Synthesis of linear polymers

Cationic ROP of ethylene oxide is not useful for the synthesis of linear polymer, but is used to produce crown ethers. Propylene oxide gives less cyclic dimer than does ethylene oxide for steric reasons cyclic tetramer predominates. 

On these lines, two approaches can be proposed. The first can be applied to the synthesis of linear polymers. In this case, the degree of conversion of a monomer can be chosen as a determining factor. This degree of conversion, p, is expressed as the proportion of a monomer included in macro-molecular chains ... 

A typical effect observed in the synthesis of linear polymers by a free-radical mechanism is the auto-acceleration process. At a particular conversion, when sufficient polymer has accumulated in the system for the viscosity to reach a certain level, the rate of the bimolecular termination reaction begins to fall because of diffusional restrictions to the encounter of two chain ends. However, the initiation and growth rates are hardly affected. 

In contrast to these successful efforts to link dendrimers and linear polymer chains in the manner of bloek copolymers, only very recently has a breakthrough been achieved in the synthesis of linear polymers with dendritic side groups, and this will be highlighted in this contribution (Scheme 1). Considerable synthetic effort is required in preparing suitable dendritic monomers. The amazing kinetic and structural features observed for such monomers and the respective polymers are nevertheless highly rewarding. 

The tendency toward small ring formation precludes the synthesis of linear polymers by elimination of Hj or HCl from such compounds as RNHjBHj or RNHjBClj. Even such compounds with highly hindered amines tend toward ring formation (four- or eight-membered rings) rather than polymer formation when pyrolyzed ( 15.2.5.1.1). 

Schemes. Two ways of synthesis of linear polymers 7 constituted of (OQH4P(Ph)2=N-P(S)] repeating units...

The ratio of each specific chlorosilane produced using this process is dependent on the stoichiometry, catalyst, promoter, and exact conditions utilized. Most major manufacturers try to optimize the yield of dichloro-dimethyl silane, the raw material for the synthesis of linear polymers. The synthesis of chlorosilanes is as follows ... 

Note Combined ring-opening and polycondensation has been previously employed for the synthesis of linear polymers Namekawa, S. Uyama, H. Kobayashi, S. Biomacromolecules 2000, 7,335. 

Branching is very common and is observed during many polymerization processes. Polymers can be differentiated from each other based on the extent of branching. Some polymers are highly branched, while other polymers have only a minimal amount of branching or no branching at all. The former are called branched polymers, while the latter are called linear polymers. The synthesis of linear polymers often requires the use of special catalysts, described in the following section. 

The synthesis of linear polymer is accompanied by the formation of cyclics. The amount and structure of cyclics depends on the amount and structure of dihalide monomer Cl—R—Cl in the following order [7] ... 

Vandenberg et at. reported that cationic polymerization of those monomers leads to branched polymers, but they did not investigate the process in more detail because their interest at that time was in the synthesis of linear polymers. More recently, there has been an increasing interest in the synthesis of highly branched polymers, which in some applications may perform certain functions of dendrimers but being much easier to synthesize. 

Sulfur-containing heterocycles have rarely been used in ROP even though they are interesting for a variety of biomedical applications. Heterocycles higher than four membered cannot be polymerized by an anionic mechanism. While the cationic polymerization of thietanes leads to branched polymers or crosslinked networks, higher sulfur heterocycles were never used in the synthesis of hyperbranched polymers by ROP, since the synthesis of linear polymers is already... 

Synthesis of Linear Polymer Precursors by Living Anionic Polymerization... 

Equation 3.7 is presented in a good light for the description of curves a t) for the synthesis of linear polymers in the cases of both radical polymerisation [27] and polycondensation [5, 6]. The D value can be determined according to the slope of a linear plot of a as a function of t in double logarithmic coordinates as follows from Equation 3.7 and complex constant by a fitting method. In Figure 3.4 such a... 

Synthesis of Linear Polymers from Divinyl Compounds.63... 

Scheme 7.4 CuAAC-reaction-mediated synthesis of linear polymers examples of trialkynes and triazides used for the preparation of cross-linked polymers.

Figure 8.2 Synthesis of linear polymers by polymerizing dithiol and molecules with two thiol-reactive functionalities.

Figure 8.3 Synthesis of linear polymers by thiol-epoxy click" polymerization.

Figure 84 Synthesis of linear polymers by polyhydrothiolation of diynes with dithiols.

Figure 8.5 Synthesis of linear polymers by polymerization of monoalkyne and a dithiol...

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