Preparation and polymerization mechanism of dihydroxy-capped PCL,poly(CL-b-PEG-b-CL) and poly(DTC-b-CL-b-DTC)

PCL possesses a wide range of medical applications, such as tissue engineering and controlled drug release, because of its good biodegradability and miscibility. In order to extend the use of PCL, researchers have been exploring its structural and chemica…     

Enzymatic synthesis of poly(α-ethyl β-aspartate) by poly(ethylene glycol) modified poly(aspartate) hydrolase-1

We recently discovered that poly(aspartate) (PAA) hydrolase‐1 from Pedobacter sp. KP‐2 has a unique property of specifically cleaving the amide bond between β‐aspartate units in thermally synthesized PAA (tPAA). In the present study, the enzymatic synthesis of poly(α‐ethyl β‐aspartate) (β‐PAA) was performed by taking advantage of the substrate specificity of PAA hydrolase‐1. No polymerization of diethyl L ‐aspartate by native PAA hydrolase‐1 occurred because of the low dispersibility of the enzyme in organic solvent. Poly(ethylene glycol) (PEG) modification of the enzyme improved its dispersibility and enabled it to polymerize the monomer substrate. MALDI‐TOF MS analysis showed that the synthesized polymer was observed in the range of m/z = 750–2 500. This analysis also revealed that the polymer was composed of ethyl aspartate units, containing either an ethyl ester or a free carboxyl end group at its carboxyl terminus. ¹H NMR analysis demonstrated that the synthesized polymer consisted of only β‐amide linkages. Thus, the present results indicate that PAA hydrolase‐1 modified with PEG is useful for the synthesis of β‐PAA due to its unique substrate specificity and good dispersibility in organic solvent.

     

Self-diffusion in poly(N -vinyl pyrrolidone) – poly(ethylene glycol) systems

 We have applied the PFG NMR technique to investigate the translational mobility in the PVP-PEG system as a function of composition and temperature at the stages of PVP-PEG complex formation, its swelling, and dissolution in excess of liquid PEG. It has been found that the variations of the spin-echo attenuation with PEG content, water amount, and temperature reflect the different stages. The first two stages are characterized by a distribution of the self-diffusion coefficients of PEG involved in the network. The dissolution shows two diffusion coefficients; the fast one is attributed to PEG molecules, the slow one to the associates of PEG and PVP. The temperature dependencies can be described by an Arrhenius law with an activation energy depending on the composition of the blend. The concentration dependence of the PEG self-diffusion coefficients in the blend occurred to be independent of the molecular weight of PVP. The results are discussed in terms of the Mackie-Meares model. Received: 23 August 2000 Accepted: 19 October 2000     

Swelling-shrinking behavior of chemically cross-linked polypeptide gels from poly(α-L-lysine), poly(α-DL-lysine), poly(ɛ-L-lysine) and thermally prepared poly(lysine): effects of pH, temperature and additives in the solution

We synthesized the glutaraldehyde cross-linked hydrogels using four kinds of poly(lysine)s (PLs) and measured the equilibrium swelling ratio (Q) as a function of pH. Also measured was the temperature change of Q at a fixed pH (11.6) in the absence and presence of additives (LiBr, methanol and urea) that affect the secondary structure of PLs. The swelling data were examined using a force balance approach in which the repulsive and attractive interactions among the cross-linked PL chains were considered based on the conformational properties of PLs in aqueous solutions. It was found that the formation of the helical segments in the cross-linked chain has little effect in the gel collapse, but their association acts as the attractive interaction causing the gel to shrink. The formation of the beta-sheet structure within the network also acts as the attractive interaction. These attractive interactions are mainly due to the hydrogen bonding, but hydrophobic interactions between the lysine side chains should be considered. In addition, in the swelling behavior of all the PL gels the polyampholyte nature appears due to electrostatic interactions of the basic groups with the C-terminal carboxyl group.     

