Crosslinked species

The term "macromolecules" implies that the subject matter includes chain molecules that may be built up of repeat units, as well as more complex ring, branched, or crosslinked species (for example, see Organo-Oxo-Element Macromolecules Related to Sol-Gel Processes, and contributions by Murray (p. 408) or Seyferth (p. 143)). 

Step growth polymerization can also yield highly crosslinked polymer systems via a prepolymer process. In this process, we create a prepolymer through a step growth reaction mechanism on two of the sites of a trifunctional monomer. The third site, which is chemically different, can then react with another monomer that is added to the liquid prepolymer to create the crosslinked species. We often use heat to initiate the second reaction. We can use this method to directly create finished items by injecting a mixture of the liquid prepolymer and additional monomer into a mold where they polymerize to create the desired, final shape. Cultured marble countertops and some automotive body panels are created in this manner. 

We have found that the Cr olates produced by hydrolysis of Cr(III) ions are the reactive crosslinking species. The different gelation rates are due to the different degrees of olation. Furthermore, by controlling the degree of hydrolysis, Cr(III) derived from various sources mentioned above can exhibit the same gelation rate. 

As the amount of polymer in the system increases, the probability of interaction of growing free radicals with polymeric (inactive) species either by transfer or, sometimes, by copolymerization through residual double bonds must increase. Because such reactions automatically give rise to branched and crosslinked species, reliable experimentation aimed at studying these processes is difficult to achieve. This follows from the fact that the region of the reaction in which study is essential is precisely that region in which there are rapid changes in the characteristics of the polymer produced, particularly in solubility. This is of... 

The reaction of [(S,/ ,R,S)-BipPt(H20)2]2+ with d(GpG) also unexpectedly yielded two products of comparable abundance. One adduct was characterized to be the normal HHl form. The G H(8) shift pattern of this HH form, namely 5 -G H(8) upfield and 3 -G H(8) downfield, is the same as that found for ds-Pt(NH3)2(d(GpG)), suggesting that these two adducts have similar hydrogen bonding and base canting. The 31P-NMR signal at -2.8 ppm is also a common feature of HH adducts. The second adduct, determined to be an HT conformer, has several unique spectral features. Of particular note, the relatively upfield shifts of both G H(8) signals (7.91 and 7.77 ppm) and an upfield-shifted 31P-NMR signal (-4.6 ppm) of the HT conformer are unprecedented for a major conformer of an adjacent G -G intrastrand crosslinked species. 

We have synthesized aldehyde-functionalized silanes as a new class of spacer molecules for silica surfaces. The aldehyde group can be used to attach biomolecules directly to the surface, with no bifunctional crosslinking species required (Fig. IB) [3]. As many immobilization problems are closely related to the use of the crosslinking agent (e.g., glutaraldehyde tends to form undesirable polymers) [4], the development of a one-step immobilization method is a significant improvement. 

Figure 2. (A) Growth curve for pristine sample showing results of one site fit (dotted line) and two site fit (solid line - components are shown underneath curve in red) (B) Schematic of network structure of typical engineering silicone with both short and long chain constituents and standard four site crosslinking species and highly functional crosslinking sites. (Figure 2B is reproducedfrom reference 17. Copyright 2005 American Chemical Society.) (See page 7 of color insert.)...

Early work on the application of NMR conventional techniques to the study of solvent swollen crosslinked polymers was reported by Stenlicht and co-workers [92] and Schaefer [93]. The first detailed work on the chlorome-thylated polystyrene resins used in solid phase synthesis appears to be by Manatt and co-workers [94]. They employed a 0.095% crosslinked species supplied by the Dow Chemical Co. and chloromethylated this to varying degrees. noise decoupled C NMR spectra were recorded in the usual... 

Fig. 2.3 Reaction of IsoK/LG with primary amines to form stable adducts. Primary amines including lysine react with IsoK/LGs to form a hemiaminal adduct. Unlike most aldehydes which can only form the highly reversible Schiff base adduct, the hemiaminal adduct of y-ketoaldehydes can undergo a second nucleophilic attack to form a pyrrolidine adduct which dehydrates to form an irreversible pyrrole adduct. In the presence of oxygen, the pyrrole is converted to lactam and hydroxylactam adducts. Oxidation of the pyrrole leads to formation of stable crosslinked species...

The mica grows in a preferred lateral direction because the residual glass is fluidized by the B2O3 flux and is also designed to be deficient in the crosslinking species potassium. 

The time order of introducing the different crosslinking species in compound crosslinking was shown to lead to different morphologies, and hence different properties. The possibilities of selectively decrosslinking polymers was also discussed. 

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