Increased steady-state VO2 and larger O2 deficit with CO2 inhalation during exercise

Aim: To examine whether inhalation of CO₂‐enriched gas would increase steady‐state during exercise and enlarge O₂ deficit. Methods: Ten physically active men ( 53.7 ± 3.6 mL min^?1 kg^?1; ± SD) performed transitions from low‐load cycling (baseline; 40 W) to work rates representing light (≈ 45%; 122 ± 15 W) and heavy (≈ 80%; 253 ± 29 W) exercise while inhaling normal air (air) or a CO₂ mixture (4.2% CO₂, 21% O₂, balance N₂). Gas exchange was measured with Douglas bag technique at baseline and at min 0–2, 2–3 and 5–6. Results: Inhalation of CO₂‐enriched air consistently induced respiratory acidosis with increases in PCO₂ and decreases in capillary blood pH (P < 0.01). Hypercapnic steady‐state was on average about 6% greater (P < 0.01) than with air in both light and heavy exercise, presumably because of increased cost of breathing (ΔVE 40–50 L min^?1; P < 0.01), and a substrate shift towards increased lipid oxidation (decline in R 0.12; P < 0.01). during the first 2 min of exercise were not significantly different whereas the increase in from min 2–3 to min 5–6 in heavy exercise was larger with CO₂ than with air suggesting a greater slow component. As a result, O₂ deficit was greater with hypercapnia in heavy exercise (2.24 ± 0.51 L vs. 1.91 ± 0.45 L; P < 0.05) but not in light (0.64 ± 0.21 L vs. 0.54 ± 0.20 L; ns). Conclusion: Inhalation of CO₂‐enriched air and the ensuing respiratory acidosis increase steady‐state in both light and heavy exercise and enlarges O₂ deficit in heavy exercise.     

Lactate kinetics in human tissues at rest and during exercise

Aim: We sought to determine whether pulmonary diffusing capacity for nitric oxide (DLNO), carbon monoxide (DLCO) and pulmonary capillary blood volume (Vc) at rest predict peak aerobic capacity (O_2peak), and if so, to discern which measure predicts better. Methods: Thirty-five individuals with extreme obesity (body mass index or BMI = 50 ± 8 kg m⁻²) and 26 fit, non-obese subjects (BMI = 23 ± 2 kg m⁻²) participated. DLNO and DLCO at rest were first measured. Then, subjects performed a graded exercise test on a cycle ergometer to determine O_2peak. Multivariate regression was used to assess relations in the data. Results: Findings indicate that (i) pulmonary diffusion at rest predicts O_2peak in the fit and obese when measured with DLNO, but only in the fit when measured with DLCO; (ii) the observed relation between pulmonary diffusion at rest and O_2peak is different in the fit and obese; (iii) DLNO explains O_2peak better than DLCO or Vc. The findings imply the following reference equations for DLNO: O_2peak (mL kg⁻¹ min⁻¹) = 6.81 + 0.27 × DLNO for fit individuals; O_2peak (mL kg⁻¹ min⁻¹) = 6.81 + 0.06 × DLNO, for obese individuals (in both groups, adjusted R² = 0.92; RMSE = 5.58). Conclusion: Pulmonary diffusion at rest predicts O_2peak, although a relation exists for obese subjects only when DLNO is used, and the magnitude of the relation depends on gender when either DLCO or Vc is used. We recommend DLNO as a measure of pulmonary diffusion, both for its ease of collection as well as its tighter relation with O_2peak.     

Kinetic model of osmosis through semipermeable and solute‐permeable membranes

The gas analogy of the van't Hoff equation for osmotic pressure Δπ = RT/, where R is gas constant, T absolute temperature and mole volume of water, remained unexplained for a century because of a few misconceptions: (1) Use of supported membranes prevented the recognition that osmotic forces exert no effect on the solid membrane. During osmotic flow frictional force of solvent within membrane channels equals osmotic kinetic force π at the interface against the solution containing impermeant solute. (2) Retrograde diffusion of water is much less than osmotic flow even when dx in the gradient dc/dx approaches zero. (3) The gas analogy was thought to be accidental. Actually, the internal kinetic pressure is P = RT/, because intermolecular forces cancel out at the liquid interface, just as within a gas. The kinetic osmotic pressure is the difference in solvent pressure across the interface: π = RT/–(RT/)X₁ = (RT/)X₂, where X₁ and X₂ are the mole fractions of water and impermeant solute, respectively. Integration gives π = –(RT/)lnX₁, identical to the thermodynamic equation. This equation is correct up to 25 atmospheres, and up to 180 atmospheres by assuming that a sucrose molecule binds 4 and a glycerol molecule 2.5 water molecules. For solute‐permeable membranes, the reflection coefficient σ can be calculated by formulas proposed for ultrafiltration. Because the fraction (1–σ) of solute concentration behaves as solvent, osmosis may well proceed against the chemical potential gradient for water. The analogy to an ideal gas applies because π = –(RT/)lnX₁ is the small difference between enormous internal solvent pressures.     

Contribution of systemic arterial compliance and systemic vascular resistance to effective arterial elastance changes during exercise in humans

Background: Effective arterial elastance (Ea), an index of arterial load, increases with elevations in left ventricular elastance to maximize the efficiency of left ventricular stroke work during exercise. Systemic arterial compliance (C) and vascular resistance (R) are the primary components contributing to Ea, and R plays a greater role in determining Ea at rest. We hypothesized that the contribution of C to Ea increases during exercise to maintain an optimal balance between arterial load and ventricular elastance, and that the increase in Ea is due primarily to a reduction in C. Aim: The aim of this study was to investigate the contributions of C and R to Ea during exercise. Methods: Ea (0.9 × systolic blood pressure/stroke volume), C (stroke volume/pulse pressure), R (mean blood pressure/cardiac output), and cardiac cycle length (T) were measured at rest and during exercise of 40%, 60% and 80% maximal oxygen uptake (O_2max) using Doppler echocardiography in 45 healthy men. Results: Ea did not differ between rest and 40%O_2max, but it was greater at 60% and 80%O_2max. C markedly decreased during exercise in an exercise intensity‐dependent manner. The changes in R/T during exercise were small, whereas it decreased at 40%O_2max and gradually increased at 60% and 80%O_2max. Conclusions: The present results suggest that the contribution of systemic arterial compliance to effective arterial elastance increases during exercise. Therefore, we propose that the increase in arterial load during exercise is mainly driven by a reduction in systemic arterial compliance.     

Non‐linear dependence of interstitial fluid pressure on joint cavity pressure and implications for interstitial resistance in rabbit knee

Aims: Synovium retains lubricating fluid in the joint cavity. Synovial outflow resistance estimated as dP_j/d (P_j, joint fluid pressure and trans‐synovial flow) is greater, however, than expected from interstitial glycosaminoglycan concentration. This study investigates whether subsynovial fluid pressure increases with intra‐articular pressure, as this would reduce the estimated resistance estimate. Methods: Interstitial fluid pressure (P_if) was measured as a function of distance from the joint cavity in knees of anaesthetized rabbits, using servo‐null pressure‐measuring micropipettes and using an external ‘window’. Joint fluid pressure P_j was either endogenous (?2.4 ± 0.4 cmH₂O, mean ± SEM) or held at ～4, 8 or 15.0 cmH₂O by a continuous intra‐articular saline infusion that matched the trans‐synovial interstitial drainage rate. Results: At endogenous P_j the peri‐articular P_if was subatmospheric (?1.9 ± 0.3 cmH₂O, n = 19). At raised P_j the P_if values became positive. Gradient dP_if /dx was ～20 times steeper across synovium than subsynovium. P_if close to the synovium–subsynovium border () increased as a non‐linear function of P_j to 1.4 ± 0.2 cmH₂O (n = 23) at P_j = 4.3 ± 0.1 cmH₂O : 2.3 ± 0.2 cmH₂O (n = 17) at P_j = 7.6 ± 0.2 cmH₂O: and 3.0 ± 0.4 cmH₂O (n = 26) at P_j = 15 ± 0.2 cmH₂O (P = 0.03, anova ). Conclusions: Synovial resistivity is ～20× subsynovial resistivity. The increase in with P_j means that true synovial resistance d()/d is overestimated 1.5× by dP_j/d. This narrows but does not eliminate the gap between analysed glycosaminoglycan concentration, 4 mg ml^?1, and the net interstitial biopolymer concentration of 11.5 mg ml^?1 needed to generate the resistance.     

