摘要:

AbstractAlthough lamella‐like crystallites are a well‐established characteristic of polymer systems crystallized either in bulk or from dilute solution, major misconceptions have been engendered with respect to interfacial structures and other morphological features. A detailed analysis of a wide range of properties has allowed for a molecular description of some salient features of the structure of semi‐crystalline polymers. Solution formed crystals possess a disordered amorphous overlayer. Associated with the crystalline regions of bulk systems is a diffuse interfacial layer as well as an interzonal region, wherein the chain units which connect crystallites are in nonordered conformations. These conclusions are in complete accord with electron microscope observa

ISSN:0360-8905    

DOI:10.1002/polc.5070430103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThe morphological characteristics of poly(ethylene terephthalate) (PET) have been inferred from the selective chemical degradation of amorphous regions, including chain folds, and subsequent analysis of the molecular weight distribution of the reaction products. Bulk PET of known thermal and orientation history was reacted with 40% aqueous methylamine at 35°C and the reaction products examined by gel permeation chromatography. It was determined that the average crystalline fold period increased from six to nine monomer units over the crystallization temperature range of 126°C to 229°C. Evidence for the existence of a paracrystalline form at the lower crystallization temperatures was suggested by the presence of residual high molecular weight polymer in the reaction products. Samples crystallized at the lower temperatures exhibited multiple melting during DSC analysis. Results obtained by heating such samples in the DSC to a temperature between the two endotherms and quenching, followed by aminolysis and GPC, lead one to conclude that the first endotherm represents the initiation of melting and recrystallization. The second endotherm at ∼255°C, characteristic of PET, represents the melting of folded chain lamellae containing nine repeat units between folds. This material is formed during the DSC run as a result of melting and thermally compensatory recrystalliz

ISSN:0360-8905    

DOI:10.1002/polc.5070430104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractSince polymer crystallization rate is such a universal measure of backbone stereo structure, side chain structure, crosslinking, and the effect of additives, we have developed a routine, easily used method for its measurement. Normalized plots of the time‐honored measurement of hardness vs time compare well with results obtained by dilatometry, x‐ray diffraction, and light absorption (or optical birefringence). Sample preparation, surface roughness (especially important in the case of “nervy” rubbers), shortcuts to round‐the‐clock testing, temperature control and fine points of hardness measurements ar

ISSN:0360-8905    

DOI:10.1002/polc.5070430105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractLinear marcromolecules in the solid state may assume different macroconformations. While x‐ray diffraction and electron microscopy have been the prime instruments for the analysis of the highly ordered state, difficulties exist in the evaluation of less ordered portions. The enthalpy changes connected with changes in order can be determined by thermal analysis. Furthermore, modern instrumentation allows thermal measurements as a function of heating rate. Such mode of analysis can give kinetic information and data on metastable states. The macroconformations, thermal analyses, experimental techniques, and recent applications of thermal analysis to structural analysis giving information on folds, tie molecules, loops, and ciliae of poly(ethylene terephthalate), polyparaxylylene, selenium, and polyethylene are discusse

ISSN:0360-8905    

DOI:10.1002/polc.5070430106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractThermal relaxations in the glass transition region can be observed as spontaneous temperature drifts of the sample under adiabatic conditions. Upon the heating of a quenched glass, positive drifts are observed reaching a peak at some temperature just below its Tg. An annealed glass produces a peak in the negative drift at temperatures just above its Tg. Heat capacity measurements have been made on three linear polyethylene samples having 71 to 96% crystallinity and on one branched polyethylene sample, in an adiabatic calorimeter from 2 to 360 K. In all four samples, temperature drifts were detected with peaks occurring around 235–240 K. The temperature of the peaks is not significantly affected by the degree of crystallinity. However, the magnitude of the peaks decreases as the crystallinity is increase

ISSN:0360-8905    

DOI:10.1002/polc.5070430107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractPolybenzoxazoles, when heated up to 660°C in vacuum, lose most of their oxygen as carbon monoxide and carbon dioxide and possibly form Schiff base‐type structures. The carbon required for the formation of carbon monoxide is predominantly supplied by the benzene rings. About one out of every six CN linkages is eliminated as hydrogen cyanide, and some free nitrogen from this group is reduced to ammonia. The elimination of about 1 hydrogen atom per polymer unit (in the form of free hydrogen, hydrogen cyanide, ammonia, and methane) results in free radical formation and crosslinking.Carbon monoxide and carbon dioxide are also some of the major decomposition products of the benzoxazole in poly‐2,2′‐(1,8‐perfluorooctane)‐6,6′‐bibenzoxazole. In addition, fluorine from the perfluoroalkyl chain combines with ring hydrogen to form hydrogen fluoride, which in turn attacks the quartz of the crucible and reaction vessel to form silicon tetrafluoride.A polybenzothiazole, on heating to 625°C, crosslinks with elimination of some hydrogen. One out of every ten sulfur atoms is removed, essentially as hydrogen sulfide, leaving a Schiff‐base linkage; very few of the CN‐groups are eliminated as hydrogen cyanide. Two less stable polybenzothiazole systems, heated to 660 and 670°C, lose about 50% of their sulfur, mainly as hydrogen sulfide, and 20% of their nitrogen as hydrogen cyanide.Flash pyrolysis of model benzoxazoles and benzothiazoles was tried as a means

