Isotactic poly methyl methacrylate

Syntheses. Isotactic poly(methyl methacrylate) was synthesized by the method of Tsuruta et al. (9 ). Under a nitrogen atmosphere, a quantity of 6 mL (0.056 mole) of methyl methacrylate (MMA) dried over 4A molecular sieve was dissolved in 24 mL of similarly dried toluene. To the glass vial containing the reaction was added 0.65 mL of 1.6 M n-butyllithium, and the reaction was kept at -78°C in a dry ice/isopropanol bath. The polymerization was halted 24 hr later with the addition of hydrochloric acid and methanol (methanol/water 4.1 by volume). The polymer was dried in vacuo at 50°C, redissolved in methylene chloride, precipitated by being poured into water-containing methanol, and dried in vacuo at 50°C. Tacticlty and composition were verified with % NMR. Yield 47%. 

Isotactic poly(methyl methacrylate/methacrylic acid), a copolymer of methyl methacrylate and methacrylic acid, was synthesized by the partial hydrolysis of isotactic poly(MMA) according to the method of Klesper et al. (10-13). A hydrolyzing mixture of 8 mL dioxane and 4 mL methanolic KOH (10% by weight K0H) was mixed with 250 mg of polymer in closed vials at 85°C for 48 hr. Saponified polymer separated from the solution and adhered to the walls of the vial. The precipitated polymer was dissolved in water and then precipitated again with a few drops of HC1. The solution was warmed and the coagulated polymer removed, washed with water, and dried in vacuo at 50°C. The nmr spectrum indicated approxi-... 

Syndiotactic and isotactic poly(methyl methacrylate) are crystalline and melt at 160 and 200 °C, respectively. 

Isotactic poly(methyl methacrylate), also, is an intricate case, resolved only after a 20-year debate. The repetition period along the chain axis is 10.40 A corresponding to S monomer units the entire cell contains 20 monomer units (four chains). At first, the stmcture was resolved as a 5/1 helix (183) with = 180° and 62 — 108° but no reasonable packing was found using this assumption. Further conformational calculations showed that helices like 10/1 or 12/1 should be more stable than the 5/1 helix. The structure was solved by Tadokoro and co-workers (153b) who proposed the presence of a double helix. Two chains, with the same helical sense and the same direction but displaced by 10.40 A one from the other are wound on each other, each chain having 10 monomer units per turn [i(10/l)] and a 20.80-A repeat period. As a result, the double helix has a 10.40-A translational identity period, identical to that found in the fiber spectmm. The conformational parameters are Of = 179° and 2 = -148°. Energy calculations indicate that the double helix is more stable by 4.4 kcal per-mole of monomer units than two isolated 10/1 helices, a result that is in line with the well-known capacity of this polymer to form complexes in solution (184). 

Another result of great importance—the conformational asymmetric polymerization of triphenylmethyl methacrylate realized in Osaka (223, 364, 365)— has already been discussed in Sect. IV-C. The polymerization was carried out in the presence of the complex butyllithium-sparteine or butyllithium-6-ben-zylsparteine. The use of benzylsparteine as cocatalyst leads to a completely soluble low molecular weight polymer with optical activity [a]o around 340° its structure was ascertained by conversion into (optically inactive) isotactic poly(methyl methacrylate). To the best of my knowledge this is the first example of an asymmetric synthesis in which the chirality of the product derives finom hindered rotation around carbon-carbon single bonds. 

Because of acid-catalyzed hydrolysis of N-vinylpyrrolidone in water, polymerization was carried out in organic solvent - DMF. Three types of samples of poly(methacrylic acid) were used syndiotactic - obtained by radiation polymerization, atactic - obtained by radical polymerization, and isotactic - obtained by hydrolysis of isotactic poly(methyl methacrylate). It was found that in all cases the rate enhancement appeared in comparison with the blank polymerization (without template). The rate enhancement became more pronounced with increasing chain length and syndiotacticity of the template. According to the authors, the rate enhancement is connected with the stronger complex formation between poly(vinyl pyrrolidone) and syndiotactic poly(methacrylic acid) then with isotactic template. This conclusion was supported by turbimetric titration in DMF/DMSO system and by model considerations. It is worth noting, however, that... 

