The Action of Chain Extenders in Nylon-6, PET, and Model Compounds

The action of two complementary chain extenders is studied in model systems as well as in poly(ethylene terephthalate) (PET) and nylon–6. Chain extenders are low molecular weight compounds that can be used to increase the molecular weight of polymers in a short time. The reaction must preferably be fast enough to execute this step in an extruder. 1,3-Phenylene bis(2-oxazoline-2) (PBO) and isophthaloyl biscaprolactamate (IBC) are used in this study. Bisoxazolines react quickly with carboxylic acids. With model compounds it is shown that, under processing conditions, high conversions can be reached. However, the conversion is not complete. The high rate and the absence of volatile reactants are the most important characteristics of this reaction. Bislactamates are suitable coupling agents for hydroxy and amino functional polymers. The path of this coupling reaction depends on the type of nucleophile and on the reaction temperature. Under mild conditions the elimination of caprolactam is the main reaction. Under more severe conditions the ring opening mechanism may also be operative. The increase of the viscosity is studied with one as well as with a mixture of the two chain extenders. The effect is larger when both types of chain extenders are used simultaneously

The presence of cerebral white matter lesions and lower skin microvascular perfusion predicts lower cognitive performance in type 1 diabetes patients with retinopathy but not in healthy controls-A longitudinal study

OBJECTIVE: Cognitive impairments in type 1 diabetes may result from hyperglycemia-associated cerebral microangiopathy. We aimed to identify cerebral microangiopathy and skin microvascular dysfunction-as a surrogate marker for generalized microvascular function-as predictors of cognitive performance over time. METHODS: In this prospective cohort study, 25 type 1 diabetes patients with proliferative retinopathy and 25 matched healthy controls underwent neurocognitive testing at baseline and after follow-up (3.8 ± 0.8 years). At baseline, 1.5-T cerebral magnetic resonance imaging was used to detect WML and cerebral microbleeds. Skin capillary perfusion was assessed by means of capillary microscopy. RESULTS: In type 1 diabetes patients, but not in healthy controls, the presence of WML (ß = -0.419; P = 0.037) as well as lower skin capillary perfusion (baseline: ß = 0.753; P < 0.001; peak hyperemia: ß = 0.743; P = 0.001; venous occlusion: ß = 0.675; P = 0.003; capillary recruitment: ß = 0.549; P = 0.022) at baseline was associated with lower cognitive performance over time, independent of age, sex, HbA1c, and severe hypoglycemia. The relationship between WML and lower cognitive performance was significantly reduced after adjusting for capillary perfusion. CONCLUSIONS: These data fit the hypothesis that cerebral microangiopathy is a manifestation of generalized microvascular dysfunction, leading to lower cognitive performance

Resilience to cognitive impairment in the oldest-old: design of the EMIF-AD 90+ study

BACKGROUND: The oldest-old (subjects aged 90 years and older) population represents the fastest growing segment of society and shows a high dementia prevalence rate of up to 40%. Only a few studies have investigated protective factors for cognitive impairment in the oldest-old. The EMIF-AD 90+ Study aims to identify factors associated with resilience to cognitive impairment in the oldest-old. In this paper we reviewed previous studies on cognitive resilience in the oldest-old and described the design of the EMIF-AD 90+ Study. METHODS: The EMIF-AD 90+ Study aimed to enroll 80 cognitively normal subjects and 40 subjects with cognitive impairment aged 90 years or older. Cognitive impairment was operationalized as amnestic mild cognitive impairment (aMCI), or possible or probable Alzheimer's Disease (AD). The study was part of the European Medical Information Framework for AD (EMIF-AD) and was conducted at the Amsterdam University Medical Centers (UMC) and at the University of Manchester. We will test whether cognitive resilience is associated with cognitive reserve, vascular comorbidities, mood, sleep, sensory system capacity, physical performance and capacity, genetic risk factors, hallmarks of ageing, and markers of neurodegeneration. Markers of neurodegeneration included an amyloid positron emission tomography, amyloid β and tau in cerebrospinal fluid/blood and neurophysiological measures. DISCUSSION: The EMIF-AD 90+ Study will extend our knowledge on resilience to cognitive impairment in the oldest-old by extensive phenotyping of the subjects and the measurement of a wide range of potential protective factors, hallmarks of aging and markers of neurodegeneration. TRIAL REGISTRATION: Nederlands Trial Register NTR5867 . Registered 20 May 2016

Standing is not enough: A randomized crossover study on the acute cardiometabolic effects of variations in sitting in healthy young men

