Form II to form I transition in solution-crystallized isotactic polybutene-1.

Different polymer chains in a solution or melt have different conformations with corresponding entropy at each moment, which would be confined after crystallization. Equilibrium concept-based conformation or conformational entropy depends on chain dynamics, which is related to the effect of energy on conformational changes in polymer chains. Herein, an isotactic polybutene-1 (iPB-1) crystal was crystallized from solution by adding a precipitant at various temperatures. The solution-crystallized iPB-1 crystal was heated to 100 °C to obtain form II at different heat rates and the transition of form II was characterized. It was found that the form II to form I transition was not only related to the precipitation temperature but also to the heating rate of the solution-crystallized iPB-1. Thus, both precipitation temperature and heating rate determine the formation temperature of form II, i.e., form II that crystallized at lower temperature would transform faster. The results indicate that the conformation or conformational entropy of the amorphous region in iPB-1 is important to understand crystal transition.

Stereoselectivity Control Interplay in Racemic Lactide Polymerization by Achiral Al-Salen Complexes.

The origin of stereocontrol in ring opening polymerization (ROP) of racemic lactide (rac-LA) promoted by achiral aluminium-based catalysts has been explained through DFT calculations combined with a molecular descriptor (%VBur) and the activation strain model (ASM-NEDA) analysis. The proposed chain end control (CEC) model suggests that the ligand framework adopts a chiral configuration mimicking the enantiomorphic site control (ESC) while also incorporating control of the last inserted monomer unit. It is found that the ligand wrapping mode around the aluminium centre is dictated by the monomer configuration (R,R-LA and S,S-LA). A good correlation with experimental data is achieved only when accounting for the ligand dynamic features and its steric influences, as highlighted by %VBur steric maps and ASM-NEDA analysis. Understanding the ESC and CEC interplay is an important target for obtaining stereoselective ROP polymerization for the synthesis of biodegradable materials with tailored properties.

The Impact of Regiodefects on the Melt-Memory of Isotactic Polypropylene.

The memory of crystalline phase in the melt of isotactic polypropylene (iPP) in regiodefective samples of iPP characterized by different concentrations regiodefects, constituted by secondary 2,1 propene units, is studied. The self-nucleation (SN) experiments have demonstrated that the presence of 2,1 regiodefects produces a strong memory of the crystalline phase in the melt that persists up to temperatures much higher than the melting temperature. The extension of the heterogeneous melt (domain II) containing self-nuclei increases with increasing the concentration of regiodefects. The higher the concentration of regiodefects the higher the temperature at which the self-nuclei are dissolved and the homogeneous melt is achieved. This demonstrates that a strong memory of the crystalline phase of iPP in the melt exists not only in copolymers with noncrystallizable bulky comonomeric units rejected from the crystals but even when small defects are largely included in the crystals.

Ring Opening Polymerization of Six- and Eight-Membered Racemic Cyclic Esters for Biodegradable Materials.

The low percentage of recyclability of the polymeric materials obtained by olefin transition metal (TM) polymerization catalysis has increased the interest in their substitution with more eco-friendly materials with reliable physical and mechanical properties. Among the variety of known biodegradable polymers, linear aliphatic polyesters produced by ring-opening polymerization (ROP) of cyclic esters occupy a prominent position. The polymer properties are highly dependent on the macromolecule microstructure, and the control of stereoselectivity is necessary for providing materials with precise and finely tuned properties. In this review, we aim to outline the main synthetic routes, the physical properties and also the applications of three commercially available biodegradable materials: Polylactic acid (PLA), Poly(Lactic-co-Glycolic Acid) (PLGA), and Poly(3-hydroxybutyrate) (P3HB), all of three easily accessible via ROP. In this framework, understanding the origin of enantioselectivity and the factors that determine it is then crucial for the development of materials with suitable thermal and mechanical properties.

Ethylene-alt-α-Olefin Copolymers by Hydrogenation of Highly Stereoregular cis-1,4 Polydienes: Synthesis and Structural Characterization.

The homogeneous non-catalytic hydrogenation of several types of iso- and syndiotactic cis-1,4 poly(1,3-diene)s with diimide, formed by thermal decomposition of p-toluene-sulfonyl-hydrazide, was examined. Perfectly alternating ethylene/1-alkene copolymers having different tacticity (i.e., isotactic and syndiotactic), which in some cases are difficult to synthesize by simple stereospecific co-polymerization of the corresponding monomers, were obtained. All the copolymers synthesized were fully characterized from a structural, morphological, and rheological point of view through different analytical techniques (FT-IR, NMR, GPC, DSC, RX).

