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A series of high molar mass terpolymers are synthesized by ring-opening polymerization of l -lactide (LLA), 1,3-trimethylene carbonate (TMC) and glycolide (GA). In vitro degradation of the obtained terpolymers was realized in phosphate buffered saline (PBS) at 37 °C for one year, in comparison with PLLA-TMC copolymer and a composite made up of a PLLA-TMC-GA terpolymer matrix reinforced by poly( l -lactide-co-glycolide) (PLGA) fibers. Degradation was characterized as a function of incubation time by using GPC, DSC and 1H NMR. PLLA-TMC-GA terpolymers degrade faster than PLLA and PLLA-TMC because of lower chain regularity and lower crystallinity. In the case of the composite, the fast degradation of PLGA fibers speeds up the degradation of the PLLA-TMC-GA matrix due to internal autocatalysis. Morphological changes with increase of melting enthalpy were observed in all cases with crystallization of degradation by-products and selective degradation of amorphous domains. On the other hand, compositional changes appeared more complex since different phenomena are involved, including crystallization of LLA component, selective degradation in amorphous domains, and release of soluble oligomers. Among the various polymers, PLTG90/10/5 and PLTG95/5/5 present appropriate degradation rates, and are promising for the fabrication of totally bioresorbable stents.

The composite polylactide PLLA/β-TCP scaffolds were fabricated by solution casting and were coated with gelatin/hydroxyapatite (Gel/HAp) to improve the biological properties of the composite scaffolds. The Gel/HAp mixture was prepared using an in situ reaction, and a grafting-coating method was used to increase the efficiency of coating the PLLA/β-TCP matrix with Gel/HAp. First, free amino groups were introduced by 1,6-hexanediamine to aminolyze the PLLA/β-TCP matrix surface. Second, glutaraldehyde was coupled to Gel/HAp as a crosslinking agent. The structure and properties of Gel/HAp-modified PLLA/β-TCP films were characterized by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and water contact angle measurements (WCA). The experimental results show that 23 wt% HAp was uniformly dispersed in the gelatin coating by in situ synthesis. The Gel/HAp composite coating was successfully immobilized on the aminolyzed PLLA/β-TCP surface via a chemical grafting method, which promoted a lower degradation rate and was more hydrophilic than a physical grafting method. The Gel/HAp composite coating adhered tightly and homogeneously to the hydrophobic PLLA/β-TCP surface. Moreover, mouse embryo osteoblast precursor (MC3T3-E1) cells grown on the scaffolds were behaviorally and morphologically characterized. The results indicated that the Gel/HAp composite coating was favorable for the attachment and proliferation of preosteoblasts and that Gel/HAp-NH-PLLA/β-TCP would be a candidate scaffold for bone repair.

Three-arm poly (propylene oxide)-block-poly ( d -lactic acid) (PPO–PDLA) copolymers were successfully synthesized by ring-opening polymerization (ROP) of d -lactide using three-arm poly (propylene oxide) as a macroinitiator. PPO–PDLA copolymers were then functionalized with three ending tin (II)-alkoxide groups, and those functionalized copolymers could act as efficient initiators in polymerization of l -lactide at relative low temperature. The combination of proton nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometer supported their structures of ending tin (II)-alkoxide groups. A series of novel three-arm poly (propylene oxide)-block-poly ( d -lactic acid)-block-poly ( l -lactic acid) (PPO–PDLA–PLLA) copolymers with high molecular weight ( M n > 2.0 × 10 5 ) and equivalent D-LA/L-LA compositions, were synthesized using those functionalized initiators in polymerization of l -lactide at 130 °C. The results show that PPO–PDLA–PLLA copolymers are highly stereoregularity, and the molecular weight of enantiomeric block reaches up to 8.0 × 10 4 . Those three-arm PPO–PDLA–PLLA copolymers exhibit exclusive stereocomplex crystallization behavior with a high melting temperature about 207 °C.

Nonisothermal melt crystallization behaviour and crystallization kinetics of poly(4,4'-aminocyclohexyl methylene dodecanedicarboxylamide), a novel cycloaliphatic microcrystalline polyamide (named PA PACM12), are investigated by differential scanning calorimetry (DSC). The results show that with decreasing cooling rate, the crystallization peak becomes narrower and shifts to higher temperature, while the crystallization enthalpy increases. The Avrami equation, Ozawa model and Mo method are proved to be suitable to describe the whole crystallization process. Needle-like crystals of PA PACM12 are observed under polarizing optical microscopy (POM), which is in agreement with the characteristics of nucleation type and crystal geometry deduced from the Avrami analysis.

