Isotactic PMMA

Unlike most crystalline polymers, PVDF exhibits thermodynamic compatibiUty with other polymers (133). Blends of PVDF and poly(methyl methacrylate) (PMMA) are compatible over a wide range of blend composition (134,135). SoHd-state nmr studies showed that isotactic PMMA is more miscible with PVDF than atactic and syndiotactic PMMA (136). MiscibiUty of PVDF and poly(alkyl acrylates) depends on a specific interaction between PVDF and oxygen within the acrylate and the effect of this interaction is diminished as the hydrocarbon content of the ester is increased (137). Strong dipolar interactions are important to achieve miscibility with poly(vinyhdene fluoride) (138). PVDF blends are the object of many papers and patents specific blends of PVDF and acryflc copolymers have seen large commercial use. 

The tacticity or distribution of asymmetric units in a polymer chain can be directly determined using NMR spectroscopy and infrared (IR) spectroscopy and has been studied for a variety of polymers. Figure 5(a) and 5(b) show the proton NMR spectra [26,27] and IR spectra [28,29], respectively, for the two stereoisomers of poly(methyl methacrylate) (PMMA), syndiotactic and isotactic PMMA. These two structures in a polymer like PMMA give rise to different signatures in both the techniques. In the case of the NMR spectra [26,27], the... 

The polymerization of MMA has been shown to be subject to enantiomorphic site control when the Ci-symmetric a .va-lanthanocene complexes (196) and (197) are employed as initiators.463 When the (T)-neomenthyl catalyst (196) is used, highly isotactic PMMA is produced (94% mm at — 35 °C), whereas the (-)menthyl derived (197) affords syndiorich PMMA (73% rr at 25 °C). NMR statistical analysis suggests that conjugate addition of monomer competes with enolate isomerization processes, and the relative rate of the two pathways determines the tacticity. 

Remarkable differences in the G values of F12 were also recorded in atactic and syndiotactic polystyrene. The tacticity itself was also affected by the irradiation. Fligh-temperature irradiation with y-rays caused the reduction of isotacticity of isotactic PMMA... 

Figure 7.1.1 shows the stacked trace plot of the serial spectra for isotactic PMMA. 

The NMR information can be seen, on the x-axis, to be dependent on the elution time (in min) (y-axis). The chemical structure of isotactic PMMA is defined, as a consequence of the synthesis, as possessing a /-C4H9 group from the initiator at the chain end ... 

Figure 7.1.1 750 MHz on-line SEC-NMR data obtained for isotactic PMMA...

PMMA added previously would depend on their structure. Indeed, when polymerization was carried out in the presence of isotactic PMMA, it influenced the formation of new macromolecules, affecting the rate of polymerization, the molecular weights of the polymer formed, and the structure of its molecules. It is natural to assume that these effects are caused by the appearance of a stereocomplex during polymerization between the polymer added beforehand and the growing macroradical. It is also characteristic that the ratio of polymerization rates in the presence and in the absence of the polymer is independent of the concentrations of monomer and polymer added, depending only on their ratio. Viscosity investigations revealed that these solutions are highly crosslinked. 

FIGURE 14.2 X-band TREPR spectra of main-chain polymer radical la produced from 248 nm laser flash photolysis of atactic, isotactic, and syndiotactic PMMA in propylene carbonate at 0.8 ps delay time. The temperature for each spectrum is shown in °C, and the magnetic held sweep width is 150 G for aU spectra, which exhibit net E CIDEP in aU cases. Simulations of each fast motion spectrum (highest temperature) are shown at the bottom of each data set. Hyperflne values for each simulation are 3 anCCHs) = 22.9 G, 2aH(CH2)= 16.4 G, 2aH(CH2) = 11.7G for isotactic PMMA 3ah(CH3) = 22.9G, 2aH(CH2>= 16.2G,... 

The molecular configuration of isotactic PMMA as LB films was investigated by STM. The analysis showed that the polymer was present as a closely packed, well-ordered arrangement with helical and linear chain mixed configuration. ... 

T able 6. 500-MHz 1H NM R analysis of f-C4 H9 group in the mixture of isotactic PMMA and radically prepared PMMA in nitrobenzene-d5 ... 

Type of protons Component of r,a Isotactic PMMA Syndiotactic PMMA ... 

C NMR spin-lattice relaxations in solid PMMAs of different tacticity were studied by CP/MAS NMR spectroscopy.324-328 The relaxation proceeds more slowly in isotactic PMMA than in syndiotactic PMMA even in the solid state this is because of the faster reorientation of the a-CH3 group in the isotactic chain.135 The nC-T times of the a-methyl carbons of PMMAs with different tacticities were measured over a wide range of temperatures by cross polarization, magic-angle spinning, dipole dephasing (CP/DD)... 

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