摘要:

AbstractThe activation energy (Ea) for the dehydrochlorination of PVC and PVC stabilized with an epoxide was determined by a method involving dynamic pH measurements. TheEaincrease was 5 kcal/mole between unformulated PVC (Ea= 22.6 kcal/mole) and any of the other formulations (Ea= 27.7–28.6 kcal/mole). On the basis of this and data contained in the literature, research alternatives for the stabilization mechanism are proposed using model compound

ISSN:0021-8995    

DOI:10.1002/app.1979.070240801

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractEvolution rate measurements were conducted to determine the solubility and the diffusion constants of ethylene in three semicrystalline polymers: low‐density polyethylene (LDPE), ethylene‐ethyl acrylate (EEA), and ethylene–vinyl acetate (EVA) copolymers. The apparatus for such measurements utilizes a flame ionization detector interfaced to a computer for continuous monitoring of the ethylene evolution from the polymer pellets. Solubilities are obtained by calculating the total ethylene evolved over a 12–48‐hr period. Analysis of the evolution rate data in terms of the nonsteady‐state diffusion equation for spheres yields the diffusivity. The ethylene solubility and diffusion constants in EVA and EEA are very similar to those in LDPE. This is due to compensating effects of decreased crystallinity and increased cohesive energy density with the incorporation of bulky polar groups into the po

ISSN:0021-8995    

DOI:10.1002/app.1979.070240802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of three commercial samples of carboxy‐terminated polybutadiene (PBCT) resins was studied by thermogravimetric analysis (TGA) at heating rates varying from 2° to 100°C/min. Kinetic parameters of the decomposition process at different heating rates were evaluated by means of the Fuoss method.1The decomposition process and the activation energy values are found to be dependent on heating rate. Mass‐spectrometric analysis of the decomposition products shows that the pyrolysis products of PBCT resins are mainly low molecular weight hydrocarbons: ethylene, acetylene, butadiene, propadiene, vinylcyclohexene, etc. The rates of evolution of these hydrocarbon products vary with the carboxy content of the PBCT resin. Based on this, a carbonium ion mechanism has been suggested for the thermal decomposition. The data generated from this work are of importance for a consideration of the mechanism of combustion of composite solid propellants based on PBCT bi

ISSN:0021-8995    

DOI:10.1002/app.1979.070240803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractTriplet–triplet energy transfer has been shown to occur from poly(ethylene terephthalate) (PET) units to the 2,6‐naphthalenedicarboxylate (2,6‐ND) monomer units in a series of poly(ethylene terephthalate–co–2,6‐naphthalenedicarboxylate) (PET–2,6‐ND) copolymers, as filament yarns, by an exchange mechanism at 77°K. The radius of the “quenching sphere” has been calculated to be 19.7 Å, indicating the presence of triplet energy migration. Photostabilization was observed in the copolymer yarns with the concentration of the monomer dimethyl 2,6‐naphthalenedicarboxylate (2,6‐DMN) at or above 2 mol %; the rate of phototendering in an air atmosphere was shown to decrease from 2.0 × 10−19% breaking strength loss/quantum absorbed/cm2in the homopolymer PET to 0.7 × 10−19% breaking strength loss/quantum absorbed/cm2in the copolymer yarns. The photophysical processes in the monomers, dimethyl terephthalate and 2,6‐DMN, were examined by absorption and luminescence studies. The lowest excited singlet and triplet in both monomers were identified to be the1(π, π*) and3(π, π*) states, respectively. The phosphorescence of PET was shown to originate from a3(π, π*) state, while the complex fluorescence spectrum may arise from some oriented aggregates in the polymer matrix. In copolymer yarns, only the fluorescence emission from the 2,6‐ND monomer units at 380 nm was observed. The phosphorescence spectra of the copolymer yarns showed phosphorescence emissions from the PET and 2,6‐ND monomer units; in addition, delayed fluorescenc

