Crosslinked state

Probably most of these investigators were studying poly(dichlorophosphazene) in the partially crosslinked state. Most of this was summarized by Allcock (.9). More recently, highly purified, uncrosslinked II has been examined in the solid state (21). The unstressed polymer is amorphous at room temperature, but crystallization can be induced by cooling or stretching techniques. The glass transition temperature, measured by Torsional Braid Analysis, is -66°C (22). 

Formation, Structure and Properties of the Crosslinked State Relative to Precursor Architecture... 

Classifying polymers in their crosslinked state according to end-use properties, polymer networks include vulcanized rubbers, crosslinked thermosetting materials, protective coatings, adhesives, polymeric sorbents, microelectronics materials, soft gels, etc. Polymer networks in contrast to uncrosslinked polymers,... 

FORMATION, STRUCTURE, PROPERTIES - CROSSLINKED STATE composed of units only single-connected to network structure... 

In the crosslinked state, epoxy resins are highly resistant to chemicals, temperature, and solvents and are also endowed with good electrical properties. They are therefore employed, for example, as casting resins in electro- and electronic industry as well as resistant lacquers and coatings. Moreover, they possess excellent adhesive power for many plastics, wood, and metals ( reaction adhesives two-component adhesives ). 

In Eq. (III-9) the deformation ratios are defined with respect to a reference state in which the chain dimensions are such that they do not exert any elastic forces on the crosslinks (state of normal coiling). In general, the chains in a network may not actually be in this state at the beginning of a deformation experiment, because the ciosslinking process may quite well exert a, largely unknown, influence on the chain dimensions. 

Mason77 developed ideas about the distribution of the free-volume to explain the existence of the broad transition region from glassy to rubberlike state. He believed that there is some localization of that part of the free-volume that distinguishes the rubberlike state from the true liquid state in which the free-volume is not localized. In the non-crosslinked state of some rubbers there may be an arbitrary distribution of the free-volume Vf connected with the free-volume of each monomeric... 

The different behavior of thermoplastics and thermoset materials at increasing temperature is schematically shown in Figure 3.6. Depending on their chemical composition, softening and melting temperature of thermoplastic materials can vary to a great extent. Hot-melt adhesives, for example, are applied as melt within a temperature range of approx. 120-240 °C. In the case of thermoset materials the depicted temperature dependence depends much on the crosslinked state. 

The results show that the crosslinking state and the degradation processes in the epoxy network depend not only on the type of curing agent and the aging regime. The properties of the stainless steel also change these properties within the epoxy interphase at the contact. 

In Table 1 this bulk pol5mierization data and certain calculated values are presented. The experiments used covered a range of conversions, including one preparation carried to a highly crosslinked state. 

Dielectric constant of plastics materials generally decreases vdth frequency.This is also observed in our case. The dielectric constant of a cured polymer is less than that of its uncured state. This is diae to the restricted motion of the polar grovps present in the polymer sanple in the crosslinked state. 

K. Dusek and M. Duskova-Smrckova. Fcamation, structure and properties and the crosslinked state relative to precursor architecture, in Dendrimers and Dendritic Polymers. John Wiley Sons Ltd. West Sussex, J.M.J. Frechet and DA. Tomaha Eds. pp. 111—145, 2001. 

Many emulsifier variations have been used during the course of this research effort. The effect of emulsifiers has been observed on numerous properties of the emulsions generated. A study was initiated to determine the effect of emulsifier structure on the autoxidation rate of reaction. Figure 5 represents the oxygen pressure variation during successive reactions as a function of the time required to reach a densely crosslinked state. The Gafac RE-960 system is dramatically slower relative to the autoxidation rate when T-Det and dodecyl sodium sulfate or Igepal CO-850 and dodecyl sodium sulfate surfactants are employed. 

Figure 3.21 Schematic drawing of various crosslinking states [3]...

We will consider here cases in which linear chain molecules are randomly crosslinked. Therefore, we will deal with the crosslinked state with maximum probability given the various chain lengths and number of crosslinks. 

Here c is a geometrical constant ( 15 for 5 = 2) and N is the average number of entanglements per chain in the pre-crosslinked state T is the relaxation time (by reptation) of a chain in this state. As the gel point is approached, the longest relaxation time does not diverge, according this treatment, but approaches a constant value... 

Crosslinking with peroxides has been known since 1915 when Ostromyslenski disclosed that natural mbber could be transformed into a crosslinked state with dibenzoyl peroxide (a.27). However, little interest in peroxide crosslinking evolved until the development of fully saturated ethylene-propylene copolymers in the early 1970s. 

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