Heat evolved during polymerization

More reliable AH values can be obtained from direct measurements of the heat evolved during polymerization [34—39], or from the difference between the heats of combustion of the amorphous polymer and the liquid monomer. With respect to the very low AHp values, as compared with the heats of combustion, the latter method is very inaccurate. The evaluation of calorimetric data is more difficult for partially crystalline polymers, for which the crystallinity as well as heat of crystallization must be known [38]. Equations (19)-(21) can be applied to such monomer polymer equilibria for which the equilibrium monomer concentrations at different temperatures are available with sufficient precision [28—30, 40]. The latter method is also limited to completely amorphous polymers because the crystalline ordered areas do not take part in the monomer-polymer equilibrium [21]. 

Figure 3. Heat evolved during polymerization of BCB-1 as a function of temperature.

Bending beam theory calculation of elastic modulus, 361-362 calculation of glass temperature, 362 calculation of thermal expansion coefficient, 362 layer stress determination, 361 Benzophenone-3,3, 4,4 -tetracarboxydi-anhydride-oxydianiline-m-phenylenediamine (BTDA-ODA-MPDA) polyimide, properties, 115-116 Bilayer beam analysis schematic representation of apparatus, 346,348/ thermal stress, 346 Binary mixtures of polyamic acids curing, 116-124 exchange reactions, 115 Bis(benzocyclobutenes) heat evolved during polymerization vs. 

The conversion of n bonds into a bonds is exothermic and leads to enthalpies of polymerization in the approximate range -60 to — lOOkJ moI for the monomers most often used in free-radical polymerizations. Clearly the heat evolved during polymerization must be removed and, although this is not a significant problem on the laboratory scale, heat transfer requirements cannot be ignored when considering large-scale production of latexes. 

Also rigorous drying of solvents, monomers and initiators is usually required. The reactions are frequently rapid and violent and low-boiling-point solvents are sometimes needed in order to help to dissipate the heat evolved during polymerization by boiling of the solvent. 

As the heat of polymerization is quite high, sufficient water has to be present to control the temperature that may evolve during the process. 

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