Rapid synthesis of biodegradable poly(epsilon-caprolactone-co-p-dioxanone) random copolymers under microwave irradiation

Biodegradable poly(epsilon-caprolactone-co-p-dioxanone)(PCDO) random copolymers have been synthesized by ring-opening polymerization of epsilon-caprolactone(CL) and p-dioxanone(PDO) under microwave irradiation.The effects of irradiation time and different CL/PDO molar feed ratios on the microwave-assisted ring-opening polymerization(MROP) of PCDO have been discussed.The resultant products were characterized by ~1H NMR,GPC and DSC.It was found that the polymerization was completed within 20 min at 140℃.In th...

Design,synthesis and characterization of novel biodegradable macrodiols based on poly(DL-lactic acid) and poly(p-dioxanone)

Integrating poly（lactic acid） （PLA）, glycolic acid （GA） and ethylene glycol （EG） will hopefully result in a novel copolymer that combines such advantages as fastened and controllable release rate and improved flexibility together with good biocompatibility. In this study, p-dioxanone （PDO） was employed to copolymerize with DL-lactide （LA） via ring-opening melt polymerization using Sn（Oct）2 as an initiator and ethylene glycol as a co-initiator. The obtained degradable macrodiols （HO-P（LA-co-PDO）-OH） were just such a copolymer consisting of PLA, GA and EG. 1HNMR was employed to characterize the copolymers, and the effect of PDO/LA molar ratios in the feedstock on the molecular weights of HO-P（LA-co-PDO）-OH was investigated by means of endhydroxyl analysis, 1H NMR or GPC-MALLs. The results confirmed the successful synthesis of HO-P（LA-co-PDO）-OH and revealed that one end-hydroxyl of the micarodiols was donated by LA or PDO and the other one by the co-initiator EG. In addition, the molecular weights of HO-P（LA-co-PDO）-OH increased with decreasing PDO/LA ratios.

Enzymatic Synthesis and Characterization of Novel Amphiphilic Triblock Copolymer Poly(p-dioxanone-co-5-benzyloxytrimethylene carbonate)-block-poly(ethylene glycol)

Novel amphiphilic triblock copolymer poly（p-dioxanone-co-5-benzyloxytrimethylene carbonate）-block-poly（ethylene glycol）-block-poly（p-dioxanone-co-5-benzyloxytrimethylene carbonate） （p（PDO-co-BTMC）-b-PEG-b-p（PDO-co-BTMC）） was successfully synthesized using immobilized porcine pancreas lipase on porous silica particles （IPPL） as the catalyst for the fLrSt time. 1H NMR, 13C NMR and GPC analysis were used to confirm the structures of resulting copolymers. The molecular weight （Mn） of the copolymer with feed ratio of 69：20：11 （BTMC： PDO： PEG ） was 31300 g/mol and the polydispersity was 1.85, while the Mn decreased to 25000 g/mol and polydispersity of 1.93 with the feed ratio of 50：40：10.

Biodegradable Radiopaque Composite Filaments Based on Poly(p-dioxanone)and 2,3,5-triiodobenzoic Acid

To determine the possibility of blending 2, 3, 5-triiodobenzoic acid( TIBA) and poly( p-dioxanone)( PPDO) to produce X-ray visible PPDO filaments,melt-blended PPDO with different concentrations of TIBA was obtained. Several radiopaque filaments of PPDO polymer filled with radiopaque TIBA particles were prepared via melt-blending. Material properties of the composite filaments were investigated using various material characterization techniques,including scanning electron microscope( SEM),thermogravimetric analysis( TGA),X-ray Diffraction( XRD),dynamic rheometry and micro-CT scan. In this article,the dispersion of TIBA in PPDO,the properties of the filament,and the ratio of PPDO and TIBA and the corresponding X-ray visibility in vivo were studied. SEM results showed the dispersion of the contrast imaging agent TIBA was relatively even in the PPDO polymer. Xray analysis in vitro confirmed the enhanced radiopacity of the filaments with respect to the pure PPDO filament. The presence of iodine element in the composite filament could allow the bioabsorbable material to be monitored in vivo, and made it potential to be used in biomedical applications.

