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1.
The copolymerization of acrylic acid with methacrylic acid in bulk is investigated at 40 and 60°. It is confirmed that a “matrix effect” occurs only for high contents of acrylic acid. The critical concentration beyond which the matrix effect disappears is shifted towards lower acrylic acid contents for higher temperatures. The copolymer composition is independent of temperature. The copolymerization of acrylic acid with methyl acrylate is investigated in a mixture which determines an “exaltation of the matrix effect” in the homopolymerization of acrylic acid (molar fractions: mMonomers = 0.34; mn-Hexane = 0.52; mMethanol = 0.14). The resulting copolymers are found to contain a much larger fraction of acrylic acid residues than the copolymers formed in bulk or in toluene or DMF solutions.  相似文献   

2.
The polymerization of the system indene-titanium tetrachloride-methylene chloride gave irreproducible kinetics which have been attributed to variable concentrations of impurities in the solvent. Incomplete yields sometimes observed at ?70° are also caused by impurities, but introduction of water and hydrochloric acid then gives complete yields. A new method of solvent purification has been used giving reproducible yields and rates. In such cases, monomer consumption at ?70° follows the rate law log [M]o/[M] = kt.  相似文献   

3.
The radiation-induced polymerization of acrylonitrile with dissolved PMMA exhibits kinetics similar to those found with the pure monomer. The addition of PMMA to the monomer at first leads to an increase in polymerization rate; a maximum in rate is observed for 60 per cent acrylonitrile in the mixture. The unreacted PMMA was quantitatively extracted by toluene from the reaction mixture. In contrast, polyacrylonitrile could not be separated from the graft copolymer by fractional precipitation, presumably due to association of the graft copolymer with the precipitated homopolymer. The free radical yield of PMMA “GR effective” derived from these results was found to be 8 to 10 in mixtures containing small amounts of monomer. It rapidly decreased as the monomer concentration increased.The solubilities of the graft copolymers were characterized by the precipitation γ determined for several precipitants in DMF solutions. A maximum in solubility was found for copolymers containing 25 to 35 per cent acrylonitrile in DMF-alcohol mixtures. The glass transition temperatures (Tg) of the graft copolymers were measured using a penetrometer. Tg increased with the MMA content in the copolymer. A small minimum of Tg appeared to exist for copolymers containing 90 per cent acrylonitrile.  相似文献   

4.
The polymerization of acrylic acid proceeds with an extremely high degree of auto-acceleration in certain ternary mixtures. The most drastic effects are observed when small amounts of methanol are added to a dilute solution of acrylic acid in n-hexane. In such systems the auto-acceleration index “β” may exceed 10. β Was found to exhibit a maximum over a fairly narrow range of concentrations. Moreover, the values of β are highest at temperatures between ?5 and + 10°, where a maximum of 16 is reached. The swelling of poly(acrylic acid) in the various reacting mixtures was measured and the molecular associations of the monomer with itself and with methanol were investigated. It was concluded that the “exaltation of the matrix effect” in some of the systems is caused by the complex [(Acrylic acid)2, McOH]. This complex associates very rapidly with the polymer formed in the early stages of the reaction to produce a structure in which ultrafast propagation occurs. The swelling of the polymer favours the accessibility of the monomer to the polymeric chains during polymerization, leading to auto-acceleration which progresses with conversion and gives rise to a reaction with explosive character.  相似文献   

5.
The copolymerization of acenaphthylene (ANA) with N-vinylcarbazole (NVC) was investigated at 60° in the melt with 1% AIBN and in benzene solution at 20° with gamma ray initiation. In the melt at 60°, the polymerization rate gradually decreases with the amount of NVC in the mixture. The following reactivity ratios were determined: rNVC = 0.12; rANA = 7.0. The copolymers have a fairly narrow distribution of compositions but contain small amounts of poly NVC. Gamma ray initiation at 20° gives rise to the free radical copolymer together with significant amounts of poly NVC which results from a cationic mechanism. In addition, acenaphthylene cyclodimerizes in the process.  相似文献   

6.
The initial stage in the radiation polymerization of the hydroxyethyl methacrylate water system at low temperatures was studied. The polymerization was accelerated by the presence of water; the effect increased with rising temperature above Tg. The polymerization rate had a maximum near ?50°. The initiating and propagating radicals were identified by studies with ESR. Irradiated hydroxyethyl methacrylate at low temperatures gave a 7-line spectrum, which was assigned to the initiating radical having equivalent protons. This spectrum was changed to a 9-line spectrum at ?120 to ?100°; it was assigned to the propagating radical. The temperature dependence of the ESR spectrum of irradiated hydroxyethyl methacrylate-water systems was studied to examine the effect of water on the propagating radical.  相似文献   

