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1.
In order to synthesize the higher molecular weight poly(lactic acids) by direct condensation polymerization of lactic acid, dipentaerythritol was used as a chain branching agent. Poly(lactic acids) of high molecular weight, 67000(Mn), was obtained by using antimony trioxide catalyst with good color. This poly(lactic acids) showed Tg of 54.8 °C, Tm of 147 °C and cold crystallization temperature of 115 °C. The polymer could be melt processed into transparent films. Tensile modulus of 311 Kg/ mm2, tensile strain of 21% and tensile strength of 12.41 Kg/ mm2 were obtained for film collected at 400%/min and drawn 4 times. 相似文献
2.
Kirill T. Kalinin Dr. Nikita G. Sedush Petr V. Dmitryakov Prof. Sergei N. Chvalun 《ChemistryOpen》2020,9(10):1027-1032
The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol−1. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=44.51±5.35 kJ mol−1, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol−1 K−1. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown. 相似文献
3.
G. Bognár Cs. Pintér B. Horváth T. Sydo E. Ligeti J. Pulai D. Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2009,95(3):769-774
Osteonecrosis (ON) of the femoral frequently occurs after steroid medication. One of the final pathways leading to steroid
induced ON is thought to be pathologic fat metabolism. The pathobiological mechanism underlying the induction of fat metabolism
outslides by steroids leading to ON has not been fully elucidated. The purpose of this study was to examine the intraoperative
obtained gluteal fat tissue from ON patients with histology, gas chromatography (GC) and differential scanning calorimetry
(DSC) and to compare them with otherwise healthy patient’s samples. The histological sections showed no significant differences
compared with the control group. GC revealed that fraction of saturated fatty acids decreased in ON samples from mean values
of controls of 24% to 21, the polyunsaturated fraction from 20 to 14%. The monounsaturated acids showed an increase from mean
rate of 52% of the controls to 65% of steroid treated samples. DSC curves correlate with chromatographic analysis of the tissue
fatty acids (Steroid treated, heating between 0–100°C: T
m=5.7°C, ΔH= −15.8J/g−1; heating between −20–100°C: Tm= −9.96 and 5.85°C, ΔH= −59.17 and −16.2 J g−1. Non-necrotic, heating between 0–100°C: two separable transition with Tm=5.7 and 9.9°C, total ΔH= −20.8 J g−1; heating between −20–100°C: Tm= −10.9 and 4.95°C, total ΔH= −75.8 J g−1.)
Our preliminary findings are rather tendentious. Further investigations are needed with higher sample rate and under other
anamnestic circumstances too. 相似文献
4.
The poly(urethane–urea) (PUU) based on α, Ω, hydroxy terminated polystyrene (OH-PSt-OH), 1,6-hexamethylene diisocyanate (HMDI) and three different diamines (1,2-ethylenediamine (EDA), 1,4-butanediamine (BDA), 1,6-hexamethylene diamine (HMDA)) is prepared by a melt polymerization method. The length of the soft segment is varying from 2000 to 8900 g/mol using HMDI as a chain extender. The inherent viscosity of the polymer is found to be in the range of 0.36–2.0 dL/g suggesting that the polymer is of high molecular weight. FT-IR results conclude that the urea groups form both monodendate and bidendate assemblies. Temperature dependent FT-IR and WAXS data confirm that the crystallinity of the copolymer is very high and depends on the spacer length. DSC data show the peaks for Tg of soft and Tm of hard segments. Depending on the concentration and the type of hard segments, melting temperature of the polymers was varied from 142 °C to 266 °C. The solubility of the polymer in chloroform is depending on the concentration of the hard segment. The TGA data reveal that the polymer shows single stage decomposition cantered around 413 °C. 相似文献
5.