Synthesis, Morphology, and Crystallization Kinetics of Polyheptalactone (PHL).

Aliphatic polyesters are widely studied due to their excellent properties and low-cost production and also because, in many cases, they are biodegradable and/or recyclable. Therefore, expanding the range of available aliphatic polyesters is highly desirable. This paper reports the synthesis, morphology, and crystallization kinetics of a scarcely studied polyester, polyheptalactone (PHL). First, we synthesized the η-heptalactone monomer by the Baeyer-Villiger oxidation of cycloheptanone before several polyheptalactones of different molecular weights (in the range between 2 and 12 kDa), and low dispersities were prepared by ring-opening polymerization (ROP). The influence of molecular weight on primary nucleation rate, spherulitic growth rate, and overall crystallization rate was studied for the first time. All of these rates increased with PHL molecular weight, and they approached a plateau for the highest molecular weight samples employed here. Single crystals of PHLs were prepared for the first time, and hexagonal-shaped flat single crystals were obtained. The study of the crystallization and morphology of PHL revealed strong similarities with PCL, making PHLs very promising materials, considering their potential biodegradable character.

A Computational Evaluation of the Steric and Electronic Contributions in Stereoselective Olefin Polymerization with Pyridylamido-Type Catalysts.

A density functional theory (DFT) study combined with the steric maps of buried volume (%VBur) as molecular descriptors and an energy decomposition analysis through the ASM (activation strain model)-NEDA (natural energy decomposition analysis) approach were applied to investigate the origins of stereoselectivity for propene polymerization promoted by pyridylamido-type nonmetallocene systems. The relationships between the fine tuning of the ligand and the propene stereoregularity were rationalized (e.g., the metallacycle size, chemical nature of the bridge, and substituents at the ortho-position on the aniline moieties). The DFT calculations and %VBur steric maps reproduced the experimental trend: substituents on the bridge and on the ortho-positions of aniline fragments enhance the stereoselectivity. The ASM-NEDA analysis enabled the separation of the steric and electronic effects and revealed how subtle ligand modification may affect the stereoselectivity of the process.

Unconventional Stereoerror Formation Mechanisms in Nonmetallocene Propene Polymerization Systems Revealed by DFT Calculations.

An unconventional mechanism for the stereoerror formation in propene polymerization catalyzed by C1-symmetric salalen-M systems (M = Zr, Hf) is suggested by DFT calculations. While propagation happens with the ligand in its fac-mer conformation, a change of ligand wrapping mode from fac-mer to fac-fac is the main source of the lower stereoselectivities obtained with Zr and Hf. This is different for the Ti analogues, where the ligand fac-mer wrapping mode does not play a role. Activation strain analysis indicates that the preference for a chain stationary mechanism of the Zr/Hf species is due to the energy required to distort the reactants (ΔEStrain) rather than to their mutual interaction (ΔEInt).

Effect of Cold-Water Immersion on Elbow Flexors Muscle Thickness After Resistance Training.

Matos, F, Neves, EB, Rosa, C, Reis, VM, Saavedra, F, Silva, S, Tavares, F, and Vilaça-Alves, J. Effect of cold-water immersion on elbow flexors muscle thickness after resistance training. J Strength Cond Res 32(3): 756-763, 2018-Cold-water immersion (CWI) is commonly applied to speed up the recovery process after exercise. Muscle damage may induce a performance reduction and consequence of the intramuscular pressure induced by the muscular swelling. The aim of the study was to verify the CWI effects on muscle thickness (MT) behavior of the elbow flexors after a strength training (ST) protocol. Eleven men were submitted to an ST, performed in 2 different weeks. In one of the weeks, subjects experienced a passive recovery. In the other, subjects were submitted to a CWI (20 minutes at 5-10° C). Ultrasound (US) images were taken before, after, as well as 24, 48, and 72 hours after exercise, to evaluate the MT. Muscle thickness in both exercise arm (EA) and control arm (CA) was significantly higher 48 and 72 hours after exercise when subjects were submitted to a passive recovery compared with the CWI (p = 0.029, p = 0.028, p = 0.009, and p = 0.001, 48 hours, 72 hours, EA, and CA, respectively). When each arm was analyzed with or without using CWI individually, significantly higher MT was observed in the EA with CWI: before exercise in relation to 72 hours after exercise (p = 0.042) and after exercise in relation to the other measurements (p = 0.003, p = 0.003, p = 0.038, and p < 0.0001, before exercise and 24, 48, 72 hours after exercise, respectively). The evaluation of MT by US provides evidence that CWI after ST (and 24 hours after exercise) may reduce muscle swelling in the postexercise days when compared with a passive recovery. Seems to be a paradox between the uses of CWI for an acute reduction of muscle swelling.

