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In this longitudinal study, we investigate how demographic, cognitive and meta-cognitive variables affect students’ success in chemistry and physics exams in two Science-Technology-Engineering-Mathematics undergraduate courses, biology and engineering. Independent variables include high school final examination performance, chemistry and physics marks, self-efficacy and accuracy of self-evaluation, namely the difference between the estimation of one’s own performance in a specific task measured with a confidence rating scale and the actual performance score. We involved 81 biology and 125 engineering freshmen students in the study. Biology students were attending a General Chemistry course, while Engineering students were attending a General Physics course. Accuracy of self-evaluation scores were calculated through Rasch analysis of responses to an instrument that included chemistry and physics items, and a confidence tier. We found that for both courses, the likelihood of passing the exams of chemistry and physics was significantly predicted solely by their accuracy of self-evaluation accuracy score. We found the overconfident students had lower likelihood of passing the exam. Our results suggest that the perception of one’s own ability is a relevant factor for predicting students’ success at undergraduate level and can be a better predictor of academic success than high school performance and self-efficacy.

In this study, we present a new instrument, the Participation and Engagement Scale (PES), for the evaluation of the students��� involvement in STEM-oriented activities. The instrument was administered to about 1000 secondary school students who participated in the activities of the Italian Piano Nazionale Lauree Scientifiche in Biology, Chemistry and Physics. The activities were carried out in a remote modality due to the COVID-19 restrictions. Through an exploratory and confirmatory factor analysis, it was possible to validate a two-factor structure of the instrument: satisfaction towards the activities and value of the activities. The proposed factor structure shows a good model fit, with each of the obtained scales displaying excellent reliability. Construct-related validation evidence was obtained through the Rasch analysis, which allowed further psychometric improvement of the instrument. Convergent validation evidence was established through a correlation with the academic motivation and perceived difficulties scales. Using the proposed instrument, we found no statistically significant relationships between engagement, the different types of science activities attended, and the intention to enrol in a STEM course. Implications of the study for the evaluation of public understanding of science activities in both remote and in-presence modalities are also discussed.

This work describes the use of simple zinc(II) salts (ZnCl2, ZnCO3, Zn(OAc)2, ZnO, Zn(ClO4)2, Zn(TfO)2, and Zn(BF4)2) as effective catalysts for the esterification of fatty acids with long-chain alcohols and simple polyols through a homogeneous system that allows the gradual and selective removal of water. The results show that the catalytic activity depends on the nature of the counterion: the most effective are the salts with poorly coordinating anions (perchlorate and triflate) or containing basic Brønsted anions (oxide, acetate, and carbonate). However, only with the latter is it possible to fully recover the catalyst at the end of each run, which is easily filtered in the form of zinc carboxylate, given its insolubility in the ester produced. In this way, it is possible to recycle the catalyst numerous times, without any loss of activity. This beneficial prerogative couples the efficiency of the homogeneous catalysis with the advantage of the heterogeneous catalysis. The process is, therefore, truly sustainable, given its high efficiency, low energy consumption, ease of purification, and the absence of auxiliary substances and byproducts., Simple zinc(II) salts are effective and recyclable catalysts for the solvent-free esterification of fatty acids with medium−long-chain alcohols.

A linear dichroism study of vibrational peaks of amorphous and semi-crystalline axially stretched poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films shows an unusual behaviour of co-crystalline and nanoporous-crystalline (α and β form) phases. In fact, signs of dichroism for all vibrational peaks of α and β phases are opposite with respect to those observed for amorphous phases. This behaviour indicates the occurrence in PPO α and β forms of large polymer helices, whose thermodynamic stability can be rationalized by placement of guest molecules in intrahelical channels. A large diameter helix, with chain periodicity of 1.06 nm, is compatible with layer-line position in WAXD patterns of axially stretched α form films. The occurrence for both α and β NC forms of PPO of intrahelical empty channels, can rationalize the very high guest diffusivity of semi-crystalline PPO films, which becomes particularly high when crystalline helical axes are preferentially perpendicular to the film plane.

