Polymerization general scheme

Polymerization. The basic features of silica polymerization and its technical relevance have been summarized (9). A general polymerization scheme is shown in Figure 2. When a solution of Si(OH)4 is formed, eg, by acidification of a solution of a soluble silicate, at a concentration greater than... 

The correlation between the data on the electric conductivity of the system in the presence of monomer and those on the relationship between the structures of the catalytic complex and the polymer makes it possible to represent the general polymerization scheme (Reaction 14). In so doing, cis-trans isomerism of the polymer chain structure is not dealt with, although the same approach can be applied to this phenomenon as well. 

Scheme 7.9 Specific example of the general polymerization scheme depicted in Scheme 7.8.

The general polymerization schemes of dienes and acrylates are shown in Fig. 9.7 ... 

Our initial efforts were concentrated on the polymerization of monomers la-c, which not only established the compatibility of the functional group with the metathesis catalytic system but also suggested that a minimum of two methylene units must separate the reactive olefin from the tin atom. A general polymerization scheme is shown in Scheme 3. 

Fig. 5. Protocol for living anionic surface initiated polymerization (LASIP), with initiators attached to silica nanoparticles or clay (a) grafting of initiator and general polymerization scheme (b) nanoparticle grafting procedure. From Ref 36.

Moreover, block copolymers with two radically polymerizable monomers can be synthesized with a combination of thermal and photochemical polymerizations. Regarding their utilization in block copolymer synthesis, azocompounds with photoactive benzoin [103,109-111] and azyloximester groups [112] have been described. Two low-molecular weight azo benzoin initiators of the general formula (Scheme 32) were synthe-... 

Figure 1.9 Generalized reaction scheme for condensation polymerization 1.2.2.1 Linear Condensation Polymers...

In conclusion, several examples of free radical polymerizations under phase transfer conditions have been described in the literature since the initial reports in 1981. In all of these cases it is apparent that transfer of an active species from one phase to a second phase is intimately involved in the initiation step of the polymerization. However, it is also clear that these are complex reactions mechanistically, and one general kinetic scheme may not be sufficient to describe them all. The extent of phase transfer and the exact species transferred will depend to a large extent upon the nature of the two phases, upon the... 

Following the general approach of Oosawa and Kasai (1962), one may assume that the following set of equilibria define the polymerization scheme of tubulin protomers ... 

It has been shown recently that at 20 °C the unstable iodosulfanes (n = 1,2,...) decompose to give homocyclic sulfur molecules and iodine In a similar fashion SCjIj prepared from Se Clj and solid KI in carbon disulfide solution produces Seg and polymeric selenium Mixed sulfur-selenium ring molecules can be prepared by the reaction of mixtures of Se2Cl2 and chlorosulfanes (S Cl2 n = 1, 2, 4, 6-8) with potassium iodide in carbon disulfide solution. The subsequent decomposition of the unstable iodides results in the formation of mixed SeoS8 molecules. The general reaction scheme can be presented as follows ... 

The kinetics of step polymerizations other than polyesterification follow easily from those considered for the latter. The number of different general kinetic schemes encountered in actual polymerization situations is rather small. Polymerizations by reactions between the... 

The purification procedures to be applied depend on the monomer, on the expected impurities, and especially on the purpose for which the monomer is to be employed, e.g., whether it is to be used for radical polymerization in aqueous emulsion or for ionic polymerization initiated with sodium naphthalene. It is not possible to devise a general purification scheme instead the most suitable method must be chosen in each case from those given below. A prerequisite for successful purification is extreme cleanliness of all apparatus (if necessary, treating with hot nitrating acid and repeatedly thorough washing with distilled water). 

Among the alternative polymerization schemes, the approach involving acyl imidazolides is quite unique. Although, imidazolides are generally sufficiently... 

After three decades of accumulating experimental results, we should be expected to have an almost complete knowledge of the rate equations that describe the most important thermosetting polymerizations. Unfortunately, the situation seems to be quite different on the one hand, some authors persist in using intrinsically incorrect methodologies to analyze kinetic data on the other hand, even for the most studied systems - e.g., the epoxy-amine reaction - no general kinetic schemes are universally accepted. 

In the complete absence of acyclic olefins in the system, this polymerization scheme predicts a macrocyclization mode of propagation, whereby the resulting polymer is a mixture of cyclic macromolecules. A general equilibrium for this process can be represented by Reaction 9 ... 

Many different methods of grafting have been developed. By far the greatest effort has been via free-radical vinyl-polymerization routes. The general reaction scheme is shown below ... 

Polymers containing benzoin terminal groups can act as photochemical macroinitiators and are effective in photogenerating polymeric electron donor radicals. The initiation of polymerization by means of azo-benzoin initiators yields polymers with one or two benzoin end-groups according to the termination mode of the particular monomer involved [72-74], The general synthetic procedure is depicted below as illustrated for the case styrene polymerization (Scheme 18). 

Mixtures of alkyl halides and Lewis acids are well-known initiating systems for the polymerizations of alkenes, and the mechanism suggested for these reactions by Kennedy [55] appears to be generally accepted (Scheme 9), although the importance of the chain transfer step from initiator has been questioned [56]. 

The feasibility of the two general methods for end-functionalization in cationic polymerization (Scheme 4) has been examined and confirmed with these monomers (for example, see Ref. 131). Thus, a wide variety of end-functionalized poly(vinyl ethers) are available, as summarized in Table 1 [30,47,81,82,108,116,117,131 -147]. Inspection of this table indicates that almost all of important end groups are covered, including hydroxyl, carboxyl, amino, and aldehyde. 

Emulsion polymerization takes place over a number of steps, where various chemical and physical events take place simultaneously during the process of particle formation and growth. Figure 1 depicts the generally accepted scheme for the kinetics of emulsion polymerization. 

Figure 5.11. Illustration of the general reaction scheme responsible for RAFT polymerization.

In order to develop a sound optimization policy, a good understanding of styrene polymerization kinetics is necessary. In the following section the general kinetic scheme of styrene homopolymerization is introduced. 

Figure 5.1 General reaction scheme of radiation induced polymerization of a double bond containing monomer M.

A limited number of attempts have been made to set up a general mechanistic scheme describing cationic systems in terms of fundamental reactions, in a similar manner to that used in free radical polymerizations, and to derive generally applicable kinetic equations [3—4]. Because of the individuality of each cationic system, however, this approach has met with little success, and there has been a greater tendency towards treating each polymerization in isolation for detailed kinetic analysis. It is possible, however, to postulate at least token schemes which can be used as a guide. After the pre-initiation equilibria, polymerization can be considered in terms of classical initiation, propagation, transfer and termination reactions, i.e. for vinyl monomers... 

The specificity of the reaction mechanism to the chemistry of the initiator, co-initiator and monomer as well as to the termination mechanism means that a totally general kinetic scheme as has been possible for free-radical addition polymerization is inappropriate. However, the general principles of the steady-state approximation to the reactive intermediate may still be applied (with some limitations) to obtain the rate of polymerization and the kinetic chain length for this living polymerization. Using a simplified set of reactions (Allcock and Lampe, 1981) for a system consisting of the initiator, I, and co-initiator, RX, added to the monomer, M, the following elementary reactions and their rates may be... 

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