Effect of the polycondensation time on the crystallization of polyesteramide 6NT6

Samples of alternating polyesteramide 6NT6 obtained at short and moderate times of polycondensation have been examined. Crystallization rates and melting temperatures are reported as functions of crystallization temperature and polycondensation time. As the polycondensation time increases, both the equilibrium melting temperature and the crystallization rate decrease owing to a very small decrease of polymer alternation.     

Unperturbed dimensions of random and alternating styrene/n-alkyl methacrylate copolymers

The steric factors σ of homopolymers of ethyl, n-butyl, and n-octyl methacrylate, of equimolar random and alternating copolymers of these monomers with styrene, and of polystyrene, were determined by measuring intrinsic viscosities in a good solvent (butanone, 25°C) and extrapolating the data thus obtained to zero molecular weight of the polymer. For all comonomeric pairs under investigation, the σ² of an equimolar random copolymer and, particularly, of an alternating copolymer, is higher than the arithmetic mean (σ + σ)/2 of the σ² values of the parent homopolymers. The positive deviation from the linear dependence of σ² on the copolymer composition, expressed as an increment of σ², is proportional to the mole fraction of alternating dyads in the copolymer chain with in the limits of experimental error. The effect of copolymer microstructure on the unperturbed dimensions of the chains has been compared for equimolar copolymers of styrene with methyl, ethyl, n-butyl, and n-octyl methacrylate by using a relative increment ξ defined as the ratio of σ² of the alternating copolymer to (σ + σ)/2. The dependence of ξ on the number of carbon atoms in the alcohol substituent of the methacrylate component of the copolymer seems to exhibit a maximum for ethyl methacrylate.     

Preparation of biodegradable polyesteramide microspheres

Biodegradable polyesteramide copolymer P(CL/AU) based on -caprolactone and 11-aminoundecanoic acid was synthesized by the melt polycondensation method. Polyesteramide (PEA) microspheres were prepared by a simple O/W emulsion solvent evaporation method. The effects of variations in preparation parameters (such as emulsifier concentration, polymer concentration, polymer solution adding rate, stirring rate, and whether vacuum was applied) were studied in detail. The obtained microsphere morphologies were observed using an optical microscope and via scanning electron microscopy (SEM). The particle size distribution was determined using a Malvern laser particle sizer. When the PEA microspheres were incubated in PBS saline, the particle size increased at first, and then decreased after a longer time period; the theory that this behavior was due to degradation of the microspheres was confirmed by SEM.     

Rheological and thermal properties of a commercial liquid-crystalline polyesteramide

A commercial main-chain liquid-crystalline, naphthalene-based polyesteramide, was studied by three experimental techniques: extrusion capillary rheometry, dynamic viscoelasticity, and differential scanning calorimetry (DSC). From capillary rheometry a maximum at 360°C was observed in viscosity temperature curve. This result is compared with literature data for other thermotropics, and the possibility of a transition from a nematic to an isotropic phase is considered. The results obtained from dynamic viscoelasticity and DSC agree, and reveal the existence of a glass transition at 128°C (by DSC) and 137–147°C (by viscoelastic measurements, depending on frequency) as well as melting at 282°C. Annealing below 230°C produces two types of crystals, whereas annealing above this temperature gives rise to only one type of crystal, the melting temperature of which can be, depending on annealing time, as high as 340°C. The results are compiled in a phase diagram with six regions, four of them corresponding to the solid state, one to a liquid mesophase, and one to an isotropic phase.     

Alkaline degradation behavior of polyesteramide fibers: surface erosion

In this work, a new kind of aliphatic polyesteramide (PEA) copolymer based on -caprolactone and 6-aminocaproic acid was synthesized by the melt polycondensation method. Biodegradable PEA fibers were processed by the melt-spinning method. ¹H-NMR, FTIR, SEM, and tensile testing were used to characterize the degradation of PEA fibers in concentrated alkaline solution. The PEA fiber undergoes surface erosion in such concentrated alkaline solutions.     

The determination of ethanol by alternating current tensammetry

A method for the determination of ethanol in vodka by phase-sensitive a.c. tensammetry is described; the only prior treatment of the sample is dilution with water and addition of KCl The positive wave of the tensammetric response was used. Ethanol concentrations in the range 2–10% can be determined with a relative imprecision of 0.5%. Other species having surfactant properties, such as the fusel oils found in most distilled liquors, interfere.     

