Low Molecular Weight Analogues Research Articles

Thermodynamic properties of novolac-type phenolic resin blended with poly(ethylene oxide)

The thermodynamic properties of novolac type phenolic resin blended with poly(ethylene oxide) (PEO) were investigated by the Painter–Coleman association model (PCAM). Equilibrium constants and enthalpy corresponding to the interaction between phenolic and poly(ethylene oxide) were calculated from the Fourier transform infrared spectroscopy of low molecular weight analogues in dilute solutions. The association parameters of the model compounds are transferred to the corresponding polymers, to predict the Gibbs free energy, phase behavior, and the degree of hydrogen bonding in the polymer blend. The heat capacity (CP) and the excess heat capacity (ΔCP) are used to verify the validity of PCAM model on predicting the thermodynamics properties of phenolic/PEO blend. It is found that the hydrogen bonding interaction dominates at moderate temperatures, which is outweighed by the dispersion force at higher temperature or high PEO compositions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1647–1655, 1998

Quantitative analysis of malto-oligosaccharides by MALDI-TOF mass spectrometry, capillary electrophoresis and anion exchange chromatography

The analysis of malto-oligosaccharides by MALDI-TOF mass spectrometry (MS), capillary electrophoresis (CE) and anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) is described. Appropriate methods were developed which enabled the resolution of the oligosaccharides and quantification of the peak areas. It could be shown that each technique provided a different distribution profile of the maltodextrins. Using MALDI-TOF MS signals of higher molecular weight oligomers were enhanced while low molecular weight analogues were discriminated. Thus, the response factor depends on the degree of polymerization (DP) of the carbohydrates. Homologues up to DP-15 could be detected. Analysis of the maltodextrins by CE was accomplished by derivatization of the sugars with 4-aminobenzonitrile (ABN) and 8-aminonaphthalene-1,3,6-trisulfonic acid, respectively. By using the latter reagent oligosaccharides up to DP-13 were detected while derivatization with ABN allowed detection up to DP-9. The molecular weight distribution obtained by both approaches were the same. HPAEC-PAD enabled the determination of oligomers up to DP-9. The distribution obtained by this technique showed somewhat lower signals of the small homologues than those found by CE while the opposite held for higher molecular weight compounds. Hydrolysis of the carbohydrates by the derivatization reaction prior to CE analysis, which increased the proportion of low molecular weight homologues, may account for these findings.

Molecular Dynamics Simulation of Main Chain Liquid Crystalline Polymers

Molecular dynamics simulations of a model main-chain liquid crystalline polymer (LCP) and of a low molecular weight analogue have been carried out using an efficient parallel algorithm. A main-chain LCP is formed with the help of Gay−Berne mesogenic units connected to each other through flexible methylene spacers. We have studied the effect of varying the spacer length, and have examined the region of the isotropic-liquid crystalline transition. Our preliminary results indicate that liquid crystalline ordering may occur spontaneously on lowering the temperature, and that odd−even dependences of thermodynamic properties on spacer length occur, in agreement with existing experiments. Local orientational time correlation functions, as well as local translational mobility, have been studied both for the mesogenic elements and the bonds in the flexible spacer. The anisotropy of both orientational and translational local dynamical properties have been compared with theoretical predictions and with Brownian dynamics results for a freely jointed chain in a liquid crystalline orienting field.

The phase behaviour of novolac type phenolic resin blended with poly(adipic ester)

The association equilibrium constants and enthalpy of novolac type phenolic resin blend were determined. All the parameters were obtained from the results of Fourier transform infrared spectroscopy of low molecular weight analogues in dilute cyclohexane solutions. All the association parameters of novolac type phenolic resin obtained from the model compound were used to predict the miscibility window of phenolic/poly(adipic ester) blend, and that were consistently well with the actual phase behaviour. The results show that the association parameters of phenolic provide a reasonable utilization of Painter-Coleman Association model.