The synthesis, deprotection and properties of poly(γ-benzyl-l-glutamate)

Diethylamine, di-n-hexylamine, dicyclohexylamine and triethylamine have been used as initiators for the ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG NCA) to synthesize poly(γ-benzyl-l-glutamate) (PBLG). The relationship between the molecular weight of PBLG and the molar ratio of monomer and initiator was studied. With dicyclohexylamine as initiator, the influence of monomer concentration, and reaction temperature and time on the polymerization of BLG NCA was examined. Three reagents were used for the deprotection of benzyl groups in PBLG, including hydrobromic acid/acetic acid (33 wt.%), NaOH aqueous solution and trimethylsilyl iodide (TMSI). Through examining the molecular weight of PLGA obtained using different deprotection methods, it was revealed that TMSI could minimize chain cleavage in the process of deprotection and retain the degree of polymerization. The biocompatibilities of PBLG obtained using different initiators were evaluated by a live/dead assay against L929 fibroblast cells. The in vitro cytotoxicities of PLGA obtained using different deprotecting agents were evaluated by a methyl thiazolyl tetrazolium assay. The results revealed that both PBLG and PLGA exhibited good biocompatibilities.     

Phase separation and phase dissolution in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

A blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile having the critical composition (80/20 PCL/SAN) was studied. This PCL/SAN blend having a lower critical solution temperature (LCST) phase boundary at 122 °C offered an excellent opportunity to investigate, firstly the kinetics of phase separation above LCST (125-180 °C), and secondly the kinetics of phase dissolution below LCST (50-115 °C). The blend underwent a temperature-jump above LCST where spinodal decomposition (SD) proceeded, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below LCST when the phase dissolution proceeded. Optical microscopy was used to observe the spinodal decomposition qualitatively while light scattering was used to characterize the phase separation and phase dissolution quantitatively. It was found that during phase dissolution the peak maximum moved towards a smaller angle (wavelength of concentration fluctuations increased) while the peak intensity decreased. This behavior was explained by a model. Also it was found that the fastest phase dissolution kinetics at 80 °C, which was characterized by an apparent diffusion coefficient, was about 10 times slower than the kinetics of phase separation at 180 °C.     

A facile synthesis of hydrophilic poly(ε-caprolactone)-based poly(ether-ester-amide)s

Segmented poly(ether-ester-amide)s, (PEEA)s, of controlled hydrophilicity degree, based on poly(ε-caprolactone) (PCL), were synthesized according to a facile two-step procedure using α,ω-dihydroxy oligomeric PCL, 4,7,10-trioxa-1,13-tridecanediamine and macromers prepared from poly(ethylene glycol)s and adipoyl chloride. The PEEAs showed M _n values in the range 5–11.5 kDa. A PCL-type crystallinity was found by WAXS. DSC indicated T_m values (49–51 °C) close to that of PCL macromer. Single glass transitions were observed both by DSC and DMTA techniques and the T_g values (−58–−50 °C by DSC) were slightly higher than that of PCL. The water uptake was in the range 4.8–26.0 wt.-% depending on the length of the poly(ethylene glycol) segment.

Monomers used to prepare the PEEAs.     

Molecular simulation of an amorphous poly(methyl methacrylate)–poly(tetrafluoroethylene) interface

Molecular dynamics calculations of an amorphous interfacial system of poly(methyl methacrylate) (PMMA) and poly(tetrafluoroethylene) (PTFE) containing about 10,000 interaction sites were performed for 15 ns under constant pressure and constant temperature conditions. The time evolutions of the thickness, density and number of atomic pairs in the interfaces suggested that the interfaces reached their equilibrium states with an interfacial thickness of about 2 nm at 500 K. The molecular motion in the interface and bulk was compared using mean square displacement and torsional autocorrelation function. The separation at a PMMA/PTFE interface was mimicked using non-equilibrium molecular dynamics calculations by applying the potential energy to the MD cell in a direction perpendicular to the interface. Initially, the PTFE layer close to the interface was deformed, and before complete separation, some segments of the PTFE molecules extended from the bulk to the surface of the PMMA layer, which were attached by the intermolecular interaction. The remaining PTFE molecules were entangled in the bulk, which probably prevented the transfer of the PTFE molecules to the surfaces of the PMMA layers. On the other hand, the PMMA layer was only slightly deformed. This separation behavior can be explained by taking into account the intermolecular interaction, the barrier to the conformational changes of the backbones and the entanglement of the PTFE molecules in the bulk.     

Thermal degradation of bromine-containing polymers: Part 11—Blends of poly(2,3-dibromopropyl methacrylate) and poly(2,3-dibromopropyl acrylate) with poly(methyl methacrylate) and poly(methyl acrylate)

The products of degradation of blends of poly(2,3-dibromopropyl methacrylate) and poly(2,3-dibromopropyl acrylate) with poly(methyl methacrylate) and poly(methyl acrylate) are predominantly those to be expected from the degradation of the individual polymers. However, the appearance of methyl bromide and methanol from all four blends indicates that some interaction does occur across the phase boundary between the two constituent polymers. This is presumed to consist of the reaction of hydrogen bromide, formed by decomposition of the brominated polymers with the methyl groups of the acrylate and methacrylate polymers.     