Extensive characterizations, mainly by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) techniques, are reported for co-crystalline (CC) poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films with many different low-molecular-mass guest molecules. These characterizations are also reported for the corresponding nanoporous crystalline (NC) phases, as obtained by suitable guest-removal procedures. Two well-separated NC forms, hereafter named α and β, are obtained by guest removal from two well-separated groups of CC forms. α and β NC forms can be easily recognized by reflections in WAXD patterns as well as by suitable FTIR crystalline peaks. Density and degree of crystallinity measurements confirm that both NC phases exhibit a density definitely smaller than for the amorphous phase (ρam = 1.04 g/cm3 > ρβ = 0.95 g/cm3 > ρα = 0.93 g/cm3). Density functional theory calculations combined with geometrical analysis on PPO model systems indicate conformations suitable to fit the observed chain periodicities of the two crystalline forms (c = 5.28 and 5.47 Å, for α and β NC forms, respectively).

Relevant information on PPO crystallization, with particular emphasis on nanoporous crystalline (NC) and related co-crystalline (CC) forms, is reviewed. Preparation methods, structures, properties and possible applications of NC and CC samples are discussed. Reviewed results mainly refer to films (unoriented or with axial or planar orientations) but also to NC powders and NC aerogels. Particular attention is given to the impressive solubility and diffusivity of organic guests, which can be achieved for NC PPO samples. X-ray diffraction patterns and infrared linear dichroism, as collected for axially oriented NC films, indicate the presence of large diameter crystalline helices with intrahelical location of the guest molecules. The final section is mainly devoted to perspectives of basic and industrial research that are expected in the near future for CC and NC PPO samples. As for research studies, particularly suitable appear NC films with orientation of the crystalline empty channels perpendicular to the film plane (c⊥ orientation), mainly due to their fast guest sorption and good optical transparency.

Tip-enhanced Raman spectroscopy is a powerful tool for the analysis of system interfaces, enabling access to chemical information with nanometric spatial resolution and sensitivity up to the single molecule level. Such features are due to the presence of proper metallic nanostructures at the TERS probe apex, which, via the excitation of a plasmonic field, confine light to a nanometric region. The nano-sized characteristic of such metallic structures intrinsically renders the fabrication of high performing and reproducible TERS probes still a challenge. In this paper, we present a facile, rapid and effective approach to prepare Ag-based TERS probes. The fabrication process proposed herein is based on spinodal dewetting of Ag-coated AFM-probes through a RF plasma treatment. The obtained probes appear covered with a coral-like silver nanotexture, endowed with an excellent plasmonic activity. Intriguingly, such a texture can be easily tuned by changing some process parameters, such as Ag film thickness and exposure time to the plasma. The as-prepared TERS probes show a high TERS enhancement, reaching 107, and allow a good spatial resolution, down to 10 nm. Finally, we suggest an easy and effective procedure to restore oxidized TERS tips following exposure to ambient air, which can be applied to all types of Ag-based TERS tips.

The term disentangled refers to polymers with fewer entanglements in the amorphous regions, a metastable condition that can significantly affect the material&rsquo, s properties and processing behavior. The lower entanglement density in ultra-high molecular weight polyethylene (dis-UHMWPE) facilitates the solid-state processability into uniaxially-oriented specimens reaching very high draw ratios and crystallinities. In this study, Au/dis-UHMWPE nanocomposites were formulated and processed at variable draw ratios. Polarized light microscopy suggests gold nanoparticles are oriented in arrays following the drawing of polymer chains. The structural features, upon orientation, are studied by means of Raman spectroscopy, wide- and small-angle X-ray scattering, and near-infrared spectrophotometry. Crystallinity is found to increase by 15%, as calculated by wide-angle X-ray scattering. The change in optical absorbance in the visible spectrum indicates that, with orientation, the average size of gold aggregates increases, supported quantitatively by small-angle X-ray scattering. Since the gold nanoparticles are expected to be found within amorphous chain segments, the aforementioned findings are attributed to the increase of crystallinity and thus the decrease of available (amorphous) space.

This research investigates the preparation and characterization of new organic&ndash, inorganic geopolymeric foams obtained by simultaneously reacting coal fly ash and an alkali silicate solution with polysiloxane oligomers. Foaming was realized in situ using Si0 as a blowing agent. Samples with density ranging from 0.3 to 0.7 g/cm3 that show good mechanical properties (with compressive strength up to &asymp, 5 MPa for a density of 0.7 g/cm3) along with thermal performances (&lambda, = 0.145 &plusmn, 0.001 W/m&middot, K for the foamed sample with density 0.330 g/cm3) comparable to commercial lightweight materials used in the field of thermal insulation were prepared. Since these foams were obtained by valorizing waste byproducts, they could be considered as low environmental impact materials and, hence, with promising perspectives towards the circular economy.

