Polydiacetylene mechanical properties

A deeper insight into the reaction mechanism may elucidate the conversion dependence of the molecular weight and its distribution. Owing to the extreme insolubility of the better investigated polydiacetylenes like PTS, however, only very limited experimental data have been available until recently from indirect determinations, e.g. from mechanical properties or diffuse scattering of partially polymerized crystals. 

Resonant raman spectroscopy has proved to be another valuable tool for the study of the structure of the polydiacetylene chain. Due to the resonance enhancement the spectra are compared to greatly simplified, infrared spectra and show as principle feature only the in-plane modes of the polymer chain. The correlation of the CsC and C = C stretching modes and their temperature dependence have been interpreted as resonances between the mesomeric structures (I) and (II) i32) Hoy(rever, a model using simple anharmonic force constants for the acetylene structure (II) is in good agreement with the experiment, e.g, the temperature and pressure dependence of the vibration frequency and the mechanical properties... 

Relationship between Structure and Mechanical Properties of Polydiacetylenes... 

Folydlacetylenes offer a unique opportunity of studying structure/property relationships in polymers. This paper is concerned with structural factors which control mechanical properties. The effect of the size of side-groups upon the Young s moduli of different polydiacetylenes is discussed briefly. The effect of internal and surface defects upon the strengths of individual fibres is also described. Examples are given of how Raman spectroscopy can be used to follow the deformation of fibres and it is shown how this can be extended to fibres in composites. The general mechanical properties of the composites are also described. 

This paper reviews recent work upon structure/mechanical-property relationships in polydiacetylenes. It is shown how this has led to the development of high strength polydiacetylene single crystal fibres and their performance as reinforcing fibres in composites is described. 

Polydiacetylenes allow a unique opportunity to study the relationship between structure and mechanical properties in polymer crystals. The technique of solid state polymerization 11] enables highly-perfect poiydiacetylene single crystals to be produced with macroscopic dimensions. For example single crystal fibres can be grown with lengths in excess of 50 mm 12.3]. Crystalline polymers produced by crystallization from both dilute solution and the molten state are invariably only semi-crystalline 14]. Melt-crystallized... 

One of the most remarkable aspects of the mechanical properties of polydiacetylenes Is that it Is not possible to measure any time-dependent deformation (or creep) when crystals are... 

It is well-established that the composites produced by incorporating high-modulus fibres in a matrix of epoxy resin or metal can have outstanding mechanical properties. Polydiacetylenes offer considerable promise for reinforcement In polymeric matrices because they have the following properties which have been described in previous sections. 

Recent investigations [61. 623 into the behaviour of polydiacetylene fibres In epoxy resin matrices have shown that not only such composites have good mechanical properties but that Important fundamental details of the mechanisms of fibre reinforcement can also be revealed from their study. 

This work upon the mechanical properties of polydiacetylene/epoxy composites has proved to be extremely... 

The per chain modulus of this pol3nner is about equal to that of diamond in the [110] direction. A polyethylene fiber with the same per chain mechanical properties would have an ultimate tensile strength in excess of one million psi. The theoretical modulus calculated for a defect free polydiacetylene chain using a spectroscopic force field is within 10% of the observed modulus. This contrasts with the case for conventional polymers, where the bulk tensile modulus is typically much less than 50% of the theoretical (spectroscopic) modulus. 

Owing to the mechanism of the topochemical reaction the polyconjugated polymer chain is of exceptional purity and stereochemical regularity. Polydiacetylene crystals are thus ideally suited to study the inherent optical and electrical properties of polyconjugated chains. These unique features have attracted considerable attention and in recent years the topochemical polymerization of diacetylenes has developed to... 

It is the main purpose of the following articles by V. Enkelmann, H. Bassler and H. Sixl to review the present status of polydiacetylene research from the point of view of structure and reactivity including all the details known on the mechanism of polymerization of various diacetylenes. The material science aspects will not be treated to the same depth with exception of the photopolymerization and its possible application in the contribution of H. Bassler. Similarly, the solution properties of polydiacetylenes are not touched upon. The interested reader is refered to the current literature where the problems encountered when studying the solutions and the recrystallization behaviour of polyconjugated macromolecules have just started to be discussed adding a new chapter to the statistical mechanics and hydrodynamic behaviour of macromolecules... 

In this scenario, polydiacetylenes were nevertheless interesting, as the mechanisms of their large non-linearity form a good basis to build on. Only a few modifications were well characterised and there was a general lack of measurements with single crystals due to problems with sample preparation. Therefore, the aim was to characterise systematically the influence of side groups on the optical properties, preferably in the macroscopically ordered, stable, and reproducible framework of good and - later on - thin crystals. 

In this chapter, a detailed description is given of these intriguing optical properties of certain polythiophene derivatives, and their analogy with chromic effects found in other 7r-conjugated (polydiacetylenes) and or-conju-gated polymers (polysilanes) is discussed. In order to explain these transitions, various molecular mechanisms are described. Finally, potential applications of these interesting optical effects are presented. 

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