摘要:

By polymerizing phenylacetylene in the absence of initiator and in vacuo while observing electron spin resonance, it was established that the paramagnetism in the thermal polymer (PPA-T) cannot be due to interaction with oxygen but must be a property of the chemically uncontaminated macromolecule. The ESR behavior of a concentrated solution of PPA(T) in monomer and of solid (amorphous) PPA(T) displays a Curie dependence, whereas the ESR absorption of crystalline polymer made with coordination catalysts increases by one to two orders of magnitude over the temperature of about 60 to 140°C. The major portion of the XRD crystallinity disappears more sharply, at about 120°C. The paramagnetism in PPA must therefore be associated with “conformational defects” in the individual macromolecules.

ISSN:0022-2348    

DOI:10.1080/00222346808212446

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The crystal structure of trans-1,4-polybutadiene has been reported by Natta et al. to be pseudo-hexagonal below its solid-phase transition temperature. In the present X-ray structure analysis, it is revealed that the crystal belongs to the monoclinic system with the space group P21/a. The unit cell, with the lattice constants a = 8.63 Å, b = 9.11 Å, c = 4.83 Å, and β = 114°, includes four molecular segments.

ISSN:0022-2348    

DOI:10.1080/00222346808212447

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

It is shown that a free-volume treatment of the relaxational behavior of a polymer can be extended into the glassy region. A modified form of the WLF equation is derived in which the temperature is replaced by Te, a parameter related to the “frozen” free volume in the glass and defined such that Te = T at equilibrium. Measurements of the isothermal volume contraction of polystyrene and poly(methyl methacrylate) between −20 and + 95°C are used to estimate the “frozen” free volume and to calculate the temperature dependence of log(aT) below Tg. The calculated shift factors are compared to experimental values for the glassy state, and good agreement is obtained by selecting an arbitrary, but reasonable, equilibrium glass volume-temperature curve. The slope of this equilibrium glass curve is smaller than the experimental volume curve at some finite cooling rate. The data indicate that the glass is not an “iso-free volume” state and that the relaxation mechanisms in the glass are controlled primarily by the free volume, at least in the vicinity of Tg. A quantitative definition of the role of free volume in the glassy state requires evaluation of the quantities ∂ log aT/∂V)T,Pand (∂ log aT/∂T)v,p; sufficient data of this type are not presently available.

ISSN:0022-2348    

DOI:10.1080/00222346808212448

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The phenomenon of polymorphism in poly(vinylidene fluoride) has been observed recently by several authors. It has also been reported that high-resolution NMR measurements demonstrate the presence in this polymer of head-to-head linkages, resulting from the “backward” addition of from 5-6% of the monomer units. Since the van der Waals radii of fluorine (1.35 Å) and hydrogen (1.1-1.2 Å) are similar, the cocrystallization in a polymer chain of units that differ only by the substitution of fluorine atoms for hydrogen atoms is not unexpected. The two polymorphic forms of poly(vinylidene fluoride), examined in this investigation, have different chain conformations. Chains in phase I have a planar zigzag conformation, while chains in phase II are assumed to exhibit a 21helical conformation. The incorporation into the polymer chain of small amounts of tetrafluoroethylene or trifluoroethylene comonomer favored the crystallization of phase I. This is in accord with the relative abilities, deduced from consideration of atomic size, of these comonomers to cocrystallize with vinylidene fluoride units in the two indicated chain conformations of the polymer. Since tetrafluoroethylene units are present in the head-to-head structure in the homopolymer, it can be concluded that the elimination of the head-to-head structure will eliminate or restrict crystallization in phase I.

ISSN:0022-2348    

DOI:10.1080/00222346808212449

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The crystallization and melting of poly(vinylidene fluoride) as a function of hydrostatic pressure was investigated. Poly(vinylidene fluoride) can be crystallized in at least two crystalline modifications at pressures of 1 atm (phase I and phase II). The crystallization of poly(vinylidene fluoride) under hydrostatic pressure over a range of conditions yields a new crystalline phase, designated phase III. The new phase melts at 185°C, approximately 25C° higher than phase I or phase II.

ISSN:0022-2348    

DOI:10.1080/00222346808212450

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Infrared spectra of poly[3,3-bis(chloromethyl)oxacyclobutane] (Penton) single crystals indicate that annealing perfects the crystals in a manner not involving a change in the relative amount of side-group rotational isomers. Other spectral and nonspectral considerations indicate that Penton has a highly crystalline but imperfect paracrystalline structure. The spectral differences between the two polymorphic forms are associated with differences in the magnitude of crystalline interactions rather than differences in relative amounts of side-group rotational isomers. An explanation for the nonthickening annealing behavior of Penton single crystals is offered.

ISSN:0022-2348    

DOI:10.1080/00222346808212451

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

An infrared spectroscopic method for measuring the percentage of the crystalline material in the α-modification is developed for poly[3,3-bis(chloromethyl)oxacyclobutane] (Penton). Good agreement with an X-ray method is found. This spectroscopic analysis is used to study the limiting conversion of β- to α-crystallinity during the heat-induced polymorphic transformation in Penton. The observed behavior is interpreted using the independent domain theory coupled with nucleation concepts.

ISSN:0022-2348    

DOI:10.1080/00222346808212452

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Wide-angle X-ray diffraction, small-angle X-ray diffraction, and electron microscopy have been applied to the study of the deformation of spherulitic polyoxymethylene at 125°C. The results show that a specific form of deformation occurs; during the early stages the molecules and the lamellae become oriented at an angle of 30° to the draw direction (the molecular axes are therefore tilted within the lamellae). The number of molecules so oriented increases with increasing draw up to about 150% deformation, after which the molecular axes tilt further, into the draw direction. The mechanism of deformation is seen to differ in different sectors of a spherulite. Folds are retained in the fully drawn material.

ISSN:0022-2348    

DOI:10.1080/00222346808212453

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

In a limited temperature range above the clearing point of crystal suspensions, submicroscopic entities representing unmeasurably small portions of the original crystal population may survive whose existence is revealed by crystals nucleated on subsequent cooling [1]. Factors influencing the number of these nuclei and the nature of these nuclei themselves were explored in the case of polyethylene.

ISSN:0022-2348    

DOI:10.1080/00222346808212454

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The paper demonstrates the potentiality of the self-seeding technique [3] for the growing of single crystals of polyethylene. It is shown that with appropriate measures, uniform single-layer crystals of strictly controlled habit can be obtained. Concrete recipes are given for the growing technique. The habit features are systematized as functions of crystallization temperature and concentration. Novel twin formations with coincident centers arising from this work are described and analyzed. Their origin is correlated with the result suggested by an associated investigation that the nuclei have a multicomponent structure [4]. The advantages of the new crystal-growing technique for other lines of work are pointed out.

ISSN:0022-2348    

DOI:10.1080/00222346808212455

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor