Poly syndiotactic polymer synthesis

The synthesis of isotactic polymers of higher a-olefins was discovered in 1955, simultaneously with the synthesis of isotactic PP (1,2) syndiotactic polymers of higher a-olefins were first prepared in 1990 (3,4). The first commercial production of isotactic poly(l-butene) [9003-29-6] (PB) and poly(4-methyl-l-pentene) [9016-80-2] (PMP) started in 1965 (5). 

The synthesis of isotactic and syndiotactic polymers has been achieved for a number of polymers. For example poly (methyl methacrylate) can be prepared in either isotactic or syndiotactic configurations depending on the details of the polymerisation conditions. 

On the contrary, the synthesis leading to a syndiotactic polymer and the corresponding studies of the polymerization mechanism are substantially advanced. Structures 9b and 9c are typical examples of catalysts, which afford poly[(R,S)-p-BL],... 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

Iodine readily reacts with polymers bound to coordination centres, yielding macromolecules containing iodide end groups. The C—I bond can react with silver salts of superacids yielding carbocations essentially in the sense of the last steps of eqn. (32). Doi et al. [251, 252] have used this reaction for the synthesis of the copolymer poly(propene)-Mocfc-poly(tetramethylene oxide) with blocks of syndiotactic polypropylene. 

Monomers Figure3.8 shows a small selection of cyclic monomers suitable for ROP [43]. Additionally, three different stereoisomers of lactide exist as a consequence of the presence of two stereocenters per monomer unit, namely meso-, L- and d-lactide, see Fig. 3.9. Further, racemic mixture of L- and D-lactide are commercially available. While ROP of either pure l- and D-lactide enables synthesis of highly crystalline poly(L-lactic acid) or poly(D-lactic acid), ROP of rac- or wcj< -lactide with adequate catalysts allows the synthesis of stereoblock copolymers, heterotactic and syndiotactic poly(lactic acid). Notably, stereoregular PLAs display much lower rates of degradation than the amorphous atactic polymer. 

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. 

The first living metathesis polymerizations were established using metallacyclobutane complexes 3 and 4 as catalysts (Figure 20.11) and NB as the monomer. The latter complex has been employed for the synthesis of moderately regular (80 20 transicis) poly(anft-7-methylnorbornene) (poly(anti-7-MeNB)) that contains a small excess of syndiotactic structures. Trans double bonds are primarily associated with r dyads (r m = 75 25), whereas cis double bonds are predominantly associated with m dyads. The overall r m ratio of the hydrogenated derivative of the polymer (poly-H-(fl fi-7-MeNB), Figure 20.12) is 64 36. 

Optically active lactones are valuable building blocks in organic synthesis (4) and in the preparation of optically active biodegradable polymers (7,5). Several chemical methods for producing these compounds and their corresponding polymers have been explored (6) but unfortunately all of these methods are either experimentally cumbersome or afford the lactones with only modest enantioselectivities. Examples of chemically prepared optically active polyesters include poly(a-phenyl-P-propiolactone) (7), poly(a-ethy(-a-phenyl-P -propiolactone) (S, 9), poly(a-methyl-a-ethyl-P-propiolactone) (70) and poly(lactic acid) (77, 72). Use of enantioselective polymerization catalysts to carry out stereoelective polymerizations of racemic lactones has produced mixed results. For example, stereoelective polymerization of [/ ,S]- P-methyl-P-propiolactone with a catalyst from Zn ( 2115)2 and [7 ]-(-)-3,3-dimethyl-l,2-butanediol showed only a small enantiomeric enrichment in the final polymer (75). Stereoselective copolymerizations of racemic (LL/DD monomers) and meso (LD monomer) lactides using chiral catalyst that gives heterotactic and syndiotactic PLA, respectively have also been studied (77). 

The synthesis of crystalline, syndiotactic 1,2-polybutadiene is also successful with compounds of titanium, cobalt, vanadium, and chromium [194,206-210]. Alcoholates [e.g., cobalt(II) 2-ethylhexanoate or titanium(III) butanolate] with triethylamine as cocatalyst, are especially well suited for this purpose. They are capable of producing polymers with up to 98% 1,2 structure. Amorphous 1,2-polybutadiene is produced with molybdenum(V) chloride and diethylmethoxyaluminum [211]. Addition of esters of carboxylic acids raises the vinyl content of the products [212]. The influence of the coordination at the center atom is remarkable. Trisallylchromium polymerizes 1,3-butadiene to 1,2-polybutadiene, while bisallylchromchloride gives 1,4-poly butadiene. 

The NMR spectroscopy results show that the maleic anhydride addition is carried out as an ene-reaction [59-61] by the vinyl bonds of the polymer without the cycle disclosure and the double bond is moved to the p-carbon atom of the vinyl bond [55,57], The maleic anhydride addition to the >C=C< double bonds of 1,4-units of poly diene macromolecules does not take place. As in synthesis of the arylamino derivatives of syndiotactic 1,2-PB, it is connected with steric difficulties preventing the interaction of bulk molecules of the maleic anhydride with iimer double bonds of the polymer chain [56]. 

The Cp and its related complexes have also inherited tolerance toward functional protic groups. Ru-6 was also effective in producing very narrow MWDs (M /Mn= 1.07-1.20) of poly (MMA) and poly(HEMA) even at 0 ° C in fluorinated alcohols of (CF3)3C0H and (Cp3)2C(Ph)OH or in dimethylformamide (DMF), which were solvents for changing the syndiotacticity of the resultant polymers to rr= 50-80%. ° ° The controllability of the molecular weights along with the specific stereocontrol enabled the synthesis of stereoblock and unprecedented stereogradient polymers via ruthenium-catalyzed... 

Miura Y, Satoh T, Narumi A, Nishizawa O, Okamoto Y, Kakuchi T. Synthesis of weU-defmed syndiotactic poly(methyl methacrylate) with low-temperature atom transfer radical polymerization in fluoroalcohol. / Polym Sd Part A Polym Chem. 2006 44 1436-1446. 

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