Molecular Weight Grades Research Articles

Fourier transform Raman spectroscopic study of the interaction of water vapor with amorphous polymers

Water associated with amorphous polymers is known to affect their chemical and physical properties. The purpose of this study was to investigate the nature of water–polymer interactions for some polymers of pharmaceutical interest. Using Raman spectroscopy, polymer–water hydrogen bond interactions were probed for two molecular weight grades of poly(vinylpyrrolidone), namely PVP K90 and PVP K12, and also for poly(vinylacetate) and poly(vinyl pyrrolidone‐co‐vinyl acetate). Water vapor absorption isotherms were obtained for the polymers, and the effect of the absorbed water on the glass transition temperature was determined. A knowledge of the water content and physical state of the polymer was used to aid interpretation of Raman spectral changes. The strength of the hydrogen bond formed with water was found to depend on the chemistry of the polymer, with the pyrrolidone group interacting more strongly than the acetate group. However, minor differences were also observed between the degree of interaction of water and polymer for PVP K12 and PVP K90 at some water contents. This result is attributed to differences in the structural relaxation changes accompanying plasticization by water for the two molecular weight grades. Using principal components analysis of the spectral data, it was also possible to differentiate between samples in the rubbery state and samples in the glassy state. In conclusion, water sorbed into polymers causes changes in the polymer Raman spectra not only because of hydrogen bonding, but also as a result of the plasticizing effect of water on polymer mobility. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:888–901, 2001

Effect of molecular weight and glass transition on relaxation and release behaviour of poly( dl-lactic acid) tablets

Different molecular weight grades of poly( dl-lactic acid) were applied as release controlling excipients in tablets for oral drug administration. The role of molecular weight and glass transition in the mechanism of water-induced volume expansion and drug release of PDLA tablets was investigated. Modulated differential scanning calorimetry (MDSC) was used to determine the glass transition temperature of both dry and hydrated PDLA samples. The absorption rate and total amounts of sorbed water by the polymer were determined by dynamic vapour sorption (DVS). Expansion behaviour of PDLA tablets was measured using thermal mechanical analysis (TMA). At 95% relative humidity all molecular weight grades of PDLA sorbed 1.1–1.3% w/w water, as was determined with DVS. MDSC showed glass transition temperature reductions of 10–11°C for all molecular weight grades of PDLA in water. Volume expansion studies using TMA showed that the molecular relaxation time and equilibrium porosity of the tablets increased with molecular weight. The mean relaxation time increased exponentially with the temperature interval T g− T. The onset temperature of shape recovery of hydrated tablets was approximately 8°C lower than for dry samples. Drug release was only slightly affected by molecular weight. It is concluded that volume expansion of compressed PDLA tablets is related to the glass transition behaviour, originates from water-induced and thermally stimulated shape memory behaviour and is therefore highly dependent on the molecular weight of PDLA.

The Relationship Between “BET” and “Free Volume”‐Derived Parameters for Water Vapor Absorption into Amorphous Solids

Water vapor absorption isotherms for amorphous solids with the same chemical composition but differing in molecular weight (i.e., PVP‐90, PVP‐30, and PVP‐12), and for glucose, trehalose, and two molecular weight grades of dextran were obtained at 30 °C and analyzed using the Brunauer–Emmett–Teller (BET) equation to obtain the parameters, Wm and CB. Similar analyses were carried out for the same molecule (e.g., glucose or fructose) at −10 and 40 °C. Within each chemical group, Wm, the apparent BET‐like parameter that is generally referred to as the “monolayer‐limit of absorption”, changed very little. In contrast, CB, a measure of the free energy of absorption, significantly increased with increasing molecular weight or decreasing temperature, leading to a shift from a Type III to a Type II isotherm. The shift in isotherm shape correlates directly with the glass transition temperature, Tg, of the dry sample relative to the operating temperature, T (i.e., Type III when T >Tg and Type II when T <Tg. These results are shown to be consistent with the combined Flory–Huggins solution model and Vrentas structural relaxation model; wherein Type II isotherm behavior, observed for T <Tg, reflects nonideal volumetric contributions to the overall free energy of absorption due to plasticization by water, as described by Vrentas, whereas Type III behavior only reflects the Flory–Huggins solution model. These volumetric free energy changes within each chemical group are shown to be correlated to the values of the “BET” parameter CB. ©2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 1063–1072, 2000

Effects of Physical Properties of PEG 6000 on Pellets Produced by Melt Pelletization

This study examined the effects of polyethylene glycol (PEG) binders of different physical forms and from different commercial sources on size and size distribution of pellets produced. The meltable binders used were PEG 6000 in the form of flakes, and coarse and fine powders, and melt pelletization using lactose 450 M was carried out in an 8-liter high-shear mixer. Binder particle size, molecular weight, tack, and viscosity were determined. The results showed that the size and size distribution of the pellets obtained could not be explained by the binder particle size. The size and size distribution of the pellets were related to the tack and viscosity of the molten binders. PEGs used were labeled as the same nominal molecular weight grade, although their determined molecular weights could be quite different. Differences in tack and viscosity of the molten binders were associated with determined molecular weight of the binders. The melt pelletization process is sensitive to tack and viscosity of the molten binders. When different PEG brands of the same nominal molecular weight or different batches of the same brand are used in melt pelletization, it is important to characterize the tack and viscosity of the binders used. The effects of the physical form of binders on the pellet quality appear to be less important when compared to the influences of tack and viscosity of the molten binder.

Effect of polycarbonate molecular weight and processing conditions on mechanical behaviour of blends with a core-shell impact modifier

Morphology, tensile properties and impact strength behaviour of blends of three different molecular weight (or viscosity) grades of polycarbonate (PC) and a core-shell type impact modifier (3–18 wt%) were prepared in a single screw extruder with an intensive mixing head and in a co-rotating, fully intermeshing twin screw extruder at different conditions. The morphology of these blends were quantitatively analysed from transmission electron photomicrographs. Tensile properties and Izod impact strength, as a function of temperature for 3.13 mm specimens, were also measured. All mechanical properties were found to be very sensitive to the degree of dispersion of the impact modifier in the PC matrix. Blends made in the twin screw extruder consistently showed better dispersion and mechanical properties: higher tensile modulus, yield strength and elongation at break; higher notched Izod impact strength and lower ductile-brittle temperature. Blends with higher molecular PC show better impact properties reflecting the matrix properties. A subsequent paper explores a more complete analysis of the fracture toughness of such blends and the modes of deformation they undergo during fracture.

Desorption of residual monomer from PVC resins in a fluidized bed drier

AbstractThe present study deals with the investigation of the desorption of vinyl chloride from various commercial and experimental suspension PVC resins in a laboratory fluidized bed drier simulating an industrial drier. The results show that PVC resins may differ widely in the rate at which the monomer is desorbed. The rate of diffusion of the monomer is a function of the drying time, the fluidization air temperature, the porosity, and the amount of glassy particles in the PVC. The residual monomer content decreases with increasing air temperature, drying time, and resin porosity. After 105 min of drying with hot air at 80°C, the residual monomer content in the grade with the highest porosity is reduced from 3400 to 2 ppm, whereas for the grade with the lowest porosity, it is reduced from 4300 to 172 ppm on a dry basis. It appears that the resins of the high molecular weight grades are more porous and the low molecular weight grades contain a high proportion of nonporous or glassy particles and, hence, the desorption rate is smaller in these grades. The proportion of glassy particles and the size of glassy domains are estimated in this study by applying the experimental desorption data at long times to a desorption model. The model is useful in differentiating the interior structure of various PVC grades. © 1994 John Wiley &amp; Sons, Inc.

The influence of thermal treatment on the physical-mechanical and dissolution properties of tablets containing poly(DL-lactic acid).

