Polymerization parameters, hydrogen

Keii119> studied recently the effect of polymerization time, hydrogen, donor and aluminum alkyl on the MWD of propylene obtained with the MgCl2/TiCl4/EB— AlEtj/EB catalyst system. The isotactic and atactic fraction polydispersity indexes were found to be independent of the above parameters, and very close to each other (Mw/Mn = 3-5) as previously reported by Suzuki133) and Kashiwa,34). The Mw/Mn values of the overall polymer are lower than in the case of TiCl3 and are better represented by a Wesslau-type log-normal correlation than by a Tung-type correlation, as is the case of unsupported catalysts. 

Little data is available concerning the effect polymerization parameters such as monomer concentration, type and concentration of aluminum alkyl, hydrogen, and temperature have on Cp and kp values. The polymerization rate is generally considered proportional to the monomer concentration 32,38, The widest range of pro-... 

For AA, bulk polymerization parameters are not accessible because of the insolubility of poly(AA) in its own monomer. The a( p,aa) values for polymerization in aqueous solution containing 20 and 40 wt.-% AA (entries 5 and 6 in Table 1), respectively, are both close to 12 kJ moL It appears reasonable to assume that a value of this size should also apply to bulk AA polymerization. Thus, also with the acrylic systems, the value of the acid monomer, a(Vaa). would be by about 6 kJ moL below the methyl ester value, a(Vma)> which indicates a similar effect of the hydrogen bonded interactions on the activation barrier for the propagation reaction upon passing from MAA to MMA and from AA to MA. It should be noted that the quantum-chemical calculations in Ref.P predicted a lowering of a( p,aa) upon introducing a water solvent field as compared to a(, aa) in the gas phase. These calculations, however, did not... 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Incineration of a collection of polymers with 10 different kinds of brominated flame retardants has been studied under standardized laboratory conditions using varying parameters including temperature and air flow. Polybrominated diphenyl ethers like the deca-, octa-, and pentabromo compounds yield a mixture of brominated dibenzofurans while burning in polymeric matrices. Besides cyclization, debromination/hydrogenation is observed. Influence of matrix effects and burning conditions on product pattern has been studied the relevant mechanisms have been proposed and the toxicological relevance is discussed. 

In principle, carbometallation of an alkene (RCH=CH2) with a coordinatively unsaturated organotransition metal compound (R1 M I. ) can produce a monomeric carbometallation product 1 (Scheme 6). This reaction may not, however, stop at this stage. It can be accompanied by other processes of which (i) hydrogen-transfer hydrometallation to produce a potentially thermodynamically more favorable mixture of a 1,1-disubstituted alkene and a hydrometallation product 2 and (ii) polymerization to produce polyalkenes 3 are representative. The extents to which these side-reactions occur are functions of relative rates of various competing processes. For example, accumulation of the monomeric carbometallation product 1 can be favored in cases where the starting R1 MTL is more reactive toward alkenes than 1. The organometal/alkene ratio is also an important parameter, since neither of the two side-reactions can proceed after all of the starting alkene has reacted. 

Experimental data on Op and On for different polymer materials exhibit unique correlations with (hydrogen bonding) and 6(j (dispersion) components respectively of solubility parameter 6gp of polymer (53,60) which can be calculated from data on structural group contributions to and available in the literature (61). The existence of such correlations (Figures 9(a) and 9(b)) indicate that LSC data can be used to characterize the chemical nature of polymeric membrane materials. 

The kinetic and activation parameters for the decomposition of dimethylphenylsilyl hydrotrioxide involve large negative activation entropies, a significant substituent effect on the decomposition in ethyl acetate, dependence of the decomposition rate on the solvent polarity (acetone-rfe > methyl acetate > dimethyl ether) and no measurable effect of the radical inhibitor on the rate of decomposition. These features indicate the importance of polar decomposition pathways. Some of the mechanistic possibilities involving solvated dimeric 71 and/or polymeric hydrogen-bonded forms of the hydrotrioxide are shown in Scheme 18. 

The nucleation mechanism of dispersion polymerization of low molecular weight monomers in the presence of classical stabilizers was investigated in detail by several groups [2,6,7]. It was, for example, reported that the particle size increased with increasing amount of water in the continuous phase (water/eth-anol), the final latex radius in their dispersion system being inversely proportional to the solubility parameter of the medium [8]. In contrast, Paine et al.[7] reported that the final particle diameter showed a maximum when Hansen polarity and the hydrogen-bonding term in the solubility parameter were close to those of steric stabilizer. 

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