Syndiotactic 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. 

Figure 4 Molecular structures of isotactic and syndiotactic PMMA.

The lanthanocene alkyls (190) and (191) are also highly active initiators for MMA polymerization. These too are syndioselective, producing 82-85% rr PMMA at 0°C with high initiator efficiencies and narrow molecular weight distributions. Ln11 complexes such as (192)-(194) also generate syndiotactic PMMA, but exhibit much lower efficiencies (30 10%). 

On the other hand, Matsuzaki et al studied TLC behavior of a PMMA prepared with a phenylmagnesium bromide-tetrahyrofuran complex in toluene79). Good separation into two components was achieved using either ethyl acetate singly or a binary ethyl acetate + dioxane. However, these components could not be identified with either isotactic or syndiotactic PMMA, and the separation took place rather... 

Another problem is TLC separation of atactic and syndiotactic PMMA. More exactly speaking, this concerns a question whether or not PMMA can be separated with TLC by the difference inheterotactic sequences. Inagaki and Kamiyama were engaged in this separation32. The TLC experiments were carried out mainly under the condition that the adsorption mechanism was operative. However, no developer... 

There has been no report of oriented crystalline syndiotactic PMMA so far as the author knows. The author and his coworkers (39) found that oriented crystalline samples of syndiotactic PMMA can be obtained by adsorption of various solvents such as chloro-acetone and diethyl ketone. Figure 8 shows the x-ray diagrams. When the polymer is cast from chloroform solution and is stretched in hot water at 80°C, the sample is noncrystalline as shown in Figure 8. By adsorption of the solvent the fiber diagram can be... 

Figure 9 shows the change of the polarized infrared spectra by adsorption of diethyl ketone. Several bands appear by crystallization especially at 858 cm-. The bands due to diethyl ketone itself are not observed. The essential features of the x-ray diagrams and infrared spectra are the same irrespective of the kinds of solvents. From these results it may be considered that formation of a complex of syndiotactic PMMA and solvent molecules is not reasonable, and the adsorbed molecules contribute to the stabilization of crystallites of syndiotactic PMMA. 

Fig. 33a-d. Solvent effect on the formation of the stereocomplex of isotactic polyfmethyl methacrylate) (iso-PMMA) with syndiotactic PMMA (synd-PMMA)300. (a) In chloroform, (b) in benzene, (c) in dimethylformamide, (d) in acetone... 

Fig. 34 a, b. Effect of the mixing ratio of isotactic po y(methyi methacrylate) (iso-PMMA) and syndiotactic PMMA cm the melting temperature (Tm) and specific area of the melting endotherms299, (a) Relationship between Tm and crystallization temperature (Tc) for different mixtures of stereoregular PMMA [iso-PMMA]/[synd-PMMA] 1/2, O 1/1, C 2/1, 4/1, (b) Specific areas of melting endotherms of stereocomplexes with different [iso-PMMA]/[synd-PMMA] ratio in bulk mixtures. Ciystallization time O 4 h, O 16 h, 4 days, 2 weeks... 

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,... 

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. 

Although the anionic polymerization of MMA in THF leads to highly syndiotactic PMMA (Table 1), that one of tBuMA results in an equimolar mixture of syndiotactic and heterotactic triads (Table 1). For both monomers an increase in temperature results in higher heterotacticity at the expense of the syndiotacticity . The chain tacticity has a direct influence on the macroscopic properties, as illustrated in Table 2 for both the glass transition (Tg) and the melting (T a) temperatures of 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. 

This strategy requires that the preformed polymers are end-capped by groups reactive towards a coupling agent as illustrated by Hatada and coworkers, who prepared PMMA (67) with a stereoblock structure. Isotactic )-hydroxyl-PMMA (64) and syn-diotactic (w-hydroxyl-PMMA (66) were coupled by reaction with sebacoyl chloride (65) (equation 57) . Nevertheless, this process is not selective because the stereodiblock was contaminated by chain-extended isotactic and syndiotactic PMMAs, respectively. 

The stereocontrol in the polymerization of MMA mediated by chiral organolanthanide metallocenes has been investigated. Flydride, hydrocarbyl, and amido bis(cyclopentadienyl) complexes (Scheme 268) were used as precatalysts for the processes. The achiral hydride precatalysts yielded syndiotactic PMMA with narrow polydispersities (Mw/Mn = 1.02-1.05). The polydispersities of PMMA from the chiral and achiral hydrocarbyl precatalysts are larger then those from the hydride precatalysts, and amide precatalysts gave the largest polydispersities.982... 

The deuterium-labelled initiator method was also applied to the polymerization of macromonomer to determine the number of initiator fragments in a polymacromonomer chain (N) and initiator efficiency (/)-77 Isotactic and syndiotactic PMMA macromonomers having a styrene group as polymerizable function were polymerized with AIBN-<7 2 in toluene at 60°C and the resultant polymacromonomers were analysed by 2H NMR spectroscopy (Table 8). The N values were less than unity (0.50 0.72), indicating some kind of chain transfer reaction in the radical polymerization of macromonomer. The / values were 0.18 0.28 and much smaller than those for styrene polymerization (0.5 0.7). The isotactic macromonomer gave larger N and / values than the syndiotactic... 

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