Isotactic and Syndiotactic Alternating Ethylene/Propylene Copolymers Obtained Through Non-Catalytic Hydrogenation of Highly Stereoregular cis-1,4 Poly(1,3-diene)s.

The homogeneous non-catalytic hydrogenation of cis-1,4 poly(isoprene), isotactic cis-1,4 poly(1,3-pentadiene) and syndiotactic cis-1,4 poly(1,3-pentadiene) with diimide, formed by thermal decomposition of para-toluenesulfonylhydrazide, is examined. Perfectly alternating ethylene/propylene copolymers having different tacticity (i.e., isotactic and syndiotactic), which are difficult to synthesize by stereospecific copolymerization of the corresponding monomers, are obtained. Both isotactic and syndiotactic alternating ethylene/propylene copolymers are amorphous, with very low glass transition temperatures.

Order effects of combined strength and endurance training on testosterone, cortisol, growth hormone, and IGF-1 binding protein 3 in concurrently trained men.

Concurrent training (CT) has been widely used in fitness centers to simultaneously optimize cardiovascular and neuromuscular fitness, and induce a high-energy expenditure. Therefore, the aim of this study was to compare the acute effects of 2 different orders of CT on hormonal responses in concurrently trained men. Fourteen men (mean ± SD: 24.7 ± 5.1 years) were randomly divided into 2 groups: endurance training followed by strength (ES, n = 7) and strength training followed by endurance (SE, n = 7). Serum concentrations of testosterone, cortisol, growth hormone, and IGF-1 binding protein 3 (IGFBP-3) were measured before and after both training orders. A significant interaction between exercise order and time was only found in the IGFBP-3 levels (p = 0.022). The testosterone and IGFBP-3 concentrations significantly increased in the ES group after the exercise trainings (57.7 ± 35.1%, p = 0.013 and 17.0 ± 15.5%, p = 0.032, respectively) but did not change significantly in the SE group (15.5 ± 36.6%, p = 0.527 and -4.2 ± 13.9%, p = 0.421, respectively). Conversely, cortisol and growth hormone concentrations significantly increased in both ES (169.2 ± 191.0%, p = 0.021 and 13,296.8 ± 13,009.5%, p = 0.013, respectively) and SE (92.2 ± 81.5%, p = 0.017 and 12,346.2 ± 9714.1%, p = 0.001, respectively) groups compared with baseline values. No significant correlations were found between the changes in the hormonal concentrations. In conclusion, these results suggest that immediately postexercise testosterone and IGFPB-3 responses are significantly increased only after the ES order. Therefore, an ES training order should be prescribed if the main focus of the training intervention is to induce an acute postexercise anabolic environment.

Stereocomplexed poly(limonene carbonate): a unique example of the cocrystallization of amorphous enantiomeric polymers.

We report the cocrystallization of the regio- and stereoregular chiral copolymer poly(limonene carbonate). To the best of our knowledge, this marks the first example of an amorphous, enantiomerically pure polymer that becomes crystalline upon stereocomplexation with its complementary enantiomer. By analyzing X-ray powder diffraction data, we propose a packing model in which sheets of enantiopure chains interdigitate with layers of the opposite enantiomer, forming a "steric zipper".

Mechanistic insights on 1-butene polymerization catalyzed by homogeneous single-site catalysts: a DFT computational study.

