Star precursors

The Chemistry of Radical Polymerization Tabic 9,29 Star Precursors for NMP... 

Deuterated poly( 1,4-butadiene) (PB) networks have also been investigated [18-22], The linear precursor chains Mn from 75000 to 116000 g.mol 1) are homogeneously, selectively deuterated in the 1,4 positions, and randomly crosslinked with different types or amounts of crosslinkers. Star precursor chains deuterated at the center have also been used. 

The synthesis of tailor-made star-shaped polymers can be performed in several ways by means of a plurifunctional organometallic initiator, or by reacting a living precursor polymer with a plurifunctional reagent, to build the centra] body, or by block copolymerization involving a diunsaturated monomer (Scheme 3). 

The second method is the most efficient way to synthesize well defined star polymers. It involves preparation of a living monocarbanionic precursor, which can be accurately characterized. In a second step, this polymer is reacted with a pluri-... 

Testiculat androgens are synthesized in the interstitial tissue by the Leydig cells. The immediate precursor of the gonadal steroids, as for the adrenal steroids, is cholesterol. The rate-limiting step, as in the adrenal, is delivery of cholesterol to the inner membrane of the mitochondria by the transport protein StAR. Once in the proper location, cholesterol is acted upon by the side chain cleavage enzyme P450scc. The conversion of cholesterol to pregnenolone is identical in adrenal, ovary, and testis. In the latter two tissues, however, the reaction is promoted by LH rather than ACTH. 

Miktoarm stars of the A(BC)2 type, where A is PS, B is poly(f-bulyl acrylate) (PtBA), and C is PMMA [161] have been synthesized, by using the trifunctional initiator 2-phenyl-2-[(2,2,6,6-tetramethyl)-l-piperidinyloxy] ethyl 2,2-bis[methyl(2-bromopropionato)] propionate (NMP, ATRP) (Scheme 86). In the first step, a PS macroinitiator with dual < -bromo functionality was obtained by NMP of styrene in bulk at 125 °C. This precursor was subsequently used as the macroinitiator for the ATRP of ferf-bulyl acry-... 

In a typical synthesis, the corresponding precursor and calcium methoxyethoxide are dissolved in ethanol in an acidic medium (commonly HC1, 1N) under an argon atmosphere. The critical factors in obtaining crack-free star gels monoliths are the temperature and processing times, as indicated in Table 12.2. 

Fig. 12.12 29Si CP-MAS NMR spectra of star gels obtained from Star A and Star B precursors. Trifunctional silicon centers were named with the conventional T notation, where T refers to (SiO) R Si(OR)3 units and n to the number of bridging oxygen atoms surrounding the central silicon atom. In both BSC materials, the T2, T1 and T° relative contribution was...

Sharp, K.G. and Michalczyk M.J. (1997) Star gels New hybrid network materials from polyfunctional single component precursors. Journal of Sol-Cel Science and Technology, 8, 541-546. 

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