ISSN:0021-8995    

DOI:10.1002/app.1979.070240804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractRadiation‐induced polymerization of ethylene using aqueoustert‐butyl alcohol as medium was carried out in a large‐scale pilot plant with a 50‐liter central source‐type reactor at a pressure of 105 to 395 kg/cm2, temperature of 30° to 80°C, mean dose rate of 4.5 × 104to 1.9 × 105rads/hr, ethylene feed rate of 5.5 to 23.5 kg/hr, and medium feed rate of 21 to 102 l./hr. The space–time yield and molecular weight of the polymer were in the range of 4.7 to 16.8 g/l.‐hr and 1.3 × 104to 8.9 × 104, respectively. The space–time yield and molecular weight increased with mean residence time at 30°C, whereas at 80°C they became almost independent of the time. The space–time yield increased with pressure and dose rate, slightly decreased with temperature, and was maximum at ethylene molar fraction of 0.5. The polymer molecular weight increased with pressure and ethylene molar fraction, and decreased with dose rate and temperature. The total amount of deposited polymer on the reactor wall, source case wall, and scraping blades was usually less than 1 kg, which was negligibly small for the analysis of polymerization. Continuous discharge of the polymer slurry and production of fine‐powder polyethylene were successfully carried out. In the central source‐type reactor, a dose rate of 1.9 × 105rads/hr was obtained w

ISSN:0021-8995    

DOI:10.1002/app.1979.070240805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThe refractive index increments of linear and branched polyethylene were determined for several solvents and various wavelengths (403, 436, 546, and 633 nm), mainly at 135°C. Differences were observed between values for linear and branched samples. Data obtained in this investigation are compared with the reported ones

ISSN:0021-8995    

DOI:10.1002/app.1979.070240806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractA preliminary analysis of deconvolution of a nylon model is given. This is then developed to give the available deconvolution strain in cotton. The total extension is then given by adding the fibrillar strain and is compared with experimental values of breaking extension. The relation between convolution extension and stress is calculated in terms of structural and mechanical parameters. An earlier analysis derived cotton fiber modulus in terms of fibril extension and volume change. A new analysis shows that the introduction of shear resistance does not have a significant effect when rotation is prevented. However, false untwisting can occur at the helix reversal in cotton fibers. An analysis which allows for this rotation shows a strong dependence on shear modulus as well as fibril extension and helix angle. There is no volume change.

ISSN:0021-8995    

DOI:10.1002/app.1979.070240807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractPoly(vinyl chloride) films blended with plasticizers, stabilizers, and fillers are irradiated with a beam of H2plasma. The polymer partially loses its solubility in cyclohexanone. The viscosity of the soluble part decreases in the initial stages and then increases on further irradiation. Crosslinking was followed by dehydrochlorination and discoloration of the polymer. The electrical conductivity was measured as a function of the irradiation dose and time. The plasticizers enhanced the action of plasma while the stabilizers and fillers reduced it.

ISSN:0021-8995    

DOI:10.1002/app.1979.070240808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractSolubility and diffusivity have been determined for bis‐(2‐chloroethyl)sulfide in isotactic polypropylene at temperatures from 15 to 40°C and relative pressures from 0.34 to 1.00. While the solubility in films annealed above 90°C followed the normal variation with the amorphous content, the quenched film had a significantly lower amorphous volume fraction than determined from its density, 46 instead of 60%. The diffusion behavior in the film was found to be invariably Fickian and not dependent on the amorphous volume fraction of the polymer between 0.34 and 0.46. The solubility was found to be independent of the temperature over the range 15–40°C, but dependent on the diffusant concentration. The isotherms were well represented by the Flory‐Huggins relation for crosslinked polymers, and values for the interaction constant and the average molecular weight between crystallites have been obtained. The value of the interaction constant, μ = 1.13, is an expression of the low affinity bis‐(2‐chloroethyl)sulfide has for polypropylene. The intrinsic diffusivity was only weakly dependent on the diffusant concentration. The results were found to be in agreement with Fujita's free‐volume theory. The apparent activation energy for the diffusion of bis(2‐chloroethyl)sulfide in isotactic polypropylene was found

ISSN:0021-8995    

DOI:10.1002/app.1979.070240809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY

摘要:

AbstractThis article reports molecular weights and mechanical and processing properties of a series of styrene/alpha‐methylstyrene copolymers produced by emulsion polymerization at various temperatures. Molecular weights were measured by solution viscosity, membrane osmometry, light scattering, and gel‐permeation chromatography. Molecular weight development is controlled by chain transfer to monomer, but the molecular weight distributions are broader than would be expected for such reactions. This is attributed to polymer branching resulting from chain‐transfer events. Molecular weight distributions of copolymers were multimodal. Thermal stability of the copolymers is somewhat lower than that of polystyrene, but addition of conventional antioxidants produces compositions with good stability in thermoplastic processing operations. Copolymers containing 25 wt. % of alpha‐methylstyrene have usage temperatures about 12°C higher than that of pol

ISSN:0021-8995    

DOI:10.1002/app.1979.070240810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1979

数据来源: WILEY