Oligomers methyl methacrylate polymerizations

The steepest part of the T (t) curve, shown in Fig. 3.10, corresponds to the transition of epoxy resin into the rubbery state. In MDI curing and methyl methacrylate polymerization the amplitude of the response signal (T ) decreases monotononically and then becomes constant when the rigidity of the system reaches a certain level. The completeness of the reaction can be determined by saturation of the dT/dt(tf) curve. The product pCp is relatively insensitive to the transition of an oligomer to a polymer. The shape of the dT/dt(tf) curve is determined primarily by changes in the... 

For methyl methacrylate polymerization U2), at conversion lower than 10% (Fig. 3.3), no autoacceleration is observed with respect to the formation of oligomers (p 1), contrary to that of polymers (p 2) in the presence of a solvent other than methanol. Similar results have been found for butadiene polymerization initiated by thermal decomposition of hydrogen peroxide at 120 °C 100). 

NMR analysis of the resulting oligomers,19-22 supported by IR spectroscopy23 and labeling experiments,19 indicated that the product of methyl methacrylate polymerizations is 3. 

The first is diffusion capture. This theory was originally proposed by Fitch and Tsai (13) for the aqueous polymerization of methyl methacrylate. According to this theory, any oligomer which diffuses to an existing particle before it has attained the critical size for nucleation is irreversibly captured. The rate of nucleation is equal to the rate of initiation minus the rate of capture. The rate of capture is proportional to both the surface area and the number of particles. 

Many papers have been published on the polymerization of methyl methacrylate (MMA) with alkylllthlum. It was reported that In the Initiation step an attack of alkylllthlun on monomer occurred In the first few seconds and took place on both olefinlc and carbonyl double bonds and a considerable amount of oligomer was formed in the early stage of the polymerization (1, 3 4 ... 

This value has been checked very recently (169), by polymerizing methyl methacrylate in the presence of varying amounts of pure polystyrene oligomers of different molecular weights (ranging from 1000 to 5000). After separating carefully the resulting polymers, it was shown... 

Although the polymerization of e-caprolactam was described above, there is no difference in principle from the process flow sheets for centrifugal molding of items from other polymers and oligomers. Nevertheless, in most cases, the high temperatures used in lactam polymerization are not required, and the flow sheet as a whole is simplified. In industrial practice, poly(methyl methacrylate) pipes,172 and sheets of polyurethanes and unsaturated polyesters are obtained by centrifugal casting. 

A typical example of frontal polymerization is the polymerization of methyl methacrylate (or an oligomer), placed inside a long aluminum tube 249 these tubes continuously dip into a bath with a liquid heated up to temperature of 70 - 80°C. The part at the tubes above the bath are cooled so that the reactive material does not polymerize. Polymerization shrinkage is compensated by continuous injection of a monomer or oligomer into the reaction zone. The appropriate combination of injection rate, velocity of tube movement through the reaction zone, and tube diameter are chosen according to experimental studies of the process. 

Such process is described as resusdtable free radical polymerization [204]. It has been applied to the synthesis of poly(a-Me styrene)-b-poly(methyl methacrylate) copolymers from a-methyl styrene oligomers [206] and of amphiphilic copolymers containing polymethacrylic acid and PS sequences [205]. However, macroinitiation from styrene oligomers failed as a probable consequence of the too high stability of the end-groups. 

Only one kinetic study exists on initiation of methacrylate polymerization by a sodium compound. The initiator was the disodium oligomer ( tetramer ) of a-methylstyrene and polymerization was investigated at 25°C in toluene in presence of 0.05—0.2 mole fraction of tetrahydrofuran [181]. An internal first order disappearance of monomer was observed, the first order coefficient being directly proportional to active chain and tetrahydrofuran concentrations. The rate coefficients evaluated, e.g. fep = 3.1—13 X 10 1 mole sec at various tetrahydrofuran concentrations, are much lower than those for lithium initiators. They were, however, evaluated using a methyl iodide titration technique to estimate the active chain concentration. In view of the reactivity of tritiated acetic acid with many short chains which are clearly not active in chain propagation, there must be suspicion of similar behaviour with methyl iodide. If this happens, the active chain concentration would be over-estimated and the derived fep value would be too low. Unfortunately no molecular weights of the precipitable polymer were determined, so that it is impossible to check on active chain concentration using this alternative method. 

Usually, all the initiator used cannot be accounted for if each macromolecule or oligomer is assumed to contain only one initiator fragment. By polymerizing methyl methacrylate-d8 with nondeuterated n-butylmagnesium bromide, the fate of the initiator molecules could be studied in detail by H-NMR [22,38-44]. In toluene at —78 C, n-butylmagnesium bromide attacks equally the C=C [Eq. (2)]... 

The hindrance of desorption does not affect the mobility of radical-anions on the metal surface. Hence, their dimerization with formation of still adsorbed dimeric dianions is very likely, and these may grow and form living oligomers. Degree of polymerization of the attached oligomers depends on their lifetime on the surface, and the lifetime is shortened by a cationsolvating solvent that facilitates removal of the cation from the metal lattice and therefore the desorption. This is demonstrated by Overberger (13), who studied the co-polymerization of styrene and methyl methacrylate initiated by a fine suspension of particles of metallic lithium. 

Optically active oligomers of methyl methacrylate were obtained by the asymmetric polymerization of triphenylmethyl methacrylate, followed by the substitution of methyl for triphenylmethyl, and subsequent GPC separation275 and optical resolution.276 Detailed study on the stereostructure of the oligomer made it possible to discuss precisely the mechanism of polymerization leading to the formation of polymer with one-handed helical conformation. 

Few monomers have been studied in addition-fragmentation polymerization. Mainly styrene, acrylate, and methacrylates have been used so far in addition-fragmentation to obtain telechelic oligomers. As an example, styrene and methyl methacrylate (MMA) [60,61] were polymerized through an addition-fragmentation process, using allylic sulfides as CTAs (entries 12... 

The most common acrylic polymer is polymethyl methacrylate, which is obtained by polymerization of methyl methacrylate (MMA). The material consists of a highway-grade aggregate and a matrix produced by cross-linking MMA with trimethylol propane trimethacrylate or other polyfunctional acrylic oligomers. 

Compositions of these adhesives are suggested in a number of recent patents (5- )- All of these reactive adhesive patents indicate essentially the same concept an elastomer is colloidally dispersed in a monomer, or a monomer/oligomer/polymer solution. The system is then polymerized using a free radical mechanism. What occurs is a rapid, "in situ" polymerization of a (typically) methyl methacrylate system, toughened by elastomeric domains which have beer, incorporated into the structure by grafting. 

---