Conventional polymerization

Freeze-Resistant Polymers. Chloroprene homopolymers made at conventional polymerization temperatures of 40—50°C are not sufftcientiy freeze resistant for some appHcations. In particular, automotive parts such as belts, boots, and air springs are used in dynamic appHcations and need... 

When initiators are decomposed thermally, the rates of initiator disappearance (/rj) show marked temperature dependence. Since most conventional polymerization processes require that kj should lie in the range 10 6-1 O 5 s 1 (half-life ca 10 h), individual initiators typically have acceptable >fcd only within a relatively narrow temperature range (ca 20-30 °C). For this reason initiators are often categorized purely according to their half-life at a given temperature or vice For initiators which undergo unimolecular decomposition, the half-life is... 

The use of initiators such as 68 has been promoted for achieving higher molecular weights or higher conversions in conventional polymerization and for the production of block and graft copolymers. The use and applications of multifunctional initiators in the synthesis of block and graft copolymers is briefly described in Section 7.6.1. 

Much of the interest in ring-opening polymerizations stems from the fact that the polymers formed may have lower densities than the monomers from which they are derived (i.e. volume expansion may accompany polymerization).168-171 This is in marked contrast with conventional polymerizations which typically involve a nett volume contraction. Such polymerizations are therefore of particular interest in adhesive, mold filling, and other applications where volume... 

From this we can see that knowledge of k f and Rf in a conventional polymerization process readily yields a value of the ratio kp fkt. In order to obtain a value for kf wc require further information on kv. Analysis of / , data obtained under non-steady state conditions (when there is no continuous source of initiator radicals) yields the ratio kvlkx. Various non-stcady state methods have been developed including the rotating sector method, spatially intermittent polymerization and pulsed laser polymerization (PLP). The classical approach for deriving the individual values of kp and kt by combining values for kp kx. with kp/k, obtained in separate experiments can, however, be problematical because the values of kx are strongly dependent on the polymerization conditions (Section... 

Copolymers produced by living polymerization processes differ from those produced by conventional polymerization in one important aspect. Living polymerization processes produce gradient or tapered copolymers. Such copolymers are known from anionic living polymerization. 

Combining control over architecture with control over the stereochemistry of the propagation process remains a holy grail in the field of radical polymerization. Approaches to this end based on conventional polymerization were described in Chapter 8. The development of living polymerization processes has yet to substantially advance this cause. 

Phenol, the simplest and industrially more important phenolic compound, is a multifunctional monomer when considered as a substrate for oxidative polymerizations, and hence conventional polymerization catalysts afford insoluble macromolecular products with non-controlled structure. Phenol was subjected to oxidative polymerization using HRP or soybean peroxidase (SBP) as catalyst in an aqueous-dioxane mixture, yielding a polymer consisting of phenylene and oxyphenylene units (Scheme 19). The polymer showed low solubility it was partly soluble in DMF and dimethyl sulfoxide (DMSO) and insoluble in other common organic solvents. 

Development of the PLFNCs is one of the latest evolutionary steps in polymer technology. The PLFNCs offer attractive potential for diversification and application of conventional polymeric materials. Some of the PLFNCs are already commercially available and applied in industrial products. 

As is expected from these results, it is very difficult to control the polymerization of monomers other than St, e.g., that of MMA, because of the too small dissociation energy of the chain end of poly(MMA). In fact, the polymerization of MMA in the presence of TEMPO yielded the polymer with constant Mn irrespective of conversion, and the Mw/Mn values are similar to those of conventional polymerizations [216]. The disproportionation of the propagating radical and TEMPO would also make the living radical polymerization of MMA difficult. In contrast, the controlled polymerization of MA, whose propagating radical is a secondary carbon radical,has recentlybeen reported [217]. Poly(MA) with a narrow molecular weight distribution and block copolymers were obtained. 

During conventional polymerizations of both HEMA and DEGDMA, complications resulting from diffusion limitations to termination and propagation are observed. Features such as autoacceleration, autodeceleration and incomplete conversion of double bonds characterize the rate behavior of these polymerizations. As TED is added to the reacting system, the carbon-DTC radical termination reaction is introduced. Diffusion limitations to carbon-DTC radical combination are lower than those to carbon-carbon radical termination as the DTC radical is smaller and much more mobile than a typical polymeric carbon radical. As a result, the cross-... 

