity, resulting in comparable properties to the commercially relevant styrene-based TPEs.

Microspheres from Poly(D,L-Lactide)/Poly(1,5-Dioxepan-2-One) Miscible Blends for Controlled Drug Delivery

Novel biodegradable microspheres were designed from blends of poly(D,L-lactide) (PDLLA) and poly(1,5-dioxepan-2-one) (PDXO). The addition of PDXO to PDLLA yielded a more pliable and versatile matrix, where the properties can be controlled by means of composition. The components were fully miscible and formed homogeneous, amorphous, smooth and dense microspheres. Blend composition was a vital factor in determining the blend properties, morphology and in vitro degradation. Diclofenac sodium, a non-steroidal anti-inflammatory drug, was incorporated into PDLLA-PDXO microspheres of various composition ratios. Sustained release of drug was obtained. The degradation and release rates of PDLLA-PDXO microspheres were dependent on the blend composition, providing a powerful means of controlling drug delivery.

Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization

The need for polymers for high-end applications, coupled with the desire to mimic nature's macromolecular machinery fuels the development of innovative synthetic strategies every year. The recently acquired macromolecular-synthetic tools increase the precision and enable the synthesis of polymers with high control and low dispersity. However, regardless of the specificity, the polymerization behavior is highly dependent on the monomeric structure. This is particularly true for the ring-opening polymerization of lactones, in which the ring size and degree of substitution highly influence the polymer formation properties. In other words, there are two important factors to contemplate when considering the particular polymerization behavior of a specific monomer: catalytic specificity and thermodynamic equilibrium behavior. This perspective focuses on the latter and undertakes a holistic approach among the different lactones with regard to the equilibrium thermodynamic polymerization behavior and its relation to polymer synthesis. This is summarized in a monomeric overview diagram that acts as a presynthetic directional cursor for synthesizing highly specific macromolecules; the means by which monomer equilibrium conversion relates to starting temperature, concentration, ring size, degree of substitution, and its implications for polymerization behavior are discussed. These discussions emphasize the importance of considering not only the catalytic system but also the monomer size and structure relations to thermodynamic equilibrium behavior. The thermodynamic equilibrium behavior relation with a monomer structure offers an additional layer of complexity to our molecular toolbox and, if it is harnessed accordingly, enables a powerful route to both monomer formation and intentional macromolecular design.

An aromatic/aliphatic polyester prepared via ring-opening polymerisation and its remarkably selective and cyclable depolymerisation to monomer

The ring-opening polymerisation of 2,3-dihydro-5H-1,4-benzodioxepin-5-one gives polyester homopolymers and copolymers that contain both aromatic and aliphatic linkages. The polymers can be easily depolymerised by Al catalysts.

Capillary zone electrophoresis as a tool to monitor the last stages of the degradation of water-sensitive polymers

In order to monitor the formation of the water-soluble by-products from chain-scission of degradable polymers used in the biomedical field, four capillary electrophoresis methods are discussed with the aim of giving the limits and performance for each. Three of them (electroosmotic flow reversal by dynamic adsorption of a polycation, multilayer polyelectrolyte coatings and physical binding of polyethylene oxide) are based on the use of dynamic coatings onto the inner surface of a fused silica capillary, a simple means to adapt performance to specific separations via modification and control of the electroosmotic flow of fused capillary. Using oligomers of lactic acid considered as standards the methods are compared. Other examples of ester-containing macromolecules (poly(hydroxybutyrate)), as well as degradable polyanions are described, namely N-acetylneuraminate polymer and poly(beta-malic acid).

