Table II: Weight-average and number-average molecular weight and polydispersity of polyethylene oxide (PEO) and PEO blends.
Weight-average molecular weight, number–average molecular weight, and polydispersity were determined by aqueous size-exclusion
chromatography with a multiangle laser light-scattering (SEC-MALLS) detector. The SEC system consisted of a pump (Waters 2690
pump, Milford, MA), connected with a DAWN (MALLS) detector (Wyatt Technology, Santa Barbara, CA) and a Wyatt differential
refractive index detector. The SEC fractionation of analyzed sample was evaluated to ensure an ideal SEC separation was obtained.
Figure 1: Differential weight fraction versus molar mass for Polyox 1105 water-soluble resin (WSR) samples and blend components,
Polyox 205 NF WSR and Polyox N-12K WSR. (FIGURE COURTESY OF THE AUTHORS)
PEO samples were formulated into matrix tablets using theophylline and diltiazem HCl as model drugs. The formulations were
comprised of the following by weight: 40% API; 30% polymer or polymer blend; 29.5% MCC; and 0.5% magnesium stearate. Tablets
weighing 400 mg were prepared by direct compression using a 16-station tablet press (Manesty Beta,Knowsley, Merseyside, UK),
equipped with 0.4063-in. (10.2-mm) flat-faced bevel-edge tooling at a compression force of 4000 lb (17.8 kN). Tablet hardness
(n = 10) was measured with a hardness tester (Model HT-300, Key International, Englishtown, NJ). Drug dissolution was measured
in a USP II apparatus (Varian/VanKel VK 7025, Varian, Palo Alto, CA) dissolution system with an ultraviolet–visible spectrophotometer,
using three-prong capsule weights, in deionized water at 37.0 ± 0.5 °C, and a paddle speed of 50 rpm.
Results and discussion
Figure 2: Differential weight fraction versus molar mass for Polyox 1105 water-soluble resin samples and polyethylene oxide
blends. (FIGURE COURTESY OF THE AUTHORS)
Effect of blending on viscosity. Table I compares the viscosity values for blended PEO samples to individual samples of Polyox 205 NF WSR, Polyox 1105 NF
WSR, and Polyox N-12K NF WSR. Samples obtained of commercially available Polyox 1105 NF WSR only covered a narrow viscosity
range of 9120–11,520 centipoise (cP) within the broader product-viscosity specification of 8800–17,600 cP. The lack of Polyox
1105 NF WSR samples with viscosities at the upper extremes of the product specification make it difficult to assess the impact
of variability in product viscosity on drug- formulation properties. Thus, blends of Polyox 205 NF WSR and Polyox N-12K NF
WSR were prepared in varying proportions to achieve a range of sample viscosities representative of Polyox 1105 NF WSR product
viscosity. The viscosity results showed that blending of Polyox NF WSR product grades adjacent to the targeted Polyox product
grade is a reasonable approach for obtaining representative Polyox NF WSR product viscosities for formulation testing.