摘要:

Loss of capacity of magnetic micro ion-exchange resins has been suggested to be caused by cleavage of unstable linkages formed during the graft polymerization reaction. The nature of the grafting process was investigated by using a series of model compounds having the same structural features as the glutaraldehyde-crosslinked poly(vinyl alcohol) core matrix. These compounds were then subjected to hydrogen peroxide oxidation, followed by the addition of monomer in the presence of iron(II). The identity and extent of peroxidation of the intermediate compounds was determined. In each of the peroxidation reactions the tertiary acetal hydrogen was oxidized to a hydroperoxy derivative. Some of these derivatives were able to dimerize to form peroxy compounds. The reactions occurred rapidly at room temperature when an acetal compound was shaken with hydrogen peroxide. Good yields could be obtained by precipitation of the sodium salts of the hydroperoxides. The hydroperoxy derivatives were shown to initiate polymerization of methyl acrylate, acrylic acid, and acrylamide when in the presence of iron(II).

ISSN:0022-233X    

DOI:10.1080/00222338008066627

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

There are many practical situations, particularly in the food and pharmaceutical industries, in which it is desirable to adsorb low molecular weight, unwanted, constituents from a turbid process stream without reducing the concentration of larger product molecules. The preparation of magnetic adsorbents, as described in this paper, has provided materials capable of such adsorption.

ISSN:0022-233X    

DOI:10.1080/00222338008066628

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The chemiluminescence from stabilized nylon 66 fibers during oxidation above Tghas been studied to determine the activation energies of the initiation, propagation and termination reactions. When oxygen is admitted to a nylon 66 sample heated in an inert atmosphere, a pulse of chemiluminescence is observed corresponding to a nonstationary alkyl peroxy radical concentration in the polymer. The analysis of the decay to the steady state can provide kinetic data for peroxy radical reactions in the induction period of the oxidation and the effect of stabilizers on these reactions.

ISSN:0022-233X    

DOI:10.1080/00222338008066629

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

In this paper a preliminary report is presented on studies of the reaction of several commercially important hydroxyphenyl-benzotriazole light stabilizers during AIBN initiated oxidation of cumene in chlorobenzene at 65°C. Each of the compounds studied reacted readily, the rate of reaction depending on the substitution pattern of the phenolic ring. In the case of 5-chloro-2-(3′-tert-butyl-2′-hydroxy-5′-methyl)phenylbenzotriazole, the major product was characterized as the corresponding cumyl-peroxycyclohexa-2,5-dienone. Thermal decomposition of tert-butylperoxycyclohexa-2,5-dienones derived from 2,6-di-tert-butyl-4-methylphenol, 2,4,6-tri-tert-butylphenol, and several hydroxyphenylbenzotriazole light stabilizers is reported. Decomposition by both O-O and C-O bond scission is observed, the CO bond scission mechanism being the major pathway for thermal decomposition of the benzotriazolyl substituted tert-butylperoxycyclohexa-2,5-dienones.

ISSN:0022-233X    

DOI:10.1080/00222338008066630

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.

ISSN:0022-233X    

DOI:10.1080/00222338008066631

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Consideration of crystallization kinetics in high molecular weight polymers shows that adjacent re-entry is unlikely in melt crystallization and that sections of individual chains will crystallize concurrently at several sites. Surface nucleation controlled growth models can be set up which do not require adjacent re-entry but are in agreement with observations on growth rates and crystal thicknesses. The predominant process in crystallization with random re-entry is the incorporation into the crystal of a loop of chain which has both ends attached to the crystal surface. This leads to predictions of the crystallinity of quenched, spherulitic polymers. Radii of gyration of chains in the crystalline state can be calculated and are in agreement with neutron scattering results.

ISSN:0022-233X    

DOI:10.1080/00222338008066632

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Different types of unplasticized cast polyurethanes with hardness around 60 Shore A have been compared. The tensile properties, tear strength, resistance to hydrolysis, and swelling in solvents and water were examined. The influence of composition on the properties of cast polyurethanes prepared from a polyadipate polyol and diisocyanates, including the effect of a range of fillers, was investigated in detail. Fumed silica, fumed alumina, and carbon black significantly increased the hardness and tensile strength of the rubber, whereas kaolin and talc gave small increases. Ground silica, calcite, and rutile had no effect. No significant increases in tensile strength were obtained with silane and titanate coupling agents with a fumed silica filler. The rate of hydrolysis or extent of swelling in xylene was unchanged by fillers.

ISSN:0022-233X    

DOI:10.1080/00222338008066633

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Many reactive polymers used to shrink-resist wool fabric are derived from poly(propylene oxide) (PPO). Shrink-resist polymers derived from PPO were identified on wool by their oxidation characteristics using differential scanning calorimetry. The amount of PPO-based polymers on the fabric was estimated using isothermal scans after calibration with suitable standards. Polyacrylates applied with the PPO did not interfere with the oxidation of the PPO component, but a polyester-polyurethane dispersion suppressed PPO oxidation and made identification and estimation of the PPO component unreliable. The technique was used to determine the distribution of shrink-resist polymer on men's trousers.

ISSN:0022-233X    

DOI:10.1080/00222338008066634

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Many polymeric substrates which swell on adsorption exhibit sorption hysteresis; the phenomenon is most striking for water sorption by natural polymers and proteins. Some interpretations of hysteresis for swelling systems have invoked the concept that there are more active sites available for association with sorbate during desorption than for adsorption to the same relative pressure. Chemical modification of hydrophilic groups, which markedly alters the amount of water sorbed by keratin, or the filling of possible voids in the substrate has little effect on keratin-water vapor sorption hysteresis. Sorption in swelling systems occurs by a coupled diffusion-relaxation mechanism. It is demonstrated that the occurrence of hysteresis is associated with the stress relaxation of the cohesive forces opposing swelling. Changes in the structural conformation may be considered as the variable which differs between the adsorption and desorption states. The segmentai mobility of the macromolecular chains plays a major role in the irreversibility of the sorption isotherm, leading to wide diversity in hysteresis effects in polymers.

ISSN:0022-233X    

DOI:10.1080/00222338008066635

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Two methods for developing GPC calibration parameters for any polymer are described and compared. The first method assumes a quadratic calibration curve of the form log M = C1+ C2V + C3V2, where V is the retention volume, and utilizes molecular weight averages of a polymer standard combined with nonlinear regression analysis to determine values of the constants C1, C2, and C3. No reference to a standard polystyrene curve is necessary. The second method assumes the validity of the universal calibration technique in which the calibration curve of any polymer can be determined with reference to a standard polystyrene curve provided representative Mark-Houwink parameters are available. The chromatographic data is used to determine these parameters for any polymer. Results of applying both procedures to polystyrene, polybutadiene, poly(methyl methacrylate), and poly(vinyl chloride) are presented and show that in most instances the second method is simpler to apply and more accurate.

ISSN:0022-233X    

DOI:10.1080/00222338008066636

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor