摘要:

We first summarize in a table the salient features of three dynamic mechanical measuring instruments featured at this symposium: torsion pendulum, torsional braid and Rheovibron viscoelastometer. It is concluded that while each instrument performs one or more functions better than the other, there is a tendency for all three instruments to approach each other's capabilities with time. Some general observations are presented about the main uses of dynamic mechanical testing and about the nature of mechanical loss spectra. The correlation of these mechanical loss spectra with other types of physical measurements is stressed. The Simha-Boyer free volume quantity, Δα Tg, is shown to decrease with trans content in a series of butadiene polymers and copolymers, presumably because of an in-chain crankshaft loss mechanism whish generates free volume in the glassy state. Related cases for the nylons, ethylene-vinylacetate copolymers, and polyethylene are cited. It is suggested that the strength of T < tg mechanical relaxation process may correlate directly with the quantity, αg - 2 × 10−4°−1where αg is the coefficient of cubical expansion immediately below Tg. Several examples are included to show that thsi quantity varies regularly with chemical structure. Finally we invoke a theory of Goldstein that every glass transition should have a Tβ<Tg transition, and the empirical finding of Matsuoka and Ishida that Tβ = 0.75 Tg to conclude that Tg of amorphous polyethylene cannot be 145 ± 10°K and is probably 195 ± 10°K. The importance of dynamic mechanical loss data in understanding other physical data on polymers is affirmed.

ISSN:0022-2348    

DOI:10.1080/00222347408212190

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A review of the present status of torsional braid analysis (TBA) includes discussion of instrumentation, specimen preparation, theory, and data reduction. The obtained thermomechanical spectra (∼1 cps) are discussed in terms of advantages which result from the use of small specimens. Applications include structure-property relationships, kinetics of crosslinking, and optimization of thermomechanical behavior in reactive systems.

ISSN:0022-2348    

DOI:10.1080/00222347408212191

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A general review of our investigations in the last few years on the cryogenic dynamic mechanical properties of polymers is discussed. The differences in the mechanical spectra between cis and trans polybutadienes and polyisoprenes are considered in terms of molecular structure and packing density. Tensile stress-strain properties of these polymers are considered in relation to secondary glass transitions, free volume, and rate of cooling. Also, the effect of simple organic liquids and solid fillers on the mechanical spectra of polymers is presented. The nature of the polystyrene γ and δ peaks is considered in relation to our investigations on substituted polystyrenes and mechanisms by which diluent molecules modify the polystyrene spectra.

ISSN:0022-2348    

DOI:10.1080/00222347408212192

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The dynamic mechanical relaxation behavior (1cps) of two series of amorphous polyolefins, ─(CH2)mC(CH3)2─ and ─(CH2)mC(CH3)(CH2CH3)─ where m = 1, 2, 3 was investigated from 4.2°K to the glass transition. Most of the polymers show a damping maximum or pleateau in the 40 to 50°K region. Various mechanisms which have been suggested for cryogenic relaxations in amorphous polymers are considered as they might relate to the polyolefins. Two secondary relaxation processes above 80°K are distinguished. A relaxation at about 160°K (β) in the second and third member of each series is associated with restricted backbone motion. This process requires a certain degree of chain flexibility since it is not observed in the first member of each series. A lower Temperature process (γ) is observed in each member of the second series and is attributed to motion of the ethyl side group.

ISSN:0022-2348    

DOI:10.1080/00222347408212193

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The results from broad-line NMR and dynamic mechanical studies on solid polymers over a broad temperature range are compared in general terms. Measurements on specific polyamides are then presented and discussed. These polyamides include four synthetic aromatic materials: poly(1, 3-phenylene isophthalamide), poly(1, 4-phenylene terephthalamide), poly(diphenylene isophthalamide), and poly(diphenylene terephthalamide), three synthetic poly (α-L-amino acids): poly(γ-benzyl L glutamate) (PγBLG), poly(L-leucine)(PLL), and poly(L-proline) (PLP), and the naturally occurring material collagen.

