Influence Of Polymer Molecular Weight Research Articles

Preparation and evaluation of insulin-loaded poly( dl-lactide) microspheres using an experimental design

Twenty formulations of bovine insulin in poly( dl-lactide) ( dl-PLA) microspheres were elaborated to study the influence of polymer molecular weight, insulin content and polyvinylalcohol (PVA) concentration on microsphere characteristics and in vitro release profile. Ten of them released nearly all the incorporated insulin in 24 h. Of the rest, four were porous, presenting a burst effect over 40% and releasing 70% in 48 h. The other six formulations were non-porous; four released the insulin in 1 week and the other two only released 28% in 15 days. None of these 10 formulations were able to release the total amount of incorporated insulin, probably due to the adsorption of insulin by the polymer. From the results obtained with the experimental design, one more lot was prepared and tested in vitro and in vivo. The in vitro release profile was much slower than the in vivo one; 16% and 28% were released in vitro on the first day and in the following 10 days, respectively, while the corresponding figures for in vivo release were 60% and 90%.

Interfacial Tension of Poly(ethylene glycol) + Salt + Water Systems

The interfacial tension of eight poly(ethylene glycol) (PEG) + salt aqueous two-phase systems, PEG+(NH 4 ) 2 SO 4 , PEG+K 2 HPO 4 , PEG+xK 2 HPO 4 +KH 2 PO 4 (x is the molar ratio of K 2 HPO 4 to KH 2 PO 4 , x=1.42, pH=7.0), PEG4000+xK 2 HPO 4 +KH 2 PO 4 (at different pH or x values), PEG+K 3 PO 4 , PEG+Na 2 SO 4 , PEG+MgSO 4 , and PEG+Na 2 CO 3 systems, is reported. The influence of polymer molecular weight and concentration, salt concentration and type, and the total solute compositions on the interfacial tension has been studied.

Pyrolytic conversion of methyl- and vinylsilane polymers to Si-C ceramics

Poly(methylsilane) and poly(vinylsilane) were synthesized using a titanocene catalyst, and their pyrolytic conversion to ceramics was followed using a combination of thermal analysis and infrared spectroscopy. The two polymers have distinctly different backbone structures, as determined by29Si NMR; methylsilane polymerizes to a polysilane, while vinylsilane polymers have a predominately polycarbosilane backbone, with some polysilane structure as well. The pyrolysis path and char yield were dependent primarily on backbone structure, with little influence of polymer molecular weight. The majority of the weight loss on conversion occurs below 650 °C, although bond rearrangement continues to 1400 °C. Poly(vinylsilane) produced a carbon-rich Si-C ceramic in which the carbon was dispersed on a sufficiently fine level to show resistance to oxidation on heating in air to 1400 °C. Copolymerization of methyl- and vinylsilane produced stoichiometric SiC; however, polymers of methylsilane were sensitive to oxygen incorporation and sometimes pyrophoric. Polymerization of vinylsilane with disilylethane permitted control of rheology and imparted thermoset behaviour.

Aqueous two-phase systems of poly(ethylene glycol) and dextran — experimental results and modeling of thermodynamic properties

Experimental results for some properties (activity of water, change of enthalpy on mixing and diluting, compositions of coexisting liquid phases) of aqueous solutions of hydrophilic polymers poly(ethylene glycol) and dextran between 277 and 333 K are reported. The results are used to develop and test a semiempirical group contribution expression for the excess Gibbs energy of diluted aqueous polymer solutions. The model is applied to correlate some of the new experimental data, while the remaining experimental results are used to test its potential for predicting the influence of polymer molecular weight and temperature on the phase behavior of aqueous two-phase systems — a field where most previously known methods fail.

Aqueous Two‐Phase Systems of Poly(ethylene glycol) and Di‐Potassium Hydrogen Phosphate with and without partitioning Biomolecules – Experimental Results and Modeling of Thermodynamic Properties

AbstractExperimental results for thermodynamic properties of aqueous two‐phase systems of poly(ethylene glycol) and di‐potassium hydrogen phosphate with and without partitioning biomolecules (glycine, phenylalanine and lysozyme) are reported for temperatures between 277 and 333 K. The results are used to develop a semiempirical group‐contribution expression for the excess Gibbs energy of dilute aqueous solutions containing polymeric as well as ionic solutes. The model is applied to correlate some of the new experimental data, while other experimental results are used to test its ability for predicting the electrical potential difference between the coexisting phases, the partition coefficient of lysozyme and the influence of polymer molecular weight on the phase behaviour of aqueous two‐phase systems – a field where most previously known methods are often inadequate.