Allyl methacrylate was polymerized in CCl4 solution by α,α′‐azoisobutyronitrile at 50, 60, and 70°C. The kinetic curves were auto‐accelarated types at 60 and 70°C, but almost linear at 50°C. Arrhenius activation energy was 77.5 kJ/mol. The polymer was insoluble in common organic solvents. It was characterized by FT‐IR, NMR, DSC, TGA and XPS methods. About 98–99% of allyl side groups were remained as pendant even after completion of the polymerization. The spectroscopic and thermal results showed that polymerization is not a cyclopolymerization type, but may have end group cyclization. The high molecular weight is the main cause of a polymer being insoluble even in the early stage of the polymerization. Molecular weight of 1.1×106 for a soluble polymer fraction was measured by light scattering method. The Tg of polymer was 94°C, and after curing at 150–200°C, increased to 211°C. The thermal pyrolysis of polymer at about 350°C gave an anhydride by linkage type degradation, and side group cyclization. The XPS analysis showed the presence of radical fragments of AIBN (initiator) and CCl4 (solvent) associated with oligomers. 相似文献
6.
Six-membered D,L-, L,L- and D,D-lactides were polymerized by lipase over a temperature range of 80 to 130 °C to yield the polylactide with a molecular weight (Mw) of greater than 270000. Among the lipases tested, lipase PS gave the greatest molecular weight of polylactide. The polymerization of D,L-lactide by lipase was better than that of L,L- and D,D-lactides. The polymerization of lactide by lipase showed the characteristic features, such as induction period for the initiation of polymerization, formation of oligomer and subsequent formation of high molecular weight polylactide, which may imply the characteristic polymerization by lipase. Immobilization of lipase on celite significantly enhanced the polymerization of lactide particularly with respect to the low concentration of the enzyme and the Mw of the resultant polymer. It was found that there is no clear relationship between enzymatic polymerizability and enzymatic degradability with respect to the enzyme origin and the stereochemistry of lactide. 相似文献
7.
Characterization, Solution Behavior, and Microstructure of a Hydrophobically Associating Nonionic Copolymer 总被引:1,自引:0,他引:1
To obtain an oil-displacement polymer with good thermal stability and solution properties, self-assembling acrylamide (AM)/4-butylstyrene
(BST) copolymers (PSA) were synthesized by the micellar copolymerization technique. The resulting polymer was characterized
by elemental analysis and UV and FT-IR spectroscopy. Conventional DSC measurement was used successfully to characterize the
hydrophobic microblock structure of PSA, and two glass transition temperatures were found in the polymer: at 203 °C for the
AM segments and at 106 °C for the hydrophobic BST segments. The initial decomposition temperature (234 °C) of the polymer
is higher than that of polyacrylamide (210 °C). The DSC and TG results suggest that incorporation of BST into PSA enhances
the molecular rigidity and thermal stability of the polymer. The apparent viscosity of a PSA solution greatly depends on the
amount of BST in the polymer, and the polymer exhibits salt-thickening, temperature-thickening, thixotropy, pseudo-plastic
behavior, anti shearing, and good anti-aging properties at 80 °C. In addition, the apparent viscosities of PSA solutions are
increased remarkably by the addition of a small amount of surfactant. AFM measurements show that large block-like aggregates
and small compact aggregates are formed in aqueous solutions of 0.4 g⋅dL−1 PSA because of strong intermolecular hydrophobic associations, despite the low molecular weight, and their sizes increase
upon addition of a small amount of salt. 相似文献
8.
This
study discussed the phenomena on thermal polymerization of α-methylstyrene
(AMS). A curve scanned by temperature-programmed technique was performed by
differential scanning calorimetry (DSC). Heat of polymerization (ΔH) and onset temperature of exothermic (T0) behavior were determined
to be 280±10 J g-1 and about 138±1°C,
respectively. A dimer formation mechanism was proposed for initiation of the
propagating chain. Spectroscopic identification of dimer structure was conducted
by infrared (IR) spectroscopy in the wavenumber from 650 to 1100 cm-1associated
with molecular fingerprint characteristics. The mechanism of thermal polymerization
on α-methylstyrene proposed in this study was similar to that of styrene
suggested by Mayo. 相似文献
9.
