Polymerization temperature dependence

Dilution with toluene slowed the copolymerization rate, and kinetic measurements were carried out in toluene at 0°-30°C. As reported previously (II), the over-all activation energy of the spontaneous copolymerization of CPT and S02 was calculated to be 16.5 kcal/mole from the Arrhenius plot of the initial rate vs. polymerization temperature. Dependence of the intial rate of copolymerization upon monomer concentration was checked at various monomer concentrations and found to be quite high (II) this could not be explained without participation of the monomer in the initiation step. 

DRFs by means of restriction of the trans opening, and revealed that the polymerization temperature dependence of /In is drastically changed with the structure of ester alkyl groups (Figure 3) [25] the difference in activation enthalpies for meso and racemo additions is positive for DMF, but negative for DtBF. Moreover, the absolute rate constants for meso and... 

Little was known initially about the driving forces underlying the phenomenon of site epimerization. Empirically, it has been observed that (in addition to low monomer concentration and higher polymerization temperature dependency) the catalysts formed with metallocene structures with inherently lower stereorigidity or higher flexibility (such as structures 5, 10, and 11) tend to undergo a more frequent site epimerization than those known to be less flexible, as can be seen from data presented in Table 13. Additionally, it was shown that the frontal substituents in more stereorigid catalysts systems impact the site epimerization rate (see 9/MAO rrmr in... 

The sensitivity of the microstmcture to polymerization temperature depends on the Lewis base and the R value ([base]/[Li]) as shown in Table 11. Although the strongly chelating bidentate bases promote 1,2-polybutadiene microstmcture at low temperatures, they generally exhibit a dramatic decrease in their ability to promote vinyl microstmcture at elevated temperatures as shown in Table 11. This temperature dependence presents a particular problem in high-temperature processes, for example, commercial batch or continuous processes, in which medium vinyl polybutadienes are desired. ... 

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

Note that the initiator decomposition makes the largest contribution to E therefore photoinitiated processes display a considerably lower temperature dependence for the rate of polymerization. 

Many different combinations of surfactant and protective coUoid are used in emulsion polymerizations of vinyl acetate as stabilizers. The properties of the emulsion and the polymeric film depend to a large extent on the identity and quantity of the stabilizers. The choice of stabilizer affects the mean and distribution of particle size which affects the rheology and film formation. The stabilizer system also impacts the stabiUty of the emulsion to mechanical shear, temperature change, and compounding. Characteristics of the coalesced resin affected by the stabilizer include tack, smoothness, opacity, water resistance, and film strength (41,42). 

The choice of initiator system depends on the polymerization temperature, which is an important factor in determining final product properties. Cold polymers are generally easier to process than hot polymers and in conventional cured mbber parts have superior properties. The hot polymers are more highly branched and have some advantages in solution appHcations such as adhesives, where the branching results in lower solution viscosity and better cohesion in the final adhesive bond. 

Fig. 1. Examples of temperature dependence of the rate constant for the reactions in which the low-temperature rate-constant limit has been observed 1. hydrogen transfer in the excited singlet state of the molecule represented by (6.16) 2. molecular reorientation in methane crystal 3. internal rotation of CHj group in radical (6.25) 4. inversion of radical (6.40) 5. hydrogen transfer in halved molecule (6.16) 6. isomerization of molecule (6.17) in excited triplet state 7. tautomerization in the ground state of 7-azoindole dimer (6.1) 8. polymerization of formaldehyde in reaction (6.44) 9. limiting stage (6.45) of (a) chain hydrobromination, (b) chlorination and (c) bromination of ethylene 10. isomerization of radical (6.18) 11. abstraction of H atom by methyl radical from methanol matrix [reaction (6.19)] 12. radical pair isomerization in dimethylglyoxime crystals [Toriyama et al. 1977].

The number of active centers determined by the quenching technique was dependent on the polymerization temperature (98) that was the reason for the difference between the overall activation energy and the activation energy of the propagation step. 

The reactivity of the propagation centers in oxide polymerization catalysts depended on the nature of the transition metal, support, activation temperature of the catalyst, and type of reducing agent (168a). 

When initiators are decomposed thermally, the rates of initiator disappearance (/rj) show marked temperature dependence. Since most conventional polymerization processes require that kj should lie in the range 10 6-1 O 5 s 1 (half-life ca 10 h), individual initiators typically have acceptable >fcd only within a relatively narrow temperature range (ca 20-30 °C). For this reason initiators are often categorized purely according to their half-life at a given temperature or vice For initiators which undergo unimolecular decomposition, the half-life is... 