Mesoporous organosilica (MO) films are prepared using precursor 1,2-bis(triethoxysilyl)ethane (BTEE) and porogen template poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (P123). The effects of annealing temperature, P123/BTEE molar ratio, and moisture adsorption on the characteristics of the MO films are investigated. It is indicated that MO films prepared at a P123/BTEE molar ratio of 0.016 display the lowest dielectric constant (κ) of 1.80, a small dissipation factor of 0.0068 at 100 kHz, an extremely low leakage current density of 2.01 × 10−9 A cm−2 at 0.5 MV cm−1, a modulus (E) of 6.27 GPa, and a hardness (H) of 0.58 GPa. Following moisture adsorption, the κ value increases by ∼12%. However, ultraviolet treatment significantly reduces the extent of increase of the κ value to 4%. The films maintain an ultralow κ value of ∼2.0 and a very low leakage current density of 1.7 × 10−9 A cm−2 at 0.5 MV cm−1. Following annealing at 500 °C, the superior performance of the MO films is demonstrated by their κ value of ∼1.92, leakage current density of 7.08 × 10−9 at 0.5 MV cm−1, and improved E of ∼9.1 GPa and H of ∼0.8 GPa. Such MO films are very promising for advanced interlevel insulators.

Flight feathers stand out with extraordinary mechanical properties for flight because they are lightweight but stiff enough. Their elasticity has great effects on the aerodynamics, resulting in aeroelasticity. Our primary task is to figure out the stiffness distribution of the feather to study the aeroelastic effects. The feather shaft is simplified as a beam, and the flexibility matrix of an eagle flight feather is tested. A numerical method is proposed to estimate the stiffness distributions along the shaft length based on an optimal Broyden–Fletcher–Goldfarb–Shanno (BFGS) method with global convergence. An analysis of the compressive behavior of the shaft based on the beam model shows a good fit with experimental results. The stiffness distribution of the shaft is finally presented using a 5th order polynomial.

International audience; High molecular weight terpolymers based on L-lactide (LLA), trimethylene carbonate (TMC) and glycolide (GA) are synthesized and characterized with the aim of assessing their potential in the development of bioresorbable cardiovascular stents. The effect of the composition on the thermal and mechanical properties of terpolymers is investigated in comparison with the corresponding PLLA-TMC copolymers as well as a PLLA homopolymer. Incorporation of GA units strongly decreases the crystallinity of PLLA-TMC-GA terpolymers due to its more random microstructure as evidenced by C-13 NMR. Meanwhile, the toughness is greatly improved, with only a slight loss of tensile strength. Plasma-treated poly[(L-lactide)-co-glycolide] (PLGA) fibers are used to reinforce the terpolymer matrix. Composite with 8 wt% fibers exhibits much higher tensile strength and modulus. A minitube is fabricated using a single-screw extruder, and a stent prototype is successfully manufactured from a terpolymer by a CNC engraving machine, thus showing the feasibility of the terpolymers for the development of bioresorbable cardiovascular stents. POLYM. ENG. SCI., 54:1418-1426, 2014. (c) 2013 Society of Plastics Engineers

N-phenylmaleimide(NPMI)-styrene(St)-maleic anhydride (MAH) copolymer was synthesized in xylene solution by one-step free radical copolymerization, using di-tert-butyl diperoxyterephthalate as initiator. The resulting heat-resistant NPMI-St-MAH (NSM) copolymer was characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography, differential scanning calorimetry, elemental analysis, and nuclear magnetic resonance spectroscopy (1H-NMR and 13C-NMR). The results show that NPMI-St-MAH exhibits a random sequence distribution with a NPMI: St: MAH weight ratio of 47:51:2. The glass transition temperature (Tg) is about 190.0°C. Blends of acrylonitrile-butadiene-styrene (ABS) with various contents of NSM were prepared using a twin-screw extruder, and the effects of NSM content on the thermal and mechanical properties of ABS blends were investigated. It was found that the Vicat softening point, tensile strength, flexural strength, flexural modulus, and Rockwell hardness of the ABS/NSM blends were all significantly enhanced with increasing NSM content, whereas the impact strength shows the opposite trend. The impact fracture surface morphology was characterized by scanning electron microscope. It was revealed that cavitation and cavity coalescence resulted in the toughening of the material, which well accounts for the decrease of impact strength with increasing NSM content. In addition, the rheological properties of the blends were examined using a capillary rheometer. The blends present excellent processing property and are suitable for injection molding, although a pseudoplastic behavior was observed in all cases. POLYM. COMPOS., 34:920–928, 2013. © 2013 Society of Plastics Engineers

A PLLA-TMC-GA terpolymer of 90/5/5 molar ratio was synthesized by ring-opening polymerization of l-lactide (LLA), trimethylene carbonate (TMC), and glycolide (GA), using stannous octoate as initiator. In vivo degradation of the obtained terpolymer and a composite made up of the terpolymer matrix reinforced by PLLA-GA fibers was realized by subcutaneous implantation in rats for 9 months, in comparison with PLLA homopolymer and PLLA-TMC copolymer of 95/5 molar ratio. The terpolymer shows ideal degradation profile because it is expected to maintain relatively high radial support for 3 months and lose its mechanical properties in 3 to 6 months inferred from molar mass changes. Increase of crystallinity and LLA content in the terpolymer and composite is observed during degradation. According to the gross observation and H&E staining appearance, all samples present good tissue compatibility. These results suggest that the terpolymer is promising for uses as fully biodegradable vascular scaffold. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44355.