Distinct Pattern of Immunophenotypic Features of Innate and Adaptive Immunity as a Putative Signature of Clinical and Laboratorial Status of Patients with Localized Cutaneous Leishmaniasis

In this study, we have analysed the phenotypic features of innate/adaptive immunity of patients with localized cutaneous leishmaniasis (LCL), categorized according to their clinical/laboratorial status, including number of lesion (L1; L2–4), days of illness duration (≤60;>60) and positivity in the Montenegro skin test (MT^?;MT⁺). Our findings highlighted a range of phenotypic features observed in patients with LCL (↑%HLA‐DR⁺ neutrophils; ↑CD8⁺ HLA‐DR⁺/CD4⁺ HLA‐DR⁺ T cell ratio; ↑HLA‐DR in B lymphocytes, ↑%CD23⁺ neutrophils, monocytes and B cells; ↑α‐Leishmania IgG and ↑serum + ). Selective changes were observed in L1 (↑%HLA‐DR⁺ neutrophils, ↑CD8⁺ HLA‐DR⁺/CD4⁺ HLA‐DR⁺ T cell ratio and ↑serum + ) as compared to L2–4 (↑%CD5^? B cells; ↑CD23⁺ B cells and ↑α‐Leishmania IgG). Whilst ≤60 presented a mixed profile of innate/adaptive immunity (↓%CD28⁺ neutrophils and ↑%CD4⁺ T cells), >60 showed a well‐known leishmanicidal events (↑CD8⁺ T cells; ↑serum + and ↑α‐Leishmania IgG). MT⁺ patients showed increased putative leishmanicidal capacity (↑%HLA‐DR⁺ neutrophils; ↑%CD23⁺ monocytes; ↑CD8⁺ HLA‐DR⁺/CD4⁺ HLA‐DR⁺ T cell ratio and ↑ serum + ). Overall, a range of immunological biomarkers illustrates the complex immunological network associated with distinct clinical/laboratorial features of LCL with applicability in clinical studies.     

Relationship between reduced lower abdominal blood flows and heart rate in recovery following cycling exercise

Aim: To examine the blood flow (BF) response in the lower abdomen (LAB) in recovery following upright cycling exercise at three levels of relative maximum pulmonary oxygen consumption () and the relationship of BF_LAB to heart rate (HR) and target intensity. Methods: For 11 healthy subjects, BF (Doppler ultrasound) in the upper abdominal aorta (Ao) above the coeliac trunk and in the right femoral artery (RFA) was measured repeatedly for 720 s after the end of cycling exercises at target intensities of 30%, 50% and 85%, respectively. Blood flow in the lower abdomen (BF_LAB) can be measured by subtracting bilateral BF_FAs (≈twofolds of BF_RFA) from BF_Ao. Change in BF_LAB (or BF_LAB volume) at any point was evaluated by difference between change in BF_Ao and in BF_FAs. Heart rate and blood pressure were also measured. Results: At 85%, significant reduction in BF_LAB by approx. 89% was shown at 90 s and remained until 360 s. At 50%, reduction in BF_LAB by approx. 33% was found at 90 s although it returned to pre‐exercise value at 120 s. On the contrary at 30%, BF_LAB showed a light increase (<20%) below 70 bpm of HR. There was a close negative relationship (P < 0.05) between change in BF_LAB and recovery HR, as well as between change in BF_LAB volume and both recovery HR and %. Conclusion: This study suggests that the lower abdominal BF in recovery may be influenced by sympathetic‐vagus control, and dynamics of BF_LAB may be closely related to the level of relative exercise intensities.     

