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The structure, the morphology and mechanical properties of crystalline block copolymers formed by polyethylene (PE) block linked to isotactic polypropylene (iPP) or syndiotactic polypropylene (sPP) blocks are presented. Samples of polyethylene-block-syndiotactic polypropylene (PE-block-sPP) and polyethylene-block-isotactic polypropylene (PE-block-iPP) crystalline-crystalline block copolymers with different block lengths have been synthesized by using living, stereoselective polymerization catalysts (Figure 1). A detailed structural characterization has been performed on both block copolymers for samples crystallized in the bulk, thin films and stretched fibers and stress-induced phase transformations have been analysed. PE-block-sPP samples have been epitaxially crystallized onto crystals of p-terphenyl (3Ph) to achieve a control over the crystallization of both blocks and study the dependence of the thin film morphology on the sequential crystallization of the two blocks by cooling from the melt. Ordered nanostructures where the two blocks are organized in separated alternating lamellar domains guided by the orientation of the crystalline lamellae are obtained. We demonstrate that, tuning the block length and using a specific substrate, it is possible to control the crystallization process and obtain large-sized, well-oriented lamellar microstructures with long range order achieved over the area in contact with the crystalline substrate.

In this thesis were studied the structure and the physical properties of novel materials prepared with different synthetic strategies aimed at producing the desired molecular structure: 1. Organometallic catalysts for polymerization of dienes to stereoregular polydienes and successive hydrogenation for producing polyolefins and copolymers with novel molecular architectures; 2. Organometallic non-metallocene catalysts for producing semicrystalline block copolymers; All research topics are pursued with the main aim to exploit the concept of retro-design of the physical properties, that is, to identify the best molecular architecture, synthetic approach, and processing conditions that ensure to obtain the target tailored properties. Regarding the first topic the crystals structures of isotactic 1,2-poly((E)-3-methyl-1,3-pentadiene) (iP3MPD12) and isotactic poly((R,S)-3-methyl-1-pentene) (iP(R,S)3MP) have been determined by analysis of the X-ray powder and fiber diffraction patterns and conformational and packing energy calculations. The iP3MPD12 has been synthesized with the catalytic system CoCl2(PnPrPh2)2/MAO and is one of the very few examples of crystalline isotactic 1,2-polydienes described in the literature. From the successive hydrogenation of iP3MPD12 a novel isotactic poly((R,S)-3-methyl-1-pentene), characterized by a random enchainment of R- and S-3-methyl-1-pentene, has been obtained. The crystal structure analysis has revealed that iP3MPD12 is characterized by chains in 7/2 helical conformation packed in an orthorhombic unit cell with axes a = 17.4 Å, b =16.5 Å, c = 15.3 Å according to the space group P21ab. The hydrogenated polymer of iP(R,S)3MP is instead characterized by chains in 4/1 helical conformation packed in in a monoclinic unit cell with parameters a = 10.02 Å, b = 18.48 Å, c = 6.87 Å, and γ = 109.9° according to the space group P21/b or P21. A high degree of disorder is present in the crystals due to the random enchainment of the enantiomeric R and S monomeric units, whose chirality influences the handedness of the helical chains and the conformation assumed by the lateral groups. The crystal structure of iP(R,S)3MP is different from the tetragonal structure of the pure enantiomer iP(S)3MP. This is due to different entropic effects, related to the presence of different types of disorder included in the crystals that drive crystallization in different packing modes. The crystal structure of iP(R,S)3MP provides an example of the effect of the chirality of side groups on the crystal packing and is an example of symmetry breaking in the structures of polymers. In the second part of this thesis the structure, the morphology and the physical properties of crystalline-crystalline diblock copolymers synthesized with living, stereospecific polymerization using an Hf-based post-metallocene catalyst have been investigated. Samples of isotactic polypropylene-block-polyethylene (iPP-b-PE) and isotactic polypropylene-block-linear low density polyethylene (iPP-b-LLDPE), of different block lengths have been prepared and characterized. The influence of the molecular architecture, in terms of molecular mass, different block lengths and composition, on the crystallization behavior, morphology and mechanical properties of these systems has been studied. This analysis has shown that the physical properties of these crystalline block copolymers can be easily tailored by controlling the molecular parameters, and conditions of crystallization.

Additional file 1.1H NMR spectra of HO2CC1MImCl (Figure S1) and HO2CC1MImNTf2 (Figure S3). 13 C NMR spectra of HO2CC1MImCl (Figure S2) and HO2CC1MImNTf2 (Figure S4). Thickness determination by SEM for CHT and CHT/BTA (Figure S5). ATR-FTIR spectra of CHT/BTA coating on bronze disk before and after 12 h of accelerated corrosion treatment (Figure S6).

