Primary radicals, properties

The newly formed short-chain radical A then quickly reacts with a monomer molecule to create a primary radical. If subsequent initiation is not fast, AX is considered an inhibitor. Many have studied the influence of chain-transfer reactions on emulsion polymerisation because of the interesting complexities arising from enhanced radical desorption rates from the growing polymer particles (64,65). Chain-transfer reactions are not limited to chain-transfer agents. Chain-transfer to monomer is ia many cases the main chain termination event ia emulsion polymerisation. Chain transfer to polymer leads to branching which can greatiy impact final product properties (66). 

NMR methods can be applied to give quantitative determination of initiator-derived and other end groups and provide a wealth of information on the polymerization process. They provide a chemical probe of the detailed initiation mechanism and a greater understanding of polymer properties. The main advantage of NMR methods over alternative techniques for initiator residue detection is that NMR signals (in particular nC NMR) are extremely sensitive to the structural environment of the initiator residue. This means that functionality formed by tail addition, head addition, transfer to initiator or primary radical termination, and various initiator-derived byproducts can be distinguished. 

The properties of the primary radicals produced by the radiolysis of water are collected in... 

As we have seen in Sections 1 and 4, the principal primary products of the radiolysis of water are powerful oxidizing and reducing radicals in approximately equal yields. For water radiolysis to be a useful tool in general chemistry, it is desirable to convert the primary radicals to a single kind of secondary radical to achieve either totally oxidizing or reducing conditions. Moreover, there is the possibility of designing the system to have the required redox properties by suitable selection of the secondary radicals. Some useful systems that meet these requirements are described below. 

Primary steps of photoinduced electron transfer have been studied in plant reaction centers (PS-I and PS-II), by flash absorption and EPR. In PS-I two questions wereinvestigated i) the properties of the primary radical pair P-700+, A0 (kinetics of decay nature of A0, presumably a specialized chlorophyll a decay by recombination to populate the P-700 triplet state) and ii) the nature of the secondary acceptor A,. Extraction-reconstitution experiments indicate that A, is very probably a molecule of vitamin K,. 

In the recent years, our work on the PS-II reaction center has mainly involved EPR spectroscopy, to identify and understand the functional properties of the secondary acceptors, essentially two quinones QA and QB interacting with a Fe2+ iron, and of the manganese enzyme which realizes the oxidative cleavage of water (see e.g. Beijer and Rutherford, 1987 or Styring and Rutherford, 1987). The recent development of a method permitting to simply isolate a PS-II reaction center core (Nanba and Satoh, 1987) allowed us to study the primary radical-pair (P-680+, I ). We first worked in collaboration with the Japanese group, then developed our own preparation (Hansson et al., 1987 Frank et al., 1987 Takahashi et al., 1987) and also collaborated with the group of Professor Barber (London, UK). 

Reaction (6) produces the radical T with properties identical to those of the primary radicals RJ(T = R ). Both particles R and T react quantitatively with the monomer at a rate controlled by kp, and they do not terminate (thus they do not contribute to changes in kt with macroradical length). 

Properties ofthe primary radicals from water radiolysis... 

The molar absorption coefficients of the radicals can be easily determined by this method because the primary radical yields, as well as the properties of the one-electron oxidizing species are well known. The molar absorption coefficient of C1P+ was determined to be 1 x 104 M x cm-1 at 525 nm, which is agreement with the literature value obtained by chemical oxidation (Fenner, 1974). 

CAS 61788-46-3 EINECS/ELINCS 262-977-1 Synonyms Cocoamine Coconut amine Classification Primary aliphatic amine Formula RNFIj, R represents the coconut radical Properties Solid or liq. m.p. 14-18 C cationic Toxicology TSCA listed... 

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