Chain anchoring

Fig. 3 a-c. Summary of data from different laboratories, obtained by surface force measurement, on the average layer thickness L as a function of tethered chain length for flat, tethered layers constructed by adsorption of amphiphilic polymers on mica. Adapted from Ref. 21. (a) Data of reference 20 on poly-tert-butylstyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (b) Data of references 11 and 12 on polystyrene chains anchored by adsorbing blocks of poly-2-vinylpyridine. (c) Data of references 13 and 14 on polystyrene chains anchored by adsorbing zwitterionic groups [13] or by small adsorbing blocks of polyethyleneoxide [14]... 

M-L Valero, E.Giralt, D Andreu. Optimized Asp/Glu side chain anchoring in synthesis of head-to-tail cyclic peptides by Boc/OFm/benzyl chemistry on solid phase, in R Ramage, R Epton, eds. Peptides 1996. Proceedings of the 24th European Peptide Symposium, Mayflower, Kingswinford, 1998, pp 857-858. 

If the small particles did not deposit as a coating but tended to form chains anchored to the large particle, the physical floe diameter would be... 

A number of approaches may be adopted to achieve chemical synthesis of a peptide. The Merrifield solid phase synthesis method is perhaps the most widely used. This entails sequential addition of amino acids to a growing peptide chain anchored to the surface of modified polystyrene beads. The modified beads contain reactive chloromethyl (—CH2CI) groups. 

Table 9 Examples for the Synthesis of Head-to-Tail and Side-Chain-to-Tail Cyclic Peptides Using the Side-Chain Anchor Method 109 340 347352-i7 wm-i9R t071...

B) Cleavage of a polypeptide loop formed as in (A) by a leader peptidase to give a polypeptide chain anchored by a positively charged cluster near its C terminus. (C) Membrane topology of the E. coli leader peptidase. The active site is in the periplasmic domain. See Tschantz et al.5S0... 

About four dimethylsiloxane pendent chain units next to the grafting site were immobilised due to chain anchoring to the silica surface. 

Polymer chains anchored on solid surfaces play a key role on the flow behavior of polymer melts. An important practical example is that of constant speed extrusion processes where various flow instabilities (called sharkskin , periodic deformation or melt fracture) have been observed to develop above given shear stress thresholds. The origin of these anomalies has long remained poorly understood [123-138]. It is now well admitted that these anomalies are related to the appearance of flow with slip at the wall. It is reasonable to think that the onset of wall slip is related to the strength of the interactions between the solid surface and the melt, and thus should be sensitive to the presence of polymer chains attached to the surface. 

With chains anchored to the surface, either by a chemical grafting or an insoluble block, good solvent conditions always produce a repulsion. Consequently, copolymers, e.g., diblock, comb, or graft, tend to comprise the most effective stabilizers. Direct grafting to the particle is feasible but requires chemistry specific to the particle (e.g., Green et al., 1987). Advances in synthetic polymer chemistry continue to increase the types of polymers available for this application (e.g., Reiss et al., 1987). 

Another measurement on a system of copolymers consisting of polyfcthylene-oxide-fc-styrene) (PEO-PS) chains anchored to a glass surface in toluene solution was reported by Fytas et al. [18], The picture of the layer is that the PEO part attaches to the glass while the PS part dangles in the solution. The thickness of... 

Role of polymer chains anchored to the wall at low surface densities... 

The amplification factor P/Ng is responsible for a strong dissipation and this is the origin of the suppression of slip at low shear rates when chains anchored to the solid wall are present. Knowing Vtube. the friction force associated with one P chain can be estimated the dissipation... 

Side-chain anchoring of protected Asp or Glu to the Phacm resin 5 can take place with both low yields and substantial levels of epimerization at the a-carbon. The best route to overcome these problems is to use the corresponding cesium or zinc salts in conjunction with bromomethylbenzyl resins,or through a Mitsunobu reaction using triphenylphosphine and DEAD.[i 2]... 

Besides the methods described above for the side-chain anchoring of Ser and Thr, the 3,4-dihydro-2//-pyran-2-functionalized-resin and handle 331 23,124] Table 3) allows the preparation of peptide alcohols by treatment with TEA in the presence of scavengers. Furthermore, the alkylation of Fmoc amino alcohols with a diphenyldiazomethane polymeric resin 34 gives rise to a benzhydryl ether, which can be cleaved with TFA/CH2CI2 (2 98) to give protected peptide alcohols. 

Figure 3.21. Monte Carlo surface pressure Isotherms for lipid-like molecules having 10 different conformational states available. 10.000 chains anchoring groups not specified. The filled circles are computed drawn lines are guides for the eye. Model parameters mimic dlpalmltoyl phosphatidyl choline (DPPC) monolayers. (Redrawn from Mouritsen et al. (1989).)...

Frinha, J.P.S. d Oliveira, J.M.R. Martinoho, J.M. Xu, R. Winnik, M.A. Structure in tethered chains polymeric micelles and chains anchored on polystyrene latex spheres. Langmuir 1998, 14, 2291-2296. 

AB graft with several B chains — Anchor chain A... 

As mentioned earlier, the acceleration type behavior is explained by an increase in surface due to breakup of catalyst particles subjected to mechanical pressure of growing polymer chains anchored to the catalyst active centers. The smaller the particle size, the greater the mechanical energy required for further size reduction, and so the particle size—and hence the specific surface area—would reach some asymptotic value. The stationary polymerization rate would correspond to this catalyst particle size. 

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