New insight into the formation of structural defects in poly(vinyl chloride)

The monomer conversion dependence of the formation of the various types of defect structures in radical suspension polymerization of vinyl chloride was examined via both H-1 and C-13 NMR spectrometry. The rate coefficients for model propagation and intra- and intermolecular hydrogen abstraction reactions were obtained via high-level ab initio molecular orbital calculations. An enormous increase in the formation of both branched and internal unsaturated structures was observed at conversions above 85%, and this is mirrored by a sudden decrease in stability of the resulting PVC polymer. Above this threshold-conversion, the monomer is depleted from the polymer-rich phase, and the propagation rate is thus substantially reduced, thereby allowing the chain-transfer processes to compete more effectively. In contrast to the other defects, the chloroallylic end groups were found to decrease at high conversions. On the basis of the theoretical and experimental data obtained in this study, this decrease was attributed to copolymerization and abstraction reactions that are expected to be favored at high monomer conversions. Finally, a surprising increase in the concentration of the methyl branches was reported. Although a definitive explanation for this behavior is yet to be obtained, the involvement of transfer reactions of an intra- or intermolecular nature seems likely, and (in the latter case) these could lead to the presence of tertiary chlorine in these defects

Mobility, Balance and Falls in Persons with Multiple Sclerosis

BACKGROUND: There is a lack of information concerning the relation between objective measures of gait and balance and fall history in persons with MS (PwMS). This investigation assessed the relation between demographic, clinical, mobility and balance metrics and falls history in persons with multiple sclerosis (MS). METHODS: 52 ambulatory persons with MS (PwMS) participated in the investigation. All persons provided demographic information including fall history over the last 12 months. Disease status was assessed with Expanded Disability Status Scale (EDSS). Walking speed, coordination, endurance and postural control were quantified with a multidimensional mobility battery. RESULTS: Over 51% of the participants fell in the previous year with 79% of these people being suffering recurrent falls. Overall, fallers were older, had a greater prevalence of assistive devices use, worse disability, decreased walking endurance, and greater postural sway velocity with eyes closed compared to non-fallers. Additionally, fallers had greater impairment in cerebellar, sensory, pyramidal, and bladder/bowel subscales of the EDSS. CONCLUSIONS: The current observations suggest that PwMS who are older, more disabled, utilize an assistive device, have decreased walking coordination and endurance and have diminished balance have fallen in the previous year. This suggests that individuals who meet these criteria need to be carefully monitored for future falls. Future research is needed to determine a prospective model of falls specific to PwMS. Additionally, the utility of interventions aimed at reducing falls and fall risk in PwMS needs to be established

Diagnosis of childhood febrile illness using a multi-class blood RNA molecular signature

BACKGROUND: Appropriate treatment and management of children presenting with fever depend on accurate and timely diagnosis, but current diagnostic tests lack sensitivity and specificity and are frequently too slow to inform initial treatment. As an alternative to pathogen detection, host gene expression signatures in blood have shown promise in discriminating several infectious and inflammatory diseases in a dichotomous manner. However, differential diagnosis requires simultaneous consideration of multiple diseases. Here, we show that diverse infectious and inflammatory diseases can be discriminated by the expression levels of a single panel of genes in blood. METHODS: A multi-class supervised machine-learning approach, incorporating clinical consequence of misdiagnosis as a "cost" weighting, was applied to a whole-blood transcriptomic microarray dataset, incorporating 12 publicly available datasets, including 1,212 children with 18 infectious or inflammatory diseases. The transcriptional panel identified was further validated in a new RNA sequencing dataset comprising 411 febrile children. FINDINGS: We identified 161 transcripts that classified patients into 18 disease categories, reflecting individual causative pathogen and specific disease, as well as reliable prediction of broad classes comprising bacterial infection, viral infection, malaria, tuberculosis, or inflammatory disease. The transcriptional panel was validated in an independent cohort and benchmarked against existing dichotomous RNA signatures. CONCLUSIONS: Our data suggest that classification of febrile illness can be achieved with a single blood sample and opens the way for a new approach for clinical diagnosis. FUNDING: European Union's Seventh Framework no. 279185; Horizon2020 no. 668303 PERFORM; Wellcome Trust (206508/Z/17/Z); Medical Research Foundation (MRF-160-0008-ELP-KAFO-C0801); NIHR Imperial BRC

Assessment of errors in the determination of Mark-Houwink-Sakurada and Stockmayer-Fixman constants using size-exclusion chromatography with on-line viscometric detection: Analyses of poly(p-substituted styrenes) in tetrahydrofuran

In this work, we present values for the Mark-Houwink-Sakurada (MHS) and Stockmayer-Fixman (SF) constants for a series of homopolymers of para-substituted styrenes (4-X-styrene; X = OCH3, OCH2CH3, CH3, F, Cl, and Br) in THF at room temperature. The respective values of K (in 10(-5) dL/g) and alpha were: 0.685 and 13.2; 0.662 and 14.1; 0.740 and 8.41; 0.781 and 5.24; 0.726 and 8.95; 0.700 and 7.79. The respective values for K-theta (in 10(-4) dL/g) and K' (in 10(-7) dL/g) were: 6.01 and 16.1; 6.22 and 9.07; 7.64 and 17.4; 5.59 and 23.7; 6.29 and 17.3; 4.44 and 10.3. These constants were measured using size-exclusion chromatography with on-line viscometry. As part of this work, we investigate the applicability of common model fitting procedures to this method of measuring MHS/SF constants and the effect of uncertainties in their estimated values on the accuracy of molecular weight analysis. (C) 1999 John Wiley & Sons, Inc

Prediction and measurement of propagation rate coefficients in terpolymerization reactions. Part 1. Derivation of equations

In this paper we have derived a full penultimate model for describing terpolymerization propagation kinetics and composition. This model can be simplified into an implicit model by setting restrictions on the parameters. We discuss how these equations can be used to test the implicit penultimate unit model

Prediction and measurement of propagation rate coefficients in terpolymerization reactions. Part 2. Experimental study

The terpolymerization propagation kinetics of p-methoxystyrene, styrene and methyl methacrylate were investigated using pulsed-laser polymerization. In this work we used parameters obtained from the constituent copolymerization reactions to predict the propagation rate coefficients expected on the basis of an implicit penultimate unit model. In other words the model prediction was made with no adjustable parameters. We showed that this model could predict the experimental propagation rate coefficient values in this terpolymerization. This provides strong evidence for the validity of the implicit penultimate unit model

Propagation kinetics of para-substituted styrenes: A test of the applicability of the Hammett relationship to free-radical polymerization

In this work, pulsed laser polymerization measurements of the homopropagation rate coefficients (k(p)) for a series of para-substituted styrene monomers ( 4-X-styrene: X = OCH3, CH3, F, Cl, Br) at 20, 30, and 40 degrees C are reported. On the basis of nonlinear least-squares fits of the Arrhenius model to these data, the following point estimates for the activation energy (kJ mol(-1)) and frequency factor (x 10(7) L mol(-1) s(-1)) for each of the above five monomers were obtained: 34.9 and 6.35, 32.4 and 2.84, 32.0 and 3.50, 32.1 and 4.48, 33.9 and 9.57, respectively. The k(p) data were also used to test the applicability of the Hammett relationship. It was found that neither the Hammett relationship nor the extended Hammett relationship could quantitatively describe the substituent effects on the rate coefficients, though both could provide a reasonable qualitative description of the trends in the data