Innovation of the Ziegler–Natta polymerization process for polymerization of propene that allows tailoring of the mechanical properties of isotactic polypropylene (iPP) directly in the polymerization stage is presented. The catalyst is modified by prepolymerization of trimethylallylsilane or vinylcyclohexane so that the catalyst particles are coated by a thin skin of poly(trimethylallylsilane) or poly(vinylcyclohexane) that will act as a nucleating agent for the crystallization of iPP. The presence of the nucleating agent accelerates the crystallization of iPP and affords crystallization of the α form even upon fast crystallization by quenching the melt, a condition that generally produces crystallization of the mesomorphic form. Crystals of the α form so obtained show a nodular morphology and the absence of the spherulitic superstructure. This novel iPP material is characterized by outstanding and unexpected properties of high mechanical strength and modulus and contemporarily high ductility, flexibility and good transparency due to the nodular morphology of the α form.

For the first time, hybrid organic&ndash, inorganic geopolymeric foams were successfully used as monolithic adsorbents for the removal of metallic ions pollutants from wastewaters. The foams were realized by the in situ foaming of a hybrid geopolymer obtained by a reaction of metakaolin and polysiloxane oligomers under strong alkaline conditions and then cured at room temperature. In this way, porous materials with densities ranging from 0.4 to 0.7 g/cm3 and showing good mechanical properties were produced. With the aim of producing self-standing monolithic adsorbents for the removal of metallic ions pollutants from wastewaters, these porous hybrid geopolymers were subjected to a washing pretreatment with ultrapure water, dried, and then used for absorption tests by dipping them into an aqueous solution with an initial concentration of 20 ppm of Pb2+, Cd2+, Cu2+, and Zn2+ ions. Preliminary results indicated that all the tested materials are effective in the adsorption of the tested metal ions and do not release the removed metal ions upon sinking in ultrapure water, even for a very long time. Interestingly, compressive strength tests performed before and after the washing treatments show that the foamed samples remain intact and maintain their physical&ndash, mechanical characteristics, suggesting that these kinds of materials are promising candidates for the production of self-standing, monolithic adsorbent substrates that can be easily collected when exhausted, which is a major advantage in comparison with the use of powdered adsorbents. Moreover, since these materials can be obtained by a simple and versatile experimental procedure, they could be easily shaped or directly foamed into precast molds to be used in packed beds as membranes.

Oriented nanoporous crystalline (NC) phases of poly(2,6-dimethyl-1,4-phenylene) oxide (PPO) are for the first time described. In particular, PPO films with orientations of crystalline chain axes preferentially parallel (c//) or perpendicular (c⊥) to the film plane are obtained by suitable procedures of solution casting or of solvent-induced crystallization, respectively. 2D-WAXD patterns of NC PPO films, exhibiting c// and c⊥ orientations, have allowed indexing of reflections and establishing unit cell parameters of NC modifications (e.g., for the NC modification from carvone an orthorhombic unit cell with a = 1.97 nm; b = 1.24 nm; c = 0.53 nm). FTIR spectra of NC PPO films exhibiting c// or c⊥ orientations, have allowed establishing the direction of transition moment vectors of polymer chain vibrational peaks. NC films with c// and c⊥ orientations, are expected to allow control of guest diffusivities as well as orientation of active guest molecules.

This research has investigated the properties of thermally insulating geopolymer composites that were prepared using waste expanded polystyrene as lightweight aggregate. The geopolymer matrix was synthetized using metakaolin and an alkaline activating solution. To improve its mechanical properties, this matrix was modified by the addition of an epoxy resin to form an organic-inorganic composite. Moreover, in order to reduce drying shrinkage marble powder was used as an inert filler. The materials obtained were characterized in terms of physico-mechanical properties, thermal performance and microstructure. The geopolymer expanded polystyrene composite have improved properties compared to Portland cement-based materials, with higher strengths and lower thermal conductivity. The research demonstrates the manufacture of sustainable lightweight thermally insulating geopolymer composites using waste expanded polystyrene.