Objectives: Standing desks and stability balls are increasingly popular to increase muscle activity and thereby prevent potential adverse cardiometabolic effects of prolonged sitting. The present study examined the effects of (1) sitting on a stability ball (‘active sitting’) and (2) hourly 10-min standing interruptions during prolonged sitting on postprandial cardiometabolic biomarkers. Design: Experimental crossover study. Methods: Twenty healthy-weight males (19.2 ± 0.6 years) participated randomly in three 5-h conditions: (1) sitting on an office chair (SIT), (2) sitting on a stability ball (SIT-ACTIVE) and (3) sitting with hourly 10-min standing interruptions (SIT-STAND). In each condition, participants consumed a standardized mixed meal at baseline. Hourly blood samples and pre/post saliva samples were collected and analyzed for levels of insulin, glucose and cortisol. Pre/post hemodynamic monitoring (middle finger; Nexfin-monitoring) was conducted; heart rate was measured continuously (Polar) and muscle activity (leg and lower-back, Portilab) was measured during periods of sitting (on an office chair and on a stability ball) and standing. Results: Muscle activity and heart rate during standing periods were significantly higher than during sitting (both SIT and SIT-ACTIVE). Generalized estimating equations revealed no significant difference in any of the biomarkers between the three experimental conditions. Systolic blood pressure was lower during SIT-STAND, while stroke volume was lower during SIT-ACTIVE than during SIT. Although significant, these differences were small, approximating the day-to-day variability in blood pressure and stroke volume. Conclusions: We conclude that hourly standing interruptions during 5 h prolonged sitting or continuously sitting on a stability ball do not significantly affect postprandial cardiometabolic biomarkers in healthy young men. Trial registration: This trial is registered in the NTR trial register (NTRcode 5723)

Effects of Multiple Sedentary Days on Metabolic Risk Factors in Free-Living Conditions: Lessons Learned and Future Recommendations

BACKGROUNDRecent experimental studies in adults have demonstrated that interruptions to prolonged sitting have beneficial effects on metabolic risk factors in adults, compared to prolonged sitting. We explored the hypothesis that multiple consecutive days of predominantly prolonged sedentary time may have an unfavorable effect on the postprandial response of C-peptide, glucose and triglycerides in free-living healthy young men.METHODSIn this explorative pilot study, healthy young men (n=7; 18-23yrs) consumed standardized mixed meals at 1 and 5 hours during two experimental laboratory-sitting days, with six days of predominantly prolonged sedentary time in between. Serum and plasma samples were obtained hourly from 0 to 8 hours for measurement of glucose, C-peptide and triglycerides. Participant’s sedentary time was monitored using an accelerometer during the prolonged sedentary days as well as during six normal days prior to the first laboratory day. Differences in postprandial levels were assessed using generalized estimating equations analysis. Due to the explorative nature of this study and the small sample size, p-value was set at <0.10. RESULTSOverall, when expressed as % of wear time, sedentary time was 5% higher during the six prolonged sedentary days, which was not significantly different compared to the six normal days (n=4). Following six prolonged sedentary days, postprandial levels of C-peptide were significantly higher than at baseline (B=0.11; 90%CI=[0.002; 0.22]; n=7). Postprandial levels of glucose and triglycerides were not significantly different between the two laboratory days.CONCLUSIONSDue to the relatively high sedentary time at baseline, participants were unable to increase their sedentary time substantially. Nevertheless, postprandial C-peptide levels were slightly higher after six prolonged sedentary days than after six normal days

The Action of Chain Extenders in Nylon-6, PET, and Model Compounds

The action of two complementary chain extenders is studied in model systems as well as in poly(ethylene terephthalate) (PET) and nylon–6. Chain extenders are low molecular weight compounds that can be used to increase the molecular weight of polymers in a short time. The reaction must preferably be fast enough to execute this step in an extruder. 1,3-Phenylene bis(2-oxazoline-2) (PBO) and isophthaloyl biscaprolactamate (IBC) are used in this study. Bisoxazolines react quickly with carboxylic acids. With model compounds it is shown that, under processing conditions, high conversions can be reached. However, the conversion is not complete. The high rate and the absence of volatile reactants are the most important characteristics of this reaction. Bislactamates are suitable coupling agents for hydroxy and amino functional polymers. The path of this coupling reaction depends on the type of nucleophile and on the reaction temperature. Under mild conditions the elimination of caprolactam is the main reaction. Under more severe conditions the ring opening mechanism may also be operative. The increase of the viscosity is studied with one as well as with a mixture of the two chain extenders. The effect is larger when both types of chain extenders are used simultaneously.