Condensations in polymerization

Condensation polymerization is the most common kind of step growth polymerization. In condensation polymerization, the monomers link together with loss of a small molecule such as water. 

The method described by Swain and Hillis (41) applied to wine (40) gives V /LA which is related to the state of polymerization in condensed tannins. The tannin sample is put through two tests whose reactions depend on the state of condensation. These two reactions are... 

On the other hand, the initiators created by high-energy radiation of monomers initiate radiation polymerization in condensed phases. The initiator that controls the overall radiation polymerization could be cation, anion, or free radical depending on the purity of the monomer. Nevertheless, the concentration of the initiator must be very small and the majority of monomer must remain unaffected otherwise the formation of sufficiently high molecular weight polymers cannot occur. 

Some metal alkyls are polymerized in condensed phases. Li(CH3> forms a tetramer containing Li—CH3—Li bridges in the solid state, and its CH3 frequencies are lower than those of nonbridging compounds tv (CH3) and v (CH3) are 2840 and 2780 cm , respectively]. ... 

Condensation polymerization differs from addition polymerization in that the polymer is formed by reaction of monomers, each step in the process resulting in the elimination of some easily removed molecule (often water). E.g. the polyester polyethylene terephthalate (Terylene) is formed by the condensation polymerization (polycondensation) of ethylene glycol with terephthalic acid ... 

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

Synthesis of large heterocycles usually involves condensation reactions of two difunctional molecules. Such molecules tend to polymerize. So far two special techniques have been described above to avoid this important side-reaaion , namely high dilution and use of templates. The general procedure to avoid polymerizations in reactions between difunctional molecules is, of course, the application of protecting groups as described in sections 4.1.2 and 2.6. 

In Chaps. 5 and 6 we shall examine the distribution of molecular weights for condensation and addition polymerizations in some detail. For the present, our only concern is how such a distribution of molecular weights is described. The standard parameters used for this purpose are the mean and standard deviation of the distribution. Although these are well-known quantities, many students are familiar with them only as results provided by a calculator. Since statistical considerations play an important role in several aspects of polymer chemistry, it is appropriate to digress into a brief examination of the statistical way of describing a distribution. 

In the next group of chapters we shall discuss condensation or step-growth polymers and polymerizations in Chap. 5, addition or chain-growth polymers and polymerizations in Chap. 6, and copolymers and stereoregular polymers in Chap. 7. It should not be inferred from this that these are the only classes of polymers and polymerization reactions. Topics such as ring-opening polymeri-... 

Since acrylic polymerizations liberate considerable heat, violent or mnaway reactions are avoided by gradual addition of the reactants to the kettie. Usually the monomers are added by a gravity feed from weighing or measuring tanks situated close to the kettie. The rate of monomer addition is adjusted to permit removal of heat with full flow of water in the condenser and a partial flow in the cooling jacket. Flow in the jacket can be increased to control the polymerization in cases of erroneous feed rates or other unexpected circumstances. A supply of inhibitor is kept on hand to stop the polymerization if the cooling becomes inadequate. 

Polymerization in Hquid monomer was pioneered by RexaH Dmg and Chemical and Phillips Petroleum (United States). In the RexaH process, Hquid propylene is polymerized in a stirred reactor to form a polymer slurry. This suspension is transferred to a cyclone to separate the polymer from gaseous monomer under atmospheric pressure. The gaseous monomer is then compressed, condensed, and recycled to the polymerizer (123). In the Phillips process, polymerization occurs in loop reactors, increasing the ratio of available heat-transfer surface to reactor volume (124). In both of these processes, high catalyst residues necessitate post-reactor treatment of the polymer. 

The reaction section consists of the high pressure reactors filled with catalyst, and means to take away or dissipate the high heat of reaction (300-500 Btu/lb of olefin polymerized). In the tubular reactors, the catalyst is inside a multiplicity of tubes which are cooled by a steam-water condensate jacket. Thus, the heat of reaction is utilized to generate high pressure steam. In the chamber process, the catalyst is held in several beds in a drum-type reactor with feed or recycled product introduced as a quench between the individual beds. 

