摘要:

AbstractThe various structures encountered in block and graft polymers are reviewed and a nomenclature useful for the description of these macromolecules is proposed. The concept of living polymers is elucidated and its ramifications discussed. It is shown how greatly the control of polymerization and the uniformity of the products is improved when living polymers are used as the reagents. Their application in the synthesis of block and graft polymers is illustrated by numerous examples. Other synthetic techniques yielding block and graft polymers are briefly sketched, their advantages and shortcomings being considered. Properties of block and graft polymers are described, special attention being devoted to the problems of mesomorphic phases and to the morphology of block polymers. The incompatibility phenomena observed in block and graft polymer systems are compared with those encountered in studies of the polymeric blends.Finally, the present and future applications of block and graft polymers are considered and their potential evaluated.

ISSN:0032-3888    

DOI:10.1002/pen.760130102

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe processing of polymers typically includes steps involving heat transfer, such as quenching and crystallization. The mechanical properties of a polymer are thus affected by processing conditions, such as the amount of time spent by each portion of the polymer at each temperature in the processing sequence.This paper presents the results of a mathematical modeling study of the unsteady‐state temperatures inside a crystallizing polymer during quenching. This model differs from usual methods in including temperature dependence of induction times and kinetic processes, and in not treating the polymer as a simple, small molecule system. The model permits the prediction of the final morphological distribution within the polymer. Use of the model will aid in tailoring processing conditions to produce a product with specified morphology. The method is applicable to a wide variety of problems in polymer processing, particularly for those polymers which exhibit crystallizatio

ISSN:0032-3888    

DOI:10.1002/pen.760130103

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe applicability of fracture mechanics to the description of initial notch extension under tension in quasi‐isotropic fiberglass laminates is tested experimentally. It is found that classical elastic fracture mechanics, without modifications of couple stress effects, as represented in the theory of Muki and Sternberg, is sufficient to describe initial notch extension in prenotched specimens which are sufficiently thick to avoid transplanar bucklings of the specimen under tension. The fracture toughness (KIC) is found to be 15 ksi √in. However, it is noted that in these specimens (0.035 in. thick) transplanar postbuckling deformation becomes pronounced well before fracture, and that different modes of buckling seen in externally notched and internally notched specimens have opposite effects on the apparent fracture toughness of the specimen. It is pointed out that the effect of transplanar buckling on fracture of fiber glass, with its high compliance and high strength, is a potential source of serious problems in design with this mater

ISSN:0032-3888    

DOI:10.1002/pen.760130104

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractWhen tested in tension, a cross‐linked epoxy resin can be made to exhibit shear yielding. A modified von Mises criterion, τ = τ0− μPdescribes the yielding behavior of the same resin under a biaxial stress system, indicating that the flow of the material is pressure sensitive.Butadien‐acrylonitrile elastomer particles suspended in the cross‐linked epoxy matrix induce large local deformations when the composite material is stressed. Particles a few hundred Angstroms in diameter cause the glassy matrix to exhibit shear banding, and the macroscopic failure envelope of such a system follows a modified von Mises criterion similar to that of the matrix resin. It was found that the coefficient of internal friction, τ, and the activation energy for yielding are approximately the same for the two cases. With larger particles (5‐15,000 Å diam) the failure mode changes as shown by the macroscopic yield envelope and the associated activation energy. Electron micrographs of the fracture surfaces show microcavitation, similar to crazing around each particle; the deformed glassy polymer around each particle retracts upon heating the matrix above itsTg. The fracture surface work value of the unmodified matrix is 1.75 × 105ergs/cm2. With 10 pph small particles, the value increases to 3.32 × 105and with 10 pph of large particles, to 15.

ISSN:0032-3888    

DOI:10.1002/pen.760130105

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractPlasticized polyvinyl chloride was thermally stabilized by barium, cadmium, and zinc laurates, epoxidized soybean oil, and monoalkyl diaryl phosphite, and by combinations of these stabilizers. Of 26 possible combinations, 18 showed some improvement, 8 showed useful improvement, 7 showed marked improvement, and 3 systems were outstanding. Of the 26 combinations, 10 showed distinct synergism, based mainly upon combinations of Group II‐B metals with Group II‐A metals, “secondary” stabilizers, or both. Combinations of Group II‐B metals with “secondary” stabilizers were particularly interesting

