摘要:

The relation &Dgr;Cp&Dgr;&kgr; =TV(&Dgr;&agr;)2is shown to be obeyed under the same assumptions that Davies and Jones used to derive the weaker condition &Dgr;Cp&Dgr;&kgr; ≥TV(&Dgr;&agr;)2. This means that if a material is found experimentally not to obey the above equality, then it is not describable by an order‐parameter theory. A prescription is given which allows one to determine within the context of order‐parameter theory whether the glass transition of a given material is basically thermodynamic or kinetic in origin.

ISSN:0021-8979    

DOI:10.1063/1.1663027

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Optical and x‐ray observations of polyethylene have been made at high pressures and temperatures using a gasketed diamond‐anvil cell. The experiments confirm the existence of the high‐pressure phase previously postulated by Bassett and Turner. The new phase is hexagonal, with orthohexagonal lattice parameters ofa= 8.46Å andb= 4.88Å. Comparison with the previously measured volume change indicates that there is a decrease in thecdimension to 2.45Å per ethylene unit in transforming from orthorhombic to hexagonal structures. The likely implication is that the molecules in the hexagonal phase do not have an all‐trans conformation. Chain‐extended growth is the result of crystallization from the melt into the hexagonal phase, whereas chain‐folded growth is the familiar process of melt crystallization.into the orthorhombic phase. Chain‐extended lamellae are observed to grow outwards behind a growing edge with a permanent narrowed profile, showing that the lamellar thickness is determined in a region extending several microns behind the growth front.

ISSN:0021-8979    

DOI:10.1063/1.1663028

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both quenched and as‐received polyphenylene oxide. The curves are linear below 110°C with slopes of 0.098 cal/g°C and linear above 110°C with slopes of 0.032 cal/g°C. The inflection at 110°C is attributed to a &bgr; transition. The plot for the as‐received material is displaced vertically from that of the quenched material by 2.75 cal/g which is attributed to the fact that the as‐received material contains about 27.5% crystallinity. The major component of the heats of solution is the exothermic contribution from the solvent‐induced freeing or relaxation of the constrained molecular motions.

ISSN:0021-8979    

DOI:10.1063/1.1663029

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both as‐reprecipitated and quenched atactic polymethylmethacrylate. The as‐reprecipitated curve decreases linearly with a slope of 0.096 cal/g°C from room temperature to 90°C, and above 110°C has a constant value of +1.5 cal/g. The quenched material data decreases linearly with a slope of 0.12 cal/g°C from room temperature to 55°C, jumps +2 cal/g at 55°C, and continues the linear decrease with a slope of 0.096 cal/g°C from 55 to 90°C. The data suggests that isotactic stereochemical impurities in the atactic material are able to crystallize at 55°C which is theTgofi‐PMMA, and therefore must be associated asi‐PMMA islands in a rigid atactic‐syndiotactic PMMA matrix. This also suggests that the &bgr; transition in PMMA may be associated with the isotactic impurities

ISSN:0021-8979    

DOI:10.1063/1.1663030

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The fracture surface morphology of block copolymers of (i) tetramethyl‐p‐silphenylenesiloxane/dimethylsiloxane (TMPS/DMS) and (ii) propylene/ethylene (P/E) has been studied. The TMPS/DMS samples had compositions ranging from 90/10 to 30/70 wt% ratios. The ethylene content in the P/E samples ranged from 8 to 13%. A few polyolefin blends were also examined. Materials were fractured at liquid‐nitrogen temperatures and studied under ambient conditions by scanning and transmission electron microscopy. X‐ray methods and differential scanning calorimetry (DSC) techniques were also used. Copolymers with higher TMPS compositions exhibited a lamellar texture, but at high DMS contents fracture appeared ``glassy''. All TMPS/DMS samples exhibited spherulitic structures. Spherulites were mainly banded and were negatively birefringent. In samples with higher TMPS content, fracture occurred predominately between lamellar bands. The DMS component rejected by the crystalline TMPS hard segments is largely responsible for the observed fracture behavior and for the tensile properties of these copolymers particularly where this phase predominates. In the P/E copolymers both large and small globular particles are observed. Ethylene and propylene form separate crystalline phases. The interfacial characteristics between the large aggregates and the polypropylene matrix are believed to be responsible for impeding fracture porpagation in these materials, as assessed by impact tests. The influence of annealing conditions on the observed morphology has been investigated.