7.
Infra-red spectra of pure acrylic acid and solutions of monomer in toluene indicate that increasing the temperature from 20 to 60° displaces the equilibrium of H-bonded species from cyclic dimer to open oligomer. Viscosity measurements on the same solutions confirm this conclusion. In methanol solutions. alcohol-alcohol and alcohol-acid associations are found together with the acid-acid associations and the interpretation of the results is extremely difficult. Polymerization kinetics are directly influenced by the shift of association equilibria. In hexane, an increase in temperature results in a sudden increase in reaction rate as the linear oligomeric structures appear in the solution. In methanol increase in temperature reduces the kinetic anomalies observed at 20 and the polymerization no longer exhibits any stereospecificity. At the same time, a chain transfer process sets in. These various results confirm the earlier assumption of an assisted propagation step occurring in auto-associated aggregates of acrylic acid.  相似文献   

8.
A study of cyclopentadiene polymerization, initiated by φ3C+SbCl6? in methylene chloride solution, has been carried out at temperatures between ?70 and +20° using a dilatometric method. An overall external second order with respect to monomer has been found. At very low temperature (?70°), the concentration of active centres remains low and roughly constant, in agreement with a quasi-stationary state assumption. Between ?50 and + 10°, experimental determination of (kp. M*), obtained from variation of vp and [M] with time, shows that the concentration of centres goes through a maximum, sharper and more rapidly reached as the temperature is raised. Initiation is slower than propagation and active centres are rapidly destroyed when termination becomes faster than initiation. This explains the partial conversions and the observed maximum for concentration of active centres. Propagation and unimolecular termination rate constants have been determined at each temperature: activation energies are Ep = ?8 ± 0·5 kcal mole?1 and Ep = ?0·3 ± 0·1 kcal mole?1. These negative values can be explained by an exothermic process of solvation of active centres, leading to more reactive propagating species.  相似文献   

9.
The kinetics of the γ-ray induced polymerization of acrylic acid in bulk is investigated in a temperature interval of 20–50°C and a dose rate of 2.8–24.6 Gy/min. The reaction rate was observed to increase with increasing temperature and dose rate. The order of the reaction α, with respect to initiation i.e. dose rate, changed between 1.51 and 0.79 in the temperature interval studied. The kinetic analysis of the conversion curves was made according to equations developed by Magat for nonsteady state polymerizations taking place in precipitating media. kp/kt ratio thus determined for bulk polymerization of acrylic acid increased with increasing temperature and decreased with dose rate at a given temperature. This behavior as well as the change in the molecular weights of the poly(acrylic acid)s were explained to be as due to the termination of growing chain radicals occluded in the precipitated polymer by primary radicals.  相似文献   

10.
Acrylic acid (A Ac) and methacrylic acid (MA Ac) form a eutectic mixture for the equimolecular composition; its melting point is ?30°. Most polymerization experiments were carried out at ?37° with gamma-ray initiation. The irradiation of the eutectic mixture generates a random copolymer with a narrow distribution of compositions and containing 80% MA Ac. In solid mixtures which contain an excess of MA Ac with respect to the eutectic, the reaction product is essentially the same copolymer as generated in the eutectic, the rate of polymerization in MA Ac crystals being negligible as compared with the reaction in the eutectic. When A Ac is in excess, the phenomena are more complex. A pronounced minimum is observed in the rate vs composition curve at ca 20 mole % MA Ac. Fractionation of the reaction product demonstrates the presence of a block copolymer built by sequences of A Ac and of random copolymer. An interpretation is suggested to account for the various results.  相似文献   

11.
Poly(sulfone‐arylate) was synthesized in a reaction between dihydroxy polysulfone prepolymers and either diphenyl terephthalate or terephthaloyl chloride. The dihydroxy polysulfone prepolymers had molecular weights of 2000 and 4000 g/mol. The polymerization with diphenyl terephthalate was carried out at high temperature (280 °C) in the presence of a catalyst, whereas the polymerization with terephthalic chloride was conducted in solution at low temperature in the presence of an acid acceptor. High‐molecular weight copolymers (ηinh ~ 0.60 dL/g) could be obtained through both methods. The copolymers were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, DMA, and differential scanning calorimetry measurements and were found to exhibit high Tg values. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3904–3913, 2009  相似文献   