A. M. L. Silva R. W. C. Li J. R. Matos J. Gruber 《Journal of Thermal Analysis and Calorimetry》2000,59(3):675-680
The title polymer was obtained electrochemically by the reduction of 4,4'-bis(dibromomethyl)-2,2'-dimethoxybiphenyl under
very smooth conditions. The DSC and TG/DTG curves registered at four different heating rates showed that the polymer is stable
in air up to 150°C, where smooth degradation starts. Above 300°C, decomposition is fast and exothermic (ΔH= –323 J g–1) . The activation energy (116±4 kJ mol–1 ) was determined by Ozawa's method.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
The degradation of poly(hydroxyethyl methacrylate), PHEMA obtained by γ -radiation induced polymerization of HEMA in aqueous solution, was studied. The polymer was a gel type and insoluble in common organic solvents. The DSC thermogram of the polymer gave a Tg value at 88.2°C and an endothermic peak showed further polymerization or crosslinking at 110–160°C. The degradation observed in TGA was a depolymerization type. However, the FT-IR of TGA fragments showed no monomer, which was degraded further. The degradation of monomer was studied by the GC-MS method. Similar results were also observed. 相似文献
11.
Marta Worzakowska 《Journal of Thermal Analysis and Calorimetry》2008,93(3):799-803
The preliminary studies of the thermal behaviour of polyester obtained in polycondensation process of cyclohex-4-ene-1,2-dicarboxylic
anhydride and ethylene glycol and its new epoxidized form have been performed. The thermal characterization of initial polyester
and its completely oxidized form was done by using differential scanning calorimetry (DSC) and thermogravimetric analysis
(TG). The non-isothermal DSC was applied to determine the influence of time and the temperature on the chemical modification
of initial polyester using 38-40% solution of peracetic acid. On the basis of DSC profiles it has been found that the endothermic
transition, due to the degradation process of initial polyester was characteristic feature under controlled heating program.
The two characteristic transitions for the new epoxidized polyester, the exothermic peak corresponded to the thermal crosslinking
of epoxidized polyester (322.8–336.4°C) and the endothermic decomposition peak of the cured material (363.8–388.9°C) were
observed. The peak maximum temperatures (Tmax) and the heat of cross-linking reaction (ΔHc) for epoxypolyester prepared at 20–60°C under 1–4 h were evaluated. The Tmax1 were almost independent from epoxidation conditions,
while, the values of ΔHc were dependent from conditions of synthesis. The ΔHc values of this process decreased when time of oxidation increased. The highest values of ΔHc at 40°C were obtained. Additionally, TG experiments confirmed two separated degradation steps of the new epoxidized polyester
indicating the ester (370–380°C) and ether (450–460°C) bond breakdown. 相似文献
12.
Polysiloxanes with high molecular weight (Mn > 100 000, Mw/Mn < 2.2) containing various quantity of trifluoroethylene aryl ether groups were prepared by anion ring opening polymerization (AROP) in the presence of promoters including N,N‐dimethylformamide (DMF) and N‐methyl pyrrolidone (NMP). The structures of monomers and polymers were characterized by FTIR and NMR. It was found that the addition of promoter could significantly increase the polymerization rate, decrease the polymerization temperature, and increase the molecular weight of the polymer. When DMF as the promoter, the optimal conditions for polymerization were as follows: The polymerization temperature is 100°C, the amount of catalyst is 2.0%, and the molar ratio of promoter to catalyst is 160:1. The optimal conditions for polymerization using NMP as the promoter were as follows: The polymerization temperature is 75°C, the amount of catalyst is 2.0%, and the molar ratio of promoter to catalyst is 70:1, which indicated that NMP is more effective on AROP than DMF. Thermogravimetric analysis (TGA) showed that the polymer has good heat temperature resistance. Differential scanning calorimetry (DSC) showed that the introduction of NMP in bulk polymerization could improve the randomness of polymer structure, which leads to the disappearance of crystal peak and improve the low temperature resistance of polymer. 相似文献
13.