ISSN:0021-8979    

DOI:10.1063/1.1663031

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A simple model has been developed to account for the viscosity‐temperature dependence of liquids. It is predicated upon the valid assumption that the activation energy for flow is Arrhenius‐like at sufficiently high temperatures, and that this activation energy varies inversely as the probability of finding sufficient local volume for transport at lower temperatures. The model yields a viscosity reducing equation very similar to the Magill‐Li empirical equation for the zero shear viscosity &eegr; as the function of temperatureT. The relation isln&eegr;&eegr;s=Aexp [B (x+&phgr;−1)−1]x−exp(B/2 &phgr;)1+&phgr;,whereA= 2.68,B= 0.432, &phgr; = 0.238,x=T/Tg, &eegr;Sis the reference viscosity at the reference temperatureTs, andTgis the glass temperature. This relation has been successful in reducing data for several viscous materials unto a single master curve which extends over about 16 orders of magnitude in viscosity and encompasses a broad temperature range extending fromTgto about 2.5Tgin some instances.

ISSN:0021-8979    

DOI:10.1063/1.1663032

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

After exposure to ionizing radiation, trioxane polymerizes rapidly at temperatures between 50 and 60°C. The nature of the molecular motions involved in this solid‐state reaction is not clear. Line narrowing in nuclear magnetic resonance absorption has been reported as one indication of such motions. No related dielectric loss peaks were found in trioxane at temperatures from −180 to 55°C and frequencies from 1 to 10 000 Hz. Ionic conductivity is large above room temperature and it may play an important role in this polymerization reaction.

ISSN:0021-8979    

DOI:10.1063/1.1663033

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The unit‐cell dimensions of a given polyethylene have previously been shown to vary nearly linearly with the reciprocal of lamella thickness. Data obtained at 153.2 and 296.2°K are presented to show that the slope of this dependence is different for crystals of orthorhombicn‐paraffins, melt‐crystallized polyethylene, and solution‐crystallized polyethylene. Within the limits of error, all extrapolate to the same basal area at infinite lamella thickness, and this agrees with the measured value for a sample crystallized from the melt under high pressure to yield a long period of about 3500 Å. Since the effect is a surface one, it is proposed that these differences result from the differences between methyl interactions, fold interactions, different fold planes, domains, etc. It is shown that the variation of cell dimension with lamella thickness leads to a quadratic term in the variation of macroscopic density. This term permits the separation of the thickness and density of a lower‐density surface layer in a two‐phase model.

ISSN:0021-8979    

DOI:10.1063/1.1663034

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The morphology, rheo‐optical behavior, and mechanical relaxation properties were investigated for a series of three segmented copolyesters containing blocks of crystalline poly(tetramethylene terephthalate) and amorphous poly(tetramethylene ether). Transmission and replica electron micrographs show that if cast from a hot solution of 1,1,2‐trichloroethane on a heated surface, all the samples show distinct spherulitic structures. Annealing appears to increase the lamellar thickness. On the other hand, casting from a solution of 1,1,2,2‐tetrachloroethane produced a film that showed no evidence of the presence of spherulites, although microphase separation persists and crystallites appear to be randomly oriented in the amorphous matrix. Small‐angle light‐scattering experiments for trichloroethane‐cast samples confirmed the existence of spherulites. Dynamic mechanical data of these copolyesters show three principal relaxation peaks. These are the melting peak of the poly(tetramethylene terephthalate) block, the primary glass transition peak of the poly(tetramethylene ether) block, and the local mode relaxations of both blocks at low temperatures. Annealing and casting from different solvents did not affect the relaxation behavior of these copolyesters.

ISSN:0021-8979    

DOI:10.1063/1.1663035

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Recent measurements have shown that mechanical relaxation peaks commonly observed inn‐paraffins are absent in single crystals ofn‐eicosane (C20H42). This work has now been extended to include polycrystalline samples of several highly pure long‐chain hydrocarbons. Internal friction data obtained for a variety ofn‐paraffins, pure or otherwise, have revealed no low‐temperature &ggr; relaxation. Moreover, the &agr; relaxation peak is suppressed completely by purification. In attempts to induce an &agr; or &ggr; loss peak, several dilute mixtures of othern‐paraffins in pure C20H42have been examined. Only the addition of odd‐numbered shorter chains induced loss peaks. On the other hand, the presence of a branched impurity, in this case the C20H42isomers 2‐methylnonadecane and 10‐methylnonadecane, did induce loss peaks, one of which correlates very well to the &agr; process found in as‐received C20H42. It is proposed here that isomer impurities are an important factor in the mechanics of many of the loss processes in long‐chain hydrocarbons observed both mechanically and dielectrically.

ISSN:0021-8979    

DOI:10.1063/1.1663036

出版商:AIP    

年代:1974

数据来源: AIP