Polymer-monomer Systems

The mechanical synthesis of block and graft copolymers by vibromilling a polymer-monomer blend has been performed by many researchers. Natural polymers (14,17) vinyl polymers (18—27), and heterochain polymers (18, 28-34) have been formed during polymer mechanochemical degradation. Importantly, Simionescu, Vasiliu-Oprea and Neguleanu studied the possibility of carrying out mechanically-induced polycondensations starting from polyesters and diamines (33,35-37). 

Mechanical synthesis by cold mastication of rubber and monomers depends on the reaction condition (monomer concentration, temperature, solvent concentration, atmosphere, presence of transfer agents, or catalyst) and on the physical and chemical properties of the rubbers, the monomers and the product inter-polymers. A critic factor is the shear stress developed in the system rather than instrumentally-deilned shear rates. The degree of reaction of polymer and consequently also the concentration of free macroradicals depends on stress. As a consequence, the influence of the above parameters may be connected to their influence on the viscosity of the reaction medium since an increase in viscosity causes an increase in stress at constant shear rate. 

O) fractional precipitation by methanol after removal of free rubto (-------------) fraction 

Influence of Rubber Properties. The physical and dieinica] pnqierties of rubbers, monomers and interpolymers must be considered together, as in the main stage of the reaction all of these are present and the properties of the mixture at any moment determine the subsequent reaction. 

The diemical nature of the rubber determines whidi bonds are the weakest and are therefore more likely to be ruptured during mastication by the statistical concentration of mechanical energy about such bonds. An increase in the degree of asymmetry, an increase in the stiffness and the packing density of macromolecules facilitate mechanical scission resonance stability will influence the 

Initial intrinsic viscosity, dl/g Free poly(methyl acrylate) Free polystyrene Block arpolymer 

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There are a number of important factors that must be considered before applying gamma radiation-induced grafting. These factors include the radiation sensitivity of the polymer/monomer system, radiation dose and dose rate, type and concentration of inhibitor, type of solvent or diluent, and monomer concentration. The effect of such parameters on the grafting efficiency during mutual grafting is given below. 

In Table 1 a collection of some general polymer/ monomer systems in radiation grafting is given. These references are only representatives as the number of references in this area is very huge. 

Dielectric relaxation measurements of polyethylene grafted with acrylic acid(AA), 2-hydroxyethyl methacrylate (HEMA) and their binary mixture were carried out in a trial to explore the molecular dynamics of the grafted samples [125]. Such measurements provide information about their molecular packing and interaction. It was possible to predict that the binary mixture used yields a random copolymer PE—g—P(AA/HEMA), which is greatly enriched with HEMA. This method of characterization is very interesting and is going to be developed in different polymer/monomer systems. 

Radiation Induced Reactions. Graft polymers have been prepared from poly(vinyl alcohol) by the irradiation of the polymer-monomer system and some other methods. The grafted side chains reported include acrylamide, acrylic acid, acrylonitrile, ethyl acrylate, ethylene, ethyl methacrylate, methyl methacrylate, styrene, vinyl acetate, vinyl chloride, vinyl pyridine and vinyl pyrrolidone (13). Poly(vinyl alcohols) with grafted methyl methacrylate and sometimes methyl acrylate have been studied as membranes for hemodialysis (14). Graft polymers consisting of 50% poly(vinyl alcohol), 25% poly(vinyl acetate) and 25% grafted ethylene oxide units can be used to prepare capsule cases for drugs which do not require any additional plasticizers (15). 

The experiments of Latinen (1962) and those of Biesenberger and Kes-sidis (1982), when viewed side by side (Table I), present an interesting contradiction, for which there is no obvious explanation. Both sets of investigators used the same polymer-monomer system, both used singlescrew extruders, and both ran experiments at reduced pressure. Latinen found that the extraction efficiency depended on whereas Biesenberger and Kessidis found the efficiency to be independent of screw speed. 

Table 8 summarizes the polymer-monomer systems investigated in mechanical synthesis in the solid state. 

In the case of polymer-monomer systems, it is possible to regulate the reaction by adding monomer at different stages or in different order with reactions being sufficiently rapid for commercial processes. 

The ozonization method has been extended to the most varied polymer/monomer systems, such as polybutadiene-03 with acrylamide, methyl methacrylate or styrene, cellulose-03 with styrene or acrylonitrile (127), starch-03 with styrene (126). In this last case the formation of some homopolystyrene as side-product has been mentionned by the authors. The starch-styrene graft copolymers are claimed to be good emulsifiers for water-oil suspensions. 

First, we note that miscibility and compatibility mean the same thing. The former refers generally to liquid systems, whereas, the latter usually designates solid systems. There are two aspects of the question of miscibility Will the two liquids mix (thermodynamics), and how long would this process take (kinetics) The second aspect is important in polymer-polymer and polymer-monomer systems, because of the low diffusivities involved. Thermodynamically, the mixture will be stable if, at temperature T,... 

Figure 14.1 Phase diagram for rubber-glassy polymer-monomer system [11] a, Initial composition b, phase separation c, phase inversion d, complete conversion. Reproduced from W. A. Ludwico and S. L. Rosen, J. Appl. Polym. Sci., 19, 757 (1975) with permission of John Wiley Sons, Inc.

Because of the scarcity of numerical values of the Flory-Huggins interaction parameter and the interfacial tension for different polymer-monomer systems, few calculations can be made of the expected emulsion polymerization behavior of different monomers. 

Thus, new materials on the base of polymer-monomer system have been produced. The results of researches have allowed to develop methods of creating shock-resistant, heat-resistant, abrasion-resistant and aggression resistant compounds. 

Polymerization starts in the micelles of the emulsifier, because a considerable part of the monomer is dissolved in its hydrocarbon moiety. At 13-20% conversion of the monomer, emulsifier micelles are completely destroyed, and the emulsifier passes into the adsorption layer on the surface of polymer particles. Polymerization continues in the polymer-monomer system, i.e. in a latex into which the monomer penetrates by diffusion from drops. 

Angier, D.J., Ceresa, R.J., Watson, W.F., 1959. Mastication of rubber 8. Preparation of block polymers by mechanical shear of polymer-monomer systems. J. Polym. Sci. 34 (127),... 

Figure 6. DSC transition heats of cho-lesterylvinylfumarate polymer/monomer systems...

Figure 9. Cu-Ka x-ray diffractograms of cholesterylvinylfumarate polymer/monomer systems prepared by different ways...

In the case of polymer-monomer systems, it is possible to regulate the reaction by adding monomers at different stages or in different order with reactions being sufficiently rapid for commercial processes. The mastication equipment most commonly employed is standard rubber instrumentation such as roll mills, internal mixers, extruders, or related laboratory devices (see Volume 2, Section VIIA.B). 

The observations of critical swelling in polymer-monomer systems was demonstrated by Ceresa, who used this method to synthesize many block copolymers, for example, poly(methyl methacrylate) with acrylonitrile, styrene, vinylidene chloride, or vinyl acetate polyethylene with methyl methacrylate or styrene and cellulose acetate with acrylonitrile [114, 168, 170-172]. For the last system, the critical change in swelling rate occurred after 40 min at a monomer uptake of 15%. Below this point no polymerization occurred (see Table 5.23 [114]). 

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