低相对分子质量苯乙烯-马来酸酐交替共聚物的合成

将引发剂偶氮二异丁腈(AIBN)、共聚单体苯乙烯(St)和马来酸酐(MA)溶解于甲苯中,采用沉淀聚合法合成苯乙烯-马来酸酐共聚物(SMA).分别研究了反应温度、引发剂用量、反应时间、单体配比和单体浓度对聚合物得率和酸酐含量的影响.采用正交实验确定最优反应条件为:单体浓度20%,单体物质的量比为1∶1,引发剂用量为0.60%,反应温度为86℃,反应时间2h,产物得率为86.86%,酸酐含量为50.28%.并利用傅里叶变换红外光谱(FTIR)、核磁共振碳谱(~(13)C NMR)、凝胶渗透色谱(GPC)和热分析法分别研究聚合物的分子结构、相对分子质量及相对分子质量分布和热稳定性.结果表明产物是苯乙烯-马来酸酐交替共聚物,相对分子质量分布较窄,具有良好的热稳定性.     

The crystal structure of the alternating copolymer of hexafluoroisobutylene and vinylidene fluoride

The crystal structure of the alternating copolymer of hexafluoroisobutylene and vinylidene fluoride, P(HFIB/VF₂), was determined using x-ray diffraction techniques. Oriented specimens of the copolymer were produced by drawing melt-pressed film at 300°C. The unit cell of P(HFIB/VF₂) is orthorhombic with dimensions at a = 1.064, b = 1.837, and c = 0.783 nm. The chain conformation is a 2₁ helix with an approximate trans-trans-gauche-gauche backbone dihedral-angle sequence. Severe intrachain steric crowding exists; as a consequence, the chain is quite rigid and some of the backbone bond angles are highly extended. The unit cell contains four such chains packed according to the symmetry of space group Iba2. Neighboring chains in a crystal are mechanically interlocked; in combination with the rigidity of the chains, this is the basis for the superior mechanical properties of the copolymer compared to PTFE. A structure containing up to 20-30% of head-to-head residues was found to be statistically indistinguishable from a completely head-to-tail structure.     

The dual-site alternating cyclocopolymerization of 1,3-butadiene with ethylene

The copolymerization of ethylene with 1,3-butadiene was studied with the series of ansa-metallocenes Me2Si(Cp)(9-Flu)ZrCl2 (1), Me2Si(1-Ind)(9-Flu)ZrCl2 (2), and Me2Si(9-Flu)2ZrCl2 (3) with methylaluminoxane (MAO) as cocatalyst. The catalyst 2/MAO yields a cyclocopolymer composed of two ethylene monomer units for every one butadiene in a novel periodic architecture of 1,2-enchained cyclopentane units separated by three methylenes. The high butadiene content in the copolymer and the high selectivity for alternating cyclocopolymerization to form methylene-1,2-cyclopentane units implicate a dual-site mechanism where butadiene and ethylene are enchained at different coordination sites.     

Nanostructure and crystallization phenomena in multilayered films of alternating iPP and PA6 semicrystalline polymers

The present work is concerned with the study of the crystalline morphology and the nanostructure of a multilayered system of two alternating immiscible semicrystalline polymers: isotactic polypropylene (iPP) and polyamide 6 (PA6). Films with a volume ratio of 70/30 were prepared by means of layer multiplying coextrusion. Contrary to previous experiments, performed with semicrystalline/amorphous and amorphous/amorphous nanolayered systems, the studied iPP/PA6 film does not exhibit a well defined maximum in the USAXS patterns. This result accounts for an irregular layered structure, as further confirmed by means of TEM images. Nevertheless, such a layered assembly still influences the crystallization behaviour of both constituent polymers. On the one hand, the crystallization of PA6 within the multilayered material is substantially hindered as evidenced by its weak scattering intensity. Real time studies as a function of temperature undoubtedly detect the presence of a WAXS peak and a SAXS maximum associated to PA6 above the melting temperature of iPP. Room temperature AFM studies also confirm the occurrence of crystalline structures within the PA6 layers. On the other hand, SAXS and WAXS measurements at room temperature reveal the occurrence of an oriented lamellar morphology within the iPP layers bearing uniaxial symmetry around an axis perpendicular to the layers surface. Results show that the crystalline molecular chains are placed mainly parallel to the layer surfaces forming edge-on lamellae. Moreover, X-ray scattering results are in agreement with the occurrence of two populations of lamellae, both edge-on and perpendicular to each other, in agreement with the crosshatched morphology observed by AFM.     

