The development is described of the twin impinger, a two-stage separation device for assessing the drug delivery from metered dose inhalers and other oral inhalation delivery devices. The discharged aerosol is fractionated by firing through a simulated oropharynx and then through an impinger stage of defined aerodynamic particle size cut-off characteristics. The fine (pulmonary) fraction which penetrates is collected by a lower impinger. It is demonstrated that this device is able to assess individually the fine particle delivery of both components of two-drug aerosols. Formulations showing undue agglomeration or serious crystal growth of drug are readily detected. The twin impinger is shown to be a valuable device for routine quality assessment of aerosols during product development, stability testing and for quality assurance and comparison of commercial products.
An experimental methodology has been developed which combines a continuous-flow system and an electron spin resonance time sweep experiment to study the batch emulsion polymerization of methyl methacrylate (MMA). This system allows essentially continuous monitoring of the propagating free-radical concentration during the reaction. The polymerization was initiated by a redox initiator system at a relatively low temperature (45 °C). This technique has been used to study the effect of varying latex particle size on polymerization kinetics. This study demonstrates that latex particle size has a significant effect on the PMMA propagating radical concentration profile, which is hypothesized to be due to changing the balance of the radical termination reactions. This study also provides evidence for an inhomogeneous distribution of the propagating PMMA radicals in the latex particle. The magnitude of the proposed inhomogeneity depends on the size of the particles.
The IUPAC Working Party on modeling free-radical kinetics' noted that pulsed-laser polymerization (PLP) (e.g., ref 2) provides ameans of measuring the propagation rate coefficient (k,) that is virtually assumption-free. PLP involves pulsed-laser illumination of monomer and photoinitiator, under conditions such that a significant amount of macroradicals is terminated by a very short radical species formed in the pulse immediately subsequent to that in which the longer macroradical was formed. If one can identify the degree of polymerization up of polymer terminated as above, then k, is given by up/ [MI tp, tf being the time between pulses and [MI the monomer concentration. This paper shows that matrix-assisted laser desorptionlionization (MALDI) mass spectrometry can be used to measured up and provides an alternative to the only present means of carrying out this measurement, gel permeation chromatography (GPC).Modeling polymerization under PLP conditions-shows that (i) up can be identified as the point of inflection occurring at the lowest molecular weight in the number molecular weight distribution (MWD) of the formed polymer (this point of inflection is within a few percent of vp for all models for polymerization kinetics tested thus far) and (ii) up also corresponds closely to the lowmolecular-weight point of inflection on the weight MWD, and hence on a GPC trace.Despite its advantages, PLP suffers from some major limitations,interaZia from the need to use GPC to identify v , . These include (i) the need for molecular-weight calibration, through either a reliable monodisperse standard or "universal" calibration and (ii) the necessity of accumulating sufficient polymer. Optimization with regard to these constraints is often opposed by having to ensure that (i) laser illumination of the sample is uniform (including negligible attenuation of the laser beam over the length of the sample cell); (ii) [MI changes negligibly over the course of the experiment5i6 (both of which restrict the total amount of polymer that can be formed); (iii) a large proportion of polymer is formed by termination involving one chain that started in a given pulse and a second chain of a very low degree of polymerization that formed in the next pulse (as distinct from chain stoppage by termination between two chains that both have a large degree of polymerization, etc.); and (iv) the GPC is calibrated to provide accurate MWDs.MALDI offers the potential for obtaining the number MWD directly and is applicable to polymers of moderate molecular weight (up to lo5 under favorable condition^).'^ derivative c 10 10 molecular weight weight distribution calculated from MALO1 (b) MALDI I I : , , : ' I t MALDI signal = number distribution) derivative I 10 I O molecular weight Figure 1. (a) GPC trace (full line), which is the weight MWD, number MWD (broken line) and derivative of weight MWD (points), for product from PLP of MMA at -8 "C, as described in the text. (b) Corresponding quantities for the same sample from MALDI, deduced from the data of Figur...
The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.
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