Atactic Polybutene-1 Research Articles

Regulation of alkoxysilane on stereoregular polymerization of Butene-1 catalyzed by TiCl4/MgCl2 Ziegler-Natta catalysts

External electron donors (ED) as one of the components in traditional Ziegler-Natta (Z-N) catalysts play important roles in determining the activity, stereoregularity of the active species for ɑ-olefin polymerization. Alkoxysilanes with different size and different electron-donating alkyl substituents were investigated to study the stereoregular polymerization of butene-1 catalyzed by TiCl4/MgCl2 Z-N catalysts. The obtained polybutene-1 (PB) was fractionated into three components including high isotactic PB (HiPB), medium isotactic PB (MiPB) and atactic PB (aPB) and the number of active centers ([C*]/[Ti]) of each component were measured accordingly. The mmmm sequence concentration, weight-average molecular weight (Mw), molecular weight distribution (MWD), and crystallizability of PB were studied by carbon-13 nuclear magnetic resonance spectrometry (13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The addition of dimethyldimethoxysilane (D1) with 120.1 Å3 volume and 0.6802 a.u. electron density had little influence on the stereoregular polymerization of butene-1. The incorporation of diphenyldimethoxysilane (D3) with higher steric hindrance (231.2 Å3 volume), stronger electro-donating ability (0.6969 a.u. electron density) produced PB with higher HiPB component, higher mmmm sequence concentration, accompanying by the reduced catalytic activity and [C*]/[Ti]. The probably active center models absorbing different ED were proposed to explain the catalytic behaviors for butene-1 polymerization and formation of PB with different components.

An improved method for the high isotacticity measurement of polybutene-1

High isotactic polybutene-1 (HiPB) plays important roles in presenting outstanding resistance to creep and crack at high temperature. Therefore, rapid and accurate measurement of the HiPB is extremely important for both synthesis and application of polybutene-1 (PB). In this work, solvent extraction fractionation with diethyl ether (DE) and n-hexane (C6) as solvents (DE-C6 method) and an improved fractionation method combining isothermal crystallization and solvent extraction with xylene (Xyl) and n-pentane (C5) as solvents (Xyl-C5 method) were used to fractionate PB samples. The carbon-13 nuclear magnetic resonance spectrometry (13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) were used to conduct the composition analysis of PB original samples and PB fractions. It was found that the DE-C6 method was greatly depended on the molecular weight of the fractions, while the Xyl-C5 method was biased on the isotacticity of PB fractions and fractionated PB samples into atactic PB (aPB), medium isotactic PB (MiPB) and HiPB, which showed independence on the molecular weight of fractions. Therefore, the Xyl-C5 method is recommended for more accurate measurement and isolation of HiPB fractions from PB samples.

The influences of alkylaluminium as cocatalyst on butene-1 polymerization with MgCl2-supported TiCl4 Ziegler-Natta catalysts

The influences of alkylaluminium compounds including triethylaluminium (TEA), triisobutylaluminium (TIBA) and diethylaluminium chloride (DEAC) on the catalyst activity, isotacticity and weight-average molecular weight (Mw) of the products in butene-1 (Bt-1) polymerizations with MgCl2-supported TiCl4 Ziegler-Natta catalysts were investigated. The catalytic activity of polybutene-1 (PB) increased in the order of TEA > TIBA > DEAC, while the Mw of PB synthesized with TEA was the lowest when compared with that with other alkylaluminium compounds. Solvent extracted fractionation combining with differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and carbon-13 nuclear magnetic resonance spectrometry (13C-NMR) were used to conduct composition analysis of PB. Fractions including atactic polybutene-1 (aPB), high isotactic polybutene-1 with high Mw (HiPB) and medium high isotactic polybutene-1 with medium high Mw (MHiPB) were isolated for the first time from the PB. Using TIBA resulted more HiPB fractions with higher Mw. A minor incorporation of TIBA or DEAC in TEA increased the HiPB fractions of PB. The contribution mechanism of alkylaluminium compound in TiCl4/MgCl2 Ziegler-Natta catalyst was proposed to explain the influence of alkylaluminium compound with different structures on the active species and polymer components in PB.

Temperature rising elution fractionation and fraction compositional analysis of Polybutene-1/Polypropylene in-reactor alloys

A series of isotactic polybutene-1/polypropylene (PB/PP) in-reactor alloys were prepared by Ziegler-Natta catalyst using sequential two-stage polymerization technology. Temperature rising elution fractionation (TREF) combining with DSC, GPC and 13C-NMR were used to analyze the compositional heterogeneity of the resulting PB/PP alloys. Fractions in the PB/PP alloys, including isotactic polybutene-1, isotactic polypropylene, atactic polybutene-1, a series of copolymers with different length of PB segments, PP segments, and poly(propylene-co-(butene-1)) segments, were isolated for the first time by TREF whereby the chain structure and sequence distribution of these fractions were characterized. A possible mechanism was proposed to explain the fraction formation in this sequential two-stage polymerization technology. The mechanical properties and polymorphic transition of the PB/PP alloys were also studied and correlated with the fraction structure and distribution.

