Rapid step growth polymerization

Rapid Step-Growth Polymerization (RSGP) Mechanism... 

The way in which a plasma polymer is formed has been explained by the rapid step growth polymerization mechanism, which is depicted in Figure 5.3. The essential elementary reactions are stepwise recombination of reactive species (free radicals) and stepwise addition of or intrusion via hydrogen abstraction by impinging free radicals. It is important to recognize that these elementary reactions are essentially oligomerization reactions, which do not form polymers by themselves on each cycle. In order to form a polymeric deposition, a certain number of steps (cycle) must be repeated in gas phase and more importantly at the surface. The number of steps is collectively termed the kinetic pathlength. 

Step-growth polymerization. Epoxy resins were prepared from nadlc methyl anhydride and Epon 828. This blfunctlonal oxirane also supplies reactive hydrogen sites. The major component is at 1=0, minor components include oligomers with 1=1,2,3. Their concentrations rapidly diminish as degree of polymerization Increases. 

Dendritic polymers with enhanced amplification and interior functionality were prepared by Tomalia et al. (3) by slow step-growth polymerization techniques including polyimine formation followed by rapid ring-opening reactions. 

The reaction continues until one of the reagents is almost completely used up equilibrium is established that can be shifted at will at high temperatures by controlling the amounts of reactants and products. In step-growth polymerization, the monomer molecules are consumed rapidly, and chains of any length x and y combine to form longer chains. 

Addition polymerization is usually such a rapid process that only monomer and final polymer chains are present. Very little of the active material in the system is oligomeric, that is, consisting of only a small number of linked monomer units en route to polymer, at any one point in time. Also, in addition polymerization the whole monomer molecule adds to form polymer. No small molecule is lost in the process. Further details of the polymerization processes involved and the structural properties of the products obtained from addition polymerization are discussed in Chaps. 22 and 23. This chapter will focus on the background theory of synthetic polymers, and condensation, or step-growth, polymerization. 

The data in Table 5.4 reveal that Xn, and hence molecular weight, increases very rapidly with conversion in the high conversion range (p > 0.99). An increase in con rsion from 0.990 to 0.999, for example, leads to a 10-fold increase in X thus, it is not practical to try to control polymer molecular weight by adjusting the level of conversion in factory scale step-growth polymerization. An alternative procedure would be to provide, deliberately, an imbalance in the ratio of the two types of functional groups in the feed. 

There is a wide range of polymers that are polar in their compositional makeup. These macromolecules can be produced in numerous ways, including chain growth polymerization and step growth polymerization. Chain growth polymerization involves a rapid macromolecule formation that suddenly stops. Step growth polymerization exhibits condensation kinetics. It includes not only small molecule removal, but also reactions in which there is no small molecule removal. Analytical pyrolysis can be a useful qualitative as well as quantitative tool in the characterization of these macromolecules. 

Reaction injection molding (RIM) is suitable for some step-growth polymerization processes in which no condensation byproducts are generated, and reactions are very rapid (e.g., polyurethane synthesis from diisocyanates and diols or multifunctional alcohols) ... 

A step-growth polymerization from two types of bi- or polyfunctional primary molecules, e.g., polyurethane formation. This irreversible, rapid process is caused, usually through heteroatoms, by bond displacement without the splitting off any component. 

Chain-growth catalyst-transfer polycondensation (CTP) is a rapidly developing polymerization method, as it allows, in many cases, the above-mentioned limitations of step-growth polymerizations to be overcome. CTP provides a straightforward access to well-defined conjugated homopolymers (e.g., polythiophenes (1), polyfluorenes (2), polyphenylenes (3), etc.), alternate donor-acceptor copolymer e.g., 4) and all-conjugated block polymers (e.g., 5), Chart 20.1. 

Polymerization, bulk Also called mass polymerization or step-growth polymerization. It is from undiluted low molecular weight starting materials. It is the simplest and oldest method for the synthesis of macromolecules. This method has a reaction, which is relatively simple, and rapid, plastics of high purity are formed, and the plastics obtained are immediately processable. Basically, the polymerization process involves only monomer and polymerization initiator or catalyst. It is carried out in the absence of a solvent or other dispersion media. This technique is applicable to both addition and condensation polymerization. Fundamentally differences exist. 

Scheme 2.4 Step-growth polymerization via the thiol-isocyanate reaction, yielding poly(thiourethane)s. (Reproduced with permission from AJ. Inglis and C. Bamer-Kowollik, Ultra rapid approaches to mild macromolecular conjugation, Macromolecular Rapid Communications, 2010, 31, 14, 1247-1266. Wiley-VCH Verlag GmbH Co. KGaA.)...

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