Copolymerization Studies

In order to find out how the spedfic base-base interactions occurring between complementary nucleic acid bases can be utilized for free-radical polymerization systems, the radical copolymerization of vinyl-type monomers bearing complementary nudeic add bases, MAOA (24 a) and MAOU (26 a) was studied in different solvents, using AIBN as the initiatoi  

The rates of copolymerization investigated in DMSO, DMF and pyridine are to those calculated with 0 = 1 (cross-termination constant) while the rates in enthanol and dioxane deviate largely from the calculated ones (Fig. 4). In the latter cases, it is assumed that the alternating propagation is accelerated by the effective formation of specific base-base pairing between uracil and adenine units. 

From the values of the monomer reactivity ratios, the relative reactivity of the monomers toward the growing free radicals derived from MAOThe, MAOA and MAOU (t, a and u, respectively) was estimated (Table 6). As for the growing radical of MAOThe (t), for example, the reactivities of MAOThe and MAOU monomer are equal Iwt higher than that of MAOA monomer in ethanol solution while the reactivities of these monomers are nearly equal in dioxane solution. The copolymerization proceeds predominantly under the influence of base-base pairing between adenine and uracil rin.  

In the copolymerization systems, two types of interactions between nucleic acid bases, i.e. (1) monomer-monomer interactions and (2) growing end unit-monomer interactions, can be considered  

In this scheme A- denotes a growing chain end, A and T denote MAOA and MAOT, respectively, and A T is the hydrogen-bonded complex. The interactions between the polymers formed and the monomers should be assumed to be ne igibly small because of low conversions. 

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Many copolymerization studies have been made. A detailed discussion and critique of the results has been pubHshed (1) and the breadth of the comonomers studied has been summarized (6). Among the comonomers used are oxiranes, oxetanes, 1,3-dioxolane, substituted tetrahydrofurans. 

Similar anomalies have been encountered by several workers in the bulk and solution polymerization of this monomer induced by classical free-radical initiators84-86) also, particularly low rates of conversion were observed. The most thorough kinetic study was carried out by Aso and Tanaka86) who again found normal results and a value of k jkt much lower than that for styrene. Copolymerization studies of 2-vinylfuran (Mj) have given the following values of the reactivity ratios ... 

Labeled initiators have been used in evaluating the relative reactivity of a wide range of monomers towards initiating radicals.159 The method involves determination of the relative concentrations of the end groups fanned by addition to two monomers (e.g. 119 and 120) in a binary copolymer formed with use of a labeled initiator. For example, when AlBMe-a-13C is used to initiate copolymerization of MMA and VAc (Scheme 3.99),157 the simple relationship (eq. 14) gives the relative rate constants for addition to the two monomers. Copolymerizations studied in this way arc summarized in Tabic 3.13. 

Anionic copolymerization of lactams presents an interesting example of copolymerization. Studies of the copolymerization of a-pyrrolidone and e-caprolactam showed that a-pyrrolidone was several times more reactive than e-caprolactam at 70 °C, but became less reactive at higher temperatures due to depropagation210 2U. By analyzing the elementary reactions Vofsi et al.I27 concluded that transacylation at the chain end occurred faster than propagation and that the copolymer composition was essentially determined by the transacylation equilibrium and the acid-base equilibrium of the monomer anion together with the usual four elementary reactions of the copolymerization. 

The pseudo-kinetic rate constant method for multicomponent polymerization has been applied in some copolymerization studies (3-5), and its derivation and specific approximations have been made clear (6,7). The pseudo-kinetic rate constants basically... 

B. Measurement of Property Distributions for Copolymers. Figure 12 shows chromatograms of typical products in the copolymerization study (Column Code B2). Since the detector is responding to concentration, composition, and periiaps sequence length, the direct single detector interpretation as described for PMMA is not immediately applicable here. Tacticity variation is yet another consideration but ]s assumed of sa ond order importance for th samples (22). 

The high electron richness of vinylferrocene as a monomer is illustrated in its copolymerization with maleic anhydride, where 1 1 alternation copolymers are formed over a wide range of monomer feed ratios and ri -2 = 0.003. Subsequently, a large number of detailed copolymerization studies have been undertaken using metal-containing vinyl monomers. 