Isotactic poly (1-butene) (iPB) is an interesting semi-crystalline thermoplastic material characterized by notable physical and mechanical attributes encompassing superior creep and stress resistance, elevated toughness, stiffness, and thermal endurance. These distinctive features position iPB as a viable candidate for specific applications; however, its widespread utilization is hindered by certain inherent limitations. Indeed, iPB manifests an intricate polymorphic behavior, and the gradual and spontaneous transition of the kinetically favored form II to the thermodynamically favored form I during aging introduces alterations to the material's properties. Despite its potential, the attainment of iPB with an exceedingly high molecular mass remains elusive, particularly when employing homogeneous catalysts renowned for their efficacy in propene polymerization. In this study we analyze the mechanistic aspects governing 1-butene polymerization by using DFT calculations modelling the regioselectivity of 1-butene insertions and the termination reactions occurring after primary (1,2) and secondary (2,1) insertions. Finally, the isomerization pathways leading to the formation of 4,1 units in iPB samples synthesized by homogenous catalysts is also discussed. All these aspects, furnish a mechanistic picture of the main drawbacks of an "old" but still interesting material.

Keto-Polyethylenes with Controlled Crystallinity and Materials Properties from Catalytic Ethylene-CO-Norbornene Terpolymerization.

Recent advances in Ni(II) catalyzed, nonalternating catalytic copolymerization of ethylene with carbon monoxide (CO) enable the synthesis of in-chain keto-functionalized polyethylenes (keto-PEs) with high-density polyethylene-like materials properties. Addition of norbornene as a bulky, noncrystallizable comonomer during catalytic polymerization allows tuning of the crystallinity in these keto-PE materials by randomly incorporated norbornene units in the polymer chain, while molecular weights are not adversely affected. Such crystallinity-reduced keto-PEs are characterized as softer materials with better ductility and may therefore be more suited for, e.g., potential film applications.

Revisiting Stereoselective Propene Polymerization Mechanisms: Insights through the Activation Strain Model.

The stereoelectronic factors responsible for stereoselectivity in propene polymerization with several metallocene and post-metallocene transition metal catalysts have been revisited using a combined approach of DFT calculations, the Activation Strain Model, Natural Energy Decomposition Analysis and a molecular descriptor (%VBur). There are in most cases two different paths leading to the formation of stereoerrors (SE), and the classical model does not suffice to fully understand stereoregulation. Improving stereoselectivity requires raising the energies of both SE insertion transition states. Our analyses show that the degrees of deformation of the active site (catalyst+chain) and the prochiral monomer differ for these two paths, and between different catalyst classes. Based on such analyses we discuss: a) the subtle differences in SE formation between stereoselective catalysts with different ligand frameworks; b) the reason for exceptional stereoselectivity reported for a special ansa-metallocene catalyst; c) the (double) stereocontrol origin for isoselective catalysts; d) the electronic contribution for isoselective catalysts generating SE by a modification of the ligand wrapping mode during the polymerization. Although this study will not immediately suggest new catalyst structures, we believe that understanding stereoregulation in great detail will increase our chances of success.

Combining Cyclic Units and Unsaturated Pendant Groups by Propene/1,5-Hexadiene Copolymerization Toward Functional Isotactic Polypropylene.

The precise use of a widely available and inexpensive metallocene catalyst enabled the synthesis of isotactic polypropylene copolymers characterized by the copresence of randomly distributed cyclic units in the backbone and unsaturated pendant units employing 1,5-hexadiene as comonomer. Optimization of the polymerization conditions avoided the cross-linking phenomena that negatively affects the material processing and final properties, resulting in good yields of samples featuring high molecular masses and a precisely controlled microstructure. Such polypropylene-based copolymers exhibit a broad spectrum of properties ranging from thermoplastic to surprising elastomeric behavior, with the additional value of being functionalizable by post-polymerization reactions.

Mechanism of Alternating Poly(lactic-co-glycolic acid) Formation by Polymerization of (S)- and (R)-3-Methyl Glycolide Using an Enantiopure Aluminum Complex.

The mechanism(s) of alternating PLGA synthesis by ring-opening polymerization of (S)- and (R)-3-methyl glycolide promoted by enantiopure aluminum complexes have been rationalized by density functional theory (DFT) calculations. The high regioselectivity of the (S)-MeG polymerization is obtained by repetitive ring opening at the glycolyl site by the (R)-catalyst whereas a lower regioselectivity is predicted by the ROP of (R)-MeG. The behavior of the two monomers is rationalized by unveiling the active site fluxionality of the enantiopure catalyst, identifying the rate-limiting steps that encode a preference at the glycolyl site versus the lactyl site, and revealing selection of the opposite monomer enantioface. The microstructure of the PLGA copolymers is predicted by considering the influence of the configuration of the last inserted unit. The identification of the preferred mechanistic paths may allow for a targeted catalyst design to enhance control of the polymer microstructures.