12.
In a previous paper we have shown that at 740°C and under an oxygen pressure less than 1,3 torr the electrical conductance G of a NiO powder reaches rapidly an apparently stabilized signal Gi which sharply decreases after a sufficiently long time to a G0 value independent of PO2.From this observation we have studied the influence of the temperature successively on the electrical conductance Gi and G0. The Arrhenius law is only verified for the G0 = f(T) curve. G0 appears as the representative value of the gas-solid equilibrium.  相似文献   

13.
The kinetics of the radiation initiated polymerization of acrylonitrile at 20° have been investigated in the presence of a highly divided polyacrylonitrile obtained by polymerizing the crystalline monomer. This polymer catalyses the reaction to a much larger extent than polymer formed at 20°. The analogy between the kinetic features of the polymerizations of acrylic acid and acrylonitrile in bulk leads to extending to this last monomer the assumption of a “matrix effect” in its polymerization. This effect is believed to result from the dipole interaction of the nitrile groups which lead to the formation of a complex in which the double bonds are favourably oriented for the propagation. If the matrix-polymer is produced with a pre-irradiation dose at low temperature exceeding a critical value, inhibition occurs perhaps resulting from the addition of growing chains to the CN double bonds present in the matrix-polymer.  相似文献   

14.
This research was focused on the design and execution of new synthetic routes to low‐temperature‐curable poly(silarylene–siloxane)polyimides. The synthesis of individual oligoimide and silarylene–siloxane blocks was followed by hydrosilylation polymerization to produce crosslinked copolymers. The silarylene–siloxane and polyimide blocks were structurally characterized by IR and 1H NMR spectroscopy and size exclusion chromatography. The high‐temperature resistance of the copolymers was evaluated through the measurement of heat distortion temperatures (THD's) via thermomechanical analysis and by the determination of the weight loss at elevated temperatures via thermogravimetric analysis. Glass‐transition temperatures (Tg's) of the silarylene–siloxane segments were measured by differential scanning calorimetry. Hydrosilylation curing was conducted at 60 °C in the presence of chloroplatinic acid (H2PtCl6). The copolymers displayed both high‐temperature resistance and low‐temperature flexibility. We observed Tg of the silarylene–siloxane segment as low as ?77 °C and THD of the polyimide segment as high as 323 °C. The influence of various oligoimide molecular weights on the properties of copolymers containing the same silarylene–siloxane was examined. The effect of various silarylene–siloxane molecular weights on the properties of copolymers containing the same oligoimide was also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4922–4932, 2005  相似文献   

15.
Block, random, and gradient copolymers of styrene (S) and acrylic acid (AA) are synthesized by conventional or controlled radical polymerization, and their glass transition temperature (Tg) behaviors are compared. The location and breadth of the Tgs are determined using derivatives of differential scanning calorimetry heating curves. Each S/AA random copolymer exhibits one narrow Tg, consistent with a single phase of limited compositional nanoheterogeneity. Block copolymers exhibit two narrow Tgs originating from nanophase separation into ordered domains with nearly pure S or nearly pure AA repeat units. Each gradient copolymer exhibits a Tg response with a ~50–56 °C breadth that extends beyond the upper Tg of the block copolymers. For copolymers of similar composition, the maximum value in the gradient copolymer Tg response is consistent with that of a random copolymer, which has an enhanced Tg relative to poly(acrylic acid) due to more effective hydrogen bonding when AA units are separated along the chain backbone by S units. These results indicate that gradient copolymers with ordered nanostructures can be rationally designed, which exhibit broad glass transitions that extend to higher temperature than the Tgs observed with block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2842–2849, 2007  相似文献   

16.
tButyl-lithium in the presence of TMEDA progressively adds ethylene molecules to produce a linear alkyl-lithium compound. This oligomerization has been studied at low pressures (0–1 atm) and temperature (0°). The rate of consumption of ethylene depends on the pressure, tBuLi concentration, and TMEDA concentration. By varying the molar ratio r, (TMEDA/|tBuLi|0), from 0–1 to 4·3, the rate of consumption increased up to r = 1, where it becomes independent of r. A mechanism for the addition reaction is proposed.  相似文献   

