Stannous Octanoate Research Articles

Synthesis and catalytic performance of wood cellulose nanofibers grafted with polylactic acid in rare-earth complexes based on tetrazole carboxylic acids

Stannous octanoate [Sn(Oct)2] and 4-dimethylamino pyridine (DMAP) were used to catalyze the synthesis of amphiphilic cellulose-based graft copolymers, but the acute toxicity of tin ions and DMAP prompts the need for the application of less harmful catalysts. Herein, green catalyst complexes 1–3 [M(H0.5L)2(H2O)5]·2(H2O) (M = Sm, 1; M = Nd, 2; M = Eu, 3; H2L = 4-(3-(tetrazol-5-yl)pyridin-5-yl)benzoic acid) were synthesized, and their properties were systematically investigated. Single-crystal X-ray diffraction showed that the complexes possessed a zero-dimensional structure, while the thermogravimetry and scanning electron microscopy results confirmed their stability after heating at 110 °C for 10 h. Using complexes 1–3 and DMAP as the catalysts, CNFs were grafted with l-lactide via homogeneous ring-opening polymerization to form wood cellulose nanofibers grafted with l-lactide (WGLAs), and the effects of the ratio of wood cellulose nanofibers (WCNFs) to l-lactide ([AGU]/[LA]) and catalyst dosage were studied. The polymerization followed the coordination–insertion mechanism. Under comparable reaction conditions, the grafting ratio of WGLA-1 reached 84.7 %, and the grafting ratio of complex 1 was found to be higher than those achieved using DMAP. WGLAs demonstrated good thermal stability without cytotoxicity, and the residual catalysts in the WGLAs exhibited fluorescence characteristics. Overall, amphiphilic cellulose-based materials with fluorescence emission offered a promising modification strategy to prepare high-performance polymer composites for agriculture and biomedical application.

Synthesis and Characterization of Cellulose Diacetate-Graft-Polylactide via Solvent-Free Melt Ring-Opening Graft Copolymerization

Cellulose diacetate (CDA) and L-lactide (L-LA) were used to prepare CDA-g-PLLA with a low glass transition temperature under different process conditions. Given the high glass transition temperature (Tg) of CDA, the thermal processing performance of CDA is poor, which greatly limits its application fields. To decrease the Tg of CDA, graft copolymerization was used in this research. A CDA-g-PLLA graft copolymer was synthesized by grafting CDA with L-LA under different reaction conditions using stannous octanoate as the catalyst and variations in the grafting rate under different reaction conditions were compared. The chemical structure and crystal structure of the CDA-g-PLLA were investigated, and thermal properties were also studied. The results showed that the grafting rate was the highest at the L-LA/CDA mass ratio of 4:1 under a reaction temperature of 150 °C for 90 min, and no poly-L-lactide (PLLA) homopolymer was found among the CDA-g-PLLA graft copolymers after purification. The Tg of CDA-g-PLLA was 54.2 °C, and the initial temperature of weightlessness of CDA-g-PLLA was 218.7 °C. The regularity of the original CDA molecular chains was destroyed after grafting PLLA molecular chains. In this research, we investigated the optimal grafting conditions for CDA-g-PLLA and the CDA-g-PLLA had a low Tg, which improves the thermal processing performance of CDA and broadens its application prospects in the industry.

Real-Time 1H and 31P NMR spectroscopy of the copolymerization of cyclic phosphoesters and trimethylene carbonate reveals transesterification from gradient to random copolymers