Amji's salamander (Hynobius amjiensis) is a critically endangered species (IUCN Red List), which is endemic to mainland China. In the present study, five haplotypes were genotyped for the mtDNA cyt b gene in 45 specimens from three populations. Relatively low levels of haplotype diversity (h = 0.524) and nucleotide diversity (π = 0.00532) were detected. Analyses of the phylogenic structure of H. amjiensis showed no evidence of major geographic partitions or substantial barriers to historical gene flow throughout the species' range. Two major phylogenetic haplotype groups were revealed, and were estimated to have diverged about 1.262 million years ago. Mismatch distribution analysis, neutrality tests, and Bayesian skyline plots revealed no evidence of dramatic changes in the effective population size. According to the SAMOVA and STRUCTURE analyses, H. amjiensis should be regarded as two different management units.

Calcium carbonate whisker (CCW) particles were surface modified by grafting of poly(L-lactide) (PLLA) chains in order to improve their affinity to a poly(L-lactide-trimethylene carbonate-glycolide) (PLTG) terpolymer matrix. Composites of the PLTG matrix with CCW and PLLA-g-CCW of various contents were prepared by mixing in solution followed by solvent evaporation. The structure and properties of pure CCW, surface modified PLLA-g-CCW and PLTG/PLLA-g-CCW composites were investigated using Fourier transfer-infrared spectrometry (FT-IR), mechanical testing, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), contact angle measurement, thermal gravity analysis (TGA) and differential scanning calorimetry (DSC). Data show that PLLA chains were successfully grafted on the CCW surface. The PLTG/PLLA-g-CCW composites exhibit a higher tensile strength and elongation at break than neat PLTG. Optimal values are obtained with a PLLA-g-CCW content of 2 wt%. It is assumed that PLLA-g-CCW particles present both reinforcing and toughening effects on the PLTG matrix. The cytocompatibility of the materials was evaluated from cell morphology and MTT assay using the L929 mouse fibroblast cell line. The results indicate that the composite presents very low cytotoxicity. Therefore, PLTG/PLLA-g-CCW composites with improved mechanical properties and good cytocompatibility could be promising as a potential bone substitute material.

Complete checklist records are essential to understand regional bird diversity and the status of the distribution of birds. The Zhejiang bird checklist was last presented as the Aves Branch of Zhejiang Fauna in 1990. Since then, many new records had been added, of which most remain unpublished. We have collected and examined all published and unpublished new records from Zhejiang habitats as well as those from the Aves Branch of Zhejiang Fauna. We have confirmed the evidence of the new records, which includes specimens, photographs, videos, sounds and tissue samples. We changed the Latin names of 131 species and subspecies and 41 Chinese names according to the new taxonomy and nomenclature. We provide an updated Zhejiang bird checklist for a total of 483 species and 24 subspecies, including 70 new species records, of which 47 species are reported for the first. Most of the new records are based on recent photographs taken by bird watchers.

This paper aims to evaluate the potential of totally bioresorbable composites as cardiovascular stent material. Copolymers were synthesized by ring-opening polymerization of L-lactide (LLA) and 1,3-trimethylene carbonate (TMC) with LLA-TMC ratios of 3/1, 4/1, and 5/1 and characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Wt. 5% of poly(L-lactide)-co-(glycolide) (PLGA) fibers are used to reinforce PTMC-LLA copolymer matrices to prepare totally bioresorbable composites. Heat treatment under vacuum and oxygen plasma treatment are applied to improve the mechanical performance of the composites in terms of eliminating the imperfections inside, enhancing interfacial affinity, surface roughness, and enriching surface oxidative chemical bonds. After plasma treatment, the viscosity and tensile strength of the fibers decrease, but the surface chemical bonds are enriched and surface roughness is increased. The composites with 15-min plasma-treated fibers and 2 h heat treatment exhibit the highest tensile strength of 46 MPa, i.e., very close to that of PLLA (48 MPa), which is usually used as biodegradable stent material. Moreover, the tensile modulus of the above composite is 1711 MPa, which is only 34% of PLLA's modulus (4985 MPa). Therefore, novel composites with sufficient tensile strength and better flexibility are obtained as promising cardiovascular stent material. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

A series of biodegradable chitosan-graft-polylactide (CS-g-PLA) copolymers were prepared by grafting of poly(L-lactide) (PLLA) or poly(D-lactide) (PDLA) precursor to the backbone of chitosan using N,N′-carbonyldiimidazole as coupling agent. The composition of the copolymers was varied by adjusting the chain length of PLA as well as the ratio of chitosan to PLA. The copolymers synthesized via this ‘graft-onto’ method present interesting properties as shown by NMR and infrared spectroscopy, gel permeation chromatography and solubility tests. Hydrogels were prepared by mixing water-soluble CS-g-PLLA and CS-g-PDLA solutions. Gelation was assigned to stereocomplexation between PLLA and PDLA blocks as evidenced by differential scanning calorimetry and wide-angle X-ray diffraction measurements. Thymopentin (TP5) was taken as a model drug to evaluate the potential of these CS-g-PLA hydrogels as drug carriers. An initial burst and a final release up to 82% of TP5 were observed from high-performance liquid chromatography analysis. Copyright © 2011 Society of Chemical Industry

