Effect on rate of polymerization

Fig. 1. Field effects on rate of polymerization, o styrene-boron trifluoride etherate-1,2-dichloroethane. A a-methylstyrene-iodine-nitrobenzene. Reproduced, with permission, from Ise and Havashi Kobunshi 15, 957 (1966)...

A free-radical polymerization is carried out with a monomer concentration of Mo, initiator of /q, and at an absolute temperature of Jo- What will be the effects on rate of polymerization and the number-average degree of polymerization for the following system changes ... 

Solvent effects on radical polymerization have been reviewed by Coote and Davis,59 Coote et. Barton and Borsig,71 Gromov,72 and Kamachi" 1 A summary of kinetic data is also included in Beuennann and Buback s review.74 Most literature on solvent effects on the propagation step of radical polymerization deals with influences of the medium on rate of polymerization. 

As a photoinitiator for the polymerization of bulk methyl methacrylate, benzil was found to be considerably less efficient than benzoin or benzoin methyl ether (20), e,g. at photoinitiator concentrations of 10 M, the polymerization rate observed using benzoin was eight times that observed using benzil, despite the fact that the latter was found to absorb three times as much of the incident radiation (Fig. 1). The photo-initiating efficiency of benzil was improved by a factor of three on addition to the methyl methacrylate of 10% v/v tetrahydrofuran, whereas the same additive had no appreciable effect on rates of benzoin- and benzoin methyl ether-photoinitiated polymerizations direct evidence that photoinitiation by benzil proceeds by a hydrogen abstraction mechanism rather than by fragmentation. 

These copolymerize ideally and changes in monomer composition are without effect either on rate of polymerization or polymer molecular weight [78b]. 

Figure 6.19 Effect of rate of radical entry into particle (i ) on rate of polymerization per particle (Epp).

Figure 6.16 A ba r ffia-gram showing the effect of rate of radical entry into particle on rate of polymerization per particle iRpp). The total period of activity (sum of shaded regions) is not changed even if the rate of radical entry into particle is increased from Ryp to 2Rrp and further to 3Rrp. (After Williams, 1971.)...

Table IV. Effect of 1,2-Vinyl Content of Polybutadiene on Rate of Polymerization ...

Figure 4 Effect of injection of allene on rate of polymerization of propylene. Solvay Cie ether treated catalyst AlEt ClrTiCl = 2 1 P = 1 atm, temperature = 50 °C.

Investigation of the effect of the hydroxyl containing additives on rate of polymerization and final properties of UV cured films. 

The presence of hydroxyl containing compounds in the photocurable formulation induced an increase on rate of polymerization and final conversion. These results can be interpreted on the basis of a chain transfer reaction with a flexibilization of the network. In the presence of epoxy-hydroxy-funcitonalized polybutadiene the Tg values of the cured films decreased sharply confirming the strong flexibilization effect together with an increase on toughness properties. 

Equation (6.32) allows us to conveniently assess the effect of temperature variation on the rate of polymerization. This effect is considered in the following example. 

It is apparent from these reactions how chain transfer lowers the molecular weight of a chain-growth polymer. The effect of chain transfer on the rate of polymerization depends on the rate at which the new radicals reinitiate polymerization ... 

If the rate constant kj is comparable to kp, the substitution of a polymer radical with a new radical has little or no effect on the rate of polymerization. If kj hp, the rate of polymerization will be decreased by chain transfer. 

The spontaneous polymerization of styrene was studied in the presence of various acid catalysts (123) to see if the postulated reactive intermediate DH could be intentionally aromatized to form inactive DA. The results showed that the rate of polymerization of styrene is significantly retarded by acids, eg, camphorsulfonic acid, accompanied by increases in the formation of DA. This finding gave further confirmation of the intermediacy of DH because acids would have Httie effect on the cyclobutane dimer intermediate in the Flory mechanism. 

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

Thus the thiol 0 2 25511 is capable of terminating a growiug chain and also initiating a new chain. If the initiation-rate constant, k is not much slower than the propagation-rate constant, the net result is the growth of a new chain without any effect on the overall polymerization rate (retardation). That represents a tme chain transfer, ie, no effect on the rate but a substantial decrease iu molecular weight (12). 

In addition to monomers and the initiator, an inert liquid (diluent) must be added to the monomer phase to influence the pore structure and swelling behavior of the beaded resin. The monomer diluent is usually a hydrophobic liquid such as toluene, heptane, or pentanol. It is noteworthy that the namre and the percentage of the monomer diluent also influence the rate of polymerization. This may be mainly a concentration or precipitation effect, depending on whether the diluent is a solvent or precipitant for the polymer. For example, when the diluent is a good solvent such as toluene to polystyrene, the polymerizations proceed at a correspondingly slow rate, whereas with a nonsolvent such as pentanol to polystyrene the opposite is true. 

Table 3 Effect of [p-ABTAY] on the Rate of Polymerization of Styrene Initiated by p-Acetylbenzylidene Triphenylarsonium ylide at 60 0.1 °C ...

Samal et al. [25] reported that Ce(IV) ion coupled with an amide, such as thioacetamide, succinamide, acetamide, and formamide, could initiate acrylonitrile (AN) polymerization in aqueous solution. Feng et al. [3] for the first time thoroughly investigated the structural effect of amide on AAM polymerization using Ce(IV) ion, ceric ammonium nitrate (CAN) as an initiator. They found that only acetanilide (AA) and formanilide (FA) promote the polymerization and remarkably enhance Rp. The others such as formamide, N,N-dimethylformamide (DMF), N-butylacetamide, and N-cyclohexylacetamide only slightly affect the rate of polymerization. This can be shown by the relative rate (/ r), i.e., the rate of AAM polymerization initiated with ceric ion-amide divided by the rate of polymerization initiated with ceric ion alone. Rr for CAN-anilide system is approximately 2.5, and the others range from 1.04-1.11. 

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