ABSTRACT:Three types of semicrystalline ultra high molecular weight polyethylene, obtained with amorphous SiO 2 -supported Ziegler-Natta catalyst systems modified by vanadium and titanium, have been studied by wide angle XRay scattering, dynamic mechanical thermal analysis and microhardness methods. In all the cases a significant amount of monoclinic modification is observed, which is estimated to be of the order of 10%. With increasing the degree of crystallinity and quantity of entanglements, storage modulus and α relaxation increase and γ relaxation decreases. A weak β relaxation occurs only in the sample obtained with vanadium catalytic systems. Microhardness measurements give the possibility of distinguishing the effect of crystallinity from the effect of entanglements: Vickers microhardness is sensitive predominately to crystalline phase, while total microhardness is sensitive also to the structural peculiarities in the amorphous phase.KEY WORDS Ultrahigh Molecular Weight Polyethylene (UHMWPE) / Dynamic Mechanical Thermal Analysis (DMTA) / Wide-Angle X-Ray Diffraction (WAXS) / Microhardness / Ultrahigh Molecular Weight Polyethylene (UHMWPE) (M>10 6 ) possesses excellent mechanical properties and some advantages over conventional polyolefins as a high level of durability, excellent creep characteristics and abrasion resistance. [1][2][3][4][5] For this reason it is used in demanding applications such as artificial hip and knee joints, machine parts, fibres, polymer coating on metal surface, separators, acoustic diaphragms, etc.It is established that this semicrystallyne polymer has a specific morphology. There are many reports concerning the structure of nascent 6 and differently processed UHMWPE samples. 3,[7][8][9] The occurrence of polymorphism 3, 7, 10-12 is characteristic for crystal part, the orthorhombic crystals lattice being the most typical. It was established that the crystal lamellae in both nascent and processed unoriented UHMWPE have similar dimensions, close to 20 nm on average. 6 This thickness could be varied from 10 nm after necking 13 up to 100 nm in highly oriented fibres. 8 There are reported some cases where a part of the typical, stable and prevailing orthorhombic crystals could be transformed into a monoclinic or transient hexagonal phase. 3, 7-11, 14, 15 Thus, monoclinic crystals are observed in highly deformed samples (fibers) 7-10 or in the samples crystallized under stress. 16 Moreover, there are experimental results showing that polyethylene crystals transform from the stable orthorhombic crystal into a transient hexagonal phase, observed when the polymer is subjected to the action of fast electrons 14 or at high pressure and temperature. 3,15 Since the chain mobility is rather high in the hexagonal phase, sintering has been achieved via this transient phase. 3 There were found reports concerning to the study of the amorphous phase by NMR 8 and by positron annihilation lifetime spectroscopy. 17 It was reported a 5% of disordered all-trans interfacial material and/or tie molecu...

ABSTRACT:The correlation between the modulus of elasticity, on the one side, and Vickers microhardness and total microhardness, on the other side, was analyzed in the case of ultrahigh molecular weight polyethylenes. An extension of the application of the power relation between microhardness and the modulus (MH ϭ aE b ) obtained by different methods was suggested. A linear dependence between constants obtained by Vickers and total microhardness measurements and other different techniques of modulus measurement was established, which signifies that both microhardness characteristics change their sensitivity toward the modulus in a similar way.

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The molecular dynamics of new poly (ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers (DL/CL/PAC) has been investigated by using dynamic mechanical thermal analysis (DMTA) and dielectric relaxation spectroscopy (DRS) measurements. The copolymers were synthesized via anionic polymerization of relevant lactams activated with carbamoyl derivatives of telechelic hydroxyl terminated polypropylene oxide with isophorone diisocyanate (PAC). The calorimetric, X‐ray diffraction, and DMTA measurements were performed to recognize the influence of the composition ratio and the type of PAC on the physical, thermal, and mechanical properties of the synthesized copolymers. The DRS was used to study the frequency dependence of the dielectric permittivity of some isotherms from −110 to 145 °C. Copolymerization of ε‐caprolactam with about 10 wt % ω‐dodecalactam results in a copolymer that has lower water absorption, a melting point close to that of polyamide 6 and has a high enough degree of crystallinity in respect to high storage modulus. Five dielectric relaxations have been observed in the dielectric spectra, three at lower temperature and two at higher temperature. The copolymers have two glass transition temperatures for polyamide segments and polyether blocks, indicating microphase separation in the copolymers. Other studies directed toward molecular dynamics of polyamide DL/CL/PAC copolymers have not been reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

The positron annihilation lifetime technique has been used to study the structure of three types of ultrahigh molecular weight polyethylene, obtained via different supported catalyst systems and hence having different molecular weights and degree of crystallinity. Pores with two different mean radii, about 1.8 Å and 3.3 Å, were observed in the studied samples. A comparison between positron annihilation and wide angle X‐ray scattering and microhardness measurements has been made. There are evidences that crystalline phase contributes to o‐Ps formation. The existence of a shorter long‐lived component τ3 is explained by the latter fact.

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