Polymer matrix effects

Gaylord et al. [49] reported the dilution and matrix effects in grafting of the styrene/AN binary mixture onto cellulose with K2S2O8 as the initiator. Titledman and coworkers [50] reported the effect of hydroxypro-pylmethyl cellulose on the course of (NH4)2S20 decomposition and claimed a route for grafting of vinyl monomers onto the polymer backbone. The decomposition of the peroxo salt, under the catalytic influence of the... 

Incineration of a collection of polymers with 10 different kinds of brominated flame retardants has been studied under standardized laboratory conditions using varying parameters including temperature and air flow. Polybrominated diphenyl ethers like the deca-, octa-, and pentabromo compounds yield a mixture of brominated dibenzofurans while burning in polymeric matrices. Besides cyclization, debromination/hydrogenation is observed. Influence of matrix effects and burning conditions on product pattern has been studied the relevant mechanisms have been proposed and the toxicological relevance is discussed. 

Nappom WT, Laborde H, Leger J-M, Lamy C. 1995. Flectro-oxidation of Ci molecules at Pt-based catalysts highly dispersed into a polymer matrix Effect of the method of preparation. J Electroanal Chem 404 153-159. 

SFE has now been available long enough to allow an evaluation of its prospects for polymer/additive extraction. SFE is still around, but EPA and FDA approved SFE methods are still wanting. The main problem is strong matrix effects. SFE is not a cookbook method for one s matrix. Not unlike microwave extraction, SFE requires that a specific method be developed to optimise the recovery for each polymer/additive system. Therefore, the success of SFE depends on the polymer... 

When the analyte is present in the polymer at very low concentrations some special precautions are needed to enhance the sensitivity of the extraction process, i.e. to lower the detection limit. The sample may be concentrated prior to analysis by SCF or solvent evaporation (at as low a temperature as possible to avoid degradation or partial loss of volatile analytes). Alternatively, a larger amount of polymer sample may be extracted (followed by LVI). Samples may also be concentrated or matrix effects minimised by using SPE [573,574],... 

Many additives fragment quite extensively with FAB. The observation of molecular ion and many fragment ions for each additive makes the determination of the number of additives in the extract difficult if not impossible. Moreover, due to the matrix effect , not all the additives in polymer extracts are detected under FAB. 

Desorption/ionisation techniques such as LSIMS are quite practical, as they give abundant molecular ion signals and fragmentation for structural information. In the conditions of Jackson et al. [96], all the molecular ion and/or protonated molecule ion species were observed in the LSIMS spectrum when only 1 pmol of each additive was placed on the probe tip. However, as mentioned above, in LSIMS/MS experiments the choice of the matrix (e.g. NBA, m-nitrobenzylalcohol) is very important. Matrix effects can lead to suppression of the generation of molecular ions for some additives. LSIMS is not ideal for the quantitative detection of polymer additives, as matrix effects are very important [96]. 

Selection of a suitable ionisation method is important in the success of mixture analysis by MS/MS, as clearly shown by Chen and Her [23]. Ideally, only molecular ions should be produced for each of the compounds in the mixture. For this reason, the softest ionisation technique is often the best choice in the analysis of mixtures with MS/MS. In addition to softness , selectivity is an important factor in the selection of the ionisation technique. In polymer/additive analysis it is better to choose an ionisation technique which responds preferentially to the analytes over the matrix, because the polymer extract often consists of additives as well as a low-MW polymer matrix (oligomers). Few other reports deal with direct tandem MS analysis of extracts of polymer samples [229,231,232], DCI-MS/MS (B/E linked scan with CID) was used for direct analysis of polymer extracts and solids [69]. In comparison with FAB-MS, much less fragmentation was observed with DCI using NH3 as a reagent gas. The softness and lack of matrix effect make ammonia DCI a better ionisation technique than FAB for the analysis of additives directly from the extracts. Most likely due to higher collision energy, product ion mass spectra acquired with a double-focusing mass spectrometer provided more structural information than the spectra obtained with a triple quadrupole mass spectrometer. 