Syndiotactic polystyrene (s-PS) is able to form different kinds of co-crystalline phases with guest molecules of different size, shape and property. Several advanced materials have been produced starting from s-PS co-crystalline films. In particular, sulfonated s-PS (s-sPS) can be used as proton-conductive membrane in some fuel cells applications, as it presents high proton conductivity (comparable with Nafion). Besides, it shows a high chemical and thermo-mechanical stability and a low cost. The morphology of different s-PS clathrates and the structural behavior of s-sPS upon hydration can be thoroughly understood by SANS. In fact, exploiting the neutron contrast variation between various hydrogenated and deuterated components of s-PS and s-sPS clathrates, additional and unique information about the distribution of guest molecules in the crystalline and amorphous regions and about the hydrated domains of the polymer were obtained. Moreover, using uni-axially deformed films the occurrence and distribution of scattering features from typical morphologies on specific directions and sectors of detection plan enable an accurate structural study of such complex polymeric systems. We report in the present paper a detailed SANS investigation of s-PS films, starting from their crystallization with guest molecules to the subsequent sulfonation and hydration. FT-IR, neutron PGAA, WAXD and cryo-TEM were used complementary to SANS to check the state of the samples after each step of the treatment process and to obtain additional structural information as support for the understanding of the SANS data. The current experimental analysis has highlighted that the morphology of these polymeric films is characterized by hydrated channels in the bulk amorphous phase alternated to stacks of crystalline lamellae, oriented along the stretching direction.

The structure and the mechanical properties of metallocene-made butene-pentene (iPBC5) and butene-hexene (iPBC6) isotactic copolymers are studied. The effect of the presence of pentene and hexene units on the crystallization behavior and the mechanical properties of isotactic polybutene (iPB) is analyzed. All iPBC5 copolymers crystallize from the melt in form II of iPB, which transforms into form I by aging at room temperature. On the contrary, in iPBC6 copolymers the presence of hexene units stabilizes the form II and, for hexene concentrations higher than 11 mol%, prevents the transformation of form II into form I at room temperature. Both iPBC5 and iPBC6 copolymers show mechanical behavior of highly flexible and ductile materials with enhanced ductility compared to iPB, with values of stress at yielding and of Young's modulus that decrease with increasing comonomer content. In all the iPBC5 copolymers, form II crystallized from the melt transforms into form I by stretching, whereas in iPBC6 copolymers form II is stabilized and the transformation of form II into form I by stretching is completely inhibited at high hexene concentrations.

Hybrid composite materials based on geopolymer and epoxy melamine resins have been designed to produce a novel material showing high compatibility between the organic and inorganic phases. This has been realized through a synthetic method based on the co-reticulation in mild condition of the two phases. These materials show good interpenetration of the resin into the inorganic matrix up to nanometric level and significantly improved mechanical properties in respect to un-modified geopolymer without compromising the good thermal stability and fire resistance typical of unmodified geopolymers. These properties make the novel materials very attractive for the realization of thermo-resistant and thermo-insulating panels.

For the δ form of syndiotactic polystyrene, a nanoporous triclinic modification, different from the well-established and widely used nanoporous monoclinic modification, is presented. Detailed routes to triclinic or monoclinic modifications, which involve different guest removal procedures from different δ-clathrates, are described and rationalized. Surprisingly, both triclinic and monoclinic δ modifications can be obtained by both triclinic and monoclinic δ-clathrates. The triclinic modification, with respect to the monoclinic one, presents the advantage of higher uptake of pollutants having molecular volume in the range 0.13–0.22 nm 3 , mainly when present only as traces in water or in air. In particular, the different molecular selectivity of triclinic and monoclinic δ modifications, favoring n -decane and n -hexane sorption, respectively, is described. This behavior is attributed to the crystalline cavities of the triclinic δ modification, which are halved in number and increased in volume with respect to those of monoclinic δ modification.

The present study reports on the preparation and characterization of new organic-inorganic geopolymer based hybrid foams obtained by reacting an aluminosilicate source and an alkalisilicate solution with mixtures of dialkylsiloxane oligomers or organic resins precursors. By using different amounts of Si 0 powder as in situ foaming agent, hybrid geopolymer-based foams with densities ranging from 0.25 to 0.85 g/cm 3 were successfully prepared. These new materials are characterized by remarkable mechanical properties, good fire resistance and low thermal conductivity, significantly better than those shown by neat geopolymer foams reported in the literature and comparable or even better than those of typical (not geopolymer) inorganic foamed materials with similar densities.

A study of the nucleating effects of isotactic poly(trimethylallylsilane) (iPTMAS) and poly(vinylcyclohexane) (iPVCH) for isotactic polypropylene (iPP) and their influence on the mechanical behavior of iPP is reported. The particles of catalyst are covered by poly(trimethylallylsilane) or poly(vinylcyclohexane) by polymerization of the corresponding monomers before polymerization of propylene. The method guarantees that the nucleating agents are perfectly dispersed into the iPP samples, with their consequent high efficiency. Isotactic poly(vinylcyclohexane) and poly(trimethylallylsilane) favor crystallization from the melt of α and β forms, respectively. Both nucleating agents affect the morphology greatly reducing the size of shperulites. This in turn affects the mechanical properties improving ductility and flexibility. All nucleated samples crystallize by rapid cooling from the melt in the α form and not in the mesophase, as occurs in the pure iPP. The resulting α form presents nodular crystals and behaves as a stiff material with high deformability.

A study of the mechanical properties and of the crystallization behaviour of samples of isotactic polybutene (iPB) of different stereoregularity prepared with metallocene catalysts, is presented. Stereoregular samples with concentration of rr defetcs lower than 2 mol% crystallize from the melt by compression-molding and fast cooling to room temperature in form II, whereas more stereoirregular samples crystallize surprisingly mainly in form III. The stereodefective iPB samples show interesting mechanical properties of high ductility and flexibility that increase with increasing concentration of rr stereodefects, with values of deformation at break higher than 1000% for the most stereoirregular sample containing about 5 mol% of stereodefects. The aging at room temperature produces transformation of form II into form I in more stereoregular samples, whereas no phase transformation occurs in more stereoirregular samples crystallized mainly in form III. A strong increase of Young’s modulus and of stress at yield is observed after transformation of form II into form I. For more stereoirregular samples with concentration of rr defects higher than 2 mol% crystallized in form III, the mechanical properties do not change significantly upon aging at room temperature because no phase transformations occur during aging. Also for the aged samples a remarkable increase of ductility and flexibility with increasing concentration of rr stereodefects is observed. The mechanical deformation is associated with stress induced transformations of form II and form III into form I. These results indicate that mechanical properties of iPB can be modified by the controlled incorporation of stereodefects and improvement of ductility is easily obtained while maintaining high crystallinity by inclusion of small amounts of rr stereodefects.

A study of the morphology and the mechanical properties of the mesomorphic form of isotactic polypropylene (iPP) that crystallizes in samples of different stereoregularity prepared with metallocene catalysts is reported. Highly isotactic samples slowly crystallized from the melt in the α form show the typical lamellar morphology with organization in spherulites. Bundle-like elongated crystalline entities and needle-like crystals of γ form are instead observed for stereoirregular samples slowly crystallized from the melt in the γ form. All samples crystallize by fast quenching the melt at 0 °C in the mesomorphic form, regardless of stereoregularity. Crystals of the mesomorphic form always exhibit a nodular morphology and absence of lamellar spherulitic superstructures, independent of the stereoregularity. This morphology accounts for the similar good deformability of all the quenched samples, whatever the concentration of stereodefects. For all samples and any stereoregularity, the nodular morphology with absence of spherulites is preserved after annealing and transformation of the mesophase into α form. The formation of a nodular α form accounts for outstanding properties of high ductility and mechanical strength of the annealed samples crystallized in the α form. The most stereoirregular sample with rr concentration of 11% shows elastic behavior either when it is slowly crystallized in the γ form or when it is crystallized in the mesomorphic form and also after annealing and transformation of the mesophase into the nodular α form.

s-PS ε-clathrates with different n-alkanes, ranging from n-hexane to n-dodecane, have been obtained for the first time and their structure has been investigated by means of X-ray diffraction, FT-IR spectroscopy, and molecular mechanics calculations. The diffraction data of all the s-PS/n-alkane ε-clathrates are in agreement with the orthorhombic unit cell with axes a = 1.62 nm, b = 2.20 nm, and c = 0.79 nm and the space group Pbcn, proposed for the nanoporous ε form, indicating that the crystal packing of the chains in the clathrate forms remains substantially unaltered independently of the length of the n-alkane. Molecular mechanic calculations provided conclusions that the n-alkanes’ guest, independent of their length, are arranged in the channels in fully trans-planar conformation with their main molecular axis almost parallel to the axis of the cavity. The possibility of having n-alkane guest with a bent conformation in the channels was also ruled out. A detailed structural study was carried out for the cocrystalline form containing n-octane.

The crystal structure of the δ clathrate form of syndiotactic polystyrene (s-PS) containing CHCl 3 , a molecule having a pivotal role in respect to the co-crystalline phases formation of this polymer, has been determined through X-ray diffraction data and molecular mechanics calculations. Analogously to all the other δ clathrate forms of s-PS, this structure presents a monoclinic unit cell (cell constants a = 1.77 nm, b = 1.32 nm, c = 0.78 nm and γ = 121.5°) in which the s(2/1)2 polymer helices and guest molecules are packed according the space group P 2 1 / a . At variance with all the other δ clathrate forms of s-PS whose crystal structure has been reported in the literature, probably due to the not planar shape of the chloroform guest molecule, in this structure guest molecules occupy each centrosymmetric cavity in a very low efficient way, giving rise to a disorder in the positioning of the guest molecules along the b + a / 2 direction of the unit cell. A comparison with the e type clathrate with the same guest, for which some preliminary results have been reported too, is also presented.

The detailed description of the crystalline structure of a channel type e clathrate cocrystal of syndiotactic polystyrene (s-PS) is presented here for the first time. The proposed structure is base...

The crystal structure of the clathrate form of syndiotactic poly(p-methylstyrene) containing benzyl chloride is presented. This structure presents a monoclinic unit cell (cell constants a = 26.2 A, b = 11.8 A, c = 7.9 A and γ = 116°) in which the s(2/1)2 polymer helices and guest molecules are packed according the space group P21/a. This molecular complex represents, to our knowledge, the first case of polymeric clathrate form in which in the same crystal are present two kinds of cavities having different shape and dimensions: α class cavities (containing two guest molecules) and β class cavities (containing one guest molecule). The contemporaneous presence of these two types of cavities is originated by a disorder in the arrangement of right- and left-handed helices in the crystals related to the particular staggered layout of the layers of chains containing the cavities in which helices of a given chirality can be randomly substituted by enantiomorphous ones.

New hybrid materials with no phase separation up to nanometric level were obtained by performing the in situ co-reticulation of an aluminosilicate source (metakaolin), a mixture of dialkylsiloxane oligomers with different degrees of polymerization and an alkaline solution. As supported by SEM and NMR analyses, these hybrid materials are characterized by a highly interpenetrated structure due to the chemical similarity between the components, resulting in excellent physical and mechanical properties compared to neat geopolymers. These promising results represent a further step in developing alternative “low-carbon” binders (as also geopolymers) with improved engineering properties in the concrete technology. The enhanced mechanical properties, along with the high fire resistance, also suggest their utilization for structural applications as heat insulating and heat-resistant panels for the construction industry, and in the production of heat-resistant protective coatings or adhesives for technologically advanced uses. Keywords: Alkali activated cement, Hybrid, SEM, Spectroscopy, Mechanical properties

A new type of rigid rod polymer is reported, easily obtained by thermal cyclization of a soluble/meltable polyamidic precursor. The polyamides are based on a diaminobenzodifurane monomer and are prepared by polycondensation reaction. The polymers are characterized by NMR, FTIR, GPC, TGA, DSC. The cyclization reaction produces insoluble/unmeltable benzodifuroxazinonic based polymers with rigid rod structure. Due to their thermotropic liquid crystalline behavior the polyamides are easily obtained from melt as oriented films under shear and as fibers by extrusion. High degree of orientation and smectic-like arrangement of polyamides are demonstrated by X-ray fiber diffraction. Retention of the orientation upon cyclization is demonstrated by XRFD, optical and electron microscopy.