TMC/LLA copolymers with several TMC/LLA ratios are synthesized and a composite is obtained by reinforcing with short PLGA fibers. In vitro degradation is studied at 37 °C in pH = 7.4 buffer and compared with a PLLA homopolymer. The degradation of the copolymers appears slower than that of PLLA, showing that TMC units are more resistant to hydrolysis than LLA. Compositional changes indicate a preferential degradation of LLA units as compared to TMC ones. Morphological changes with crystallization of degradation by-products are observed. The composite degrades much faster than the neat copolymer and PLLA because the faster degradation of PLGA fibers speeds up the degradation of the matrix. The composite appears promising for the fabrication of totally bioresorbable stents.

SummaryThe Chinese Crested Tern Thalasseus bernsteini is a Critically Endangered species and very little is known about its breeding biology and behaviour. Only two small breeding colonies have been recorded on the eastern coast of China. Between 2004 and 2009, their breeding biology was studied in two mixed species colonies on the Jiushan and Wuzhishan archipelagos in Zhejiang province. Chinese Crested Terns started breeding in late May and departed in late August, and nests were generally found within large colonies of Greater Crested Terns T. bergii. The nesting grounds of the mixed colony included grass, rock and interlaced zones on small, uninhabited islets. A total of six Chinese Crested Tern nests were identified, four of which were monitored. In these, the average clutch size was one, with an incubation period of 22–28 days and a fledging period of 31–35 days. The chicks subsequently joined chicks of the Greater Crested Tern, forming the same crèche. Adult Chinese Crested Terns foraged within approximately 5 km of the breeding islets and fed their chicks mainly with small and/or young shoaling fishes. The breeding success of Chinese Crested Tern was 100% in both 2008 and 2009. In addition to mixed nesting, other traits of breeding biology, such as breeding site shifts and re-nesting, provide valuable information for surveying, monitoring and conservation of the Chinese Crested Tern.

The non-isothermal crystallization kinetics of poly(L-lactide) (PLLA) in comparison with a polylactide stereocopolymer (PLA98) containing98% L-lactyl and2% D-lactyl unitswere investigatedusingdifferentialscanningcalorimetrytoexaminetheeffectof the configurational structure. Avrami, Ozawa and Liu models were applied to describe the crystallization process. The Avrami analysis exhibited two stages in non-isothermal crystallization, while the Ozawa and Liu models did not successfully describe the crystallization behaviour. The activation energy was calculated with Kissinger’s method. The energy barrier was found to be the same for PLLA and PLA98 with a value of 126 kJ mol −1 . c � 2010 Society of Chemical Industry

Polylactide (PLA) homo- and stereocopolymers containing 100, 98, 96, 94, and 92% L-lactyl units, respectively, were synthesized by ring opening polymerization of L-lactide and DL-Lactide, using zinc lactate as catalyst. Differential scanning calorimetric analysis measurements show that incorporation of D-lactyl units leads to decrease of the crystallization rate of the copolymers. However, the crystallization mechanism and the amount of crystallizable fraction are not affected. The enzymatic degradation was performed at 37 °C in a pH 8.6 Tris buffer containing proteinase K. Two distinct morphologies were obtained by melt crystallization for PLA films with ca. 80 μm of thickness. It is confirmed that proteinase K can degrade both the free and confined amorphous regions. Lamella stacks in spherulites retain their orientation during enzymatic degradation. PLA crystal morphologies are affected by the content of D-lactyl units. Factors such as the nucleus location and the D-lactyl units' exclusion as amorphous fraction were considered to elucidate the observed PLA spherulite morphologies. Infrared spectroscopy and mass loss measurements were also combined to better understand the degradation behaviors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 959–970, 2008

The surface properties of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) with various particle sizes were characterized by inverse gas chromatography (IGC). The dispersive components γsd of surface free energy of TATB samples increase as the temperature increases. The larger the particle size, the faster the increasing rate of the disperse component as the temperature increases. The γsd of the coarse TATB is the largest (193.2 mJ/m2) and that of the submicron TATB is the smallest (64.0 mJ/m2) at 353 K. Because of different preparation processes and particle sizes, the samples show obviously different Lewis acid-base properties. The fine TATB can provide positive Lewis acid-base active sites and have higher acidity. But the other three types of TATB with the specific components of the adsorption of polar probes on the surface were found to be endothermic because the strong hydrogen bond of inter- and intra-TATB molecules. Hence, their surface acidity and basicity constants, Ka and Kb, are negative.

