The influence of HPMC substitution pattern on solid-state properties
ABSTRACT The solid-state properties were studied for different batches of hydroxypropyl methylcellulose (HPMC). The batches had similar chemical composition, but different degree of heterogeneity with regard to the distribution of the substituents along the polymer chains. The glass transition temperature, Tg, was analysed using a new developed method where dynamic mechanic analysis, DMA, was performed in compression mode on compacts, utilizing a wedge-shaped probe. The method was verified by conventional DMA on films. Molecular interactions were studied using FT-IR. In addition, the water vapour sorption was determined by gravimetric measurements and the plasticization by water vapour was studied on film samples using DMA. The results revealed a linear relationship between increasing Tg and increasing percent glucose liberated after enzyme hydrolysis. The percent glucose liberated can in turn be considered to account for both the heterogeneity of the substituents and the total degree of substitution. The results indicated that more heterogeneously substituted cellulose derivatives and derivates with a lower degree of substitution had stronger interactions between polymer chains. As expected from these results, some small difference in the plasticization by water vapour could be detected. However, no significant differences were found in molecular interactions using FT-IR or in the sorption of water vapour. The correlation between heterogeneity in the distribution of the substituents and Tg is of much interest as heterogeneously substituted batches of HPMC have been previously shown to exhibit very different behaviour in solution and in gelling tablets.
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ABSTRACT: Particle characteristics, chemical substitution, compaction behavior, and tablet properties of hydroxypropyl methylcellulose powders from two different suppliers were related using multivariate data analysis. By Principal Component Analysis it was shown that the the degree of substitution of the HPMC powders did not correlate to the particle and compaction properties as strongly as anticipated. Particle shape and powder surface area seem to be more important for the compaction behaviour of the powders than the degree of substitution. In addition, particle and tablet properties were predicted from infrared spectral data. Fourier transform infrared (FTIR) and near infrared (NIR) spectral data of the powders were combined with measured values of the particle characteristics, compaction behavior, and tablet properties using the multivariate data analysis program SIMCA 7.1. Properties like density, particle shape, tablet tensile strength, and drug release characteristics of the HPMC powders and corresponding tablets in this study could be predicted using Partial Least Squares models. In conclusion, the particle shape and powder surface area of HPMC powders seem to be important factors for the quality of tablet attained. Further, this study confirms that NIR and FTIR analysis used in combination with multivariate analysis are powerful tools for predicting the properties of materials and the quality of the end product.Journal of Pharmaceutical Sciences 04/2003; 92(3):494-504. · 3.13 Impact Factor
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ABSTRACT: The substituent patterns of some chemically modified celluloses were characterized as a function of their size distribution, using size-exclusion chromatography coupled to both nuclear magnetic resonance spectroscopy (NMR) and cloud-point measurements. Intact and enzymatically hydrolyzed methyl cellulose (MC) was fractionated according to size, and the level of substitution of the fractions was measured off-line using NMR. Clouding behavior was also measured as a function of size. Clear differences between hydrolyzed and nonhydrolyzed samples were observed using both techniques. For samples that had been selectively hydrolyzed using cellulose-degrading enzymes, NMR data showed a direct link between the degree of degradation and the level of substitution. Differences in the clouding behavior highlighted changes in substituent levels and substituent patterns across the size distribution. The techniques gave valuable and somewhat complementary information on the substituent distributions of the samples before and after enzymatic hydrolysis.Biomacromolecules 11/2006; 7(10):2909-17. · 5.37 Impact Factor
Article: Glass transition in polymers[show abstract] [hide abstract]
ABSTRACT: Glass transition phenomena in several polymers were studied by dielectric and dilatometric measurements. The dielectric measurements were made over the frequency range of 10−4 or 10−1 to 106 cycles/sec. and the temperature range of the glass transition. In the dilatometric study, volume relaxation curves and volume vs. temperature curve were obtained. The transition in three amorphous polymers, (polyvinyl acetate, polystyrene, and polymethyl methacrylate), depends upon frequency or rate of cooling and seems to be an apparent transition. In three crystallizable polymers, (vinylidene chloride-vinyl chloride copolymer, polyethylene terephthalate, and polyacrylonitrile), the magnitude of the dielectric absorption decreases steeply with decreasing temperature in the transition range, and the transition by the volume expansion remains when equilibrium is attained. The transition in the three crystallizable polymers seems to be a real one. Temperature dependences of the activation energies of the dielectric relaxation processes have been described.Journal of Applied Polymer Science 03/2003; 2(4):93 - 99. · 1.40 Impact Factor