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.     

Thermal characterization of biodegradable methoxy poly(ethylene glycol)-b-poly(d,l-lactide)/methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) blend nanoparticles

Biodegradable methoxy poly(ethylene glycol)-b-poly(d,l-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-b-PCL) diblock copolymers were synthesized by ring-opening polymerization of DLL and CL monomers in bulk using stannous octoate, and MPEG as the initiating system. Surfactant-free MPEG-b-PDLL/MPEG-b-PCL blend nanoparticles were prepared by the nanoprecipitation method. The influences of block length and blend ratio on morphology, average size, and thermal properties of the blend nanoparticles were determined. The blend nanoparticles were spherical in shape. The average particle sizes slightly decreased as the MPEG-b-PCL blend ratio increased. ¹H-NMR and thermogravimetry revealed the different MPEG-b-PDLL/MPEG-b-PCL blend ratios of the nanoparticles. Differential scanning calorimetry showed that the MPEG-b-PCL crystallinity steadily decreased as the MPEG-b-PDLL blend ratio increased, suggesting miscible blending between the MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the nanoparticle matrix.     

Blends of a novel high-temperature poly(oxy-1,4′-diphenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) with poly(ether imide): structure, interaction, and miscibility

 Polymer miscibility has been discovered in a blend system comprising poly(ether imide) (PEI) and a new poly(ether diphenyl ether ketone) (PEDEK). The miscibility of the PEDEK/PEI polymer system (quenched from the molten state) was investigated in this study using differential scanning calorimetry and Fourier transform (FT-IR) spectroscopy. A composition-dependent single glass-transition temperature (T _g) in the PEDEK/PEI blends over a full composition range was observed; the sharp transition width and the T _g–composition relationship both suggest that the scale of mixing is fine and uniform. Evidence based on observation of the cold-crystallization peak and suppression of the blend crystallinity and melting peak also indicated intimate intermolecular mixing. The FT-IR result yielded further evidence that the physical interactions leading to miscibility were weak, with no apparent specific interactions between the constituent polymers. Relationships between structures and interactions responsible for the miscibility in PEI and several ether-ketone-type polymers are briefly discussed. Received: 8 July 1999 Accepted in revised form: 21 October 1999     

Enhanced photodegradation of TiO2-containing poly(ε-caprolactone)/poly(lactic acid) blends

The calamitous accumulation of plastic waste in the environment, especially single-use disposables, calls for new approaches to materials design. One method to address the persistence of plastics beyond their intended use is to impart them with functionalities that will either allow for their recyclability or their degradation to basic natural components. This work focuses on the fabrication of photodegradable polyester blends and investigates the impact of compatibilization on photodegradation rates. Specifically, we blended poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) polymers by (reactive) extrusion in the presence or absence of dicumyl peroxide (DCP), a radical generator, and titanium dioxide (TiO₂), an inorganic photocatalyst. We examined the effects of DCP and TiO₂ loadings as well as copolymer composition on the thermomechanical properties, photodegradability, and morphology. We found that the inclusion of TiO₂ dramatically increased flexural moduli and photodegradation rates in both dry and wet conditions, while reactive compatibilization had little effect of the tested properties. This simple and scalable approach is promising to fabricate materials that can readily photodegrade.     

Structure-properties correlations in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)/nanosilica mixtures: Interrelationship among phase behavior,morphology and non-isothermal crystallization kinetics

In this work, the effects of amorphous poly(styrene-co-acrylonitrile) (SAN) chains and hydrophilic and hydrophobic nanosilica at different loadings on the non-isothermal crystallization kinetics of PCL phase have been evaluated using different theoretical models including Avrami, modified Avrami, Ozawa and Mo equations. Using microscopic observations, the interrelations among the changes in the kinetics parameters and the morphology and phase behavior of PCL/SAN and PCL/SAN/nanosilica mixtures have been thoroughly investigated. Microscopic observations on the nanocomposites showed differences in the nanofiller dispersion and distribution state as well as preferential migration and localization state. These differences lead to contradictory trends in the effects of hydrophilic and hydrophobic nanosilica on the crystallization kinetics of pure PCL and PCL/SAN blends. The nanoparticle migration during non-isothermal DSC tests in PCL/SAN blends, the formation of nanoparticle agglomerates at higher loadings, the restrictions imposed on the molecular movements in the crystallization growth stage and slower phase separation and dissolution of PCL/SAN/silica mixtures result in the cooling rate dependence of the kinetics parameters.     