International audience; PLLA-TMC-GA terpolymer was prepared by ring-opening polymerization of l-lactide, 1, 3-trimethylene carbonate (TMC), and glycolide (GA). The biocompatibility of terpolymer was evaluated in comparison with PLLA and PLLA-TMC with the aim of assessing their potential in the development of bioresorbable cardiovascular stents. Various aspects of in vitro biocompatibility were considered, including MTT assay, hemolytic test, dynamic clotting time, platelet adhesion, platelet activation, protein adsorption, plasma recalcification time and release of cytokines. The results revealed that the terpolymer presents good cytocompatibility and hemocompatibility. Moreover, no significant increase in the release of cytokines was detected. It is thus concluded that these polymers, in particular PLLA-TMC-GA terpolymer present good biocompatibility for cardiovascular

A series of high molecular weight polymers were prepared by ring opening polymerization of L-lactide (L-LA), 1,3-trimethylene carbonate (TMC) and glycolide using stannous octoate as catalyst. The resulting polymers were characterized by gel permeation chromatography, (1)H nuclear magnetic resonance, differential scanning calorimeter and tensile tests. All the polymers present high molecular weights. Compared with PLLA and PTLA copolymers, the terpolymers exhibit interesting properties such as improved toughness and lowered crystallinity with only slightly reduced mechanical strength. In vivo degradation was performed by subcutaneous implantation in rats to evaluate the potential of the copolymers as bioresorbable coronary stent material. The results show that all the polymers conserved to a large extent their mechanical properties during the first 90 days, except the strain at break which exhibited a strong decrease. Meanwhile, significant molecular weight decrease and weight loss are detected in the case of terpolymers. Therefore, the PTLGA terpolymers present a good potential for the development of totally bioresorbable coronary stents.

The crystal morphology of a thermotropic liquid crystalline polyesterimide, derived from N, N'-hexane-1,6-diylbis(trimellitimides), 4,4'-dihydroxybenzophenone and p-hydroxybenzoic acid, was investigated by means of polarized light microscopy (PLM) with a hot stage and scanning electron microscopy (SEM). The PLM observation indicates a series of phase transitions in the polyesterimide: with increasing temperature, the transformation from the amorphous state to nematic was observed at 264°C, followed by the conversion of nematic to isotropic melt at 290° C; crystallization in the isotropic phase occurred when the sample was maintained at 290°C on a glass substrate (only) for extended time. Very large and perfect Hedgehog spherulites were grown at 290°C with a fast growth rate. The SEM observation provided information on branching in crystals and spherulites impingement.

The effects of exposure time and vapor pressure on the crystallization behaviors of bisphenol-A polycarbonate (BAPC) films were investigated at 25°C by using differential scanning calorimetry (DSC). Double melting peaks were observed for various BAPC samples after vapor-induced crystallization. The low temperature melting peak shifted to higher temperature and became sharper with increasing exposure time, and could be assigned to defective crystals with smaller crystal size. Crystallinity and average crystal dimension normal to (020) were calculated from wide-angle X-ray diffraction spectra. A good agreement was obtained between crystallinity values obtained from WAXD and those from DSC. The morphology of crystallized samples after various exposure time periods was examined by means of polarized optical microscopy. Nucleation occurred at the initial stage of vapor-induced crystallization. Poor crystals become perfect through segment reorganization with increasing exposure time, and spherulites' growth was observed. The average diameter of spherulites increased from 2 μm for 1 h, to 7 and 16 μm after 3 and 56 h, respectively. POLYM. ENG. SCI., 46:729–734, 2006. © 2006 Society of Plastics Engineers

Freeze-dried samples were prepared from dilute solutions of atactic polystyrene (a-Ps) in benzene in a concentration range of 1 x 10 -1 to 2 x 10 -5 g/mL, and their glass transition temperatures (Tg) were determined by differential scanning calorimetry. It was found that below a critical concentration (Cg), the Tg of samples decreases linearly with decreasing logarithmic concentration of solutions. The freeze-dried samples were annealed at a constant temperature for various times or at various temperatures for the same period of time. The Tg of samples prepared from solutions of concentration below Cg was observed to shift to higher temperature with increasing annealing temperature or annealing time, finally approaching that of the bulk sample. Fourier transform infrared (FTIR) spectra of the freeze-dried samples were determined and were compared with the bulk sample. Significant changes in line width and absorption intensity were observed in the spectra of the freeze-dried samples, indicating that the packing of segments is in a more dilatant state. During annealing, the packing of segments in the samples gradually approaches that of the bulk sample, diminishing the differences in FTIR spectra between the freeze-dried sample and the bulk sample. The experimental observations are discussed, and it is assumed that intrachain and interchain entanglements may play an important role in glass transition.

