摘要:

AbstractThe kinetics of anionic polymerization of α‐methylstyrene with Na+as counterion have been studied in mixed solvents of tetrahydrofuran (THF) and toluene in various compositions at −25 to 5°C. The ion‐pair rate constantk(±) increases by about a factor of 50 at −10°C, whereas the activation energy decreases from 5.1 to −2.2 kcal/mole, when THF in the mixed solvent increases from 30 to 100 vol‐%. The plot of logk(±) against (D− 1)/(2D+ 1) is a curve, whereDis the dielectric constant of the medium. This deviation from linearity is explained in terms of propagation by two

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140601

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractHigh resolution 94‐MHz19F‐ and 100‐MHz1H‐NMR spectra were measured on a series of tetrafluoroethylene (TFE)‐propylene (P) copolymers having a range of composition (TFE/P molar ratio = 37/63–55/45) and polymerized at different temperatures (−23, 25 and 65°C). The spectra were analyzed in relation to copolymer compositions. The assignment of19F resonance in terms of tetrads proposed previously was confirmed, and the tentative assignment of1H resonances was proposed in terms of triads. The spectra thus interpreted revealed the sequence distribution of the copolymers. Copolymer compositions calculated from NMR spectra and elemental analysis agreed rather well with each other. Monomer reactivity ratios were calculated from the sequence distributions and compared with those obtained from the elemental analysis. It was observed that highly alternating copolymers are obtained in this system over a wide range of monomer composition at lower temperatures and that a deviation from alternancy increases slightly with rising polymerizati

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140602

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractESR spectra of methyl methacrylate (MMA) adsorbed on solid surfaces such as silica, alumina, and CPG‐10 show a seven‐line absorption due to monomer radicals when γ‐irradiated at −196°C. These spectra turn into conventional nine‐line spectra by annealing at −86°C as a result of polymerization. The intensity ratio of the four‐line component to the five‐line component changes with further polymerization. The ratio depends on the kind of solid and the smallest value is obtained in the spectra of alumina‐MMA. The temperature of irradiation strongly affects the value in alumina‐MMA. These results suggest that MMA is strongly adsorbed and deformed the conformat

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140603

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractA kinetic study has been made of polymerization of methyl methacrylate initiated by an electron donor–acceptor complex of liquid SO2(electron acceptor) and nicotine (donor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free‐radical intermediates similar to the cases of liquid SO2–pyridine and liquid SO2–poly(2‐vinylpyridine) complexes. The overall rate of polymerization is proportional to the square root of both liquid SO2and nicotine concentrations, and the values ofkp/kt½under various polymerization conditions are in satisfactory agreement with the literature values. For the activation energy of initiation, 13.6 kcal/mole is estimated from thekp/kt½values obtained at temperatures ranging fro

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140604

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractBase‐catalyzed hydrogen‐transfer polymerization and copolymerization of acrylamide and its methyl‐substituted derivatives were studied in pyridine at 110°C.n‐Butyllithium was used as an initiator. The observed rates of these homopolymerizations were found to decrease in the following order: acrylamide>crotonamide>methacrylamide>N‐methylacrylamide>N‐methylcrotonamide>tiglinamide>N‐methylmethacrylamide ≫ α‐chlorocrotonamide ≃ α‐cyanocrotonamide = 0. Acrylamide gave the polymer with the highest degree of polymerization among the monomers examined. It was found that the number and the position of the methyl substituent in acrylamide affected significantly both the rate of polymerization and the molecular weight of the polymer. Although all polymers obtained, except theN‐methyl derivatives, contained both methanol‐soluble and methanol‐insoluble fractions, a polyamide structure with unsaturated terminal monomer unit was confirmed by both infrared and NMR determinations. From the NMR determination of the saturated and terminal unsaturated units, the degree of polymerization of the resulting polyamides were also obtained. The monomers were also found to copolymerize by a hydrogen‐transfer mechanism. However, the main chain of the resulting copolymers was composed of the more reactive monomer unit, and the less reactive monomer was incorporated only as a terminal unit when a less reactive monomer was copolymerized with a more reactive one. From these results, it was concluded that these polymerizations proceeded via an intermolecular hydrogen‐transfer me