17.
Blends of poly(acrylic acid) (PAA) and poly(p‐vinylphenol) (PVPh) were prepared from N,N‐dimethylformamide (DMF) and ethanol solutions. The DMF‐cast blends exhibited single Tg's, as shown by modulated differential scanning calorimetry, whereas the ethanol‐cast blends had double Tg's. Fourier transform infrared spectroscopy showed that there was a specific interaction between PAA and PVPh in the DMF‐cast blends. The single‐Tg blends cast from DMF showed single‐exponential decay behavior for the proton spin–lattice relaxation in both the laboratory frame and the rotating frame, indicating that the two polymers mixed intimately on a scale of 2–3 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 789–796, 2003  相似文献   

18.
A polyurea macromer (PUM) was synthesized and dispersed in basic conditions to form self‐assembled nanoparticles (<20 nm dispersions, up to 30 wt % aq. soln.). These nanoparticles enabled surfactant‐free emulsion polymerization to form hybrid polyurea‐acrylic particles despite the absence of a measureable water‐soluble fraction. The Tg of the starting PUM material was a strong function of the PUM's extent of neutralization and hydration (varying between 100 °C and >175 °C) due to changes in hydrogen and ionic bonding. Two separate hybrid polyurea‐acrylic emulsion systems were prepared: one by direct polymerization of (meth)acrylic monomers in the presence of the nanodispersion and a second by a physical blend of PUM nanodispersion with an acrylic latex control. The direct polymerization method resulted in a hybrid emulsion particle size that developed by a mechanism resembling conventional emulsion polymerization and was unlike that described for seeded polyurethane dispersion systems. Film hardness was shown to increase with increasing coating thickness for the hybrid film prepared by direct polymerization. The resulting mechanical properties could be explained by applying mechanical models for a composite foam structure. These results were unprecedented for normal elastomer films. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1373–1388  相似文献   

19.
《中国化学快报》2020,31(5):1197-1200
Partially biobased polysilylethers (PSEs) are synthesized via dehydrocoupling polymerization catalyzed by an anionic iridium complex. Different types (AB type or AA and BB type) of monomers are suitable. Levulinic acid (LA) and succinic acid (SA) have been ranked within the top 10 chemicals derived from biomass. BB type monomers (diols) derived from LA and SA have been applied to the synthesis of PSEs. The polymerization reactions employ an air-stable anionic iridium complex bearing a functional bipyridonate ligand as catalyst. Moderate to high yields of polymers with number-average molecular weights (Mn) up to 4.38 × 104 were obtained. A possible catalytic cycle via an Ir-H species is presented. Based on the results of kinetic experiments, apparent activation energy of polymerization in the temperature range of 0–10 °C is about 38.6 kJ/mol. The PSEs synthesized from AA and BB type monomers possess good thermal stability (T5 = 418 °C to 437 °C) and low glass-transition temperature (Tg = −49.6 °C).  相似文献   

20.
Benzoxazine monomer (Ba) was blended with soluble poly(imide‐siloxane)s in various weight ratios. The soluble poly(imide‐siloxane)s with and without pendent phenolic groups were prepared from the reaction of 2,2′‐bis(3,4‐dicarboxylphenyl)hexafluoropropane dianhydride with α,ω‐bis(aminopropyl)dimethylsiloxane oligomer (PDMS; molecular weight = 5000) and 3,3′‐dihydroxybenzidine (with OH group) or 4,4′‐diaminodiphenyl ether (without OH group). The onset and maximum of the exotherm due to the ring‐opening polymerization for the pristine Ba appeared on differential scanning calorimetry curves around 200 and 240 °C, respectively. In the presence of poly(imide‐siloxane)s, the exothermic temperatures were lowered: the onset to 130–140 °C and the maximum to 210–220 °C. The exotherm due to the benzoxazine polymerization disappeared after curing at 240 °C for 1 h. Viscoelastic measurements of the cured blends containing poly(imide‐siloxane) with OH functionality showed two glass‐transition temperatures (Tg's), at a low temperature around ?55 °C and at a high temperature around 250–300 °C, displaying phase separation between PDMS and the combined phase consisting of polyimide and polybenzoxazine (PBa) components due to the formation of AB‐crosslinked polymer. For the blends containing poly(imide‐siloxane) without OH functionalities, however, in addition to the Tg due to PDMS, two Tg's were observed in high‐temperature ranges, 230–260 and 300–350 °C, indicating further phase separation between the polyimide and PBa components due to the formation of semi‐interpenetrating networks. In both cases, Tg increased with increasing poly(imide‐siloxane) content. Tensile measurements showed that the toughness of PBa was enhanced by the addition of poly(imide‐siloxane). Thermogravimetric analysis showed that the thermal stability of PBa also was enhanced by the addition of poly(imide‐siloxane). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2633–2641, 2001  相似文献   

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