Isotactic and syndiotactic PMMA

Figure 4 Molecular structures of isotactic and syndiotactic PMMA.

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. 

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 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... 

The magnitudes of the intra- and inter-group contributions of 1H relaxation in isotactic and syndiotactic PMMAs were determined in toluene-d8 at 110°C using four types of copolymers of totally deuterated MMA with a small amount of undeuterated MMA and of the following three specifically deuterated MMAs 303... 

ARRHENIUS EQUATIONS FOR ISOTACTIC AND SYNDIOTACTIC PMMA (MONOMER FORMATION)3 [93]... 

Poly(methyl methacrylate) is an amorphous polymer composed of linear chains. The bulky nature of the pendant group (-O-CO-Me), and the absence of complete stereoregularity makes PMMA an amorphous polymer. Isotactic and syndiotactic PMMA may be produced by anionic polymerization of metiyl methacrylate at low temperatures. However, these forms of PMMA are not available commercially. Modified PMMA can be obtained by copolymerizing methyl methacrylate with monomers such as acrylates, acrylonitrile, and butadiene. 

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). 

Katime et al. have studied flic influence of cosolvency on stereo-complex formation of isotactic and syndiotactic PMMA. The formation of PMMA stereo-complex has been attributed to the interactions between flic ester group of flic isotactic form and the a-methyl group of the syndiotactic form. ... 

For many applications where complete saturation has not yet been reached, increasing the saturation time increases the amount of CO2 dissolved in a polymer. The higher supersaturation that is achieved with longer saturation times will result in cells of smaller size. Semi-crystaUine PMMA (a mixture of isotactic and syndiotactic PMMA) foams were produced by Mizumoto et al. [20] in batch experiments. The microceUular nucleation was caused by the supersaturation created by the depressurization of CO2 in an isothermal condition. 

Liquori et al. [23] first discovered that isotactic and syndiotactic PMMA chains form a crystalline stereocomplex. A number of authors have since studied this phenomenon [24]. Buter et al. [25,26] reported the formation of an in situ complex during stereospecific replica polymerization of methyl methacrylate in the presence of preformed isotactic or syndiotactic PMMA. Hatada et al. [24] reported a detailed study of the complex formation, using highly stereoregular PMMA polymers with narrow molecular weight distribution. The effect of tacticity on the characteristics of Langmuir-Blodgett films of PMMA and the stereocomplex between isotactic and syndiotactic PMMA in such monolayers at the air-water interface have been reported in a series of papers by Brinkhuis and Schouten [27,27a]. Similar to this system, Hatada et al. [28] reported stereocomplex formation in solution and in the bulk between isotactic polymers of / -(+)- and S-(—)-a-methylbenzyl methacrylates. 

The degradation of isotactic and syndiotactic PMMA has been studied by TG with an emphasis on their behaviour in ultra-thin films on silica. Both PMMA tacticity and adsorbed amounts were found to affect the degradation. In bulk, syndiotactic PMMA (syn-PMMA) had higher thermal stability than isotactic PMMA (iso-PMMA) due to its lower chain mobility. The (maximum rate decomposition temperature) was reported to be lower than that of bulk samples at higher adsorbed amounts for both iso- and syn-PMMA. The value increased when the adsorbed amount on the silica surface decreased... 

The 20 MHz proton-decoupled spectra of isotactic and syndiotactic PMMA at 38 C in pyridine-d5 (solvent peaks eliminated). Each spectrum represents 7000 accumulated FID s. Symbols m and r refer to meso and racemic stereochemical relationships between adjacent repeat units. Structural representation of syndiotactic and isotactic stereochemical triads are included above the respective spectrum the S3nnbol R represents the methyl ester side group. (Figure from reference 2.)... 

Sterocomplexation between two layers can occur between two stereoregular polymers, as in the case of multilayers obtained with isotactic and syndiotactic PMMA and enantiomeric (l- and D-) polylactides. This type of interaction for LbL assembly has not been extended to many stereoregular materials however, because of the advantages of stmctural regularity observed within stereocomplexed PMMA LbL films, they have found the incorporation of other materials, such as enzjunes and antibodies, within the films important. 

SEC-NMR for the analysis of polymethacrylates. He studied isotactic PMMA with different molar masses to analyze the end-groups and the number average molar mass as well as the CCD of (methyl methacrylate)-co-(butyl methacrylate) copolymers. These polymers were studied at slow flow rates in fully deuterated solvents. Blends of isotactic and syndiotactic PMMA were also studied regarding the stereocomplexation in non-deuterated solvents. ° Kramer et reported about SEC-NMR for the chemical composition analysis of poly... 

---