To develop approaches for modification of a new class of copolymers of ethylene and 1-octene, the effect of gamma-irradiation with doses ranging from 0.2 to 10 MGy on their structure and mechanical and thermal characteristics was studied. Copolymers containing 3.5-13 mol % of 1-octene units and having a degree of crystallinity of 4-33% and a branched low-density polyethylene with a low degree of crystallinity were investigated. The conclusion was made that, even at low irradiation doses, crosslinking processes play a key role. As a result of crosslinking processes, marked amounts of the gel fraction are formed, elongation-at-break is reduced, and thermal characteristics are changed. As the irradiation dose is increased, structural rearrangements and related changes in thermal characteristics take place that are associated with the formation of radiation-induced defects in crystallites and with a marked decrease in the entropy of melt due to intermolecular crosslinking. A comparative study of radiation-induced behavior of ethylene-1-octene copolymers and the branched polyethylene allowed one to gain a deeper insight into the role of different types of crystallites and their sensitivity to irradiation.

The structure of alternating propylene-carbon monoxide copolymers is studied. The polymers are synthesized either without any regularity control or with the use of an enantioselective catalyst. It turned out that poly(propyleneketone) crystallizes with the formation of two lattice types depending on the conditions of its synthesis. Copolymers that contain one of the enantiomers crystallize into an orthorhombic cell (a = 10.68 Angstrom, b = 6.18 Angstrom, and c = 9.01 Angstrom). Samples consisting of a mixture of two enantiomers form a stereocomplex, which crystallizes with the formation of a triclinic lattice (a = b = 9.45 Angstrom, c = 9.04 Angstrom, (alpha = beta = 109.41degrees, and gamma = 109.0degrees). The macroscopic properties of these samples significantly differ. Both crystal forms are shown to have identical chain conformations represented by a 3(l) helix. The cells contain two polymer chains each. The unit cell parameters and the melting point of the triclinic modification significantly depend on the chain regularity. For example, samples containing the stereocomplex of isotactic regioregular L- and D-helices melt at 239 degreesC. As the number of attachment defects increases, the melting point notably decreases and amounts to 68 degreesC for samples synthesized without any regularity control. Nevertheless, the process of stereocomplex formation remains energetically favorable, a fact explained by the existence of a selective interaction between the helices.

For microphase-separated polyblock thermoplastic elastomers composed of alternating soft [poly(tetramethylene oxide) with M = 2 x 10(3))] and hard [poly(butylene terephthalate), polyamide-12, diphenylmethane diisocyanate] blocks, the stress-induced reversible crystallization of poly(tetramethylene oxide) was studied by the methods of deformation calorimetry and wide-angle X-ray diffraction. The presence of the pure soft-block phase allows its reversible stress-induced crystallization. The effect of the tensile strain and temperature on the stress-induced crystallization of poly(tetramethylene oxide) was studied. Above the glass transition temperature of hard blocks, the stress-induced crystallization of poly (tetramethylene oxide) does not occur. Intramolecular components of energy effects were assessed by thermodynamic analysis of the deformation process. A comparative quantitative estimation of the maximum degree of crystallinity of poly(tetramethylene oxide) upon its stress-induced crystallization was performed. In poly(ether urethane), the stress-induced crystallization of poly (tetramethylene oxide) is fully reversible. However, in the poly(ether ester) thermoplastic elastomer and especially in poly(ether amide), even though reversible deformations are localized in amorphous regions, poly(tetramethylene oxide) crystals are partially preserved after the stress release.

The effect of the conditions of synthesis on structure and mechanical and thermal properties is studied for thermoplastic elastomers based on terpolymers of ethylene, propylene, and carbon monoxide. Samples synthesized at a preset concentration of the monomers in an autoclave are characterized by a microblock structure and contain crystallites of distorted beta form of poly(ethylene ketone) and triclinic modification of poly(propylene ketone). The use of a new method of synthesis based on the pulse feeding of ethylene significantly reduces the blockiness of the polymer chain. Terpolymers with an ethylene content of about 40% thus prepared are characterized by low crystallinity (below 10%) and the absence of the crystalline phase of poly(ethylene ketone). The tensile drawing of such samples leads to the development of an ordered structure whose parameters are close to those of the orthorhombic crystal lattice of the poly(propylene ketone) copolymer. The formed crystalline domains serve as a physical entanglement network and impart good elastomeric properties to the resultant material.

The complex investigation of copoly(ether-ester) based on poly(butylene terephthalate) (PBT) and poly(tetramethylene oxide) (PTMO) reveals its microphase separated nanodomain structure. Initial morphology includes the stacks of crystalline blocks of α-PBT embedded in amorphous matrix with the different degree of continuity of the crystalline network. Two types of amorphous regions can be distinguished, the PTMO-rich phase and the other one containing the PTMO and PBT segments. Reduction of PBT content and proper decrease of its fragments length results in dramatic change in crystalline ordering, the crystallites became smaller and distorted, and more and more PBT segments are included in the amorphous phase. The initial reversible stage of deformation is controlled mostly by elastic deformation of amorphous phase, highly constrained by the network of crystallites. The further stretching results in plastic deformation and reorganisation of the crystalline blocks of PBT and a new crystalline morphology arises. Moreover, at large deformations the soft blocks of PTMO can crystallise and form very distorted paracrystalline regions. Finally, at high enough stress (≈25–30 MPa) the transition from α to β crystalline form in PBT crystal lattice occurs due to conformational changes in the tetramethylene segments. After large deformation, both the morphology and the polymer conformations are far from the equilibrium state. Annealing of the stretched samples at high temperature results in partial recovery of material properties, however the morphology is still far from the initial one even after such annealing.

