Parameters for copolymerizations

The copolymerization parameters for copolymerization of dilactide and e-caprolactone catalyzed by stannous octoate, stannous chloride, and tetrabutyl titinate have been determined (5). 

TABLE IXa Reactivity Ratios and Q-e Parameters for Copolymerization of Allyl Esters (A/ ) with Vinyl Acetate (A/2) [64]... 

Table 4-15. Parameters for copolymerization of transition metal acrylates (M ) with (C2H5)2Ti(OCOC(CH3)=CH2)2 [134].

The Price-Alfrey approach begins by defining three parameters-P, Q, and e-for each of the comonomers in a reaction system. We shall see presently that the parameter P is rapidly eliminated from the theory. As a result, the Price-Alfrey system is also called the Q-e scheme for copolymerization. 

Tables IV and V contain appropriate balance equations for nonisothermal free-radical polymerizations and copolymerizations, which are seen to conform to equation 2k. Following the procedure outlined above, we obtain the CT s for homopolymerizations listed in Table VI. Corresponding CT s for copolymerizations can be. obtained in a similar way, and indeed the first and fourth listed in Table VII were. The remaining ones, however, were derived via an alternate route based upon the definitions in Table VI labeled "equivalent" together with approximate forms for pj, which were necessitated by application of the Semenov-type runaway analysis to copolymerizations, and which will subsequently be described. Some useful dimensionless parameters defined in terms of these CT s appear in Tables VIII, IX and X.

This type of reaction is involved as an intermediate step in few synthetically useful reactions, in the formation of polysulfones by copolymerization of an olefin with SO 2, as well as in aerosol formation in polluted atmospheres. We will discuss later in some detail the most important chain reactions involving step 11. However, Good and Thynne determined the Arrhenius parameters for the addition of methyl and ethyl radicals to SO2 in gas phase, the rate constants being 5 x 10 and 4 x 10 s respectively at ambient... 

Although the basic mechanisms are generally agreed on, the difficult part of the model development is to provide the model with the rate constants, physical properties and other model parameters needed for computation. For copolymerizations, there is only meager data available, particularly for cross-termination rate constants and Trommsdorff effects. In the development of our computer model, the considerable data available on relative homopolymerization rates of various monomers, relative propagation rates in copolymerization, and decomposition rates of many initiators were used. They were combined with various assumptions regarding Trommsdorff effects, cross termination constants and initiator efficiencies, to come up with a computer model flexible enough to treat quantitatively the polymerization processes of interest to us. 

An alternative route for the preparation of styrenic macromonomers is the reaction of living chains with 4-(chlorodimethylsilyl)styrene (CDMSS) [192]. The key parameter for the successful synthesis of the macromonomers is the faster reaction of the living anionic chain with the chlorosilane group rather than with the double bond of the CDMSS. Anionic in situ copolymerization of the above macromonomers (without isolation) with conventional monomers leads, under appropriate conditions, to well-defined comb-like chains with a variety of structures. 

The polymerization time as a polymerization parameter for adjustment of the porous properties of thermally initiated copolymers has recently been characterized [111]. A polymerization mixture comprising methylstyrene and l,2-bis(p-vinylbenzyl)ethane as monomers was subjected to thermally initiated copolymerization for different times (0.75, 1.0, 1.5, 2, 6, 12, and 24h) at 65°C. The mixtures were polymerized in silanized 200pm I.D. capillary columns as well as in glass vials for ISEC and MIP/BET measurements, respectively. 

The copolymerization parameters for the higher temperatures were calculated from the values at lower temperatures using the Arrhenius equation. The copolymerization curves calculated by Equations 33 and 34 do not agree with the experimental results. 

Figure 8.16 Reaction coordinate diagram with activation parameters for the copolymerization of oxetane and C02 and for the ring-opening polymerization of TMC.

Shen et al. determined the BD/IP copolymerization parameters for the polymerization with the ternary catalyst system NdN/TIBA/EASC at 50 °C ted = 1.4 and np = 0.6 [92]. Over a wide range of BD/IP copolymer compositions the experimentally determined Tg values significantly deviate from the theoretical curve which was calculated by the Fox equation for random copolymers. Only for IP-contents < lOwt. % does the experimentally determined data coincide with the theoretical curve. Shen et al. also succeeded to synthesize block copolymers comprising poly(butadiene) and poly(isoprene) building blocks [92]. 

