HIGHLY CROSS-LINKED POLYMERS

A unique feature of in situ encapsulation technology is that polymerization occurs ia the aqueous phase thereby produciag a condensation product that deposits on the surface of the dispersed core material where polymerization continues. This ultimately produces a water-iasoluble, highly cross-linked polymer capsule shell. The polymerization chemistry occurs entirely on the aqueous phase side of the iaterface, so reactive agents do not have to be dissolved ia the core material. The process has been commercialized and produces a range of commercial capsules. 

LDPE homopolymers in the 0.2—150 melt index or 100, 000 20,000 mPa s(= cP) viscosity range. Specialty polymers such as greases and waxes or highly cross-linked polymers are not included. 

The ultraphosphates are situated between P O q and the metaphosphates. These comparatively Htde-known, highly cross-linked polymers contain at least some of the phosphoms atoms as triply coimected branching points. This stmctural feature is quite unstable toward hydrolysis. Ultraphosphates undergo rapid decomposition upon dissolution. In amorphous ultraphosphates, the cross-linking is presumably scattered randomly throughout the stmctural matrix in contrast, crystalline ultraphosphates have a regular pattern. 

As will be seen from curves A, B and C of Figure 9.1, the softening point of an amorphous polymer, i.e. the temperature at which the modulus drops catastrophically, is closely associated with the T. (Such softening does not of course occur in highly cross-linked polymers, as in type D, unless degradation also takes place.)... 

Le May JD, SwetlinBJ, Kelley FN (1984) In Labana SS, Dickie RA (eds) Characterization of highly cross-linked polymers, ACS Symposium Series 243, p 165... 

C13-0122. Glyptal is a highly cross-linked polymer made by heating glycerol and phthalic anhydride. Show the structure of glyptal. 

S.S. Labana and R.A. Dickie (Eds.), Characterization of Highly Cross-Linked Polymers, American Chemical Society, Washington, DC, 1984. 

Varian (see Catalog, SPE products) Bond Elut Plexa Highly cross-linked polymer with hydroxylated surface Hydrophobic retention of small molecules and hydrophilic exclusion of proteins See catalog... 

It is not possible to determine the molecular weight of highly cross-linked polymers and natural polymers by GPC as they do not dissolve in tetrahydrafuran. Accurate results for molecular weight can only be obtained if the polymer standards used have similar properties to the polymer employed to prepare the nanoparticles. In most cases, this similarity is absent. 

Crosslinking reduces the solubility dramatically. Medium or highly cross-linked polymers do not dissolve at all but form more or less swollen gels, depending on the degree of crosslinking. 

As the polymerization proceeds, the viscosity of the polymer system increases steadily to finally yield a solid and rigid highly cross-linked polymer in which the segmental mobility is quite restricted. Consequently, the encounter probability of the polymer radicals with the reactive acrylate double bonds is then sharply reduced, which accounts for the rate slowing down observed in the latter stages of the irradiation (Figure 2). 

Figure 29-2 Schematic representation of the conversion of an uncross-linked thermosetting polymer to a highly cross-linked polymer. The crosslinks are shown in a two-dimensional network, but in practice three-dimensional networks are formed.

Cooper, A. I. Hems, W. P. Holmes, A. B. Synthesis of Highly Cross-Linked Polymers in Supercritical Carbon Dioxide by Heterogeneous Polymerization. 

Each phenol nucleus in this molecule has two additional reactive sites (the other ortho and/or para positions) where connections to other phenols can occur by this same mechanism. Ultimately, a highly cross-linked polymer is formed. 

The second component of the glue is composed of a trifunctional amine such as di-ethylenetriamine. When the two components are mixed, the three nucleophilic nitrogens of the triamine react with the epoxide groups to form a highly cross-linked polymer, as shown in the following equation ... 

This is referred to higher cross-linking than in case of THF. A low chlorine content (0.06 wt. %) is found for the reaction of tetrachlorosilane with bis(trimethylsilyl)carbodiitnide which indicates that the reaction proceeds almost quantitatively. The pyrolysis of the highly cross-linked polymer leads to... 

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