Homopolymerization mechanics and kinetics

Chain Homopolymerization Mechanism and Kinetics Free radical and ionic polymerizations proceed through this type of mechanism, such as styrene polymerization. Here one monomer molecule is added to the chain in each step. The general reaction steps and corresponding rates can be written as follows ... 

Step Growth Homopolymerization Mechanism and Kinetics Here any two growing chains can react with each other. The propagation mechanism is an infinite set of reactions ... 

Dubois R, Jacobs C., Jerome R., Teyssie R, Macromolecular engineering of polylactones and polylactides. 4. Mechanism and kinetics of lactide homopolymerization by aluminum isopropoxide. Macromolecules, 24, 1991, 2266-2270. 

Chain Propagation. Chain propagation proceeds by radical reaction with ethylene or comonomer molecules. In the case of ethylene homopolymerization, the mechanism and kinetics are straightforward. 

FRP leads to the formation of statistical copolymers, where the arrangement of monomers within the chains is dictated purely by kinetic factors. However, reactivity of a monomer in copolymerization cannot be predicted from its behavior in homopolymerization. Vinyl acetate polymerizes about 30 times more quickly than styrene (see Table 4.2), yet the product is almost pure polystyrene if the two monomers are copolymerized together in a 50 50 mixture. a-Methylstyrene cannot be ho-mopolymerized to form high-MW polymer due to its low ceiling temperature (see Table 4.6), yet is readily incorporated into copolymer at elevated temperatures. These and other similar observations can be understood by considering copolymerization mechanisms and kinetics. 

Dubois, Ph., Jacobs, C., Jerome, R., and Tessie, Ph., 1991, Macromolecular engineering of polylactones and polylactides. 4. Mechanism and kinetics of lactide homopolymerization by aluminum isopropoxide. Macromolecules 24 2266-2270 Kricheldorf, H. R., Lee, S., and Bush, S., 1996, Polylactones 36. Macrocyclic Polymerization of Lactides with Cyclic Bu2Sn Initiators Derived from 1,2-Ethanediol, 2-Mercaptoethanol, and 1,2-Dimercaptoethane. Macromolecules 29 1375-1381 Stevels, W. M., Dijkstra, and P. Feijen, J., 1997, New initiators for the ring-opening polymerization of cyclic esters. Trends Polym. Sci. 5 300-305. 

However, the preparation of useful polymers does not mean that the chemistry and kinetics of these copolymerizations are well understood. It is known that the copolymerizations proceed by the usual mechanisms that are available to the individual monomers. Sometimes more than one mechanism operates simultaneously that is, more than one type of catalyst site is present. All the problems inherent in the interpretation of homopolymerization are still present and new problems are generated as a result of the simultaneous presence of two polymerizable monomers and their interaction with each other. The familiar problems from homopolymerizations include doubts about the nature and number of growing... 

Theoretical treatment of this polymerization is difficult because of the presence of both primary and secondary amine reactions as well as tertiary amine catalyzed epoxy homopolymerization. To obtain kinetic and viscosity correlations, empirical methods were utilized. Various techniques that fully or partially characterize such a system by experimental means are described in the literature ( - ). These methods Include measuring cure by differential scanning calorimetry, infra-red spectrometry, vlsco-metry, and by monitoring electrical properties. The presence of multiple reaction mechanisms with different activation energies and reaction orders (10) makes accurate characterizations difficult, but such complexities should be quantified. A dual Arrhenius expression was adopted here for that purpose. 

Hunkeler, D., F. Candau, et al. (1994). Heterophase polymerizations a physical and kinetic comparison and categorization Theories and mechanism of phase transitions, heterophase polymerizations, homopolymerization, addition polymerization, Springer, Berlin/Heidelherg 115-133. 

In this communication we give preliminary results aimed at the elucidation of the mechanism and the estimation of the rate of radical generation in the spontaneous copolymerization of styrene and maleic anhydride. First, we show experiments that give order-of-magnitude estimates of the rate of radical generation in the copolymerization system, as compared with the homopolymerization of styrene. Second, we show additional results that give a preliminary estimation of the corresponding kinetic rate constant under some... 

In this chapter we have shown that studies of the thermodynamics and kinetics of ROP play an indispensable role in our understanding of polymerization mechanisms. The results of these investigations have helped to establish controlled polymerization conditions, allowing the preparation of polymers with required molar masses and microstructures. The presence of various heteroatoms within the macromolecular main chain introduces an almost infinite number of possible homopolymeric and copolymeric properties. A recent development has been the controlled synthesis of aliphatic polyesters, mostly via ROP, based on their potential applications as biodegradable thermoplastics or as biomedical polymers. Moreover, as some cyclic ester monomers are prepared from renewable resources, some of the examples provided here have related to the ROP of aliphatic cyclic esters. 