Stress‐strain behavior and dynamic mechanical properties of poly(1,1‐dimethyl‐1‐sila‐cis‐pent‐3‐ene), poly(1‐methyl‐1‐phenyl‐1‐sila‐cis‐pent‐3‐ene) and of these polymers after crosslinking with sulfur

AbstractMechanical properties of polymers can be described by their stress/strain curves and by their behavior under dynamic mechanical thermal analysis (DMTA). The purpose of this paper is to report such mechanical properties for two unsaturated polycarbosilanes: poly(1, 1‐dimethyl‐1‐sila‐cis‐pent‐3‐ene) (I) and poly(1‐methyl‐1‐phenyl‐1‐sila‐cis‐pent‐3‐ene) (II). Tensile strength, elongation at break, modulus, bending modulus, Tg, and tan δ for I, II and for sulfur crosslinked I and II have been measured. The influence of polymer molecular weight, quantity of crosslinking agent, cure time, presence of carbon black filler, the effect of crosshead speed, and frequency on these properties was investigated.

Conversion of Polymers of Methyl- And Vinylsilane To Sic Ceramics

ABSTRACTPoly(methylsilane) and poly(vinylsilane) were synthesized using a titanocene catalyst, and their pyrolytic conversion to ceramics was followed using a combination of thermal analysis and infrared spectroscopy. The two polymers have distinctly different backbone structures, as determined by 29Si NMR; methylsilane polymerizes to a polysilane, while vinylsilane polymers have a predominately polycarbosilane backbone, with some polysilane structure as well. The pyrolysis path and char yield were dependent primarily on backbone structure, with little influence of polymer molecular weight. The majority of the weight loss on conversion occurs below 650 °C, although bond rearrangement continues to 1400 °C. Poly(vinylsilane) produced a C-rich Si-C ceramic in which the carbon was dispersed on a sufficiently fine level to show resistance to oxidation on heating in air to 1400 °C.

Fusarium solani pisi recombinant cutinase partitioning in peg/potassium phosphate aqueous two-phase systems

An aqueous two-phase system of polyethylene glycol (PEG) and potassium phosphate was developed for extraction of a cutinase from cell debris of a recombinant Escherichia coli strain. Basic studies to identify the primary factors which affect cutinase partition, namely the influence of polymer molecular weight, polymer concentration and pH were carried out using a purified preparation of the cutinase. The enzyme partition coefficient was enhanced with decreasing PEG molecular weight, increasing tie-line length and pH.

Protein partitioning at the isoelectric point: Influence of polymer molecular weight and concentration and protein size

We report the partition coefficient, K(p') at the isoelectric point of lysozyme, chymotrypsinogen A, albumin, transferrin, and catalase in 64 different polyethylene(PEG)/ dextran(Dx)/water systems. We study the trends of the partition coefficient with protein type, polymer concentration, and polymer molecular weight. We find that the partition coefficient decreases with increasing tie line length for lysozyme, albumin, transferrin, and catalase for which K(p) is less than 1, but increases for chymotrysinogen for which K(p) is larger than 1. The effect of the tie line length on the partition coefficient is larger for the large proteins than for the small proteins. The partition coefficient decreases with increasing protein molecular weight except for lysozyme suggesting that lysozyme is present as a dimer or a trimer. The partition coefficient decreases with increasing PEG molecular weight, but the magnitude of the increase is larger for the smaller PEG molecular eights and tends to level of at high PEG molecular weight. The partition coefficient increases with increasing dextran (Dx) molecular weight for chymotrypsinogen but decreases for catalase. The partition coefficients of lysozyme, albumin, and transferrin increase with increasing Dx molecular weight from Dx 10(4) to Dx 1.1 x 10(5) and then slightly decrease from Dx 1.1 x 10(5) to Dx 5 x 10(5). The experimental results are analyzed using a statistical thermodynamics model. The experimental results are analyzed using a statistical thermodynamics model. The experiments suggest that protein partitioning at the isoelectric point in aqueous two-phase systems is strongly related to the size of the proteins and polymers. Finally, the impossibility of obtaining data completely independent of polymer concentration is emphasized.