The crystallization behavior and the mechanical properties of random isotactic butene–octene copolymers (iPBC8) prepared with a metallocene catalyst are presented. Samples with low octene concentrations, up to nearly 6 mol%, crystallize from the melt in form II. In these samples octene units stabilize the tetragonal form II, decelerating or even preventing the transformation of form II into the trigonal form I. Octene concentrations higher than 7 mol% prevent crystallization of the samples from the melt and the obtained amorphous samples crystallize by aging at room temperature in mixtures of form II and form I'. The sample with the highest octene concentration of 11.5 mol% crystallizes surprisingly from the amorphous phase directly in the pure form I'. In these samples, form I' crystallized from the amorphous phase transforms into form II by stretching. Form II transforms back into form I' upon releasing the tension. Therefore, in samples where form I' is favored in powder samples, form II is favored in stretched fibers. The transformation of form I into form II by stretching and the back transformation of form II into form I after releasing the tension is unusual for isotactic polybutene (iPB) and rather unexpected. The presence of octene comonomer units also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing comonomer content, and samples with octene concentration higher than 6–7 mol% show unexpected remarkable elastomeric properties. The formation of crystals of form II or form I' during aging allows development of elastomeric properties and enhancement of mechanical strength. The elastic properties are associated to the reversible crystal–crystal phase transition between form II and form I occurring during stretching and when the tension is removed.

Guest molecules, like cyclopentanone (CPO), N,N-dimethylformamide (DMF) tetrahydrofuran (THF) and 1,3-dioxolane (DOL), which are able to cocrystallize with poly(l-lactic acid) (PLLA), can also generate high degree of crystalline phase orientation, by simple sorption in amorphous unoriented PLLA films. This crystalline phase orientation is defined as a∥c∥ (a-parallel, c-parallel) because the ac plane of most crystallites is preferentially parallel to the film plane. This crystalline phase orientation, which is achieved without stretching even for high thickness films, is unprecedented for PLLA and can be maintained after suitable guest exchange procedures. The reported results confirm the recent hypothesis that cocrystallization with low-molecular-mass guest molecules could be a common route for getting uniplanar orientations of polymer crystalline phases, even in the absence of stretching. Wide angle X- ray diffraction analyses of unoriented and oriented PLLA samples have allowed proposing the structure of the cocrystalline form of PLLA with CPO. In particular, four PLLA chains exhibiting the 10/7 helical conformation and 16 CPO guest molecules are packed according the space group P212121 in an orthorhombic lattice with a = 1.61 nm, b = 1.26 nm, and c = 2.90 nm. The presence in PLLA cocrystalline structures of dense bc layers with close-packed polymer helices allows an easy rationalization of the observed uniplanar orientation.

The structure and thermal properties of a new class of isotactic copolymers of ethylene (E)/4-methyl-1,3-pentadiene (4MPD) with 4MPD content in the range 40–73 mol % and of isotactic poly-1,2-(4-methyl-1,3-pentadiene) (iP4MPD) homopolymer have been analyzed. The copolymers have been synthesized using 1,4-dithiabutanediyl-linked bis(phenolate) titanium complexes as catalyst precursors, activated by methylaluminoxane. Solution 13C NMR analysis reveals the tendency of the catalyst system to produce copolymers with alternating 4MPD/E constitution. All copolymers are crystalline and show melting temperatures in the range 90–100 °C. The samples with nearly equimolar concentration of units crystallize in a new crystalline form because of the alternating constitution. Structural analysis indicates that in this new form the alternating 4MPD-E sequences assume a nearly trans-planar conformation with periodicity c = 5.13 Å and are arranged in a monoclinic unit cell with parameters a = 5.70 Å, b (unique axis) = 14.95 Å, c (chain axis) = 5.13 Å, and β = 114.4°, according to the space group symmetry Pn.

The crystalline structure of form I of syndiotactic poly(para-methylstyrene) is described. In this form, the polymer chains assume a s(2/1)2 helical conformation and are packed according to the space group P2 1 /a in a unit cell with a = 24.5 A, b = 12.4 A, c = 8.1 A, and y = 143.5°. The proposed model may be described by a stacking of layers of alternating right- and left-handed helical chains efficiently packed in an "interdigital structure" in which phenyl rings belonging to one chain interlock with the phenyl rings of the two adjacent chains of opposite chirality. A disorder in the correct succession of the layers is suggested. A possible similarity between this form and the nanoporous 6 form of syndiotactic polystyrene, suggested by the fact they are both obtainable by guest removal from a class clathrates, is analyzed.