Addition Polymerization
Addition polymerization is a process in which monomers join together to form a polymer without the formation of any by-products. This reaction occurs through the repeated addition of monomers to a growing polymer chain, typically initiated by a catalyst or initiator. The resulting polymer has a high molecular weight and a linear structure.
8 Key excerpts on "Addition Polymerization"
- Laurence W. McKeen(Author)
- 2009(Publication Date)
- William Andrew(Publisher)
...The two most common methods are called addition and condensation polymerization. In Addition Polymerization, a chain reaction adds new monomer units to the growing polymer molecule one at a time through double or triple bonds in the monomer. Each new monomer unit creates an active site for the next attachment. The net result is shown in Figure 3.1. Many of the plastics discussed in later chapters of this book are formed in this manner. Some of the plastics made by Addition Polymerization include polyethylene, polyvinyl chloride (PVC), acrylics, polystyrene, and polyoxymethylene (acetal). Figure 3.1 Addition Polymerization. The other common method is condensation polymerization in which the reaction between monomer units and the growing polymer chain end group releases a small molecule, often water as shown in Figure 3.2. This reversible reaction will reach equilibrium and halt unless this small molecular by product is removed. Polyesters and polyamides are among the plastics made by this process. Figure 3.2 Condensation polymerization. Understanding the polymerization process used to make a particular plastic gives insight into the nature of the plastic. For example, plastics made via condensation polymerization, in which water is released, can degrade when exposed to water at high temperature. Polyesters such as polyethylene terephthalate (PET) can degrade by a process called hydrolysis when exposed to acidic, basic, or even some neutral environments severing the polymer chains. As a result the polymer’s properties are degraded. 3.2. Copolymers A copolymer is a polymer formed when two (or more) different types of monomer are linked in the same polymer chain, as opposed to a homopolymer where only one monomer is used. If exactly three monomers are used, it is called a terpolymer. Monomers are only occasionally symmetric; the molecular arrangement is the same no matter which end of the monomer molecule you are looking at...
- Laurence W. McKeen(Author)
- 2019(Publication Date)
- William Andrew(Publisher)
...Since plastics are rarely “neat,” reinforcement, fillers, and additives are reviewed. A basic understanding of plastic and polymer chemistry will make the discussion of properties of specific films easier to understand and it also provides a basis for the introductions of the plastic families in later chapters. This section is taken from The Effect of Temperature and Other Factors on Plastics [1] and Permeability Properties of Plastics and Elastomers [2], but it has been rewritten, expanded, and refocused on polymers as they relate plastics that may be exposure to various weathering processes. 1.1 Polymerization Polymerization is the process of chemically bonding monomer building blocks to form large molecules. Commercial polymer molecules are usually thousands of repeat units long. Polymerization can proceed by one of several methods. The two most common methods are called addition and condensation polymerization. 1.1.1 Addition Polymerization In Addition Polymerization (sometimes called chain-growth polymerization), a chain reaction adds new monomer units to the growing polymer molecule one at a time through double or triple bonds in the monomer. The polymerization process takes place in three distinct steps: 1. Chain initiation—usually by means of an initiator which starts the polymerization process. The reactive initiation molecule can be a radical (free radical polymerization), cation (cationic polymerization), anion (anionic polymerization), and/or organometallic complex (coordination polymerization). 2. Chain propagation—a monomer adds onto chain and each new monomer unit creates an active site for the next attachment. The net result is shown in Fig. 1.1. 3. Chain termination—the radical, cation, or anion is “neutralized” stopping the chain propagation. Figure 1.1 Addition Polymerization. Many of the plastics discussed in later chapter of this book are formed in this manner...
- Shashanka Rajendrachari, Orhan Uzun(Authors)
- 2021(Publication Date)
- Bentham Science Publishers(Publisher)
...It is defined as a polymerization reaction in which bifunctional or polyfunctional monomers undergo an intermolecular condensation reaction with the elimination of byproducts like H 2 O, HCl, NH 3, etc. Bakelite, polyester (Dacron) and polyamide (Nylon 6,6) can be prepared by condensation polymerization. 5. DIFFERENCES BETWEEN ADDITION AND CONDENSATION POLYMERIZATION Some of the differences between addition and condensation polymerizations are given below [ 13 ]. Table 2 Differences between addition and condensation polymerization. Addition Polymerization Condensation Polymerization This polymerization reaction involves addition of monomers This polymerization involves condensation reaction It is a chain reaction of monomers It precedes step wise Monomers with double bonds undergo Addition Polymerization Monomers with functional groups undergo condensation polymerization No by-products will be eliminated It involves elimination of by-products like H 2 O or HCl or NH 3 The reaction is spontaneous (fast) The rate of reaction is slow Addition Polymerization results in thermoplastics Condensation polymerization results in thermosetting plastics It is a chain growth polymerization It is a step growth polymerization Product yield does not depends upon duration of the reaction Product yield depends upon duration of the reaction. More the reaction time, more is the product 6. FREE RADICAL MECHANISM DURING Addition Polymerization [ 3 ] Addition Polymerization takes place through the free radical mechanism and it involves three different stages: initiation, propagation, and termination [ 14, 15 ]. Initiation A free radical is an atomic or molecular species having an odd or unpaired electron...
