Degree Of Isotacticity Research Articles

Synthesis and polymerization of racemic and optically active β‐substituted β‐propiolactones. III. β‐monosubstituted monomers and polymers

AbstractOptically active β‐(1,1‐dichloroethyl)‐β‐propiolactone (CH3CCl2‐PL), β‐(1,1‐dichloropropyl)‐β‐propiolactone (C2H5CCl2‐PL), and β‐(1,1‐dichlorobutyl)‐β‐propiolactone (C3H7CCl2‐PL) were synthesized with enantiomeric excesses of 100, 100, and 84%, respectively. Polymerization was conducted in bulk and toluene solution, under vacuum, using mainly ZnEt2/H2O as initiator. Osmometry analyses indicate molecular weights in the range 10,000–25,000. The polymers thus prepared are semi‐crystalline and show large optical rotation values.13 C‐NMR was used to show that they have a high degree of isotacticity, indicating that little or no racemization occurs in the course of polymerization. Glass transition, melting and decomposition temperatures are given as a function of the size of the substituent, and their variations are discussed.

Polymerization of Propene and Butene with a Chiral Zirconocene and Methylalumoxane as Cocatalyst

A novel, soluble Ziegler‐Natta catalyst enables the preparation of isotactic polypropylene, which exhibits a higher degree of isotacticity than polymers that can be produced industrially with heterogeneous catalysts. Furthermore, isotactic polybutene can also be obtained with such a catalyst. The chiral, rigid zirconocene derivative 1 and methylalumoxane 2 are used for the catalysis. The polymerization activity is remarkably high. equation image

Template molecular weight effects on the polymerization of acrylic acid

Acrylic acid was polymerized in dilute aqueous solution in the presence of a series of polyvinylpyrrolidones (PVP) of different molecular weight. Both inhibition time and rate of polymerization increased with PVP molecular weight. Purification of the PVP had no effect on these results. The complex produced by the polymerization was separated by methylation of the acrylic acid. The degree of polymerization ( DP ) of the polyacrylic acid formed in template polymerizaton was found to be remarkably similar to the DP of the template PVP. A significant degree of isotacticity had also been induced in the PAA.

Pyrolysis of polypropylene: I. Identification of compounds and degradation reactions

Pyrolysis of two polypropylene samples (degrees of isotacticity 0.50 and 0.85) has been carried out by flash pyrolysis and distillation pyrolysis. The analytical coupling of flash pyrolysis, gas chromatography and mass spectrometry allowed the analysis of the degradation products and their evolution with temperature between 500 and 900°C to be followed under different experimental conditions. The mechanism of polypropylene degradation is compared with the radical mechanism of polystyrene degradation. The depolymerization reaction leading to the production of monomer (25%) is not the most important degradation reaction. The transfer reactions predominate and generate the following products: 2,4-dimethyl-1-heptene (27–32%), pentane (ca. 8%), 2,4,6,8-tetramethyl-1-hendecene (7–18%) and 2,4,6-trimethyl-1-nonene (4–10%).

Living anionic stereospecific polymerization of 2‐vinylpyridine, 1. Initiation of polymerization and stereoregularity of polymers

AbstractInitiation of the polymerization of 2‐vinylpyridine by organomagnesium compounds in hydrocarbon solvents, was obtained without side reactions on the pyridine rings. The resulting active centres are unsymmetrical. They are stable and stereospecific, leading to living polymers with an isotacticity degree of about 0,9.