Boosting thermal stability and crystallization of closed-loop-recyclable biodegradable poly(p-dioxanone) by end-group regulation

A chemically closed-loop-recyclable biodegradable polymer,poly(p-dioxanone)(PPDO),is one of the ideal candidates for single-use plastic products due to its suitability for different application scenarios.Fascinatingly,when PPDO wastes can be collected,its monomer p-dioxanone(PDO) will be obtained through chemical recycling of these wastes;when cannot be collected,the wastes are able to be biodegraded into harmless substances.However,unsatisfied thermal stability and low crystallization rate of PPDO restrict its wider applications.Herein,based on end-group regulation,we simultaneously realized the significant enhancement of thermal stability and crystallization of PPDO through the simple melt processing with tributyl phosphite(TBP) or triphenyl phosphite(TPP).The model reactions were conducted to investigate the reaction mechanism and theoretical products during the preparation of PPDO/phosphite compounds.Two kinds of phosphites were proved to act as the end-capped reagent and chain extender in the melt processing,while TBP presented better reactivity.As a result,the activation energy of thermal decomposition was largely elevated,and the unprecedented T_(5%)(the temperature at a weight loss of 5%) and Tmax(the temperature at a maximum rate of weight loss) of PPDO were obtained,i.e.,T_(5%)of ~330 ℃ and Tmaxof ~385 ℃ in N_(2) atmosphere,T_(5%)of ~240 ℃ and Tmaxof ~317 ℃ in air atmosphere,respectively.Furthermore,the increased crystallization rate,crystallinity,crystalline orderliness,and realizable monomer recovery(yield >90%,purity >99.9%) of PPDO/phosphite compounds were confirmed.

Electrospun Poly(p-dioxanone)/Poly(ester-urethane)ureas Composite Nanofibers for Potential Heart Valve Tissue Reconstruction

Electrospun nanofibrous mats represent a new generation of medical textiles with promising applications in heart valve tissue reconstruction. It is important for biomaterials to mimic the biological and mechanical microenvironment of native extracellular matrix(ECM). However, the major challenges are still remaining for current biomedical materials, including appropriate mechanical properties,biocompatibility, and hemocompatibility. In the present work, the novel composite nanofibrous mats of poly(p-dioxanone)(PDO) and poly(ester-urethane)ureas(PEUU) are fabricated by electrospinning system. The optimal combination ratio of PDO to PEUU may balance the mechanical properties and cellular compatibility to match the newly formed tissue. In PDO/PEUU composite nanofibrous mats, PEUU can provide the biomimetic elastomeric behavior, and PDO could endow the excellent biocompatibility. In comparison to nanofibrous mat of neat PDO, the composite showed significantly improved mechanical properties, with 5-fold higher initial elongation at break.Furthermore, human umbilical vein endothelial cells(HUVECs) were cultured on the composite to evaluate its ability to rapidly endothelialize as heart valve tissue engineering. The results revealed that PDO/PEUU composite nanofibrous mats could promote cell adhesion and proliferation, especially for the ratio of 60/40. Overall, PDO/PEUU composite nanofibrous mats(60/40) show the excellent mechanical properties, appropriate biocompatibility and hemocompatibility which meet the necessary norm for tissue engineering and may be suitable for potential heart valve tissue reconstruction.

Design,synthesis and characterization of novel poly(urethane-urea) based on a macrodiol from poly(lactic acid) and poly(p-dioxanone)

A series of novel poly（urethane-urea）（PUU） was synthesized from poly（lactide-co-p-dioxanone） macrodiol（HO-P（LA-co-PDO）-OH）, hexamethylene diisocyanate（HDI） and butanediamine（BDA）.The obtained PUU,which is recorded as P（LA-co-PDO）-PUU here,may demonstrate enhanced phase separation and thus improved shape memory property.FTIR was employed to characterize the copolymers,and the effects of NCO/OH molar ratios on Tg of PUU was investigated by means of differential scanning calorimetry （DSC）.The results revealed the successful synthesis of P（LA-co-PDO）-PUU.In addition,the Tg of P（LA-co-PDO）-PUU increased from 37.9℃to 44.2℃with the increase NCO/OH ratios from 1.1 to 1.2.The P（LA-co-PDO）-PUU with Tg close to body temperature will have potential applications as shape memory polymers in biomedical fields,especially in minimally invasive surgery.

Synthesis of novel copolymer:Poly(p-dioxanone-co-L-phenylalanine)

In order to expand the application of poly（p-dioxanone） or PPDO in biomedical area,a series of novel copolymers were synthesized successfully by one-step,melted copolymerization of p-dioxanone（PDO） and L-phenylalanine N-carboxyanhydride（L-Phe-NCA） monomers.With the in-feed molar ratio of L-PheNCA /PDO equal to 1/20,the conversions of the two kinds of monomers were calculated from 1H NMR. The average molecular weight and polydispersity of the copolymer increase with the increasing reaction time and catalyst concentration.However,the conversions of the two kinds of monomers did not change with the reaction conditions.A three-step mechanism is presented and proved by high resolution 1H NMR and IR spectrums.

