Functionality-type distribution of poly(ethylene oxide) and poly(propylene oxide) macromonomers: Critical-chromatography study

Functionality-type distributions of macromomoners with poly(ethylene oxide) and poly(propylene oxide) chains are studied by chromatography under critical conditions. It is shown that, in the critical separation mode, separation of macromolecules with respect to size disappears and only information on the functionality-type distributions of the test samples may be derived. The critical conditions are determined experimentally with a normal phase (unmodified silica gel) for poly(propylene oxide) and with a reversed phase C₁₈ for poly(ethylene oxide). The experimental retention volumes for bifunctional macromolecules are in satisfactory agreement with the values calculated under approximation of the Gaussian chain model.     

On the feasibility of separation of star macromolecules with terminal groups according to their arm lengths by critical chromatography

The potential of critical chromatography is considered for determination of the arm length distribution of branched star macromolecules. In the critical regime of separation, the retention volumes of macromolecules containing adsorbable terminal groups are shown to reflect the distribution of the macromolecules according to their arm lengths. By the example of OH-terminated propylene oxide oligomers produced on the basis of glycerol, it is established that the model of separation of starlike Gaussian chains matches the experimental data.     

Effect of molecular dimensions of components on phase transitions in solutions of oligomeric polyethers

The molecular masses and intrinsic viscosities of a series of oligomeric poly(propylene glycols) have been studied by light scattering, analysis of chain ends, viscometry, and the cloud-point method. Phase diagrams are plotted and the Flory-Huggins thermodynamic interaction parameters and the second virial coefficients are calculated for oligomeric poly(propylene glycol)-n-alkane systems. The effects of the molecular dimensions of components on their mutual solubility and positions of boundary curves are determined. UCST decreases with an increase in the size of poly(propylene glycol) macromolecules and increases with an increase in the size of n-alkane molecules.     

Microporous polycyanurate networks

A general means of generating nanofoams from thermosetting materials was investigated. Foams were prepared from a thermosetting monomer copolymerized with a thermally labile material, such that the thermally labile coblock is the dispersed phase. Upon thermal treatment, the thermally unstable block undergoes thermolysis, leaving pores where the size and shape are dictated by the initial morphology. For this investigation the thermosetting resin was prepared from a cyanate monomer (4,4′-(hexafluoroisopropylidene) diphenyl-cyanate), with either poly(propylene oxide) or a propylene oxide–urethane copolymer as the thermally labile block. The propylene oxide-based oligomers were molecularly miscible with the cyanate resin over the entire range of compositions, and molecular weights investigated, but developed a two-phase structure upon reaction to form the polycyanurate thermoset. The molecular weight and composition of propylene oxide chemically incorporated into the polycyanurate was varied along with the curing condition, solvents, and catalyst. Dynamic mechanical and small-angle x-ray scattering measurements demonstrated a two-phase morphology in the cured networks wherein the propylene oxide domains are dispersed in the polycyanurate matrix. Upon decomposition of the propylene oxide component, however, the foam was found to collapse. Samples with the larger void size retained, to a large extent, their void composition upon the thermolysis of the propylene oxide component. © 1996 John Wiley & Sons, Inc.     

Capillary zone electrophoretic analysis of positively charged poly(ethylene oxide) macromolecules using non-covalent polycation-coated fused-silica capillary and indirect UV detection

Capillary zone electrophoresis was used to show the coupling between NH2-terminated poly(ethylene oxide) and oligomers of lactic acid activated by transforming carboxyl chain ends to acyl chloride ones. The demonstration was based on the use of fused-silica capillary physically modified by pre-adsorption of polycations in the reversed polarity mode. As poly(ethylene oxide) macromolecules are UV transparent, indirect UV detection was used. A creatinine solution at pH 4.8 was selected as background electrolyte. Commercially available polycations with different structures were tested. It was shown that the reversed electroosmosis could be modulated according to the structure of the polycation. The method was then applied to analyse a commercial alpha,omega-diamino poly(ethylene oxide), namely Jeffamine ED 600 characterised by a broad mass dispersion. Data showed that the method can detect and separate amino poly(ethylene oxide) of different structures. When applied to analyse post coupling products, no free NH2-terminated poly(ethylene oxide) segments were detected. Moreover, the method allowed detection of water-soluble oligomers generated by partial degradation of lactic segments during the reaction.     

Molecular mass distribution of oligomers in products of tetrafluoroethylene radical telomerization

The molecular mass distributions (MMD) of perfluorinated oligomers in products of tetra-fluoroethylene (TFE) radical polymerization in various solvents (telogens) were determined from an analysis of differential thermogravimetric curves and data of gel permeation chromatography and mass spectrometry. Radiolysis of the telogens generates radicals initiating polymer chain growth. The choice of the solvent and TFE concentration makes it possible to obtain oligomers with the controlled average chain length from 4 for 40 CF₂ fragments and specified terminal groups. The polymerization of TFE in THF and propylene oxide affords oligomers with cyclic terminal groups capable of further polymerization due to ring opening. The appearance of two MMD maxima (low-molecular-weight at n ₁ ～6–8 and high-molecular-weight at n ₂ > 10 shifting towards high n with an increase in the TFE concentration) is caused by the formation of colloidal solutions of oligomers.     

Tetrablock Copolymers Based on Oligoether Diols, 2,4-toluene diisocyanate,Isophorone Diisocyanate,and Methylene-bis-о-chloroaniline

Tetrablock polyurethane ureas with mixed soft segments and dissimilar hard urethane urea blocks, based on oligo(propylene oxide)diol, oligo(tetramethylene oxide)diol, 2,4-toluene diisocyanate, isophorone diisocyanate, and methylene-bis-o-chloroaniline as a low-molecular-mass chain extender were synthesized and studied. The fragmentary ordering of the polymer chains of the new polyurethane urea was proved by rheokinetic data. The structure–property relationship for the polymer was found. The new polyurethane ureas surpass in the true strength the available diblock polyurethane ureas with poly(propylene oxide) soft segments by a factor of 1.5. The strength properties of the new tetrablock polyurethane ureas only weakly depend on the strain rate varied in the range 0.56–0.006 s^–1.

     

Correlation between the temperature dependence of apparent specific volume and the conformation of oligomeric propylene glycols in aqueous solution

The apparent specific volumes, ?₂, of a series of poly(propylene glycol) and poly(ethyleneglycol) oligomers in aqueous solution were determined as a function of temperature from 4 to 25°C. The slope, d?₂/dT, was taken as a measure of the extent of interaction between the hydrophobic portions of the oligomer and water, higher values of d?₂/dT representing diminished hydrophobic interaction. It is suggested that the observed increase in d?₂/dT with chain length for the poly(propylene glycol) oligomers can be attributed to the previously proposed disk coiled conformation of the chain which reduces the degree of contact between the side-chain methyl groups and water as the chain length increases. This interpretation is supported by (1) the direct relationship between the difference in the thermal expansion behavior of the two oligomer series and the accessibility of the methyl groups in the poly(propylene glycol) disk-coil, and (2) the agreement between the calculated volume changes on mixing for the methyl groups and the values predicted for the disk-coil model from the Némethy and Scheraga theory.     

Synthesis of oligomeric urethane dimethacrylates with carboxylic groups and their testing in dental composites

Carboxyl urethane dimethacrylate oligomers with poly(ethylene oxide) sequences in the structure were synthesized and examined in photopolymerizable resins that could better adhere to various kinds of materials, including tooth substrates. Aspects of the morphogenesis of dental composites formed through a photochemically initiated radical copolymerization of the carboxylic derivatives, in addition to other partners encountered frequently in such materials, were studied comparatively with the corresponding urethane dimethacrylate monomer. The effect of a small quantity of a carboxylic macromer (ca. 10%) on the formation of a network with a non‐carboxyl urethane dimethacrylate oligomer (90%) as a potential substitute for diglycidyl methacrylate of bisphenol A and a filler (1/1 70% Aerosil/glass) was visualized by fluorescence spectroscopy with a pyrene methanol probe. The results showed the following: (1) the degree of conversion in the formulations into which carboxyl urethane dimethacrylate was incorporated decreased with increasing poly(ethylene oxide) chain length, (2) the formation of excimers was inhibited in the derived composites, and (3) an important quenching of the monomer fluorescence emission with the UV–vis irradiation time was observed in the formulation containing a filler (Aerosil+Zr/Sr glass). Preliminary testing of the resin composites suggested that all urethane oligomers containing carboxylic acid could lead to dental materials with reduced polymerization shrinkage and good mechanical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1956–1967, 2007     

Melting behavior of ethylene oxide–propylene oxide (sym-PEP) block copolymers

Melting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym-PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σ_e for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once-folded-chain) σ_e is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σ_e is lower, the more highly folded the poly(ethylene oxide) chain.     

Formation of a linear-polyurethane-linear-polystyrene blend in situ

Blends of linear poly(urethane) and linear polystyrene formed simultaneously in situ by different mechanisms (radical polymerization and polyaddition) at various initial mixture compositions and initiator and catalyst concentrations have been studied by DSC and light scattering. It has been shown that formation of the poly(urethane)-polystyrene blend is characterized by the same kinetic and thermodynamic features as the previously studied poly(urethane)-poly(methyl methacrylate) system. However, the poly(urethane)-polystyrene blend forms much slower than the poly(urethane)-poly(methyl methacrylate) blend owing to different reactivities of the starting components, which are determined by their chemical nature. Phase separation in the poly(urethane)-polystyrene system, which at initial stages proceeds via the spinodal mechanism, occurs much faster than that in the poly(urethane)-poly(methyl methacrylate) system because of a poor mutual solubility of the poly(urethane) and polystyrene being formed and probably because of a higher mobility of their macromolecules at the onset of phase separation.     

Design and characterization of bi-soft segmented polyurethane microparticles for biomedical application

Bi-soft segmented poly(ester urethane urea) microparticles were prepared and characterized aiming a biomedical application. Two different formulations were developed, using poly(propylene glycol), tolylene 2,4-diisocyanate terminated pre-polymer (TDI) and poly(propylene oxide)-based tri-isocyanated terminated pre-polymer (TI). A second soft segment was included due to poly(?-caprolactone) diol (PCL). Infrared spectroscopy, used to study the polymeric structure, namely its H-bonding properties, revealed a slightly higher degree of phase separation in TDI-microparticles. TI-microparticles presented slower rate of hydrolytic degradation, and, accordingly, fairly low toxic effect against macrophages. These new formulations are good candidates as non-biodegradable biomedical systems.     

Supramolecular nanostructures from self‐assembly of T‐shaped rod building block oligomers

T‐shaped coil–rod–coil oligomers, consisting of a dibenzo[a,c]phenazine unit and phenyl groups linked together with acetylenyl bonds at the 2,7‐position of dibenzo[a,c]phenazine as a rigid segment have been synthesized. The coil segments of these new molecules composed of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO) incorporating lateral methyl groups between the rod and coil segment and two flexible alkyl groups connecting with the rigid segment at the 4,6‐position of dibenzo[a,c]phenazine, respectively. The experimental results reveal that the length of the flexible PEO coil chain influence construction of various supra‐nanostructures from lamellar structure to rectangular columnar structure. It is also shown that introduction of different length of alkyl side chain groups in the backbone of the T‐shaped molecules affect the self‐organization behavior to form hexagonal perforate layer or oblique columnar structures. In addition, lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self‐assembling behavior in the crystalline phase. T‐shaped molecules containing a lateral methyl group at the surface of rod and PEO coil segments, self‐assemble into 3D body‐centered tetragonal structures in the crystalline phase, while molecules without a lateral methyl group based on PEO coil chain self‐organize into 2D oblique columnar crystalline structures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5021–5028     

Hydrogen effects in propylene polymerization reactions with titanium‐based Ziegler–Natta catalysts. I. Chemical mechanism of catalyst activation