Five molecular weight grades of poly(DL-lactic acid) (PLA) were incorporated as organic and aqueous pseudolatex binders into matrix tablet formulations containing microcrystalline cellulose and the model drug theophylline. The tablets were thermally treated to temperatures above and below the glass transition temperature (Tg) of the PLA. The results of the dissolution studies showed that thermally treating the tablets to temperatures above the Tg of the PLA significantly retarded the matrix drug release compared to tablets which were not thermally treated. The retardation in drug release could be attributed to a stronger compact and a more efficient redistribution of polymer throughout the tablet matrix, based on fundamental principles of annealing. In addition, results from tablet index testing supported the dissolution results. The bonding index of the compact formulations increased after thermal treatment above the Tg of the PLA. Gel permeation chromatography and differential scanning calorimetry studies demonstrated that thermal treatment had no significant effect on the molecular weight and the glass transition temperature of (PLA) alone and in combination with other components of the tablet formulation.

Inverse gas chromatography of lignocellulosic fibers coated with a thermosetting polymer: Use of peak maximum and conder and young methods

The Conder and Young (CY) and the peak maximum (PM) methods were used to estimate the retention time of n-alkane probes on chemithermomechanical pulp (CTMP) wood fibers treated with a low molecular weight grade phenol-formaldehyde resin (PFR). Thermodynamic functions (Δ H a o , Δ G a o , and ΔS a o ) and the London dispersive component of the surface energy were derived from these retention times. Treated wood fibers show a high energy surface due to the presence of the thermoset resin on their surface. Values of Δ H a o obtained from the CY method were higher than those obtained with the PM method at relatively high temperatures and with relatively low molecular weight alkanes. The results from the two methods were identical at low temperature (293 K) and with the relatively high molecular weight alkane n-undecane.

Binder-substrate interactions in wet granulation. 3: The effect of excipient source variation

The effect of excipient source variation on the interactions during wet granulation between microcrystalline cellulose and aqueous solutions of two molecular weight grades of two polymer binders has been studied using an instrumented mexer torque rheometer. The wet massing data confirmed previous observations that dissimilar polymers interact differently with cellulose substrates during the wet massing process. In addition, for a second cellulose material, variations were also observed in the pattern of interaction between the binders and the excipient. An examination of particulate and surface energetic properties revealed differences in the cellulose materials which were then related to the observed rheological behaviour.

The influence of polymer glass transition temperature and molecular weight on drug release from tablets containing poly(DL-lactic acid).

Five molecular weight grades of poly(DL-lactic acid) were characterized using gel permeation chromatography, differential scanning calorimetry, and viscometry to determine the effect of molecular weight on the glass transition temperature and the intrinsic viscosity. In addition, dynamic mechanical thermal analysis was used to assess the dynamic storage modulus and the damping factor of the polymer samples by detecting motional and structural transitions over a wide temperature range. Significant relationships were found between the molecular weight and these polymer properties. The five grades of poly(DL-lactic acid) were also incorporated as binders into matrix tablet formulations containing the model drug theophylline and microcrystalline cellulose. Dissolution studies showed significant correlations between the properties of the polymer and the matrix release profiles of the tablets. The release of theophylline slowed down progressively as the polymer molecular weight increased. The differences in release became less significant and reached a limiting asymptotic value as the molecular weight increased to 138,000. Further, tablet index testing was utilized to determine the compaction properties of the polymer granulations. Although there was no correlation with the molecular weight of PLA, brittle fracture index testing indicated very low brittleness for all granulations tested. However, bonding index determinations correlated very well with both the physical-mechanical properties of the polymer and drug release profiles.

