摘要:

AbstractSmall‐angle neutron scattering, SANS, stands forth as one of the most important of the new tools for evaluating polymer chain conformation and morphology. This paper reviews the SANS literature through 1982, with a few early 1983 references added. The theory of SANS is outlined and compared to light scattering. SANS values of polymer molecular weights and radii of gyration obtained in the bulk state were found to be in agreement with values obtained from dilute solutions by light scattering. In each case, deuterated fractions of polymer were inserted into the hydrogeneous matrix, or vice versa, to provide contrast. Several new research areas are then discussed, including unidirectional stretching of elastomers, stress‐relaxation, polymer‐polymer miscibility, crystallization from the melt compared with crystallization from dilute solutions, nonclassical aggregation during bulk polymerization of thermoset systems, morphology of polymer blends, block copolymers and ionomers, the core‐shell structure of latexes and polymer blocks, and grafts as surfactants in emulsions and latexes. Much new and sometimes unexpected information is being provided by the SANS research now in p

ISSN:0032-3888    

DOI:10.1002/pen.760240102

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractIn this article the kinetics of chemical‐controlled radical‐chain copolymerization have been reduced to pseudohomopolymerization kinetics by introducing the apparent rate constants, The methods for the determinations of the values of the apparent rate constants, mode of termination, and the methods for the calculation of molecular weights and distributions are proposed. The data required for these determinations and calculations are simply obtained by the usual steady‐state method. According to the traditional kinetics along with the definitions of the apparent rate constants, these apparent rate constants as functions of traditional rate constants, monomer compositions, and copolymer compositions are derived. Further utilizing the theoretical expressions obtained, we show that the apparent rate constants are the general rate constants for both radical chain homo‐ and copolymerizations. The bulk radical copolymerizations of methyl methacrylate and styrene at various monomer feed compositions at 60°C are used to test the proposed model. The empirical apparent rate constants obtained are described well, by the following expressions,\documentclass{article}\pagestyle{empty}\begin{document}$$ \beta = 0.997{\rm }F_1 + 0.398{\rm }F_2 + 0.039\left({F_1 F_2 } \right)^{\frac{1}{2}} $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ {{k_t^a } \mathord{\left/ {\vphantom {{k_t^a} {\left({k_p^a} \right)}}} \right. \kern-\nulldelimiterspace} {\left({k_p^a } \right)}}^2 = - 0.138 \times 10^4 \left({{{F_1 } \mathord{\left/ {\vphantom {{F_1 } {f_1 }}} \right. \kern-\nulldelimiterspace} {f_1 }}} \right)^2 + 0.354 \times 10^4 \left({{{F_1 F_2 } \mathord{\left/ {\vphantom {{F_1 F_2 } {f_1 f_2 }}} \right. \kern-\nulldelimiterspace} {f_1 f_2 }}} \right) - 0.114 \times 10^4 \left({{{F_2 } \mathord{\left/ {\vphantom {{F_2 } {f_2 }}} \right. \kern-\nulldelimiterspace} {f_2 }}} \right)^2 $$\end{document}and the mode of termination on the combination termination is\documentclass{article}\pagestyle{empty}\begin{document}$$ {1 \mathord{\left/ {\vphantom {1 {{\rm k}_p^a = - 0.132}}} \right. \kern-\nulldelimiterspace} {{\rm k}_p^a = - 0.132}} \times 10^{ - 2} \left({{{F_1 } \mathord{\left/ {\vphantom {{F_1 } {f_1 }}} \right. \kern-\nulldelimiterspace} {f_1 }}} \right) + 0.428 \times 10^{ - 2} \left({{{F_2 } \mathord{\left/ {\vphantom {{F_2 } {f_2 }}} \right. \kern-\nulldelimiterspace} {f_2 }}} \right) $$\end{document}whereK aaandK tadenote the apparent rate constants of propagation and termination, respectively. The termf1(= 1 −f2) stands for the mole fraction of styrene in the monomer solution fed.F1is the copolymer composition produced atf1. β is the mode

ISSN:0032-3888    

DOI:10.1002/pen.760240103

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractA mathematical model has been developed to compute the molecular weight distribution (MWD) in the polyethylene terephthalate (PET) manufacturing process. Unlike the previous efforts, this model takes into account the influence of side reactions and various interchange reactions on MWD. The process of blending of molten polyester chips has also been simulated with a view to calculate the equilibrium MWD as well as the time required to reach the equilibrium MWD. The1 significance of the results has been discussed in terms of industrial operations involving PET polymerization and PET blending.