Hydrolytic Degradation Behaviors of Poly(p-dioxanone) in Ambient Environments

The effects of temperature and relative humidity on the hydrolytic degradation of poly（p-dioxanone）（PPDO） were investigated. The hydrolytic degradation behaviors were monitored by tracing the changes of water absorption, mechanical and crystalline properties, molecular weight and its distribution, surface morphologies, as well as infrared absorption peaks and hydrogen chemical shifts during the degradation. It is found that the water absorption increases whilst the intrinsic viscosity, tensile strength and elongation at break decrease as the temperature or relative humidity increases. With degradation time growing, the molecular weight drops and its distribution broadens. The crystallinity of PPDO has a tendency to increase at first and then to decrease, while the crystalline structure is not significantly changed. At the same time, some cracks are observed on the surface and keep growing and deepening. All results show that temperature plays more significant roles than relative humidity during the degradation. The analyses of Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy reveal that the degradation of PPDO is a predominant hydrolysis of ester linkages.

Shape-memory poly(p-dioxanone)–poly(ε-caprolactone)/sepiolite nanocomposites with enhanced recovery stress

Shape-memory poly（p-dioxanone）–poly（e-caprolactone）/sepiolite（PPDO–PCL/OSEP） nanocomposites with different OSEP nanofiber loading were fabricated by chain-extending the PPDO-diol and PCL/OSEP precursors. The precursors and the composites were characterized by1 H NMR, FT-IR, GPC, SEM and TEM.The results demonstrate that a part of PCL segments grafted on the surface of OSEP and composites display a fine dispersion of OSEP fiber in nanoscale with low OSEP content. The shape memory effect（SME） was evaluated by DMA, the results reveal that the PPDO–PCL/OSEP nanocomposites exhibit desirable shape-memory performance. The reinforcement of composites by incorporation of trace OSEP nanofiber evokes an effective improvement in shape-memory recovery stress.

Crystallization induced micellization of poly(p-dioxanone)-block-polyethylene glycol diblock copolymer functionalized with pyrene moiety

Poly（p-dioxanone）-block-polyethylene glycol diblock copolymers functionalized with pyrene moieties（Py-PPDO-b-PEG） at the chain ends of PPDO blocks were synthesized for preparing anisotropic micelles with improved stability.The micellization and crystallization of the copolymers were investigated by nano differential scanning calorimetry（Nano DSC）,transmission electron microscopy（TEM）,UV-vis spectrophotometery,fluorophotometer,and dynamic light scattering（DLS）,respectively.The results indicated that the aggregation of pyrene induced by intermolecular interaction lead to micellization of Py-PPDO-b-PEG at much lower concentrations than those of PPDO-b-PEG copolymers without pyrene moieties.The aggregation of pyrene moieties may also serve as nucleation agent and therefore enhance the crystallization rate of PPDO blocks.Fluorescence measurements by using Nile Red as the fluorescent agent indicated that the micelles of Py-PPDO-b-PEG have high stability and load capacity for hydrophobic molecules.

In situ generation of biodegradable poly(p-dioxanone)microparticles by polymerization in supercritical carbon dioxide

Ring-opening suspension polymerization of p-dioxanone（PDO） in supercritical carbon dioxide（scCO_2） was investigated in the presence of poly（caprolactone）-perfluropolyether-poly（caprolactone）（PCL-PFPE-PCL）.The molecular weight,yield and particle morphology of poly（p-dioxanone）（PPDO） were studied.The stabilizer was effective to stabilize the ring-opening polymerization（ROP） of PDO in scCO_2,leading to the formation of resorbable microparticles in a＂one pot＂procedure.The mean size of PPDO microparticles obtained from suspension polymerizations was sensitive to the rate of agitation and the stabilizer concentration.The method to generate PPDO microparticles has overcome its unprocessable drawback with common organic solvents and provided new product form for biomedical applications.

Synthesis and characterization of poly(p-dioxanone)-based degradable copolymers with enhanced thermal and hydrolytic stabilities

Herein, we presented a novel biodegradable copolymer via the chain extending reaction of poly(pdioxanone)-co-poly(2-(2-hydroxyethoxy) benzoate)(PPDO-co-PDHB) prepolymer with hexamethylene diisocyanate(HDI) as a chain extender. The structures and molecular weight of PPDO-co-PDHB prepolymer and PPDO-co-PDHB-PU chain-extended copolymer are characterized via hydrogen nuclear magnetic resonance spectroscopy(1 H NMR) and viscosity test. The relationship between the molecular structures and properties of the chain-extended copolymers is established. The PPDO-co-PDHB-PU copolymers possess a better thermal stability comparing with the PPDO homopolymer. The study of mechanical properties shows that the elongation-at-break of PPDO-co-PDHB-PU is much higher than that of PPDO. The investigation of hydrolytic degradation behaviors indicates the degradation rate of PPDO can be controlled by adjusting the PDHB compositions, and proves that chain-extended copolymers exhibit an excellent hydrolytic stability being better than that of PPDO.