The acute effects of insulin on the cardiorespiratory responses to hypoxia in streptozotocin‐induced diabetic rats

Aims: We examined whether or not streptozotocin (STZ)‐induced diabetic rats, which have a lower heart rate (HR, beats min^?1) than control rats, could maintain hypoxic ventilatory response. Methods: Twenty‐six Wistar rats, which had been injected with STZ (60 mg kg^?1, EXP) or vehicle (0.1 m citrate buffer, CONT) intraperitoneally at 9 weeks of age, had their cardiorespiratory responses to normoxia and 12%O₂ examined after 5 weeks. Results: Compared with CONT rats, EXP rats had a higher blood glucose [24 ± 3 vs. 5 ± 1 (mean ± SD) mmol L^?1], a lower body weight (320 ± 23 vs. 432 ± 24 g), lower HR (303 ± 49 vs. 380 ± 44 in normoxia, and 343 ± 56 vs. 443 ± 60 in hypoxia) and a lower mean arterial blood pressure (MAP) (89 ± 6 vs. 102 ± 10 mmHg in hypoxia). In contrast, both groups had similar values in ventilation (), –metabolic rate (MR) ratio and arterial blood gases (ABGs). In EXP rats, with an acute insulin supplement (i.v., 0.75 U h^?1 for 1.5–2 h), not only blood glucose, but also HR, and MAP were normalized as those obtained in CONT rats, and in hypoxia further increased without affecting –MR ratio and ABGs. Such acute cardiorespiratory stimulating effects of insulin could not be obtained in non‐diabetic rats (n = 7, 355 ± 24 g), in which euglycaemia (mean 6.4 mmol L^?1) was maintained during the measurements. Conclusions: Our results suggest that, in STZ‐induced diabetic rats: (1) ventilation is hardly suppressed by hyperglycaemia, (2) cardiorespiratory responses can be acutely stimulated by short insulin injection, and (3) the effects, including those through acute blood glucose normalization, are possibly specific for the diabetic impairments.     

Vacuolar H+-ATPase expression is increased in acid-secreting intercalated cells in kidneys of rats with hypercalcaemia-induced alkalosis

Aims: Hypercalcaemia is known to be associated with systemic metabolic alkalosis, although the underlying mechanism is uncertain. Therefore, we aimed to examine whether hypercalcaemia was associated with changes in the expression of acid–base transporters in the kidney. Methods: Rats were infused with human parathyroid hormone (PTH, 15 μg kg^?1 day^?1), or vehicle for 48 h using osmotic minipumps. Results: The rats treated with PTH developed hypercalcaemia and exhibited metabolic alkalosis (arterial HCO: 31.1 ± 0.8 vs. 28.1 ± 0.8 mmol L^?1 in controls, P < 0.05, n = 6), whereas the urine pH of 6.85 ± 0.1 was significantly decreased compared with the pH of 7.38 ± 0.1 in controls (P < 0.05, n = 12). The observed alkalosis was associated with a significantly increased expression of the B1‐subunit of the H⁺‐ATPase in kidney inner medulla (IM, 233 ± 45% of the control level). In contrast, electroneutral Na⁺‐HCO cotransporter NBCn1 and Cl^?/HCO anion exchanger AE2 expression was markedly reduced in the inner stripe of the outer medulla (to 26 ± 9% and 65 ± 6%, respectively). These findings were verified by immunohistochemistry. Conclusions: (1) hypercalcaemia‐induced metabolic alkalosis was associated with increased urinary excretion of H⁺; (2) the increased H⁺‐ATPase expression in IM may partly explain the enhanced urinary acidification, which is speculated to prevent stone formation because of hypercalciuria and (3) the decreased expression of outer medullary AE2 suggests a compensatory reduction of the transepithelial bicarbonate transport.     