Binary blends based on poly(vinyl chloride) and multi-block copolymers containing poly(ϵ-caprolactone) and poly(ethylene glycol) segments

Binary blends based on poly(vinyl chloride) (PVC) were prepared both by casting from tetrahydrofuran (THF) and by mixing in the melt form, in a discontinuous mixer, PVC and multi-block copolymers containing poly(ϵ-caprolactone) (PCDT) and poly(ethylene glycol) (PEG) segments. PCDT-PEG copolymers were synthesized using a polycondensation reaction where the α,ω-bis-chloroformate of an oligomeric poly(ϵ-caprolactone) diol terminated (PCDT) and oligomeric PEG were employed as macromonomers. For comparison purposes, blends PVC with starting oligomers as well as with mixtures containing a typical low molecular plasticizer, dioctylphthalate (DOP), were also prepared. The copolymer miscibility was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The blend morphology was investigated by polarized light microscopy (PLM). A higher miscibility with PVC was observed for copolymers compared to PEG.     

Surface patterning and biological evaluation of semi-interpenetrated poly(HEMA)/poly(alkyl β-malolactonate)s

Semi-interpenetrating hydrogel networks were prepared by radical polimerization of monomer HEMA, co-monomer EGDMA as cross-linking agent and in the presence of 1 wt % of poly(alkyl β-malolactonate)s. Biological evaluation in terms of cell adhesion and proliferation of the prepared materials showed the ability of HEMA-based hydrogels to sustain a good cell adhesion and proliferation. Moreover, a method based on soft-lithography to obtained surface microstructured semi-interpenetrating hydrogel networks was developed, thus allowing for further investigation of the influence of surface topography on cell behavior.     

The endothermic “annealing peak” of poly(phenylene sulphide) and poly(ethylene terephthalate)

The appearance of an endothermic annealing peak in semicrystalline poly(phenylene sulphide) and semicrystalline poly(ethylene terephthalate) after annealing at or above the cold-crystallization temperature is investigated by temperature-modulated differential scanning calorimetry, thermo-mechanical analysis and dynamic-mechanical analysis. The results indicate relaxation processes in the interlamellar amorphous phase, which is in a strongly constrained state after cold crystallization. During the annealing treatments rearranging processes take place. These processes result in a separation of the amorphous phase into an interlamellar relaxed and a “pseudo-crystalline” phase. Received: 27 October 1998 Accepted in revised form: 19 January 1999     

Chemical–physical behavior of hydrogels of poly(vinyl alcohol) and poly(ethylene glycol)

New hydrogels based on polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA) of different degrees of hydrolysis were synthesized. To form the network the PEG was modified at their ends with acyl chloride groups to be used as the crosslinking agent. The compositions of the hydrogels were between 50% and 90% by weight of PEG and PVA of various degrees of hydrolysis were used. It was found that the degree of hydrolysis of the PVA and the PEG content influence the equilibrium water content of the hydrogel. The process of swelling of all the hydrogels prepared followed a second-order kinetics.     

双端羟基PCL, poly(CL-b-PEG-b-CL)和poly(DTC-b-CL-b-DTC)的制备及聚合机理

采用二醇/三(2, 6-二叔丁基-4-甲基苯酚)钇(Y(OAr)₃)体系引发己内酯(CL)开环聚合, 得到分子量可控、双端羟基聚己内酯(PCL). 经过¹H NMR和SEC分析表明聚合体系中有两种活性中心, 形成两种链结构, 二醇/Y(OAr)₃比值的增大有利于单钇活性中心的形成. 聚乙二醇(PEG)/Y(OAr)₃引发体系中只有一种活性中心, 可以制备CL和PEG的三嵌段共聚物(poly(CL-b-PEG-b-CL)). 以双端羟基PCL作为大分子引发剂引发2,2-二甲基三亚甲基环碳酸酯(DTC)聚合, 获得CL和DTC的三嵌段共聚物(poly(DTC-b-CL-b-DTC)).