A library of random copolymers comprised of MeOx, EtOx, and NonOx has been established, and the properties of the members have been studied [88], Systematic copolymerization studies and corresponding structure-property investigations have been performed in detail by Schubert et al. For this purpose, nine copolymers were synthesized with 0-100 mol% (steps of 12.5 mol%) of the second monomer, resulting in 27 polymerizations for three different combinations of MeOx, EtOx, and NonOx. The monomer conversion was followed by GC measurements. As shown in Fig. 16, the content of the second monomer increases linearly with increasing mole fraction of the second monomer, whereas the content of the first monomer decreases linearly. 

Chain copolymerization is important from several considerations. Much of our knowledge of the reactivities of monomers, free radicals, carbocations, and carbanions in chain polymerization comes from copolymerization studies. The behavior of monomers in copolymerization reactions is especially useful for studying the effect of chemical structure on reactivity. Copolymerization is also very important from the technological viewpoint. It greatly increases the ability of the polymer scientist to tailor-make a polymer product with specifically desired properties. Polymerization of a single monomer is relatively limited as to the number of different products that are possible. The term homopolymerization is often used to distinguish the polymerization of a single monomer from the copolymerization process. 

The best test for functionality would be in a copolymerization study. A polystyrene with a methacrylate terminal functional group was prepared. A review of relative reactivity ratios indicated that vinyl chloride reacts very rapidly with methacrylates. Therefore, a copolymerization of the polystyrene terminated with a methacrylate functional group in vinyl chloride would be a good test case, and one should observe the disappearance of the MACROMER if the reaction is followed by using GPC analysis. 

Fig. 33. Structures of the bisbenzocyclobutenes 55,56,57 used in the copolymerization studies summarized in Tables 15,16, and 17...

Numerous halo all enes are known, but the pethaloallenes of the type X,C C CX were unknown until a study at the Univ of Calif, LA (Ref 5) was undertaken as part of the US Dept of the Army Contract DA-04-495 ORD-527. It is expected that compds such as telrafluoroallene, FaC C CFa will be of interest as monomers for both homopolymerization and copolymerization studies and for the prepn of materials similar co Teflon which is the homopolymer of tetra-fluoroethylene FaC CFa. This study is being continued as of 1958 Refs i)Beil 7, 248,(107),[223J l922f... 

Funt et al. have already reported work on the electrocopolymerization referres to the reaction conditions. In the copolymerization study of... 

One of the first detailed studies on these systems was that of Beaman (26), who showed that methacrylonitrile polymerizes by an anionic chain mechanism when treated with various bases, including Na in liquid ammonia at —75° C. He noted also that low molecular weight polymers are obtained from reaction of acrylonitrile with butylmagnesium bromide. Foster (56) extended the liquid ammonia method to copolymerization studies in which acrylonitrile was combined with styrene, with methyl methacrylate and with vinyl butyl sulfone. Satisfactory data were obtained only with the sulfone, in which case there was some tendency for alternation. 

Terra neopentyl titanium [36945-13-8], Np4Ti, forms from the reaction of TiQ4 and neopentyllithium in hexane at —80° C in modest yield only because of extensive reduction of Ti(TV). Tetranorbomyltitanium [36333-76-3] can be prepared similady. When exposed to oxygen, (NpO)4Ti forms. If it is boiled in benzene, it decomposes to neopentane. When dissolved in monomers, eg, OC-olefins or dienes, styrene, or methyl methacrylate, it initiates a slow polymerization (211,212). Results from copolymerization studies indicate a radical mechanism (212). Ultraviolet light increases the rate of dissociation to... 

Structure and Composition of Diene Copolymers. One finds that most of the reported copolymerization studies on butadiene or isoprene involve styrene as comonomer. In part this is due to the early interest in styrene-butadiene synthetic rubbers. The free radical produced copolymers (GRS, usually about 20—25% styrene units) contain about 20% of its butadiene fraction in the 1,2 form. The ratio of 1,2 to 1,4 units is little affected by polymerization variables such as temperature, conversion and styrene content (39). Butadiene and styrene copolymers contain 50 to 60% 1,2-diene units when prepared by sodium catalysts at 50° (39). This behaviour is once more significantly different when lithium is used in place of sodium as can be seen in Table 3. 

