Polymerization conditions temperature

Polymerization conditions temperature 35 °C time 18.5 h solvent CH2C12, 100 mL total volume b TON turnover number, E ethylene, P propylene, H 1-hexene c Determined by size exclusion chromatography with polystyrene standard "Temperature 25 °C... 

It should be noted that the rate of change of fluorescence intensity and the fluorescence enhancement factor depend on the polymerization conditions (temperature, initiator concentration, monomer reactivity) and on the nature of the polymer formed. 

Chain-Transfer Agent n-dodecylmercaptan Polymerization Conditions temperature, °C time, hours Stabilizers... 

A hydrogel delivery device can also be prepared by polymerizing in the presence ofthe protein (Korsmeyer, 1991). The protein must be stable under the polymerization conditions (temperature, solvent, pH) and not react into the hydrogel matrix. The pseudo-steady-state assumptions require that the protein concentration per unit volume exceed the saturation limit (ie., A Cs). Lee (1988) used an integral method for moving-boundary problems to reduce the problem as toJlows ... 

All chain transfer reactions are influenced by the nature of the metallocene catalyst (steric/electronic factors) and polymerization conditions (temperature/pressure). Table 10.1 summarizes the effect of the ligand structure in the metallocene active site on chain transfer mechanisms and the structure of the growing polymer chain in propylene polymerization. 

Hexafluoiopiopylene and tetiafluoioethylene aie copolymerized, with trichloiacetyl peroxide as the catalyst, at low temperature (43). Newer catalytic methods, including irradiation, achieve copolymerization at different temperatures (44,45). Aqueous and nonaqueous dispersion polymerizations appear to be the most convenient routes to commercial production (1,46—50). The polymerization conditions are similar to those of TFE homopolymer dispersion polymerization. The copolymer of HFP—TFE is a random copolymer that is, HFP units add to the growing chains at random intervals. The optimal composition of the copolymer requires that the mechanical properties are retained in the usable range and that the melt viscosity is low enough for easy melt processing. 

A low temperature catalytic process has been reported (64). The process involves the divalent nickel- or zero-valent palladium-catalyzed self-condensation of halothiophenols in an alcohol solvent. The preferred halothiophenol is -bromothiophenol. The relatively poor solubiHty of PPS under the mild reaction conditions results in the synthesis of only low molecular weight PPS. An advantage afforded by the mild reaction conditions is that of making telecheHc PPS with functional groups that may not survive typical PPS polymerization conditions. 

Similarly, it is often impossible, or at least very difficult, to experimentally determine the characteristics of a measurement system under the conditions where it is used. It is certainly possible to fill an emulsion polymerization reactor with water and determine the dynamic-characteristics of the temperature measurement system. However, it is not possible to determine these characteristics when the reactor is filled with the emulsion under polymerization conditions. 

Polymerization conditions Heating time to the polymerization temperature (min) ... 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

In catalytic polymerization the reactivity of the propagation center depends on the catalyst composition. Therefore, the dependence of the molecular structure of the polymer chain mainly on the catalyst composition, and less on the experimental conditions, is characteristic of catalytic polymerization. On the other hand, in polymerization by free-radical or free-ion mechanisms the structure of a polymer is determined by the polymerization conditions (primarily temperature) and does not depend on the type of initiator. 

The shape of the kinetic curves depends on the catalyst type and polymerization conditions (ethylene pressure, temperature, concentration of inhibitors in reaction medium) (89, 97, 98). The types of the kinetic curves obtained. at ethylene polymerization under various conditions are presented in Fig. 1. 

The mechanism of chloroprene polymerization is summarized in Scheme 4.11. Coleman et ai9iM have applied l3C NMR in a detailed investigation of the microstructure of poly(chloroprene) also known as neoprene. They report a substantial dependence of the microstructure on temperature and perhaps on reaction conditions (Table 4.3). The polymer prepared at -150 °C essentially has a homogeneous 1,4-tra/rv-niicrostructure. The polymerization is less specific at higher temperatures. Note that different polymerization conditions were employed as well as different temperatures and the influence of these has not been considered separately. 

The extent of branching, of whatever type, is dependent on the polymerization conditions and, in particular, on the solvent and temperature employed and the degree of conversion. Nozakura et at.1 1 found that, during bulk polymerization of VAc, the extent of transfer to polymer increased and the selectivity (for abstraction of a backbone vs an acetoxy hydrogen) decreases with increasing temperature. 

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. 

Waste nylon-6,6 was washed in a diluted commercial detergent solution at 100°C for 0.5 h and then rinsed twice with water to remove any finishes present. The washed nylon-6,6 was then reacted with molten adipic acid for 1.5 h or more at a temperature of 175°C with a weight ratio of nylon-to-adipic acid of 0.15 1. The molten product was then exposed to steam at a temperature of 230-233°C to remove any stabilizers present. The acidolysis product was then hydrolyzed with water at a temperature of 204°C under autogenous pressure for 0.5 h or longer with a ratio of water to acidolysis product of 0.50 1 (w/w). The hot solution was then filtered at 100°C to remove any titanium dioxide present. The filtered product was then mixed with HMDA to neutralize any excess acid present. The solution was then filtered to remove any solids. A 50% by weight aqueous solution of HMDA was added to the filtrate, and under standard polymerization conditions, polyhexamethylene adipamide (nylon-6,6) was produced. 

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. 

Unfortunately, the most favorable polymerization conditions (active catalyst, neat monomer) lead rapidly to solidified, high-viscosity reaction mixtures. Highly viscous media can severely inhibit condensation polymerizations, since inefficient removal of the small molecular weight product (in this case, hydrogen) slows approach of the reaction to completion. Raising the temperature to lower the viscosity is counterproductive, since cyclic formation becomes competitive at higher temperatures. 

Table VIII. Effect of reaction temperature on molecular weight of butadiene-propylene rubber (BPR). Polymerization conditions as in Table VII, with i-Bu3Al as alkylaluminum compound. Data from Ref. 19.

Ethylene-propylene-diene terpolymers (EPDM), with their inherent complexity in structural parameters, owe their tensile properties to specific structures dictated by polymerization conditions, among which the controlling factor is the catalyst used in preparing the polymers. However, no detailed studies on correlation between tensile properties and EPDM structures have been published (l,2). An unusual vulcanization behavior of EPDMs prepared with vanadium carboxylates (typified by Vr g, carboxylate of mixed acids of Ccj-Cq) has been recently reported Q). This EPDM attains target tensile properties in 18 and 12 minutes at vulcanization temperatures of 150 and l60°C respectively, while for EPDMs prepared with V0Cl -Et3Al2Cl or V(acac) -Et2AlCl, about 50 and 0 minutes are usually required at the respective vulcanization temperatures, all with dieyclopentadiene (DCPD) as the third monomer and with the same vulcanization recipe. This observation prompted us to inquire into the inherent structural factors... 

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