摘要:

AbstractVarious aspects of polyphosphazene chemistry are reviewed. Stable poly (organophosphazenes) can be prepared from an inorganic precursor, poly(dichlorophosphazene), by careful control of polymerization and substitution reaction conditions. The bulk structure and properties of polyphosphazenes are discussed, and attention is given to those polymers which have promise as useful engineering materials. The successful preparation of stable poly(organophosphazenes) appears to have resulted in a new class of polymers for both specialty and large scale commercial development.

ISSN:0032-3888    

DOI:10.1002/pen.760150502

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractTwo component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester‐polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass‐transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress‐strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also

ISSN:0032-3888    

DOI:10.1002/pen.760150503

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe mechanical and optical properties have been examined of a series of polyurethane‐polystyrene two‐phase systems produced by simultaneous polymerization. Torsion pendulum data show two separate glass transitions which are essentially those of the constituent homopolymers. Thus these systems do not from true interpenetrating networks. Phase inversion from a continuous polyurethane to a continuous polystyrene phase occurred at the relatively low styrene concentration of 20 to 25%. Measurements of the stress‐optical coefficients supported this finding. When polystyrene formed the continuous phase, straining produced softening at strains below about 15 percent. Birefringence measurements indicated that the rubbery polyurethane domains did not orient in these compositions. The stress‐optical coefficients showed no time dependence. The strain‐optical coefficients decreased with increasing te

ISSN:0032-3888    

DOI:10.1002/pen.760150504

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe thermal data needed for the design of heat transfer equipment and distillation columns for the manufacture of a new vinyl monomer, diacetone acrylamide, were rapidly and effectively provided by differential scanning calorimetry. A method has been developed for determining the effects of inhibitors and metals on the polymerization of the vinyl monomer. The latter was an aid in the selection of materials of construction. DSC was used to determine the total inhibitor concentration in the monomer. Selection of inhibitors was facilitated by information derived from thermal analysis.

ISSN:0032-3888    

DOI:10.1002/pen.760150505

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractElongated metal or other conductive particles can be added to a polymer or other poor conductor to produce a composite of enhanced conductivity. Elongated particles are generally more effective than spherical or irregular particles but very slender particles can be dramatically more effective. For example, cylindrical copper particles with length/diameter (L/D) = 20, randomly dispersed in epoxy resin at a loading of 5 percent copper by volume yield a composite with a thermal conductivity about 1.5 times that of the base resin. However, the same volume of copper particles withL/D= 50 can increase the conductivity by a factor of 5 or more.This paper presents a new type of analysis for predicting the thermal conductivity of disperse composites from the properties of the component phases and elementary characterizations of particle shapes and orientation. This analysis successfully predicted the sensitivity to particle shape which was confirmed by experiments also reported in this paper. These results suggest that highly elongated particles may be used to achieve dramatic modifications of thermal conductivity and the analysis presented here may be a useful tool in the design or development of disperse composites of specific thermal conductivity. The analysis may also apply to other properties such as electrical conductivity or magnetic permeability.

ISSN:0032-3888    

DOI:10.1002/pen.760150506

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe effects of mixing on polymerizations in batch reactors are examined theoretically for initiations by thermal decomposition of catalyst and by absorption of ionizing radiation. Mathematical expressions for predicting the first three moments of the dead polymer size distribution are presented. Two extreme mixing states, perfect and no mixing, are considered. It is shown that in batch reactors mixing in any direction in which nonuniform initiations exist increases the polymerization rate and the number average molecular weight and decreases the weight average and thus the polydispersity.