ISSN:0022-2348    

DOI:10.1080/00222347408212194

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The swelling of polyacrylonitrile (PAN) film in aqueous I2/KI (or I3−) solutions of different concentrations up to 2.0 molal has been investigated, using both biaxially oriented and unoriented film. The absorption curve (equilibrium absorption vs concentration) for oriented film shows three distinct steps, at concentrations of 0.25, 0.65, and 1.6 molal, leading to weight increases of the sample of approximately 250%, 2000%, and 3200%, respectively. In unoriented film, smooth progressive increases of absorption are observed in place of the first and third steps; only the second abrupt step remains. A significant difference in desorption behavior is seen in extraction experiments carried out above and below the second step. It is hypothesized that the first and third steps of swelling correspond to the penetration of two different “amorphous” phases in the polymer, which together with a crystalline phase would indicate a three-phase structure for PAN. The second step of swelling may represent a conformational transition of the molecules in the phase penetrated in the first step. The effects of iodine swelling and extraction on the dynamic mechanical spectrum of PAN were also investigated, and it seems possible to associate the swelling in the region of the first and third steps with the two peaks (or transitions) in the tan δ curve of PAN, which might be regarded as glass transitions of the two amorphous phases. An unusual behavior of sample length vs temperature was observed during the dynamic mechanical measurements in the temperature region of these two transitions. Stress-strain curves were also measured on samples containing different amounts of absorbed iodine.

ISSN:0022-2348    

DOI:10.1080/00222347408212195

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Both static and dynamic thermomechanical techniques have proved to be useful in elucidating effects of molecular structure and morphology on the behavior of poly(vinyl chloride). Indeed, such methods are sometimes sensitive to rather small differences in, for example, crystallinity. In this paper, the current literature is reviewed, with emphasis on the relation between stereoregularity, crystallinity, and mechanical relaxation behavior. In order to interpret results of recent studies, simple models are then proposed for the typical morphologies encountered. Most experimental facts are consistent with the existence of very small plate-like crystallites, with intercrystallite spacings being inversely dependent on crystallinity, and, in turn, inversely dependent on polymerization temperature.

ISSN:0022-2348    

DOI:10.1080/00222347408212196

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

PET films were compressed uniaxially, below Tg, allowing slip at the surfaces, a treatment similar to cold rolling. The dimensional changes produced were fully recoverable on heating above Tg. The compressed polymer showed anomalous thermal behavior near Tgand exhibited a lower cold crystallization temperature and a greater low-temperature expansion coefficient perpendicular to the plane of the film.

ISSN:0022-2348    

DOI:10.1080/00222347408212197

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Examples are shown of the application of wide-angle X-ray diffraction, differential thermal analysis, and dynamic mechanical spectroscopy to developing an understanding of the structure-property relationships of a biological tissue, the outer layer of mammalian epidermis.

ISSN:0022-2348    

DOI:10.1080/00222347408212198

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Dynamic mechanical spectra (−180 > 140°Δ. ∼1 cps) of amorphous stereoregular poly(methyl methacrylate)s and poly(t-butyl methacrylate)s with assigned microtacticities are presented and discussed. An intermolecular argument (“interlocking”) is invoked to account for the higher Tgof syndiotactic vis a vis isotactic PMMA, in spite of the higher density of the latter at 30°C. An argument is presented to show that the Tβ/Tgratio is not only a measure of the degree of coupling of the Tβand Tgprocesses, but also of the degree to which intermolecular factors influence these processes. The greater extent of the low-temperature irreversibilities observed in the thermomechanical spectra of poly(t-butyl methacrylate)s is attributed to the brittle character induced by the bulky side groups which presumably weaken cohesive forces. Furthermore, internal stress generation and brittleness of the polymers are shown to be connected to freezing out of side group motions.

ISSN:0022-2348    

DOI:10.1080/00222347408212199

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor