Monomer functionality

A general rule which holds for many polymer systems is that if the monomer has two functional groups then a linear polymer results, but if the monomer 

The star-shaped polymers originate from a single polyfunctional point, producing a number of radiating arms. Because, in emanating from a single point, the chains there are very crowded together, normally it is not possible to synthesise such molecules with more than four arms. If the arms can then branch further, the molecules are called dendritic polymers. In the solid state these form 

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The precise control of ROMP methodology has been exploited by Schrock and co-workers in the polymerization of a norbomene monomer functionalized with a distyrylbenzene side-chain 70 [1051. When calcium is used as a cathode, an internal device efficiency of 0.3% is observed and the peak emission is in the blue (475 nm). 

Step-growth polymerization processes must be carefully designed in order to avoid reaction conditions that promote deleterious side reactions that may result in the loss of monomer functionality or the volatilization of monomers. For example, initial transesterification between DMT and EG is conducted in the presence of Lewis acid catalysts at temperatures (200°C) that do not result in the premature volatilization of EG (neat EG boiling point 197°C). In addition, polyurethane formation requires the absence of protic impurities such as water to avoid the premature formation of carbamic acids followed by decarboxylation and formation of the reactive amine.50 Thus, reaction conditions must be carefully chosen to avoid undesirable consumption of the functional groups, and 1 1 stoichiometry must be maintained throughout the polymerization process. 

Trimerization to isocyanurates (Scheme 4.14) is commonly used as a method for modifying the physical properties of both raw materials and polymeric products. For example, trimerization of aliphatic isocyanates is used to increase monomer functionality and reduce volatility (Section 4.2.2). This is especially important in raw materials for coatings applications where higher functionality is needed for crosslinking and decreased volatility is essential to reduce VOCs. Another application is rigid isocyanurate foams for insulation and structural support (Section 4.1.1) where trimerization is utilized to increase thermal stability and reduce combustibility and smoke formation. Effective trimer catalysts include potassium salts of carboxylic acids and quaternary ammonium salts for aliphatic isocyanates and Mannich bases for aromatic isocyanates. 

The formation of high molecular products during the cationic polymerization depends on whether the propagation reaction, consisting of the interaction of the cationic chain end as a reactive intermediate with the monomer, reproduces the reactive intermediate (see Eq. (1)). For this reason the monomer functions as the agent and as the substrate when in the form of the cation. This means, however, the interaction between the monomer and the cationic chain end is a function of the monomer structure itself when all other conditiones remain the same. 

Figure 1. Sketch of the primary structure (vide infra) of cross-linked polystyrene (a) and of a typical cross-linked poly-vinyil co-monomer-functional co-monomer-cross-linker (b) [14].

Figure 2.12 Effect of monomer functionality on molecular structure ...

In recent years, silica sol-gel-based inorganic-organic hybrid materials have also been reported. The introduction of various functional groups into organic alkoxide has led to organically modified sol-gel glasses (ormosils). Some of the ormosil monomers and ormosil formations can be found in Fig. 16.3. Redox molecules can be coupled with the ormosil monomer functional group. The immobilized redox molecules can... 

Characterization of the donor bound polymers follows from their spectroscopic (ir and uv-vis KBr) properties in comparison with the starting donor monomers, and from elemental analyses. That the donors are covalently bound to the polymer and not present as unreacted monomers can be seen by the absence of the characteristic monomer functional group absorption (i.e. -OH, COzH) in the donor bound polymer. For example in Figure 1, the comparative ir spectra of p-hydroxyphenyl-TTF monomer and this donor covalently bound to linear and to cross-linked polysytrene are given. Except for the presence of the hydroxyl absorption in the monomer, all three spectra are essentially identical, indicating a rather clean polymer attachment reaction. 

The reaction rate of cyanate ester resins can be increased by using catalysts such as carboxylate salts or chelates of transition metal ions. The role of transition metal ions in the polymerization reaction consists of facilitating the cycli-zation reaction of three cyanate monomer functionalities by the formation of... 

Chemical analysis of the unreacted monomer functional groups as a function of time is useful for step polymerizations. For example, polyesterification can be followed accurately by titration of the carboxyl group concentration with standard base or analysis of hydroxyl groups by reaction with acetic anhydride. The rate of chain polymerization of vinyl monomers can be followed by titration of the unreacted double bonds with bromine. 

Entry Monomer Functionality Init. Condition M [/]) Mn X 10 (PDI) Yield %) R erences... 

Finally, it must be pointed out that the close to first-order kinetic law observed in this study is by no means specific to polymerizations induced by intense laser irradiation a similar kinetic law was obtained by exposing these multiacrylic photoresists to conventional UV light sources that were operated at much lower light-intensities (27,34). This indicates that the unimolecular termination process does not depend so much on the rate and type of initiation used but rather on the monomer functionality and on the cross-link density which appear as the decisive factors. 

Heterochain polymers, which may have other atoms (originating in the monomer functional groups) as part of the chain. These polymers are usually prepared by polycondensation or step-reaction polymerisation. 

As would be expected, these properties vary widely as the monomer functionality increased. The chart below indicates the general trends that can be expected as acrylate functionality increases. 

All intermediate species are reactive, and contribute to the growing polymer Involves simple elimination reaction between monomer functional groups... 

The authors used a [5 s4p 1 d/4s 1 p] basi s set in their calculations. In order to focus on the effects of the molecular interaction, they introduced the concept of a noninteracting dimer wherein the dimer wave function is a simple product (non-antisymmetrized) of the unperturbed monomer functions. The effects of the interaction are thus in evidence by comparison of the two columns in Table 3.31 from which it may be seen that the average polarizability is little affected, increasing from 16.48 to only 16.60. The anisotropy of the polarizability, however, as measured by y, undergoes a dramatic increase. Whereas the polarizability tensor is nearly spherical in the monomer, with all a.j values between 16.3 and 16.6, is increased up to 18 when the two molecules interact with one another. This increase is thus focused along the H-bond direction. 

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