Heats of mixing of atactic polybutene-1 and of a model molecule with normal alkanes-order in long alkanes

Heats of mixing at infinite dilution of atactic polybutene-1 in the alkanes have been measured at 25° with a Calvet microcalorimeter. Heats for a model molecule, the 3,5-dimethylheptane, in the same alkanes were obtained also. The enthalpy parameter X H was found to be very close for the two sets of systems. Fitting the experimental data with the calculated free volume term of the heats, the parameter X 12 (as expressed in the Flory theory) is found to go through a minimum with chain length. This feature is explained thus: for longer alkanes, the large heat is thought to be due to loss of order in the chain solvent. For the short alkanes, X 12 is found large to compensate an overestimation of the free volume term.

Polybutene-1. Unperturbed molecular dimensions at different temperatures of isotactic and atactic stereoisomers

By viscosity measurements in θ solvents at various temperatures, values of unperturbed dimensions and of (d ln r 0 2 / dT ) are calculated for isotactic and atactic polybutene-1. (d ln r 0 2 / dT ) values for the two stereoisomers are also calculated by measurements of [η] in a good solvent at various temperatures, according to the theories of Flory-Fox, Kurata-Stockmayer-Roig and Flory-Fisk; the reliability of these theories is estimated. The conclusions are: 1. (1) Both the atactic and isotactic polymer dimensions decrease with increase of temperature, over the range investigated; however, (d ln r 0 2 / dT ) for isotactic polymer is greater than for atactic. 2. (2) The variation of log K θ with T for atactic polybutene cannot be represented by a straight line over a wide range of temperature; it tends to increase in the lower temperature region. A similar behaviour appears for isotactic counterpart. 3. (3) At fairly low temperature (i.e. at room temperature or slightly higher), isotactic polybutene shows larger dimensions than atactic polymer of the same molecular weight. 4. (4) At fairly high temperature (near the melting point of the bulk isotactic polymer), the dimensions of the two stereoisomers are practically the same.

Kinetics of autoxidation of isotactic polybutene‐1 by infrared spectroscopy

AbstractThe autoxidation of a film of isotactic polybutene‐1 (IPB) containing a relatively large amount of metallic ash (≈0.2%) was studied by means of infrared spectroscopy. Reaction temperatures were varied from 105 to 120°C and oxygen concentrations from 25 to 100% by volume. A reaction scheme previously reported for the autoxidation of atactic polybutene‐1 (APB) was utilized for the IPB. Various results obtained for IPB were compared with those previously reported for APB.

Changes in molecular weight during autoxidation of atactic polypropylene in solution

AbstractThe authors had previously reported a general scheme with corresponding kinetic expressions for the uncatalyzed thermal autoxidation of polyolefins, such as atactic polybutene‐1 (APB), in the bulk phase. Recently, Bawn and Chaudhri reported that similar kinetic expressions and scheme were also applicable to autoxidation of atactic polypropylene (APP) in solution. These workers did not attempt to correlate their results for the effect of oxidation on the molecular weight of APP as evidenced by intrinsic viscosity. In this paper, we have applied expressions, previously reported for changes in intrinsic viscosity as a function of time during the autoxidation of APB in the bulk phase, to the data provided by Bawn and Chaudhri for the autoxidation of APP in solution. The quantitative evidence obtained indicates that the intrinsic viscosity relationships which were found to be valid for the autoxidation of APB in the bulk phase are also valid for the autoxidation of APP in solution (at polymer concentrations of ca. 1.5M and above).

Molecular weight changes during polyolefin autoxidation

AbstractExpressions were derived relating changes of intrinsic viscosity to reaction time, based on a scheme previously presented for the uncatalyzed, uninhibited thermal oxidation of polyolefins. A value of the kinetic parameter A may be obtained from these expressions by using an iterative type of procedure and employing data presented by other workers for the oxidation of atactic polybutene‐1. This value of A was compared with the corresponding value obtained by the authors from rate of carbonyl formation studies in oxidation of atactic polybutene‐1 by means of infrared absorption spectroscopy methods. The good agreement between the values of A obtained from the two different experimental techniques employed lends further support to the validity of the scheme used and the expressions derived therefrom.

Unperturbed molecular dimensions of atactic polybutene-1 at different temperatures

The unperturbed dimensions of atactic polybutene-1 have been determined by viscosimetric measurements in θ solvents over the range −46° to +83°. Additional data on unperturbed dimensions, calculated by the Kurata-Stockmayer approximation from studies of solutions in good solvents, are suitable to extend the range of temperature to 100°. From all calculated and measured quantities, the following temperature coefficient is found: d 1 n r 2 0 dT ·10 3=−1·2±0·2 This value is compared with that obtained by thermoelastic measurements, which give a positive value for the coefficient: the possible causes for this fact are discussed.

Kinetics of uncatalyzed thermal oxidation of atactic polybutene-1 by infrared spectroscopy

The uncatalyzed, uninhibited thermal oxidation of a film of atactic polybutene-1 was studied by means of infrared spectroscopy. Reaction temperatures varied from 110 to 130°C. and oxygen concentrations from 12.5 to 100% by volume. A reaction scheme previously reported for the oxidation of isotactic polypropylene was utilized for the atactic polybutene-1. It was found that the scheme and the mathematical expressions derived therefrom could satisfactorily explain the experimental results obtained.