ISSN:0032-3888    

DOI:10.1002/pen.760130106

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractFracture surfaces of Epon 901/B‐3 bonded aluminum alloy joints in the lap‐shear configuration were studied using scanning electron microscopy. Major differences in the appearance of the fracture surface from those reported (8) for tensile loaded joints at 23°C are produced either by cyclic loading at 23°C or a change in test temperature to −196°C. Fracture in tensile loaded joints at −196°C is a brittle single step process in the opening mode in which rapid crack extension occurs throughout the joint with very little adhesive flow. Tensile fatigue fracture at 23°C is in the opening mode but crack extension is complicated by extensive adhesive flow throughout the

ISSN:0032-3888    

DOI:10.1002/pen.760130107

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractPoly(vinyl chlorides) having different melt viscosities were melt blended with several different incompatible polymers using a two‐roll mill and a Brabender Plasticorder. The properties of the mixtures can be easily reproduced from batch to batch only if the viscosity of the components does not change during the mixing process. Within this limitation, the order of addition of the components during the mixture preparation does not have a significant influence on the mixture properties.The shear storage modulus of the incompatible mixtures in the temperature range between theTg's of the components varies with the difference in component viscosities at the temperature of mixing. The moduli of these mixtures are compared to moduli calculated using Kerner's equations. Based on this comparison it is concluded that in any incompatible mixture the component having the lower melt viscosity at the temperature of processing tends to form a continuous phase in the mixture. The greater is the viscosity difference, the greater is this tendency. The viscosity of one component relative to the other can be changed by changing the molecular weight of the components and/or the temperature of mixin

ISSN:0032-3888    

DOI:10.1002/pen.760130108

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractExisting dynamic mechanical relaxation data on two polymers containing aromatic groups in the backbone chain,viz., polyimide PI, and poly(2,6‐dimethyl‐p‐phenylene oxide), PDMPO, are reviewed and new data bearing on specimen purity and water content are presented. It is demonstrated that three separate relaxation processes are normally present in both polymers in the temperature range from about 100–400°K. The lowest temperature relaxation, designated γ, occurs in the 100–180°K range and is considered to arise from limited rotational oscillation of some phenylene rings about the 1,4 axis. Another relaxation process, designated β arises from the presence of water in the polymer. Its strength increases with increase of water content, its activation energy is about 10–12 kcal/mole, and it occurs in the 180–190°K range at 1 Hz. A higher strength secondary glass relaxation process, designated β*, occurs in the 280–400°K range at usual measuring frequencies (1 Hz to 104Hz). This relaxation is thought to be associated with the combined reorientational motion, of rings and connecting atoms of the monomer unit in “defect” regions, or regions of poor chain packing. As such, its position is affected by sample history. Both polymers also show a rise in damping in the high temperature region indicative of additional main chain motions. In addition to the above relaxations, PDMPO shows a δ‐relaxation below liquid nitrogen temperatures, associated with onset of Me rotation and PI shows an additiona

ISSN:0032-3888    

DOI:10.1002/pen.760130109

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThe differential scanning calorimeter (Perkin‐Elmer DSC‐1) is used to characterize the cure of a general‐purpose polyester during isothermal and scanning experiments. The technique is based on a new proposed model for the kinetics of isothermal cure. The model yields results which are in good agreement with experimental isothermal rate of reaction and integral heat of reaction data. It also gives some information about the residual reactivity of the sample after an isothermal cure experiment. With the aid of the proposed kinetic model, it is possible to obtain integral heats of reaction and rates of heat generation at different temperatures during a scanning experiment. The difference between the rate of heat input to the sample and the heat of reaction at any instant during scanning may be used to calculate the specific heat of the sample at the same instant. Specific heat data show two maxima during each scanning experiment. These maxima may be associated with transitions occurring during cure in the melt and rubbery s

ISSN:0032-3888    

DOI:10.1002/pen.760130110

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractThis study presents a mechanical analysis of the deep drawing of thermoplastics in the glassy state. A theoretical stress analysis is conducted by applying principles of classical plasticity together with several assumptions. A simple model is presented relating drawing performance with the mechanical properties of the plastic measured under the conditions of the fabrication operation. An experimental procedure is described for evaluating the drawability of a plastic. Data on thirteen thermoplastics are used to demonstrate the applicability of the theory developed.

ISSN:0032-3888    

DOI:10.1002/pen.760130111

出版商:Society of Plastics Engineers, Inc.    

年代:1973

数据来源: WILEY