Poly different catalysts

Figure 7.10 shows the 60-MHz spectra of poly (methyl methacrylate) prepared with different catalysts so that predominately isotactic, syndiotactic, and atactic products are formed. The three spectra in Fig. 7.10 are identified in terms of this predominant character. It is apparent that the spectra are quite different, especially in the range of 5 values between about 1 and 2 ppm. Since the atactic polymer has the least regular structure, we concentrate on the other two to make the assignment of the spectral features to the various protons. 

The a-methyl resonance in poly(o -methyl styrene) is found to be split into three peaks which are assigned to isotactic, heterotactic and syndiotactic triads. Fractions of the polymers in the three configurations determined by the area of these peaks are given below for poly(o -methyl styrene) prepared with two different catalysts [S. Brownstein, S. Bywater, and D. J. Worsfold, Makromol. Chem., 48, 127 (1961)] ... 

Lactic acid is currently produced by fermentation of carbohydrates and is rme of the high potential and versatile biomass-derived platform chemicals, leading to various useful polymer products. PLA is produced by ROP of lactide (derived from lactic acid) and exhibits mechanical properties similar to poly(ethylene terephthal-ate) and polypropylene. Representative examples discussed herein included the synthesis of highly stereo-controlled PLAs, such as isotactic, heterotactic, and syndiotactic PLA materials, rendered by different catalyst/initiator systems. 

Two different catalysts for hydrogen peroxide decomposition, the enzyme peroxidase (isolated from the horseradish root, HRP), and polymer-supported catalyst (acid form of poly-4-vinylpyri-dine functionalized by ferric sulfate, apFe) [99,100], are examined with an aim to compare their activity. The active center in the peroxidases is the ferric ion in protoporphyrin IX. Besides the complex made of ferric ion and protoporphyrin IX, that is ferricprotoporphyrin IX, also known as ferric heme or hemin, peroxidase possesses a long chain of proteins [101,102]. On the other hand, the macroporous acid form of polyvinyl pyridine functionalized by ferricsulfate is obtained from cross-linked polyvinyl pyridine in macroporous bead form [103]. Pyridine enables it to form coordination complexes or quaternary salts with different metal ions such as iron (111) [104]. An active center on the polymeric matrix functionalized by iron, as metallic catalyst immobilized on polymer by pyridine, has similar microenvironment conditions as active center in an enzyme [105]. 

The nls-vinylene content of poly(2,3-(CF3 )2NBD) can be varied between 2% and 98% by employing mixtures of 16a and 16e at different ratios. Exchange of the alkoxide ligands between the two different catalyst species is fast compared to chain propagation, and polymer chains of uniform cis/trans composition are formed. For example, the cis content of poly(2,3-(CF3)2NBD) is approximately 30% when an equimolar ratio of 16a and 16e is used for polymerization at 20 C. 

A. Qualitative Study. The purpose of the following preliminary study was to examine the effect of using different catalysts on the biodegradability of the poly(alkylene tartrates). Poly(hexamethylene tartrate) was synthesized according to the above procedure using either tin chloride (5% w/w), zinc chloride (10% w/w), or pTSA (5% w/w) as catalysts. Films were cast from a THF/CHCI3 solution (30 mg/mL) onto the bottom of Erlen-meyer flasks. Mud and water from a local pond were poured over the... 

In the sol-gel procedure for the preparation of hybrids, polymeric acid catalysts such as poly (styrene sulfonic acid) were also used instead of hydrogen chloride [14]. The polymeric acid catalyst was effective for the preparation of hybrids at a similar level to that of hydrogen chloride catalyst. In some cases, the increased modulus was observed due to the higher extent of reaction. No difference was observed in morphologies between the hybrids prepared with polymeric and small molecule acid catalysts. The method using polymeric acid catalyst may depress the ion-conductive property, characteristic to the mobile acidic small molecules. Polymeric catalyst may also influence the rheology of the resulting hybrids. 

This strategy is used for the synthesis of three different exact-mass telechelic oligomers. GPC, NMR, and GC/MS evidence indicates that clean depolymerization chemistry occurs for all three samples. Poly( 1,4-butadiene) (38) is broken down into oligomeric units with two, three, and four repeat units using catalyst 23. Catalyst 14 is more efficient and produces even lower molecular weight oligomers, primarily one and two repeat units. When allylchlorodimethylsilane is used instead of ethylene with 14, telechelic dimers are the only product. 

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