Macromonomers reactivity ratios

The reactivity of macromonomers in copolymerizalion is strongly dependent on the particular comonomer-macromonomer pair. Solvent effects and the viscosity of the polymerization medium can also be important. Propagation may become diffusion controlled such that the propagation rate constant and reactivity ratios depend on the molecular weight of the macromonomer and the viscosity or, more accurately, the free volume of the medium. 

Yamashita and co-workers have also determined the reactivity ratios of styryl terminated PDMS macromonomers (M,) with styrene (M2) and methyl methacrylate (M2)123>. They have determined (r2) and (r2) as 1.1 and 0.60 respectively. These values... 

A second test was done by using butyl acrylate as the comonomer as shown in Figure 11. The reactivity ratios in this case are such that the methacrylate functionality would react slower with acrylates than with vinyl chloride. As predicted the butyl acrylate is at 62% conversion before the MACROMER peak is significantly diminished. These data add validity to the hypothesis that the placement of side chains in the backbone is dependent on the terminal group of the macromonomer and the relative reactivity of its comonomer. 

Table 2. Dependence of the reactivity ratio r2 and the rate of polymerization in the dispersion copolymerization of PEO-MA macromonomer and styrene (M2) with the monomer feed composition3...

The S-PIB macromonomer was copolymerized by radical copolymerization with MMA and S, and the reactivity ratio of the small comonomer was calculated by a modified copolymer equation [85]. With MMA, rMMA=0.5 was obtained, i.e., close to that reported for conventional S/MMA system. With S however, rs= 2.1 was determined which suggested that the reactivity of S-PIB is lower than that of S, possibly due to steric interference. 

The relative reactivity of the macromonomer in copolymerization with a common comonomer, A, can be assessed by l/rA=kAB/kAA> i-e-> the rate constant of propagation of macromonomer B relative to that of the monomer A toward a common poly-A radical. In summarizing a number of monomer reactivity ratios in solution copolymerization systems reported so far [3,31,40], it appears reasonable to say that the reactivities of macromonomers are similar to those of the corresponding small monomers, i.e., they are largely determined by the nature of their polymerizing end-group, i.e., essentially by their chemical reactivity. 

Narrow distribution in the backbone length as well as in the chemical composition or the branch frequency may be expected from a living-type copolymerization between a macromonomer and a comonomer provided the reactivity ratios are close to unity. This appears to have been accomplished to some extent with anionic copolymerizations with MMA of methacrylate-ended PMMA, 29, and poly(dimethylsiloxane) macromonomers, 30, which were prepared by living GTP and anionic polymerization, respectively [50,51]. Recent application [8] of nitroxide (TEMPO)-mediated living free radical process to copolymerizations of styrene with some macromonomers such as PE-acrylate, la, PEO-methacr-ylate, 27b, polylactide-methacrylate, 28, and poly(e-caprolactone)-methacrylate, 31, may be a promising approach to this end. 

The copolymerization of macromonomer with comonomer is governed by the general rules of copolymerization, the ability of any of the two polymerizable species present to participate in the process being determined by the radical reactivity ratios r. Let us denote the macromonomer as M and the comonomer as A. The well-known instantaneous composition law applies to the copolymer formed ... 

Kennedy 67,77 118) studied the ability of w-styryl-polyisobutene macromonomers to undergo free-radical copolymerization with either styrene or butyl or methyl methacrylate. Here, the macromonomers exhibited a relatively high molecular weight of 9000, and the reaction was stopped after roughly 20% of the comonomer had been converted. The radical reactivity ratios of styrene and methyl methacrylate with respect to macromonomer were found to be equal to 2 and to 0.5, respectively. From these results, Kennedy concluded that in the ra-styrylpolyisobutene/styrene system the reactivity of the macromonomer double bond is reduced whereas with methacrylate as the comonomer the polar effect is the main driving force, yielding reactivities similar to those observed in the classical system styrene/MMA. 

Here rj is the reactivity ratio (=0crit/ Dcrit) of tho monomer (Mj) in a copolymerization with the macromonomer (M2) at critical stabilization. 

Kinetic analyses were done for several copper-catalyzed copolymerizations of MMA/nBMA,263 nBA/ styrene,264 266 and nBA/MMA.267 All these studies show that there were no significant differences in reactivity ratio as well as in monomer sequence between the copper-catalyzed and conventional radical polymerizations. Only a difference was observed in the copolymerizations between MMA and ometh-acryloyl-PMMA macromonomers where the reactivity of the latter is higher in the metal-catalyzed polymerizations.267 However, this can be ascribed not to the different nature of the propagating species but to the difference in the time scale of monomer addition or other factors. Simulation has also been applied for the copolymerization study.268... 

The synthesis of polystyrene-g-polytetrahydrofurane [188] was achieved by ATR copolymerization of methacrylic PTHF macromonomer, MA-PTHF, with styrene (Scheme 105). The PTHF macromonomer was synthesized by cationic ring opening polymerization of THF with acrylate ions, formed by the reaction of methacryloyl chloride and AgC104. The polydispersity indices of the graft copolymers determined by SEC ranged between 1.3-1.4. Kinetic studies revealed that the relative reactivity ratio of the macromonomer to St was independent of the molecular weight of PTHF. 

In a similar way, n-butyl acrylate was copolymerized by ATRP with methacrylate macromonomers containing highly branched polyethylene prepared by Pd-catalyzed living ethylene polymerization. The observed reactivity ratios depend on the molecular weight and concentration of the macromonomer. The resulting graft copolymers showed microphase separation by AFM [304]. 

Gnanou and Lutz conducted a detailed kinetic study on the anionic copolymerization of co-styryl-PS macromonomers with styrene to determine the influence of the molecular weight of the macromonomer on the reactivity ratio. They selected the system to remove all the complications connected with the incompatibility between polymers. co-Styryl-PS macxomono-mers were also anionically copolymerized with p-MS (bearing almost the same substituent as the macromonomer). From the results obtained on the different systems investigated, the authors concluded that the reactivity ratios seem to be independent of the molecular weight of the macromonomer. 

Figure 2.16 depicts another important type of metallocene catalyst monocyclopentadi-enyl complexes, also called constrained geometry catalysts (CGC) or half-sandwich catalysts. Their most important property is a very high reactivity ratio toward a-olefin incorporation, allowing the easy copolymerization of ethylene with long a-olefins and polymer chains having a vinyl terminal group. The latter are called macromonomers, and. 

In all cases, complete conversion of both macromonomers was achieved as checked by SEC. The experimental molar masses were found in rather good agreement with the expected values (Table 3). To know whether the copolymerization of the two macromonomers occurred randomly or exhibited a tendency to blockiness, it would have been necessary to determine the reactivity ratios. However, the observation of only one glass transition (Tg = 40°C) of poly((Norbornenyl PS)-co-(Norbornenyl PB)) and the perfectly alignment of SEC traces arising from UV and RI detectors of poly((Norbornenyl PS)-co-(Norbornenyl PEO)) attests to the random distribution of PS, PB and PEO grafts along the polynorbornene backbone. 

The instantaneous composition for the copol3onerization of a macromonomer Mj with another monomer M can be described in terms of the Mayo-Lewis equation, Eq. 39, where r and r are the respective monomer reactivity ratios. 

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