The dimensions of a polymer chain at the coil-to-globule transition

Simple models of the star-branched and linear polymers were studied by means of a Monte Carlo method. The chains were confined on a simple cubic lattice. Star-branched polymers consisted of f=3 arms of equal length. The total number of beads in both types of polymers was varied from N=49 to N=799. The simulations were performed in different solvent qualities—from a good solvent to a collapsed globule regime. The static properties of the chains under consideration were measured as functions of the temperature of the system. It appeared that the ratio of the radius of gyration to the mean end-to-end vector is very sensitive to solvent quality. It shows that the coil-to-globule transition is a complicated phenomenon. The possible explanation of the phenomenon is discussed.     

Synthesis,characterization and in vitro degradation of biodegradable polyesteramide based on lactic acid

A new type of biodegradable polyesteramide P(LA/AU) based on lactic acid and aminoundecanoic acid was synthesized by the melt polycondensation method. The copolymers obtained were characterized by FTIR, ¹H-NMR, DSC, and XRD. The in vitro degradation behavior of the copolymers was studied using weighing, ¹H-NMR, FTIR, DSC, and SEM. With the increase in aminoundecanoic acid units, the melting temperature and crystallinity increased, but the water absorption and degradation rate decreased accordingly. During degradation in vitro, the ester moiety decreased due to ester cleavage along the macromolecular main chain. As degradation proceeded, the melting temperature and crystallinity increased at first, then started to decrease because the crystalline phase was destroyed.     

The electronic states of polyfluorene copolymers with alternating donor-acceptor units

We calculate the electronic states of the low bandgap polyfluorene-based copolymer DiO-PFDTBT, which consists of alternating 9,9-dioctyl-9H-fluorene and 4,7-di-thiophen-2-ylbenzo[1,2,5]thiadiazole (TBT) units, and compare with the steady-state absorption, emission, and excitation spectrum. Using the semiempirical quantum-chemical (ZINDO) method we can assign the characteristic bands of the "camel-back" absorption spectrum to one charge transfer state at lower energy localized on the TBT unit, and one delocalized excitonic state at higher energy corresponding to the pi-conjugated electron system. Additional "dark" charge transfer states in the gap between these bands have been revealed. Calculations are also made on the red light emitting polyfluorene-based copolymer poly(fluorene-co-benzothiadiazole) (F8BT), which contains benzo[1,2,5]thiadiazole instead of TBT. The nature of the electronic states in F8BT and DiO-PFDTBT are found to be qualitatively the same.     

The applicability of phase-sensitive alternating current measurements in flow-through detection

The applicability of phase-sensitive alternating current (a.c.) measurements in flowthrough detection is discussed. The differences between flow and non-flow conditions are examined for copper(II) and thiourea at a horizontal dropping mercury electrode in an “open system”. The possibility of using this detection system in flow-injection procedures is indicated. A glassy-carbon electrode cell is used to test the feasibility of a.c. measurements with hydroquinone as the example.     

The 'Einstein correction' to the bulk viscosity in n dimensions

We calculate the effective bulk viscosity of a dilute dispersion of rigid n-dimensional hyperspheres in a compressible Newtonian fluid at zero Reynolds number.     

The structure of hyperspherical fluids in various dimensions

The structure of hard, hyperspherical fluids in dimension one, two, three, four, and five has been examined by calculating the pair correlation function using a Monte Carlo simulation. The pair correlation functions match known results in one, two, and three dimensions. The contact value of the pair correlation functions in all the different dimensions agrees well with the theory of Song, Mason, and Stratt [J. Phys. Chem. 93, 6916 (1989)]. The decrease in ordering as the dimension is increased is readily apparent in the structure of the pair correlation function.     

The response of a colloidal suspension to an alternating electric field

This paper is concerned with the calculation of the complex conductivity K* of a suspension, a quantity which may be determined experimentally from the measurement of the alternating current which flows between a pair of electrodes in the suspension due to an alternating voltage difference. A semi-analytic formula is derived for the complex conductivity of a dilute suspension of spherical particles with small dielectric constant which is reasonably accurate for ?-potentials of less than 50 mV. For such suspensions this formula represents a very economical alternative to the exact computer calculation of K* described by DeLacey and White (ref. 2). Although the formula for K* is derived for particles with fixed surface charge, it is shown that the formula can also be applied to a more general class of suspensions, in which the surface charge arises from the dissociation of a single type of surface group.