A copolymerization study of the same two monomers using sodium in liquid ammonia by Landler (36) revealed reactivity ratios of 0.123 for styrene and 6.4 for methyl methacrylate, values which would predict as much as 10% styrene in the initially formed copolymer from a 1 1 molar styrene-methyl methacrylate mixture. However, O Driscoll and Tobolsky have disputed this result (84). 

The radical polymerization in aqueous solution of a series of monomers—e.g., vinyl esters, acrylic and methacrylic acids, amides, nitriles, and esters, dicarboxylic acids, and butadiene—have been studied in a flow system using ESR spectrometry. Monomer and polymer radicals have been identified from their ESR spectra. fi-Coupling constants of vinyl ester radicals are low (12-13 gauss) and independent of temperature, tentatively indicating that the /3-CH2 group is locked with respect to the a-carbon group. In copolymerization studies, the low reactivity of vinyl acetate has been confirmed, and increasing reactivity for maleic acid, acrylic acid, acrylonitrile, and fumaric acid in this order has been established by quantitative evaluation of the ESR spectra. This method offers a new approach to studies of free radical polymerization. 

Most data were obtained from copolymerization studies. The copolymerization parameter r (see Chap. 5, Sect. 5.2) is the rate constant ratio for the addition of two different monomers to the same active centre. The inverse values of r j determined for the copolymerization of a series of monomers with the monomer M, define the relative reactivities of these monomers with the active centre from the first monomer, M°,. Thus it is possible to order monomers according to their reactivities in radical, anionic, cationic and coordination polymerizations from the tabulated values of copolymerization parameters [101-103]. 

In addition to their synthetic utility, copolymerization studies provide a method for determining relative monomer reactivities and relative reactivities of the resulting active centers in chain polymerizations. That is,... 

In order to compare the absolute reactivities of active species and monomers it is, however, necessary to react a series of monomers with a model active center and to react a sertes of active species with one chosen monomer. This, in principle, can be conducted in copolymerization studies, which are not included in this review. Nevertheless, we may cite here at least one work conclusively demonstrating that the rate constants of the additkm of various monomers to a given active species do not change too much with monomer reactivity, most of the variations stemming from the diversity of the active species . ... 

The order of basicity found for the cyclic sulphides on the basis of ring size is 5>6>4>3. This order is different from that in cyclic ethers. Stille and Empen [66] state that this difference has been ascribed to the differences in heteroatom size, differences in ring size (ring strain), and also to differences in polarizability between oxygen and sulphur atoms. Basicity did not correlate well with reactivity in the sulphide series. Ring strain seemed to be more important. However, it should be noted that the reactivity measured in the sulphide case was in homopolymerizations. Very few copolymerization studies have been carried out so far. 

These equations show the individual steps connected with the propagation reaction, i.e. the sums in the numerator or denominator are the sums of all possible propagation reactions in which a given monomer adds to the growing chains ending in every monomer unit. The Q and e values were obtained from binary copolymerization studies. The calculated and experimental results are compared in Table 4. 

Figure 8 gives results of some copolymerization studies, namely, the addition of styrene to living a-methylstyrene tetramer and the addition of styrene to living poly(p-methylstyrene). Table III gives the propagation rate constants of some homopolymerizations and copolymerizations and the discussion of these values is interesting. 

Within the family of cycloolefin co-polymers, the most important from a material properties standpoint, are the ethylene/norbornene co-polymers. These co-polymers, dubbed COC for cycloolefin co-polymers, are produced by Ticona and Mitsui under the tradenames Topas and Apel , respectively. An overview of properties and applications (for example, blisters for pills) can be found on Ticona s Topas homepage.607 Detailed ethylene/norbornene copolymerization studies with different 4/-symmetric and ansa-Cp-amido catalysts, with listing of co-polymerization parameters, have been published.608 611 NB is inserted exclusively in the cis-2,3-exo-modc (Scheme 25), and most of the metallocene catalysts tend to produce alternating co-polymers,609 612 due to the low reactivity of the M-NB intermediate toward further NB insertion. This mode of NB insertion prevents f3-H transfer, and thus ethylene/ norbornene co-polymers have increasing molecular masses at increasing NB content.611... 

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... 

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