Copolymerization of methyl methacrylate with styrene in the presence of isotactic poly(methyl methacrylate) has been examined by O Driscoll and Capek. Copolymerization was carried out in acetone at O C and redox system benzoyl peroxide -dimethylaniline was used to initiate the polymerization process. Carrying out the process with various ratios of styrene to methyl methacrylate, it was found that the polymerization rate drops very quickly with the increase in styrene concentration. A very small amount of styrene destroys any template effect that it-poly(methyl methacrylate) exerts on the rate of the polymerization. Assuming, that the reactivity ratios are not changed by the template (ri = i2 = 0.5), the critical length of the sequence of methacrylic units is 10- 20. Complexation occurs only if longer sequences, composed of methacrylic... 

Indeed, it was observed that ov is lower for template polymerization (ASqv.t) than for blank reaction (ASov b)- Investigating polymerization of methyl methacrylate, in the presence of isotactic poly(methyl methacrylate), Gons et al. found that there is a difference in entropy of about 84 J mol" K" between template polymerization and the blank reaction. A similar value (90-100 J mol IC ) was found by Lohmeyer et al It is more likely that the decrease of AS originates predominantly in the propagation process. 

Production of materials in which the daughter polymer and the template together form a final product seems to be the most promising application of template polymerization because the template synthesis of polymers requiring further separation of the product from the template is not acceptable for industry at the present stage. Possible method of production of commonly known polymers by template polymerization can be based on a template covalently bonded to a support and used as a stationary phase in columns. Preparation of such columns with isotactic poly(methyl methacrylate) covalently bonded to the microparticulate silica was suggested by Schomaker. The template process can be applied in order to produce a set of new materials having ladder-type structure, properties of which are not yet well known. A similar method can be applied to synthesis of copolymers with unconventional structure. 

Polymers with well-defined chemical structures are a prerequisite for direct determinations of molecular weight distributions (MWDs) [1-3]. Ute and coworkers [6] have used on-line SEC-NMR coupling to determine the molecular weight distribution in isotactic poly(methyl methacrylate) (PMMA) samples. 

The intramolecular interaction energy was calculated for five isotactic polymers, namely, isotactic polypropylene, poly(U-methyl-l-pentene), poly(3-methyl-1-butene), polyacetaldehyde, and poly(methyl methacrylate) (23). The molecular structures of the first four polymers have already been determined by x-ray analyses as (3/1) (2k), (7/2) (18,25.,26), (U/l) (21), and (U/l) helices (28), respectively. Here (7/2) means seven monomeric units turn twice in the fiber identity period. For isotactic poly(methyl methacrylate) (29), a (5/l) helix was considered reasonable at the time of the energy calculation in 1970, before the discovering of... 

Figure 2 shows the energy contour map for isotactic poly( methyl methacrylate). The lowest energy minimum was found at the position corresponding to a (12/1) helix contrary to the expectation of the (5/1) helix. The minimum corresponding to the (5/1) helix is higher than the (12/1) helix by 3 kcal/mole of monomer unit. This result led to the postulation of the double stranded helix for this polymer. 

Figure 2. Potential energy map of isotactic poly (methyl methacrylate) (23)...

Figure 7. Double-stranded helix of isotactic poly(methyl methacrylate) (30)...

Fig. 36. Composition of the stereocomplex in the system of isotactic poly-(methyl methacrylate) (iso-PMAA) and syndiotacticPMMA (synd-PMMA)376). Time after mixing O 1 h, 4h,A 8h...

Because atactic polymer has no ordered structure and shows only slight intramolecular interactions, the interactions between atactic polymers is the strongest (Fig. 10 a). The isotactic polymers may be stabilized by assuming the helix conformation reported for isotactic poly(methyl methacrylate)401. Nucleic add bases are situated outside the polymer chain so that they can form the complex, although the interaction is not so strong. On the other hand, the syndiotactic polymer may have a rod-like conformation that is supported by the low solubility of the polymer and by NMR spectra321. Tlierefoie, it is well understood that the complex formation ability of the syndiotactic polymers is very low. 