Bulk Ring-Opening Transesterification Polymerization of the Renewable δ-Decalactone Using an Organocatalyst

The bulk ring-opening polymerization of renewable δ-decalactone using 1,5,7-triazabicyclo[4.4.0]dec-5-ene was carried out at temperatures between 7 and 110 °C. The equilibrium monomer concentration for reactions within this temperature range was used to determine the polymerization thermodynamic parameters (ΔH_p = -17.1 ± 0.6 kJ mol^-1, ΔS_p = -54 ± 2 J mol^-1 K^-1) for δ-decalactone. The polymerization kinetics were established and high molar mass poly(δ-decalactone) was prepared with a glass transition temperature of -51 °C. Poly(δ-decalactone) samples with controlled molar mass and narrow molar mass distributions were realized by controlling the monomer conversion and initiator concentration. A high molar mass poly(lactide)-poly(δ-decalactone)-poly(lactide) triblock copolymer with a low polydispersity index was prepared by simple sequential addition of monomers. The product triblock exhibited two distinct glass transitions temperatures consistent with microphase segregation.

Structure-Processing-Property Relationship of Poly(Glycolic Acid) for Drug Delivery Systems 1: Synthesis and Catalysis

Till date, market is augmented with a huge number of improved drug delivery systems. The success in this area is basically due to biodegradable polymers. Although conventional systems of drug delivery utilizing the natural and semisynthetic polymers so long but synthetic polymer gains success in the controlled drug delivery area due to better degradation profile and controlled network and functionality. The polyesters are the most studied class group due the susceptible ester linkage in their backbone. The Poly(glycolic Acid) (PGA), Poly(lactic acid) (PLA), and Polylactide-co-glycolide (PLGA) are the best profiled polyesters and are most widely used in marketed products. These polymers, however, still are having drawbacks which failed them to be used in platform technologies like matrix systems, microspheres, and nanospheres in some cases. The common problems arose with these polymers are entrapment inefficiency, inability to degrade and release drugs with required profile, and drug instability in the microenvironment of the polymers. These problems are forcing us to develop new polymers with improved physicochemical properties. The present review gave us an insight in the various structural elements of Poly(glycolic acid), polyester, with in depth study. The first part of the review focuses on the result of studies related to synthetic methodologies and catalysts being utilized to synthesize the polyesters. However the author will also focus on the effect of processing methodologies but due some constraints those are not included in the preview of this part of review.

Amorphous linear aliphatic polyesters for the facile preparation of tunable rapidly degrading elastomeric devices and delivery vectors

A versatile method for preparing amorphous degradable elastomers with tunable properties that can be easily fabricated into a wide variety of shape-specific devices was investigated. Completely amorphous, liquid poly(ester ether) prepolymers with number-average molecular weights between 4 and 6 x 10(3) g/mol were prepared via condensation polymerization. These liquid prepolymers were then thermally cross-linked to form degradable elastomeric structures. The ability to vary the composition of these liquid prepolymers allows for easy control of the mechanical and degradation properties of the resulting elastomeric structures. Materials can be designed to completely degrade in vitro over a range of 30 days to 6 months, while the Young's modulus can be varied over 3 orders of magnitude (G = 0.02-20 MPa). Also, the liquid nature of these prepolymers makes them amenable to a wide variety of fabrication techniques. Using traditional and modified imprint lithography techniques, we have fabricated devices that demonstrate a wide variety of biologically applicable topologies, which could easily be extended to fabricate devices with more complex geometries. Until now, no method has combined this ease and speed of fabrication with the ability to control the mechanical and degradation properties of the resulting elastomers over such a broad range.

Controllable Degradation Product Migration from Cross-Linked Biomedical Polyester-Ethers through Predetermined Alterations in Copolymer Composition

Uniformly degrading biomaterials with adjustable degradation product migration rates were customized by combining the advantages of cross-linked poly(epsilon-caprolactone) with the hydrophilic character of poly(1,5-dioxepan-2-one). Hydrolytic degradation of these random cross-linked networks using 2,2'-bis-(epsilon-caprolactone-4-yl) propane (BCP) as the cross-linking agent was studied for up to 546 days in phosphate buffer solution at pH 7.4 and 37 degrees C. The hydrophilicity of the materials was altered by varying the copolymer compositions. After different hydrolysis times the materials were characterized, and the degradation products were extracted from the buffer solution and analyzed. Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy, and gas chromatography-mass spectrometry were used to observe the changes taking place during the hydrolysis. From the results it was concluded that degradation profiles and migration of degradation products are controllable by tailoring the hydrophilicity of cross-linked polyester-ether networks.