The role of silyl groups in condensation polymerization is different from that in GTP. The use of silylated monomers in condensation polymerization was studied first by Klebe [90-92] in 1964. N-trimethylsilyl-substi-... 

The carboxyl terminated ACPA, 4,4 -azobis-(4-cya-nopentanoic acid), turned out to be a suitable reagent in condensation reactions. This compound can be prepared by Strecker s synthesis from levulinic acid following the method of Haines and Waters [12]. Regarding the formation of polymeric azo initiators, Matsakuwa et al. [13] reported on the condensation of ACPA with various diols and diamines in the presence of a condensation agent, I-methyl-2-chlorpyridinium iodide, and a cata-... 

With respect to the initiation of cationic chain polymerizations, the reaction of chlorine-terminated azo compounds with various silver salts has been thoroughly studied. ACPC, a compound often used in condensation type reactions discussed previously, was reacted with Ag X , X, being BF4 [10,61] or SbFa [11,62]. This reaction resulted in two oxocarbenium cations, being very suitable initiating sites for cationic polymerization. Thus, poly(tetrahydrofuran) with Mn between 3 x 10 and 4 x lO containing exactly one central azo group per molecule was synthesized [62a]. Furthermore, N-... 

Condensation polymerization can occur hy reacting either two similar or two different monomers to form a long polymer. This reaction usually releases a small molecule like water, as in the case of the esterifrcation of a diol and a diacid. In condensation polymerization where ring opening occurs, no small molecule is released (see Condensation Polymerization later in this chapter). 

One of the drawbacks of thermal cracking in an FCC is that a high percentage of the olefins formed during intermediate reactions polymerize and condense directly to coke. 

There have been a number of different synthetic approaches to substituted PTV derivatives proposed in the last decade. Almost all focus on the aromatic ring as the site for substitution. Some effort has been made to apply the traditional base-catalyzed dehydrohalogenation route to PTV and its substituted analogs. The methodology, however, is not as successful for PTV as it is for PPV and its derivatives because of the great tendency for the poly(u-chloro thiophene) precursor spontaneously to eliminate at room temperature. Swager and co-workers attempted this route to synthesize a PTV derivative substituted with a crown ether with potential applications as a sensory material (Scheme 1-26) [123]. The synthesis employs a Fager condensation [124] in its initial step to yield diol 78. Treatment with a ditosylate yields a crown ether-functionalized thiophene diester 79. This may be elaborated to dichloride 81, but pure material could not be isolated and the dichloride monomer had to be polymerized in situ. The polymer isolated... 

Reacts with acids to neutralize them. Prepn is. by reacting NaOH with Na in a nickel crucible at 320° under high vacuum. Yield is 96%. The oxide is stored under anhyd benz. It is also the product of the ignition of many of the sodium compds found in pyrots. It is used as a chemical reagent for organic polymerization or condensation reactions... 

Gunking This may occur when beginning the use of filming amines in condensate systems or polymeric sludge dispersants in FW systems. Here the new program may dislodge old corrosion debris or salt deposits and cause them to redeposit elsewhere (usually ultimately in the boiler section). 

At moderately high molecular weights, the reaction mass becomes highly viscous, which limits heat transfer and evaporation of the condensation water. This high viscosity limits further melt polymerization in the bulk. In the literature, the melt polymerization stage is sometimes omitted and the prepolymers are condensed to high molecular weights in the solid state.6,28 41 The polymerizations can easily be carried out without a catalyst. 

Both this and previous studies demonstrate the existence of rather long chains of consecutive ion-molecule reactions in methane, ethylene, and acetylene, and thus they provide direct evidence for ionic mechanisms of condensation or polymerization in these gases. Polymers have been found in relatively high yields among the radiolysis products of these... 

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