Ultra high molar mass polyethylene (UHPE) was melted at 160°C for various times or at various temperatures for 5 min and then the crystallization of the UHPE was carried out on cooling. It was found that the crystallization temperature decreased as the heating time or heating temperature increased. During the melting process, thermal motion of the chains leads to a change of chain conformation from parallel-extended chains to interpenetrated random coils, accompanied by the occurrence of entanglements. As a result, the crystallization temperature shifts to lower temperature. On the other hand, samples of UHPE with less entanglement were prepared from a dilute solution by a freeze-drying procedure. It was observed that the crystallization temperature of the freeze-dried samples from the melt depressed with decreasing solution concentration. UHPE would produce small crystals in the freezing process, thus leading to a reduction in melting point and a sifting of crystallization temperature to lower temperature. Based on the melting point, the average volume of small crystals was estimated; it is even smaller than that of one single chain of the UHPE.

Freeze-dried ultra-high molar mass polyethylene (UHPE) was prepared from dilute solutions, and the resulting samples are a mixture of single-, few-, and multichain particles, each containing several or a number of small crystals. Thermal analysis of the freeze-dried samples by DSC indicated that the melting point decreased as the solution concentration decreased. The depression in melting point is most likely due to the decreasing crystal size. The effect of annealing the freeze-dried samples and the samples obtained after melting and recrystallization of the nascent UHPE at 122°C are discussed. Wide-angle x-ray diffraction (WAXD) measurements of average crystal dimensions normal to (110) and (210) and crystallinity were calculated for the freeze-dried samples. The crystallinity measured by WAXD is in agreement with that by DSC. By means of polarized optical microscopy (POM), morphology of the freeze-dried samples was studied. The melt of the freeze-dried samples became optically isotropic after melting a...

The crystallization of entangled polymer chains is studied by three-dimensional Monte Carlo simulations using the bond fluctuation model. To simulate entanglement, a mobile chain is assumed to move in a frozen environment through fixed obstacles. Simulation indicates that the temperature scale can be divided into three regions. In region I, high supercooling, the crystallization rate is high while disentanglement rate is low. In region III, low supercooling, the crystallization rate is much lower compared with disentanglement. Both rates can match each other in region II. Simulation also shows different morphologies in different temperature regions. In the simulation, all chains are mobile, but entanglement may still exist due to a high concentration of monomers. A new layer of crystal is observed to form on the surface of the seed at higher temperature, while chains crystallize in situ without large-scale movement at lower temperature. In moderate temperature range, disentanglement could match crystalliz...

The structure and adsorption kinetics of poly(ethylene oxide) end-capped with perfluorodecanoyl groups either at one or both ends have been characterized. These nearly monodisperse polymers with molecular weights in the range of 400–16 K g/mol are effective nonionic surfactants with very high surface activity. For aqueous solutions with concentrations in the range of 2–8 mg/ml, surface tensions determined by the drop-volume method are as low as 13.6– 18.0 mN/m at 20°C. At high surface coverage, close-packed PEO chains with one end capped form a brush-like structure at the interface. Polarized infrared reflectance spectroscopy showed that perfluoroalkyl groups were nearly perpendicular to the air–water interface. The molecular area per chain was 30–32 A2 for poly(ethylene oxide) capped only at one end and 36–40 A2 for poly(ethylene oxide) with both ends capped. Only 22% of poly(ethylene oxide) chains with both ends capped form loops at the interface, while the remaining chains form an extended structure at high surface coverage.

A spectral method of self-consistent field theory has been applied to AB cyclic block copolymers. Phase behaviors of cyclic diblock copolymers, such as order-disorder transition, order-order transition, and domain spacing size, have been studied, showing good consistency with previous experimental and theoretical results. Compared to linear diblocks, cyclic diblocks are harder to phase separate due to the topological constraint of the ring structure. A direct disorder-to-cylinder transition window is observed in the phase diagram, which is significantly different from the mean field phase diagram of linear diblock copolymers. The domain spacing size ratio between cyclic and linear diblock copolymers is typically close to 0.707, indicating in segregation that the cyclic polymer can be considered to be made up of linear diblocks with half of the original chain length.

Enzyme-catalyzed degradation of poly(trimethylene carbonate) homo-polymer (PTMC) and poly(trimethylene carbonate-co-glycolide) co-polymer (PTGA) was investigated in the presence of lipases from Candida antarctica and Hog pancreas. Degradation was monitored by gravimetry, size-exclusion chromatography (SEC), nuclear magnetic resonance (NMR), tensiometry and environmental scanning electron microscopy (ESEM). PTMC can be rapidly degraded by Candida antarctica lipase with 98% mass loss after 9 days, while degradation by Hog pancreas lipase leads to 27% mass loss. Introduction of 16% glycolide units in PTMC chains strongly affects the enzymatic degradation. Hog pancreas lipase becomes more effective to PTGA co-polymer with a mass loss of 58% after 9 days, while Candida antarctica lipase seems not able to degrade PTGA. Bimodal molecular weight distributions are observed during enzymatic degradation of both PTMC and PTGA, which can be assigned to the fact that the surface is largely degraded while the internal part remains intact. The composition of the PTGA co-polymer remains constant, and ESEM shows that the polymers are homogeneously eroded during enzymatic degradation. Contact angle measurements confirm the enzymatic degradation mechanism, i.e., enzyme adsorption on the polymer surface followed by enzyme-catalyzed chain cleavage.