ISSN:0360-8905    

DOI:10.1002/polc.5070430108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractA method is described for performing adiabatic scanning calorimetry on thin samples heated at high speeds. Sample sheets are inserted between layers of a folded metal foil heater to form a stacked array. A thin‐foil thermocouple is inserted near the median plane of the array. The sample assembly is heated by passing a current through the foil heater. There is a brief initial period during which the sample interior heats adiabatically. During this period, the thermocouple signal is traced as a function of time on a chart recorder.Analysis of the chart yields the sample heating rate dT̃/dt at selected values of the mean sample temperatureT. Specific heat values are calculated from dT̃/dt, using an energy‐conservation equation. The sample thickness is kept small to permit attaining rapid heating rates without excessive temperature gradients. The overall thickness of the stacked array is designed to make the adiabatic period sufficient in duration, so that results are valid over the desired temperature range.Results are shown for polytetrafluoroethylene and polyethylene terephthalate at various heating rates up to 600 K/sec. At low speeds, results agree with previously published data, but at higher speeds radically different curves are obtained. Above the glass transition temperature of the polyethylene terephthalate, it is observed that the positions of inflections in the specific heat curve vary sharply with sample heating

ISSN:0360-8905    

DOI:10.1002/polc.5070430109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractBlends of poly(2‐methyl‐6‐benzyl‐1,4‐phenylene oxide) (PMBPO) with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO® resin) form clear, transparent films. Thermo‐optical analyses of solvent‐cast and compression‐molded films comprising PMBPO‐PPO resin mixtures at 0.1 weight fraction composition intervals over the complete composition range prove these blends to be homogeneous. True thermodynamic compatibility of the polymers is thus indicated. The thermo‐optical transition temperatures, TTOA, defined as the temperatures at which birefringence disappears in scratches on the films during 10°/min heating, are found to increase monotonically with increasing PPO resin weight fraction w2, in the manner: TTOA(°C) = 120 + 101 w2. Differential scanning calorimetry on the pressed films also indicates polymer compatibility yielding single glass transition temperatures Tg(DSC) increasing monotonically from 99°C for the PMB

ISSN:0360-8905    

DOI:10.1002/polc.5070430110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractFirst and second order thermal transitions have been characterized for a number of cis/trans‐polypentenamer copolymers, for blends of high cis and high trans polymers, and for high trans polypentenamer containing oil and carbon black. The extrapolated value of Tgfor 100% trans polypentenamer is −91°C at a heating rate of 10°C/min. At the same heating rate the maximum, equilibrium melting point is estimated to be 44°C. Correcting for the thermal lag in the experiment (i.e., extrapolating to infinitely slow heating rate), the above value is 40°C. The heat of fusion of trans‐polypentenamer is 1.93 ± 0.11 K cal/mole. The presence of crystalline polypentenamer slightly raises the glass transition temperature of the amorphous phase. This effect becomes measurable when the trans content is greater than 80%. Once calibrated by infrared or other spectroscopic determination of composition, thermal analysis is a rapid, precise method for measuring cis/trans contents in polyp

ISSN:0360-8905    

DOI:10.1002/polc.5070430111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY

摘要:

AbstractInvestigations of the glass transition and melting of partially crystalline polymers by nuclear magnetic resonance provide valuable information on the nature of noncrystalline regions. The broad line NMR signal was separated into a narrow component and a broad component by using a new method which does not imply the ambiguity usually present. From the intensity of the narrow component the mobile fraction was determined. This fraction was extrapolated to “infinite” temperature. By subtracting the mobile fraction from the noncrystalline fraction, the noncrystalline rigid fraction was obtained. Comparison of the measured second moments of the two components of the NMR line with calculated second moments of chains with fixed ends shows the following: The mobile fraction is formed by chains with either one end fixed or both ends fixed in a comparatively small end‐to‐end distance (for example, loops with adjacent reentry); the noncrystalline rigid fraction is formed by chains whose ends are fixed in a comparatively large or medium end‐to‐end distances (for example, tie molecules connecting different crystals).More detailed information on the chains forming the mobile fraction as well as on the structure in the melt was obtained by high resolution NMR. It was shown that near range order in the melt, for example, the formation of bundles of parallel chains, causes deviations from the lorentzian shape of the NMR line. During primary crystallization the chains within the bundles of parallel chains crystallize. During secondary crystallization, extremely mobile chains outside these bundles are incorporated into t

ISSN:0360-8905    

DOI:10.1002/polc.5070430112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1973

数据来源: WILEY