Synthesis of repeating sequence copolymers of lactic,glycolic, and caprolactic acids

Repeating sequence copolymers of poly(lactic‐co‐caprolactic acid) (PLCA), poly(glycolic‐co‐caprolactic acid) (PGCA), and poly(lactic‐co‐glycolic‐co‐caprolactic acid) (PLGCA) have been synthesized by polymerizing segmers with a known sequence in yields of 50–85% with M_ns ranging from 18–49 kDa. The copolymers exhibited well‐resolved NMR resonances indicating that the sequence encoded in the segmers used in their preparation is retained and that transesterification is minimal. The exact sequences allowed for unambiguous assignment of the NMR spectra, and these standards were compared with the data previously reported for random copolymers. The glass transition temperatures (T_gs) of the PLCA and PGCA copolymers were found to depend primarily on monomer ratio rather than sequence. Sequence dependent T_gs were, however, noted for the PLGCA polymers with 1:1:1 L:G:C ratios; poly LGC and poly GLC exhibited T_gs that differed by nearly 8 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Structure and mechanical properties controlling of elastomer modified polypropylene by compounded β/α nucleating agents

Previous work showed that there was a synergistic effect of nucleating agent (NA) and elastomer in improving the fracture resistance of isotactic polypropylene (PP), relating to the formation of large amounts of β‐PP (β‐NA nucleated system) or the decrease of the spherulites diameters of α‐PP (α‐NA nucleated system). To find the direct relation between the synergistic efficiency of NA/elastomer and the microstructures of the materials, in this work, the ethylene‐propylene‐diene terpolymer (EPDM) modified PP blends with compounded NAs (β/α) were adopted and the changes of the microstructure and mechanical properties were investigated comparatively. The results showed that, with the adjustment of the mass fraction of compounded NAs, the microstructures of PP matrix including supermolecular structure and the relative fraction of β‐PP (K_β) change accordingly. Specifically, the K_β of β‐PP was successfully adjusted in the wide range of 0–78.9%. Consequently, the stiffness and the fracture resistance of the PP/EPDM blends were easily controlled in different degrees. It is believed that this work could provide a guide map for the design and preparation of certain polymer blends satisfying certain requirement. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Characterization of chemical heterogeneity in polymer systems using hydrolysis and tapping‐mode atomic force microscopy

Characterization of polymer coatings microstructure is critical to the fundamental understanding of the corrosion of coated metals. An approach for mapping the chemical heterogeneity of a polymer system using chemical modification and tapping‐mode atomic force microscopy (TMAFM) is demonstrated. This approach is based on the selective degradation of one of the phases in a multiphase polymer blend system and the ability of TMAFM to provide nanoscale lateral information about the different phases in the polymer system. Films made of a 70:30 polyethyl acrylate/polystyrene (PEA/PS) blend were exposed to a hydrolytic acidic environment and analyzed using TMAFM. Pits were observed to form in the PEA/PS blend films, and this degradation behavior was similar to that of the PEA material. Using these results, the domains in the 70:30 blend were identified as the PS‐rich regions and the matrix as the PEA‐rich region. This conclusion was confirmed by Fourier transform infrared‐attenuated total reflection analyses that revealed the hydrolysis of the PEA material. TMAFM phase imaging was also used to follow pit growth of the blend as a function of exposure time. The usefulness of the chemical modification/AFM imaging approach in understanding the degradation process of a coating film is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1460–1470, 2001     

Relationships between strain,microstructure and oxide growth at the nano‐ and microscale

In the present article, the relationships between oxidation processes, surface strains and the microstructure of duplex stainless steels were investigated. Specimens were oxidized at 500 °C under secondary vacuum for 1 h to form a thin oxide film (thickness in the range of 20–50 nm). Such specimens were considered as the model system for developing novel methods of analysis in understanding the behavior of passive films. The interfacial strain field after oxidation was measured experimentally at the microscale using the point grid method. On the other hand, the chemical composition of the oxide film was determined at the submicroscopic scale by means of local scanning Auger spectroscopy (with a spot diameter of 50 nm). Local variations of the chemical composition of the oxide film were analyzed according to the specimen microstructure and the strain field. Copyright © 2008 John Wiley & Sons, Ltd.     