The effects of amines on the activity of ruthenium catalysts in the controlled synthesis of poly(methyl methacrylate) are
reported at 80°C. The introduction of tert-butylamine or triethylamine into the polymerization system raises the polymerization rate by 1–2 orders of magnitude without
reducing the high degree of control over the chain propagation step. The “living” character of methyl methacrylate polymerization
in the presence of ruthenacarboranes and amines is proved by the fact that, as the monomer conversion increases, the molecular
weight of the resulting polymer increases linearly and the polydispersity index decreases. The polymer can serve as a macroinitiator
for postpolymerization and block copolymer synthesis. 相似文献
14.
Berran Sanay Bernd Strehmel Veronika Strehmel 《Journal of polymer science. Part A, Polymer chemistry》2020,58(22):3196-3208
Investigation of photopolymerization kinetics of 4-(4-methacryloyloxyphenyl)-butan-2-one (1) in comparison with 2-phenoxyethyl methacrylate (2) and phenyl methacrylate (3) using a UV-LED emitting at 395 nm shows significantly faster polymerization of 1 compared to both 2 and 3 at 40°C. Vitrification affects photopolymerization kinetics of all methacrylates under investigation. Interestingly, quantitative final conversion is observed during photoinitiated polymerization of 1 and 2 whereas 3 shows limited conversion at about 80%. Furthermore, higher degree of polymerization is obtained by photoinitiated polymerization of 1 compared to 2 and 3. This shows that the 3-oxobutyl substituent at the phenyl ring of 1 significantly affects both polymerization kinetics and final conversion of the photoinitiated polymerization. Moreover, an additional higher molecular weight fraction is observed in case of polymerization of 1 at 85°C that is above the glass transition temperature of the polymer formed during photoinitiated polymerization. As a thermal polymerization at 85°C in the absence of light results in a high molecular weight polymer as well, an additional thermal process may be discussed as reason for the higher molecular weight polymer fraction in case of the photopolymer made at 85°C. 相似文献
15.
T. A. Du Plessis V. T. Stannett A. M. Goineau 《Journal of polymer science. Part A, Polymer chemistry》1974,12(11):2457-2466
The radiation-induced ionic polymerization of isobutyl vinyl ether was investigated under conditions where the monomer was dried with molecular sieves. The investigation covered the temperature range from ?16°C to 90°C, and the dose-rate range from 1015 to 1020 eV/g-sec, using both γ-rays and electrons. A very high overall activation energy of 15.9 kcal/mole was found for the process below 30°C. Above 30°C, however, the value of the overall activation energy dropped to 4.9 kcal/mole, a phenomenon which is ascribed to the solvation of the propagating carbonium ion below 30°C. The dose-rate dependence of the rate of polymerization was found to be 0.58 over the entire dose-rate range investigated. The molecular weight of the polymer was found to be far less sensitive to trace amounts of water than the rate of polymerization. The molecular weight of the polymer depended strongly on the irradiation temperature, reaching a maximum value of about 120,000 at 35°C. It is shown that at temperatures above 20°C regenerative chain transfer processes play an important role in determining the molecular weight of the polymer. 相似文献
16.
Commercially available Al isopropoxide (Al(OiPr)3) has proved to be an efficient initiator for the bulk polymerization of lactide. The ring-opening polymerization proceeds through a “coordination-insertion” mechanism and the selective rupture of the acyl-oxygen bond of the monomer. Polyester chains are selectively end-capped with an aluminum alkoxide and an isopropoxy group. Therefore, substitution of Al tris(4-penten-1-olate) for Al(OiPr)3 leads to the formation of macromonomers. In the temperature range from 110 to 150°C, polymerization is “living”, i.e. the molecular weight can be predicted by the initial monomer-to-Al molar ratio and the monomer conversion. The narrower polydispersity of poly(L,L-lactide) compared to the amorphous poly(D,L-lactide) (M̄w / M̄n 1.3 compared to 1.9, respectively), both prepared in the bulk, is thought to result from the restricted mobility of the crystallized isotactic polyester chains. When the temperature is increased up to 180°C, inter- and intramolecular transesterification reactions interfere with chain propagation. 相似文献
17.
C. A. P. Joziasse D. W. Grijpma J. E. Bergsma F. W. Cordewener R. R. M. Bos A. J. Pennings 《Colloid and polymer science》1998,276(11):968-975
The influence of morpho-logy on the hydrolytic degradation behavior of poly(L-lactide) has been studied. High molecular weight
and highly crystalline as-polymerized poly(L-lactide) was obtained in high yields through melt polymerization. Poly(L-lactide)
fiber with a draw ratio of 5.6 was obtained by hot-drawing solution-spun fiber.
During the bulk degradation of as-polymerized poly(L-lactide), a rapid decrease of molecular weight and tensile properties
was observed. This could be explained by the morphology of the material and the presence of thermal stresses and subsequent
generation of micro-cracks. The lamellar crystallites in as-polymerized poly(L-lactide) appeared to be very stable towards
hydrolysis. The resorption time of high molecular weight as-polymerized poly(L-lactide) in vivo was estimated at 40–50 yr
by extrapolation of molecular weight data.
Hot-drawn poly(L-lactide) fiber showed exceptional hydrolytic stability under a static load and substantially retained its
mechanical properties over a period of more than 5 yr. The high perfection of the crystalline fiber and the elimination of
micro-voids obtained by hot-drawing prevented penetration of water and induced surface erosion of the fiber.
Received: 10 February 1998 Accepted: 15 May 1998 相似文献
18.
The successful acyclic diene metathesis polymerization (ADMET) of an α,ω-diene containing an acetal moiety is presented. A linear, unsaturated polyacetal is produced with a number average molecular weight of 23000 as determined by gel permeation chromatography (GPC). Thermogravimetric analysis (TGA) of the polymer reveals onsets of decomposition below 300°C in both air and nitrogen atmospheres while differential scanning calorimetry (DSC) indicates that the polymer is primarily amorphous. 相似文献
19.
V. S. Prasad C. K. S. Pillai H. R. Kricheldorf 《Journal of polymer science. Part A, Polymer chemistry》2001,39(14):2430-2443
The homopolyester of 4‐hydroxyphenylacetic acid (HPAA) was synthesized by one‐pot, slurry‐melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4‐oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid‐crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001 相似文献
20.
M. Saeed Butt Zareen Akhter M. Zafar-uz-Zaman Humaira Masood Siddiqi 《Colloid and polymer science》2008,286(12):1455-1461
The diamine, 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline, was prepared via the nucleophilic substitution reaction and was polymerized with
different dianhydrides either by one-step solution polymerization reaction or two-step procedure. The latter includes ring-opening
polyaddition to give poly(amic acid), followed by cyclodehydration to polyimides. The inherent viscosity ranges from 0.61–0.79 dl/g.
Some of the polymers were soluble in most of the organic solvents such as DMSO, DMF, DMAc, NMP, and m-cresol even at room temperature. The degradation temperature of the resultant polymers falls in the ranges from 240–500 °C
in nitrogen with only 10% weight loss. Specific heat capacity at 200 °C ranges from 1.0929–2.6275 J g−1 k−1. The temperature at which the maximum degradation of the polymer occurs ranges from 600–630 °C. The glass transition temperature
(Tg) values of the polyimides ranged from 185 to 272 °C. The activation energy and enthalpy of the polyimides ranged from
47.5–55.0 kJ/mole and 45.7–53.0 kJ/mole and the moisture absorption in the range of 0.23–0.72%. 相似文献