Polymers mixed-polymeric systems

The migration of energy between phases will also have an effect in the radiolysis of mixed polymeric systems not associated with transuranic waste. For instance, the radiolysis of polymers attached to silica particles or the radiolysis of rubber in steel belted tires will probably be affected by energy deposited in the non-organic phase. Energy migration to the polymeric phase may lead to the need for lower overall doses than initially anticipated for a... 

The cosolvency phenomenon was discovered in 1920 s experimentally for cellulose nitrate solution systems. Thereafter cosolvency has been observed for numerous polymer/mixed solvent systems. Polystyrene (PS) and polymethylmethacrylate (PMMA) are undoubtedly the most studied polymeric solutes in mixed solvents. Horta et al. have developed a theoretical expression to calculate a coefficient expressing quantitatively flie cosolvent power of a mixture (dTydx)o, where T,. is the critical temperature of the system and x is the mole fraction of hquid 2 in the solvent mixture, and subscript zero means x—>0. This derivative expresses the initial slope of the critical line as a function of solvent composition (Figure 5.4.1). Large negative values of (dT/dx) are the characteristic feature of the powerful cosolvent systems reported. The theoretical expression developed for (dT dx)o has been written in terms of the interaction parameters for the binary systems ... 

Low viscosity urethane polymers have been prepared from castor od and polymeric isocyanates (82). These low mix viscosity systems are extremely usehd for potting electrical components where fast penetration without air voids, and fast dispensing cycles are desirable. Very low viscosity urethane systems containing castor polyols have been prepared for use in reclaiming water-logged buried telephone cable and for encapsulating telephone cable sphces (83—86). 

Now, let s look at a polymeric system. To begin with, the motion in polymer chains is hindered. The massive size of the polymer itself and the intermolecular forces within the chains create an inflexible system, especially when compared to the aqueous systems with which we are most familiar. Secondly, the entropy of mixing is not actually as great as that seen in typical solution formation. Polymers are inherently highly entropic, so the benefit of mixing them together is modest. Therefore, any two polymers that form a miscible blend depend primarily... 

Rytter et al. reported polymerizations with the dual precatalyst system 14/15 in presence of MAO [30]. Under ethylene-hexene copolymerization conditions, 14/MAO produced a polymer with 0.7 mol% hexene, while the 15/MAO gave a copolymer with ca. 5 mol% hexene. In the mixed catalyst system, the activity and comonomer incorporation were approximate averages of what would be expected for the two catalysts. Using crystallization analysis fractionation (CRYSTAF) and differential scanning calorimetry (DSC) analysis, it was concluded in a later paper by Rytter that the material was a blend containing no block copolymer [31],... 

Carboxylated polymers can be prepared by mechanical treatment of frozen polymer solutions in acrylic acid (Heinicke 1984). The reaction mechanism is based on the initiation of polymerization of the frozen monomer by free macroradicals formed during mechanolysis of the starting polymer. Depending on the type of polymer, mixed, grafted, and block polymers with a linear or spatial structure are obtained. What is important is that the solid-phase reaction runs with a relatively high rate. For instance, in the polyamide reactive system with acrylic acid, the tribochemical reaction leading to the copolymer is completed after a treatment time of 60 s. As a rule, the mechanical activation of polymers is mainly carried out in a dry state, because the structural imperfections appear most likely here. 

Dynamic polymeric systems utilizing the C=N exchange reaction have been reported by Lehn s group. They have suggested a polymerization system consisting of a fluorene-based dialdehyde monomer 4, cyclohexane diamine 5, and fluorene-based diamine 6 as a comonomer (Scheme 8.2) [20,21]. In principle, a 1 1 1 mixture of all monomers in ethanol was expected to yield the two-component polymers 7 and 8 together with all component-mixed polymers. However, polymer 7 was dominantly yielded (80%) due to the nucleophilicity of diamines. The nucleophilic-ity of aliphatic diaminocyclohexane is much higher than that of aromatic... 

When two polymeric systems are mixed together in a solvent and are spin-coated onto a substrate, phase separation sometimes occurs, as described for the application of poly (2-methyl-1-pentene sulfone) as a dissolution inhibitor for a Novolak resin (4). There are two ways to improve the compatibility of polymer mixtures in addition to using a proper solvent modification of one or both components. The miscibility of poly(olefin sulfones) with Novolak resins is reported to be marginal. To improve miscibility, Fahrenholtz and Kwei prepared several alkyl-substituted phenol-formaldehyde Novolak resins (including 2-n-propylphenol, 2-r-butylphenol, 2-sec-butylphenol, and 2-phenylphenol). They discussed the compatibility in terms of increased specific interactions such as formation of hydrogen bonds between unlike polymers and decreased specific interactions by a bulky substituent, and also in terms of "polarity matches" (18). In these studies, 2-ethoxyethyl acetate was used as a solvent (4,18). Formation of charge transfer complexes between the Novolak resins and the poly (olefin sulfones) is also reported (6). 

There are two principal ways to obtain experimental test results from the statistical polymer method the comparison of the predicted weight distribution and other parameters of polymeric systems with these measured for classical polymers (direct test) and the comparison of predicted structural characteristics with these found from adsorption/desorption and other measurements (indirect test). For gels, the indirect test has many advantages, while the interpretation of experimental data is not always easy, e.g., chemisorption is sometimes mixed to physisorption. 

Residual monomers in the latex are avoided either by effectively reacting the monomers to polymer or by physical or chemical removal. The use of tert-butyl peroxypivalate as a second initiator toward the end of the polymerization or the use of mixed initiator systems of K2S2Og and tert-butyl peroxybenzoate (56) effectively increases final conversion and decreases residual monomer levels. Spray devolatilization of hot latex under reduced pressure has been claimed to be effective (56). Residual acrylonitrile also can be reduced by postreaction with a number of agents such as monoamines (57) and dialkylamines (58), ammonium—alkali metal sulfites (59), unsaturated fatty acids or their glycerides (60,61), their aldehydes, esters of olefinic alcohols, cyanuric acid (62,63), andmyrcene (64). 

Because the unique properties of IPNs arise from the intimate mixing of the component polymer systems, the synthetic methodology used to produce these materials is critical. Presently, there are three main routes utilized to produce IPNs simultaneous, sequential and latex. The method employed is determined by the component polymers selected, polymerization mechanisms, miscibility and the anticipated end use of the IPN. 

Butala, D.N. Liang, W.R. Choi, K.Y. Multiobjective dynamic optimization of batch free radical polymerization process by mixed initiator systems. J. Appl. Polym. Sci. 1992, 1759-1778. 

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