Dual Linking Processes

Some fabrication processes, such as continuous panel processes, are mn at elevated temperatures to improve productivity. Dual-catalyst systems are commonly used to initiate a controlled rapid gel and then a fast cure to complete the cross-linking reaction. Cumene hydroperoxide initiated at 50°C with benzyl trimethyl ammonium hydroxide and copper naphthenate in combination with tert-huty octoate are preferred for panel products. Other heat-initiated catalysts, such as lauroyl peroxide and tert-huty perbenzoate, are optional systems. Eor higher temperature mol ding processes such as pultmsion or matched metal die mol ding at temperatures of 150°C, dual-catalyst systems are usually employed based on /-butyl perbenzoate and 2,5-dimethyl-2,5-di-2-ethyIhexanoylperoxy-hexane (Table 6). 

In this complex, Zn2(H20)3(0H)4, each zinc ion is surrounded by four oxygen atoms (of OH"" or H O), exactly as in the hydrated zinc cation or the zincate anion the loss of water without decrease in coordination number is achieved by tire dual role played by on hydroxide oxygen atom, which serves as part of the coordination tetrahedron for both zinc ions. By continuing this process ail of the tetrahedra can be linked together into an infinite framework, in c hich each tetrahedron shares its corners with four other tetrahedra. This is the structure of the Zn(OH)o precipitate. 

Figure 1. JabJonski-type diagram of the lowest energy levels of electron donor-acceptor molecules formally linked by a single bond which show dual fluorescence phenomenon. D-A, (D A), (D+-A ), (D -A ) and (D-A) denote the ground state, the primary excited and charge-transfer (CT) singlet states, and CT and locally excited triplet states, respectively. The arrows correspond to the radiative (absorption, A, fluorescence, F, and phosphorescence, Ph) and the radiationless (internal conversion, IC, and intersystem crossing, ISC) processes.

In contrast with the usually slow progress of condensation polymerization the second major classification, addition, or vinyl-type polymerizations, usually proceed very rapidly, so rapidly that they are referred to as chain reaction polymerizations. This method of producing synthetic polymers uses the potential dual functionality present in a carbon-carbon double bond. The process is initiated by the use of radical or charged initiator species to form new sigma bonds from the carbon-carbon double bonds of the monomer, to link the monomer units (Eq. 20.6). 

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