Nanocomposites from block copolymer lamellar nanostructures and selective gold deposition.

Innovative hybrid nanocomposites based on a nanostructured block copolymer (BCP) matrix whose lamellar nanodomains are selectively loaded with metal nanoparticles, have been prepared. A symmetric poly(styrene-b-methylmethacrylate) (PS-b-PMMA) amorphous BCP showing a lamellar morphology has been employed. Thin films of PS-b-PMMA were deposited by spin-coating or drop casting on indium thin oxide (ITO) substrate in order to achieve orientation of lamellae with the lamellar surface perpendicular to the substrate. The perpendicular orientation is related to the use of ITO substrate, which shows a neutral surface with non-preferential interactions with the PS and PMMA domains. Hybrid nanocomposites have been then prepared by selective incorporation of gold nanoparticles into the PS lamellar domain by using a simple method based on the selective deposition of thermally evaporated gold nanoparticles. This innovative approach can be very useful for the realization of nanocomposites that could be used as active layer in non-volatile OFET memory devices or very efficient organic solar cells, depending on the appropriate guest molecules.

The effects of nature-based interventions on individuals' environmental behaviors: protocol for a systematic review of controlled trials.

Background: The paper presents the rationale and methods of the planned systematic review to understand the effects of nature-based interventions on individuals' environmental behaviors. There is ample evidence that experiences in nature not only enhance human well-being but also help promote people's pro-environmentalism. Nevertheless, synthesized evidence regarding the effects of nature-based interventions on individuals' environmental behaviors is lacking. Methods: This protocol follows the Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) guidelines. The planned literature search will be conducted by using APA PsycInfo, APA PsyArticles, PubMed, ERIC, Education Source, GreenFILE, OpenDissertations, Scopus, and WEB of Science. In the protocol, we present search strategies for each specific database. Data items that we will seek to obtain from the selected publications are described in detail and cover general information about included studies, information about studies' methodology and participants, outcomes of the studies, and nature-based and comparative interventions. The outcomes will be behavioral, including aggregated and specific types of environmental behaviors, as well as reported and observed behaviors. Furthermore, the protocol provides a description of the prospective assessment of the risk of bias in both randomized and non-randomized studies. If studies appear sufficiently homogeneous, we will conduct a meta-analysis using the inverse-variance method. Details of the data synthesis are likewise provided in the paper. Results: Dissemination of the results of the planned review will be carried out via a peer-reviewed open-access journal publication. Implications: Given the great need to address current environmental issues, understanding what encourages people to act pro-environmentally is critical. It is expected that the findings of the planned review will provide valuable insights for researchers, educators, and policymakers who are involved in understanding and promoting human environmental behaviors.

Nationwide survey on the management of pediatric pharyngitis in Italian emergency units.

BACKGROUND: Acute pharyngitis is a frequent reason for primary care or emergency unit visits in children. Most available data on pharyngitis management come from primary care studies that demonstrate an underuse of microbiological tests, a tendency to over-prescribe antibiotics and a risk of antimicrobial resistance increase. However, a comprehensive understanding of acute pharyngitis management in emergency units is lacking. This study aimed to investigate the frequency of rapid antigen test use to diagnose acute pharyngitis, as well as other diagnostic approaches, the therapeutic attitude, and follow-up of children with this condition in the emergency units. METHODS: A multicentric national study was conducted in Italian emergency departments between April and June 2022. RESULTS: A total of 107 out of 131 invited units (response rate 82%), participated in the survey. The results showed that half of the units use a scoring system to diagnose pharyngitis, with the McIsaac score being the most commonly used. Most emergency units (56%) were not provided with a rapid antigen diagnostic test by their hospital, but the test was more frequently available in units visiting more than 10,000 children yearly (57% vs 33%, respectively, p = 0.02). Almost half (47%) of the units prescribe antibiotics in children with pharyngitis despite the lack of microbiologically confirmed cases of Group A ß-hemolytic streptococcus. Finally, about 25% of units prescribe amoxicillin-clavulanic acid to treat Group A ß-hemolytic streptococcus pharyngitis. CONCLUSIONS: The study sheds light on the approach to pharyngitis in emergency units, providing valuable information to improve the appropriate management of acute pharyngitis in this setting. The routinary provision of rapid antigen tests in the hospitals could enhance the diagnostic and therapeutic approach to pharyngitis.