A series of novel degradable triarm poly(propylene oxide)-block-polylactide (PPO-b-PLA) copolymers was synthesized by ring-opening polymerization of L-lactide (LLA) or D,L-lactide (DLLA) using low unsaturated PPO triols as macromolecular initiator. The chemical structures of the resulting copolymers were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), and proton nuclear magnetic resonance (1H-NMR) spectroscopy. Combination of FTIR, GPC, and NMR results confirmed the formation of PPO-b-PLA copolymers. One glass transition was observed by differential scanning calorimetry (DSC), suggesting good miscibility between PPO and PLA segments in the copolymers. DSC and wide-angle X-ray diffraction demonstrated that PPO-b-PLLA copolymers were semicrystalline materials, and the crystallinity increased with increasing the PLLA content. In contrast, PPO-b-PDLLA copolymers were totally amorphous. The PPO-b-PLA copolymers exhibited improved thermal stability when compared with PPO polyols according to thermogravimetric analysis. The thermal degradation behavior of the copolymers depended on the composition. Polyurethane foams were prepared by crosslinking PPO and PPO-b-PLA copolymers using isocyanate. Alkaline degradation of the foams was investigated in 10 wt/vol % NaOH at 80°C. The results show that the novel PPO-b-PLA copolymers could be promising as degradable polymeric materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Ring opening polymerization of e-caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) with M n = 1000 and 2000, using Zn(La) 2 as catalyst. The resulting PCL-PEG diblock copolymers with CUEO repeat unit molar ratios from 0.2 to 3.0 were characterized by using DSC, WAXD, SEC, and 1 H NMR. The crystal phase of PCL blocks exist in all polymers, and the crystallization ability of PCL blocks increases with CUEO ratio. PEG blocks are able to crystallize for copolymers with CUEO below 1.0 only. Melt crystallization results were analyzed with Avrami equation. The Averami exponent n is around 3.0 in most cases, in agreement with heterogeneous nucleation with three dimensional growth. The morphology of the crystals was observed by using POM. Rod-like crystals were found to grow in 1, 3 or 2, 4 quadrants for samples with low molecular weights. In the case of a copolymer with M n.PEG = 2000 and M n,PCL = 800, PEG blocks could crystallize and grow on PCL crystals after PCL finished to form rod-like crystals, leading to formation of poorly or well structured spherulites. The spherulite growth rate (G) was determined at different crystallization temperatures (T c ) ranging from 9 to 49 °C. All the copolymers present a steady G decrease with increasing crystallization temperature due to lower undercooling. On the other hand, increase of CL/EO ratio leads to increase of G in the same T c range.

International audience; A unique crystallization behavior of Poly(L-lactide) (PLLA) / poly(D-lactide) (PDLA) stereocomplex was observed when a PLLA/PDLA blend (50/50) was subjected to specific melting conditions. PLLA and PDLA were synthesized by ring opening polymerization of L- or D-lactide using zinc lactate as catalyst. PLLA/PDLA blend was prepared through solution mixing followed by vacuum drying. The blend was melted under various melting conditions and subsequent crystallization behaviors were analyzed by using DSC, XRD, NMR and ESEM. Stereocomplex was exclusively formed from the 50/50 blend of PLLA and PDLA with relatively low molecular weights. Surprisingly, stereocomplex crystallization was distinctly depressed when higher melting temperature and longer melting period were applied, in contrast to homopolymer crystallization. Considering predominant interactions between PLLA and PDLA chains, a novel model of melting process is proposed to illustrate this behavior. It is assumed that PLLA and PDLA chain couples would preserve their interactions (melt memory) when the stereocomplex crystal melts smoothly, thus resulting in a heterogeneous melt which can easily crystallize. The melt could gradually become homogeneous at higher temperature or longer melting time. The strong interactions between PLLA and PDLA chain segments are randomly distributed in a homogeneous melt, thus preventing subsequent stereocomplex crystallization. However, the homogeneous melt can recover its ability to crystallize via dissolution in a solvent.

International audience; Ring-opening polymerization of e-caprolactone was realized in the presence of monomethoxy poly(ethylene glycol) (mPEG) with Mn = 5000, using Zn(La)2 as catalyst. The resulting PCL-PEG diblock copolymers with CL/EO repeat unit molar ratios from 0.2 to 5.0 were characterized by using DSC, WAXD, SEC, and 1H NMR. Melt crystallization was studied and the results analyzed with Avrami equation. The spherulite growth rate (G) was determined at different crystallization temperatures (Tc) ranging from 30 to 44 oC. The G values were found to range between those of mPEG and PCL homopolymers. The morphology of isothermally crystallized sample B with CL/EO=0.5 was examined. Interestingly, spherulites with PCL spherulites embedded in PEG ones were observed, in contrast to concentric spherulites reported in literature.

