What Is Step-Growth Polymerization

A polymerization in which chain growth occurs in a stepwise manner between difunctional monomers, for example, between adipic acid and hexamethylenediamine to form nylon 66. Also referred to as condensation polymerization. 

Polymerizations in which chain growth occurs in a stepwise manner are called step owth or condensation polymerizations. Step-growth polymers are formed by reaction between difunctional molecules, with each new bond created in a separate step. During polymerization, monomers react to form dimers, dimers react with monomers to form trimers, dimers react with dimers to form tetramers, and so on. 

Polyamide A polymer in which each monomer unit is joined to the next by an amide bond, as for example nylon 66. 

Autoclave An instrument used to sterilize items by subjecting them to steam and high pressure. 

In the early 1930s, chemists at E. I. DuPont de Nemours Company began fundamental research into the reactions between dicarboxylic acids and diamines to form polyamides. In 1934, they synthesized the first purely synthetic fiber, nylon 66, so named because it is synthesized from two different monomers, each containing six carbon atoms. 

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The polymerization of AB -functional vinyl monomers is fundamentally different from the step-growth polymerization of AB2-monomers. Condensation of AB2-monomers results immediately in the formation of hyperbranched polymers since the reactivity of the end-groups are the same, regardless of what type of repeat unit (linear or dendritic) that is formed. 

When an equilibrium step-growth polymerization is 99.5% complete what fraction of the reaction mixture is still monomer... 

What polymer is formed by step-growth polymerization of each monomer or pair of monomers ... 

What amounts to invoking the shortsightedness principle has become standard practice in polymerization kinetics where, for most purposes, the rate coefficients of step or chain growth and termination are taken to be independent of the lengths of the polymer chains (see Sections 11.2.1, 11.3.1, 11.4.1,and 11.5.1). In fact, the principle is the basis of Carother s approach to step-growth polymerization kinetics leading to his equations 11.6 and 11.7. 

When an equilibrium step-growth polymerization is 99% complete, what fraction of the reaction mixture is still monomer (a) on mole basis and (b) on weight basis [Ans. (a) 0.01 (b) 0.0001]... 

PROBLEM 14.13 What product will mainly be formed if a diacid is treated with a large excess of a diol If a diol is treated with a large excess of a diacid These reactions represent two extremes of what can happen as the ratio of reactant concentrations deviates from 1 1 in a step-growth polymerization. 

In Chapter II, we saw some examples of reactions that lead to what are normally considered condensation polymers, but that do not split out a molecule of condensation (Example 4F and Q). By classifying the reactions according to either of the above mechanisms, we avoid any confusion. Step-growth polymerization is treated in this chapter and various types of chain growth are discussed in Chapters X and XI. 

Since step-growth polymerization is mainly concerned with condensation reactions it will be useful first of all to look at what is meant by a condensation reaction. In simple terms it is a reaction between an organic base (such as an alcohol or amine) with an organic acid (such as a carboxylic acid or acid chloride) in which a small molecule like water is eliminated (condensed out). 

A detailed description of AA, BB, CC step-growth copolymerization with phase separation is an involved task. Generally, the system we are attempting to model is a polymerization which proceeds homogeneously until some critical point when phase separation occurs into what we will call hard and soft domains. Each chemical species present is assumed to distribute itself between the two phases at the instant of phase separation as dictated by equilibrium thermodynamics. The polymerization proceeds now in the separate domains, perhaps at differen-rates. The monomers continue to distribute themselves between the phases, according to thermodynamic dictates, insofar as the time scales of diffusion and reaction will allow. Newly-formed polymer goes to one or the other phase, also dictated by the thermodynamic preference of its built-in chain micro — architecture. 

Under what conditions would you expect monomer B to polymerize (Actually it polymerizes well under all conditions). Is the polymer a chain-growth or a step-growth polymer Draw a representative segment of the polymer. 

This is a first-order reaction. The half-life of benzoyl peroxide at 100°C is 19.8 min. (a) Calculate the rate constant (in min ) of the reaction, (b) If the half-life of benzoyl peroxide is 7.30 h, or 438 min, at 70°C, what is the activation energy (in kJ/mol) for the decomposition of benzoyl peroxide (c) Write the rate laws for the elementary steps in the above polymerization process, and identify the reactant, product, and intermediates, (d) What condition would favor the growth of long, high-molar-mass polyethylenes ... 

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