Polymerization Characteristics

Whether initiated by radiation or by the thermal decomposition of free radical initiators, and whether in the bulk or in the imbibed state, the mechanisms of free radical polymerizations of monomers in wood should be essentially similar. As with any free radical polymerization, three basic steps must be involved initiation, propagation, and termination also, chain transfer reactions may occur, depending on the monomer, additives, and on the mode of initiation (Chapiro, 1962 Siau et al, 1965a see also Appendix A, Chapter 1). In such cases, the rate of polymerization should depend on the square root of the concentration of initiating radicals, which, in turn, should depend on the dose or on the concentration of free radical initiator  

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S. Manjula, Studies on Polymerization Characteristics of Naturally Occurring (Renewable) Monomers, Ph.D thesis, Regional Research Laboratory, Trivandrum and Kerala University, Trivandrum, India (1988). 

There are two types of polyethylene and polypropylene, called low density and high density. High-density polyolefins are made on a catalyst, while low-density polyolefins are made by free-radical polymerization. Characteristics of these polyolefins are summarized in Table 11-2. 

Group 6 sandwich compounds, NLO properties, 12, 113 Group 8 sandwich compounds, NLO properties, 12, 113 Group 9 sandwich compounds, NLO properties, 12, 113 Group-transfer polymerization characteristics, 1, 153... 

Olefin isomerization, with Claisen rearrangement, 1, 365 Olefin metathesis with alkyllead, 9, 415 in aqueous media, 1, 834 ESI—MS studies, 1, 812 in high-throughput catalyst discovery, 1, 365 in ionic liquids, 1, 869 for polymerization characteristics, 1, 149 Grubbs catalysts, 1, 151 Schrock catalysis, 1, 150... 

Various cocatalysts are used in Nd-carboxylate-based systems. Most commercially available aluminum alkyls were studied in detail AlMe3 (TMA) [ 174, 184-186], AlEt3 (TEA) [159,187], APBu3 (TIBA) [175,179,188] and A10ct3 [ 189,190]. One of the most referenced cocatalysts is Al Bu2H (DIBAH), e.g. in [178,179,187,191]. Some of the aluminum alkyl cocatalysts were studied comparatively [49,174,179,189,190,192,193]. Some of these studies report results and trends which seem to be contradictory. Since there are so many factors which have an influence on polymerization characteristics and on polymer properties, the discrepancies between the results of different research groups in many cases can be reconciled on the basis of different experimental conditions. 

Plasma-induced species act as initiator of polymerization. Polymerization characteristics and properties of polymers formed by plasma-induced polymerization strongly resemble those of the thermal polymerization of the corresponding monomer [2-12]. Results indicate that plasma-induced polymerization is a free radical addition polymerization initiated by difunctional free radicals created by plasma. The molecular weight of polymer increases with the polymerization time, which is distinctively different from the initiator-initiated free radical addition polymerization. 

Because of the chemical structure insensitive (nonspecific) nature of plasma polymerization illustrated above, the structure of the monomer appears to have relatively little influence on the polymerization characteristics as well as on the characteristics of plasma polymers. This is largely true in the context of selective reactivity due to the chemical structure of monomers in conventional polymerization (i.e., monomer vs. nonmonomer). However, the influence of monomer structure, as classified by five types in Table 7.2, is actually accentuated when the operational conditions are varied. In this context, therefore, the chemical structure of a monomer is a key factor in its deposition characteristics and also in determining the properties of the deposition. 

The change of polymerization characteristics and consequential properties of polymers, which can be recognized to be most sensitive to the chemical structure of monomer, may be seen in the influence of pulsed discharge [4]. The pulsed discharge changes the balance between the contribution of cycle 1 and cycle 2... 

In microscale models the explicit chain nature has generally been integrated out completely. Polymers are often described by variants of models, which were primarily developed for small molecular weight materials. Examples include the Avrami model of crystallization,- and the director model for liquid crystal polymer texture. Polymeric characteristics appear via the values of certain constants, i.e. different Frank elastic constant for liquid crystal polymers rather than via explicit chain simulations. While models such as the liquid crystal director model are based on continuum theory, they typically capture spatiotemporal interactions, which demand modelling on a very fine scale to capture the essential effects. It is not always clearly defined over which range of scales this approach can be applied. 

Although the basic principles of polyketone formation are now reasonably well understood, further studies, both of polymerization characteristics and of the elementary steps underlying polyketone catalysis, will be needed to exploit fully the potential of these selective polymerizations. 

Use A cross-linking agent with polymerization characteristics. Product is a hard, clear, infusable resin. Uses include inks, adhesives, textile products, polyesters, and photoresists. 

Silyl ketene acetals are relatively stable species and require activation by a catalyst in order to initiate polymerization of a,3-unsaturated monomers. Numerous catalysts for GTP polymerizations have been examined " and these studies have revealed that bifluorides and bioxyanions such as tris(dimethylamino) sulfonium bifluoride (TASHF2) and tetra-n-butyl ammonium bibenzoate (TBABB), respectively, afford optimum polymerization characteristics. Note. Bifluoride based catalysts are not soluble in tetrahydrofuran (THF) and thus acetonitrile is used as the solvent in these cases in general TBABB is the optimum catalyst as it is readily soluble in THF and affords better control of molecular weight, conversion, and polydispersity.) GTP has been shown to be robust < 1.1) and is compatible with... 

The availability, ease of purification, and well established polymerization characteristics of styrene. 

The synthesis and polymerization characteristics of 1,4-dimethylenecyclohexane are described. Cationic polymerization of this monomer yields relatively low molecular weight polymers containing appreciable amounts of endocyclic double bonds. In contrast to our earlier claim, 1,4-dimethylenecyclohexane does not seem to cyclopolymerize to a significant extent. 

Results of studies on the FP of oxirane and oxetanes demonstrated that some monofunctional and difunctional 3,3-disubstituted oxetane, arylalkyl, and alkyl glycidyl ether monomers display frontal polymerization characteristics [157]. 

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