Influence of polymer molecular weight and temperature on phase composition in aqueous two-phase systems

In an effort to understand the molecular weight and temperature dependence of protein partition coefficients, we have conducted experiments to determine how the binodal curve and the difference in polymer concentrations between the top and bottom phases (▵ PEG  [PEG] T — [PEG] B and Δ Dx  [Dx] B — [Dx] T); depend on polymer molecular weight and temperature. We report the equilibrium compositions at 4°, 25° and 40°C for 16 different aqueous two-phase PEG-Dx systems which consist of all possible combinations of the four PEG molecular weights (4000, 6000, 10 000, and 20 000) and the four Dx molecular weights (10 000, 40 000, 110 000 and 500 000). Four tie lines were measured for each system. We confirm that increasing polymer molecular weight increases the tie line length and depresses the binodals to lower polymer concentrations, and that this effect will be greater when the ratio of this molecular weight increase to the molecular weight of the other species is large. The increase in the tie line length and in Δ Dx and Δ PEG with increasing polymer molecular weight tends to level off at high polymer molecular weight and at high total polymer concentrations. It is shown that the effect of temperature is not symmetric, i.e. changes in temperature produce a change in Δ Dx while Δ PEG remains nearly constant. The effect of polymer molecular weight on both Δ Dx and Δ PEG is magnified with increasing temperature. The results found here suggest a series of experiments which could be used to isolate (or highlight) the effect of the second virial coefficient on the partition coefficient.

Influence of solvent and molecular weight on thickness and surface topography of spin‐coated polymer films

AbstractThe influence of polymer molecular weight, molecular weight distribution, and polymer‐solvent interactions on the thickness and topography of spin‐coated polymer films was examined. For films prepared from dilute solutions, highly volatile solvents or fair or “poor” solvents for the polymer adversely affect film surfaces causing nonuniformities (waves) to appear. However, if the concentration of these solutions is increased to approximately the concentration at which entanglements are formed, nearly uniform films are produced even if the solvent employed is highly volatile, such as dichloromethane. When toluene is employed as the solvent, which has a relatively low volatility and therefore forms nearly flat film surfaces, films prepared from dilute solution were found to have thicknesses, h, proportional to η Ω−0.49 for polystyrene and η Ω−0.49 for poly(methylmethacrylate) where ηo is the zero‐shear rate solution viscosity and Ω is the rotational speed at which the films were prepared. These results suggest that the exponents associated with ηo and Ω may be nearly independent of the type of polymer used as long as flat films are produced. Finally, the molecular weight parameter most important in controlling final film thickness for films made from dilute solutions is Mv, the viscosity‐average molecular weight.

Interaction parameters of polystyrene‐polyisoprene‐toluene systems at 45°c from gel permeation chromatography

AbstractEquilibrium phase diagrams of narrow molecular weight distribution samples of polystyrene and polyisoprene in the presence of toluene at 45°C and 1 atm pressure were established by means of gel permeation chromatography. The polymer‐polymer interaction parameter was evaluated on the basis of the Flory‐Huggins approach. The influence of polymer molecular weight and polymer‐solvent interaction parameters on (i) the shape and location of the binodal curve, (ii) the location of the critical point, and (iii) the polymer‐polymer interaction parameter was investigated.

Polymeric inhibitors of platelet aggregation. Synergistic effects and proposals for a new mechanism

We have studied the inhibition of ADP-induced platelet aggregation in sheep platelet-rich plasma by water-soluble polymers bound to the prostaglandin analogue 5-(6-carboxyhexyl)-1-(3-cyclohexyl-3-hydroxypropyl)hydantoin (‘BW 245’ C, (I)). The use of unambiguous modes of binding this antiplatelet drug to polymers has enabled us to study some structural features which influence inhibitory activity. Evidence is adduced which indicates that the chemical mechanisms responsible for inhibition by free and coupled BW 245 are similar. The most important observation is a remarkable synergism demonstrated by the greatly enhanced activity of a mixture of a polymer coupled to BW 245 with the uncoupled parent polymer. In some cases (e.g., with high-molecular-weight dextran) the effect may reach (and possibly exceed) two orders of magnitude. The influence of polymer molecular weights and ‘cross-polymer’ effects have both been examined. A mechanism has been proposed to account for these phenomena, involving adsorption of the added (inactive) polymer on to the platelet membranes, facilitating interaction of the polymer-bound drug with receptors, made more accessible by alteration to the surface geometry. This mechanism is based on physical processes, unlike other explanations of synergistic behaviour, e.g., that of prostaglandins used in conjunction with non-polymeric drugs. The observed dependences of synergistic effects upon polymer molecular weight and type and distribution of drug molecules along chains are typical ‘polymer’ phenomena which are all consistent with the proposed mechanism.