Unique effects in the copolymerization of BD and St were reported by Oehme et al. who apply a special addition and aging procedure for the catalyst system NdO/TIBA/CCU (molar composition 1/29/24) [504], Exceptionally high cis- 1,4-contents go along with high contents of incorporated St. Even at St contents as high as 80 mol % the microstructure of the BD units still is ca. 90% cis-1,4. The only disadvantage of these catalyst systems are low activities when high amounts of St are incorporated. The authors also report on the copolymerization parameters for this system ted = 4.3 and rst = 0.5. 

Copolymerization Parameters for Ethylene/a-Olefin Copolymerization with Various Metallocene/MAO Catalysts 1... 

Table 17. Copolymerization parameters for the copolymerization of captodative substituted acrylates CH2=C(rf)COOR (Mt) and styrene (M2) at 60 °C...

The intervals of the variation of parameters xin and y, where such a regime exists, have been theoretically established [17] for copolymerization of styrene with... 

Table 5. Copolymerization parameters for ethene/a-olefin copolymerization by using different metallocene/MAO catalysts...

At present, the kinetic parameters for prediction of copolymerization rates are scanty, except for a few low conversion copolymerizations of styrene and some acrylic comonomers. Engineering models of high conversion eopolymerizations are, however, overdetermined, in the sense that the number of input parameters (kinetie rate constants, activation energies, enthalpies of polymerization, and soon)... 

The lack of reliable information on kinetic parameters for the copolymerization of important cyclosiloxanes with ring sizes exceeding three is a serious deficiency. Industrial and routine laboratory syntheses rely almost entirely on such monomers, and in many cases, the processes are copolymerizations. An understanding of these constants would give valuable information on copolymer microstructure and its control. Unambiguous studies... 

The composition of copolymers obtained in a free radical polymerization can be predicted based on several kinetic parameters of copolymerization reaction. For a copolymer starting with two species of monomer P and P , it can be assumed that the rate of addition of the monomer to a growing free radical depends only on the nature of the end group. If the chain is indicated by X, this is equivalent with the assumption that the radical Ri will act equivalently with X-R, and the radical R will act equivalently with X-Ri . The following reactions will take place in the system ... 

All the above factors controlling monomer and radical reactivities contribute to the rate of polymerization, but in a manner which makes it difficult to distinguish the magnitude of each effect. Attempts to correlate copolymerization tendencies based on these factors are thus mainly of a semiempirical nature and can, at best, be treated as useful approximations rather than rigorous relations. However, a generally useful scheme was proposed by Alfrey and Price [23] to provide a quantitative description of the behavior of diferent monomers in radical polymerization, with the aid of two parameters, for each monomer rather than for a monomer pair. These parameters are denoted by Q and e and the method has been called the Q — e scheme. It allows calculation of monomer reactivity ratios r and T2 from properties of monomers irrespective of which pair is used. The scheme assumes that each radical or monomer can be classified according to its reactivity or resonance effect and its polarity so that the rate constant... 

Graft Copolymers. In graft copolymerization, a preformed polymer with residual double bonds or active hydrogens is either dispersed or dissolved in the monomer in the absence or presence of a solvent. On this backbone, the monomer is grafted in free-radical reaction. Impact polystyrene is made commercially in three steps first, solid polybutadiene rubber is cut and dispersed as small particles in styrene monomer. Secondly, bulk prepolymerization and thirdly, completion of the polymerization in either bulk or aqueous suspension is made. During the prepolymerization step, styrene starts to polymerize by itself forming droplets of polystyrene with phase separation. When equal phase volumes are attained, phase inversion occurs. The droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. R. L. Kruse has determined the solubility parameter for the phase equilibrium. 

The experimental values available for the constant Kn, in general, do not agree with those predicted by the considerations of Gordon and Taylor. Wood [7] suggested, therefore, to consider Kn as a characteristic parameter for the particular copolymeric system, not necessarily related to the A values of the homopolymers. 

Table 6. Kinetic and thermodynamic parameters for epoxide-anhydfide-initiator copolymerization ... 

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