摘要:

AbstractHighly crosslinked polymers of varying structure were produced by the reaction of poly(glycidyl acrylate) (PGA) and methacrylate (PGM) with a variety of anhydride crosslinking agents: chlorendic (CA), glutaric (GA), maleic (MeA), succinic (SA), and polyrnalonic (pMnA) anhydrides. Topology was also varied by the use of a diluent and a comonomer in the backbone chain. Oxygen permeation measurements were made on these polymers coated onto a polypropylene film substrate before crosslinking. The crosslinking process greatly reduced the O2permeability which, however, was dependent not only on the degree of crosslinking (yield of the crosslinking reaction), but also on the crosslink density, the chemical nature of the structural elements, and the topology of the polymer network. Thus the most impermeable coating (XPGA/CA) was made not from the stiffest and bulkiest components (PGM and CA), but by the reaction of the bulkiest anhydride (CA) with the more flexible polymer backbone chain (PGA). This is explained in terms of the need for chain flexibility to produce a crosslinked structure of optimum space filling character and network tightness.

ISSN:0032-3888    

DOI:10.1002/pen.760200112

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractOxygen permeation has been measured in flat sheet as a function of degree of orientation, and oxygen and water transport have been measured in oriented polyester bottles. O2permeability in flat sheets decreases gradually with orientation on either side of an abrupt decrease by about a factor of 2 after moderate orientation. The bottles tested were all more highly oriented than that critical decree; no significant effect of orientation on water or O2transport in bottles could be found. Only container intrinsic viscosity (IV) (which is determined by molecular weight, and is therefore a convenient measure of polymer degradation) was significantly related to the transport properties of the bottles. It was found that O2transport is increased with increasing IV while H2O transport decreased. The explanation for these seemingly contradictory data can be found in the chemistry of degradation of the polyester.

ISSN:0032-3888    

DOI:10.1002/pen.760200113

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe PVT properties of polymer glasses are discussed from two points of view. First, as a low frequency tool in the study of sub‐glass relaxations. Dilatometric results illustrate the sensitivity of the thermal expansivity and its temperature coefficient to dynamic processes occuring in the glass. The second point of view considers the quasi‐thermodynamics of the non‐equilibrium system, under conditions where the rates of relaxational processes are small in comparison with experimental rates, and time dependent processes are practically absent. The starting point is a theory of the equilibrium melt which describes the characteristic liquid disorder in terms of a temperature and pressure dependent hole or loosely, free volume fraction. This function is obtained by the minimization of a configurational free energy. Upon reaching the glass transition, this dependence is reduced, and further so in a sub‐glass relaxation region. However, it is not eliminated until temperatures of the order of 50 to 70 K are reached. While this picture is qualitatively universal, significant quantitative differences are observed with different chemical structures and different thermal and pressure histories. A comparison of thermal expansivities of high and lowTgsystems indicates that in the former the free volume retained upon reachingTgis comparatively large and the departure from equilibrium or degree of freeze‐in comparatively small. Similarly, it appears that the glassy densification generated by cooling the melt under pressure is more extensive in highTgglasses. Such results imply structural differences. These should be investigated by comparative studies of (a) time dependent processes in terms of the free volume functions, (b) sorption and transport, and (c) the temperature dependent dynamics of density flu

ISSN:0032-3888    

DOI:10.1002/pen.760200114

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractHigh pressure CO2sorption data in polycarbonate (PC) are reported as a function of temperature and thermal history. The bulk physical structural changes produced by annealing at 125 and 135°C were monitored by density and thermal property changes. The sorption data are analyzed by the dual sorption model which assumes the sorption isotherm to consist of Henry's law and Langmuir sorption terms; The Langmuir capacity termC H′of PC can be grossly correlated with the reported volumetric parameters of the polymer. This excess volume interpretation ofC H′has found support in the good correlation betweenC H′and the corresponding enthalpy relaxation from parallel Differential Thermal Analysis of the samples. Density measurements provide gross evidence of the free volume interpretation ofC H′. The experimental uncertainties in the data compromise a more critical test of the relationship betweenC H′and the density

ISSN:0032-3888    

DOI:10.1002/pen.760200115

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe sorption of a variety of gases and organic vapors in poly(vinyl chloride) (PVC) powders has been studied gravimetrically with a recording microbalance and volumetrically with a gas pycnometer and an automatic surface area analyzer. For nitrogen, carbondioxide, vinyl chloride, methanol, acetone, n‐butane, and benzene at low penetrant activities and temperatures belowTg, sorption isotherms exhibit the downward curvature characteristic of dual‐mode sorption. The solubility of each of these penetrants is lower in heat‐treated PVC samples than in samples recovered from the polymerization without additional heating. It has been possible to estimate the parameters of the dual‐mode sorption model for carbondioxide, vinyl chloride, and methanol. The results indicate that the history‐dependence of gas or vapor solubility is associated only with the “hole‐filling” term of the dual‐mode model; the normal dissolution or Henry's Law term is essentially unaffected by the prior heat tre

ISSN:0032-3888    

DOI:10.1002/pen.760200116

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effects of prior thermal and swelling history on the kinetics and apparent equilibria of subsequent n‐hexane sorption in monodisperse, submicrometer diameter, glassy polystyrene microspheres were studied. Repetitive sorption and desorption cycling was compared with continuous sorption and desorption experiments. The apparent equilibrium uptake of n‐hexane in preswollen samples decreased monotonically with the cumulative time under vacuum independent of the cycle frequency or the number of sorption‐desorption cycles. This consolidation was modeled as a first order relaxation process with a single characteristic relaxation time. “As‐received” samples swelled in the presence of the penetrant and the apparent equilibrium n‐hexane content increased monotonically with the time under n‐hexane. The Berens‐Hopfenberg diffusion‐relaxation model accurately describes the cyclic and continuous swelling behavior of the “as‐received” sample. At each temperature studied, a true equilibrium n‐hexane content was approached asymptotically for the preswollen and “as‐received” samples after sufficient time under vacuum or n‐hexane, respectively. Whereas the apparent sorption equilibria were controlled by the cumulative time under vacuum or n‐hexane for the preswollen and “as‐received” samples, respectively, the absorption kinetics are subject to a systematic variation which depends only on the immediate prior vacuum history of the sample. The temperature dependence of the kinetic and equilibrium parameters describing diffusion, consolidation, and swelling suggests a unified molecular interpretation of these diverse glas

ISSN:0032-3888    

DOI:10.1002/pen.760200117

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760200101

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY