Polymerization reaction classifying

In the last section we examined some of the categories into which polymers can be classified. Various aspects of molecular structure were used as the basis for classification in that section. Next we shall consider the chemical reactions that produce the molecules as a basis for classification. The objective of this discussion is simply to provide some orientation and to introduce some typical polymers. For this purpose a number of polymers may be classified as either addition or condensation polymers. Each of these classes of polymers are discussed in detail in Part II of this book, specifically Chaps. 5 and 6 for condensation and addition, respectively. Even though these categories are based on the reactions which produce the polymers, it should not be inferred that only two types of polymerization reactions exist. We have to start somewhere, and these two important categories are the usual place to begin. 

Methanol is stable under normal storage conditions. Methanol is not subject to hazardous polymerization reactions, but can react violendy with strong oxidizing agents. The greatest hazard involved in handling methanol is the danger of fire or explosion. The NFPA classifies methanol as a serious fire hazard. 

Polymerization reactions are classified as being either chain growth or step growth. In chain-growth polymerization, a small molecule reacts with a growing polymer chain to form an incrementally longer chain ... 

Polymerizations are classified as either step (condensation) or chain (addition) polymerizations. The two differ in the time-scale of various reaction events, specifically in the length of time required for the growth of large-sized molecules. The synthesis of polysulfides (Eq. 1) and polyurethanes (Eq. 2) are... 

Among governmental regulations, voluntary guidelines, or trade association codes of practice, there is no standard approach to classifying hazardous chemical reactivity. A variety of methods are used to address self-reactivity (e.g., decomposition reactions and some polymerization reactions) and chemical incompatibility. 

The following Sample Problem shows how to classify a polymerization reaction. 

Tetrafluoroethene polymerizes to form the slippery polymer that is commonly known as Teflon . Teflon M is used as a non-stick coating in frying pans, among other uses. Classify the following polymerization reaction, and name the product. (The letter n indicates that many monomers are involved in the reaction.)... 

Classify each polymerization reaction as an addition or condensation polymerization reaction. 

Q O Draw the product of each polymerization reaction, and classify the reaction. Then circle and identify any amide or ester bonds in the product. 

On the basis of the nature of the initiation step, polymerization reactions of unsaturated hydrocarbons can be classified as cationic, anionic, and free-radical polymerization. Ziegler-Natta or coordination polymerization, though, which may be considered as an anionic polymerization, usually is treated separately. The further steps of the polymerization process (propagation, chain transfer, termination) similarly are characteristic of each type of polymerization. Since most unsaturated hydrocarbons capable of polymerization are of the structure of CH2=CHR, vinyl polymerization as a general term is often used. 

Phenol-formaldehyde adhesives are produced by a condensation polymerization reaction between phenol and formaldehyde. The phenolics used for exterior particleboard are made at a formalde-hyde/phenol ratio greater than 1.0 i.e., they are classified as resoles and additional formaldehyde is not required to complete the curing reaction to a highly cross-linked network structure. Many characteristics can be incorporated into the adhesives by changes in the F/P ratio, condensation pH, and condensation time. The reactive solids content is normally between kO and 50 percent since the stability and viscosity are adversely affected at higher solids. 

Scheme VII classifies potential spectator ligands according to their ligation mode. Ansa, doubly charged A-type ligands, have been prominent in catalytic investigations up to now and are usually employed in a neutral, heteroleptic form. The additional Ln-R moiety directs the catalytic reactivity in a nonspectator manner Due to its kinetic lability, the Ln-R bond is accessible to ligand exchange reactions, as shown in ansa-cyclopentadienyl-supported catalysts for hydrogenation and polymerization reactions [83]. Biphenol or binaphthol ligands [175], the latter of which was recently successfully applied (e.g. in...

Plastics can be classified according to whether they are made from converted natural products (regenerated cellulose) or from completely synthetic products. They can then be further classified according to their manufacturing method in terms of their polymerization reactions, either condensation or addition reactions. They are then further divided, according to their physical properties, into thermoplastics, elastomers and thermosets. 

According to this classification, the polymerization type can usually be easily determined. The structure of the initiator, the manner of its reaction with the monomer, the effects of the medium and last, but not least, sensitive spectroscopic or resonance methods usually, but not always, provide sufficiently convincing information. We know systems containing radical ions. Several years ago it was sometimes assumed that stereospecific polymerizations (now classified as coordination polymerizations) proceed by a radical or cationic mechanism. 

Retarders and inhibitors differ only in the frequency with which propagating radicals react with them rather than with monomer and possibly also in the ability of the radicals resulting from such reactions to reinitiate. It is lo be expected, then, that a compound may not exert the same elTect in the polymerization of different monomers. For example, aromatic nitro compounds that are inhibitors in vinyl acetate polymerizations are classified as retarders in polystyrene syntheses. 