Copolymerization is the general approach to combine properties of different polymers in a single material. We prepared the first trimethylene carbonate (TMC) phosphoester (PE) copolymers by statistical copolymerization using either stannous octanoate or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the respective catalyst. Variation of comonomer feed, reaction temperature and solvent, resulted in a library of copolymers with molar masses of up to 83,000 g/mol and moderate molar mass dispersities (<1.8). The monomer consumptions during the copolymerizations were followed by real-time 1H and 31P NMR spectroscopy in solution and in the bulk. As ring-opening copolymerization of cyclic esters often leads to gradient copolymers, also TMC and PE copolymerizations resulted in gradient copolymers, i.e. P(TMC-grad-PE)s, with different gradient strength depending on the copolymerization conditions. If a suitable transesterification catalyst like stannous octanoate was used, randomization of the gradient copolymer occurred. The 31P NMR shift of incorporated phosphoester units was used as a probe to monitor the randomization of the gradient copolymers in real-time by 31P NMR spectroscopy. The P-comonomer acts as an ideal NMR probe for in situ monitoring the changes of the copolymers’ microstructure during the transesterification by following the evolution of diads and triads. This paper focusses on the randomization procedure and gives detailed information about the copolymer structure and the kinetics of the copolymerization. The data give the possibility to understand randomization processes on a molecular scale and to fine-tune properties of polycarbonate-polyphosphoester copolymers in future applications.

Fast-Tracking the l-Lactide Polymerization Activity of Group 4 Metal Complexes of Amine Tris(phenolate) Ligands

Zirconium complexes of amine tris(phenolate) ligands wherein the substituents ortho to the phenolate oxygens are aryl groups are introduced, and their application in the catalysis of ring-opening polymerization of l-lactide at 180 °C is described. Spectroscopic and crystallographic characterization revealed that for ortho-phenyl substituents, bridging dinuclear complexes were obtained, whereas for ortho-mesityl-substituents, fluxional mononuclear complexes were obtained. Melt polymerizations employing catalyst ratios reaching as low as 5 ppm for unpurified l-lactide and 1 ppm for purified l-lactide revealed ultra-high activities for the zirconium complex featuring the mesityl-phenolate substituents, yielding high-molecular-weight stereoerror-free poly(l-lactic acid) that exhibited enhanced stability toward thermal degradation. Slightly lower activities were found for the corresponding hafnium complex and for the zirconium complex featuring the phenyl-phenolate substituents. These catalysts could thus serve as drop-in replacement for the industrially employed stannous octanoate.

Synthesis of Poly(Trimethylene Carbonate) from Amine Group Initiation: Role of Urethane Bonds in the Crystallinity.

Semi-crystalline poly(trimethylene carbonate) (PTMC) can be efficiently prepared by ring-opening polymerization (ROP) initiated by amine using various catalysts. More promising results were reached with the one-step process of stannous octanoate unlike the two-step one-pot reaction using TBD and MSA catalysts. The ROP-amine of TMC consists in a simple isocyanate free process to produce polycarbonate-urethanes, compatible with the large availability of amines ranging from mono- to multifunctional until natural amino acids. ROP-amine of TMC leads to urethane bonds monitored by FTIR spectroscopy. The relationship between the nature of amines and the crystallinity of PTMC was discussed through X-ray diffraction and thermal studies by DSC and TGA. The impact of the crystallinity was also demonstrated on the mechanical properties of semi-crystalline PTMC in comparison to amorphous PTMC, synthesized by ROP initiated by alcohol. The semi-crystalline PTMC synthesized by ROP-amine opens many perspectives.

Preparation of Poly(3-hydroxybutyrate-b-ε-caprolactone) by Reactive Extrusion and Production of Electrospun Fibrous Mats

Poly(3-hydroxybutyrate) (PHB) has been proposed to be a potential candidate to be used as biomaterial. However, its poor processability, high brittleness and rigidity have limited its applicability. Transesterification reactions with poly(e-caprolactone) (PCL), one of the most promising biomedical materials, emerge as an attractive alternative to improve its mechanical properties. In this work, poly(3-hydroxybutyrate-b-e-caprolactone) (PHB-b-PCL) was prepared straightforwardly by transesterification of the parent homopolymers by reactive extrusion in the presence of stannous octanoate. After purification by solvent fractionation, PHB-b-PCL was characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy of carbon (13C NMR) and hydrogen (1H NMR) and, subsequently, submitted to electrospinning. The results indicate that PHB was modified, showing lower crystallinity as compared to the original homopolymers. The electrospun mats are tough and flexible and analysis by scanning electron microscopy indicates the formation of uniformly smooth morphology with average fiber diameter of 900-1200 nm and voids in the range between a few microns up to a few tens of microns, suitable for cell diffusion in biomedical applications.