ISSN:0032-3888    

DOI:10.1002/pen.760240104

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractKevlar 29 fiber has been widely considered for the manufacture of very‐long high‐performance cables. Due to low transverse strength fiber‐on‐fiber rubbing leads to rapid deterioration. The usefulness of impregnating Kevlar 29 braids with resin to overcome this drawback has been evaluated by performing reverse bending fatigue tests. Braids of identical construction, one of them being impregnated with a polyurethane resin by a patented process, were fatigued to failure on a purpose‐built rig under varying applied loads. Fatigue tests were also carried out to 30 percent and 50 percent of total braid life and residual strength values measured. It was found that high applied loads (∼50 percent of ultimate) lead to premature braid failure dominated by a creep mechanism. Both braids showed similar behavior, although the impregnated braid was superior. At low applied loads, however, where the failure mechanisms was dominated by wear or internal abrasion, it was seen that resin impregnation could increase braid life by a factor of four. Resin impregnation coupled with bending fatigue significantly stiffens braids, as was demonstrated by tensile testing up to br

ISSN:0032-3888    

DOI:10.1002/pen.760240105

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractThe modification of an amorphous random ethylene‐propylene rubbery copolymer (EPM) has been accomplished by solution grafting of maleic anhydride molecules promoted by radical initiators, The resulting EPM‐g‐succinic anhydride (EPM‐g‐SA) and EPM have been used to obtain binary polyamide 6/EPM or polyamide 6/EPM‐g‐SA and ternary polyamide 6/EPM/EPM‐g‐SA blends by melt mixing. The formation of an EPM‐g‐PA6 graft copolymer during the blend preparation has been assumed. Different blend morphologies were observed by scanning electron microscopy (SEM) according to the nature and content of the rubber used. The tensile mechanical properties and the impact behavior of the prepared blends were investigated and correlated with the SEM analysis of the fracture surfaces. Binary and ternary blends containing 20 percent by weight of total rubber show a significant improvement of the impact properties at low temperature (−20°C) when the rubber is partly or entirely EPM‐g‐SA. In the case of PA6/EPM‐g‐SA (80/20) blend these results are related to the presence of rubbery domains of very small size strongly adherent to the PA6 matrix. In the case of 80/10/10 ternary blends, a much more complicated overall morphology is observed. Such morphology is characterized by the presence of large EPM domains, likely containing some EPM‐g‐PA6 graft molecules acting as an interfacial agent, and domains of EPM‐g‐PA6 of smaller size strongly adhere

ISSN:0032-3888    

DOI:10.1002/pen.760240106

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

摘要:

AbstractEffects of pressure and temperature on time‐dependent changes in physical/mechanical properties of graphite/epoxy composites were investigated. Samples were cut from the eight‐ply‐thick laminates of commercially used composites, post‐cured, and then quenched to environments of various temperature and pressure. Time‐dependent changes in their properties were analyzed by thermal and thermomechanical (dynamic mechanical) measurements. An increase in the glass‐transition temperature was found to occur as a function of time. The rate of this process was enhanced by an increase in temperature and/or a decrease in pressure. An explanation was offered in terms of types and mechanisms of molecular events that occur in the glassy state. Time dependent decrease in free volume (and enthalpy) takes place but is not the sole mechanism responsible for the observed increase inTg. After a certain period of time (which depends onTandPof the environment), additional crosslinking appears to

ISSN:0032-3888    

DOI:10.1002/pen.760240107

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760240101

出版商:Society of Plastics Engineers, Inc.    

年代:1984

数据来源: WILEY