Static investigation of the influence of polymer molecular weight and loading in the gas chromatographic determination of poly(dimethylsiloxane) interaction parameters

Static investigation of the influence of polymer molecular weight and loading in the gas chromatographic determination of poly(dimethylsiloxane) interaction parameters

Enzymatic hydrolysis of cellulose in aqueous two‐phase systems. I. partition of cellulases from Trichoderma reesei

The partitioning of endo-beta-glucanase, exo-beta-glucanase, and beta-glucosidase from Trichoderma reesei QM 9414 in aqueous two-phase systems has been studied with the object of designing a phase system for continuous bioconversion of cellulose. The partitioning of the enzymes in two-phase systems composed of various water soluble polymeric compounds were studied. Systems based on dextran and polyethylene glycol (PEG) were optimal for one-sidedly partitioning the enzymes to the bottom phase. The influence of polymer molecular weights, polymer concentration, ionic composition of the medium, pH, temperature, and adsorption of the enzymes to cellulose on the enzyme partition coefficients (K) were studied. By combining the effects of polymer molecular weight and adsorption to cellulose, K values could be reduced for endo-beta-glucanase to 0.02 and for beta-glucosidase to 0.005 at 20 degrees C in a phase system of Dextran 40-PEG 40000 in the presence of excess cellulose, At 50 degrees C, K values were increased by a factor of two. In a phase system based on inexpensive crude dextran and PEG, the partition coefficient for endo-beta-glucanase was 0.16 and for beta-glucosidase was 0.14 at 20 degrees C with excess cellulose present.

Hydrodynamical behaviour of the poly(ethylene oxide)-sodium dodecylsulphate complex

We have studied by various methods (conductimetry, ionic activity measurement, viscometry, ultracentrifugation) the formation of poly(ethylene oxide)-sodium dodecylsulphate complex, focusing attention on the influence of polymer molecular weight. The net charge of the complex is calculated and its hydrodynamical behaviour is compared to that of a simple polyelectrolyte of the same charge density. The molecular weight dependence of the intrinsic viscosity is of the classical Mark-Houwink form.

Influence of polymer molecular weight on selected thermodynamic properties of polymer/solvent systems and the application of the UNIFAC theory

The intrinsic viscosities of eleven narrow molecular weight distribution polystyrene samples ranging from number-average molecular weight 1820 to 1 292 000 have been determined in pure solvents of tetrahydrofuran and chloroform with a Ubbelohde No. 1 viscometer at 25°C. By combining the original and modified Fox-Flory viscosity treatments, respectively, with the Flory-Huggins Lattice theory, the interaction parameters were calculated. With the aid of original and modified UNIFAC methods the solvent activity, clustering function of the solvent, and the interaction parameter were computed and compared with the experimental data. It was established that the influence imposed by the polymer molecular weight on the activity of the solvent, the clustering function of solvent, and interaction parameter is insignificant. The modified UNIFAC method satisfactorily predicted the solvent activity as illustrated by previous investigators. However, both UNIFAC methods failed to predict the interaction parameter.

Structural studies of ultrahigh‐modulus polyethylene using nitric acid etching and gel permeation chromatography. II. Influence of polymer molecular weight, draw temperature, and annealing

AbstractThe technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh‐modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lengths less that 500 Å. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small‐angle x‐ray scattering. Possible reasons for these discrepancies are discussed.

Dissolution of Macromolecules I: Surface Phenomena Associated with Polymer Dissolution

A series of polymer free acids, derived from ethylene maleic anhydride resins has been used to study solvent penetration into a polymer compressed disk and polymer swelling. The influence of polymer molecular weight and solvent pH on solvent penetration and polymer swelling was determined. The rate of disappearance of the hydrated layer, formed by simultaneous swelling and solvent penetration, was found to agree closely with the rate of solvent penetration.