Acute hyperoxaemia‐induced effects on regional blood flow,oxygen consumption and central circulation in man

Aim: Despite numerous in vitro and animal studies, circulatory effects and mechanisms responsible for the vasoconstriction seen during hyperoxaemia are yet to be ascertained. The present study set out to: (i) set up a non‐invasive human model for the study of hyperoxia‐induced cardiovascular effects, (ii) describe the dynamics of this effect and (iii) determine whether hyperoxaemia also, by vasoconstriction alters oxygen consumption (O₂). Methods: The study comprised four experiments (A, B, C and D) on healthy volunteers examined before, during and after 100% oxygen breathing. A: Blood flow (mL min^?1·100 mL^?1 tissue), venous occlusion plethysmography was assessed (n = 12). B: Blood flow was recorded with increasing transcutaneous oxygen tension (P_tcO₂) levels (dose–response) (n = 8). C: Heart rate (HR), stroke volume, cardiac output (CO) and systemic vascular resistance (SVR) was assessed using echocardiography (n = 8). D: O₂ was measured using an open circuit technique when breathing an air‐O₂ mix (fraction of inhaled oxygen: F_iO₂ = 0.58) (n = 8). Results: Calf blood flow decreased 30% during O₂ breathing. The decrease in calf blood flow was found to be oxygen dose dependent. A similar magnitude, as for the peripheral circulation, of the effect on central parameters (HR/CO and SVR) and in the time relationship was noted. Hyperoxia did not change O₂. An average of 207 (93) mL O₂ per subject was washed in during the experiments. Conclusion: This model appears suitable for the investigation of O₂‐related effects on the central and peripheral circulation in man. Our findings, based on a more comprehensive (central/peripheral circulation examination) evaluation than earlier made, suggest significant circulatory effects of hyperoxia. Further studies are warranted to elucidate the underlying mechanisms.     

Maximum oxygen consumption in marginally malnourished Colombian boys and girls 6–16 years of age

Treadmill measurements of maximum oxygen intake were made in 218 boys and 136 girls 6–16 years of age who were classified as nutritionally normal or marginally malnourished. max (1· min^?1)increased with age, was lower in the undernourished than in the normal, and was significantly lower in girls than in boys. The sex differences persisted when max was expressed in terms of body weight and lean body mass, indicating that differences in physical activity between sexes may be the cause. The lower values of absolute max have implications for the productive ability of these children in heavy physical work when they are adults. When expressed in terms of body weight there are no major differences between Colombian and European children in the magnitude of their max values.     

Evoked Potential and Behavioral Signs of Attentive Dysfunctions in Hyperactive Boys

Subjects were 12 boys (12–14 yrs old) who had previously been diagnosed for hyperactivity (clinical group) and 15 age-matched normal controls. For the selective attention (SA) task vertex ERPs were recorded to dichotically presented tone pips, with differing frequencies to each ear. Each series contained randomly interspersed signals and subjects were instructed to count the signals to one ear (targets). Behavioral tasks consisted of responses to SA targets, a 10-min vigilance series, and dichotic listening. No significant group differences were found to non-attended channels for N and P amplitudes and latencies. N amplitude enhancements to the attended channels were significant for the controls (44%), but not for the clinical boys (14%). Also, P latencies and amplitudes to the target pips were significantly greater for the control than the clinical group. Behavioral responses showed significant deficits by the clinical boys for SA and vigilance, but not for dichotic listening. Correct behavioral SA responses correlated significantly with P target amplitudes, but not with N amplitude enhancements. These findings indicate severe dysfunctions by the clinical boys for selective attention, involving both stimulus and response sets.     

Stereokontrolle. IV. Konstitutionseinflüsse bei radikalischen Polymerisationen

A compensation effect exists between the quantities (ΔH ? ΔH) and (ΔS ? ΔS) in the free radical polymerization of a monomer in different solvents ΔH, ΔH, ΔS, and ΔS are the activation enthalpies and entropies, resp. for the formation of isotactic and syndiotactic dyads. The quantities ΔΔH and T₀ are by definition independent of the temperature of polymerization and other polymerization conditions and thus a pair of constants characteristic for each monomer. A linear relationship between ΔΔH and T₀ has been found for acrylic and vinyl monomers each. Both true activation and conformational effects seem to be responsible for the stereocontrol in free radical polymerizations.     