The importance of the cage reaction increases according to the viscosity of the reaction medium. This contributes to a decrease in initiator efficiency with conversion. 15 1 155 Stickler and Dumont156 determined the initiator efficiency during bulk MMA polymerization at high conversions ca 80%) to be in the range 0.1-0.2 depending on the polymerization temperature. The main initiator-derived byproduct was phenyl benzoate. 

The mechanism of B polymerization is summarized in Scheme 4,9. 1,2-, and cis- and trews-1,4-butadiene units may be discriminated by IR, Raman, or H or nC MMR speclroseopy.1 92 94 PB comprises predominantly 1,4-rra//.v-units. A typical composition formed by radical polymerization is 57.3 23.7 19.0 for trans-1,4- c7a -1,4- 1,2-. While the ratio of 1,2- to 1,4-units shows only a small temperature dependence, the effect on the cis-trans ratio appears substantial. Sato et al9J have determined dyad sequences by solution, 3C NMR and found that the distribution of isomeric structures and tacticity is adequately described by Bernoullian statistics. Kawahara et al.94 determined the microslructure (ratio // measurements directly on PB latexes and obtained similar data to that obtained by solution I3C NMR. They94 also characterized crosslinked PB. 

The result indicates that the activation energy for combination is higher than that for disproportionation by ca 10 kJ mol"1. A similar inverse temperature dependence is seen for other small radicals (Section 2.5). However, markedly different behavior is reported for polymeric radicals (Section 5.2.2.2.1). 

Catala and coworkers167JuiS made the discovery that the rate of TEMPO-mediated polymerization of S is independent of the concentration of the alkoxyamine. This initially surprising result was soon confirmed by others.23 69 Gretza and Matyjaszewski169 showed that the rate of NMP is controlled by the rate of thermal initiation. With faster decomposing alkoxyamines (those based on the open-chain nitroxides) at lower polymerization temperatures, the rate of thermal initiation is lower such that the rate of polymerization becomes dependent on the alkoxyamine concentration, Irrespective of whether the alkoxyamine initiator is preformed or formed in situ, low dispersities require that the alkoxyamine initiator should have a short lifetime. The rate of initiation should be as fast as or faster than propagation under the polymerization conditions and lifetimes of the alkoxyamine initiators should be as short as or shorter than individual polymeric alkoxyamines. 

In synthetic polymeric construction materials the mechanical loss spectrum gives only a general picture of the frequency and temperature dependence of the molecular motions that couple to an applied force field 2,3). In addition to this general structural... 

Temperature dependence, for potential of zero charge on silver in contact with solution, 76 Temperature effects on the potential of zero charge, 23 upon polymerization, 406 Temperature variation of the potential of zero charge (Frumkin and Demaskin), 28... 

Cationic polymerization of cyclic acetals generally involves equilibrium between monomer and polymer. The equilibrium nature of the cationic polymerization of 2 was ascertained by depolymerization experiments Methylene chloride solutions of the polymer ([P]0 = 1.76 and 1.71 base-mol/1) containing a catalytic amount of boron trifluoride etherate were allowed to stand for several days at 0 °C to give 2 which was in equilibrium with its polymer. The equilibrium concentrations ([M]e = 0.47 and 0.46 mol/1) were in excellent agreement with that found in the polymerization experiments under the same conditions. The thermodynamic parameters for the polymerization of 1 were evaluated from the temperature dependence of the equilibrium monomer concentrations between -20 and 30 °C. 

The bicyclic acetals 43 and 45 can be regarded as 4,5-disubstituted-l,3-dioxolanes. In connection with their pdymerizabilities, it is interesting to note here that cis-4,5-dimethyl-l,3-dioxolane has a slightly greater tendency to polymerize than its trans-counterpart22, 37. The polymerization of 45 is an equilibrium reaction and the system is completely reversible. From the temperature dependence of the equilibrium... 

For polymerizations initiated with the f-BuBr/Et2AlCl/MeCl system both transfer to monomer and termination are operative and their relative importance is temperature dependent. Evidently, transfer is less important than termination. 

There is very little experimental data available on values of p for these reactants. Some isothermal data indicates that values in the neighborhood of 3 to 4 are reasonable (1 ), but virtually nothing is reported in the literature on the temperature dependence. This makes quantitative comparison with data more difficult, however certain aspects such as the polydisper-sity prediction of 2 are easily checked. Thus, we now will examine the utility of this model under various experimental polymerization conditions. 

The Temperature Dependence of the Gel Effect in Free-Radical Vinyl Polymerization... 

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