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1.
The kinetics of polymerization of D,L-lactide and glycolide are studied via differential scanning calorimetry at different temperatures and concentrations of the catalyst tin octanoate. For the polymerization of D,L-lactide and glycolide, the enthalpies are determined to be ?17 ± 1.5 and 16.5 ± 1.5 kJ/mol, respectively. The time to attain reaction equilibration decreases from 300 to 100 min with an increase in temperature from 200 to 220°C. The time of reaction at 200°C decreases from 280 to 100 min as the concentration of the catalyst is increased from 500 to 830 ppm. When the polymerization of glycolide is conducted at temperatures below 200°C, the reaction is accompanied by crystallization of polyglycolide and an increase in the total enthalpy of the process. 相似文献
2.
A. V. Lezov G. E. Polushina A. A. Lezov P. S. Vlasov N. S. Domnina 《Polymer Science Series A》2011,53(2):93-101
The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH
values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied.
For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the
chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes.
In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid
units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer
and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the
copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm.
The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to
steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of
the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along
the chain contour. 相似文献
3.
Yodthong Baimark Mangkorn Srisa-ard Jirasak Threeprom Nual-Anong Narkkong 《Colloid and polymer science》2007,285(13):1521-1525
Nanoparticle colloids of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) diblock copolymer were prepared by a modified spontaneous emulsification solvent diffusion method using acetone/ethanol
as the mixture organic solvents. The MPEG-b-PDLL was synthesized by ring-opening polymerization of D,L-lactide using stannous octoate and MPEG with molecular weight of 5,000 g/mol as the initiating system. The MPEG-b-PDLL obtained was an amorphous polymer with molecular weight of 73,600 g/mol. Influences of acetone/ethanol (v/v) ratios
and Tween 80 surfactant concentrations on characteristics of the colloidal nanoparticles were investigated and discussed.
Light-scattering analysis showed that average diameters of the surfactant-free colloidal nanoparticles were in the range of
86–124 nm. The nanoparticle sizes decreased as the ethanol ratio increased. The Tween 80 did not show the significant effect
on the nanoparticle sizes. Scanning electron micrographs of dried nanoparticles that demonstrated the aggregation of most
particles suggested they were the soft nanoparticles. However, the dried nanoparticle morphology can be observed from scanning
electron microscopy as having a spherical shape and smooth surfaces. 相似文献
4.
M. E. Matthews I. Atkinson Lubaina Presswala O. Najjar Nadine Gerhardstein R. Wei Elizabeth Rye A. T. Riga 《Journal of Thermal Analysis and Calorimetry》2008,93(1):281-287
Dielectric analysis (DEA), supported by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), powder X-ray
diffraction analysis (PXRD) and photomicrography, reveal the chiral difference in the amino acids. The acids are classified
as dielectric materials based on their structure, relating chirality to the vector sum of the average dipole moment, composed
of the constant optical (electronic) and infra-red (atomic) polarizabilities, as well as dipole orientation. This study encompasses
14 L-and D-amino acid isomers. Physical properties recorded include AC electrical conductivity, charge transfer complexes, melting,
recrystallization, amorphous and crystalline phases, and relaxation spectra, activation energies and polarization times for
the electrical charging process. 相似文献
5.
A. I. Vorob’eva M. S. Babaev L. V. Spirikhin N. M. Shishlov S. V. Kolesov 《Russian Journal of Applied Chemistry》2016,89(1):160-164
A copolymer of N,N-diallyl-N,N-dimethylammonium chloride with maleic acid of constant composition was prepared under the conditions of radical initiation. The possibility of the functionalization of the copolymer with drugs containing amino groups by polymer-analogous transformations was examined. Conditions were found for preparing conjugates of the copolymer with isoniazid. The structures and the quantitative compositions of the conjugates were determined by 13С NMR spectroscopy, and the possibility of preparing conjugates with controlled drug content was demonstrated. 相似文献
6.
