Exothermicity, polymerization

More recent process research aimed at anionic PS is that of BASF AG. Unlike the Dow Process, the BASF process utilizes continuous linear-flow reactors (LFR) with no back-mixing to make narrow polydispersity resins. This process consists of a series alternating reactors and heat exchangers (Fig. 22). Inside the reactors, the polymerization exotherm carries the temperature from 30°C at the inlet to 90°C at the outlet. The heat exchangers then take the temperature back down to 30°C. This process, which requires no solvent, results in the formation of narrow polydispersity PS. 

Polymerization Exothermic reaction Catalyst Lack of inhibitor Crystallization ... 

Polymerization Exothermic reaction which, unless carefully controlled, can run-away and create a thermal explosion or vessel overpressurization Refer to Table 7.20 for common monomers Certain processes require polymerization of feedstock at high pressure, with associated hazards Many vinyl monomers (e.g. vinyl chloride, acrylonitrile) pose a chronic toxicity hazard Refer to Table 7.19 for basic precautions... 

Polymerizes exothermically with acids, bases, certain salts and catalysts Can react with water... 

Expl limits of styrene in air are 1.1 to 6.1% at 30° Fire point (Tag open cup) is 94 °F. Styrene polymerizes exothermally at above RT conditions. A run-away polymerization can be expl... 

Water soluble Can polymerize exothermically, form explosive peroxides, or react violently with other chemicals... 

Can polymerize exothermically with strong alkalis, heat or light Can form peroxides Colourless, wrater soluble liquid... 

Acetaldehyde (Acetic aldehyde, ethanal) CHjCHO -38 185 4.0-55.0 0.8 1.5 21 Colourless fuming liquid Pungent odour Irritant Water soluble Can polymerize exothermically, form explosive peroxides, or react violently with other chemicals... 

Acrolein Allyl aldehyde, propenal) CH2 CHCHO -26 278 2.8-31.0 0.8 1.9 53 Colourless/yellow liquid Pungent unpleasant odour Water soluble Irritant Can polymerize exothermically with strong alkalis, heat or light Can form peroxides... 

Epichlorhydrin (Chloropropylene oxide, epi) CH2 OCHCH2CI 32 - 1.2 3.3 115 Colourless, partly water soluble liquid Highly toxic Polymerizes exothermically with acids, bases, certain salts and catalysts Can react with water... 

Under the DSC conditions (N, scanning rate = 10°C/min), it is apparent that the decomposition processes are occurring at a much faster rate at or near the temperature at which cure is taking place in all the pure dlcyanate samples. Both BADCy and THIOCy showed small exotherms (onset at 277°C and 226°C and peak at 308°C and 289°C, respectively). Their major decompositions began about 251°C and 246°C, respectively, as observed by TGA. On the contrary, all the 1 1 BCB/dlcyanate blends displayed the expected thermal transitions. Besides initial Tg s (20-28°C) and Tm s (171-183°C), all samples showed small exotherms in their DSC scans with maxima at 147-151°C. This is attributable to the thermally-induced crystallization in the mixtures, which also led to some initial phase separation. The polymerization exotherms are consistent with the typical temperature ranges for the known benzocyclobutene-based systems (onset 229-233°C max. 259-266°C). 

Figure 3. DSC of BCB/BMI resin blend, the initial Tg and the polymerization exotherm are indicated.

A study of benzocyclobutene polymerization kinetics and thermodynamics by differential scanning calorimetry (DSC) methods has also been reported in the literature [1]. This study examined a series of benzocyclobutene monomers containing one or two benzocyclobutene groups per molecule, both with and without reactive unsaturation. The study provided a measurement of the thermodynamics of the reaction between two benzocyclobutene groups and compared it with the thermodynamics of the reaction of a benzocyclobutene with a reactive double bond (Diels-Alder reaction). Differential scanning calorimetry was chosen for this work since it allowed for the study of the reaction mixture throughout its entire polymerization and not just prior to or after its gel point. The monomers used in this study are shown in Table 3. The polymerization exotherms were analyzed by the method of Borchardt and Daniels to obtain the reaction order n, the Arrhenius activation energy Ea and the pre-exponential factor log Z. Tables 4 and 5 show the results of these measurements and related calculations. 

The reaction of the bisbenzocyclobutene 41 with the bismaleimide 44 is similar to the reaction of 41 with the activated diacetylene 43. From the DSC thermogram in Fig. 24 it is apparent that there is one major exotherm peak at 258.8 °C associated with this reaction. This could be interpreted as either being the polymerization exotherm peak for a benzocyclobutene-maleimide Diels-Alder reaction or else it is the coincidental overlap of the exotherm peaks associated with each pure component. This latter case is a distinct possibility since both the pure bisbenzocyclobutene 41 and the pure bismaleimide 44 have... 

Two classes of reactive secondary amines (XX and XXI) were synthesized [90] for the thermoset version of the In Situ Molecular Composite concept. The thermoset chemistry of the bisnadimide (XX) involved that of PMR systems (polymerization of monomeric reactants) [95], The secondary amine (XXI) embodied the more recent ringopening polymerization of benzocyclobutene (BCB) [96]. Polymerization exotherms for both thermoset amines occurred with an onset at 225 °C, maximizing at approximately 260 °C as evidenced by DSC at a heating rate of 10 °C/m. 

Uninhibited acid polymerizes exothermally at ambient temperature, and a violent reaction or explosion may occur.3,4... 

Figure 4. Temperature-time curves. Effects of varying concentrations of Vazo catalyst on the polymerization exotherm of basswood-MMA...

A very important characteristic of polymerization reactors is their thermal stability as discussed by Sebastian (6). Chain addition polymerizations are thermally simple reactions, in that the polymerization exotherm is attributable almost in its entirety to the chain propagation step. For chain addition polymerization reactors the rate of reaction r is proportional to the product of the square root of initiator concentration, cu and to monomer concentration, cm... 

However, the most important furan resins are those produced with 2-furfuryl alcohol, for example, the 2-furfuryl alcohol-formaldehyde-based resins, which are normally synthesized by a condensation reaction catalyzed by acidic sites and promoted by heat [224] or the poly(furfuryl alcohol) thermosetting resin that is usually synthesized by the cationic condensation of its monomer 2-furfuryl alcohol, which polymerizes exothermically in the presence of a catalyst such as acid and iodine in methylene chloride, producing black, amorphous, and branched and/or cross-linked structures [225],... 

Figure 6. Temperature-time curves showing the effects of various monomers catalyzed with the same vazo concentration, on the polymerization exotherms of basswood-monomer composites (35). Key MM A, methyl methacrylate TBS, tert-butylstyrene and VT, vinyltoluene.

Table IV. Influence of Wood Moisture Content on the Polymerization Exotherm Temperature...

Figure 9, Temperature-time curves showing how the wood moisture content affects the polymerization exotherm of maple-MM A composite (39),...

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