Optically active poly[thio-1-( N, N-diethylaminomethyl) ethylene

Poly[thio-1-( N, N-diethylaminomethyl) ethylene] [poly(TDAE)] of different optical purities were prepared by stereoelective polymerization of racemic N, N- diethyl- N-(thiirane-2-ylmethyl) amine (TDAE) using a (1:1) ZnEt 2 R (−) 3,3-dimethyl 1,2-butanediol (R(−)DMBD) chiral initiator system. Optically enriched TDAE samples were isolated as residual monomers. These monomers were thermally polymerized to give optically active poly(TDAE) with randomly distributed R and S repeat units in various proportions. The configuration of the enantiomer preferentially incorporated into growing chains during the stereoelective polymerization was determined as R on the basis of the presence of a positive Cotton effect at 260 nm in the c.d. spectrum of residual monomers. This configuration agrees well with the known homosteric character of the ZnEt 2 (−) DMBD initiator system. 13C n.m.r. spectra of the different optically active poly(TDAE) samples and those of more or less stereoregular racemic ones were compared. It was found that the carbon atom of the main chain methine group is the only one which is stereosensitive. Observed triad effects were used to determine the degree of isotacticity of optically active poly(TDAE)s prepared by thermal polymerization of partly enriched monomers. The stereoelectivity of the initiator system and the optical activity of optically pure TDAE and poly(TDAE) were deduced. Side-chain nitrogen atoms did not show any competitive effect with sulphur atoms in the coordination process to the chiral initiator system.

Polymerization by amine–metalloid fluoride salts. I. Polymerization of ethyl vinyl ether by anilinium hexafluoroantimonate

AbstractAnilinium hexafluoroantimonate is shown to be a very efficient cationic initiator for the polymerization of ethyl vinyl ether from −78°C to 25°C. The polymer molecular weight varied with temperature and solvent and ranged from very low to near 200,000. After a threshold concentration of catalyst had been obtained, yields were semiquantitative. The catalyst requirement was quite low, near quantitative yields being obtained at concentrations as low as 10−3 mole‐%. Polymer obtained in heptane had a small degree of isotacticity.

The stereoregularity of polypropylene from i.r. and nmr data

A comparison is made between three spectral methods for determination of stereoregularity in polypropylene. Two of them were based on the i.r.-spectrum of the polymer, the first measuring polypropylene isotacticity degree a (linear function of the value of D 973/ D 1460) and the second-polypropylene macrotacticity M (the value of D 998/ D 973). The third spectral method, based on the NMR-spectrum of polypropylene, allows measurement of the content of the isotactic diad in polymer D 180. A simple statistical description of the polymer structure is given, allowing calculation of the ratio between the isotactic and syndiotactic rate constants of macromolecule growth ( K 150/ K syndin) from the spectral data. The comparisons of the values of K 150/ K syndio obtained from the values a, M and D 150 for different polypropylene samples show satisfactory correlations. Some examples are given of the measurement of stereoregularity for samples of polypropylene obtained with different catalytic systems and for polymer fractions.

Study of polymer breakdown using kinetic data of evolution of gaseous products

All the foregoing is confirmed by results of a spectroscopic study of polybut-1-ene samples synthesized with an a-TlCl,-Al(C,H,),Cl catalytic system. Results are tabulated. It can be seen that the optical density ratio of bands at 1221 and 1150 cm-l (D1881/D1150) in spectra of polybutene samples converted by different methods into a hexagonal modification, is independent of the method of transfer. The value of D1821/D1150 for polybutene samples, in which phase transitions are complete, does not vary as a result of elongation (Table, experiment 5). This proves that the ratio of %lllD1l~O only varies as a result of phase transitions accompanying orientation stretching and not by the action of the orientation factor. Thus, uniaxial elongation of polybutene samples enables the time required for determining the degree of isotacticity to be reduced several hundred-fold. Spectroscopic studies were carried out in a UR-10 spectrophotometer. Films 100-200 p in thickness were compressed at 170’ and at a pressure of 150 kg/cm*.

STUDIES ON THE RELATIONSHIP BETWEEN ORIENTATION MECHANISM AND MECHANICAL PROPERTIES OF ORIENTED POLYPROPYLENE

The orientation behavior of crystalline and non-crystalline phases of three kinds of polypropylene during uniaxial stretching and after annealing under a given degree of the stretching, were observed by means of simultaneous measurements of x-ray diffraction, infrared dichroic ratio and birefringence. The three kinds of polypropylene were different in isotacticity but almost same in viscosity average molecular weight with each other.The orientation behavior of crystallites differed with the degree of isotacticity of the polymers; i.e., for lowly isotactic polymers, the preferential orientation of the crystal c-axis but random orientation of crystal a′-and b-axis around the c-axis, both with stretching, while for highly isotactic polymers, more preferential negative orientation of crystal b-axis than a′-axis, especially at low degrees of stretching, were observed. This feature suggests that some super-structures of aggregated crystallites, such as spherulite structure, would be formed for the highly isotactic polymers, but not for the lowly isotactic ones.The orientation of crystalline and non-crystalline phases proceeded much more prominently as the increase of degree of isotacticity. This may be interpreted in terms of the effective orientation of the structural units, which should be governed by various structural factors being sensitive to the isotacticity, such as the degree of crystallinity, the size and perfection of crystallite, and the average length of non-crystalline chains.The changes of the degree of crystallinity and the orientation of crystallites and non-crystalline chain segments during annealing under a given degree of stretching, were much affected by the degree of stretching of molecular chains before the annealing. Little change of orientation of the structural units but considerable increase of degree of crystallinity occured at relatively low degrees of stretching, and vice versa at high degrees of stretching.

