Stereoregular polymerization of β-butyrolactone by aluminoxane catalysts

A study was conducted on the application of aluminoxane catalysts to the polymerization of β-butyrolactone, including the effects of polymerization solvent, temperature, type of aluminoxane, aluminoxane preparation, aluminoxane concentration, and modifications of the aluminoxane on the yield and tacticity of the polymer obtained. Optimal conditions for the synthesis of high molecular weight, highly isotactic poly-β-butyrolactone, PBL, were determined. Quantitative yields of crude PBL could be obtained, but removal of aluminum residues from the crude PBL by treatment with acetylactone resulted in large polymer losses. The polymer lost had a low molecular weight and an atactic stereochemistry. The purified PBL was of high molecular weight and high isotacticity.     

Polymerization and copolymerization of β-butyrolactone and benzyl-β-malolactonate by aluminoxane catalysts

High molecular weight poly-β-hydroxybutyrate (PHB) and poly (β-hydroxybutyrate-co-β-benzyl malate) [P (HB? BM)], were prepared by ring-opening polymerization reactions of racemic β-butyrolactone (BL) and racemic β-benzyl malolactonate (BM) using two types of oligomeric aluminoxane catalysts prepared by the reaction of water with either triethyl-aluminum (EAO) or triisobutylaluminum (IBAO). The stereoregularities, crystallinities, and molecular weights were determined for both the PHB homopolymers and the P (HB? BM) copolymers by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). All homopolymers and copolymers obtained could be separated into acetone-soluble and acetone-insoluble fractions. In every case the latter had higher degrees of crystallinity, higher molecular weights and higher degrees of stereoregularity (84–87% isotactic dyads) than the former. Hence all of the polymers obtained from both types of catalysts apparently had stereoblock isotactic structures. Copolymer compositions and monomer dyad sequence distributions were determined by NMR spectroscopy.     

Copolymerization of N-carboxy Nϵ-carbobenzoxy L-lysine anhydride with N-carboxy β-benzyl L-aspartate anhydride in acetonitrile

Copolymerization of N-carboxy N^?-carbobenzoxy L -lysine anydride with N-carboxy β-benzyl L -aspartate anhydride was initiated with n-butylamine in acetonitrile. The copolymerization proceeded almost homogeneously except for the initial stage, when the proportion of N-carboxy anhydride (NCA) in the polymerization mixture varied from 25 to 75 mol %. This was due to the fact that the copolypeptides formed were soluble or highly swollen in the solvent, in contrast to the homopolymerization of NCAs such as N^?-carbobenzoxy L -lysine NCA and β-benzyl L -aspartate NCA in acetonitrile, which proceeds heterogeneously. The compositions of the copolymers obtained were, within experimental error, the same as their monomer feed compositions. The initial rates of copolymerization were almost the same as the rate of homopolymerization of β-benzyl L -aspartate NCA, which propagates with a nonhelical polypeptide, but were slower than the rate of homopolymerization of N^?-carbobenzoxy L -lysine NCA, which propagates with a helical polypeptide.     

Copolymerization of ethylene with linear α‐olefins by 2‐phosphinophenolate nickel catalysts

2‐Dicyclohexyl‐ and 2‐diphenylphosphinophenol, CCHH and PPHH , react with Ni(1,5‐COD)₂ to form catalysts for polymerization of ethylene in or copolymerization with α‐olefins. The more P‐basic CCHH/Ni catalyst allows concentration‐dependent incorporation of olefins to give copolymers with isolated side groups and higher molecular weights, whereas the PPHH/Ni catalyst undergoes mainly stabilizing interactions with the olefins and leads to ethylene oligomers with no or marginal olefin incorporation. Pressure–time plots of the batch reactions show that the ethylene conversion is usually slower by catalysis with CCHH/Ni than by PPHH/Ni . The microstructure of the copolymers was determined by ¹³C NMR spectra, the number of side groups per main chain was estimated by ¹H NMR analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 258–266, 2009     

Radical-initiated homo- and copolymerization of α-methylene-γ-butyrolactone

The kinetics of α-methylene-γ-butyrolactone (α-MBL) homopolymerization was investigated in N,N-dimethylformamide (DMF) with azobis(isobutyronitrile) as initiator. The rate of polymerization (R_p) was expresed by R_p = k[AIBN]^0.54[α-MBL]^1.1 and the overall activation energy was calculated as 76.1 kJ/mol. Kinetic constants for α-MBL polymerization were obtained as follows: k_p/k_t^1/2 = 0.161 L^1/2 mol^?1/2·s^?1/2; 2fk_d = 2.18 × 10^?5 s^?1. The relative reactivity ratios of α-MBL(M₂) copolymerization with styrene (r₁ = 0.14, r₂ = 0.87) were obtained. Applying the Q–e scheme led to Q = 2.2 and e = 0.65. These Q and e values for α-MBL are higher than those for MMA     

Copolymerization of β-pinene with styrene oxide and N-vinylpyrrolidone

The copolymerization of β-pinene with styrene oxide (SO) and β-pinene with N-vinylpyrrolidone (VP) was investigated by using SnCl₄ in dichloromethane diluent at low temperature. Monomer reactivity ratios were evaluated for both copolymers at ?80°C; these are r₁(SO) = 2.979 and r₂(β-pinene) = 0.002 and r₁(VP) = 0.096 and r₂(β-pinene) = 0.294.     

Conformational transitions of poly(β-benzyl L-aspartate)

Conditions that affect the conformation of poly(β-benzyl L-aspartate) in films have been studied. A slow transition from the left-handed to the right-handed α-helical form is observed under certain conditions in half-dried film cast from chloroform solutions and after exposure of amorphous films of the left-handed β-helical form to chloroform vapor. This transition is caused by adsorption of moisture. Thermal transitions of these films were examined by differential scanning calorimetry and infrared spectroscopy. The right-handed α-helices change to left-handed ω-helices around 140°C, and sharp exothermic peak is observed in this region for some films.     

Anionic polymerization of 4-methyl-2-oxetanone (β-butyrolactone)

Polymerization of 4-methyl-2-oxetanone ( 1 ) initiated with potassium acetate-dibenzo-18-crown-6 complex ( 2 ) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (k_p, k_tr, k_ri, and K_ass and respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constants k_p : k_t : k_ri is fairly constant and equal to 10⁻⁴ : 10⁻⁶ : 10⁻⁶, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4-methyl-2-oxetanone) with $\bar M_n$ as high as 1.7 × 10⁴ and ${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$ have also been elaborated.     

Polymerisations of -caprolactone and β-butyrolactone with Zn-, Al- and Mg-based organometallic complexes

The reaction of EtAlCl₂ with 1,2-{LiN(PMes₂)}₂C₆H₄ (Mes = 2,4,6-Me₃C₆H₂) and of butyloctylmagnesium with 1,2-{NH(PPh₂)}₂C₆H₄ gave [AlEt(1,2-{N(PMes₂)}₂C₆H₄-κ²N,N′)(THF)] (1) and [Mg(1,2-{N(PPh₂)}₂C₆H₄-κ²N,N′)(THF)₂] (2), respectively. Complexes 1 and 2 were fully characterised by NMR (¹H, ¹³C, ³¹P) and IR spectroscopy and mass spectrometry. Complexes 1 and 2 were employed as catalysts in the polymerisation of -caprolactone, which produced polymers with a narrow molecular weight distribution. For comparison the polymerisations of -caprolactone and β-butyrolactone were carried out with the Zn complex [ZnPr{1-N(PMes₂)-2-N(PHMes₂)C₆H₄-κ²N,N′}] (3) as catalyst, which produced polymers with narrow molecular weight distributions and high molecular weights.     

Supramolecular structure investigation of poly(γ-benzyl, α-l-glutamate)-benzyl alcohol system by static light scattering

The cholesteric mesophase of the PBLG-BA system in concentrated solutions and in the gel phase has been investigated by static laser light scattering. The observed ‘distortion’ of the patterns in terms of their dependence on the azimuthal angle was studied. Effect of form-optical rotation on the pattern is discussed. The manner of distortion in the H_v pattern determines the sense of cholesteric twisting. The observed scattering patterns are analogous to those obtained by previous investigators in other solvents. Quantitative measurements of the intensity as a function of scattering vector provide information on the sense and pitch of the cholesteric twisting, as a function of temperature and concentration. Optical microscopy studies reveal onset and build-up of the cholesteric structure. Optical rotation and differential scanning calorimetry (DSC) studies support the conclusions obtained from light-scattering experiments.     