The hydrogen activation effect in propylene polymerization reactions with Ti‐based Ziegler–Natta catalysts is usually explained by hydrogenolysis of dormant active centers formed after secondary insertion of a propylene molecule into the growing polymer chain. This article proposes a different mechanism for the hydrogen activation effect due to hydrogenolysis of the Ti? iso‐C₃H₇ group. This group can be formed in two reactions: (1) after secondary propylene insertion into the Ti? H bond (which is generated after β‐hydrogen elimination in the growing polymer chain or after chain transfer with hydrogen), and (2) in the chain transfer with propylene if a propylene molecule is coordinated to the Ti atom in the secondary orientation. The Ti? CH(CH₃)₂ species is relatively stable, possibly because of the β‐agostic interaction between the H atom of one of its CH₃ groups and the Ti atom. The validity of this mechanism was demonstrated in a gas chromatography study of oligomers formed in ethylene/α‐olefin copolymerization reactions with δ‐TiCl₃/AlEt₃ and TiCl₄/dibutyl phthalate/MgCl₂–AlEt₃ catalysts. A quantitative analysis of gas chromatography data for ethylene/propylene co‐oligomers showed that the probability of secondary propylene insertion into the Ti? H bond was only 3–4 times lower than the probability of primary insertion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1353–1365, 2002     

Differences in Reactivity of Epoxides in the Copolymerisation with Carbon Dioxide by Zinc-Based Catalysts: Propylene Oxide versus Cyclohexene Oxide

The homogeneous dinuclear zinc catalyst going back to the work of Williams et al. is to date the most active catalyst for the copolymerisation of cyclohexene oxide and CO₂ at one atmosphere of carbon dioxide. However, this catalyst shows no copolymer formation in the copolymerisation reaction of propylene oxide and carbon dioxide, instead only cyclic carbonate is found. This behaviour is known for many zinc‐based catalysts, although the reasons are still unidentified. Within our studies, we focus on the parameters that are responsible for this typical behaviour. A deactivation of the catalyst due to a reaction with propylene oxide turns out to be negligible. Furthermore, the catalyst still shows poly(cyclohexene carbonate) formation in the presence of cyclic propylene carbonate, but the catalyst activity is dramatically reduced. In terpolymerisation reactions of CO₂ with different ratios of cyclohexene oxide to propylene oxide, no incorporation of propylene oxide can be detected, which can only be explained by a very fast back‐biting reaction. Kinetic investigations indicate a complex reaction network, which can be manifested by theoretical investigations. DFT calculations show that the ring strains of both epoxides are comparable and the kinetic barriers for the chain propagation even favour the poly(propylene carbonate) over the poly(cyclohexene carbonate) formation. Therefore, the crucial step in the copolymerisation of propylene oxide and carbon dioxide is the back‐biting reaction in the case of the studied zinc catalyst. The depolymerisation is several orders of magnitude faster for poly(propylene carbonate) than for poly(cyclohexene carbonate).     

Characteristics of polyether urethanes with mixed soft segments,prepared by two- and three-step procedures

A three-step procedure for preparing polyurethanes with mixed polyether segments was suggested. It involves preparation of the “inverse” prepolymer by the reaction of one of oligodiisocyanates with 1,4-butanediol taken in a double excess, followed by the reaction with the other oligodiisocyanate. Polyurethanes with alternating poly(tetramethylene oxide) and poly(propylene oxide) soft segments were prepared by this procedure. Such materials surpass polyurethanes prepared from a mixture of oligodiisocyanates in the strength and softening point of the hard phase. In contrast to poly(tetramethylene oxide) urethane, elastomers with mixed polyether segments do not crystallize.     

Synthesis of polyrotaxanes from acetyl-β-cyclodextrin

Polyrotaxanes are intermediary products in the synthesis of topological gels. They are created by inclusion complex formation of hydrophobic linear macromolecules with cyclodextrins or their derivatives. Then, pairs of cyclodextrin molecules with covalently linkage were practically forming the nodes of the semi-flexible polymer network. Such gels are called topological gels and they can absorb huge quantities of water due to the net flexibility allowing the poly(ethylene oxide) chains to slide through the cyclodextrin cavities, without being pulled out altogether. For polyrotaxane formation poly(ethylene oxide) was used like linear macromolecules. There are hydroxyl groups at poly(ethylene oxide) chains, whereby the linking of the voluminous molecules should be made. To avoid the reaction of cyclodextrin OH groups with stoppers, they should be protected by, e.g., acetylation. In this work, the acetylation of the OH groups of β-cyclodextrin was performed by acetic acid anhydride with iodine as the catalyst. The acetylation reaction was assessed by the FTIR and HPLC method. By the HPLC analysis was found that the acetylation was completed in 20 minutes. Inserting of poly(ethylene oxide) with 4000 g/mol molecule mass into acetyl-β-cyclodextrin with 2:1 poly(ethylene oxide) monomer unit to acetyl-β-cyclodextrin ratio was also monitored by FTIR, and it was found that the process was completed in 12 h at the temperature of 10°C. If the process is performed at temperatures above 10°C, or for periods longer than 12 hours, the process of uncontrolled hydrolysis of acetate groups was initiated.     