Ultrafiltration (UF) is an important component in wastewater treatment and in food industry [109,110]. With increasing concerns and regulations in environment as well as in food safety, the process of ultrafiltration has become more critical, whereby new technology development to provide faster and more efficient water treatment is not only necessary but also urgent. Currently, conventional polymeric UF membranes are prepared mainly by the phase immersion process, typically generating an asymmetric porous structure with two major limitations (1) relatively low porosity and (2) fairly broad pore-size distribution [111,112],... 

Reduction is an important method for polymer modification resulting in a variety of useful elastomers and thermoplastics with unique structures and properties. Reduction also offers a convenient synthetic route to polymers with special monomer sequences, which are inaccessible, difficult or too expensive to prepare by conventional polymerization... 

Conventional polymerizations were carried out by rapidly adding the BCI3 coinitiator to stirred inifer/isobutylene/solvent charges. The composition of the final charges was identical to the final composition of the corresponding semicontinuous runs. Heat evolution could often be observed in conventional batch polymerization upon BCI3 addition. 

Table I. Comparison of Semicontinuous and Conventional Polymerization Techniques for the Preparation of Telechelic Polyisobutylenes by Binifer and Trinifer...

Many drawbacks of conventional polymeric supports, such as hmited solubilities/ sweUabilities in many organic solvents, limited site accessibility and poor loading... 

Conventional polymerization methods yield macromolecules mostly with random (statistical) or nearly statistical and only very seldom with alternating distribution of the monomer units (see Sect. 3.4.1). Special methods are required in order to synthesize block and graft copolymers (Sect. 3.4.2). 

The observation of these dielectric relaxation processes arising from carbonyl features, has also been reported by Tibbit and co-workers in plasma polytetra-fluoroethylene as well as other plama polymers. In measuring the dielectric loss tangents over a frequency range of 10 -10 Hz at temperatures of — 150 to 100 °C, they have demonstrated that the dielectric loss curves of plasma polymers derived from hydrocarbon and fluorocarbon monomers are very similar, but bear no resemblence to their conventionally polymerized counterparts. 

The deposition of polymeric films by plasma polymerization of styrene in a 800 kHz discharge was investigated by Lam et al. . It was proposed that the observed deposition kinetics could be explained by a scheme in which the initiation of monomers by electron impact is followed by propagation and termination, as in conventional polymerization. This scheme is summarized by the following three reactions ... 

To study template systems it is important to compare the template process and products of the reaction with conventional polymerization carried out under the same conditions. It is typical to replace template hy a low molecular non-polymerizable analogue. The influences of the template on the process and the product are usually called template effect or chain effect . ... 

Template polymerization can be used for production of polymers with much higher molecular weights in comparison with those obtained by conventional process (in the last case a degradative addition frequently takes place). It was shown based on the example of N-vinylimidazole polymerization. By the template process, polymers with up to 70 times higher molecular weight than in conventional polymerization were obtained. 

Substituents have an effect as in conventional polymerization reactions. In radiation grafting certain substituents activate monomers, and others deactivate them.2 2 These effects can be seen in Table 5.11. 

In a plasma polymerization process, the growth of low molecular weight monomer species to a high molecular weight plasma polymer network takes place. In a chemical sense, plasma polymerization is different from conventional polymerizations, such as radical or ionic. The term radical polymerization means that propagating reactions of monomers are initiated by radical species. Ionic polymerization means that chemical reactions are propagated by ionic species in the polymerization step. Plasma polymerization involves an energy source to... 

Polymer modification is of particular interest when the desired polymer is not readily available from its corresponding monomer by conventional polymerization methods. The primary challenge of polymer modification is to achieve a high conversion and selective modification of the appropriate functional group. In this paper, we describe a new convenient polymer modification to prepare novel silanol polymers by a rapid and selective oxidation of the Si—H bond with a dimethyldioxirane solution in acetone from their corresponding precursor polymers. 

Figure 2. Conventional polymerization reactor with top-driven agitator, baffle, and wall-cooling (volumes up to 40 ms)...

In a conventional polymerization, termination is the irreversible step which prevents the attainment of an equilibrium between polymer and its monomer. Hence, if a sufficiently large amount of initiator is available, all the monomer will be converted eventually into polymer. This is in principle impossible in a polymerization involving living" polymers. 

Distribution of molecular weights in these homogeneous systems has been uncertain. A recent discussion and review of this topic is that of Bamford, Jenkins, Johnston, and White (10). They assume a simple exponential distribution and consider both transfer and bimolecular termination. Peebles (112) observed conventional polymerization kinetics but he concluded from light scattering results that there are deviations from normal behavior in the higher molecular weight fractions. He associated these with the same mechanism that causes microgel. 

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