Copolymerization of styrene. V. Copolymerization with α-cyanocinnamamide

Copolymers of styrene with α-cyanocinnamamide were prepared by free radical initiation in bulk and in DMF solution and also by thermal initiation in bulk. The copolymerization parameters were determined by the conventional scheme of copolymerization and by an improved scheme taking into account the penultimate unit. Different values of the copolymerization parameters were obtained at the above mentioned different polymerization conditions, indicating the existence of a solvent effect. The influence of the comonomer on some of the basic properties, like intrinsic viscosity, solubility, melting range, and glass transition temperature and on some mechanical and behavior properties of the copolymers was studied in comparison with homopolystyrene.     

Copolymerization of acrylonitrile. III. Copolymerization with α-cyanocinnamamide

Acrylonitrile was copolymerized in solution with α-cyanocinnamamide up to low conversions. The conventional scheme of copolymerization fitted this copolymer. The basic properties, such as solubility, viscosity, and thermal behavior, of the copolymer prepared in bulk and in solution were determined.     

Copolymerization of ethylene and α‐olefins with combined metallocene catalysts. II. Mathematical modeling of polymerization with single metallocene catalysts

The relation between the polymerization conditions and the distributions of molecular weight (MWD) and chemical composition (CCD) of poly(ethylene‐co‐1‐hexene) made with single supported metallocene catalysts was investigated. Understanding the behavior of each metallocene under different polymerization conditions is necessary for designing combined metallocene catalysts to produce tailor‐made polyolefins. In this article, a simple mathematical model based on experimental results is developed and combined with the bimodality criterion developed in Part I of this series to predict polymerization conditions and metallocene combinations that will produce polymers with desired MWDs and CCDs. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1417–1426, 2000     

Copolymerization of trioxane by γ-radiation

High molecular copolymers of trioxane with different cyclic ethers and formals were produced by γ-radiation from a ⁶⁰Co source. It was polymerized in the solid state at 53°C. Polymerization does not occur in the melt. Irradiation was carried out with exclusion of air at a dose rate of 7 × 10³ rad/hr. The polymerization rate was increased very considerably in the presence of 1,3-dioxolane and epichlorhydrin; the addition of other comonomers may reduce the yield. The concentration of the comonomer is generally higher in the polymer than in the initial mix. These comonomers which increase the polymerization rate are introduced preferentially into the polymer chain; this is proved by the unstable polymer part and the thermal stability. Experiments with the trioxane–1,3-dioxolane system revealed that the unstable polymer part is markedly reduced and the heat stability considerably inproved with rising concentrations of this monomer. The thermal stability and the reduced viscosity of these copolymers are within the range of technical processability.     

Crystallinity and conformational changes in poly(β-benzyl L-aspartate)

The crystallinity of poly(β-benzyl L -aspartate) is highly variable, in a series of specimens prepared under various conditions: films cast from chloroform solutions at various evaporation rates, films cast comparatively slowly from chloroform–trifluoroacetic acid solutions, films prepared from dichloroacetic acid solution by treatment with ethyl alcohol, precipitates formed from trifluoroacetic acid solution by addition of ether. Film cast slowly from chloroform is in the highly crystalline ω form. In contrast, the conformation of the benzene rings in the ω helix obtained from the α helix by heating is distorted to some extent in comparison with the structure of the highly crystalline ω form. Crystallization and conformational changes from the α to the ω form, and from the ω to the β form upon heating, are correlated with the dispositions of the side chains, the packing of the benzene rings, and the motion of the side chains. The main chain of the α helix is distorted into the ω form when its side chains are in a favorable conformation. The α helix is stable in the disordered conformation, and it is distorted to some extent at high temperature.     

Preparation and structure-property studies on copolypeptides of γ-methyl glutamate-glutamic acid and γ-methyl glutamate–γ-benzyl glutamate

A series of copolypeptides of poly(methyl glutamate-glutamic acid) (PBC) and poly(methyl benzyl glutamate) (PMB) were prepared from homopolymeric poly(methyl D-glutamate) (PMDG) via a variety of synthetic routes. Following their characterization, these copolymers were then investigated via dynamic mechanical spectroscopy, stress-strain analysis (wet and dry), and wide-angle x-ray scattering (WAXS). It was found that the copolymers could be prepared from homopolymeric PMDG with minimal chain degradation or side reactions. The mechanical properties of either series did not follow a simple trend, in that specific properties such as Young's modulus went through either a maximum or minimum with composition ratio of the two comonomers. based on the WAXS studies, some rationalization for this behavior was established. Specifically, the nature of the side-chain interaction, and therefore chain packing, was strongly affected by comonomer ratio.