Condensation polymers conversion

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).]...

A polymerization that provides a transition into a discussion of gelation is the condensation of an excess of A-B with a small amount of an /-functional monomer, R-A/, that contains / equivalent functional groups of Type A, but no functional groups of Type B.[3 Linear chains are obtained when / is 1 or 2, but multichain condensation polymers are produced when/>2. At high conversion the polydispersity index depends only on/. 

Much better defined, moderate molecular weight (M 8900) poly(ferro-cenylphosphines) 24 were prepared by Seyferth and co-workers via the polycondensation reaction of l,r-dilithioferrocene tmeda with PhPCb in dimethoxyethane at 25°C followed by conversion of the proposed Cp-Li and P-CI end groups of the condensation polymer 23 to Cp-H and P-OH or P-Ph, respectively (73). Furthermore, under certain carefully con-... 

This section briefly describes the thermal behaviour and conversion of other plastics, including materials such as PET, that are condensation polymers. As described in Chapter 2, condensation polymers are best depolymerized by chemolysis. However, the knowledge of both their thermal stability and the products derived from their thermal decomposition is of interest because in many cases they are present as contaminants in wastes containing addition polymers. 

In the majority of cases, one is concerned with the polymerization of a liquid monomer to a condensed polymer, that is, in A This represents the Gibbs energy for the conversion of 1 mol of liquid monomer into 1 mol of monomeric units of amorphous polymer above the glass transition... 

As a consequence of the lack of special active centers, the chain formation in step growth polymerizations occurs via a sequence of accidental and independent reaction events. It proceeds via dimers, short and longer oligomers until, finally, at conversions higher than 99% long chains are formed which are called condensation polymers (polycondensates) or addition polymers, respectively. Apart from high... 

A polydispersity of about 2 is typical of high molecular weight condensation polymers. A polydispersity of 1.5-2.0 is typical of the instantaneous molecular weight distribution of a free-radical polymer, but the composite distribution from a moderate- to high-conversion reactor will often be broader than this due to thermal inhomogeneities. Coordination catalysis produces very broad distributions, while some low-temperature, ionic polymerizations can give nearly monodisperse polymers (see Peebles [1] for a comprehensive treatment of molecular weight distributions). 

Polymerization may occur simultaneously with devolatilization. This is the case for condensation polymerizations such as that for PET and in free-radical polymerizations such as that for styrene. For the condensation polymers, high molecular weights are achieved only at very high conversions so that the polymerization occurring during devolatilization is obviously desirable. It typically gives low molecular weights in free-radical polymerizations and is typically undesirable. 

In all the preceding polymerization methods we have seen how to utilize the double bond in an unsaturated organic compoimd to link many molecules together into a polymeric chain. Also, in all of these processes the polymer was produced starting from a single monomer. In contrast in this section we will look at polymers that are prepared from the reaction of two difunctional monomers with each other. In all the polymerization reactions that we have seen so far there was no side-product formation. For example, ethylene was converted into polyethylene acrylonitrile was converted into polyacrylonitrile and so on. During this conversion the entire stmc-tural unit of the monomer was incorporated into the polymer without any side-product formation. However, in the preparation of condensation polymers a small molecule (such as water or methanol) is eliminated as the side-product. Another important difference is that condensation polymerization is usually a step-growth polymerization. This means that the polymerization proceeds in a series of steps. To make this point clear let us recall the polymerization of ethylene by the free-radical method. In the free-radical process the polymerization of various chains are initiated by the... 

Tertiary or quaternary recycling, (recovery of chemicals or energy), should only be considered when other types of recycling are not economically or technologically feasible. In tertiary recycling, waste plastics are converted to either monomers or fuels or petrochemical feedstocks. Conversion to monomers by solvolytic methods is feasible for condensation polymers but often requires pure polymer streams. Sorting and cleaning of the waste stream increases the cost of the process. 

Fourth, one may think of chemical recycling recycling constituents or conversion products of the nanocomposite. In the case of condensation polymers with ether, ester, or amide linkages, depolymerization is an option that can give rise to relatively high yields of the original constituents of the polymer [69,71-73,99]. The constituents obtained by depolymerization in turn can be used for repolymerization [69]. 

This rather simple conclusion was reached by W.H. Carothers, the discoverer of nylon and one of the founders of polymer science, in the 1930s. (The same result may be obtained in a more laborious fashion by inserting Equation 8.3 into Equation 5.24.) Its importance becomes obvious when it is realized that typical linear polymers must have values on the order of at least 100 to achieve useful mechanical properties. This requires a conversion of at least 99%, assuming difunctional monomers in perfect stoichiometric equivalence. Such high conversions are almost unheard in most organic reactions, but are necessary to achieve high molecular weight condensation polymers. 

---