摘要:

The effect of stress on chemical equilibrium in solids is treated by a Moutier cycle without using the concept of chemical potential. The derivative of the natural logarithm of the equilibrium constant with respect to stress is a tensorial quantity and after multiplying byRT(R: gas constant,T: absolute temperature) is defined as thestrain volumeof the reaction.

ISSN:0021-8979    

DOI:10.1063/1.1659820

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A recently elaborated theory of thep‐V‐Tproperties successfully describes the behavior of amorphous polymers above the glass temperature. The improvement over earlier results arises from the introduction of a vacancy fraction which is obtained as a function of volume and temperature by a maximization of the partition function. We now explore a possible application of this theory to the glassy state by introducing an assumption following a frequently used idea, namely, the freezing of one parameter, (or more), for example, an unoccupied volume ratio. The natural quantity to consider is the vacancy fraction and its effect on the thermal expansion coefficient at the glass temperature. Experimental data at atmospheric pressure on a series of polymers, encompassing a wide range ofTg's, are examined and compared with theoretical predictions. The computed expansivities &agr;gatT=Tgare uniformly smaller than is observed. We suggest as the primary reason for this discrepancy the assumption of a complete freezing of the hole fraction at the glass temperature, which should be replaced by a decreased dependence on volume and temperature as compared with the liquid. Additional factors are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1659821

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The preparation of highly crystalline polyethylene at low pressure is reported. We demonstrate that with careful control of the substrate, melting and crystallization schedule, and physical state of the specimen (film thickness), it is possible to prepare polyethylene having a density in excess of 0.999 g cm−3, a melting temperature of ∼140°C, and a heat of fusion in excess of 70 cal/g. The approach appears to be general and should be applicable to a wide variety of polymers. An analysis of the heat‐of‐fusion data suggests a value of 79 cal g−1for the infinitely extended chain crystal.

ISSN:0021-8979    

DOI:10.1063/1.1659822

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The morphology of as‐polymerized poly‐p‐xylylene grown between −17 and 30 °C is found to consist of lamellar &agr; crystals oriented with the (010) plane parallel to the support surface. The crystallinity decreases with decreasing polymerization temperature. Spherulitic and nonspherulitic portions of the polymer film consist of folded chain lamellas (∼80 Å fold length) with the chain axis parallel to the support surface. The results were obtained by small‐ and wide‐angle x‐ray measurements, electron and optical microscopy, and differential thermal analysis.

ISSN:0021-8979    

DOI:10.1063/1.1659823

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A crystal structure of &agr; poly‐p‐xylylene is proposed with the help of data of oriented crystals grown during polymerization. The unit cell is monoclinic,a=8.57 Å,b=10.62 Å,c=6.54 Å (chain axis), &bgr;=101.3°. Four repeating units per cell lead to a calculated density of 1.185 g/cm3and a packing density of 0.71. The probable space group isP21/m.

ISSN:0021-8979    

DOI:10.1063/1.1659824

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The anisotropic morphology of amylose films is described by solid‐state light‐scattering analysis. A wide range of supermolecular structures was found, varying from ``rodlike'' texture for water‐cast films to ``ringed spherulitic'' texture for those cast from dimethyl sulfoxide (DMSO). After treatments, such as alcohol swelling or prolonged exposure at high relative humidity, the DMSO‐cast films undergo significant textural modification which is best characterized by the observed changes in the scattering envelopes. Electron microscopy is, in general, in accord with these observations, although the advantage of the light‐scattering method over electron and simple polarization microscopy for characterizing such systems is clearly shown.

