摘要:

AbstractThe miscibility of various amorphous polybutadienes with mixed microstructures of 1,4 addition units (cis, 1,4 andtrans1,4) and 1,2 addition units have been investigated. The studies here involved optical transparency, differential scanning calorimetry, and small angle light scattering. It was found that a 90 percent (cis) 1, 4 addition polybutadiene was immiscible with high (91 percent) 1,2 addition polybutadiene. Reduction of the 1,2 content to 71 percent induced an upper critical solution temperature (UCST) with thecis1,4 polymer. Polybutadienes with 50 percent and 10 percent 1,2 contents were miscible above the crystalline melting temperature of thecis1,4 polybutadiene. Immiscibility of the 91 percent 1,2 addition polymer was also found with a 10 percent 1,2 polybutadiene. The latter polymer also exhibits an UCST with the 71 percent 1,2 polymer. The results are used to interpret the characteristics of blends of polybutadienes of varying microstructure.

ISSN:0032-3888    

DOI:10.1002/pen.760282002

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractAn extrusion‐grade of high density polyethylene (HOPE) (3 ethyl groups per 1000 carbons) has been divided into 16 fractions by preparative GPC and selective p‐xylene extraction. The fractions, with molecular weights ranging from 900 to 1,000,000, have been studied by IR spectros‐copy, DSC, WAXS, polarized microscopy, and small‐angle light scattering (SALS), The average degree of chain branching (percent C2H5) is 0.5 percent for the part of the sample having a molecular weight lower than 10,000 and it decreases monotonically with increasing molecular weight, finally approaching 0.1 percent C2H5. A crystallinity depression with respect to linear PE equivalent to 20 percent/(percent C2H5) is recorded for all samples except for the very low molecular weight samples for which the crystallinity depression is much larger (30 to 35 percent/ (percent C2H5)). The unit cell volume increases with increasing percent C2H5, presumably due to the inclusion of ethyl groups in the crystals as interstitlals at 2gl kinks. The concentration of ethyl groups in the crystals (ϵc) unanimously follows the relationship: ϵc(percent) = 0.32 + 0.25 log(percent C2H5) except for the low molecular weight fractions which have significantly lower values for ϵc. Our admittedly speculative explanation for this major discrepancy between high and low molecular weight samples is based on the idea that segments with ethyl groups close to chain ends have a greater difficulty in crystallizing than segments containing ethyl groups located at positions far from the chain ends. The fractions obtained from the extrusion‐grade HDPE show a solidification temperature depression with respect to linear PE which can only be explained by the presence of chain branches in these samples. The depression is particularly pronounced for the low molecular weight samples as is expected from the data on molecular structure. Well‐developed non‐banded spherulites are observed in rapidly cooled (crystallized at about 35 K supercooling), low molecular weight samples (6,000

ISSN:0032-3888    

DOI:10.1002/pen.760282003

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractWe have determined the degree of stiffness of a poly(γ‐benzyl α, L‐glutamate) (PBLG) chain in benzyl alcohol by measuring the intrinsic viscosities of dilute Solutions with differing molecular weights. Viscoelastic properties in oscillatory shear flow have been studied and the dependence of the loss and storage moduli on temperature, composition, and frequency are reported. We have also studied the transient shear stress relaxation behavior of the PBLG gel at different temperatures and concentrations. A comparison has been made between these gels and a classical poly(dimethyl siloxane) (PDMS) network, as well as, typical glassy polymers. Shear creep and recovery measurements have been made for this system. Some extensional step strain experiments using lubricated squeezing have been investigated. Tensile experiments have been made to determine stress‐strain relationship during elongation. Preliminary experiments using the impulse approach to viscoelasticity further indicate the high elastic contribution in

ISSN:0032-3888    

DOI:10.1002/pen.760282004

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractIn the past, time‐temperature superposition has been used to extend the time scale of creep tests in polymers from the short times easily obtained in the laboratory to long times seen in actual use. A fundamental assumption of time‐temperature superposition is, however, that the polymer does not change in structure as a function of time. Because ductile amorphous thermoplastics physically age belowTg, the structure of the polymer changes on a time scale comparable to the time duration of the creep test. Thus, the time‐temperature superposition prediction greatly exaggerates the amount of creep in amorphous thermoplastics. For samples aged at the test temperature for one hour before testing, the difference between the time‐temperature superposition prediction and the actual creep data after 10 days is greater than a factor of ten

ISSN:0032-3888    

DOI:10.1002/pen.760282005

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractDynamic mechanical measurements have been performed in order to get information on the morphology of butyl‐acrylate (BuA)‐vinyl‐acetate (V Ac) based systems. The samples were obtained after emulsion polymerization by three different pathways: (a) Physical blending from homopolymer latexes (b) a conventional batch process leading to a BuA rich core‐V Ac rich shell latex particle (c) a two‐step polymerization leading to an abrupt concentration gradient Inside the particle. Films were obtained by evaporation of water at room temperature. The spectra of the films were interpreted with the help of Kerner's model, and new information has been obtained on the morphology: (i) in the simple blend (case a), thep(V Ac) latexes tend to coalesce to form the matrix; and (ii) it is possible to determine whether random copolymer formed during a polymerization process is located at the interface ofp(BuA) andP(V Ac) (case b) or inside thep(BuA) inclusion

ISSN:0032-3888    

DOI:10.1002/pen.760282006

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe thermal and crystallization behavior of blends of three thermoplastic polyesters with different degrees of crystallizability, with an amorphous aromatic polyamide is reported. The thermoplastic polyesters used in the investigation were poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET) and a co‐polyester of 1,4 cyclohexane‐dimethanol, ethylene glydol and terephthalic acid (PETG). The blends exhibited a single glass transition temperature indicating mlseibility in the amorphous phase. The results of thermal analysis indicated that the crystallization of all the three polyesters is facilitated in the molten phase as a result of blending. The blending significantly Increased the degree of crystallinity of PET, but there was no change in the crystallinity of PBT. It is thus observed that the extent of change in both the crystallization rate and the degree of crystallinity of polyesters depend on the inherent crystallizability of the individual polyes

ISSN:0032-3888    

DOI:10.1002/pen.760282007

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effects that the inclusion of low concentrations (0 to 0.6 percent by Volume) of cellulosic fibers have on the polymerization of a polyurethane was tested by monitoring the viscosity of a reacting diol‐diisocyanate system under isothermal conditions. An increase in viscosity due to the presence of the cellulosic fibers is observed, in addition to the expected rise related to polymer formation. However, a slackening effect appears as more cellulosic fibers are added to the polymerizing medium, in contrast to a system with comparable concentrations of glass fibers. On the basis of reaction kinetics arguments, it is suggested that the hollow nature of the cellulosic fibers and their sorbency play important roles in the effect observed, by reducing the effective concentrations of one of the monomers in the reacting phase, thereby diminishing the overall reaction rate. If similar portions of both monomers are extracted from the bulk of the reacting mass, the reaction is not affected as markedly as when only part of one of the monomers is abstracted. The results found illustrate the type of constraints that arise when certain types of polymerizations are carried outin situto obtain cellulosic fiber composite

ISSN:0032-3888    

DOI:10.1002/pen.760282008

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760282009

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760282001

出版商:Society of Plastics Engineers    

年代:1988

数据来源: WILEY