Styrene polymerization initiator efficiency

The Instantaneous values for the initiator efficiencies and the rate constants associated with the suspension polymerization of styrene using benzoyl peroxide have been determined from explicit equations based on the instantaneous polymer properties. The explicit equations for the rate parameters have been derived based on accepted reaction schemes and the standard kinetic assumptions (SSH and LCA). The instantaneous polymer properties have been obtained from the cummulative experimental values by proposing empirical models for the instantaneous properties and then fitting them to the cummulative experimental values. This has circumvented some of the problems associated with differenciating experimental data. The results obtained show that ... 

The effect of the nitrone stmcture on the kinetics of the styrene polymerization has been reported. Of all the nitrones tested, those of the C-PBN type (Fig. 2.29, family 4) are the most efficient regarding polymerization rate, control of molecular weight, and polydispersity. Electrophilic substitution of the phenyl group of PBN by either an electrodonor or an electroacceptor group has only a minor effect on the polymerization kinetics. The polymerization rate is not governed by the thermal polymerization of styrene but by the alkoxyamine formed in situ during the pre-reaction step. The initiation efficiency is, however, very low, consistent with a limited conversion of the nitrone into nitroxide or alkoxyamine. 

Zhao and Brittain [280-282] reported the LCSIP of styrene on planar silicon wafers using surface modifications of 2-(4-(ll-triethoxysilylundecyl)phenyl-2-methoxy-propane or 2-(4-trichlorosilylphenyl)-2-methoxy-d3-propane respectively. Growth of PS brushes from these SAMs has been successfully achieved factors that influence PS thickness included solvent polarity, additives and TiC concentration. Sequential polymerization by monomer addition to the same silicate substrate bearing the Hving polymer chains resulted in thicker PS films. FTIR-ATR studies using a deuterated initiator indicated that the initiator efficiency is low, and the... 

The ability to conduct radical reactions without the use of tin reagents is important. Allylic triflones have been used to conduct allylation reactions on a range of substrates (39) as a replacement for allyltributylstannane (Scheme 28). The main limitation was that unactivated or trisubstituted triflones failed to undergo reactions. In other nontin radical methods, arenesulfonyl halides have been used as functional initiators in the CuCl/4,4 -dinonyl-2, 2 -bipyridine-catalysed living atom-transfer polymerization of styrenes, methacrylates, and acrylates.The kinetics of initiation and propagation were examined with a range of substituted arylsulfonyl halides with initiator efficiency measured at 100%. 

The rate expression Eq. 3-32 requires a first-order dependence of the polymerization rate on the monomer concentration and is observed for many polymerizations [Kamachi et al., 1978], Figure 3-2 shows the first-order relationship for the polymerization of methyl methacrylate [Sugimura and Minoura, 1966], However, there are many polymerizations where Rp shows a higher than first-order dependence on [M], Thus the rate of polymerization depends on the -power of the monomer concentration in the polymerization of styrene in chlorobenzene solution at 120°C initiated by t-butyl peresters [Misra and Mathiu, 1967]. The benzoyl peroxide initiated polymerization of styrene in toluene at 80°C shows an increasing order of dependence of Rp on [M] as [M] decreases [Horikx and Hermans, 1953], The dependence is 1.18-order at [M] = 1.8 and increases to 1.36-order at [M] = 0.4. These effects may be caused by a dependence of the initiation rate on the monomer concentration. Equation 3-28 was derived on the assumption that Rt is independent of [M], The initiation rate can be monomer-dependent in several ways. The initiator efficiency / may vary directly with the monomer concentration... 

Difunctional initiators such as sodium naphthalene are useful for producing ABA, BABAB, CAB AC, and other symmetric block copolymers more efficiently by using fewer cycles of monomer additions. Difunctional initiators can also be prepared by reacting a diene such as /n-diisoprope ny I benzene or l,3-bis(l-phenylethenyl)benzene with 2 equiv of butyl-lithium. Monomer B is polymerized by a difunctional initiator followed by monomer A. A polymerizes at both ends of the B block to form an ABA triblock. BABAB or CABAC block copolymers are syntehsized by the addition of monomer B or C to the ABA living polymer. The use of a difunctional initiator is the only way to synthesize a MMA-styrene-MMA triblock polymer since MMA carbanion does not initiate styrene polymerization (except by using a coupling reaction—Sec. 5-4c). 

According to their recent reports [11], 5 provides livingness of polymerization for styrene (ST) and methyl methacrylic acid (MA). Irrespective of the type of monomer, the initiator efficiency / was over 0.9, and the polydis-persity index, Mw/Mn (Mw weight-average molecular weight, Mn number-average molecular weight), was close to unity (approximately 1.2). The polymerization rate was very low (on the order of an hour), i.e., a very slow... 

Monomers which can be polymerized with aromatic radical anions include styrenes, dienes, epoxides, and cyelosiloxares. Aromatic radical anions which are too stable do not efficiently initiate polymerization of less reactive monomers thus the anthracene radical anion cannot initiate styrene polymerization. 

Block copolymers of e-CL with D,L-lactide, styrene, or butadiene have been synthesized using these initiators. Efficient and versatile initiators based on a,(3,y,6-derivatives of tetraphenylporphinato-aluminum for the polymerization of e-CL, (3-lactones, 6-lactones, and lactides have been reported [99,100]. 

The key feature of Inisurfs is their surfactant behavior. They form micelles and are adsorbed at interfaces, and as such they are characterized by a critical micelle concentration (CMC) and an area/molecule in the adsorbed state. This influences both the decomposition behavior and the radical efficiency, which are much lower than those for conventional, low molecular weight initiators. Tauer and Kosmella [4] have observed that in the emulsion polymerization of styrene, using an Inisurf concentration above the CMC resulted in an increase in the rate constant of the production of free radicals. This was attributed to micellar catalysis effects as described, for example, by Rieger [5]. Conversely, if the Inisurf concentration was below the CMC the rate constant of the production of free radicals decreased with an increase in the Inisurf concentration, which was attributed to enhanced radical recombination. Also note that a similar effect of the dependence of initiator efficiency on concentration was reported by Van Hook and Tobolsky for azobisisobutyronitrile (AIBN) [6]. 

Waak 15) also used other unsaturated lithium organic initiators (such as allyl-lithium, crotyllithium) for styrene polymerization. Though more efficient than vinyllithium, these initiators exhibit the same disadvantages. Therefore, the same conclusions apply. 

In contrast, recent kinetic investigation of the polymerization of spacerless G2 dendron-substi-tuted styrene and methylmethacrylate, respectively, in solution lead to the unexpected conclusion that above a certain critical monomer concentration a strong increase in the rate of the free radical polymerization is observed [21]. The results can be explained by self-organization of the growing polymer chain to a spherical or columnar superstructure in solution, depending on the degree of polymerization (DP, Fig. 2). The rate constants and low initiator efficiency lead one to conclude that the self-assembled... 

Although carboxylic acids generally form 1 1 adducts with alkenes, the resulting esters are easily ionized in the presence of either Lewis or protonic acids. The higher efficiency of chlorinated acetic acids relative to hydrogen halides is ascribed to the ability of their 1 1 adducts to coordinate with excess acid. Alkyl halides are eventually formed when carboxylic acids are used to initiate polymerization in the presence of a Lewis acid due to migration of the carboxylate moiety to the Lewis acid [Eq. (25)]. Similarly, styrene and isobutene polymerizations initiated by preformed alkyl acetate adducts in the presence of BC13 always produce Cl-terminated chains [104,105]. 

On the basis of the obtained results we have assumed, that in case of styrene polymerization in the presence of BZ2O2 the rate of initiation changes on ly due to change of concentration of peroxide. Possible chsmge of initiation efficiency will, in this case, be included in the effective value of Kp/Kt. 

The -fluorenyl titanium compound Ti(771-Flu)(OPr1)3 has been prepared by reaction of TiCKOPr1 with equimolar amounts of LiFlu. It is obtained as a mixture with the derivative Ti -FluX -FluXOPr1) The complex has been characterized by X-ray analysis and variable-temperature NMR spectroscopy. In combination with MAO, the compound is a highly efficient initiator for styrene polymerizations, producing highly syndiotactic polymers.20... 

In another example, the novel Rh(I) complex Rh-2 was employed with CC14 for MMA and styrene bulk polymerizations at 60 °C, which reached 90% conversion in 14 h.140 The MWD of PMMA was narrower than that of polystyrene MJMn = 1.43 vs 2.08), while the initiation efficiency was very low in both cases. 

A group 6 metal complex can be a candidate as a catalyst for radical polymerization because of its variable oxidation states, despite its sensitivity to air and protic compounds. A lithium molybdate(V) complex (Mo-1) can polymerize styrene in conjunction with benzyl chloride in toluene at 80 °C to yield polystyrene with relatively broad MWDs (MJMn = 1.5—1.7).144 The initiation efficiency was low ( 10%), and decomposition of the complex was observed. 

Perfluoroalkanesulfonyl halides 1-35 and 1-36 induced controlled polymerization of styrene and MMA in the presence of copper catalysts, although the initiation efficiency is lower.177 With the alkanesulfo-nyl halides 1-35 and 1-36, decomposition by loss of S02 from the initial sulfonyl radical occurs to give a perfluoroalkyl radical, which then adds to the monomer to initiate the polymerization. 

Problem 8.28 Consider styrene polymerization by triflic (trifluoroethanesul-fonic) acid in 1,2-dichloroethane at 20°C where is 4.2x10 mol/L (23]. For experiments performed (using stopped-flow rapid scan spectroscopy) at a styrene concentration of 0.397 M and acid concentration of 4.7x10 M at 20°C, the maximum concentration of cationic ends (both free ions and ion pairs) was found [23] to be 1.4x10 M, indicating that the initiator efficiency is 0.030. At 20°C, kf / is reported [23] to be 12. 

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