Precision synthesis of microstructures in star‐shaped copolymers of ϵ‐caprolactone,L‐lactide,and 1,5‐dioxepan‐2‐one

Star‐shaped homo‐ and copolymers were synthesized in a controlled fashion using two different initiating systems. Homopolymers of ε‐caprolactone, L ‐lactide, and 1,5‐dioxepan‐2‐one were firstly polymerized using (I) a spirocyclic tin initiator and (II) stannous octoate (cocatalyst) together with pentaerythritol ethoxylate 15/4 EO/OH (coinitiator), to give polymers with identical core moieties. Our gained understanding of the versatile and controllable initiator systems kinetics, the transesterification reactions occurring, and the role which the reaction conditions play on the material outcome, made it possible to tailor the copolymer microstructure. Two strategies were used to successfully synthesize copolymers of different microstructures with the two initiator systems, i.e., a more multiblock‐ or a block‐structure. The correct choice of the monomer addition order enabled two distinct blocks to be created for the copolymers of poly(DXO‐co‐LLA) and poly(CL‐co‐LLA). In the case of poly(CL‐co‐DXO), multiblock copolymers were created using both systems whereas longer blocks were created with the spirocyclic tin initiator. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 1249–1264, 2008     

Microstructural characterization and optical polarization of glass with needle-like micro–nano silver oriented arrangement

Homogeneous glasses in the Na₂O–B₂O₃–Al₂O₃–SiO₂ system doped with proper amount of AgCl were obtained by melting at a temperature of 1450 °C. Then, with several steps of treatment, including crystallization, elongation and reduction, the glass with oriented arrangement of needle-like micro–nano silver particles was produced. The microstructure and the optical properties of the glass samples in different stages were studied by SEM-EDAX, FE-SEM and UV–Vis spectrum. The results showed that the glass after elongation and reduction exhibits excellent polarization performance in the wavelength range from 600 nm to 900 nm, with an extinction ratio larger than 45 dB. The glass only elongated shows also slight polarizing performance, which may result from the formation of filament structure of Ag during elongation processing.     

Effect of structural relaxation on Curie temperature and magnetostriction investigated by magnetoelastic waves in metglas

Summary Magnetoelastic wave amplitude, a, was measuredvs. the temperature during thermal cycles in Metglas 2826. When the Curie temperature,T _C, has been reached, theA value vanishes due to the fall of the magnetoelastic coupling in the paramagnetic state. This allows evaluation of theT _c temperature. The latter increases after the iterated thermal treatments while the magnetic anisotropyK _u decreases. Also theA amplitude, measured at room temperature after the subsequent thermal treatments, shows an increasing behaviour. The values ofK _u ,T _c andA approach saturation after the same number of thermal cycles; this suggests that the structural relaxation produced by annealing is the microscopic mechanism governing all the three physical quantities. In particular we explain the connection betweenK _u andA by means of the longitudinal magnetostriction.

---

Riassunto L'ampiezza delle onde magnetoelastiche,A, è stata misurata in funzione della temperatura eseguendo cicli termici nel Metglas 2826. Raggiunta la temperatura di Curie,T _C l'ampiezzaA si annulla a causa della transizione dell'accoppiamento magnetoelastico nello stato paramagnetico. Ciò ci mette in grado di misurare la temperaturaT _C; quest'ultima aumenta in seguito ai ripetuti trattamenti termici mentre l'anisotropia magneticaK _u diminuisce. Anche l'ampiezzaA, misurata a temperatura ambiente dopo i trattamenti termici, mostra un andamento crescente. I valori diK _u,T _c eA tendono alla saturazione dopo lo stesso numero di cicli termici; ciò suggerisce che il rilassamento strutturale prodotto dalla ricottura è il meccanismo microscopico che regola le tre grandezze fisiche menzionate. In particolare noi mostriamo cheK _u eA sono legati dalla magnetostrizione longitudinale.

