Group 16 systems chains

The stable phase in the Zn3(P04)2-Zn3(V04)2 system has the composition Zn3P1.5V0.sOs. The structure consists of sheets parallel to (100) formed of chains containing rings of comer-shared (Zn-1)04 and (V,P)04 tetrahedra the (Zn-2)04 groups form chains parallel to the b axis through corner sharing (Zn—O = 1.95, 1.96 A). 

There are two basic methods for making polymer materials photo-chemically degradable.1,2 One method is to chemically incorporate a chromo-phore into the polymer chains. One commercially successful chromophore is the carbonyl group.1,2,7 Absorption of UV radiation leads to degradation by the Norrish type I and II processes or by an atom abstraction process (Scheme 1). Note that once radicals are introduced into the system, chain degradation occurs by the autoxidation mechanism (Scheme 2). 

Experimentally, also, reactive systems are much more complex than the preformed block copolymer systems because, typically, the reactive species have a distribution of molecular weights and may have several reactive groups per chain. Then there is not only the issue of how much of the graft copolymer is formed at the interface (Z) but also of which species react, e.g. is there preferential reaction of low N species ... 

Since reactive systems have a great practical relevance, many attempts have been made in recent years to adapt the techniques used for pre-made block copolymers to obtain more detailed information on the correlation between the interfacial structure and fracture toughness. The simplest case is that of a dilute solution of monodisperse chains with one reactive group per chain, located at the chain end. In this case, the mechanical problem of reinforcement becomes similar to that of single connector diblock copolymers discussed earlier. The important issues are then mostly related to the competition between grafting ki-... 

The polymers possess one sulfonyl group per chain, which can be utilized as end-functional polymers as discussed later (section III.B.l). Narrower MWDs (MJMn = 1.2—1.4) were obtained in MMA polymerization with 1-32 as well as 1-33 and 1-34 in conjunction with CuCl/L-1 in />xylene at 90 °C.175 In a homogeneous system with CuCl/L-4,1-32 can afford narrow MWDs MJMn = 1.1—1.3) for styrene, MMA, and nBA.176 The fast addition of the sulfonyl radical to these monomers was evidenced by H NMR analysis of the reactions, where the apparent rate constants of initiation are 4 (for styrene and MMA), 3 (nBA), and 2 (MA) orders of magnitude higher than those of propagation. A similar controlled and homogeneous polymerization of MMA with 1-32 (X = CH3)/ CuBr/L-4 was reported in diphenyl ether at 90 °C.178 A better control of molecular weights and MWDs with 1-32 (X = CH3)/CuBr/L-9 in diphenyl ether was also... 

Alkali metal and alkaline earth polyphosphates crystallize as short chains, two to six phosphate groups per chain or very long chains with hundreds to thousands of PO3 per chain. All polyphosphates in the alkali metal and alkaline earth systems are amorphous in the intermediate chain lengths. Control of the short chain length polyphosphates, both crystalline or amorphous, is a function of R, the M2O-P2O5 ratio. The control of the chain lengths of very long crystalline polyphosphates as Maddrell s salt, Kurrol s salt, and calcium phosphate fibers is not well understood. 

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