eBook - ePubBiermann's Handbook of Pulp and Paper
Volume 2: Paper and Board Making
- Pratima Bajpai(Author)
- 2018(Publication Date)
- Elsevier(Publisher)
...Epoxy resins, phenol-formaldehyde resin, and polystyrene cross-linked with divinyl benzene are several examples of thermosetting materials. Other polymers consisting of linear chains or linear chains with little or no branching are called thermoplastics, which soften when heated and harden when cooled to ambient temperatures. 18.2. Addition Polymers There are two categories for types of polymerization reactions used to form polymers: condensation and addition mechanisms to form condensation and addition polymers, respectively. The addition mechanism is used to make polymers from monomers with ring structures or double bonds by a chain reaction. The “extra” bond of the monomer is used to form the bond between monomers; this means that no molecules are lost during polymerization, that is, there is no change in the molecular weight of the monomer incorporated into the polymer. These polymers are usually formed by free radical reactions; however, anionic and cationic mechanisms may also be used but require special solvents and reaction conditions. Free radical reactions are started using initiators. Initiators are compounds that form free radicals, such as peroxides, to start the reaction. The free radical is always carried by the terminal carbon atom between propagation steps. Initiation may also be carried out with high-energy radiation, photolysis, or thermal energy. The reaction of a vinyl monomer, which has the form CH 2 CHR, is shown in Fig. 18.2. Monomers almost invariably add head to head, CH 2 CHR CH 2 CHR, as opposed to head to tail, which is CH 2 CHR CHRCH 2. Head to head addition can form three types of polymers, which differ in rotation around a carbon–carbon single bond: in atactic polymers the R groups are randomly oriented around the longitudinal axis of the polymer; in isotactic polymers the R groups branch out on one side of the polymer chain; and in syndiotactic polymers the R groups alternate from one side of the axis to the opposite side of the axis...
eBook - ePubFundamentals of Polymer Science
An Introductory Text, Second Edition
- Michael M. Coleman, Paul C. Painter(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...In certain cases we might also have solvent, initiator, and perhaps one or two other additives present. These conditions are characteristic of most laboratory studies of polymerization that we will be concerned with here, as these provide the fundamental insights into mechanism and its relationship to the nature of the product. On the industrial scale of production continuous processes are widely used, but we will only qualitatively discuss some of these large-scale systems, at the end of this chapter. B. STEP-GROWTH POLYMERIZATION The central feature of this type of polymerization is the slow building of chains in a systematic stepwise fashion as depicted schematically in figure 2.1. Monomers combine with one another to give dimers: M 1 + M 1 → M 2 dimers and trimers can also combine with themselves or each other to give higher oligomers: M 1 + M 2 → M 3 M 2 + M 2 → M 4 M 2 + M 3 → M 5 M 3 + M 3 → M 6 and so on. As a result of this step-growth mechanism, high molecular weight polymer is only produced at the end of the polymerization. More on this later. There are a number of important types of polymers that are produced by this type of polymerization, including the polyamides (nylons), polyesters, polyurethanes, polycarbonates, phenolic resins, etc. We will give examples of each of these, but will start with a brief description of the discovery of nylon 6,6. This not only serves to introduce features that are characteristic of all polycondensations, but is a great and ultimately tragic story. Historical Background—The Discovery of Nylon Near the end of 1926 Charles Stine, Chemical Department director at DuPont, submitted a short proposal to his Executive Committee to initiate a program of “pure” or fundamental scientific research. In those days this was unusual (one could argue that the cycle has gone full circle and we are once again in the same unfortunate state)...
