Free radical polymerization reactions

Calcium Chelates (Salicylates). Several successhil dental cements which use the formation of a calcium chelate system (96) were developed based on the reaction of calcium hydroxide [1305-62-0] and various phenohc esters of sahcyhc acid [69-72-7]. The calcium sahcylate [824-35-1] system offers certain advantages over the more widely used zinc oxide—eugenol system. These products are completely bland, antibacterial (97), facihtate the formation of reparative dentin, and do not retard the free-radical polymerization reaction of acryhc monomer systems. The principal deficiencies of this type of cement are its relatively high solubihty, relatively low strength, and low modulus. Less soluble and higher strength calcium-based cements based on dimer and trimer acid have been reported (82). 

The accepted kinetic scheme for free radical polymerization reactions (equations 1-M1) has been used as basis for the development of the mathematical equations for the estimation of both, the efficiencies and the rate constants. Induced decomposition reactions (equations 3 and 10) have been Included to generalize the model for initiators such as Benzoyl Peroxide for... 

In a CSTR the steady-state concentration of monomer is at a lower average value than it would be for the same feed conditions if the same reaction were carried out batchwise. In many free radical polymerization reactions, holding the monomer concentration at a constant level has the effect of reducing the variation in degree of polymerization (or molecular weight). 

The tacky polymeric microspheres that comprise the pressure-sensitive adhesive layers of repositionable notes are patented inventions. One such material (U.S. Patent 5,714,237) is prepared by a free-radical polymerization reaction of isooctyl acrylate (Fig. 14.3.1) in the presence of polyacrylic acid with a chain-... 

Figure 14.3.1 The molecular structure of isooctyl acrylate, a monomer in a free-radical polymerization reaction.

Free-radical polymerization reactions are also known as chain-growth or addition polymerization reactions. Let s look at a chain-growth polymerization re-... 

Derive the equations for the rate of reaction and chain length of a free radical polymerization reaction. 

Research Focus Synthesis of lV-alkoxy-4,4-dioxy-piperidine and A-oxide derivatives for use as controlling agents in free radical polymerization reactions. 

Initially, the polymerization of macromonomers was achieved by free radical polymerization reactions, which allowed only a limited control of the final properties. With the advent of ROMP and new free radical polymerization techniques, such as atom transfer radical polymerization (ATRP) the control of final properties became more facile (16). ATRP and ROMP techniques can be combined for the synthesis of macroinitiators (17). 

The concept of using the functional groups of electrode surfaces themselves to attach reagents by means of covalent bonding offers synthetic diversity and has been developed for mono- and multi-layer modifications. The electrode surface can be activated by reagents such as organosilanes [5] which can be used to covalently bond electroactive species to the activated electrode surface. Recently, thermally induced free-radical polymerization reactions at the surfaces of silica gel have been demonstrated [21]. This procedure has been applied to Pt and carbon electrode surfaces. These thermally initiated polymer macromolecules have the surface Of the electrode as one of their terminal groups. Preliminary studies indicate that the... 

For free radical polymerization reactions, the initiating radicals must be generated from azo-initiators because peroxides cause oxidation of the metal. In polymerizations of the type shown in reaction (2) the side group ferrocene units are the source of both the... 

This section discusses free-radical chain reactions that have been successfully conducted in sc C02. Notably missing from this section are free-radical polymerization reactions in sc C02, which are discussed in detail in other chapters of this book. 

Theory of Compartmentalized Free-Radical Polymerization Reactions... 

Although the reaction between the peroxide and the growing end of the anionic polymer chain is very rapid, the subsequent free radical polymerization reaction is relatively slow. Data in Table IV show that the conversions of methylvinylpyridine and acrylonitrile increase with increasing polymerization time. More than 4 hours are required for maximum reaction. 

Dithiocarbonylated ethyl xanthates, (IV), dithiophosphorylates, (V), and azo derivatives, (VI), prepared by Wilczewska [2], Destarac [3], and Charmot [4], respectively, and were effective as chain transfer agents in free radical polymerization reactions. 