---

Резюме Измеряется зависимость амплитуды магнитноупругой волны,A, от температуры в течение температурных циклов в металлическом стекле 2826. При достижении температуры Кюри,T _c, величинаA обращается в нуль из-за уменьшения магнитноупругой связи в парамагнитном состоянии. Это позволяет оценить темпаратуру Кюри,T _c. Температура Кюри увеличивается после повторных температурных обработок, тогда как магнитная анизотропияK _u уменьшается. Также отмечается увеличение амплитудыA, измеренной при комнатной температуре после последовательных температурных обработок. ВеличиныK _u,T _c иA приближаются к насьщению после одинакового числа температурных циклов. Это результат предполагает, что структурная релаксация, обусловленная отжигом, представляет микроскопический механизм, определяющий все три физические величины. В частности, мы объсняем связь междуK _u иA с помощью продольной магнитострикции.

     

Grab vs. composite sampling of particulate materials with significant spatial heterogeneity—A simulation study of “correct sampling errors”

Sampling errors can be divided into two classes, incorrect sampling and correct sampling errors. Incorrect sampling errors arise from incorrectly designed sampling equipment or procedures. Correct sampling errors are due to the heterogeneity of the material in sampling targets. Excluding the incorrect sampling errors, which can all be eliminated in practice although informed and diligent work is often needed, five factors dominate sampling variance: two factors related to material heterogeneity (analyte concentration; distributional heterogeneity) and three factors related to the sampling process itself (sample type, sample size, sampling modus). Due to highly significant interactions, a comprehensive appreciation of their combined effects is far from trivial and has in fact never been illustrated in detail. Heterogeneous materials can be well characterized by the two first factors, while all essential sampling process characteristics can be summarized by combinations of the latter three. We here present simulations based on an experimental design that varies all five factors. Within the framework of the Theory of Sampling, the empirical Total Sampling Error is a function of the fundamental sampling error and the grouping and segregation error interacting with a specific sampling process. We here illustrate absolute and relative sampling variance levels resulting from a wide array of simulated repeated samplings and express the effects by pertinent lot mean estimates and associated Root Mean Squared Errors/sampling variances, covering specific combinations of materials’ heterogeneity and typical sampling procedures as used in current science, technology and industry. Factors, levels and interactions are varied within limits selected to match realistic materials and sampling situations that mimic, e.g., sampling for genetically modified organisms; sampling of geological drill cores; sampling during off-loading 3-dimensional lots (shiploads, railroad cars, truckloads etc.) and scenarios representing a range of industrial manufacturing and production processes. A new simulation facility “SIMSAMP” is presented with selected results designed to show also the wider applicability potential. This contribution furthers a general exposé of all essential effects in the regimen covered by “correct sampling errors”, valid for all types of materials in which non-bias sampling can be achieved.     

Effect of chain stiffness on the morphology of diblock copolymer melts

The authors have studied the microphase separation of symmetric diblock copolymers with variable block stiffness and different block chain lengths using coarse-grained molecular dynamics simulations. The simulation results show that for symmetric diblock copolymers, a combination of chain length and relative stiffness between the blocks may play the major role in determining the equilibrium morphology of the system. When the variation in stiffness between blocks is small, the equilibrium morphology of the diblock system is found to be lamellar; this is also the case for systems with small chain lengths, regardless of the difference in block stiffness. However, in systems with longer chains with modest variation in stiffness between the blocks, an ordered cylindrical phase is formed in which the stiffer blocks form cylinders completely surrounded by the flexible components. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2556–2565, 2009     

Facile method to prepare monodispersed Ag/polystyrene composite microspheres and their properties

This article presents a facile method to prepare silver/polystyrene composite microspheres. In this approach, monodispersed polystyrene (PS) particles were synthesized with carboxyl acid groups on the surfaces of the PS particles via dispersion polymerization at first. With the addition of [Ag(NH₃)₂]⁺ to the PS dispersion, [Ag(NH₃)₂]⁺ was absorbed to the surfaces of the PS particles, and then by heating the system, [Ag(NH₃)₂]⁺ complex ions were reduced to silver to form the Ag/PS composite microspheres. In the synthesis of PS dispersion, PVP was used as dispersant to stabilize the PS particles, it also acted as reducing agent in the reduction of [Ag(NH₃)₂]⁺ complex ions to silver, so no additional reducing agent was needed. The resulting composite microspheres were characterized by TEM, SEM, XPS, and XRD. The catalytic properties and surface‐enhance Raman scattering (SERS) was studied as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4547–4554, 2009