Qian Zhong 《Polymer Science Series A》2018,60(3):266-277
Poly(L-lactide)-based (PLLA) poly(ester-urethane)s are particularly relevant and gain significant attention due to their environment-friendly degradability and elastomeric shape memory capability. The tensile properties, resilience and degradation are strongly affected by their crystallization. This work was to investigate crystallization behaviors of the poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) (PLLA-PBAPLLA) based thermoplastic polyurethane elastomers (PLAEUs) we synthesized previously. Dynamic scanning calorimetry (DSC) and polarized optical microscopy (POM) in combination with Avrami, Jezioney and Hoffman-Weeks models were used to analyze the impact of the PLLA block length on the crystallization temperature Tc, degree of crystallinity Xc, nucleation and spherulite growth mode and crystallization regime kinetics of the PLAEUs. The results indicate the low melting point poly(butylene adipate) (PBA) block resides in the amorphous domains while the PLLA block resides in both crystalline and amorphous phases. The Xc of the PLAEUs increase with the increased length of the PLLA block (i.e. higher content of PLLA block). The analyses with Avrami and Jezioney models show the PLAEU copolymers follow a disc-like spherulite growth. The covalently bonded PBA block decreases both nucleation velocity and spherulite growth rate in the isothermal crystallization. Such an impact is lessened as PLLA block length increases. The PLLA homopolymers demonstrate crystallization regime transition from II to III at a certain Tc of isothermal crystallization, while the crystallization regime kinetics of PLLA block in the PLAEUs are explained by a single regime III at low molecular weights of PLLA and the transition is restored as the PLLA block length increases (i.e. regime II to III). 相似文献
7.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2008,93(2):423-428
Heat capacity C
p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these measurements. At 298.15 K the values of heat capacity, C
p; entropy, S
m0(T)-S
m0(0); difference in the enthalpy, H
m0(T)-H
m0(0), are equal, respectively, to 144.6±0.3 J K−1 mol−1, 169.0±0.4 J K−1 mol−1 and 24960±50 J mol−1. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial
increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample. 相似文献
8.
P. A. Nikishev Yu. A. Piskun I. V. Vasilenko L. V. Gaponik P. S. Timashev A. A. Akovantseva S. V. Kostjuk 《Polymer Science Series B》2017,59(6):655-664
The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl4–pyridine is studied in a mixture CH2Cl2–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (Mn = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)2] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (Mn = 10000–17000 g/mol) and a relatively low molecular-weight distribution (Mw/Mn = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by 1Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy. 相似文献
9.
O. G. Strukov V. B. Kondrat’ev Z. V. Vlasova V. A. Petrunin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2017,91(1):100-105
Conformers of the biologically active compounds CH3P(O)(OR)(SCH2CH2NR 2 ′ ), where (I) R = i-C4H9, R′ = C2H5 and (II) R = C2H5, R′ = i-C3H7, are calculated within the AM1 level of theory. The elongated and twisted forms with maximum and minimum distances between a nitrogen atom and those of a phosphorus tetrahedron, respectively, and bearing a syn and anti oriented alkoxy group relative to a phosphoryl oxygen, are studied. It is found that the differences between the energy, electronic, and geometric parameters of these forms are apparent in differences between their properties, e.g., the ability to participate in complexation and protonation, reactions that to some extent simulate the interaction between a substance and a biological object. 相似文献
10.
11.
Summary. A new synthetic route was developed for the preparation of trans-3-hydroxy-16,17-seco-pregna-5,17(20)-dien-16-al, using Grob fragmentation as the key step. This seco-steroid contains a formyl group and an unsaturated side-chain in a sterically favourable position, and is therefore a promising starting material for the synthesis of novel condensed steroid heterocycles.Received March 22, 2003; accepted April 22, 2003
Published online September 25, 2003 相似文献
12.
Lili Liang Wenge Li Yaoyao Sun Min Li Xia Xu Tao Wu Shihang Xie 《Journal of Cluster Science》2018,29(1):151-157
One tetranuclear nickel cluster [Ni4L4(CH3CH2OH)4] (1, H2L = N-(2-hydroxyphenyl)salicylaldimino) was synthesized by solvothermally reaction and characterized by elemental analysis, IR, TGA and X-ray single-crystal diffraction. It exhibits a cubane-type [Ni4O4] structure with four Schiff base ligands and four alcohol molecules in the unit. Magnetic susceptibility studies indicate that there are ferromagnetic interactions within the tetranuclear nickel(II) cluster. Furthermore, Thermogravimetric analyses display the stability of complex 1. 相似文献
13.
Ermakova S Sokolova R Kim SM Um BH Isakov V Zvyagintseva T 《Applied biochemistry and biotechnology》2011,164(6):841-850
Fucoidans were isolated by water extraction and ion-exchange chromatography from brown algae Eclonia cava, Sargassum hornery, and Costaria costata collected near of Korean coasts. The structures of fucoidans were investigated. Fucoidan from E. cava was mixture of sulfated rhamnogalactofucan and galactofucan. Fucoidan from C. costata was a sulfated galactofucan. Fucoidan isolated from S. hornery was separated into three fractions: a homofucan sulfate, a homofucan but without sulfate groups, and a sulfated rhamnofucan.
The results clearly showed that fucoidans play an inhibitory role in colony formation in human melanoma and colon cancer cells
and may be effective antitumor agents. 相似文献
14.