Changes in polyvinylpyrrolidone coil dimensions by complexation with organic anions: effect of chain length

Changes in polyvinylpyrrolidone (PVP) coil dimensions by complexation with small organic anions were studied by dilure solution viscometry Intrinsic viscosity provides a convenient measure of the dimensions assumed by a flexible polymer chain in solution as a result of interactions with all components in its environment. Molecular interactions between PVP and sodium benzoate and salicylate were investigated over a range of low concentrations of each anion, from 2.5 to 90 mM, and as a function of five molecular weight grades of PVP. This study showed that both contraction and expansion of polymer coils were sensitive to the concentration and chemical structure of the cosolute. In addition, at high anion concentrations changes in polymer conformation by complexation were dependent on both the chain length of PVP and charge density of bound anions through excluded volume effects. Experimental results demonstrating these observations are presented in a three-dimensional surface plot of intrinsic viscosity ratio, polymer size, and anion concentration. A distinct local minimum in the surface plane was exhibited for each cosolute.

CELANESE NYLON 1100, NYLON 1200/1200N-186

Abstract CELANESE Nylon 1100 is an intermediate molecular weight grade for extrusion into monofilaments. CELANESE Nylon 1200 is a high molecular weight grade for extrusion. CELANESE Nylon 1200N-186 is a heat stabilized version of Celanese Nylon 1200 grade. This datasheet provides information on physical properties, and tensile properties as well as fracture toughness. Filing Code: P-28. Producer or source: Hoechst Celanese Corporation.

Binder-substrate interactions in wet granulation. 2: The effect of binder molecular weight

The interactions during wet granulation between microcrystalline cellulose and aqueous solutions of two molecular weight grades of two polymer binders, have been monitored using an instrumented mixer torque rheometer. The rheological behaviour indicated that different molecular weight grades of the same polymer exhibited different behaviour at equivalent viscosity. This observation could only partly be explained using traditionally considered theories relating binder surface tension to granule strength. An examination of polymer adsorption phenomena gave results consistent with earlier data indicating a different degree of interaction between the two polymer types, and possible preferential adsorption of high molecular weight molecules. A model to describe particle: binder behaviour during wet massing has been suggested to explain the observed differences in rheological behaviour.

Spread and adsorbed monolayers of hydroxypropyl cellulose and hydroxyethyl cellulose at the air—water interface

Spread and adsorbed monolayers at the air-water interface of various molecular weight grades of hydroxypropyl cellulose (HPC) and hydroxyethyl cellulose (HEC) have been compared using a surface light scattering technique and have been shown to exhibit almost identical surface viscoelastic properties. Data from spread monolayer surface pressure isotherms have been used to analyze initial adsorption kinetics in the context of a simple diffusion model, and diffusion constants estimated are in very good agreement with independently determined values. Adsorption of HPC and HEC, which occurs independent of molecular weight over a wide concentration range, appears to produce a monolayer with about 64% and 49%, respectively, of the monomer units “adsorbed” at the interface and the rest “desorbed” into the aqueous subphase. This is consistent with the relative degree of hydrophobicity of these polymers.

Binding of 1-anilinonaphthalene-8-sulphonate to poly (N-vinyl-2-pyrrolidone)

The binding of 1-anilinonaphthalene-8-sulphonate (ANS) to poly(N-vinyl-2-pyrrolidone) (PVP) of molecular weight grades k30 (molecular weight 40,000) and k90 (360,000) was studied by a dialysis technique in 0·05 M phosphate buffer, pH 7·1, at different temperatures. The intrinsic binding constant,K, was determined. The binding was favoured by negative enthalpy and positive entropy in both the systems indicating respectively that energetic forces and hydrophobic interactions were contributing to the binding affinity. The effects of addition of urea and palmitic acid on binding were investigated by dialysis and fluorescence techniques. The results showed that the binding of ANS to PVP was dependent on the nature and microenvironment of the binding sites and thereby pointed out the importance of the iceberg structure of water in the binding system.

