Molecular Weight Regulating Agents

Molded products can be obtained without employing melt molding methods, such as injection molding, extrusion molding, and 

Various molded products can be made from the materials. In particular, transparent molded products can be obtained. The materials exhibit excellent mechanical strength, such as impact resistance, low permeation of water or water vapor and excellent solvent resistance. Therefore, they can be used for optical uses such as lens, prisms, and polarizing films. 

Further, they can be used for medical purposes, such as press-through packages, disposable syringes, liquid medicine vials, and infusion bags. They are suitable for electric or electronic materials, such as wire coating. In addition, packaging films, such as wrapping films, stretch films, shrink films, and blister packs can be produced. 

---

With 1,3-dimethylimidazolidinone as a solvent, higher condensation temperatures can be reached. Higher molecular weights are also obtained, therefore 1,3-dimethylimidazolidinone is favored as a solvent. Monovalent nitriles, such as 2-fluorobenzonitrile, act as a molecular weight regulation agent ... 

Monovalent nitriles, such as 2-lluorobenzonitrile, act as a molecular weight regulation agent [8]. 

Essentially, at a fixed monomer feed composition and temperature such a dependence is of universal character irrespective of the way of molecular weight regulation, which could be performed by changing the concentration either of the initiator or the transfer agent. Just on this universal curve the points fall which characterize the composition and molecular weight of the fractions isolated from copolymers synthesized under different contents of initiator and transfer agent. 

Acyclic olefins act as chain scission agents in cycloolefin polymerization hence, they are employed as molecular weight regulators. Equations (48)-(50) illustrate the sequence by which chain scission is achieved ... 

SCHEME 16.4 Mechanism of molecular weight regulation hy the use of a-olefins as chain transfer agents (CTAs) in the addition polymerization of norhomene hy Ni-hased catalysts. 

Figure 8 Mechanism of the molecular weight regulation by the use of 1 -olefins as chain transfer agents in the addition polymerization of norbomene by Ni-based catalysts.

Very often one introduces into the medium of polymerization reaction some compounds, which serve as achain transfer agents. They are known in the polymer ehemistry under the name of moderators or molecular weight regulators. As examples one ean cite chlorinated hydrocarbons, dodecyl... 

The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... 

The concentrations of both chain transfer agent and initiator are important for the polymerization when the concentration of HPMA is constant. The molecular weight of the ST HPMA polymers was regulated by the concentration ratio of mercaptan (S) to HPMA (M), according to the Mayo equation, lT>P (end) = + Q[S]/[M] [27]. DP (end) are the num-... 

Chain-transfer agents have been called and employed as regulators (of molecular weight). When used in large proportions, they are called telogens, since they produce low-molecular weight polymers (telomers). 

In polymerizations with Ziegler-Natta catalysts, molecular hydrogen is the preferred regulation agent for controlling the molecular weight. 

The chain transfer agent (X-A) that will regulate the molecular weight of the polymer. 

---