CH2 Sequences Research Articles

Polymorphism and Stretch-Induced Transformations of Sustainable Polyethylene-Like Materials.

Herein we demonstrate that polyethylene-like bioderived, biodegradable, and fully recyclable unbranched aliphatic polyesters, such as PE-2,18, develop hexagonal crystal structures upon quenching from the melt to temperatures <∼50 °C and orthorhombic-like packing at higher quenching temperatures or after isothermal crystallization. Both crystal types are layered. While all-trans CH2 packing characterizes the structure of the orthorhombic-like form, there is significant conformational disorder in the staggered long CH2 sequences of the hexagonal crystals. On heating, the hexagonal crystals transform to the orthorhombic type at ∼60 °C via melt recrystallization, but no change is apparent during heating samples with the orthorhombic form up to the melting point (∼95 °C). The hexagonal structure is of interest not only because it develops under very rapid quenching from the melt but also because under uniaxial tensile deformation it undergoes a stretch-induced transformation to the orthorhombic structure. Compared to deformation of orthorhombic specimens that maintain the same crystal type, such transformation results in larger strains and enhanced strain hardening, thus representing a desired toughening mechanism for this type of polyethylene-like materials.

Use of SSA to detect structural changes in metallocenic ethylene/α-olefin copolymers and their free radical post-reactor modifications

The successive self nucleation and annealing (SSA) methodology has been shown to be successful to characterize the lamellae structure of many polyolefins. The differences in molecular structure of metallocenic α-olefin copolymers with varied comonomer type and content were characterized by this technique with a conventional DSC. This thermo-structural characterization process was also applied to analyze the changes induced on a 1-octadecene - ethylene copolymer modified with different post-reactor methods: several doses of gamma-radiation, peroxide modification and oxidative degradation. These modifications induced crosslinking and branching on the original copolymer affecting its molecular weight and the crystalline structure. The SSA technique revealed detailed changes in the lamellae formation of the materials obtained as a consequence of the different methods of modification employed in this work. Mainly, crosslinking and branching sites restrained the mobility and length of CH2 sequences to form lamellae, while degradation led to preferential chain scission at branched carbons making easier the formation of higher melting temperature lamellae.

Kinetic Control of Chlorine Packing in Crystals of a Precisely Substituted Polyethylene. Toward Advanced Polyolefin Materials

The crystallization of a polyethylene with precise chlorine substitution on each and every 15th backbone carbon displays a drastic change in crystalline structure in a narrow interval of crystallization temperatures. The structural change occurs within one degree of undercooling and is accompanied by a sharp increase in melting temperature, a change in WAXD patterns, and a dramatic increase in TG conformers around the Cl substitution while the main CH2 sequence remains with the all-trans packing. These changes correlate with the formation of two different polymorphs characterized by a different packing and distribution of Cl atoms in the crystallites. Under fast crystallization kinetics, the chains assemble in an all-trans planar packing (form I) with a layered Cl distribution that presents some longitudinal disorder, while slower crystallization rates favor a more structured intermolecular halogen staggering consistent with a herringbone-like nonplanar structure (form II). The drastic change in morpholog...

A Raman study of nylon 6 annealed under high pressure

AbstractUsing a cubic-anvil high pressure apparatus, nylon 6 samples were annealed under 400 MPa to 1.5 GPa. The structure changes of nylon 6 are studied by the methods of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and Raman spectra. Compared with sample prepared at ambient pressure, high pressure treatment makes the hydrogen-bonded sheets pack more closely and thus enhanced CH2 vibration out of the hydrogen-bonded sheets. After high pressure treatment, it is observed that all changes of C-C related vibration modes in nylon 6 are similar with ones in nylon series when the CH2 sequence number increased, from which it is deduced that high pressure treatment reduces the effects of amide group on the chain conformation of nylon 6.