The samples of a Nylon-6-polyimide-Nylon-6 triblock copolymer containing 5 and 15% of polyimide (PI) were studied by DSC and X-ray diffraction in the WAXS and SAXS modes. Crystalline regions in the block copolymers studied comprise small Nylon-6 polyamide (PA) crystallites (predominantly in the a modification), which are subjected to rather insignificant influence of the rigid imide blocks squeezed out into the amorphous phase. The samples with 15% PI contain a small fraction of the crystalline Nylon-6 γ * phase, which is related to the hindered crystallization of the PA chains in the presence of PI. Analysis of the results of SAXS measurements shows that the structure of samples is most adequately described by a two-phase model with a crystalline phase of Nylon-6 and an amorphous phase comprising a mixture of PA and PI chains. Increased mechanical and thermal properties of the copolymers, as well as their low moisture absorption, can be explained using a concept of molecular composites comprising a flexible PA matrix reinforced by rigid PI fragments.

The samples of a triple Nylon-6-polyimide-Nylon-6 block copolymer containing 5 and 15% of polyimide (PI) were studied by DSC and X-ray diffraction in the WAXS and SAXS modes. Crystalline regions in the block copolymers studied comprise small Nylon-6-polyamide (PA) grains (predominantly in the a modification), which are subjected to rather insignificant influence of the rigid imide blocks squeezed out into the amorphous phase. The samples with 15% PI contain a small fraction of the crystalline Nylon-6 gamma* phase, which is related to hindered crystallization of the PA chains in the presence of PI. Analysis of the results of SAXS measurements shows that the structure of samples is most adequately described by a two-phase model with a crystalline phase of Nylon-6 and an amorphous phase comprising a mixture of PA and PI chains; Increased mechanical and thermal properties of the copolymers, as well as their high moisture resistance, can be explained using a concept of molecular composites comprising a flexible PA matrix reinforced by rigid PI fragments.

Structural transformations in ultra-high-molecular-weight polyethylene films, prepared from a reactor powder by cold pressing with shear, were studied by X-ray diffraction and DSC in the course of drawing, high-pressure annealing followed by drawing. The annealing under high pressure leads to samples with a highly crystalline structure, comprising large crystals with an average effective longitudinal size of up to 100 nm, and exhibiting high plasticity during the subsequent drawing. This behavior is related to a complicated morphology of the material: the high-pressure annealing induces epitaxial crystallization of a partial melt on the rigid PE fibrils containing chain-extended crystals, which results in the formation of a row texture. It is shown that mechanical properties of the final oriented material can be significantly modified by variation of the sample formation conditions.

Structure, properties, and deformation behavior of a high molecular weight propene-CO alternating copolymer (EIPCO 200) and ethene-CO/propene-CO terpolymers (EPEC I; E-CO = 47% and EPEC 2; E-CO = 69%) were investigated. The terpolymer with high molar ratio of ethene-CO to propene CO (EPEC I) is a typical thermoplastic and reveals relatively high crystallinity, while the terpolymer of Lower content of ethene-CO groups (EPEC I) and the propene-CO copolymer (EIPCO 200) exhibit elastomeric behavior. In spite of the possible random stereo- and regioregularity, the propene-CO chains crystallize with regular 3/1 chain conformation. According to X-ray data the synthesized terpolymers consist of blocks of propene-CO segments and blocks enriched with ethene-CO groups. The main structural changes at deformation were studied by means of X-ray diffraction and deformation calorimetry. It is established that the large reversible deformation of the samples studied is determined mostly by the amorphous regions. Deformation calorimetry results, treated according to the modern theory of thermoelasticty of rubber-like materials, showed that the energy contribution (Delta U/W)(V,T) and the temperature coefficient of the unperturbed dimension of chains d ln[r(2)](0)/dT are more negative than for PE and PP, which seems quite reasonable owing to the chemical structure of the 1,4-polyketone macromolecules.

Structural transformations in ultra-high-density polyethylene films, prepared from a reactive powder by cold pressing with shear, were studied by X-ray diffract-ion and DSC in the course of drawing or high-pressure annealing followed by drawing. The annealing under high pressure leads to samples having a highly crystalline structure, comprising coarse crystals with an average effective longitudinal size of up to 100 nm, exhibiting high plasticity during the subsequent drawing. This behavior is related to a complicated morphology of the material: the high-pressure annealing induces epitaxial crystallization of a partial melt on the rigid PE fibrils containing chain-extended crystals, which results in the formation of a row texture. It is shown that mechanical properties of the final oriented material can be significantly modified by variation of the sample formation conditions.

The supermolecular and crystal structure of poly(p-xylylene) films, obtained by pyrolytic polymerization of [2,2]-paracyclophane, was studied by X-ray diffraction. It was found that the degree of crystallinity and the type of texture of the poly(p-xylylene) films were determined by the temperature regime of film preparation. Under certain conditions, the resulting poly(p-xylylene) films have a highly regular structure, in which a high degree of crystallinity combines with a regular organization of the amorphous phase. Stretching of the films at 350 degrees C yields highly oriented samples with a degree of drawing up to 40. The oriented poly(p-xylylene) samples are characterized by high elastic modulus (90-100 kPa) and strength (up to 1.8 GPa). The orientational drawing leads to a transition of poly(p-xylylene) from alpha to beta modification with retained b-texture, which indicates that plastic deformation of the polymer does not involve melting. The oriented has a structure of the macroscopic single crystal type, with the crystallographic c-axis pointing in the direction of drawing, the b-axis being perpendicular to the film plane, and the a-axis parallel to the plane.