A simple and general approach for the synthesis of biodegradable triblock copolymers by organocatalytic ROP from poly(lactide) macroinitiators

To overcome the present limitations in the synthesis of biodegradable triblock copolymers with PLA as central building block, three different reactional mechanisms (coordination-insertion, anionic and cationic) have been involved, while employing the transition from organometallic to organic catalysis. Even though activated chain-end mechanism with stannous octanoate is well known for the successful ROP catalytic reactivity, the synthesis of PLA based triblock copolymers according to this route revealed not negligible transesterification reactions. In the same way, the activated chain-end mechanism through nucleophilic activation (TBD) presented either no reactivity or weak control over the anionic polymerization process. Herein, we therefore propose an activated monomer mechanism as general and simple route for obtaining controlled PTMC-b-PDLLA-b-PTMC and PCL-b-PDLLA-b-PCL triblock copolymers by using cationic organocatalysis (MSA). 1H, 13C NMR and DOSY-NMR spectra confirmed the well-controlled polymer architecture of the B-A-B triblock copolymer.

Enhanced Crystallization Rate of Poly(L-lactide)/Hydroxyapatite-graft-poly(D-lactide) Composite with Different Processing Temperatures

Hydroxyapatite-graft-poly(D-lactide) (HA-g-PDLA) was synthesized by ring-opening polymerization with HA as initiator and stannous octanoate (Sn(Oct)2) as catalyst. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) results indicate that PDLA chains are successfully grafted onto HA particles by covalent bond. Under two different processing temperatures (190 and 230 °C), the effect of the grafted PDLA chains on the crystallization behavior of poly(L-lactide)/HA-g-PDLA (PLLA/HA-g-PDLA) composite was investigated in the current study, comparing to neat PLLA and its four composites (PLLA/HA, PLLA/HA-g-PLLA, PLLA/PDLA, and PLLA/HA/PDLA). The crystallization rate of PLLA/HA-g-PDLA composite is highly enhanced comparing to PLLA, PLLA/HA and PLLA/HA-g-PLLA composites in which there are no stereocomplex (SC) crystallites. In addition, when the processing temperature rises from 190 °C to 230 °C, the acceleration of PLLA crystallization in PLLA/HA-g-PDLA composite is not influenced so much as other composites containing SC crystallites, such as PLLA/HA/PDLA or PLLA/PDLA. The differential scanning calorimetry (DSC) results demonstrate that even without SC crystallites, the crystallization of PLLA can still be accelerated a lot in this composite. This may be related to the interaction between the grafted PDLA chains and the amorphous PLLA chains in PLLA/HA-g-PDLA composite. The isothermal crystallization kinetics studies indicate that the nature of nucleation and crystal growth of PLLA/HA-g-PDLA composite are more likely 3D crystalline growth with heterogeneous nucleation mode, which are different from PLLA or other composites. This investigation could shed new light on the application of PLLA/HA composites.

Synthesis of triblock stabilizers with and without end-capped for dispersion polymerization in supercritical carbon dioxide

