Atactic PMMA

Feldman et a .210 211 and Wulff et ul v have examined other forms of template controlled oligomerization of acrylic monomers. The template (23) has initiator and transfer agent groups attached to a rigid template of precisely defined structure.210 "11 Polymerization of MMA in the presence of 23 gave a 3 unit oligo(MMA) as ca 66% of the polymeric product. The stereochemistry of the oligomer was reported to be different" from that of atactic PMMA. 

Materials. The nearly monodisperse atactic PMMA, which was used for the electron beam lithography and fluorescence spectroscopy studies, was obtained from Pressure Chemical. It has a weight average molecular weight (Mw) of 188,100 and Mw/Mn< 1.08. Pyrenedodecanoic acid (PDA) used in the fluorescence studies was obtained from Molecular Probes and used as supplied. Spectroscopic grade benzene purchased from J.T. Baker was used as the spreading solvent in the PMMA and PMMA/PDA solutions. 

Fig.2.7. Aliphatic regions of H-NMR spectra of a syndiotactic, b isotactic, and c atactic PMMA...

Polymethyl methacrylate (PMMA) An atactic PMMA with a Ts of HOC and an intrinsic viscosity of 1.4 was obtained from Scientific Polymer Products, Inc. 

Atactic PMMA is a brittle amorphous polymer with low elongation at break. Without molecular orientation, PVDF has also a low elongation under tensile stress as shown in Figine 7.9. However, the elongation of PVDF/PMMA blends... 

The quasi-static modelling of the dynamics of the ester group flip in an amorphous cell of atactic PMMA has yielded information complementary to that derived from dynamic mechanical analysis, dielectric relaxation and, mainly, multidimensional 13C and 2H solid-state NMR. The main results are ... 

FIGURE 14.8 TREPR data obtained during 248 nm laser flash photolysis of atactic PMMA in five different solvents at ambient temperature. Delay time is 0.6 is for all spectra, and the sweep width is 150 G. (A) 1.61 g in 20 mL dichloromethane. (B) 1.53 g in 20 mL chloroform. (C) 1.04 gin 20 mL acetonitrile. (D) 1.20gin20mLTHF. (E) 1.49 gin 25 mL dioxane. Note the changes in width and shape for the alternating broad and sharp packets of lines. 

A. Draw and label a schematic diagram of the NMR spectrum you might expect to observe for the methylene and a-methyl protons of an atactic PMMA. 

C. Briefly, describe two methods that you could use to distinguish between a sample of atactic PMMA and a mixture of isotactic and syndiotactic PMMA. 

A wide range of trialkylaluminum with different bulkiness and Lewis acidity was investigated They influenced differently the PMMA tacticity. EtsAl and i-BusAl led to syndiotactic PMMA, whereas atactic PMMA was formed in the presence of f-BusAl. Ballard and coworkers successfully polymerized MMA in toluene at 0 °C in the presence of a mixture of f-BuLi and (2,6-di-f-butyl-4-methylphenoxy)diisobutylaluminum, that was prepared by reaction of triisobutylaluminum with 2,6-di-f-butyl-4-methylphenol. In order to shed light on the origin of the polymerization control, a mechanistic study was undertaken by NMR techniques. In the f-BuLi/EtsAl system, the actual polymerization initiator is a f-butyl carbanion. Actually, f-BuLi forms an ate complex with EtsAl. Later on, Muller and coworkers analyzed the unimeric model in the presence of EtsAl and MMA, and they confirmed the formation of a bimetallic ate complex It was accordingly proposed that the propagating species is an ate complex, which exhibits a decreased nucleophilicity compared to the uncomplexed species. 

Both TNM and AGV equations describe satisfactorily the non-linear variation of heat capacities observed in the case of atactic PMMA, shown as an example in Figure 9.07. Analysis of enthalpy relaxation in several... 

The broad resonance of the a-methyl carbon observed in the CP/MAS/DD 13C NMR spectrum of atactic PMMA can be decomposed to three peaks corresponding to different tacticities by taking advantage of the differences in the rotational motions of the a-methyl carbons in different... 

IPN crosslinked PBA, crosslinked uncrosslinked SAN Poly(p-hydroxy styrene), PVPh and EVAl Acrylic core-shell copolymer and either PBT or PET Poly(allyl methacrylate-co-butyl acrylate-co-butanediol dimethacrylate-co-styrene-co-methyl methacrylate) or poly (aery lonitrile-co-butyl aery late-co-tricy clodeceny 1 aery late-co- styrene) Poly(acrylate-V-cyclohexyl maleimide), PMI, and a copolymer PMMA — core, crosslinked butyl acrylate-styrene copolymer — middle layer, and PMMA shell d = 200-300 nm PEG/atactic PMMA blends were characterized by PVT at T = 20-200°C and P = 0-200 MPa. Free volume fraction was calculated from an equation of state... 

Polymerization of MM A in the presence of 23 gave a 3 unit oligo(MMA) as ca 66% of the polymeric product. The stereochemistry of the oligomer was reported to be "different" from that of atactic PMMA. 

Clearly the spectra differ the spectrum of the syndiotactic polymer resembles that of atactic PMMA. The spectrum of the atactic polymer shows a repeat pattern of seven clusters per pattern, while the isotactic polymer has only two clusters per pattern. Even more interesting is that the masses of the isotactic clusters correspond to an integral number of repeat units plus an odd mass that is not simply related to chain structure. For example, the more intense cluster corresponds to R + C2HgO, cationized with silver. The pattern... 

In addition to these secondary relaxations exhibited by atactic PMMA there are other prominent relaxations in stereoregular PMMA as well as isotactic and syndiotactic PMMA that have been discussed and summarized by McCrum et al. (1967). 

Many of the molecular orientation studies have been performed with ATR. In particular, orientation of PMMA LB films on Ge has been shown [731] to depend on the tacticity of the PMMA. Uniaxial orientation of the methylene and carbonyl TDMs is characteristic for atactic PMMA films, whereas the isotactic films have biaxial symmetry. In-plane orientation of polymer molecules found in thin polyimide films has been attributed [732] to cooperative effects at the fihn-substrate interface. The perpendicular orientation of the N—H and C=0... 

This value is slightly different to that quoted in Table 23.3, based on a density of 1.2 gm cm , which is an average over the atactic, isotactic and syndiotactic homopolymers. For atactic PMMA, p Ci l.lSgm cm . ... 

PEG/atactic PMMA blends were characterized by PVT at T = 20-200 °C and P = 0-200 MPa. Free-volume fraction was calculated from an equation of state Schmidt and Maurer 1998... 

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