EVALUATION OF POLYMER ADSORPTION-GEL FORMATION AND SLIP IN POLYMER SOLUTION FLOWS

A superposition model for evaluation of the effects of polymer adsorption-gel formation and slip of polymer solutions exhibiting both phenomena has been applied to the capillary flow of aqueous solutions of two molecular weight grades of hydroxyethyl cellulose (Natrosol 250, types G and HR, supplied by Hercules Powder Company). The flow behaviour of the solutions investigated was non-Newtonian. Evaluations are presented of the effective thicknesses of polymer adsorption-gel formation and pure solvent layers, as a function of the wall shear stress, tube radius and polymer concentration, corresponding to the determinations of the effective velocity at the wall. The results of the analysis indicate the surface characteristics undergo a dramatic change from polymer adsorption-gel formation at the tube surface to the phenomenon characterized by slip in a narrow tube radius interval which has important implications in enhanced oil recovery by polymer solution floods. It also provides an explanation for the contrasting behaviours observed in the flow of aqueous Natrosol solutions through packed beds (Sadowski, 1963) and filter cakes (Kozicki et al., 1972).

The effect of the molecular weight of ethyl cellulose on the drug release properties of mixed films of ethyl cellulose and hydroxypropylmethylcellulose

The effect of the molecular weight of ethyl cellulose on the drug release properties of mixed films of ethyl cellulose and hydroxypropyl methylcellulose has been studied by coating spherical granules with a film and measuring the release of a water-soluble model drug substance. Drug release was found to decrease with increasing molecular weight and on the addition of plasticizer. diethyl phthalate, to the films prepared from the low molecular weight grades. At molecular weights in excess of 35.000 (equivalent to a grade with a nominal viscosity of 20 mPas) the addition of a plasticizer had no effect on drug release. The results have been correlated with the mechanical properties of films prepared from the various molecular weight grades of ethyl cellulose, the rapid release with the low molecular weight grades being caused by the presence of cracks and flaws in the film.

A study of the drawing behavior of polyvinylidene fluoride

AbstractThe drawing behavior of different molecular weight PVDF grades has been investigated over the temperature range 140–160°C, with particular reference to the production of material with enhanced mechanical and electrical properties. Lower molecular weight grades, which have been subjected to a slow‐cooled rather than a quenched moulding procedure yield higher Young's moduli when drawn to a given draw ratio. X‐ray diffraction measurements have demonstrated that the crystalline regions of specimens drawn to high draw ratios under these conditions consist predominantly of the piezo‐ and pyroelectric form I phase. The relationship between the proportion of from I phase and the final drawing stress has been shown to be unique over the temperature range investigated, irrespective of molecular weight and thermal processing history.

The tearing of highly oriented linear polyethylene

The tearing behaviour of oriented linear polyethylene has been studied with particular emphasis on the effects of draw ratio, draw temperature and molecular weight distribution. In all cases the values of fracture surface energy were in the range 102 to 104 Jm−2. The differences between the low molecular weight grades and high molecular weight grades of linear polyethylene were large. At high molecular weight the energy for crack propagation parallel to the direction of orientation fell by a factor of approximately two as the draw ratio was increased from 10 to 20. At low and medium molecular weights, increasing the draw ratio above a value of 10 had no significant effect on the fracture surface energy. Observation of the fracture surfaces showed a simple relationship between the nature of the fracture surface and the value of the fracture surface energy. In general, the higher the value of fracture surface energy the less fibrillar is the fracture surface. Furthermore the fibrillar nature of the fracture surface is essentially determined by the void content of the material.

Nucleate boiling in drag‐reducing polymer solutions

This paper summarizes the important findings of all our previous work concerning nucleate boiling in drag-reducing polymer solutions. Nucleate boiling curves are presented for aqueous solutions of three different molecular weight grades of hydroxyethyl cellulose and three different types of polyacrylamide. The boiling curves have been measured using an electrically heated platinum wire submerged in a saturated pool of liquid at atmospheric pressure. When compared to the boiling curve of the pure solvent, in this case water, all of the polymer solution boiling curves showed higher temperature differences as the polymer solution viscosity increased. These results differ from those reported by earlier investigators for pool boiling of dilute polymer solutions on heated flat plates.