Preparation and Characterization of Inclusion Complexes of Poly(alkyl vinyl ether) with Cyclodextrins

Abstract γ-Cyclodextrin (γ-CD) has been found to form inclusion complexes with poly(methyl vinyl ether) (PMVE), poly(ethyl vinyl ether) (PEVE), and poly(n-propyl vinyl ether) (PnPVE) of various molecular weights to give stoichiometric compounds in crystalline states. α-Cyclodextrin (α-CD) and β-cyclodextrin (β-CD) did not form complexes with poly(alkyl vinyl ether)s of any molecular weight. γ-CD did not form complexes with the low molecular weight analogs, such as diethyl ether and trimethylene glycol dimethyl ether. The yields of the complexes of γ-CD with PMVE increased with increasing molecular weight (MW) of PMVE and reached saturation at about MW 2000. The yields of the complexes of γ-CD with PEVE and PnPVE increased with increase in MW, reached a maximum at a MW of about 1000 for PEVE and about 250 for PnPVE, and decreased with a further increase in the MW. Complexes were isolated and found to have a 3 : 1 (monomer unit : CD) ratio. The complexes were characterized by IR, 1H NMR, 13C NMR, and X-ray (powder), thermal and elemental analyses. The structures of the complexes are discussed.

Optical anisotropy of comb-like macromolecules of lateral and semilateral structure

Maxwell effect and Kerr effect techniques were used to study the intramoleculare axial ordering of anisotropic side groups of an isolated macromolecule in solution. Three comb-like polymers with a methacrylic main chain were investigated. The side chains contain aliphatic spacers separating the mesogenic fragments R from the backbone. R contains two or three phenylene rings with ester linking groups and cyano end groups. Fragments R are attached to the side chains, by the end or middle-point, through the para- or ortho-phenylene ring. The main-chain conformation in solution was identified to assess the hydrodynamic data using the Gaussian coil approximation. The optical anisotropy of the macromolecule segment was determined and related to the monomer unit structure. The specific Kerr constant obtained in diluted benzene solution of polymer was compared with those of low molecular weight analogues of the polymer mesogenic groups. The mobility and intramolecular ordering of the mesogenic groups in the isolated macromolecules are discussed. These properties are compared with those of comb-like polymers with another type of attachment of mesogenic groups, and with another (siloxane) chemical structure of the backbone chain. The differences in restrictions of side-chain mobility due to the backbone linkage in different types of comb-like polymers are also discussed.

Optical anisotropy of comb-like macromolecules of lateral and semilateral structure

Maxwell effect and Kerr effect techniques were used to study the intramoleculare axial ordering of anisotropic side groups of an isolated macromolecule in solution. Three comb-like polymers with a methacrylic main chain were investigated. The side chains contain aliphatic spacers separating the mesogenic fragments R from the backbone. R contains two or three phenylene rings with ester linking groups and cyano end groups. Fragments R are attached to the side chains, by the end or middle-point, through the para- or ortho-phenylene ring. The main-chain conformation in solution was identified to assess the hydrodynamic data using the Gaussian coil approximation. The optical anisotropy of the macromolecule segment was determined and related to the monomer unit structure. The specific Kerr constant obtained in diluted benzene solution of polymer was compared with those of low molecular weight analogues of the polymer mesogenic groups. The mobility and intramolecular ordering of the mesogenic groups in the isolated macromolecules are discussed. These properties are compared with those of comb-like polymers with another type of attachment of mesogenic groups, and with another (siloxane) chemical structure of the backbone chain. The differences in restrictions of side-chain mobility due to the backbone linkage in different types of comb-like polymers are also discussed.

Optical anisotropy of comb-like macromolecules of lateral and semilateral structure

Maxwell effect and Kerr effect techniques were used to study the intramoleculare axial ordering of anisotropic side groups of an isolated macromolecule in solution. Three comb-like polymers with a methacrylic main chain were investigated. The side chains contain aliphatic spacers separating the mesogenic fragments R from the backbone. R contains two or three phenylene rings with ester linking groups and cyano end groups. Fragments R are attached to the side chains, by the end or middle-point, through the para- or ortho-phenylene ring. The main-chain conformation in solution was identified to assess the hydrodynamic data using the Gaussian coil approximation. The optical anisotropy of the macromolecule segment was determined and related to the monomer unit structure. The specific Kerr constant obtained in diluted benzene solution of polymer was compared with those of low molecular weight analogues of the polymer mesogenic groups. The mobility and intramolecular ordering of the mesogenic groups in the isolated macromolecules are discussed. These properties are compared with those of comb-like polymers with another type of attachment of mesogenic groups, and with another (siloxane) chemical structure of the backbone chain. The differences in restrictions of side-chain mobility due to the backbone linkage in different types of comb-like polymers are also discussed.