Additional file 1.1H NMR spectra of HO2CC1MImCl (Figure S1) and HO2CC1MImNTf2 (Figure S3). 13 C NMR spectra of HO2CC1MImCl (Figure S2) and HO2CC1MImNTf2 (Figure S4). Thickness determination by SEM for CHT and CHT/BTA (Figure S5). ATR-FTIR spectra of CHT/BTA coating on bronze disk before and after 12 h of accelerated corrosion treatment (Figure S6).

Isotactic polypropylene-block-polyethylene block copolymers (iPP-b-PE) composed of crystalline blocks of isotactic polypropylene (iPP) and linear polyethylene (PE) of different block lengths have been synthesized with a living and stereoselective pyridylamidohafnium catalyst. The structure and morphology of iPP-b-PE that develop upon crystallization from the melt are presented. Temperature and time resolved X-ray diffraction experiments in wide (WAXS) and small angles (SAXS) recorded during cooling from the melt indicate that PE blocks crystallize first upon cooling and the iPP block crystallizes at lower temperatures and nucleates over the crystals of PE formed before. The SAXS data indicate that PE lamellar stacks formed first at high temperature have higher periodicity of 30 nm, whereas iPP lamellar stacks formed after at lower temperature have lower periodicity of 11–12 nm. The crystallization of the iPP and PE blocks drives microphase separation and determines the final morphology leading to a lamellar morphology characterized by alternation of amorphous and crystalline layers. At nanoscale the morphology is characterized by alternating iPP and PE microdomains, each domain including stacks of lamellar crystals of iPP or PE of different periodicities, separated by the corresponding amorphous regions of iPP or PE. Polarized optical micrographs of the melt-crystallized samples show the presence of bundle-like crystals in samples with longer block of iPP and of small banded spherulites in samples with longer block of PE. The observation of banded spherulites typical of PE suggests that the crystallization of PE defines the global morphology and is not altered by the structure of the melt, confirming that crystallization of PE occurs first upon cooling from the melt.

Hypothesis Multi-component supramolecular hydrogels are gaining increasing interest as stimuli-responsive materials. To fully understand and possibly exploit the potential of such complex systems, the hierarchical structure of the gel network needs in-depth investigations across multiple length scales. We show that a thorough structural and rheological study represents a crucial pillar for the exploitation of this class of functional materials. Experiments Supramolecular hydrogels are prepared by self-assembly of hexadecyltrimethylammonium bromide (CTAB) and azobenzene-4,4′-dicarboxylic acid (AZO) in alkaline aqueous solution. The CTAB/AZO concentration was varied from ϕ = 0.25 to 4 wt% keeping the CTAB:AZO molar ratio fixed at 2:1. The systems were thoroughly studied through a combination of X-ray scattering, microscopy, rheological and spectroscopic analyses. Findings The CTAB/AZO solutions form a self-supporting gel with nanofibrillar structure below ~30 °C. The critical gelation concentration is ϕc = 0.45 wt%. Above this threshold, the gel elasticity and strength increase with CTAB/AZO content as ~(ϕ-ϕc)1. The hydrogels exhibit self-healing ability when left at rest after a stress-induced damage. Moreover, the light-induced isomerization of the AZO moieties provides the gel with light-responsiveness. Overall, the multi-stimuli responsiveness of the studied CTAB/AZO hydrogels makes them a solid starting point for the development of sensors for mechanical vibrations and UV/visible light exposure.

A study of the mechanical behavior of isotactic 1,2-poly(E-3-methyl-1,3-pentadiene) (iP3MPD) and of the structural and morphological transformations that take place upon stretching is presented. Amorphous samples do not show viscous flow but show high ductility, strain hardening, and elastomeric behavior. An unusual double yielding appears in the stress- strain curves that may be correlated to occurrence of events typical of yielding at low deformation followed by stress-induced crystallization of a mesomorphic form at higher deformation (200-300%). The yielding stress and an endothermic hysteresis effect at the glass transition simultaneously increase upon aging of the amorphous glass due to a local densification or formation of local order in the amorphous glass upon physical aging. The elasticity is accompanied by the crystallization of the mesophase during deformation and its melting upon relaxation. During successive cycles of tensile deformation and elastic recovery the yielding peak is still observed during every stretching step. The elasticity of iP3MPD is an unusual case of a polymer that shows rubbery elastomeric properties below the glass-transition temperature.