Polyfunctional dithiocarbamate derivatives, (VI) and (VII), were prepared by charmot [4] and used as chain transfer reagents in free radical polymerization reactions. 

Bifunctional stable free radical polymerization reactions were prepared by Georges [4] using divinylbenzene. 

A single-step method for preparing -(a, a -disubstituted-a"-acetic acid) substituted dithiocarbonate derivatives is described. These agents are effective as modulators in free radical polymerization reactions. 

Nesvadba [2] used both aromatic and cyclohexene spiro-ketal derivatives, (I) and (II), respectively, as free radical polymerization reaction regulators. 

Dithiocarbamic-5-oxo-4,5-dihydro-oxazole derivatives have been prepared that are useful in controlled free radical polymerization reactions. When these azlactone photoiniferters were used in the polymerization of styrene or methyl methacrylate, the Mr, as a function of reaction time was constant. 

The primary objective of the theory of compartmentalized free-radical polymerization reactions is to predict from the physicochemical parameters of e reaction system the nature of the locus population distribution. By this latter term is meant collectively the proportions of the total population of reaction loci which at any instant contain 0, l,2,...,i,... propagating radicals. The theory is concerned with the prediction of these actual populations and also with such characteristics of the locus population distribution as the average number of propagating radicals per reaction locus and the variance of the distribution of locus populations. 

Apart from intrinsic interest, the theoiy of compartmentalized free-radical polymerization reactions is of importance primarily because it is believed that most of the polymer which is form in the course of an emulsion polymerization reaction is formed via reactions of this type. The general sl pe of the conversion-time curve for many emulsion polymerization reactions suggests (see Fig. I) that the reaction occurs in three more-or-less distinct stages or intervals. The first of these, the so-called Interval I, is interpreted as the stage of polymerization in which the discrete reaction loci are formed. In the second and third stages—Intervals II and III—the polymerization is believed to occur essentially by compartmentalized free-radical polymerization within the loci which were formed during Interval I. 

The theory also has relevance to the so-called seeded " emulsion polymerization reactioas- In these reactions, polymerization is initial in the presence of a seed latex under conditions such that new particles are unlikely to form. The loci for the compartmentalized free-radical polymerization that occurs are therefore provided principally by the particles of the initial seed latex. Such reactions are of interest for the preparation of latices whose particles have, for instance, a core-shell" structure. They are also of great interest for investigating the fondamentals of compartmentalized free-radical polymerization processes. In this latter connection it is important to note that, in principle, measurements of conversion as a function of time during nonsteady-state polymerizations in seeded systems offer the possibility of access to certain fundamental properties of reaction systems not otherwise available. As in the case of free-radical polymerization reactions that occur in homogeneous media, investigation of the reaction during the nonsteady state can provide information of a fundamental nature not available through measurements made on the same reaction system in the steady state. 

Since most of the monomer in a compartmentalized free-radical polymerization reaction is consumed in the propagation reaction, it is customary to write the overall rate of polymerization as... 

The fundamental equations that govern the behavior of a compartmentalized free-radical polymerization reaction in which the radicals are generated exclusively in the external phase are most readily derived by considering the rates of the various processes by which loci containing exactly i propageting radicals are formed and destroyed. These processes are illustrated in Fig. 2 as transitions between various states of radical occupancy of the loci, each state of occupancy being defined as the number of... 

Kinetica of Comparttnentalized Free-Radical Polymerization Reactions 173... 

Kinetics of Compartmeniaifeed Free-Radical Polymerization Reactions 183... 

This chapter has been concerned exclusively with predictions for the distribution of locus populations within a compartmentalized free-radical polymerization reaction system. Other matters of considerable interest are the distribution of polymer molecular weights which the polymerization reaction produces, and the distribution of sizes of the reaction loci at the end of the reaction. A significant literature concerning both these aspects is beginning to develop, but because of the complexity of the subject and limited space, only a brief summary of the various contributions can be given here. 

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