Conventional XRF analysis uses calibration by regression, which is quite feasible for known matrices. Both single and multi-element standards are in use, prepared for example by vacuum evaporation of elements or compounds on a thin Mylar film. Comparing the X-ray intensities of the sample with those of a standard, allows quantitative analysis. Depending on the degree of similarity between sample and standard, a small or large correction for matrix effects is required. Calibration standards and samples must be carefully prepared standards must be checked frequently because of polymer degradation from continued exposure to X-rays. For trace-element determination, a standard very close in composition to the sample is required. This may be a certified reference material or a sample analysed by a primary technique (e.g. NAA). Standard reference material for rubber samples is not commercially available. Use can also be made of an internal standard,... 

It is possible to determine components in complex EPs where matrix effects can be severe. For example, zinc (as zinc borate), chlorine (as dechlorane flame retardant), antimony (as oxide) and fibre-glass have been determined in nylon using just one standard. Many users have refined the universal precalibrated programmes for standardless XRF and made them more efficient for matrix correction by using variable correction coefficients. OilQuant offers possibilities for analysing polymers [243]. Software packages usually provide ... 

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

The gradual accumulation of structures III in the initial stages of the reaction could account for its auto-catalytic character until a "stationary-state" is reached in which the surface of the precipitated polymer available for such association with monomer remains practically constant. A structure such as III could also be responsible for the stereo-control of the propagation step. Indeed, the polymer formed at conversions below 2 per cent exhibits much lower stereoregularity than at higher conversions (see Figure 6). These various peculiar consequences connected with the arizing of structure III will be referred to as "matrix effect". 

It should be noted that the absence of matrix effect when the monomer is only associated in the cyclodimeric form suggests that structure I is more stable than the association of the monomer with the polymer and that therefore long ordered structures of type III do not arise. In very dilute acrylic acid solutions in hydrocarbons or chlorinated compouds a matrix effect (autoacceleration) is again observed. This is believed to arise as a result of a structure III formed by the association of the polymer with "free" monomer (4). 

Auto-acceleration was observed in the homopolymerization of methacrylic acid solutions over limited concentration ranges in methanol and in water. Perhaps under such conditions swelling of the polymer favors monomer diffusion leading to a larger amount of pre-oriented structures III. Alternatively, a monomer-solvent complex may arise which favors a pre-oriented structure and thus, may be responsible for the onset of a matrix effect (9). 

The auto-acceleration observed under such conditions is reduced ( = 1.15) and could partially result from non-steady-conditions but also from a "matrix effect" operating on the surface of unswollen polymer particles. It should be noted in this respect that the post-polymerization which is induced by the growing chains occluded in the precipitated polymer exhibits an initial rate very much lower than the rate observed during irradiation (Curve 1 in Figure 91 which suggests that the contribution of the growth of occluded chains to the over-all rate is small. 

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

However, DMF is a solvent for polyacrylonitrile and the polymerization occurs in a homogeneous medium for solutions containing 30 per cent monomer or less. This reduces the value of these experiments as an argument to show the influence of a matrix effect. Indeed the fact that auto-acceleration disappears when DMF is added to acrylonitrile was considered as a proof for the fact that precipitation of the polymer was the cause of autoacceleration. 

All OFDs reported in the literature suffer from spectral interferences, long response times, and narrow dynamic responses. Many of these obstacles exist as a result of limitations due to the properties of UY/visible fluorescent dyes. These dyes typically absorb and fluoresce between 300 and 650 nm, a region susceptible to extensive interference, especially from biomolecules (Figure 7.1). The fluorescence of sample impurities combined with the inner effect of the matrix and polymer support greatly increase the signal interference of the analysis. 

Asloun, El. M., Nardin, M. and Schultz, J. (1989). Stress transfer in single-fiber composites Effect of adhesion, elastic modulus of fiber and matrix and polymer chain mobility. J. Mater. Sei. 24, 1835-1844. 

Fan, C.F. and Hsu, S.L. (1992). A study of stress distribution in model composite by finite-element analysis. II fiber/matrix interfacial effects.. /. Polym. Sci. Part B Polym. Physics 30, 619-635. 

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