Strictly speaking, the Smith-Ewart model applies only to the batch polymerization of a completely water-insoluble monomer in the presence of micellar soap. (The terms soap, suifactanf, and emulsifier are used interchangeably in this technology.) Its predictions do in fact apply neatly to the case of styrene. Tlie polymerization reaction, after the induction period, can be classified conveniently into three stages, as shown schematically in Fig. 8-2. 

Polymerization reactions can be further classified into batch and continuous processes. Continuous operation is feasible for the production of large quantities of... 

Once a radical enters a reaction locus, it is presumed to initiate a chain polymerization reaction which then continues at a constant rate until the activity of the radical is lost. The processes whereby the activity of the propagating radicals is lost from the reaction loci can be classified into two broad types ... 

The polymerization of oxiranes, a reaction of importance for both industry and commerce, has been abundantly described in the literature. Several hundred articles are published in this field annually. The quantity and great variety of themes discussed mean that a survey of this immense literature material exceeds the scope of the present review. Accordingly, we shall merely mention some of the works attempting to clarify the situation regarding the mechanism of polymerization reactions. ° We shall also outline the fundamental types of oxirane polymerizations. These can be classified into three groups with anionic, cationic, " and coordination mechanisms. 

The chemist classifies polymers in several ways. There are thermosetting plastics such as Bakelite and melamine and the much larger category of thermoplastic materials, which can be molded, blown, and formed after polymerization. There are the arbitrary distinctions made among plastics, elastomers, and fibers. And there are the two broad categories formed by the polymerization reaction itself (1) addition polymers (e.g., vinyl polymerizations), in which a double bond of a monomer is transformed into a single bond between monomers, (2) condensation poly-... 

All the methods can be classified into two groups depending on whether the nanoparticles are formed at the same time than the polymer itself requiring a polymerization reaction or are directly obtained from a polymer. There are numerous valuable reviews on the subject. The general principles of the methods leading to nanoparticle preparation are described and details of the most representative over are given. 

The traditional way to classify polymerization reactions has been by stoichiometry—i.e., whether or not the molecular weight of the polymer produced is an exact multiple of the molecular weight of the monomer (exclusive of end groups). If so, the reaction has been termed an addition polymerization if weight was lost during polymerization, it was named condensation polymerization. Vinyl polymerization (Reaction 5) and polyurea formation (Reaction 6) are examples of the former, whereas polyesterification (Reaction 7) and formation of poly(a-amino acids) from N-carboxyanhydrides (Reaction 8) are examples of the latter. 

When dealing with catalysis it is best, however, to classify polymerization reactions according to the mechanism of chain propagation (2). One may distinguish in this way between chain-reaction polymerization and step-reaction (stepwise) polymerization. The essential features of these classes are shown in Table I (15). The diflFerences between the two types of polymerization are also evident from equations of rate (Rp) and average degree of polymerization (DP). For a free-radical polymerization of vinyl compounds (an example of a chain reaction), Rp and DP are functions of monomer and catalyst concentration (Equations 9 and 10) ... 

Polymerization reactions involve the union of a number of similar molecules to form a single complex molecule. A polymer is any compound, each molecule of which is formed out of a number of molecules which are all alike, and which are called monomers. In many cases polsonerization can be reversed and the poisoner be resolved to the monomer. Many polymerization reactions which are of industrial importance involve in the initial stages condensations, that is, reactions in which elimination of water or other simple molecules takes place. Compounds which polymerize have some type of unsaturation in the molecule. Olefins, unsaturated halides, esters, aldehydes, dicarboxylic acids, anhydrides, amino acids and amides are among the important groups of compounds which are used in industrial polymerization reactions. The commercial products produced by polymerization reactions may be conveniently classified into (a) resinotds, or synthetic resins (b) elastomers, which possess rubber-like properties and (c) fibroids, used as textile fibers. Two types of resinoids are illustrated in this experiment Bakelite, formed from phenol and formaldehyde, and methacrylate resin formed from an unsaturated ester. 

The formation of polymers from the monomers is known as polymerization reaction. When more than one basic unit forms the polymer, the process is also named copolymerization. The polymerization reactions can be classified into two main groups, addition polymerizations and condensation polymerizations (or polycondensations). For the addition polymerizations, the resulting polymer has the repeating unit with the same molecular formula as the monomer, and the molecular mass of the polymer is the sum of the molecular masses of all the monomer molecules. For the condensation polymerizations, the resulting polymer has the repeating unit with fewer atoms than that of the monomer or monomers, and the molecular mass of the polymer is less than the sum of molecular masses of the original monomer unit or units because small molecules are eliminated following this reaction. This classification is not adequate for the characterization of the polymer itself, because the same polymer can be formed by more than one type of reaction. For example, a polyamide can be formed by addition from a lactam or by condensation from an co-aminocarboxylic acid as shown below ... 

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