Yu. V. Frantsuzova A. Yu. Neverovskaya A. P. Voznyakovskii 《Russian Journal of Applied Chemistry》2007,80(6):979-982
The formation of 3D chemical networks in siloxane block copolymers in the course of room-temperature vulcanization (RTV) was studied. The influence of the moisture content of the reaction medium on the RTV of the systems under consideration was analyzed for the case of preparation of films from solutions. 相似文献
15.
16.
R. N. Shakhmaev A. Sh. Sunagatullina D. A. Akimova V. V. Zorin 《Russian Journal of Organic Chemistry》2017,53(4):615-617
An efficient synthetic approach to 2E,4E and 2E,4Z isomers of ethyl 5-chloropenta-2,4-dienoate has been developed on the basis of one-pot oxidation–olefination of readily accessible (E)- and (Z)-3-chloroprop-2-en-1-ols by the action of barium manganate and ethyl (triphenyl-λ5-phosphanylidene)acetate. 相似文献
17.
I. E. Efremova M. I. Vakulenko K. A. Lysenko I. S. Bushmarinov L. V. Lapshina G. A. Berkova V. M. Berestovitskaya 《Russian Journal of General Chemistry》2010,80(11):2298-2305
A modification of 1-nitrocyclohexene synthesis is proposed; its reaction with phenylhydrazine and benzoic acid hydrazide is
shown to afford monoadducts, and with hydrazine hydrate, bisaduct. With diphenylguanidine occurs heterocyclization to 1-phenyl-2-N-phenylamino-4,5,6,7-tetrahydrobenzimidazole, whose structure is confirmed by the X-ray diffraction data. The analysis performed
for this compound of the electron density distribution function in the crystal made it possible to estimate the charge distribution,
π-electrons delocalization nature, and the role of N-H…N, C-H…H-C and C-H…C interactions in the formation of the crystal packing. 相似文献
18.
T. F. Ibragimov M. G. Levkovich V. A. Saprykina Kh. M. Shakhidoyatov 《Chemistry of Natural Compounds》2010,46(5):767-770
N-Chloroacetylcytisine was synthesized by acylation of (–)-cytisine. Stable Z- and E-conformers with respect to rotational isomerism around the N-12–CO bond were found in PMR spectra at room temperature. The
point at which PMR resonances of the Z- and E-conformers coalesced upon heating was measured. The transition barrier between the conformers was estimated. 相似文献
19.
Two pairs of amino-acid functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) derivatives, namely, poly(N-(tert-butoxycarbonyl)-L-methionyl (3,4-ethylenedioxythiophene-2’-yl)methylamide) (L-PEDOT-Boc-Met) and poly(N-(tert-butoxycarbonyl)-D-methionyl (3,4-ethylenedioxythiophene-2’-yl)methylamide) (D-PEDOT-Boc-Met); poly(L-methionyl (3,4-ethylenedioxythiophene-2’-yl)methylamide) (L-PEDOT-Met) and poly(D-methionyl (3,4-ethylenedioxythiophene-2’-yl)methylamide) (D-PEDOT-Met) were synthesized via chemical oxidative polymerization of corresponding monomers. The structural characterization, spectroscopic properties and thermal stability of these monomers and polymers were systematically explored by FTIR spectra, Raman spectra, XRD spectra, UV-Vis spectra and thermogravimetric analysis. As chiral electrode materials, these polymers were employed to successfully recognize 3,4-dihydroxyphenylalanine (DOPA) enantiomers by cyclic voltammetry (CV) in sulphuric acid solution. The measurement results reveal that the tendency was hetero-chiral interaction between L-PEDOT-Met/PVA/GCE and D-DOPA, D-PEDOT-Met/PVA/GCE and L-DOPA, respectively. Also, the mechanism of chiral discrimination was discussed. All the results implied that the combination of electrochemical molecular recognition technology and chiral PEDOT materials can be a promising approach for chiral recognition and may open new opportunities for facile, biocompatible, sensitive and robust chiral assays in biochemical applications. 相似文献
20.
C. G. Mothé A. D. Azevedo W. S. Drumond S. H. Wang 《Journal of Thermal Analysis and Calorimetry》2010,101(1):229-233
Samples of poly(l,l-lactide)-block-poly(ethylene glycol)-block-poly(l,l-lactide) (PLLA-PEG-PLLA) were synthesized from l,l-lactide polymerization using stannous 2-ethylhexanoate, Sn(Oct)2 as initiator and di-hydroxy-terminated poly(ethylene glycol) (PEG) (M
n
= 4000 g mol−1) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was characterized by Fourier transform
infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) revealed the copolymers composition and was capable to show the
deleterious effect of an excess of Sn(Oct)2 in the polymer thermal stability, while Differential Scanning Calorimetry (DSC) allowed the observation of the miscibility
between the PLLA and PEG segments in the different copolymers. 相似文献