Linear condensation polymers

Consider linear condensation polymerization of monomers AB. An unreacted A group of any monomer is capable of forming a bond with any unreacted B group of any other monomer. Thus, an unreacted B group at the end monomer of an A-mer (molecule containing N monomers) can react with an unreacted A group at the end monomer of a A-mer, forming an N -(- A)-mer  

The ratio of the number of formed bonds to the maximum possible number of bonds in a reaction is called the extent of reaction p. If we select any group (A or B) randomly,/ is the probability that the group has reacted. In linear condensation polymerization, each chain has one unreacted A group at one end of the chain and one unreacted B group at the other end. Flory 

This probability is the number of A-mers per monomer the number of -V-mers in the sample at extent of reaction p divided by the total number of monomers in the system. The number of A-mers per monomer n(p. A) is the ratio of the number density of A-mers c M Mpno N) and the number density of all monomers cj fin the sample 

It is important to clarify the difference between the number of A-mers per monomer n p,N) and the number fraction of A-mers (the 

The sum in the denominator is equal to the total number of molecules per monomer and hence, is the reciprocal of the number-average degree of polymerization l/Aj, thereby providing the final result in Eq. (1.45) 

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The condensation reaction is promoted by certain polar solvents and of the many which have been tested dimethyl sulphoxide appears to be the most effective. As usual with linear condensation polymers molecular equivalence and near-absence of monofunctional material is necessary to ensure a high molecular weight. Moisture and alcohols can also have a devastating effect on the molecular weight. In the case of water it is believed that 4-chlorophenyl 4-hydroxyphenyl sulphone is formed which functions as an effective chain terminator. Gross contamination with air is also believed to reduce the maximum attainable molecular weight as well as causing intense discolouration. 

Consider a linear condensation polymer of type i formed from a... 

Fig. 51.—Mole fraction distribution of chain molecules in a linear condensation polymer for several extents of reaction p.

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

Linear condensation polymers are produced when the constituent monomers contain two functional groups each. When a single monomer is polymerized, the product is made of chains whose repeat unit corresponds to the monomer. An example of this type is nylon 6, the structure of which is shown in Fig. 1.10. If two different monomers are polymerized, the result most often is a chain whose repeat unit corresponds to the two different monomers arranged alternately. An example of this type is nylon 66, the structure of which is shown in... 

Fig. 1.11. The molecular weight of linear condensation polymers is generally controlled by the addition of a small percentage of monofunctional molecules.

Flory, P. J., Molecular size distribution in linear condensation polymers,... 

Flory, P. J., Random reorganization of molecular weight distribution in linear condensation polymers, J. Am. Chem. Soc., 64, 2205-2212 (1942). 

The average DP for formation of linear condensation polymers can be calculated using Carothers equation, average DP = 1/(1 — p). 

Condensation polymerizations (polycondensations) are stepwise reactions between bifunctional or polyfunctional components, with elimination of small molecules such as water, alcohol, or hydrogen and the formation of macromo-lecular substances. For the preparation of linear condensation polymers from bifunctional compounds (the same considerations apply to polyfunctional compounds which then lead to branched, hyperbranched, or crosslinked condensation polymers) there are basically two possibilities. One either starts from a monomer which has two unlike groups suitable for polycondensation (AB type), or one starts from two different monomers, each possessing a pair of identical reactive groups that can react with each other (AABB type). An example of the AB type is the polycondensation of hydroxycarboxylic acids ... 

Fig. 13.42 Simulation results of the RIM process involving a linear step polymerization T0 = Tw = 60°C, kf— 0.5L/moles, t(lii = 2.4 s. (a) Conversion contours at the time of fill, (h) Temperature contours at the time of fill. [Reprinted hy permission from J. D. Domine and C. G. Gogos, Computer Simulations of Injection Molding of a Reactive Linear Condensation Polymer, paper presented at the Society of Plastics Engineers, 34th Armu. Tech. Conf, Atlantic City, NJ, 1976. (Also published in the Polym. Eng. Sci., 20, 847-858 (1980) volume honoring Prof. B. Maxwell).]...

J. D. Domine and C. G. Gogos, Compuiter Simulations of Injection Molding of a Reactive Linear Condensation Polymer, SPE ANTEC Tech. Papers, 22, (1976). 

Like nylon, polyester fibers are made from linear-condensation polymers by melt spinning, followed by drawing. Similar to nylon, the drawing treatment involves a stretch ratio of 5. The drawing of polyester fiber is done above its glass transition temperature of 80°C. 

A functionality of 2 is required in each of the monomer units in order to obtain a linear condensation polymer from esterification reactions. The initial dimeric product still has residual, potentially reactive functionalities (Eq. 20.4). 

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