The thermodynamics of polymerisation of aldehydes and cyclic ethers, 4.1,3-dioxocane and 1,3,6-trioxocane

The equilibrium between gaseous monomer (g) and amorphous polymer (c) has been studied for 1,3-dioxocane and 1,3,6-trioxocane between 100 and 137°C. From the equilibrium pressures of monomer, the ΔH and ΔS values have been calculated. Thermodynamic data for the vaporisation of each monomer have also been measured so that values of ΔH and ΔS for the polymerisations could be calculated (l: liquid phase). For 1,3-dioxocane: For 1,3,6-trioxocane:      

Regulation of glutamate metabolism in the cyanobiont Nostoc ANTH by nitrogen sources

Growth, heterocyst differentiation, nitrogenase activity and glutamate uptake were studied in the cyanobiont Nostoc ANTH , a free-living isolate of the liverwort Anthoceros punctatus. Nostoc ANTH grew well in N₂-medium and produced heterocyst and nitrogenase activity whereas NO- and NH-grown cultures did not show heterocyst differentiation and nitrogenase activity. Also, glutamate inhibited the diazotrophic growth, heterocyst differentiation and nitrogenase activity. However, the availability of NO and NH to the glutamate-medium resulted in the recovery of growth. NO- and NH-grown cells showed reduced levels of glutamate uptake which further reduced by the supplementation of NO- and NH in the reaction mixture during experimentation. These results suggest that in Nostoc ANTH glutamate acts as an inhibitor of heterocyst differentiation and nitrogenase activity rather than as a nitrogen source and that availability of NO- and NH alleviates the glutamate toxicity by inhibiting its uptake. This glutamate toxicity may be the reason for the localization of glutamate forming enzyme, glutamate synthase (GOGAT) within vegetative cells and not within heterocysts.     

Effects of aerobic fitness on hypohydration-induced physiological strain and exercise impairment

Aim: Hypohydration exacerbates cardiovascular and thermal strain and can impair exercise capacity in temperate and warm conditions. Yet, athletes often dehydrate in exercise, are hypervolaemic and have less cardiovascular sensitivity to acute hypervolaemia. We tested the hypothesis that trained individuals have less cardiovascular, thermoregulatory and performance affect of hypohydration during exercise. Methods: After familiarization, six trained [O_{2 peak} = 64 (SD 8) mL kg⁻¹ min⁻¹] and six untrained [O_{2 peak} = 45 (4) mL kg⁻¹ min⁻¹] males cycled 40 min at 70%O_{2 peak} while euhydrated or hypohydrated by 1.5–2.0% body mass (crossover design), before a 40-min work trial with euhydration or ad libitum drinking (in Hypohydration trial), in temperate conditions (24.3 °C, RH 50%, v_a = 4.5 m s⁻¹). Baseline hydration was by complete or partial rehydration from exercise+heat stress the previous evening. Results: During constant workload, heart rate and its drift were increased in Hypohydration compared with Euhydration for Untrained [drift: 33 (11) vs. 24 beats min⁻¹ h⁻¹ (10), 95% CI 5–11] but not Trained [14 (3) vs. 13 beats min⁻¹ h⁻¹ (3), CI −2 to 3; P = 0.01 vs. Untrained]. Similarly, rectal temperature drift was faster in Hypohydration for Untrained only [by 0.57 °C h⁻¹ (0.25); P = 0.03 vs. Trained], concomitant with their reduced sweat rate (P = 0.05) and its relation to plasma osmolality (P = 0.03). Performance power tended to be reduced for Untrained (−13%, CI −35 to 2) and Trained (−7%, CI: −16 to 1), without an effect of fitness (P = 0.38). Conclusion: Mild hypohydration exacerbated cardiovascular and thermoregulatory strain and tended to impair endurance performance, but aerobic fitness attenuated the physiological effects.     