Changes in structural characteristics of LLDPE functionalized with DEM using gamma-irradiation

This work studies the structural changes produced by gamma-radiation as a source of free radicals for functionalizing linear low-density polyethylene (LLDPE) with diethyl maleate (DEM). The grafting of the DEM onto the LLDPE was carried out in solution using gamma-rays from a 60Co source in air at room temperature, at a dose rate of 4.8 kGy/h and absorbed doses ranging from 15 to 400 kGy. The increase in the dose produced a higher concentration of free radicals and hence a higher grafting degree. The effects of DEM concentration are only perceptible at absorbed doses higher than 50 kGy. For a concentration of 30% DEM, the functionalization degrees ranged from 0.04 to 0.44 mol%. The use of gamma radiation modifies the structural and physical characteristics of the functionalized polyethylene with respect to the unmodified one, because, depending on the dose, the effects of gamma-rays can lead to crosslinking of materials with decreased flowability. The effects of gamma-radiation onto the molecular structure and molecular weight distribution of LLDPE are mitigated by the presence of DEM, due to the competition with the chain scission, branching and crosslinking reactions, for the consumption of the free radicals. The results provided by applying the successive self-nucleation and annealing technique allow reaching an unequivocal conclusion: that the free radicals formed by gamma radiation for the DEM insertion and main chain modifications are preferentially generated in the secondary carbons of the more regular CH2 sequences. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Facies analysis and palaeoenvironmental interpretation of the Late Oligocene Attard Member (Lower Coralline Limestone Formation), Malta

AbstractThe Oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale. So far, few studies have considered the impact that these early reefs had on ramp development. Consequently, this study aimed at presenting a high‐resolution analysis of the Attard Member of the Lower Coralline Limestone Formation (Late Oligocene, Malta) in order to decipher the internal and external factors controlling the architecture of a typical Late Oligocene platform. Excellent exposures of the Lower Coralline Limestone Formation occurring along continuous outcrops adjacent to the Victoria Lines Fault reveal in detail the three‐dimensional distribution of the reef‐associated facies. A total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp. The inner ramp was characterized by a very high‐energy, shallow‐water setting, influenced by tide and wave processes. This setting passed downslope into an inner‐ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals. The middle ramp lithofacies were deposited in the oligophotic zone, the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents. Compositional characteristics and facies distributions of the Attard ramp are more similar to the Miocene ramps than to those of the Eocene. An important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone. This expansion may have commenced in the Late Oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies. Stacking‐pattern analysis shows that the depositional units (parasequences) at the study section are arranged into transgressive–regressive facies cycles. This cyclicity is superimposed on the overall regressive phase recorded by the Attard succession. Furthermore, a minor highstand (correlated with the Ru4/Ch1 sequence) and subsequent minor lowstand (Ch2 sequence) have been recognized. The biota assemblages of the Attard Member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions. The apparent low capacity of corals to form wave‐resistant reef structures is considered to have been a significant factor affecting substrate stability at this time. The resulting lack of resistant mid‐ramp reef frameworks left this zone exposed to wave and storm activity, thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths.

Molecular Dynamics Simulations of a Main-Chain Liquid Crystalline Polyether in the Crystalline State. 1. Chain Conformation and Dynamics of the Spacer Methylene Sequences

Molecular dynamics simulations have been performed for the main-chain thermotropic liquid crystalline polyether (EDMB-10), which is composed of the 3,3′-dimethyl-4,4′-biphenylene mesogens and 10-methylene spacers, in order to compare the spacer conformation and dynamics with those revealed by solid-state 13C NMR spectroscopy. A three-dimensional periodic cell that contains 4 or 16 molecular chains composed of four mesogen and five spacer units are employed, the central CH2 sequences of the five spacer sequences being focused on for four chains in the 4-chain model or for the central four chains in the 16-chain model. For both models, the initial structure stays unchanged below 150 K. At 200 K, three dimensional structure begins to change and the molecular arrangement and the cell parameters are finally varied without any significant change in conformation. Below 250 K the torsion angles of the O–CH2 bonds at the spacer ends are ±90° and all the C–C bonds adopt the trans conformation for both structural models. At 300 K, the O–CH2 bond and its second neighboring C–C bond are found to undergo the cooperative counter rotation of ±90°tt↔ttg± keep the periodic length between the neighboring mesogen units along the chain almost constant. At 450 K, the CH2 sequences start to adopt a conformational pair of g+tg−, which is frequently called the 2g1 kink, for the 4-chain model, but the introductions of the kinks are restricted to the alternate four C–C bonds. This result is qualitatively in good accord with the result previously obtained for EDMB-10 by the solid-state 13C NMR analysis, but the t/g probabilities at the alternate C–C bonds for the simulations significantly disagree with the experimental results. In contrast, for the 16-chain model, a pair of the g+ and g− conformations are allowed to introduce to the alternate four C–C bonds at almost equal probabilities without any restriction of the forms of the kinks, resulting in the good qualitative and quantitative agreements with the experimental results. The time evolution of the torsion angles for the respective C–C bonds of the spacer CH2 sequences are also described for the 16-chain model to reveal cooperative conformational transitions.