Supercritical carbon dioxide (ScCO2) has been more and more widely applied for polymerization to replace organic solvents. For the dispersion polymerization, especially for the powder products used in the medical fields, the stabilizer plays a role key. The hydroxylpropyl-terminated polydimethylsiloxane (HTPDMS) was used as the CO2-philic chain and poly (L- lactide) (PLLA) was selected as the hydrophilic chain. The triblock stabilizer PLLA-PDMS-PLLA and AcO-PLLA-PDMS-PLLA-OAc with end-capped were prepared by ring-opening dispersion polymerization of L-lactide initiated by hydroxyl terminated polydimethylsiloxane (PDMS) and stannous octanoate ((Sn(Oct)2). Their synthesis methods and procedures were presented, and their structures and the thermal properties were characterized by fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometers (NMR), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG) respectively. The size and size distribution and molecular weight of the powders prepared were characterized by laser particle size analyzer and gel permeation chromatography (GPC) respectively. The effects of synthesis conditions on the molecular weight and yield of the stabilizer prepared were studied. The optimum synthesis conditions were obtained. The effects of the stabilizer with and without end-capped on the characters of product PLLA prepared by the dispersion polymerization in ScCO2 were investigated. The reaction conditions were easy to control. The results inferred that the terminal hydroxyl stabilizer PLLA-PDMS-PLLA did play a role in the initiation for the dispersion polymerization of PLLA in ScCO2.

Synthesis and Characterization of Terpolymers of poly(L-lactide-glycolide-ε-caprolactone)

Random terpolymers of poly(L-lactide-glycolide-ε-caprolactone) (PLLGC) was prepared by ring-opening polymerization of L-lactide, glycolide and ε-caprolactone monomers initiated with stannous octanoate. Fourier transform infrared spectra, nuclear magnetic resonance and gel permeation chromatography were employed to characterize the obtained PLLGC terpolymers. The effects of polymerization temperature, reaction time, the amount of initiator and the polymerization pressure on the weight average molecular mass and polydispersity index of the PLLGC were investigated. In addition, the water contact angle of the PLLGC was also tested. The characterization of chemical structure showed that the PLLGC was successfully synthesized. For instance, a PLLGC terpolymer with a weight average molecular mass of about 12.435 × 104 Da and a polydispersity index of 1.28 was obtained when the polymerization was conducted with a molar ratio of monomer to initiator ([M]/[I]) of 2000, polymerization temperature of 140 °C, polymerization pressure of 5.0 Pa and reaction time of 24 h. The random incorporation of ε-CL monomer units decreased the wettability of the PLGA copolymers.

Enhancing the grafting amount of Poly(ε-caprolactone) on MgO nanoparticles by modifying with ethylene glycol for improving mechanical properties of Poly(ε-caprolactone)

A new surface modification method to improve the graft polymerization of e-caprolactone (CL) on MgO surface was developed. The MgO nanoparticles were first modified with ethylene glycol (EG), and then used for initiating graft polymerization of CL. The modified MgO nanoparticles were attested by fourier transform infrared spectroscopy, thermal gravimetric analysis and dispersion stability test. The results showed that EG was successfully grafted onto the MgO surface, the hydroxyl group of the grafted EG initiated the graft polymerization of CL onto the MgO surface in the presence of stannous octanoate. The PCL grafting amount (11.13%) on MgO modified with EG (MgO-EG) is much higher than that of unmodified MgO (3.95%). MgO-EG-PCL with 11.13 wt% of grafted PCL exhibited the most excellent dispersibility in chloroform. The MgO-EG-PCL/PCL composites exhibited the most significant improvement, tensile strength and the elongation at break of PCL increased from 15.64 to 19.58 MPa and from 272.34% to 420.73%, respectively.

One pot biocatalytic synthesis of a biodegradable electroactive macromonomer based on 3,4-ethylenedioxytiophene and poly(l-lactic acid)

