Difunctional unit

The specific volumes of all the nine siloxanes were predicted as a function of temperature and the number of monofunctional units, M, and difunctional units, D. A simple 3-4-1 neural network architecture with just one hidden layer was used. The three input nodes were for the number of M groups, the number of D groups, and the temperature. The hidden layer had four neurons. The predicted variable was the specific volumes of the silox-... 

As expected, addition of IV tended to increase the sol fraction in the cured specimens. The statistical theory of gelation (9) can be used to calculate the expected gel fraction as a function of crosslink functionality, extent of reaction, and proportion of difunctional units in the mixture. For these mixtures, an adequate fit to the extraction data was obtained by assuming that the primary reaction is isoindoline formation (Figure 5). Triazine or phthalocyanine formation alone cannot account for the data. 

There is no starting linear polymer Tgi corresponds to a hypothetical copolymer containing all the network difunctional units and must be calculated. The following solutions have been proposed (Bellenger et al., 1981) ... 

If we denote a monofunctional building unit by e (end group) and a difunctional unit by m (middle group), the equilibria involving all molecules including the neso molecule are summarized in the following general equations ... 

The combination of monofunctional units, M, with difunctional units, D, leads to straight chain polyorgano-siloxanes terminated by M-units. Combination of only difunctional units produces cyclic polyorgano-siloxancs or open-chain polydiorganosiloxanes with, for example, a hydroxy or alkoxy end group. The incorporation of T- and optionally also Q-units leads to branched polyorgano-siloxanes. 

Table II shows the values of Em (the modulus corresponding to the ultimate Maxwell element), and Me (the molecular weight of the network chain) for the samples dried at a low temperature. It is clear from the table that McexP/Mccal is larger than 1, which means that some of the 3-arm PIB ionomers function as difunctional polymers, i.e. some of the ions are present as free pairs. It is also seen that the higher the temperature, the more of the polymer chains act as difunctional units. This result confirms that ionic aggregates are disrupted by increasing the temperature, a phenomenon fundamental to the use of these materials as thermoplastic elastomers. Moreover, this result parallels the finding of Neppel et al. (5-6) who showed that clusters decompose progressively to multiplets as the temperature is increased.

Linear volatile and nonvolatile fluids, e.g., Dimethicone polymer chains of difunctional units (monomer) (D) terminated with monofunctional (M) units ma/wwwwv... 

The basic statistical theory of gelation was first derived by Flory who considered the reaction of an /-functional monomer RAf (/> 2) with the difunctional monomers RA2 and RB2. It is necessary to define a parameter called the branching coefficient, a, which is the probability that an /-functional unit is connected via a chain of difunctional units to another... 

In a gel network, the multifunctional monomer acts as a branch unit. These branch units are connected to chains, which are linear segments of difunctional units that lead either to another branch unit or to an unreacted end ... 

---