It is noteworthy that the polymerization of MAOA, particularly in the presence of isotactic polyMAOU, is eminently accelerated at 20 °C but not at 40 °C in pyridine solution. Such an acceleration at low temperature was also observed for the polymerization of methyl methacrylate in the presence of isotactic poly(methyl methacrylate)43). In our case, it can be suggested that isotactic polyMAOU has a special conformation at 20 °C which is favored by the formation of a complex between this polymer and a growing chain of MAOA. This conformation may be a helix, as reported for isotactic poly(methyl methacrylate)40) and may change into a random coil at higher temperature. 

In dimethylformamide, in the range of the first acceleration of methyl methacrylate polymerization, changes in the mean lifetime of the radicals were observed [8.4 s for the control and 64 s for polymerization with the matrix effect caused by the presence of isotactic poly(methyl methacrylate)] fcp fell from 26.6 to 5.9 mol-1 dm3 s and fct from 140 x 104 to 1.7 x 104mol-1 dm3 s l [66]. 

The influence of preformed stereoregular polymethylmethacrylate on the polymerization mechanism is particularly interesting. Grignard compounds at — 50 C in toluene give syndiotactic poly(methylmethacrylate) when preformed isotactic poly(methyl-methacrylate) is present, and vice versa [30,31]. In this replica polymerization, the primary structure formed is the 1 1 (isotactic/syndiotactic) complex. Further association between this complex and syndiotactic macromolecules results in the 1 2 (isotactic/syndiotatic) complex [32]. In the absence of preformed polymer, isotactic poly(methylmethacrylate) was obtained under the same conditions. 

P. J. Flory and G. Ronca, Mol. Cryst. Liq. Cryst., 54(3-4), 311 (1979). Theory of Sptems of Rodlike Particles. II. Thermotropic Systems with Orientation-Dependent Interactions. M. Vacatello and P. J. Flory, Polym. Commun., 25(9), 258 (1984). Helical Conformations of Isotactic Poly(methyl Methacrylate). Energies Computed with Bond Angle Relaxation. 

Glycidyl methacrylate High density polyethylene Isotactic copolymer of styrene and p-methyl styrene Isotactic poly(ethyl methacrylate) Isotactic poly(methyl methacrylate) Isotactic polystyrene Low density polyethylene Linear low density polyethylene Maleic anhydride Poly(4-methyl pentene) Random copolymer of phenyl ether and phenyl ketone... 

Examples of these three types of structural arrangements are known in general, stereoregular polymers are synthesized by the use of coordination catalysts, whereas atactic polymers are formed by uncoordinated catalysts such as free radicals or free ions. Stereoregular polymers are often partially crystalline, and usually, even the isotactic and syndiotactic isomers have different properties. For example, isotactic poly(methyl methacrylate) (PMMA) has a glass-transition temperature of 35 °C, while that of the syndiotactic polymer is 105 °C. 

Hartmann L, Gorbatschow W, Hauwende J, Kremer F (2002) Molecular dynamics in thin films of isotactic poly(methyl methacrylate). Eur Phys J E 8 145-154... 

There were attempts at controlling steric placement by a technique called template polymerization. An example is methyl methacrylate polymerization in the presence of isotactic poly(methyl methacrylate). The presence of template polymers, however, only results in accelerating the rates of polymerizations. 

Polymerizations of polar monomers, like acrylic and methacrylic esters with alkyllithium initiators, yield the greatest amount of steric control. Almost all isotactic poly(methyl methacrylate) foims at low temperatures. Addition of Lewis bases such as ethers or amines reduces the degree of isotactic placement. Depending upon the temperature, atactic or syndiotactic polymers form. Also, butyllithium in heptane yields an isotactic poly(A, A -dibutylacrylamide) at room temperature. ... 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

De Sterck and coworkers [90] studied solvent effect on tacticity of methyl methacrylate in free-radical polymerization. They observed that solvents CH3OH and (C[F3)3COH, which are H-bonded with the carbonyl oxygens and are located on the same side of the backbone of the growing polymer radical hinder the formation of isotactic poly(methyl methacrylate) to some extent. Methanol is less effective in reducing the isotacticity because of its small size and also because of the relatively loose hydrogen bonds with the carbonyl oxygens. 

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