A novel electroactive macromonomer based on poly(l-lactic acid) (PLLA) with (3,4-ethylenedioxythiophene) (EDOT) functional end groups, was prepared by a traditional approach of organometallic polymerization with stannous octanoate [Sn(oct2)] and enzymatic polymerization using immobilized Candida antarctica Lipase B (CAL-B) and Amano lipase Pseudomonas cepacia(PS-IM), as catalysts. In the synthetic strategy, (2,3-dihydrothieno[3,4-b] dioxin-2-yl)methanol (EDOT-OH) was used to initiate the ring opening polymerization of lactide to yield PLLA with EDOT end group. All macromonomers (EDOT-PLLA) were characterized by 1H and 13C RMN, MALDI-TOF, GPC and EDX. Moreover, ICP-OES analysis showed the presence of Sn traces in the material synthesized by the traditional approach, but that pathway led to macromonomers with higher molecular weight while the enzymatic route led to completely metal-free macromonomers with medium and lower molecular weights. Also, electrochemical and chemical polymerization of EDOT-PLLA were tested showing that it is possible to prepare degradable conducting polymers based on poly(3,4-ethylenedioxythiphene) (PEDOT). The biocatalytic synthesis is a very promising and environmental friendly pathway for the preparation of biodegradable materials for short time applications.

Enhancement of Mechanical and Thermal Properties of Poly(L-lactide) Nanocomposites Filled with Synthetic Layered Compounds

The effects of a layered double hydroxide (LDH) (Zn/Al palmitate) and two layered hydroxide salts (LHS), intercalated with the anion salicylate or palmitate, on the properties of poly(L-lactide) (PLLA) nanocomposites were investigated. PLLA and the nanocomposites were synthesized by ring opening polymerization of the cyclic dimer of lactic acid (lactide), using tin(II) 2-ethylhexanoate (stannous octanoate) as catalyst. PLLA nanocomposites containing two different fillers concentrations (1 wt% and 2 wt%) were produced. Compared to PLLA, almost all the nanocomposites exhibited an enhancement on thermal resistance. The sample containing 1 wt% of Zn/Al palmitate exhibited a decomposition temperature 51°C higher than neat polymer. Results of flexural properties demonstrated that the nanocomposites containing Zn/Al palmitate displayed the highest values of maximum flexural stress and elongation at break. The sample with 2 wt% of this filler revealed values of maximum flexural stress and strain at break, 15% and 157%, respectively, higher than PLLA. Contrary to PLLA, which only exhibited break point, this nanocomposite showed a less fragile behavior, as a yield point was observed. In this case, it was possible to promote a higher flexibility without reducing the flexural stress, revealing an advantage of the Zn/Al palmitate under the plasticizers that have been used so far for PLLA.

Kinetic studies on the cure reaction of hydroxyl-terminated polybutadiene based polyurethane with variable catalysts by differential scanning calorimetry

Abstract This paper employs differential scanning calorimetry (DSC) to investigate the reactions of hydroxyl-terminated polybutadiene (HTPB) binder and isophorone isophorone diisocyanate (IPDI) with two different cure catalysts, namely, dibutyl tin dilaurate (DBTDL) and stannous octanoate (TECH). This study evaluates the effects of two cure catalysts (i.e. DBTDL and TECH) on rate constants of the polyurethane cure reactions. Throughput the study, the kinetic parameters and the curing reaction rate equations are obtained. The present work concludes that both catalysts had a catalytic effect on the HTPB-IPDI system, but that the catalytic effect of DBTDL was higher than that of TECH. The binder system with the TECH catalyst displayed a longer pot-life and lower toxicity compared with the DBTDL. Additionally, this study investigates the binder system’s viscosity build-up at 35°C and the viscosity build-up results were in agreement with the DSC analysis results.

Novel tri- and tetrafunctional cholic acid-based initiators for the synthesis of star-shaped poly(L-lactide)s

In this investigation, two novel multifunctional initiators for ring-opening polymerization were synthesized in three steps starting from cholic acid. Thus, cholic acid (1a) and its methyl ester (1b) were quantitatively transformed, via solvent-free reaction with succinic anhydride, to the corresponding 3, 7, 12-tri-hemisuccinate derivatives (3a-b). The polyacidic compounds (3a-b) were treated with thionyl chloride affording the corresponding acyl chlorides 4a-b which, in turn, were reacted with ethylene glycol to give the derivatives 2a-b having three and four primary alcohol end groups. These compounds, fully characterized by 1H, 13C NMR and mass spectrometry, have been assessed as initiators in the ring-opening polymerization of L-lactide using stannous octanoate as catalyst. The resulting three- and four-armed star-shaped poly(L-lactide)s, which were characterized by 1H NMR, SEC, DSC and TGA analysis, were amorphous, and their glass transition temperatures ranged from 13.7 to 36.5 °C. Additionally, some cholic acid-based star-shaped polylactic structures recently published have been critically reconsidered showing that these molecules, described as star polymers, were actually linear polymers.