Controlled synthesis and closed-loop chemical recycling of biodegradable copolymers with composition-dependent properties

The closed-loop recycling concept of the polymer wastes into building-block chemicals is attractive,but the closed-loop recycling of copolymers enabled by energy-efficient chemical recycling and cost-effective separations is still facing great challenges.Herein,for the first time,a one-pot sequential copolymerization of γ-butyrolactone(γ-BL) and p-dioxanone(PDO)using an economical ureas/alkoxides catalytic system is conducted to synthesize biodegradable and chemically recyclable poly-(γ-butyrolactone)-block-poly(p-dioxanone)(PγBL-b-PPDO) diblock copolymers with well-defined and controlled structures.The composition-dependent properties of PγBL-b-PPDO copolymers,including thermal properties and crystallization behavior,are investigated.The results show that the thermal stability and crystalline ability of PγBL are enhanced observably by introducing the PPDO block.Significantly,the PγBL-b-PPDO copolymers can be depolymerized efficiently into the corresponding co-monomers with a yield of over 95% by simply low-temperature pyrolysis under vacuum.Moreover,γ-BL and PDO monomers are selectively separated with an isolated purity of about 99% based on the difference in their physicochemical properties.Subsequently,their repolymerization is realized to obtain the copolymers with nearly identical structures and thermostability,demonstrating the closed-loop recycling of copolymers,i.e.,polymerization-depolymerization-repolymerization.This research provides important guidance for the design of novel sustainable polymers towards more efficient chemical recycling,separation and regeneration.

Synthesis of depsipeptides from L-amino acids and lactones

By using the corresponding L-amino acid sodium as initiator,ε-caprolactone-depsipeptides CL-Ala and CL-Leu were prepared by the reactions ofε-caprolactone(CL)with L-alanine and L-leucine,respec-tively,and p-dioxanone-depsipeptide(PDO-Leu)was prepared by the reaction of p-dioxanone(PDO)with L-leucine.Two poly(ε-caprolactone)oligomers(PCL-Ala and PCL-Leu)of different molecular weights with depsipeptide unit were synthesized by controlling the feed ratio of L-amino acid sodium and CL.The presence of the depsipeptide structure in these obtained products was confirmed by 1H NMR spectra and the molecular weight of the poly(ε-caprolactone)oligomers was measured by gel permeation chromatography(GPC).These products con-tain a hydroxyl group and a carboxyl group in one molecule,which means they could act as bifunctional monomers for further polymerization to prepare high molecular weight polymers.By this way,the depsipeptide unit could be introduced into the polymers and the biodegradation rates of the novel polymers could be well controlled in vivo by the tailored molecular structures.

Preparation of polymer nanocomposites with enhanced mechanical properties using hybrid of graphene and partially wrapped multi-wall carbon nanotube as nanofiller

Triblock copolymer of poly（p-dioxanone） and polyethylene glycol end-capped with pyrene moieties（（Py-PPDO）_2-b-PEG） was synthesized and used as modifier for multi-wall carbon nanotubes（MWCNTs）.Nano-aggregates（（Py-PPDO）_2-b-PEG@MWCNTs） with shish-kebab like partially wrapped morphology and very good stability were obtained by incorporating the copolymer with MWCNTs.The bare MWCNT sections of（Py-PPDO）_2-b-PEG@MWCNTs were able to induce n-n interactions with graphene（GE） and resulted in a novel GE/（Py-PPDO）_2-b-PEG@MWCNTs hybrid.The dispersity of GE in solution or polymer matrix was therefore greatly improved.The PCL nanocomposite films using GE/（Py-PPDO）_2-bPEG@MWCNTs as hybrid nanofiller exhibited obviously improved mechanical properties especially at very low hybrid nanofiller content.The influence of the nanofiller content and feed ratio of GE/MWCNTs on the mechanical properties of composites films was evaluated.When the feed ratio of GE to MWCNTs is 2：8 and the total loading of nanofiller is only 0.01 wt%,the tensile strength of the composite film increased by 163%and the elongation at break increased by 17% compared to those of neat PCL These results can be attributed to fine dispersion of the nanofillers in PCL matrix and the hybrid interactions between GE and MWCNTs.Therefore,this work provides a novel method for preparing polymer nanocomposites with high mechanical performance and low nanofiller loading.