ISSN:0021-8979    

DOI:10.1063/1.1659825

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Single‐crystal x‐ray diffraction studies of trans, trans‐1, 4‐bis‐[&bgr;‐pyridyl‐(2)‐vinyl]‐benzene (P2VB) and its solid‐state addition photopolymerization to a high‐crystallinity nearly three‐dimensionally aligned linear polymer are presented. Both P2VB and poly‐P2VB are orthorhombic. The lattice parameters area=21.09±0.16,b=9.61±0.05, andc=7.29±0.03 Å for P2VB, anda=19.16±0.20,b=10.69±0.05, andc=7.45±0.15 Å for poly‐P2VB. For both monomer and polymer the unit cell contains four monomer molecules. From systematic absences, the probable space group of P2VB isPbca. The observed absences for poly‐P2VB are also consistent with this space group. The solid‐state photopolymerization of P2VB is controlled by the crystal structure of this monomer with the orthorhombic axes of monomer and polymer on the average aligned in the same direction. The slight change in unit cell dimensions, the probably identical unit cell symmetry, and the invariance of average unit cell orientation suggest that minimal molecular rearrangement occurs during polymerization. Models are proposed for the polymerization mechanism and are related to the configuration and lattice structure of the resulting polymer. To obtain more detailed knowledge of the structure of crystalline P2VB and hence of the polymerization mechanism, energy minimization packing calculations have been performed. This monomer was found to deviate appreciably from a planar molecular structure. The present study is compared with recent work on the solid‐state photopolymerization of an isomeric compound trans, trans‐2, 5‐distyrylpyrazine (DSP).

ISSN:0021-8979    

DOI:10.1063/1.1659826

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Previous electron microscopic studies have demonstrated the presence of intercrystalline links between thin lateral edges of chain‐folded lamellar crystals in spherulitic polymers. We now present evidence that links also connect broad faces of superimposed neighboring lamellae. The latter links have been observed by electron microscopy of polyethylene lamellae standing normal to the surface of uniaxially drawn Mylar on which they had been crystallized epitaxially. Links of this kind are similar to those observed in the first instance and are evidently produced by the same mechanism. We consider also, in a critical way, the formation of intercrystalline links and tie molecules, and their important influence on mechanical properties, in bulk polymers crystallized either from quiescent or flowing melts. We show that links and tie molecules are formed mostly during primary crystallization, and few additional ones are produced during later stages. We examine, finally, a variety of ways in which links and tie molecules strengthen adhesion between crystals to promote ductile, rather than brittle, response to applied stress.

ISSN:0021-8979    

DOI:10.1063/1.1659827

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An apparatus based on Bridgman's bellows method, originally devised for fluids, has been constructed for use with solid samples. Mercury is employed as the confining liquid. The operating range is 0≤t≤200 °C and 1≤P≤2000 bar. Calibration with benzene and mercury shows an accuracy of ±2×10−4cm3/g in the measurement of the specific volume change. A detailed investigation of two systems, polystyrene and poly(orthomethylstyrene) in the glassy and liquid states is undertaken. TheP‐V‐Tresults in both states can be well represented by the Tait equation, with the single parameterBas an exponentially decreasing function ofT. Similar to the earlier result for polystyrene, a &bgr;‐relaxation region is observed in terms of the isothermal compressibility of the methylated polymer withT&bgr;/Tg≃0.70 for both. The pressure coefficients for the two transition temperatures are discussed. For the glass transition, the Ehrenfest‐type equation appears to be obeyed by the low‐pressure glasses (formed by cooling the liquid at atmospheric pressure) but not the high‐pressure glasses (formed by pressurizing the melt isothermally). The experimental compressibility factors, the internal pressures, and the changes in internal energy upon compression are compared with the predictions of the cell theory of the Brussels group and the hole theory of Simha‐Somaynsky. The characteristic parameters are evaluated by a superposition of the experimental and theoretical atmospheric‐pressure isobars and from the ordinates of one isotherm. In the temperature and pressure range considered here, the performance of the cell theory is quite satisfactory. Very good agreement in respect to theP‐V‐Tfunction is obtained for the hole theory.

ISSN:0021-8979    

DOI:10.1063/1.1659828

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Morphological changes produced by the annealing and melting of the polyoxymethylene crystals that polymerize inside irradiated trioxane crystals were observed. The crystals in which the polyoxymethylene chains were oriented parallel to the threefold axis of the trioxane underwent major reorganization when held at 184°C for 30 sec. The polyoxymethylene crystals in which the chain axis was inclined at a large angle with respect to the threefold axis of the trioxane transformed and melted at temperatures approximately 5°C lower.

ISSN:0021-8979    

DOI:10.1063/1.1659829

出版商:AIP    

年代:1971

数据来源: AIP