Copolymerization of ethylene and vinyl acetate at low pressure. Determination of the kinetics by sequential sampling

Monomer reactivity ratios in ethylene-vinyl acetate copolymn. at 62.deg. and 33.9 atm were detd. to be 0.746 +- 0.005 and 1.515 +- 0.007, resp., by sequential sampling of monomer feed, quant. gas chromatog., and computer calcn. based on nonlinear least-squares metho

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends. Correlation between Poisson ratio and adhesion

The deformation behavior of blends contg. polystyrene (I) [9003-53-6], low-d. polyethylene (II) [9002-88-4], and a hydrogenated butadiene-styrene diblock copolymer (III) was examd. by tensile testing with simultaneous vol. measurements. Assuming that shearing causes no vol. changes, crazing, after yielding, was the only deformation mechanism in blends with low I and III contents. Shearing became important in blends with high I concns. due to formation of a semicontinuous low modulus phase. The decrease in the Poisson ratio with increasing II content in I-II blends, as opposed to an increase in the presence of III, shows the Poisson ratio to be very sensitive to adhesion between the components. The toughness of I-II blends is discussed in terms of concns. of craze nuclei. Too few craze nuclei give rise to brittle failure because the resulting low no. of crazes cannot accommodate much deformation of the matrix whereas too many craze nuclei also cause brittle failure because of the high probability of combination of the crazes to form a crack. The concn. of craze nuclei depends on the no. of dispersed particles and their adhesion to the matrix. [on SciFinder (R)

Determination of the kinetics by sequential sampling

synopsis In behalf of a detailed study on the course of copolymerization reactions, this paper describes an improved and generally applicable experimental method and an efficient computational procedure to match. The experimental method is based on quantitative gas chromatography, and permits frequent measurement of the monomer feed composition throughout (co)polymerization processes a t pressures up to 40 kgf/cm2 ( = 38.7 atm). The given method is applied to the study of the radical copolymerization of ethylene with vinyl acetate in a series of kinetic experiments, a t 62OC and 35 kgf/cm2 (= 33.9 atm) in tert-butyl alcohol, in which 20-40q7, conversion is reached. Monomer feed composition and degree of conversion are entered into a computational procedure based on nonlinear least-sqnares methods applied to the integrated version of the copolymer equation. The experimental data, covering a region of ethylene molar feed frartions between 0.24 and 0.74 and copolymer concentrations up to 8 wt-%, are precisely consistent with the usual model. The respective reactivity ratios are Fe = 0.743 f 0.00<5 and P, = 1.515 f 0.007

Effect of the COVID-19 Pandemic on Surgical Breast Cancer Care in the Netherlands: A Multicenter Retrospective Cohort Study

BACKGROUND: Coronavirus disease 2019 (COVID-19) has put a strain on regular healthcare worldwide. In the Netherlands, the national screening programs, including for breast cancer, were halted temporarily. This posed a challenge to breast cancer care, because ∼40% of cases are detected through national screening. Therefore, the aim of the present study was to evaluate the effects of the COVID-19 pandemic on the surgical care of patients with breast cancer in the Netherlands. MATERIALS AND METHODS: The present multicenter retrospective cohort study investigated the effects of COVID-19 on patients with breast cancer who had undergone surgery from March 9 to May 17, 2020. The primary endpoints were the number of surgical procedures performed during the study period, tumor characteristics, surgery type, and route of referral. The secondary endpoint was the incidence of postoperative complications during the study period. RESULTS: A total of 217 consecutive patients with breast cancer requiring surgery were included. We found an overall decrease in the number of patients with breast cancer who were undergoing surgery. The most significant decline was seen in surgery for T1-T2 and N0 tumors. A decline in the number of referrals from both the national screening program and general practitioners was observed. The incidence of postoperative complications remained stable during the study period. CONCLUSIONS: The temporary halt of the national screening program for breast cancer resulted in fewer surgical procedures during the study period and a pronounced decrease in surgery of the lower tumor stages

Risk factors of postoperative intensive care unit admission during the COVID-19 pandemic: A multicentre retrospective cohort study

BACKGROUND: During the Coronavirus disease 2019 (COVID-19) pandemic, intensive care unit (ICU) capacity was scarce. Since surgical patients also require ICU admission, determining which factors lead to an increased risk of postoperative ICU admission is essential. This study aims to determine which factors led to an increased risk of unplanned postoperative ICU admission during the COVID-19 pandemic. METHODS: This multicentre retrospective cohort study investigated all patients who underwent surgery between 9 March 2020 and 30 June 2020. The primary endpoint was the number of surgical patients requiring postoperative ICU admission. The secondary endpoint was to determine factors leading to an increased risk of unplanned postoperative ICU admission, calculated by multivariate analysis with odds ratios (OR's) and 95% confidence (CI) intervals. RESULTS: One hundred eighty-five (4.6%) of the 4051 included patients required unplanned postoperative ICU admission. COVID-19 positive patients were at an increased risk of being admitted to the ICU compared to COVID-19 negative (OR 3.14; 95% CI 1.06-9.33; p = 0.040) and untested patients (OR 0.48; 95% CI 0.32-0.70; p = 0.001). Other predictors were male gender (OR 1.36; 95% CI 1.02-1.82; p = 0.046), body mass index (BMI) (OR 1.05; 95% CI 1.02-1.08; p = 0.001), surgical urgency and surgical discipline. CONCLUSION: A confirmed COVID-19 infection, male gender, elevated BMI, surgical urgency, and surgical discipline were independent factors for an increased risk of unplanned postoperative ICU admission. In the event of similar pandemics, postponing surgery in patients with an increased risk of postoperative ICU admission may be considered