Near-Infrared Combination and Overtone Bands of the CH2 Sequence in CH2X2, CH2XCHX2, and CH3(CH2)5CH3 and Their Characteristic Frequency Zones

We characterized near-infrared spectra of the CH2 sequence in CH2X2 (X=halogen), CH2ClCHCl2, and CH3(CH2)5CH3. Each near-infrared absorption in the region from 3500 to 10,000 cm-1 is consistently assigned to one of the five different combination or overtone groups, in the order of increasing frequency, of the {[v(CH)]+[delta(CH)]} (A), {[v(CH)]+[2delta(CH)]} (B), [2v(CH)] (C), {[2v(CH)]+[delta(CH)]} (D), and [3v(CH)] (E) types, where v(CH) and delta(CH) denote the CH stretching and CH deformation normal modes, respectively. Each group has its own characteristic frequency zone. The bands of B, D, and E, which are second-order combinations or overtones, are weaker by 1/10-1/50 than those of A and C, which are first-order combinations or overtones. The near-infrared spectra of the CH2 sequence show "window zones" of very weak or no absorptions. This suggests that we can perceive the characteristic near-infrared bands of a functional group through the window zones, and we give an example to demonstrate this. The first-order combination bands of type A only of CH2X2 are reasonably assigned to a pair of the normal modes of v(CH) and delta(CH). From this we predict that the first-order combination bands should give structural information on the CH2 chain, similar to the infrared fundamental bands.

The glass transition of polymer crystals

The statement: “A solid is a condensed phase at a temperature below its glass transition”, is an operational definition. It leads to the corollary that for crystals to be solid, they must be below their glass transition. In this paper evidence for the usefulness of this definition is presented. It is based on the measurement of the glass transition of crystals in the presence of melting and crystallization. The experimental tool is temperature-modulated differential scanning calorimetry, TMDSC, which enables the measurement of heat capacity in the presence of irreversible latent heat of melting and crystallization. Not only is the expected change of the heat capacity during the first-order phase transition identified, but it was also discovered that in some flexible polymer crystals the glass transition of the crystal can occur at a lower temperature than the order/disorder process without a change in crystal structure. Typical examples for such behavior are seen in poly(oxyethylene), poly(oxytetramethylene), aliphatic nylons, and most likely also in polyesters, polyurethanes, and polymers with other functional groups, separated by longer CH 2-sequences. Such order/disorder transitions above the vitrification to a solid are well-known for the mesophases described as liquid crystals, plastic crystals, and condis crystals of small and large molecules, attesting for the universality of the operational definition.

Introduction of amino functionalities on ethylene-co-tetrafluoroethylene film surfaces by NH3 plasmas

In order to form active sites for grafting amino groups, a predominant elimination of fluorine atoms from fluoropolymers such as poly(tetrafluoroethylene), ethylene-co-tetrafluoroethylene co-polymer (ETFE) and poly(vinylidene fluoride) was carried out using the plasma irradiation technique, and the possibility that amino functional groups could be formed on the fluoropolymer surfaces was investigated. The NH3 plasma irradiation led to considerable elimination of fluorine atoms from the fluoropolymers, as well as grafting of nitrogen functionalities. The formation of nitrogen-containing groups was strongly influenced by the magnitude of the W/FM parameter, and the NH3 plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable for the surface modification process. XPS spectra for the NH3 plasma-modified surfaces showed that the NH3 plasma attacked predominantly CF2—CF2 sequences rather than CH2—CH2 sequences in the ETFE polymer. The primary amino groups formed on the ETFE film surfaces were determined by fluorescence measurements. The concentration of the amino groups formed on the surfaces was not constant but varied according to the W/FM parameter. NH3 plasma operated at a low W/FM parameter of 79 MJ/kg was found to be preferable in grafting amino groups on the ETFE film surfaces.