Resilient Bioresorbable Copolymers Based on Trimethylene Carbonate,l-Lactide, and 1,5-Dioxepan-2-one

The new combinations of monomers presented in this work were evaluated in order to create an elastic material for potential application in soft tissue engineering. Thermoplastic elastomers (TPE) of trimethylene carbonate (TMC) with L-lactide (LLA) and 1,5-dioxepan-2-one (DXO) have been synthesized using a cyclic five-membered tin alkoxide initiator. The block copolymers were designed in such a way that poly(trimethylene carbonate-co-1,5-dioxepan-2-one) formed an amorphous middle block and the poly(L-lactide) (PLLA) formed semicrystalline terminal blocks. The amorphous middle block consisted of relatively randomly distributed TMC and DXO monomer units, and the defined block structure of the PLLA terminal segments was confirmed by 13C NMR. The properties of the TMC-DXO-LLA copolymers were compared with those of triblock copolymers based either on LLA-TMC or on LLA-DXO. Differential scanning calorimetry and dynamic mechanical analysis data confirmed the micro-phase separation in the copolymers. The mechanical properties of the copolymers were evaluated using tensile testing and cycling loading. All of the copolymers synthesized showed a highly elastic behavior. The properties of copolymers could be tailored by altering the proportions of the different monomers.

Amphiphilic copolymers of epsilon-caprolactone and gamma-substituted epsilon-caprolactone. Synthesis and functionalization of poly(D,L-lactide) nanoparticles

Fully biodegradable and surface-functionalized poly(D,L-lactide) (PLA) nanoparticles have been prepared by a co-precipitation technique. Novel amphiphilic random copolyesters P(CL-co-gammaXCL) were synthesized by controlled copolymerization of epsilon-caprolactone and epsilon-caprolactone substituted in the gamma-position by a hydrophilic X group, where X is either a cationic pyridinium (gammaPyCL) or a non-ionic hydroxyl (gammaOHCL). Nanoparticles were prepared by co-precipitation of PLA with the P(CL-co-gammaXCL) copolyester from a DMSO solution. Small amounts of cationic P(CL-co-gammaPyCL) copolymers are needed to quantitatively form stable nanoparticles (ca. 10 mg/ 100 mg PLA), although larger amounts of non-ionic P(CL-co-gammaOHCL) copolymers are needed (> or = 12.5 mg/ 100 mg PLA). Copolymers with a low degree of polymerization (ca. 40) are more efficient stabilizers, probably because of faster migration towards the nanoparticle-water interface. The nanoparticle diameter decreases with the polymer concentration in DMSO, e.g. from ca. 160 nm (16 mg/ml) to ca. 100 nm (2 mg/ml) for PLA/P(CL-co-gammaPyCL) nanoparticles. Migration of the P(CL-co-gammaXCL) copolyesters to the nanoparticle surface was confirmed by measurement of the zeta potential, i.e. ca. +65 mV for P(CL-co-gammaPCL) and -7 mV for P(CL-co-gammaOHCL). The polyamphiphilic copolyesters stabilize PLA nanoparticles by electrostatic or steric repulsions, depending on whether they are charged or not. They also impart functionality and reactivity to the surface, which opens up new opportunities for labelling and targeting purposes.

Recent Developments in Ring Opening Polymerization of Lactones for Biomedical Applications

Aliphatic polyesters prepared by ring-opening polymerization of lactones are now used worldwide as bioresorbable devices in surgery (orthopaedic devices, sutures, stents, tissue engineering, and adhesion barriers) and in pharmacology (control drug delivery). This review presents the various methods of the synthesis of polyesters and tailoring the properties by proper control of molecular weight, composition, and architecture so as to meet the stringent requirements of devices in the medical field. The effect of structure on properties and degradation has been discussed. The applications of these polymers in the biomedical field are described in detail.