Polymerization modes

The azo initiator initially present therefore has to be classified as a transfer agent—it is able to combine monomers polymerized by different polymerization modes with each other. Three different modes of block copolymer synthesis via azo transfer agents can be distinguished ... 

Lipase is an enzyme which catalyzes the hydrolysis of fatty acid esters normally in an aqueous environment in living systems. However, hpases are sometimes stable in organic solvents and can be used as catalyst for esterifications and transesterifications. By utihzing such catalytic specificities of lipase, functional aliphatic polyesters have been synthesized by various polymerization modes. Typical reaction types of hpase-catalyzed polymerization leading to polyesters are summarized in Scheme 1. Lipase-catalyzed polymerizations also produced polycarbonates and polyphosphates. 

C2-symmetric species, which can produce isotactoid and isotactic polymers, are obtainable by occupation of one and two vicinal positions.123 An easy switch between these three polymerization modes has recently been proposed on the basis of a high-resolution 13C NMR microstructural analysis.119d... 

The introduction of HF reduces the pH value of the final suspension and increases its viscosity this influences further the polymerization mode of silicate species, leading to the formation of regular hexagonal silica framework. The experimental results reveal that, for F7Si molar ratio of 0.20-0.39, the pH value of the suspension changes from 12.5 to 9.5 and the XRD patterns of the synthesized materials display distinct four-peak profiles. 

The patents quoted in Table 20 give rather broad temperature ranges. An explanation for this feature is the polymerization mode which is used for the large-scale polymerization of Nd-BR. To the best of our knowledge, adiabatic rather than isothermic modes are used. In the adiabatic mode polymerization heat is neither removed by external nor by evaporation cooling. Therefore,... 

The relationship between monomer structure and its polymerization mode... 

This is a very important polymerization mode. Usually these polymerizations can be made to proceed by the living mechanism, even cationic. Important polymers are produced in this way (some polyamides, polysiloxanes, polyacetals, polyethers, polyimines, etc.). 

The rheological and flow properties of ordered block copolymers are extraordinarily complex these materials are well-deserving of the apellation complex fluids. Like the liquid-crystalline polymers described in Chapter 11, block copolymers combine the complexities of small-molecule liquid crystals with those of polymeric liquids. Hence, at low frequencies or shear rates, the rheology and flow-alignment characteristics of block copolymers are in some respects similar to those of small-molecule liquid crystals, while at high shear rates or frequencies, polymeric modes of behavior are more important. 

The in vitro polyester synthesis can proceed via two major polymerization modes (see Scheme 4.1) ... 

In a paper devoted to the investigation of radical co-polymerization of vinylidene cyanide with a variety of monomers, an unusual autocatalytic behavior was reported for the pair vinylidene cyanide - vinyl ether251. The authors suggested a possible mutual co-initiation of anionic polymerization of vinylidene cyanide, inducing a cationic polymerization mode of vinyl ether. 

The transformation reactions may be realized within the same polymerization mode, without changing the nature of the propagating species. Such transformations combine different initiation processes of the same polymerization mechanism. Although the most common of these are among the controlled radical... 

Lim et al. used a palladium complex for the cationic polymerization of TH F and the ROMP of NB [10]. The same group also showed that even condensation and chain polymerization could be performed simultaneously in one step (Scheme 11.45). This was achieved by the use of unimolecular compounds which can simultaneously act both as an initiator for chain polymerization, and as an end-capper for condensation polymerization. The method provides a simple means of combining NMRP with a condensation polymerization to yield interesting and useful block copolymers [207]. Another interesting new system for the combination of chain (AROP of CL) and step (dehydration polycondensation) polymerizations for polyester-based new material, in which scandium trifluoromethane sulfonate catalyzed both polymerization modes, was reported by Takasu et al. (Scheme 11.46) [208]. 

Although, normally, in the aqueous environment associated with a living system, Hpase wiU catalyze the hydrolysis of fatty acid esters, certain isolated lipases have been found to be stable in organic solvents and capable of serving as a catalyst for the reverse reaction [1, 2]. Hence, by employing a lipase-mediated catalysis of esterifications and transesterifications in an organic medium, functional aliphatic polyesters have been created with a variety of polymerization modes (Scheme 23.7). 

Fink synthesized a series of siUcone-based surfactants [39] and used these to examine the emulsion polymerization of vinyl pyrrolidone (VP) in CO2. These monomers are liquids under ambient conditions, and hence phase behavior in CO2 was measured to determine under what conditions one could operate in an emulsion polymerization mode (Fig. 7.7). As is the case with NVF, the phase behavior of 1-vinyl-2-pyrrolidone offers the possibility for distinct polymerization regimes. Above pressures of ca. 28 MPa at 338 K, VP is miscible with carbon dioxide in all proportions. Below 28 MPa, VP and CO2 will either phase split into monomer-rich and C02-rich phases, or exist as a single phase, depending upon the initial VP concentration and system pressure. Consequently, a polymerization can be conducted initially in the single phase regime above 28 MPa, leading to a purely dispersion mechanism, or initially within the two-phase dome in P-x space, leading to an inverse emulsion polymerization. Finally, a polymerization can be conducted where pressure and composition are chosen to initially... 

The positive curvature and the following maximum of the creep compliance L(r) indicate the contribution of polymeric molecular modes of motion to the recoverable compliance. Since no positive curvature is seen in the volume contraction Lq t), no polymeric modes are present and no long range coordinated motions of any kind are detected. 

A very interesting and promising technology is the polymerization of propylene under supercritical conditions. On the one hand, this polymerization mode enhances the heat removal capabilities drastically. On the other hand, this technology combines the advantages of both the gas phase and bulk processes in respect to polymer solubility, comonomer and hydrogen miscibility and space-time yield. A precondition of this... 

Both chain and stepwise polymerization modes have been used to form polymer I. However, only limited studies have been done using a stepwise polymerization for polymer II. 

To produce high-fidelity printed stmctures, the bioink needs to polymerize quickly, within seconds, or already be in a gelled state. Two distinctive polymerization modes... 

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