Crystalline transition of polyamide‐10,20 investigated by in situ Fourier transform infrared spectroscopy

AbstractReal‐time Fourier transform infrared spectroscopy was used to investigate the crystalline transition of even–even polyamide‐10,20. During the crystalline transition, the intensity of the hydrogen bonds became weak, the twisting of the CCO and CN bonds improved, and the gauche conformation of the CH2 sequences increased, along with the strengthening of the vibration of the methylene units. The ordered stacking of methylene segments with the trans‐zigzag conformation gradually became disordered by the insertion of the gauche conformation upon heating. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4017–4022, 2004

Studies of the Phase Transitions, Structure, and Dynamics for Main-Chain Thermotropic Liquid Crystalline Polyethers and Polyurethanes with the Same Mesogen and Spacer Units

Phase transition behavior, structure, and dynamics have been investigated for main-chain thermotropic liquid crystalline polyethers (EDMB-10) and polyurethanes (UDMB-10) with the same mesogen and spacer units by mainly using DSC and solid-state 13C NMR spectroscopy. The liquid crystallization temperature (Tlc), which corresponds to the isotropic melt → nematic phase transition temperature determined by DSC, is found to stay almost constant irrespective of the cooling rate from the isotropic melt for EDMB-10 while the crystallization temperature (Tc) greatly decreases with increasing cooling rate. This fact leads to the preparation of the liquid crystalline glass by quenching from the isotropic melt to ice−water. In contrast, Tlc and Tc for UDMB-10 are observed as an overlapped single exothermic peak in DSC, and both temperatures are found to significantly depend on the cooling rate. This fact suggests that somewhat larger-scale reorientation of the mesogen and spacer units, which may result in the formation of segmental assemblies through intermolecular hydrogen bonding, are inevitable for the liquid crystallization from the isotropic melt in the case of UDMB-10. The CSA spectra of the respective carbons for the mesogen and spacer units, which were successfully measured by the MAT method, have been elucidated in detail to characterize molecular motion of the constituent units in the EDMB-10 and UDMB-10 samples that were crystallized from the isotropic melt through the nematic phase: The mesogen units are found to be in the rigid state or undergo restricted fluctuation with amplitudes less than ±20° in the crystalline and noncrystalline regions for both samples. In contrast, the CH2 sequences are subjected to much enhanced motion such as cooperative t−g exchanges or the thermal fluctuation around chain axis with the planar zigzag conformation in the crystalline region for EDMB-10 or UDMB-10, respectively. Interestingly, similar cooperative t−g exchange motion is also allowed to occur for the noncrystalline CH2 sequences in UDMB-10 whereas the corresponding CH2 units adopt random conformation in EDMB-10. On the basis of these experimental results, the structural models have been proposed for the nematic phase in EDMB-10 and UDMB-10.

Solid-State 13C and 15N NMR Analyses of Structure and Dynamics of Spacer Methylene Sequences and Mesogen Groups for Liquid Crystalline Polyurethanes with Different Spacer Lengths

Solid-state 13C NMR analyses of the structure and dynamics have been performed for liquid crystalline polyurethanes with different spacer CH2 lengths, which were polymerized from 3,3‘-dimethyl-4,4‘-biphenyldiyl diisocyanate, α,ω-alkanediols having various even numbers m of carbons, and 1-hexanol. Each sample was crystallized by cooling from the melt through the liquid crystalline phase at an appropriate cooling rate depending on its phase transition behavior detected by DSC. 13C spin−lattice relaxation analyses have revealed that each CH2 carbon resonance line contains three components with different T1C values which are assigned to the crystalline, medium, and noncrystalline (supercooled liquid crystalline) components. For the polyurethane samples with m = 8 and 12, it has been found that the spacer CH2 sequences for the noncrystalline component will adopt the alternate trans (t) and trans−gauche exchange (x) conformation in the central part whereas those of the crystalline and medium components may be in the all-trans conformation. Accordingly, the conformation of the spacer CH2 sequences can be generally expressed as ttx(tx)𝓁 tt (𝓁 = m/2 − 3) for 8 ≤ m ≤ 12, including the result for m = 10 reported previously. Furthermore, to examine molecular motion of the mesogen units in detail, 13C CSA spectra have been measured at room temperature for the mesogen carbons by 2D SASS 13C NMR spectroscopy and compared with those simulated by using the two-site exchange model for the flip motions of the phenylene group. As a result, it has been suggested that flip angles of fluctuations around the phenylene axis may be limited to less than about 20° without any 180° flip motion in all components, including the supercooled liquid crystalline component. Natural abundant CP/MAS 15N NMR measurements also suggest that such rigidity of the mesogen groups may be due to the formation of intermolecular hydrogen bonding between NH and CO groups, and resulting segmental assemblies will induce the characteristic spacer conformation in the supercooled liquid crystalline component.