eBook - ePub- Marianne Gilbert, Marianne Gilbert(Authors)
- 2016(Publication Date)
- Butterworth-Heinemann(Publisher)
...It can readily be seen that if the relative proportion of the two reactants is controlled, branched and then cross-linked molecules can be formed, so that this is a route to thermosetting plastics. In order for cross-linking to occur, the average functionality of the reactants must be >2. To produce thermosets it is often convenient to first produce relatively low molecular weight branched molecules, which can be deformed to shape and then cross-linked under the influence of either heat or catalysts. There are basically two main types of polymerization, namely chain reaction polymerization (see Section 2.5) and step reaction polymerization, (see Section 2.6) with polymerizations classified by the details of their mechanism, as discussed below. Chain and step reaction polymerizations are often referred to by their older names, Addition Polymerization and condensation polymerization, respectively, since these describe the most common chemistries associated with each type. In a common example of chain reaction polymerization, a simple, low molar mass molecule possessing a C C double bond, referred to in this context as a monomer, reacts with an initiator or already-growing polymer chain by breaking the double bond, leaving a free valence for further reaction with other monomers. The first three examples in Table 2.1 are produced by this process. For example, poly(vinyl chloride) (PVC) is produced by the double bonds of vinyl chloride molecules opening up and linking together by adding one by one to the end of a growing chain (Eqn (2.1)). x (CH 2 CHCl) → (CH 2 CHCl) x (2.1) In this equation, x is the degree of polymerization. In the above example the polymerization takes place by the opening of a carbon–carbon double bond. It is also possible to open other double bonds such as carbonyl carbon–oxygen and to open a wide range of rings in cyclic monomers...
- Enrique Saldivar-Guerra, Eduardo Vivaldo-Lima(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
...Flory classifies polymerizations into two categories: Step-growth polymerization; Chain polymerization. 1.2.2.1 Step-growth Polymerization The simplest scheme of this polymerization involves the reaction of a difunctional monomer AB, which contains both functional groups A and B in the molecule. For example, A can be an amine and B a carboxylic acid group. Another scheme involves the reaction between two difunctional monomers of the type AA and BB. In any case, each polymer linkage will have involved the reaction of the functional groups A and B coming from two molecules (monomers or chains). Some examples of polymers synthesized by this mechanism are polyurethane, polyamide, and polyester. This mechanism shows the following features: 1. The chain growth occurs by steps; at each step, a reaction between the functional groups belonging to two monomers or chains occurs. If M 1 denotes monomer, M 2 dimer, M 3 trimer, and so on, the mechanism can be schematically represented as follows: 2. The size of the chains increases gradually and relatively slowly. 3. Any two species in the system can react as long as they possess unreacted dissimilar functional groups. 4. Monomer disappears at low conversions. 5. Conversion is measured in terms of the functional groups reacted. 1.2.2.2 Chain Polymerization This is characterized by: 1. It requires a generator of active centers (usually an initiator for free radicals, anions, or cations). 2. Chain growth occurs by propagation of the active center (chain reaction of the active center with monomer). 3. The monomer only reacts with active centers (not with more monomer). 4. Monomer is present throughout all the reaction. 5. There is high molecular weight polymer present at any time during the polymerization, so the contents of the reaction at any time are unreacted monomer, unreacted initiator, and high molecular weight polymer. There are no significant amounts of intermediate size species (dimer, trimers, etc.). 6...
eBook - ePub- Jacob A. Moulijn, Michiel Makkee, Annelies E. van Diepen(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
...Illustrate this for the production of PET. 11.2.2 Chain growth Polymerization − Radical and Coordination Pathways In chain growth polymerization (also called Addition Polymerization) reaction occurs by successive addition of monomer molecules to the reactive end (e.g., a radical end) of a growing polymer chain. The vinyl monomers such as ethene, propene, styrene, and vinyl chloride are the most important examples: (11.2) in which X = H, CH 3, C 5 H 6, or Cl, respectively. An initiator or a catalyst is usually required to start the chain growth reaction. Chain growth polymerization can be classified (in order of commercial importance) as radical, coordination, anionic, and cationic polymerization, depending on the type of initiation. The next two sections briefly discuss radical and coordination polymerization, respectively. 11.2.2.1 Radical Polymerization Scheme 11.4 outlines a typical reaction scheme for radical polymerization. Most radical polymerizations need an initiator to produce the first radical and thus start the chain of addition reactions. The most common initiation reaction is the thermal decomposition of molecules containing weak bonds, for example, peroxides (–O–O–) or azo compounds (–N=N–). The formed radicals then react with the monomers. Once initiated, a chain will grow by repeated additions of monomer molecules with simultaneous creation of a new radical site. This propagation is very fast, so very long polymer chains will form already in the earliest stage of the reaction. Scheme 11.4 Steps in radical polymerization. M1, Mn, number of monomers in chain. Termination can occur by disproportionation or recombination. In the case of disproportionation, the final polymers have, on average, the same length as the growing chains. Termination occurs by transfer of a hydrogen atom from one of the radicals to the other, leading to unsaturation at one chain end...
