Polymerization of monomer reactants

Bis-maleimide resins composed of BMI and diamines have been reported in the early 1960s in the patent literature. Since that time, a number of patents have appeared describing improvements in their properties and uses [3]. Although many bis-maleimide resins are commercially developed, relatively few reports of their use as adhesives are to be found in scientific journals [4-10]. Improvements of maleimide resins are mirrored in the improvements of thermosetting polyimides. For example, the method of in situ polymerization of monomer reactants (PMR method) was developed [6]. 

NASA Lewis Research Center further developed the norbornene project, culminating in the PMR concept, where a class of addition type poiyimides was formed by the in situ Polymerization of Monomer Reactants (PMR) [42]. 

Figure 9.18 Chemical sequences involved in the polymerization of monomer reactants (PMR) process. The average molecular weight of intermediate oligomer 43 is controlled by the relative amounts of monoester 41, diester 42, and diamine 34. Chain extension of bisnadimide 43 occurs at high temperature by the reverse Diels-Alder polymerization process.

Describe the contents of the reaction flask 10 min after the polymerization of (a) reactants in a stepwise polymerization such as dimethyl terephthalate and ethylene glycol and (b) monomer in chain reactions, such as isobutylene. 

Although the mechanism of copolymerization is similar to that discussed for the polymerization of one reactant (homopolymerization), the reactivities of monomers may differ when more than one is present in the feed, i.e., reaction mixture. Copolymers may be produced by step-reaction or by chain reaction polymerization. It is important to note that if the reactant species are Mi and M2, then the composition of the copolymer is not a physical mixture or blend, though the topic of blends will be dealt with in this chapter. 

As mentioned previously, the behavior of systems containing bifunctional as well as trifunctional reactants is also governed by the equations developed above. The variation of wx for the polymerization of bifunctional monomers, where the branching coefficient a is varied by using appropriate amounts of a trifunctional monomer, is similar to that observed for the polymerization of trifunctional reactants alone. The distribution broadens with increasing extent of reaction. The effect of unequal reactivity of functional groups and intramolecular... 

A large percentage of the total volume of commercial polymers—many of which are amorphous—is produced by chain or addition polymerization of vinyl monomers. Nevertheless, several important widely used commercial polymers and most of the engineering plastics and fibers are produced by stepwise or condensation polymerization of two reactants. Many of these engineering plastics and most fibers are crystalline products. 

Most commercial processes use this type of polymerization to produce small uniform capsules in the range of 20-30 micron diameter however, the process can be tuned to produce large microcapsules. The size of these microcapsules and the properties of the wall material/polymer matrix can be altered by using different monomers, utilizing additives, and adjusting reaction conditions. The encapsulation occurs by wall formation around the dispersed core material via the rapid polymerization of monomers at the surface of the droplets or particles. The solution of a multifunctional monomer in the core material is dispersed in an aqueous phase. The polymerization is commenced at the surfaces of the core droplets forming the capsule walls, by adding a reactant to the monomer dispersed in the aqueous phase. 

We now turn to two of the problems we have sidestepped until now. In this section we consider the polymerization of reactants in which a stoichiometric imbalance exists in the numbers of reactive groups A and B. In the next section we shall consider the effect of monomers with a functionality greater than 2. 

Uses. Furfuryl alcohol is widely used as a monomer in manufacturing furfuryl alcohol resins, and as a reactive solvent in a variety of synthetic resins and appHcations. Resins derived from furfuryl alcohol are the most important appHcation for furfuryl alcohol in both utihty and volume. The final cross-linked products display outstanding chemical, thermal, and mechanical properties. They are also heat-stable and remarkably resistant to acids, alkaUes, and solvents. Many commercial resins of various compositions and properties have been prepared by polymerization of furfuryl alcohol and other co-reactants such as furfural, formaldehyde, glyoxal, resorcinol, phenoHc compounds and urea. In 1992, domestic furfuryl alcohol consumption was estimated at 47 million pounds (38). 