Reactivity of electrophilic reagents towards silyl enol ether groups incorporated into vinyl polymers

Vinyl polymers containing about 20 mol-% of trimethylsilyl or tertbutyldimethylsilyl enol ether functionalities were synthesized by copolymerizing styrene or methyl methacrylate with either 2-trimethylsiloxybutadiene or 2-(tertbutyldimethysiloxy)butadiene under classical free-radical polymerization conditions. The reactivity of the resulting polymers toward a set of classical electrophilic reagents was investigated. Selected electrophiles included water, p-toluenesulfonyl isocyanate ([2+2]-cycloaddition), aromatic and aliphatic aldehydes (aldol reaction), benzaldehyde dimethyl acetal (Noyori condensation), and bromine. Detailed analysis of the polymer final structure - including quantitative 1H- and 13C-NMR analysis - demonstrated that in most cases the silyl enol ether group displays the same reactivity pattern as low-molecular weight analogs.

Entrapment of nucleic acids in liposomes

The entrapment efficiency of three main methods used in the literature for the encapsulation of nucleic acids in liposomes were studied using 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) liposomes. In particular the reverse phase method, the dehydration/rehydration method, and the freeze/thawing method were compared to each other under standardised conditions, i.e. using in every case the same concentration of guest molecules (DNA, tRNA and ATP as low molecular weight analogue) and equally extruded liposomes. The percentage of entrapment strictly referred to the material localized inside the liposomes, i.e. particular care was devoted to ruling out the contribution of the nucleic acid material bound to the outer surface of the liposomes: this was eliminated by extensive enzymatic digestion prior to column chromatography. Depending on the conditions used, the percentage of the entrapped material varied between 10 and 54% of the initial amount. Further, the encapsulation efficiency was markedly affected by the salt concentration, by the size of liposomes, but to a lower degree by the molecular weight of the guest molecules. In general, we observed that the freeze/thawing encapsulation procedure was the most efficient one. In a second part of the work the freeze/thawing method was applied to encapsulate DNA (369 bp and 3368 bp, respectively) using liposomes obtained from POPC mixed with 1–10% charged cosurfactant, i.e. phosphatidylserine (PS) or didodecyldimethylammonium bromide (DDAB), respectively. Whereas PS had no significant effect, the entrapment efficiency went up to 60% in POPC/DDAB (97.5 : 2.5) liposomes. The large entrapment efficiency of DNA permits spectroscopic investigations of the DNA encapsulated in the water pool of the liposomes. UV absorption and circular dichroism spectra were practically the same as in water, indicating no appreciable perturbation of the electronic transitions or of the conformation of the entrapped biopolymer. This was in contrast to the DNA bound externally to the POPC/DDAB liposomes which showed significant spectral changes with respect to DNA dissolved in water.

Polymer-polymer interaction and modeling

The nature of intermolecular interaction in PVC/EVA system was investigated. Bathochromic shifts in infrared region revealed that not only EVA carbonyl but the ester group participates on interaction with PVC chain. These shifts were proportional to acetate content in the copolymer and the composition of EVA in the blend. The PVC group that effectively participates on interaction was not elucidated by infrared spectrometry, but molecular modeling of low molecular weight analogues indicated that hydrogen bonding is the most probable kind of intermolecular interaction present in this system.

Prediction of Thermodynamic Properties of Novolak-Type Phenolic Resin and Aliphatic Polyester Blends: Painter−Coleman Association Model Study of Compositional Homogeneity

The interassociation constants of Painter−Coleman association model, obtained from the results of Fourier transform infrared spectroscopy of low molecular weight analogues in dilute solution, were used to predict the thermodynamic properties of phenolic and polyester polymer blends. The miscibility window, phase diagram, and degree of hydrogen bonding were discussed with the transferability of the association constant between the model compound and the polymer blends. All the predicted results coincided with the actual hydrogen bonding, regular photograph, and proton spin−lattice relaxation in the rotating flame (T1ρH). This model provides a reasonable explanation of analogues of phenolic resin blends. The predicted thermodynamic properties are in harmony with the experimental results due to the high hydroxyl group density and low molecular weight of the phenolic resin which improves the compositional homogeneity of the phenolic/polyester blend.