Chain Conformation of Spacer Methylene Sequences for a Liquid Crystalline Polyether As Revealed by Solid-State 13C NMR Spectroscopy

Solid-state 13C NMR analyses of the structure and chain conformation have been carried out mainly at room temperature for a main-chain thermotropic liquid crystalline polyether which was newly polymerized from 3,3‘-dimethyl-4,4‘-dihydroxybiphenyl and 1,10-dibromodecane by using a phase transfer catalyst. This sample was crystallized by cooling from the melt through the nematic liquid crystalline state. Differential scanning calorimetry measurements and polarizing optical microscopic observations have confirmed that the nematic liquid crystalline phase appears in both heating and cooling processes. 13C spin−lattice relaxation analyses have revealed that there exist three components with different T1C values, which correspond to the crystalline, medium, and noncrystalline (supercooled liquid crystalline) components. By employing the difference in T1C, the spectrum of each component is separately recorded, and the conformation of the CH2 sequence is evaluated by considering the γ-gauche effect on the 13C chemical shifts. As a result, the crystalline component is found to adopt the alternate trans (t) and trans−gauche exchange (x) conformation (txtxtxtxt), in good accord with the result separately obtained by the molecular dynamics simulation. In contrast, all the C−C bonds of the CH2 sequence for the noncrystalline component are in the rapid trans−gauche exchange conformation (xxxxxxxxx), reflecting the same conformation in the liquid crystalline phase or at the melt.

PFab-CMV, a single vector system for the rapid conversion of recombinant Fabs into whole IgG1 antibodies

We have constructed a single vector system for the rapid conversion of recombinant Fabs into whole IgG1 antibodies and their expression in eukaryotic cells. This vector, named pFab-CMV, utilizes the same unique cloning sites present on the pComb3 phagemid thus allowing for the direct subcloning of light chains and heavy chain Fd regions. pFab-CMV also allows for the expression of recombinant Fabs in eukaryotic cells by removal of a cassette containing part of the hinge, CH2 and CH3 sequences. Stable cell lines are rapidly obtained with pFab-CMV by NEO selection without the need for co-transfection of heavy and light chain expressing vectors.

NMR molecular characterization of lubricating base oils: Correlation with their performance

The NMR technique was used to characterize some base oils of different nature (mineral, saturated polyolefins, hydrocracked and from waxes hydroisomerization) at the molecular level. Base oils are used in the formulation of lubricants with the addition of suitable additives which improve the final products performance. The studied base oils are used particularly in the formulation of engine oils. In this paper we have compared two “NMR editing” techniques which allow one to quantify the CHn (n = 0−3) fractions of an “average” base oil molecule: 1) the gated spin echo (GASPE) and 2) the distortionless enhancement by polarization transfer (DEPT). We found that the quantitative data obtained from GASPE have a better accuracy than those from DEPT and so we chose GASPE to study the molecular characteristics of the aliphatic moieties of the base oils. On the basis of the GASPE data and of the average molecular mass obtained via VPO (Vapor Pressure Osmometry), the average number of branches and aliphatic rings were calculated. Moreover, on the basis of GASPE the distribution of side chain lengths and the positions of the methyl groups along the straight chain (methyls are the only groups for which the positions are directly obtained from NMR spectra) were obtained. A confirmation of the reliability of the NMR approach was achieved by comparing the branching degree, found with the NMR approach, of some base oils with their heats of fusion measured with the Differential Scanning Calorimetry (DSC). The heats of fusion are expected to be directly related to the length of straight CH2 sequence and therefore to be lower for more branched molecules. We found that for base oils with similar aliphatic moieties, the heats of fusion are lower for more branched base oil molecules with a nearly linear correlation. The exception to this rule is represented by the two olefinic oils. Besides, we found that the fraction of the methyls on aliphatic chains longer than three carbons, determined with GASPE, correlates very well with the pour points values, with the only exception of the mineral oil.