Supramolecular Polylactides by the Cooperative Interaction of the End Groups and Stereocomplexation

The controlled ring-opening polymerization of l-lactide and d-lactide using 2-aminopyridine (AP), isocytosine (IC), uridine (U), and 2-ureido-4[1H]-pyrimidinone (UPy-OH) initiators with stannous(II) octanoate as catalyst leads to polylactides (AP-PLA-OH, IC-PLA-OH, U-PLA-OH, and UPy-PLA-OH), which are capable of forming strong hydrogen bonds and consequently self-assemble. By means of “1H NMR titration”, the association constant (Ka) was determined for chosen model system composed of polylactides with uridine and aminopyridine end groups. The coupling reaction of UPy-PLA-OH with diisocyanates was used to obtain PLLA and PDLA with UPy end groups on both sides of the chain: UPy-PLLA-UPy and UPy-PDLA-UPy. The SEC analysis of the telechelic UPy-PLA-UPy revealed the presence of a supramolecular polymer with a high-molecular-weight fraction (Mn ≈ 70 000 g/mol) compared with the molar mass of the starting dimer (UPy-PLA-OH, Mn ≈ 7000 g/mol), which confirms the strong complementary interactions of the end groups. Moreover, the influence of the end groups of enantiomeric PLAs on their thermal properties and morphology was investigated. Additionally, the influence of the modified PLA enantiomers on the stereocomplexation phenomenon was analyzed. It was observed that stereocomplexes prepared from PLAs with UPy or U end groups on one chain end lead to the formation of microspheres during precipitation from N-methylpyrrolidone into methanol. The microscopic analysis of the telechelic UPy-PLLA-UPy/UPy-PDLA-UPy stereocomplex resulting from the precipitation from chloroform into methanol revealed a fibrous morphology. The probable mechanism of formation of the hierarchical structure of this stereocomplex material, which can be related to the specific geometry of the enantiomeric chains (mainly in a parallel arrangement), was proposed.

Synthesis and Cytocompatibility of Biodegradable Poly (L-Lactide-r-5-Hydroxyl Trimethylene Carbonate) Copolymer

The biomedical applications of poly(L-lactide) (PLLA) were limited by its high crystallinity, hydrophobicity and lack of functional groups, which resulted in poor cell affinity. In this paper, L-lactide (85 mol%) and 5-benzyloxy-trimethylene carbonate (BTMC) (15 mol%) were copolymerized via ring-opening polymerization in the presence of stannous octanoate as catalyst. The copolymer was unprotected to receive poly(L-lactide-r-5-hydroxyl trimethylene carbonate) copolymer with functional hydroxyl pendant groups. The copolymer was characterized by 1H NMR, FTIR, GPC, DSC, TGA and XRD. The results showed that the reactivity of BTMC monomer was lower than that of LLA in the copolymerization. Both the protected and unprotected copolymers were amorphous. C2C12 myoblasts were seeded on the copolymer films to evaluate the cytocompatibility of the copolymer. The adhesion, proliferation and spreading of cells on poly(L-lactide-r-5-hydroxyl trimethylene carbonate) films were much better than those on PLLA films. The cell affinity of PLLA was improved greatly after the functionalization.