Mechanism of the Anionic Ring-Opening Oligomerization of Propylene Carbonate Initiated by the tert-Butylphenol/KHCO3 System

The ring-opening oligomerization reaction of propylene carbonate in the presence of the tert-butylphenol/KHCO₃ initiating system was studied by means of Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) and Electrospray Ionization Time of Flight Mass Spectrometry (ESI-TOF MS). According to the MS spectra obtained, different series of peaks were identified. The MS spectra clearly showed that besides the chain-extension reaction yielding oligomers with all propylene oxide units, the formation of oligomers containing carbonate linkages in the chain, and condensation reaction between the latter two also took place. The structure of the oligomers carrying carbonate linkages was determined by the post-source decay (PSD) MALDI-TOF MS/MS method. Based on the MS results, a mechanism for the oligomerization reaction is proposed.     

Nanostructured polybenzoxazine thermosets via reaction‐induced microphase separation

A multiblock copolymer consisting of main‐chain polybenzoxazine and poly(propylene oxide) blocks was synthesized via Mannich polycondensation among 4,4′‐dihydroxyldiphenylisopropane, 4,4′‐diaminodiphenylmethane, amino‐terminated poly(propylene oxide), and paraformaldehyde, which was evidenced by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The multiblock copolymer was incorporated into polybenzoxazine to access the nanostructured polybenzoxazine thermosets. The morphology of the thermosets was investigated by means of atomic force microscopy and small angle X‐ray scattering. It was judged that the formation of the nanostructures in the thermosetting composites follows the mechanism of reaction‐induced microphase separation. Owing to the big difference in thermal stability between polybenzoxazine thermosets and poly(propylene oxide), the nanostructured thermosets were subjected to the pyrolysis at moderate elevated temperatures to remove poly(propylene oxide) microdomains, to access the nanoporous polybenzoxazine thermosets. The nanoporosity of the resulting polybenzoxazine thermosets was investigated by means of Fourier transform infrared spectroscopy and field‐emission scanning electronic microscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1148–1159, 2010     

Propylene bulk phase oligomerization with bisiminepyridine iron catalysts: Mechanistic investigation of 1,2-versus 2,1-propylene insertion

Iron(II) complexes were synthesized with bisiminepyridine ligands of different steric demand. Activation with modified MAO (25 mol% isobutyl groups) generated very active catalysts for propylene oligomerization. These oligomerizations were carried out in liquid propylene in a heat flow calorimeter. The oligomers were separated by preparative gas chromatography and the dimers and trimers analyzed using analytical gas chromatography, ¹H-NMR-, and ¹³C NMR-spectroskopy. By means of the knowledge of the dimer and trimer structure, we were able to establish a mechanistic pathway for propylene insertion and obtained knowledge about the iron alkyl species involved. Analysis of the various dimers formed allowed us to determine the percentage of 1,2-versus 2,1-propylene insertions. Considering the same iron alkyl species with ligands of different steric demand, a change in the probabilities for 1,2-versus 2,1-propylene insertions can be observed. With this knowledge, the catalyst behaviour for ligands of varying steric demand can be predicted. The question of how to produce oligomers versus polymers is one of knowing how to control the ratio of the 1.2-and 2.1-insertion. One method is to alter the steric demand in the ortho position of the ligand. The more bulky the ligand, the more often a 2,1-propylene insertion happens and, therefore, the higher the molecular mass of the oligomers, i.e., polymer is formed. Another important observation is that the formation of α-olefines is favored with a higher steric demand of the catalyst. The text was submitted by the authors in English.