The fractionation of polypropylene oxide polymerized by ferric chloride

Polypropylene oxide prepared with the ferric chloride-propylene oxide complex has been fractionated from isooctane solution by incremental lowering of the temperature. Fractions have been characterized by intrinsic viscosity, melting point and density determinations and the data compared with those for the polymer prepared with the zinc alkyl catalyst. When the difference in crystallinity of the two polymers and the difference in molecular weight of the crystalline fractions of the two polymers are taken into account, the fractionation results may be explained in terms of a polymer similar to that prepared from zinc diethyl, i.e. one having a single distribution of molecular weight and degree of isotacticity.

THE BUTYLLITHIUM-INITIATED POLYMERIZATION OF METHYL METHACRYLATE: PART II. MOLECULAR WEIGHT DISTRIBUTIONS

Samples of poly (methyl methacrylate) have been made in toluene solution at −30° C with n-butyllithium initiator. Different monomer and initiator concentrations were used to obtain products of different overall molecular weights; polymerization times were varied to achieve partial as well as complete polymerization. The polymer samples were divided into fractions which were examined as to molecular weight and microstructure. It was found that the whole polymers have unusually wide molecular weight distributions which can be attributed to a combination of two narrower distributions, one of which occurs at a low and the other at a higher molecular weight region. This "double peak" phenomenon was observed for polymers at lower conversions as well as for polymers representing complete conversion of monomer. Proton magnetic resonance measurements showed that the degree of isotacticity of various fractions of a whole polymer is not the same at all molecular weights.In one case a second portion of monomer was polymerized after the complete polymerization of a first portion. Comparison of the molecular weight distribution before and after the second addition of methyl methacrylate indicated that polymer chains in all molecular weight regions, above a very low minimum value, are capable of further addition of monomer.

Idealized helical stereospecific polymerization

AbstractThis paper presents a mechanism for ascribing the observed stereoregular effects of certain polymerizations to helical stereospecific polymerization. The potential energy “sink” inherent in helical addition of monomer to a growing chain is taken as the controlling factor in such polymerizations. Two combinations, ∼mdmdmd− and ∼mlmlml− out of the eight possible random combinations of three units of two isomers, are presumed to be capable of sustained helical polymerization; the rest are not and are presumed unlikely to become fertile based on the disorder inherent in an atactic chain. With this assumption of idealized helical polymerization as a basis various conclusions may be drawn concerning isotactic‐atactic ratio, molecular weights of each portion, and degree of isotacticity of “isotactic” polymer.

Estimation of isotacticity in semicrystalline polymers

AbstractA new method is suggested for estimating the degree of isotacticity and the distribution of block lengths in semicrystalline polymers. The method is based upon the maximum attainable crystallinity and its dependence upon temperature. An alternate approach is based upon the dynamic shear modulus and its temperature dependence above the glass temperature.

Kinetics of spherulite and crystallite growth in isotactic polystyrene

AbstractThe rates of spherulite and crystal growth in isotactic polystyrene have been studied as a function of temperature by microscopic, x‐ray, and density methods. The effects of molecular weight and degree of isotacticity upon the spherulite growth are shown. Degree of isotacticity is the predominant factor in growth rate. Maximum rate of spherulite growth was observed at 175°C., while the maximum rate of crystal growth was observed at 190°C. Some evidence exists that polystyrenes made with the use of heterogeneous catalysts of the Ziegler type consist of heterogeneous blocks of isotactic and atactic polymers rather than polyblends.