It may not be appropriate to compare the thermal stability characteristics of VC/VAc copolymer to that of a VC homopolymer (PVC). The copolymerization would involve different kinetics and mechanism as compared to homopolymerization resulting structurally in quite different polymers. Hence, copolymerization of VC with VAc cannot be regarded as a substitution of chlorines in PVC by acetate groups. To eliminate the possibility of these differences Naqvi [45] substituted chlorines in PVC by acetate groups, using crown ethers (18-crown-6) to solubilize potassium acetate in organic solvents, and studied the thermal stability of the modified PVC. Following is the mechanism of the substitution reaction ... 

This chapter is primarily concerned with the chemical microstructure of the products of radical homopolymerization. Variations on the general structure (CHr CXY) are described and the mechanisms for their formation and the associated Tate parameters are examined. With this background established, aspects of the kinetics and thermodynamics of propagation are also considered (Section 4.5). 

Crosslinked polymer networks formed from multifunctional acrylates are completely insoluble. Consequently, solid-state nuclear magnetic resonance (NMR) spectroscopy becomes an attractive method to determine the degree of crosslinking of such polymers (1-4). Solid-state NMR spectroscopy has been used to study the homopolymerization kinetics of various diacrylates and to distinguish between constrained and unconstrained, or unreacted double bonds in polymers (5,6). Solid-state NMR techniques can also be used to determine the domain sizes of different polymer phases and to determine the presence of microgels within a poly multiacrylate sample (7). The results of solid-state NMR experiments have also been correlated to dynamic mechanical analysis measurements of the glass transition (1,8,9) of various polydiacrylates. 

The homopolymerization of DADMAC is possible in several organic solvents such as acetone, l-methyl-2-pyrrolidone, tetramethylurea, or dimethylform-amide. Various initiation methods including radical, ionic, or x-ray induced polymerization have been employed [19]. Since the monomer solubility is limited in these solvents, and the resulting homopolymer is soluble only in water, methanol and acidic acid, the polymerization in aqueous solutions are preferred. Polymerization in both homogeneous and heterogeneous systems have been studied and the kinetics and mechanisms were investigated in aqueous solution and in inverse-emulsion [6-16,52,53]. 

However, for several epoxy-amine systems, the simple kinetic model expressed by the set of Eqs (5.18) (5.21) does not provide a good fitting with experimental results. Reaction mechanisms, including the formation of different kinds of complexes, have been postulated to improve the kinetic description (Flammersheim, 1998). Also, a more general treatment of the kinetics of epoxy-amine reactions would have to include the possibility of the homopolymerization of epoxy groups in the reaction path. Sets of kinetic equations including this reaction have been reported (Riccardi and Williams, 1986 Chiao, 1990 Cole, 1991). 

This review will feature the kinetics and mechanism of RLi-initiated, homo- and copolymerization of hydrocarbon diene and olefin monomers, with and without polar ligands. Hydrocarbon olefin homopolymerization in nonpolar media will not be discussed per se because simple olefins such as ethylene do not polymerize under such conditions, and such reactive, hydrocarbon a-olefins as styrene behave similarly to dienes in... 

Usually or most widely applied, polymer latexes are made by emulsion polymerization [ 1 ]. Without any doubt, emulsion polymerization has created a wide field of applications, but in the present context one has to be aware that an inconceivable restricted set of polymer reactions can be performed in this way. Emulsion polymerization is good for the radical homopolymerization of a set of barely water-soluble monomers. Already heavily restricted in radical copolymerization, other polymer reactions cannot be performed. The reason for this is the polymerization mechanism where the polymer particles are the product of kinetically controlled growth and are built from the center to the surface, where all the monomer has to be transported by diffusion through the water phase. Because of the dictates of kinetics, even for radical copolymerization, serious disadvantages such as lack of homogeneity and restrictions in the accessible composition range have to be accepted. 

Very recently the spontaneous, simultaneous homopolymerization of vinylidene cyanide and cyclic ethers including THF has been reported [105]. Polymerizations were initiated via a donor—acceptor complex but further investigation of the mechanism of initiation is continuing. It is still too early for kinetics to have been reported but they should be interesting when they do come. 

To evaluate the effect of Me-P-CD on polymerization kinetics, the free uncom-plexed monomers 9-12 and the corresponding Me-P-CD complexes (9a-12a) are homopolymerized in water by a free radical mechanism under identical conditions. In the case of the aqueous polymerization of the free monomers 9-12 the initial... 

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