FTIR and Calorimetric Analyses of the Specific Interactions in Poly(ε-caprolactone)/Poly(styrene-co-acrylonitrile) Blends Using Low Molecular Weight Analogues

It has been known that blends of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) show a miscibility window in a relatively narrow range of copolymer composition in SAN. In order to study the interactions in this miscibility window in detail, FTIR and calorimetric measurements were carried out by using low molecular weight analogues corresponding to monomers of each polymer, because respective homopolymer pairs are not miscible. The FTIR study showed shifts of spectral peaks that is thought as a proof of presence of specific interactions. The acid−base self-interaction energies (Eii) and association energies for respective pairs (Eij) were also estimated by the detailed study of interactions by calorimetry. If the FTIR results were combined with the calorimetric ones, the acid−base spectral shifts of peaks, Δνab (CO stretch, C⋮N stretch, and benzene ring out-of-plane CH bending), indicated a linear relation with Eij values that fits well with Drago's treatment based on quantum mechanics. The data of two independent experiments justified the presence of specific interactions. Finally the heats of mixing of homopolymer−copolymer pairs were calculated by using the self-interaction and association energies and compared with the behavior of miscibility window.

Thermodynamics of Hydrogen Bonding in Solutions of Poly(vinylpyrrolidone) in Ethanol/CCl4 Mixtures

The Gibbs free energy, the enthalpy, and the entropy of mixing of ethanol with the polymer poly(vinylpyrrolidone) (PVP) and with its low molecular weight analog, N-ethylpyrrolidone (NEP) were calculated. The calculation of the free energy of mixing was achieved with the thermodynamic model for hydrogen-bonded polymer systems developed by Painter, Coleman, and Graf. This model, based on the use of an association model, gives the free energy of mixing as a function of the Flory-Huggins interaction parameter, the composition of the mixture, and the association equilibrium constants. The self-association of the ethanol molecules was described by two equilibrium constants, one for the formation of dimers and one for the formation of multimers. The equilibrium constants of interassociation of PVP or NEP with ethanol were determined from the quantitative analysis of NEP/ethanol and PVP/ethanol FTIR spectra at various temperatures and compositions. The values of the equilibrium constants were then used to calculate the theoretical Gibbs free energy of mixing as a function of the composition. The enthalpic and entropic contributions to mixing were compared for the NEP/ethanol and PVP/ethanol mixtures.

Sulfur-containing optically active polymers. V. Synthesis and chiroptical properties of optically active poly(γ-ketosulfide)s prepared by polyaddition of 1,3-dimercaptobenzene to 4,4-dimethyl-2,5-cyclohexadien-1-one or totrans, trans-2,5-heptadien-3-one in the presence of chiral amines

Optically active poly(γ-ketosulfide)s having the asymmetric centers disposed along the main chain have been prepared by step polyaddition of 1,3-dimercaptobenzene to 4,4-dimethyl-2,5-cyclohexadiene-1-one, or to trans, trans-2,5-heptadiene-3-one, in the presence of catalytic amounts of chiral amines. The extent of asymmetric induction on the resulting polymeric product is found to be higher when the alicyclic ketone reagent is employed and is enhanced by lowering the catalyst concentration. The comparison of stereochemical features and chiroptical properties of appropriate low molecular weight analogues with those of the polymeric derivatives indicates that a comparable asymmetric induction occurs in polymers and model compounds, and that the former systems do not display appreciable evidence of ordered secondary structures, in agreement with a low stereoregularity degree along the macromolecular backbone.

Polymer electrolytes — low molecular weight analogues as mimics of high concentration crystalline phase materials

The use of a well determined crystalline reference state to provide information pertaining to dilute amorphous polymer electrolyte systems has been suggested. In this paper, we explore some implicit aspects which may limit the applicability of such a reference state only to oligomeric analogues.

Recent Advances on Photosensitive Polymers: Polymeric Photoinitiators

This overview deals with recent developments on structure—activity relationships in polymeric photoinitiators for UV curable coatings. In particular, polymeric systems bearing side-chain benzoin methyl ether moieties are examined and the effect on the photoinitiation activity discussed in connection with the different anchorage positions of the photosensitive group to the polymer backbone. In addition, novel polymeric photoinitiators based on acyldiphenylphosphinoxide moieties are discribed and their photoinitiation activity related to the nature of the acyl group in the photoreactive molecule. Finally, polymeric systems having pendant thioxanthone and α-morpholino acetophenone moieties in the same macromolecule that are able to behave as photosensitizing and photoinitiating species, respectively, are reported. The much higher photoinitiation activity found for the above copolymers, compared with the mixtures of the corresponding low molecular weight analogs, is interpreted in terms of excitation energy transfer from the side-chain thioxanthone to α-morpholino acetophenone moieties, favored by their forced proximity along the polymer chain.