Ring opening polymerization of L-lactide was realized in the presence of monomethoxy poly(ethylene glycol), using zinc lactate as catalyst. The resulting PLLA-PEG diblock copolymers were characterized by using 1H-NMR, SEC, WAXD, and DSC. All the copolymers were semicrystalline, one or two melting peaks being detected depending on the composition. Equilibrium melting temperature (Tm0) of PLLA blocks was determined for three copolymers with different EO/LA molar ratios. Tm0 decreased with decreasing PLLA block length. A copolymer with equivalent PLLA and PEG block lengths was selected for melt crystallization studies and the resulting data were analyzed with Avrami equation. The obtained Avrami exponent is equal to 2.6 ± 0.2 in the crystallization temperature range from 80 to 100°C. In addition, the spherulite growth rate of PLLA-PEG was analyzed by using Lauritzen-Hoffmann theory in comparison with PLLA homopolymers. The nucleation constant was found to be 2.39 × 105 K2 and the free energy of folding equal to 53.8 erg/cm2 in the range of 70–94°C, both higher than those of PLLA homopolymers, while the spherulite growth rate of the diblock copolymer was lower. POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers

A series of terpolymers obtained from glycolide/L-lactide/e-caprolactone were compression molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. Analytical techniques such as 1H-NMR, DSC, ESEM and SEC were used to monitor the degradation. Heterogeneous degradation was observed due to internal autocatalysis of carboxylic endgroups formed by ester bond cleavage. Nevertheless, the copolymers present various degradation behaviors depending on the initial composition. The PCL component appears the most resistant to degradation, and the PGA, the most degradable according to compositional changes. Terpolymers could crystallize during degradation even though they were amorphous initially. Degradation-induced increase of crystallinity was also found during hydrolysis. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 2451–2456, 2007

Isothermal melt-crystallization, glass transition and melting behavior of poly( l -lactide) (PLLA) with different molecular weights were investigated by using differential scanning calorimetry. Analysis by Avrami equation showed that crystallization was initiated by heterogeneous nucleation, followed by 3-dimensional growth. The maximum reciprocal half-time of crystallization (1/t1/2) was detected at 105 °C. Double endothermic peaks were observed around the glass transition for PLLA with intermediate crystallinities, indicating the coexistence of bulk-like and confined amorphous regions. Double-melting behavior was analyzed and combined with the equilibrium melting temperature evaluation by non-linear Hoffman–Weeks extrapolation, from which a value of 207.6 °C was deduced for PLLA of infinite molecular weight. Lauritzen–Hoffman theory was employed to analyze the crystallization kinetics. Regime II-III transition was found to occur at 120 °C for PLLA of lower molecular weight. The crystal morphology was also examined by scanning electron microscopy through chemical etching method.

The morphology and melt crystallization of zinc catalyzed poly(L-lactide) (PLLA) were investigated by using differential scanning calorimetry (DSC), polarized optical microscopy, and scanning electron microscopy. Isothermal melt crystallization performed at 95–135°C showed that the morphology depends on the degree of supercooling, as illustrated by crystallite perfection and lamellar thickening behaviors. Double melting peak was observed on DSC thermograms and attributed to the melt-recrystallization mechanism, small and imperfect crystals becoming gradually more stable ones. Circumferential and hexagonal cracks were detected in PLLA spherulites, which were formed during melt-crystallization at 135°C and quenching in liquid nitrogen. Rhythmic growth and thermal shrinkage are suggested to be the two main factors accounting for the formation of periodic cracks. Spherulite growth rates of PLLA were evaluated by using combined isothermal and nonisothermal procedures, and were analyzed by the secondary nucleation theory. The maximum growth rate reached 9.1 μm/min at 130°C. The temperature range investigated (120–155°C) belongs to the Regime II of crystallization. The value of U* was found to be 1890 cal/mol, instead of 1500 cal/mol commonly used in literature, and Kg and σ were estimated to be 3.03 × 105 K2 and 1.537 × 10−4 J/m2, respectively. As a result, no distinct difference between PLLA catalyzed by zinc metal and those prepared with stannous octoate catalyst exists in this work. POLYM. ENG. SCI., 46:1583–1589, 2006. © 2006 Society of Plastics Engineers.

The Critically Endangered Chinese crested tern Sterna bernsteini is a poorly known species. From June 2003 to August 2007 we therefore surveyed the Zhejiang and Shandong coasts of eastern China for breeding colonies and to document any threats. Our results indicated that (1) the colonies at Matzu and Jiushan are the only two in the species' potential breeding range, (2) the total population is no more than 50, (3) numbers in the two extant breeding colonies fluctuate annually, and (4) threats to the breeding populations include habitat degradation, egg poaching, disturbance, overfishing and typhoons. Egg poaching is the greatest threat to the Chinese crested tern population and other breeding seabird populations along the coast of China. We make recommendations for the conservation of this species.