Poly monomer conversion

The enolate species 2, derived from methacrylates with bulkier ester groups than MMA, are sterically protected against the access of BujAl under the above-mentioned conditions, even when the porphyrin moiety is a non-ortho-substituted tetraphenylporphyrin. An example is shown by the polymerization of ethyl methacrylate (EMA) using 1 (X=Me) as an initiator, where the growing species have an EtO group in the terminal enolate unit 2 (R=Et). After the addition of BujAl to the system, polymerization proceeded to 100% monomer conversion within 10 min. The Mn of the produced polymer was close to the expected value, and the MWD was narrow (Table 5, run 5). A similar result was obtained for the polymerization of isopropyl methacrylate (PMA) with the 1 (X= Mel- soBujAl system, which quantitatively gave a narrow MWD poly(methacr-ylate) with a predicted Mn (Table 5, run 6). 

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

Three arm amphiphilic star block copolymers of IBVE and 2-hydroxyethyl vinyl ether (HOVE) were prepared using the trifunctional initiator 8 with sequential cationic polymerization of two hydrophobic monomers, IBVE and AcOVE. Subsequent hydrolysis of the acetates led to the hydrophilic poly(HOVE) segments [38]. Two types of stars were prepared depending on which monomer was polymerized first three arm star poly(IBVE-h-HOVE), with the hydrophobic part inside and three arm star poly(HOVE-h-IBVE), with the hydrophobic part outside. When IBVE was polymerized first, the experimental conditions were the same as described in Sect. 2.2.1. After reaching quantitative monomer conversion, AcOVE was added and temperature was raised from 0 to 40 °C to accelerate the reaction since this monomer is less reactive than IBVE. When starting with AcOVE as a first block, both polymerizations were carried out at 40 °C. SEC analysis showed that MWDs were narrow for the two steps whatever the se-... 

Recently, the impact of the metal alkyls TIBA, DIBAH and ZnEt2 on molar mass was comparatively studied. In these studies ternary NdV-based catalyst systems were used [178-182]. The first two of these studies focus on molar mass control by DIBAH and by TIBA. Linear dependencies of Mn on monomer conversion were obtained. In addition, PDIs decreased with increasing monomer conversion. On the basis of these observations it was concluded that chain transfer of living poly(butadien)yl chains between Nd and Al is fully reversible. A reaction mechanism which accounts for these features is outlined in Scheme 32. 

Irradiations were conducted at 366 nm (Corning 7-83 filter combination) in a merry-go-round apparatus in which the samples rotated about a stationary 450-Watt Hanovia medium pressure lamp for constant light exposure. The samples consisted of degassed 5 ml solutions of the photoinitiators in neat MMA contained in Pyrex tubes. Two initiator concentrations were utilized 1.05 x 10and 4.11 x 10 which corresponded to 16 and > 99% light absorption, respectively. Samples were irradiated to about 7% monomer conversions which required 15 min for the optically dense solutions and 30 min for the tubes with low initiator concentration. The resulting poly-... 

Reactions that convert the alkoxyamines to hy-droxylamines and alkenes can strongly limit the monomer conversion. These are either usual radical disproportionations between the nitroxide and the propagating radicals or concerted alkoxyamine decays. Both pathways lead to an exponential decrease of the concentration of the dormant chains with rate constant kdec = f)kd, where fn is the fraction of the side reaction concurring with radical coupling of alkoxyamine decay.57 kdec can be measured from the decay of the dormant alkoxyamine chains under nonscavenging conditions, and its relation with kd provides fn. From data of Fukuda et al. one can deduce fn = 0.4% for a TEMPO-polystyryl compound and fn = 1.1% for a di-tert-butylnitroxide-poly-terf-butylacrylate macroinitiator both at 120 °C.53,55 Similar small values of fn hold for TEMPO-cumyl (Scheme 10),22 TEMPO-1-phenylethyl,112 and a better mimetic compound for TEMPO-polystyryl.113 In these cases, fn probably represents the usual radical disproportionation. A much larger fn 25% holds for TEMPO—... 

Matyjaszewski and has subsequently been applied to a wide range of monomers. The first system consists of CuCl and 2,2 -bipyridine (L-l) ligand, coupled with 1-phenylethyl chloride as an initiator.28 Though a heterogeneous system, the polymers had controlled Mn, in direct proportion to monomer conversion up to 100000 amu, and narrow MWDs (MJ Mn< 1.5). The Cu(I)/L-l system also proved effective for other monomers such as MA. The use of CuBr and a bromide initiator narrows the MWDs of polystyrene and poly(MA) (MJMn l.l), while broader MWDs (MJMn 1.4) were obtained for poly(MMA).84... 

Detailed studies were performed on the copper-catalyzed suspension or emulsion polymerizations.249 Living or controlled emulsion radical polymerization of nBMA can be achieved in the presence of nonionic poly(oxyethylene)-based surfactants such as Brij 97, Brij 98, and Tween 20 with the F21 (X = Br)/CuBr/ L-3 or L-4 system.249,251,252 The Mn increased in direct proportion to monomer conversion up to 5 x 104 (MJ Mn = 1.1 —1.2). The particle sizes are around 1000— 4000 nm, suggesting a suspension, but can be reduced to about 300 nm with the use of hexadecane as a cosurfactant along with ultrasonication.249 252... 

FIGURE 12.7 Monomer conversion vs. polymerization time for two initiator concentrations. (Example for poly(NIPAM) particles polymerization temperature T = 70°C, [NIPAM] = 48.51 mmoles, [MBA] = 3 mmol,... 

This high tendency of poly(ethylene oxide) to solvate cations and from the polymeric shell around the counterion leads to autoacceleration in polymerization (polymerization faster on solvated ion-pairs), and increase of conductivity with monomer conversion. Moreover, polymerization is not sensitive to the "external" solvating agents, e.g. crown ethers. 

Pan et al. prepared a macroinitiator by chloromethylation of a commercially available AB block copolymer of poly (styrene-fe-ethylene-co-propylene) (SEP) and used it as a macroinitiator for the ATRP of ethyl methacrylate (EM A) [302]. The kinetic plot showed little evidence of termination during the reaction and the molecular weight of the graft copolymer increased linearly with the monomer conversion, resulting in a final Mn=73,200 and Mw/Mn=1.22. The weight ra-... 

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