Ion Binding Properties of Polycarboxylates Using Terbium(III) as a Fluorescent Probe: Viscosities and Coordinated Water Molecules in Polycarboxylate−Terbium(III) Complexes in Aqueous Solutions

The binding properties of trivalent ions to polyacrylate and its low molecular weight analogs (monomer, dimer, and trimer) were investigated in dilute aqueous solution (10 -2 -10 -3 M) using Tb 3+ ion as a fluorescent probe. The fluorescence intensity and lifetime of the Tb 3+ ion depend directly on the number of water molecules bound to their inner coordination sphere. The more efficiently ligands coordinate to Tb 3+ ion, the more water molecules are expelled and, consequently, the greater the fluorescence intensity and lifetime observed. Lifetime measurements in H 2 O and D 2 O showed that the number of water molecules coordinated to the Tb 3+ ion are 6.5, 6.1, 4.9, and 3.6 for monomer, dimer, trimer model compounds, and polyacrylate, respectively. The viscosities of Tb 3+ -polyacrylate complexes were measured in the presence of a large excess of sodium bromide. Viscosities (η sp /c) of the polyacrylate solutions follow Huggins' equation, and on addition of Tb 3+ ion, the intrinsic viscosities decrease abruptly from 700 to 40 mL/g. The mean end-to-end distances, 1/2 , for polyacrylate in Tb 3+ -polymer complexes were calculated using the Flory-Fox equation and were found to be reduced from 125 to 48 nm on addition of Tb 3+ . These results indicate that of the nine water molecules coordinated to Tb 3+ ion in aqueous solution, five to six are replaced with carboxylate groups attached to the polymer chain wrapped around the Tb 3+ .

Enthalpy of Mixing for a Glassy Polymer Blend from CO2 Sorption and Dilation Measurements

Carbon dioxide sorption and dilation data were fitted with the glassy polymer lattice sorption model (GPLSM) to obtain segment−segment interaction parameters for poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), polystyrene (PS), and two PPO/PS miscible blends. These interaction parameters were then used to calculate the enthalpy of mixing for the two polymers. The resulting enthalpies were −0.2 and −1.1 cal/cm3 for PPO/PS blends of 50/50 and 75/25 by weight, respectively, which compare favorably to those determined from measured heats of solution and from calorimetry with low molecular weight analogs.

A Controlled Comparison of the Efficacy of Hetastarch and Pentastarch in Granulocyte Collections by Centrifugal Leukapheresis

AbstractCompared with hetastarch (HS), the low molecular weight analog pentastarch (PS) has been reported to be equally effective for granulocyte collection by centrifugal leukapheresis, to result in fewer adverse donor reactions (ADR), and to have a more rapid elimination profile. We prospectively compared the granulocyte collection efficiency (GCE), granulocyte yield, and ADR in 72 randomly paired granulocytapheresis procedures from 36 volunteer donors using the model CS-3000 Plus Blood Cell Separator (CS) and either PS or HS as the sedimenting agent. Paired collections from each donor allowed us to compare the two agents directly while controlling for intrinsic donor differences. In 33 of 36 (92%) donors, HS procedures were significantly more efficient than PS procedures (P < .001). As an average, HS collections yielded 2.3 ± 0.67 × 1010 granulocytes at 58% ± 8.8% GCE, whereas PS procedures resulted in 1.4 ± 0.76 × 1010 granulocytes at 33% ± 15% GCE. No starch-induced ADR were seen with either agent. For granulocyte harvests using the CS, (1) in most donors, using HS as the red blood cell sedimenting agent during centrifugal leukapheresis results in significantly higher (nearly twofold) GCE and larger granulocyte yields in comparison with using PS, (2) ADR were not observed with either agent, and (3) the potential benefit of more rapid PS elimination should be balanced against significantly lower granulocyte yields.This is a US government work. There are no restrictions on its use.