ISSN:0032-3888    

DOI:10.1002/pen.760150507

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractTrans‐1,5‐polypentenamer (TPP) has some similarity to natural rubber partly because of properties that relate to crystallinity and to the position of the crystalline melting point. This similarity makes TPP a unique rubber among other synthetic hydrocarbon polymers. Requirements for attaining a good balance of physical properties include adjustment of both micro and macrostructure with processability. Natta, Dall'Asta, Haas and Pampus have described the preparation of polypentenamers based on tungsten or molybdenum catalysts. Since Eleuterio made his disclosure, there have been many important contributions disclosing special conditions for preparing TPP or variations in catalyst preparation including many catalyst activators. Natta and Dall'Asta vulcanized both the TPP and the amorphous cis‐1,5‐polypentenamer (CPP). They showed that TPP (melting point 23°C) gives good tensile properties even in pure gum vulcanizates characteristic of rubbers that crystallize on stretching. CPP gave better low‐temperature characteristics than other hydrocarbon elastomers (SBR rubber, propylene oxide/allyl glycidyl ether copolymer, cis‐1,4‐polybutadiene). For example, the CPP vulcanizates were less brittle down to −90°C measured by 100 per cent moduli and, in a comparison of temperatures at which retraction occurred, CPP showed a superiority. With CPP from 25°C to −70°C, both tensile strengths and moduli increased without appreciable variation of elongation at break. Since the crystalline melting point at rest is near 20°C for TPP, the elastic behavior is governed by this transition rather than the glass transition point (−90°C).The rate of crystallization for TPP is more rapid compared to natural rubber. Although vulcanization is a factor on elastic behavior, we suggest that further compromise may be necessary to balance the desirable properties related to crystallinity while maintaining elasticity at lower temperatures. The summary of the Haas paper noted that TPP rubber is outstanding except that the abrasion, wet skid and heat build‐up are inferior to existing tread rubber types. Our efforts suggest that TPP is not inferior.In our examination of TPP's having varied or lowered melting points, vulcanizates (tread recipes) with good low temperature flexibility were developed from TPP withTmof 5°C. Since tack and green strength are dependent on both the micro and macrostructure, properties lost by decreasing the trans content or theTmwere offset by increasing the molecular weight. With higher molecular‐weight TPP, other properties such as heat build‐up and abrasion were improved or made equivalent to other tire rubbers. Thus, by optimizing molecular weight, oil level and processability with the microstructure, a good balance of propertie

ISSN:0032-3888    

DOI:10.1002/pen.760150508

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractLittle data is available on gas transmission through thick polymer samples. There is, therefore, a temptation to assume an inverse relationship between gas transmission rate and thickness and to calculate flow through thick samples using permeability data obtained on thin films. This is incorrect, as the calculation assumes steady flow, and with thick samples this state may not be reached for months or even years. Thus both diffusivity and permeability are needed to calculate the gas flow and the calculations are more complex than simple permeability calculations. Because of the long time scale, the effects of varying the thickness are difficult to demonstrate experimentally. We describe a computer simulation of the manometric method which compares the behavior of two materials with similar permeabilities but different diffusivities. Although thin samples behave identically, they differ increasingly with thickness. The pitfalls in using the gradient and time lag of the pressure curve to calculate permeability and diffusivity are also discussed.

ISSN:0032-3888    

DOI:10.1002/pen.760150509

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractExperimental results for thermal conductivity and flow birefringence on liquid poly (dimethyl siloxane), PDMS, under a shearing strain are discussed. An increase in thermal conductivity with increasing shear rate is attributed to an increased degree of orientation in a direction at 45° to the flow direction for simple shear. A mathematical model is set up. It is based on the assumption that the macromolecules do not change their time‐average shape and otherwise behave as rigid, thin cylinders which can be influenced by convection and external fields and are endowed with rotational Brownian motion. The model predicts that thermal conductivity will reach a maximum value at moderate rates of strain and begin to decrease eventually reaching a minimum value (the transverse thermal conductivity of the basic element) at very high rates of strain when the molecules are completely aligned in the flow direction. Liquids studied were a 12,500 centipoise PDMS in the pure state and in solution in methyl ethyl ketone, MEK, as well as a 65,000 centipoise solution in M

ISSN:0032-3888    

DOI:10.1002/pen.760150510

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY

摘要:

AbstractThe Flow Analysis Network (FAN) method was adapted for solving the isothermal flow problem in a cross head die. Given the polymer rheology and the die geometry, the flow streamlines in the die and the flow rate uniformity at the exit can be calculated for any given head pressure. The optimum geometrical configuration of the die can be computed by repeated simulations. Results of the computations with the present method are shown to be in good agreement with previously published computations.

ISSN:0032-3888    

DOI:10.1002/pen.760150511

出版商:Society of Plastics Engineers, Inc.    

年代:1975

数据来源: WILEY