Synthesis and Surface Attachment of ABC Triblock Copolymers Containing Glassy and Rubbery Segments

Summary: The synthesis of an ABC triblock copolymer containing glassy and rubbery segments was conducted using a combination of living anionic and atom transfer radical polymerizations (ATRP). A poly(dimethylsiloxane) (pDMS) macroinitiator ( = 6 200; = 1.19) was prepared by living anionic ring‐opening polymerization, followed by hydrosilation reactions to incorporate 2‐bromoisobutyrate end groups for initiation of ATRP. The ATRP of styrene (S) using the pDMS macroinitiator yielded a diblock copolymer ( = 66 730; = 1.38). Chain extension of the pDMS‐b‐pS macroinitiator with 3‐(dimethoxymethylsilyl)propyl acrylate (DMSA) by ATRP yielded an ABC triblock copolymer. The latter reactive segment was covalently attached to silanol groups on a silicon wafer. The presentation of either glassy pS or flexible pDMS segments of the brushes attached to the surface was reversibly controlled by treatment with selective solvents for each segment.

Surface immobilization of pDMS‐b‐pS‐b‐pDMSA triblock copolymer to Si wafer. Treatment of brush with toluene, methanol, or annealing yields brush with hard pS surface. Treatment with hexane selectively solvates pDMS, and the soft layer is presented to the brush surface.     

Comparative reactivities of electrogenerated radical cations in cationic polymerization

Persistent radical cations were produced electrochemically from the parent hydrocarbons 9,10-diphenylanthracene (DPA), 9-phenylanthracene (9-PA), 9,10-dimethylanthracene (DMA), rubrene (Ru), triphenylene (TP), 1,3,6,8-tetraphenylpyrene (TPP), and perylene (P). The stabilities of these cations in the absence of monomer were The rates of decay of increased with the dielectric constant of the solvent and were 4 to 5 times greater in CH₃CN than in CH₂Cl₂ or C₆H₅NO₂. The kinetics of the reaction of the radical cation with monomer were investigated for styrene and isobutyl vinyl ether. For styrene and or a first order dependence on the radical cation concentration was found. However, decay was unaffected by the addition of styrene and polymerization was not initiated. With and isobutyl vinyl ether a first order dependence on cation was observed and polymers were obtained. Electropolymerizations were also conducted with the generation of radical cations in situ and the rates of monomer consumption and polymer production were measured. The passage of the same electric charge in Faradays (1 Faraday=96496 coulomb) resulted in the polymerization of different amounts of the monomer and generally paralleled the reactivities found for the various radical cations.     

Crystallization of Poly(ethylene terephthalate) in Poly(ethylene terephthalate)/Bisphenol A Polycarbonate Block Copolymers: Influence of Block Length and Role of the Rubbery Amorphous Component

Summary: Analysis was made of the crystallization of the PET blocks in PET/PC copolymers as a function of the block length, varying from = 5300 to 17100 g · mol^?1 (X_{n PET} = 28–89, PET monomeric sequences). Analysis was also made of a series of PET homopolymers with the same values. The copolymers were found to crystallize at a slower rate, with lower crystallinity and lower crystal perfection, than the homopolymers and secondary crystallization does not take place, unlike with PET homopolymers. However the crystallization mechanism is the same. The plot of the crystallization rate versus X_{n PET} shows that the homopolymers have a maximum crystallization rate at X_{n PET} ? 50 ( ? 10000 g · mol^?1), whereas the crystallization rate for copolymers continuously increases with the increment of X_{n PET} (see Figure). The decrement of the crystallization rate for homopolymers with higher than 10000 g · mol^?1 has been interpreted as due to the effect of the high melt viscosity. For copolymers with long PET blocks, instead, a phase separation is likely and improves the PET reptation and fold, causing an increment in crystallization rate. Block size and miscibility between the components are therefore the key parameters in understanding the crystallization process in PET/PC block copolymers.