The influence of the weight-average molecular weight (Mw) on the structure–properties relationship was investigated by preparing high-density polyethylenes (HDPEs) of various Mw but constant polydispersity index (Mw/Mₙ) values. The thickness of the lamellar crystalline layer increased with increasing Mw, whereas the amorphous characteristics, such as the amorphous layer thickness and tie-molecule fraction, remained unchanged. The microscopic deformation of these HDPEs was investigated by in situ Raman spectroscopy. The orientation parameter ⟨P₂⟩ showed a power law to Mw with an exponent of −3/4 in the strain-hardening region. The Mw dependence of the molecular orientation was interpreted as the realignment of the lamellar cluster units, the size of which was determined by the end-to-end distance of the polymer chains in their melt state. It was found that higher stretching stress is applied to the crystalline chains for HDPEs of lower Mw, implying that a larger amount of taut-tie chains is formed.

Microstructural Interpretation of Influences of Molecular Weight on the Tensile Properties of High-Density Polyethylene Solids Using Rheo-Raman Spectroscopy

The IR-based method of infrared transition moment orientational analysis (IR-TMOA) is employed to unravel molecular order in thin layers of the semiconducting polymer poly[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenediimide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene) (P(NDI2OD-T2)). Structure-specific vibrational bands are analyzed in dependence on polarization and inclination of the sample with respect to the optical axis. By that the molecular order parameter tensor for the respective molecular moieties with regard to the sample coordinate system is deduced. Making use of the specificity of the IR spectral range, we are able to determine separately the orientation of atomistic planes defined through the naphthalenediimide (NDI) and bithiophene (T2) units relative to the substrate, and hence, relative to each other. A pronounced solvent effect is observed: While chlorobenzene causes the T2 planes to align preferentially parallel to the substrate at an angle of 29°, using a 1:1 chloronaphthalene:xylene mixture ...

https://pubs.acs.org/doi/pdf/10.1021/jacs.5b01755

Infrared Transition Moment Orientational Analysis on the Structural Organization of the Distinct Molecular Subunits in Thin Layers of a High Mobility n-Type Copolymer

Infrared transition moment orientational analysis (IR-TMOA), X-ray diffraction (XRD), and model calculations are combined to study interface and confinement induced order and orientation in thin (h ≈ 11 μm) films of poly(ϵ-caprolactone) (PCL), as prepared by drop-casting on silicon wafers. Depending on the crystallization temperature, 303 K ≤ Tx ≤ 333 K, nonbanded spherulites with a diameter of 1 μm ≤ dS ≤ 500 μm form. Macroscopic order of the crystalline lamellae is imposed by interfacial layers and geometrical confinements of the spherulitc structures (dS > h): radial crystal growth is restricted to a disc of aspect ratio dS/h. Order is quantified by IR-TMOA and XRD pole figure measurements, which both rely on the relative orientation of the sample and the incident radiation and measure, in the case of PCL, the orientation distribution of complementary crystal directions. This enables one to (1) correlate the directions of the transition moments with the crystal axes and (2) estimate the volume fraction...

/pdf/interface-and-confinement-induced-order-and-orientation-in-2umgcyl6jm.pdf

Interface and Confinement Induced Order and Orientation in Thin Films of Poly(ϵ-caprolactone)

We investigate the influence of the type of anti-adhesive films used in the production of polyethylene thin samples on their final chemical composition. For this purpose, LDPE and XLPE films were produced by compression molding at different temperatures and using two different polyethylene terephthalate (PET, Mylar) protective sheets, polyimide (Kapton) film and aluminum (Al) foil. These films were then investigated with Fourier Transform Infrared (FTIR) analysis. The influence of peroxide concentration in XLPE granules and of the production temperature protocol on the FTIR spectra of LDPE films were studied as well. From the results we conclude that the effects of the protective films should be considered when producing polymer samples for DC conduction experiments.

FTIR analysis of LDPE and XLPE thin samples pressed between different protective anti-adhesive films

Influence of shear processing on morphology orientation and mechanical properties of styrene butadiene triblock copolymers

IR transition moment orientational analysis on semi-crystalline polyethylene films

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IR transition moment orientational analysis on semi-crystalline polyethylene films