Synthesis and crystallization of star‐shaped photocleavable poly(ε‐caprolactone)s

ABSTRACTHere, we report on the synthesis and different crystallization behavior of linear‐ and star‐ PCL's containing a photocleavable linker (5‐hydroxy‐2‐nitro benzaldehyde), modulated by photochemical switching. Basis is the attachment of a photocleavable moiety close to the star‐core of a three‐arm star poly(caprolactone), so that the crystallization behavior can be controlled via a photochemical stimulus. The polymerization of ε‐caprolactone using a trivalent photocleavable initiator and stannous octanoate catalyst resulted in the synthesis of different molecular weights of star‐shaped photocleavable polymers. Various techniques like 1H NMR and ESI‐TOF‐MS confirmed the successful synthesis of the star‐shaped polymers. Complete photocleavage is ensured via GPC, HPLC, and ESI‐TOF‐MS. DSC studies clearly indicated the enhancement in crystallinity after photocleavage of the star‐shaped poly(ε‐caprolactone)s. Hence, for the first time phototriggered crystallization behavior of PCL polymers is reported, where the confinement exerted by the star architecture is removed by photoirradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 642–649

Synthesis, Characterizations and Biocompatibility of Novel Block Polyurethanes Based on Poly(lactic acid) (PLA) and Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB)

Alternating and random block polyurethanes (abbreviated as PULA-alt/ran-3/4HB respectively) based on biodegradable polyester poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB) were synthesized using 4,4′-methylene bis(cyclohexylisocyanate) (HMDI) as coupling agent and stannous octanoate (Sn(Oct)2) as catalyst. The chemical structure, molecular weight and thermal properties were characterized by FTIR, 1H NMR, GPC, DSC and TGA. Hydrophilicity was investigated by static contact angle of deionized water and CH2I2, while the mechanical behaviors were studied by tensile testing. Their shape-memory behaviors were investigated as a function of PLA molecular weight. The lowest recovery and glass transition temperatures (T g) which approach body temperature, have shown considerable prospect in medical applications. A platelet adhesion study illustrated that PULA-alt-3/4HB possesses better hemocompatibility due to its evident surface microstructure. The cell culture assay demonstrated that the materials are well suited for cell growth and proliferation of rat aortic smooth muscle cells (RaSMCs) and the RaSMCs are more favorable for attachment on PLA-alt-3/4HB materials. Porous scaffold rat implantation indicates non-toxic to animals of the synthesized block polyurethanes.

Synthesis of pH-sensitive amphiphilic pentablock copolymers via combination of ring-opening and atom transfer radical polymerization for drug delivery

A series of poly(acrylic acid)-poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone)-poly(acrylic acid) pH-sensitive PEG-[b-PCL-b-PAA]2 pentablock copolymers were synthesized via a combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP) and acidolysis. First, hydroxyl-terminated PEG (Mn=4000gmol−1) was used as starting material and stannous octanoate (Sn(Oct)2) as a catalyst for ROP of ε-caprolactone (CL). Then, the macroinitiator transformed from PEG-[b-PCL]2 (Mn=13,700 and 21,800gmol−1, by GPC) in high conversion initiated ATRPs of tert-butylacrylate (tBA) to construct PEG-[b-PCL-b-PtBA]2 (Mn=17,000–26,000gmol−1; Mw/Mn=1.13–1.25). Finally, the PEG-[b-PCL-b-PAA]2 was obtained via the acidolysis of the PtBA segment in PEG-[b-PCL-b-PtBA]2. The composition of triblock and pentablock copolymers was controlled by changing the feed ratios of CL/PEG in ROP and time in ATRP. The chain structures of copolymers were characterized by FT-IR, 1H NMR, and gel permeation chromatography (GPC). These copolymers are self-assembled into spherical nano size micelles in aqueous solution at pH<4.5. The formation, size and morphology of nanomicelles were studied by scanning electron microscopy (SEM), dynamic light scattering (DLS) and by measuring the critical micelle concentration (CMC) using fluorescence spectroscopy. The loading and controlled release of naproxen as a model drug was investigated, and it was found that the total release in the buffer solution at pH 7.4 is higher than that at pH 4.2.