IR Laser‐Induced Degradation of Poly(vinyl acetate): Novel Thermal Reactions in Solid Polymers

Summary: Pulsed‐IR laser‐induced decomposition of poly(vinyl acetate) (PVAC) differs remarkably from its conventional pyrolysis, which results in the formation of acetic acid and non‐polar carbonaceous residue. In contrast, the products in the former case are (i) vinyl acetate (low energy channel), (ii) products of cleavage in the acetate group, and (iii) an ablatively deposited polar polymeric film containing roughly half of the acetoxy groups initially present.

Schematic of the different routes of poly(vinyl acetate) degradation.     

Direct analysis of reference biofluids by coupled in situ electrodeposition-electrothermal atomic absorption spectrometry

The application of coupled in situ electrodeposition-electrothermal atomic absorption spectrometry (ED-ETAAS) to the determination of Pb in biological standard reference materials is described. In situ electrodeposition at a cell voltage of 3.0 V from 25-μl samples onto electrodeposited Pd is used to quantitatively separate the analyte from blood and urine matrices. With subsequent withdrawal of spent electrolyte, this overcomes the atomisation problems inherent with high salt and organic contents. ED-ETAAS is applied with minimal sample pre-treatment (acidification). The electrolysis process aids decomposition of the organic matrix, and the release of trace elements. Evolution of H₂ at the cathode counters fouling of the Pd modifier surface. The palladium deposit is renewed in situ for each determination. For AMI certified lyophilised blood, diluted 1+3 with 0.1 M HCl (18.1 μg/l Pb), the R.S.D. was 3.0% (peak height; n=5) and the detection limit (3 σ_blank; n=5) was 1.5 μg/l. Results for certified blood samples were AMI 72.3±4.3 μg/l (certified 76.2±7.6 μg/l) and Seronorm 34.2±2.0 μg/l (36±4 μg/l). The result for NIST SRM 2670 normal urine acidified to 1% HNO₃ was 8.1±0.6 μg/l (recommended value 10 μg/l).     

Dispersion copolymerization of polyoxyethylene macronomer and styrene 4. Solution properties of polystyrene-graft-polyoxyethylene copolymers

The graft copolymers (polystyrene-graft-polyoxyethylene) (PSt-graft-PEO) were prepared by the radical dispersion copolymerization of methacryloyl (MA)-terminated PEO macromonomer and styrene. By means of size-exclusion chromatography, liquid chromatography at the critical adsorption point, and light scattering, the molecular weight parameters and the solution properties of PSt-graft-PEO were investigated. The apparent average molecular weight and the molecular weight distribution (MWD) of graft copolymers were found to decrease with increasing molecular weight of PEO-MA macromonomer. This decreased molecular weight was attributed to the chain transfer to PEO unit and increased contribution of the solution polymerization. The broad MWD varied with the ratio of the polymerization in the continuous phase and the polymer particles. The number of PEO grafts per PSt backbone decreased with increasing molecular weight of the PSt-graft-PEO copolymer, which was attributed to the intramolecular association of PEO segments. The intrinsic viscosity or the coil size of graft copolymer molecules varied with temperature as a result of the dehydration of PEO segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3087–3097, 1999     

Graphical Representation of Various Models for Crystal Size Distribution in Continuous Flow Crystallizers

Plots of crystal size distribution of the following crystallizer models are compared: an ideal continuous-flow MSMPR (mixed suspension, mixed product removal) crystallizer with a zero as well as non-zero initial crystal size, an MSMPR crystallizer with size dependent growth of crystals, an MSMPR crystallizer with missing fines, an MSMPR crystallizer with agglomerative growth, and a series of MSMPR crystallizers simulating a crystallizer with nonideal agitation. The shape of the individual size distribution curves can serve as a diagnostic criterion in determination of the most probable model of crystallization.     

Copolymerization of polar and non-polar monomers in direct and inverse emulsion systems

Some problems connected with the use of monomers with different solubilities in water and oil phases for copolymerization in direct and inverse (micro)emulsions are discussed. We have shown that by choosing appropriate model systems which can simulate specific effects connected with the transfer of reactants between various phases and swelling ability of polymer particles, one can contribute to the answering the questions of the propagation locus (loci) of copolymerization and of its (their) history during emulsion copolymerization as well as to recognize the effect of the nature of the interlayer in the inverse (micro)emulsion system in relation to the kinetics and mechanism of the copolymerization process and structure of the copolymer formed. The method was demonstrated on the examples of seeded methyl methacrylate emulsion polymerization, of the emulsion copolymerization of styrene and divinylbenzene and of the inverse (micro)emulsion copolymerization of acrylamide and methyl methacrylate and/or acrylamide and styrene.     

Poly(methyl methacrylate) dispersions in decane stabilized by a diblock copolymer

In a dispersion polymerization, the monomer is miscible with the reaction medium, while the resulting polymer is insoluble under the same conditions. The macroscopic precipitation of the polymer is prevented by a steric stabilizer. Methyl methacrylate was polymerized in decane in presence of polystyrene-block-poly(ethylene-co-propylene) and spherical dispersion particles of poly(methyl methacrylate) (PMMA) were obtained. The static light scattering yielded molar masses of particles in the range 4 × 10⁷ to 7 × 10⁹ g mol⁻¹. Dynamic light scattering provided the hydrodynamic radii from 60 to 190 nm and also information on the non-uniformity of the particles. The relations between the characteristics of the dispersion particles (concentration of components, particle mass and dimensions, molar mass of PMMA chains, surface density of stabilizing chains, etc.) were looked for. The kinetics of polymerization seems to be only little affected by the colloidal character of the system.