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140605

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractAqueous acrylic acid in the presence of cupric chloride has been subjected to γ‐irradiation under various reaction conditions and the molecular weights of the resultant poly(acrylic acid) measured. The results, taken in conjunction with previous findings on the dependence of the rate of polymerization on intensity, monomer concentration, and cupric chloride concentration, indicate chain termination solely by cupric ion (rate constantktCu) and chain transfer to polymer (rate constantkf). Values have been obtained forktCu/kp,kf/kpandG(radical) of acrylic acid. On the basis of these data a theoretical chain‐length distribution has been derived which agrees well with distribution measured by gel‐permeation chromato

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140606

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractA series of phosphonitrilic fluoroelastomers which have excellent solvent resistance and low temperature flexibility, and which perform well under a broad range of service conditions, have been developed. The solution properties of one of these polymers were studied more extensively in order to develop suitable quality control procedures and to gain a better understanding of the polymer structure. Solvents for these procedures were established, fractionation procedures were developed, and intrinsic viscosity, osmotic pressure, and light‐scattering measurements were conducted. We found this polymer to have a very broad molecular weight distribution. And, although fractionation by molecular weight was effected, the fractions retained a broad molecular weight distribution. Our data do not indicate significant branching for this polymer. As a result of our studies, we have theorized that a supermolecular structure may be present in this polyme

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140607

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe polymerization of methyl methacrylate with the VOCL3–ALEt2Br catalyst system inn‐hexane has been studied. The first‐order dependence of rate of polymerization on catalyst and monomer concentrations, activation energy of 6.67 kcal/mole, and NMR spectra of polymer lend support to a coordinate anionic mechanism of polymerization. It has been shown that the vanadium in V+2oxidation state is less active than V+3oxidation state of active co

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140608

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe amide‐exchange reactions which cause copolymer formation in polyamide melt blends were studied with mixtures ofN‐ethylcaproamide andN‐hexylacetamide containing small concentrations of caproic acid and hexylamine as a model system for melt blends of aliphatic polyamides. Amide exchange was found to involve acidolysis and aminolysis reactions with no detectable contribution of direct reaction between amide groups. Kinetics data are consistent with formation of an anhydride intermediate in amide acidolysis. Rate constants over the range 200–275°C and activation energies for amide acidolysis and aminolysis reactions are given. Equations are given for calculating amide exchange rates in polyamide melt blends and for relating degree of amide exchange to block copolymer com

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140609

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractOn substitution of hydrogen by deuterium the radiation yield of free radicals in polyolefins decreases ca. 2‐fold. Under ultraviolet illumination (γ<300 nm) in deuterated polyethylene (DPE), allyl radicals are converted into alkyl radicals (hfs constantsa Dα= 3.2 Oe,a Dβ= 4.4 Oe); in deuterated polypropylene (DPP), allyl and peroxide radicals are converted into alkyl radicals (a Dβ= 3.7 Oe). At 77°K under ultraviolet light in γ‐irradiated polyethylene (PE) and DPE, triene, tetraene, dienyl, trienyl, and tetraenyl radicals are formed. Deuterium substitution has no effect on absorption spectra of polyenyl radicals and polyenes. In polyolefins the quantum yields of photochemical reactions of allyl and peroxide radicals are 0.1–1.0. Photochemical reactions of peroxide radicals result in a radical concentration increase of ca. 3‐fold. In reactions of peroxide radicals in the dark, a kinetic isotope effect has been observed. Activation energies of substitution reactions of peroxide radicals are in PE, 9.3 ± 0.3 kcal/mole; in DPE, 10.2 ± 0.3 kcal/mole; in PP, 12.7 ± 0.4 kcal/mole; in DPP, 14 ± 0.5 kcal/mole. Possible mechanisms of the effect of polyolefin isotope composition on radical formation by high energy irradiation as well as on photochemical and dark reactions of free radicals are discussed. The effect of the energy released from phototransformations and radiationless deactivation of macroradicals on the migration of free val

ISSN:0360-6376    

DOI:10.1002/pol.1976.170140610

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY