Isotactic polymers propylene

The syndiotactic polymer configuration is not obtained in pure form from polymerizations carried out above 20°C and, thus has not been a serious concern to most propylene polymerization catalyst designers. Eor most commercial appHcations of polypropylene, a resin with 96+% isotacticity is desired. Carbon-13 nmr can be used to estimate the isotactic fraction in a polypropylene sample. Another common analytical method is to dissolve the sample in boiling xylene and measure the amount of isotactic polymer that precipitates on cooling. 

Erom 1955—1975, the Ziegler-Natta catalyst (91), which is titanium trichloride used in combination with diethylaluminum chloride, was the catalyst system for propylene polymerization. However, its low activity, which is less than 1000 g polymer/g catalyst in most cases, and low selectivity (ca 90% to isotactic polymer) required polypropylene manufacturers to purify the reactor product by washing out spent catalyst residues and removing unwanted atactic polymer by solvent extraction. These operations added significantly to the cost of pre-1980 polypropylene. 

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

Here m is the mode order (m — 1,3,5. .., usually 1 for polyethylenes), c the velocity of light, p the density of the vibrating sequence (density of pure crystal) and E the Young s modulus in the chain direction. The LAM band has been observed in many polymers and has been widely used in structural studies of polyethylenes [94—99,266], as well as other semi-crystalline polymers, such as poly (ethylene oxide) [267], poly(methylene oxide) [268,269] and isotactic poly(propylene) [270,271], The distribution of crystalline thickness can be obtained from the width of the LAM mode, corrected by temperature and frequency factors [272,273] as ... 

A scandium complex, Cp ScH, also polymerizes ethylene, but does not polymerize propylene and isobutene [125]. On the other hand, a linked amidocyclo-pentadienyl complex [ Me2Si( / 5-C5 Me4)( /1 -NCMe3) Sc(H)(PMe3)] 2 slowly polymerizes propylene, 1-butene, and 1-pentene to yield atactic polymers with low molecular weight (Mn = 3000-7000) [126, 115]. A chiral, C2-symmetric ansa-metallocene complex of yttrium, [rac-Me2Si(C5H2SiMe3-2-Buf-4)2YH]2, polymerizes propylene, 1-butene, 1-pentene, and 1-hexene slowly over a period of several days at 25°C to afford isotactic polymers with modest molecular weight [114]. 

Optical compensation for polymers with chiral monomeric units may also occur when the racemic polymer consists of crystallites, each composed only of the rectus chains or only of the sinister polymer chains, and a same amount of optical antipode crystallites is present. This intercrystallite optical compensation211 has been found, for instance, in isotactic poly(propylene sulfide),212 poly ((3 -methy lpropiol ac (one),213 and poly(isopropylethylene oxide),214 where isochiral 2/1 helical chains are included in orthorhombic unit cells according to the space group P2 2 2. ... 

The slurry phase, the traditional route to PP, uses Ziegler-Natta type catalyst, a hydrocarbon solvent like hexane or heptane and polymer grade propylene (99.5%). Like the stringent requirements for polyethylene plant feeds, propylene must be high purity. Water, oxygen, carbon monoxide, or carbon dioxide will poison the catalyst. The reaction takes place in the liquid phase at 150—160°C and 100—400 psi. When the isotactic polymer particles form, they remain suspended in the diluent as slurry. The atactic polymers dissolve in the diluent. 

Similarly the term isotactic was applied by Price and Osgan (78) to the crystalline polymer obtained from optically active and racemic propylene oxide. The zigzag and Fischer representations of an isotactic poly(propylene oxide) are shown in 36 and 37 (Scheme 7). Their different appearance is due, as already explained in a similar case, to the odd number of chain bonds existing in each monomer unit. Formula 36 presents alternately substituents on both sides of the chain and is very similar to the actual structure observed in the crystal state (79). 

An even simpler spectrum (a single resonance for sterically pure samples) was obtained from polymers of the two [(Z) and ( )] isomers of propylene-1,2,3,3,3-[Pg.35]

The stereochemistry of ring-opening polymerizations has been studied for epoxides, episul-fides, lactones, cycloalkenes (Sec. 8-6a), and other cyclic monomers [Pasquon et al., 1989 Tsuruta and Kawakami, 1989]. Epoxides have been studied more than any other type of monomer. A chiral cyclic monomer such as propylene oxide is capable of yielding stereoregular polymers. Polymerization of either of the two pure enantiomers yields the isotactic polymer when the reaction proceeds in a regioselective manner with bond cleavage at bond 1. 

Polymerization of Propylene to Isotactic Polymer. Independence of the Molecular Weight and of the Steric Composition from the Polymerization Time... 

Polymerization of Propylene to Isotactic Polymer with a-TiCla-Al(C2H6)3-n-/fepCatalytic System. Tests Performed at 70°, 950 mm. Hg pciHi, [CaHa] = 0.41 mol./I. 

The formation of an isotactic polymer requires that insertion always occur at the same prochiral face of the propylene molecule. Theoretically, both a chiral catalytic site (enantiomorphic site control) and the newly formed asymmetric center of the last monomeric unit in the growing polymer chain (chain end control) may... 

A very important field of polymerization, stereospecific polymerization, was opened in 1955. In this year, Natta and his coworkers (1—3) polymerized a-olefins to crystalline isotactic poly-a-olefins with the Ziegler catalyst, and Pruitt and Baggett (4,5) polymerized dl-propylene oxide to crystalline polypropylene oxide, which was later identified as an isotactic polymer by Price and his coworkers (6,7). Since then, a large number of compounds including both unsaturated and cyclic compounds were polymerized stereospecifically and asymmetrically. Development of the stereospecific polymerization stimulated... 

Analysis of the 1H-NMR spectra of the crystalline, isotactic polymer obtained from cis- and trans-propylene oxide-/3-dj indicated that the polymerization reactions proceed through the ring opening of the monomer either by retention or by inversion of the configuration of the carbon atom attacked by the active end of the growing polymer chain (65). 

Later, Ewen reported low-temperature polymerization of propylene with a Cp2Ti(C6H5)2-MAO system leading to an isotactic polymer (139, 140). With ethylene-bridged bisindenyls as ligands of Ti (141), two diastereomers are possible (Scheme 64). The chiral Ti complex (ra-... 

Isocyanophosphonates, aldol reactions, 227 Isoquinoline synthesis, enamide reactions, 33 Isomerization allylic amines, 9, 95 olefins, 118, 171 see also specific compounds Isopulegol, 102 Isotactic polymers, 174 chloral, 182 photoirradiation, 347 methacrylates, 181 propylene, 174 Isotacticity, 177... 

Outside of vinyl addition polymerizations some crystallizable stereoregular polymers also have been prepared. An example is isotactic polymer from propylene oxide made by using ferric chloride com-... 

Olefin Polymers Isotactic polymers of propylene and 1-butene obtained by optically active metallocene catalyst (145) have been reported to show large specific rotation in suspension ([a]D-123°, -250° for polypropylene [a]D+130° for polybutene), which was lost when the polymers were completely dissolved or heated [176,177]. The optical activity was ascribed to a helical conformation of the polymer chain with preferential screw sense. 

From the viewpoint of polymer applications, the full exploitation of the combined resolution/sensitivity enhancement techniques to obtain "high-resolution" spectra of rare-spin nuclei in solids requires variable temperature spinning capability. In this paper, we describe briefly a spinner assembly suitable for routine operation over a wide range of temperature at the full complement of spinning angles and report - C spectral data at low temperature on several polymers, including fluoropolymers. In addition, variable temperature spin-lattice and rotating frame relaxation times are reported for isotactic poly(propylene). 

Phillips catalysts are active in the polymerisation of propylene and higher a-olefins, yielding tacky polymers with irregular structure and small amounts of crystalline polymers in the case of polypropylene, a small amount of crystalline fraction appeared to constitute the isotactic polymer [236]. 

The main elements of chirality possibly present in the intermediates and transition states that can be hypothesised within this framework are as follows [1]. Firstly, a prochiral a-olefin molecule, e.g. propylene, coordinating via its two faces at the catalyst active site gives rise to non-superpo sable re and si diastereoisomeric complexes (Figure 3.24) [362, 363]. According to the considered mechanisms, an isotactic polymer is generated by a long series of... 

The obtained chiral ansa-metallocenes, after activation with methylaluminox-ane, were indeed found, in independent studies by Ewen [22] and by Kaminsky and Kiilper [101], to polymerise propylene and higher y-oldins to produce highly isotactic polymers [30]. 

Steric defects in isotactic polypropylene, which involve the appearance of isolated r diads or pairs of r diads, may be considered on a pentad level (Figures 3.45a and b respectively). The 13C NMR signals associated with occasional stereoerrors in the propylene isotactic polymers produced by chiral metallocene-based catalysts (pairs of r diads) indicate that the polymerisation stereochemistry is governed by the enantiomorphism of catalytic sites an error pentad distribution close to mmmr.mmrr.mmrm-.mrrm = 2 2 0 1 is observed... 

It is worth mentioning that a rar.- / ,v -titanocene methylaluminoxane catalyst, such as rac.-Ph2C(Cp)(Ind)TiCl2—[Al(Me)0]x, which yields an isotactic polymer in propylene polymerisation, promotes the syndiospecific polymerisation of styrene [73,100]. This is the first example where two different stereoregular polymers, isotactic and syndiotactic, can be obtained using the same catalyst in the case of two different monomers. 

The first report on the coordination polymerisation of epoxide, leading to a stereoregular (isotactic) polymer, concerned the polymerisation of propylene oxide in the presence of a ferric chloride-propylene oxide catalyst the respective patent appeared in 1955 [13]. In this catalyst, which is referred to as the Pruitt Baggett adduct of the general formula Cl(C3H60)vFe(Cl)(0C3H6),CI, two substituents of the alcoholate type formed by the addition of propylene oxide to Fe Cl bonds and one chlorine atom at the iron atom are present [14]. A few years later, various types of catalyst effective for stereoselective polymerisation of propylene oxide were found and developed aluminium isopropoxide-zinc chloride [15], dialkylzinc-water [16], dialkylzinc alcohol [16], trialkylalumi-nium water [17] and trialkylaluminium-water acetylacetone [18] and trialkyla-luminium lanthanide triacetylacetonate H20 [19]. Other important catalysts for the stereoselective polymerisation of propylene oxide, such as bimetallic /1-oxoalkoxides of the [(R0)2A10]2Zn type, were obtained by condensation of zinc acetate with aluminium isopropoxide in a 1 2 molar ratio of reactants [20-22]. 

In research with Ziegler catalysts, Cossee (11) and Arlmann and Cossee (12) hypothesized that the insertion of propylene monomer takes place in a cis conformation into a titanium-carbon bond. Natta et al. (8) postulated that in the stereospecific polymerization, chiral centers on the surface are needed to produce isotactic polymers. These and other issues regarding the nature of the active sites have helped to increase the interest in investigations of homogeneous metallocene catalysis. 

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