The melting points of chain polymers

The molecular characteristics which determine the melting points of high polymer crystals are considered, and it is shown that the properties of monomeric crystals often throw light on those of the polymers. The principal factors controlling melting points appear to be molar cohesion energy (of the whole molecule for monomers, or per chain unit for polymers), molecular flexibility (due to rotation round bonds), and molecular shape effects. Figures for the cohesion energy increments of a number of chain units and substituent groups are given, and melting points of polymer series are correlated with cohesion energy per chain unit. The flexibility factor is less easy to assess; barriers to rotation in appropriate monomer molecules are relevant, but available data are very rough. The approach therefore is mainly by empirical and comparative methods. When plotted against cohesion energy per chain unit, the melting points of various series of aromatic polyesters and polyurethans fall within the same band, while those of the polyamides lie on the whole higher and those of the aliphatic polyesters, polyethers, polythioethers and polydisulfides much lower. The differences are attributed to difference of molecular flexibility arising from the presence of easily rotating OC, SC and SS bonds. The low melting points of rubber and other unsaturated polymers are attributed to the fact (which can now be regarded as definitely established by independent evidence) that rotation round single bonds which are adjacent to double CC bonds is easier than in saturated chains. Easily rotating bonds which are inclined to each other, as in cis isomers, confer greater chain flexibility than the parallel bonds in trans isomers, and thus lead to lower melting points. The marked odd-even effects in saturated molecules which run through the whole of organic chemistry (the even members always melting higher than the odd) are attributed to similar effects arising from the fact that the end bonds of an odd CH2 sequence are inclined to each other while those at the ends of an even sequence are parallel.

α Heavy chain disease αmRNA contain nucleotide sequences of unknown origins

Human alpha heavy chain disease is characterized by the production of abnormally short alpha IgH chains. In previously published cases it has been found that the malignant cells produce abnormal alpha mRNA, lacking VH and CH1 sequences and composed of a leader sequence peptide, sequences of variable length (69 to 84 bp) and of unknown origin, followed by normal CH2 and CH3 sequences. In this study we established the nucleotide sequence of alpha mRNA for six cases of alpha heavy chain disease. We observed that all six alpha mRNA lack the VH and CH1 sequences as do those previously described. They also contain in-frame inserts of unknown origin between the leader peptide and the normal CH2 and CH3 coding sequences. These inserts are of variable length (42 to 105 bp) and they are unrelated. These results suggest the existence of a common mechanism defect leading to deletions/insertions in alpha heavy chain disease rather than a specific interaction between alpha 1 IgH gene with a unique defined molecular species.

Miscibility of linear and branched polyethylene in the liquid state

AbstractHDPE/LDPE blends and the pure components were crosslinked either by irradiation or by di‐tert‐butyl peroxide in the liquid state. The degree of crosslinkage was characterized by the reciprocal degree of swelling Q−1 (xylene, 2 h, 140°C). Above a critical degree of crosslinkage corresponding to Q−1 = 0,2 the DSC curves of HDPE/LDPE blends show only one single crystallization peak on cooling from the melt and only one single melting peak on subsequent heating. This is an unequivocal proof for the single phase structure of HDPE/LDPE blends in the liquid state. Crosslinking with Q−1 ≥ 0,2 prohibits fractional crystallization and forces the unbranched CH2 sequences of both components between the crosslinks into one crystal lattice.

Dynamic mechanical properties of methacrylic-acid-grafted polyethylene films

A dynamical mechanical relaxation study has been made of low density polyethylene films to which methacrylic acid has been grafted by γ irradiation. The grafted films retain the original degree of crystallinity and show only slight changes in melting points and melt viscosities. This indicates that the grafted methacrylic acid side chains are long, few in number, and completely phase separated from the polyethylene matrix. Three dispersion regions are observed in plots of the loss modulus, E″ vs. temperature at constant frequency and these are labeled γ, β, α′, in order of increasing temperature. The α′ peak, above 215°C was assigned to microbrownian segmental motions accompanying the Tg of polymethacrylic acid. The β peak, at −20°C, was assigned to motions accompanying the Tg of branched polyethylene, and the γ peak, at −120°C, was assigned to local motions of a few CH2 sequences in polyethylene.