Since acrylic polymerizations liberate considerable heat, violent or mnaway reactions are avoided by gradual addition of the reactants to the kettie. Usually the monomers are added by a gravity feed from weighing or measuring tanks situated close to the kettie. The rate of monomer addition is adjusted to permit removal of heat with full flow of water in the condenser and a partial flow in the cooling jacket. Flow in the jacket can be increased to control the polymerization in cases of erroneous feed rates or other unexpected circumstances. A supply of inhibitor is kept on hand to stop the polymerization if the cooling becomes inadequate. 

The mechanism of ion polymerization in formaldehyde crystals proposed by Basilevskii et al. [1982] rests on Semenov s [1960] assumption that solid-phase chain reactions are possible when the arrangement of the reactants in the crystal prepares the configuration of the future chain. The monomer crystals capable of low-temperature polymerization fulfill this condition. In the initial equilibrium state the monomer molecules are located in the lattice sites and the creation of a chemical bond requires surmounting a high barrier. However, upon creation of the primary dimer cation, the active center shifts to the intersite, and the barrier for the addition of the next link... 

Interfacial polymerization is mainly used in polycondensation reactions with very reactive monomers. One of the reactants, usually an acid... 

For condensation polymerization, it is necessary to have two functional groups on each monomer and to mix stoichiometric amounts of the reactants. In polyamide production, the starting materials first form nylon salt by proton transfer ... 

Figure 1 Is a flow sheet showing some significant aspects of the Iterative analysis. The first step In the program Is to Input data for about 50 physical, chemical and kinetic properties of the reactants. Each loop of this analysis Is conducted at a specified solution temperature T K. Some of the variables computed In each loop are the monomer conversion, polymer concentration, monomer and polymer volume fractions, effective polymer molecular weight, cumulative number average molecular weight, cumulative weight average molecular weight, solution viscosity, polymerization rate, ratio of polymerization rates between the current and previous steps, the total pressure and the partial pressures of the monomer, the solvent, and the nitrogen.

The rates of radical-forming thermal decomposition of four families of free radical initiators can be predicted from a sum of transition state and reactant state effects. The four families of initiators are trarw-symmetric bisalkyl diazenes,trans-phenyl, alkyl diazenes, peresters and hydrocarbons (carbon-carbon bond homolysis). Transition state effects are calculated by the HMD pi- delocalization energies of the alkyl radicals formed in the reactions. Reactant state effects are estimated from standard steric parameters. For each family of initiators, linear energy relationships have been created for calculating the rates at which members of the family decompose at given temperatures. These numerical relationships should be useful for predicting rates of decomposition for potential new initiators for the free radical polymerization of vinyl monomers under extraordinary conditions. 

The living nature of PCL obtained in the presence of Zn(OAl-(OPri)2)2 has been used to prepare both di- and triblock copolymers of e-caprolactone and lactic acid (42,43). Treatment of the initial living PCL with dilactide afforded a PCL-PLA diblock with M /Mn = 1.12, with each block length determined by the proportions of the reactants, i.e., the ratio of [monomer]/[Zn]. While the living diblock copolymer continued to initiate dilactide polymerization, it failed to initiate e-caprolactone polymerization. To obtain a PCL-PLA-PCL triblock, it was necessary to treat the living PCL-PLA-OAIR2 intermediate with ethylene oxide, then activate the hydroxy-terminated PCL-PLA-(OCH2CH2)nOH with a modified Teyssie catalyst (Fig. 5). 

The type of copolymer formed during step growth polymerization depends on the reactivity of the functional groups and the time of introduction of the comonomer. A random copolymer forms when equal concentrations of equally reactive monomers polymerize. The composition of the copolymer, then, will be the same as the composition of the reactants prior to polymerization. When the reactivities of the monomers-differ, the more highly reactive monomer reacts first, creating a block consisting predominandy of one monomer in the chain the lower reactivity monomer is added later. This assumes that there is no chain transfer and no monofunctional monomer present. If either of these conditions were to exist,... 

---