Fine structure of polyethylene prepared by γ-ray-induced polymerization in various solvents. III. Selective degradation with ozone

Ozone-degradation products of polyethylenes prepared by γ-ray-Induced polymerization in ethyl alcohol, t-butyl alcohol, and 2,2,5-trimethylhexane were analyzed by gel permeation chromatography (GPC). The ozonized polymers show two discrete peaks in the GPC traces, and the ratio of molecular weights corresponding to the peaks is close to 1:2, suggesting that these polymers are composed of folded-chain crystals similar to solution-grown single crystals. The peak profiles, however, are broad and the peaks in the chromatograms shift concertedly toward lower molecular weight in the course of degradation. These findings suggest that the fold surfaces of the polymers are coarse and that there is no unique crystalline core containing a regularly folded layer. The long period estimated from small-angle x-ray measurements increases with increasing polymerization temperature, but scarcely varies with the solvent type. This implies that when crystallization occurs during polymerization, kinetic factors may have no great effect on crystallization.     

Gel permeation chromatographic studies of the degradation of polyethylene with fuming nitric acid. I. Single crystals

This paper describes the application of gel permeation chromatography to the morphology of polymer single crystals. Various types of single crystals of polyethylene were etched with fuming nitric acid, and the molecular weight distributions of the degraded fragments determined. The crystal preparations studied were monolayer crystals grown from xylene solution at 85°C and multilayer crystals grown at 84°C and 70°C. In all cases peaks in the molecular weight distribution were observed corresponding to single and double transverses of the molecular chains through the lamellae. By using the chromatograph calibration described in a previous paper, the position of these peaks were compared and correlated with previous estimates of lamellar thickness from low-angle x-ray measurements. The relative positions of the peaks provide information regarding the nature of the fold surface. The results are found to be consistent with a model in which the majority of the molecules are tightly folded.     

Effect of polymerization temperature on the original morphology of polyethylene prepared by γ-ray-induced polymerization

Polyethylene was prepared by γ-ray-induced polymerization in the temperature range 0–180°C. The morphology and the physical properties of the polymer as polymerized were studied by electron microscopy, differential scanning calorimetry, and gel permeation chromatography. Aggregates of small lamellar crystals with irregularly growing faces were produced below 55°C. Aggregates of large spherical particles were formed above 60°C together with hemispherical particles which adhered to the substrate. A few lamellar crystals of triangular or amoeba-like shapes were also found above 55°C. The polymers formed below 55°C showed a sharp single endothermic DSC peak and a bimodal molecular-weight distribution, while the sample above 60°C had a double endotherm and a unimodal molecular-weight distribution. These facts suggest that the mechanism of crystallization during polymerization below 55°C is different from that above 60°C. The melting point, however, decreased continuously with increasing polymerization temperature and was much lower than that of extended-chain crystals. The results show that the polyethylene, as polymerized, is composed of folded-chain crystals irrespective of the reaction temperature.     

Evaluation of field desorption mass spectrometry for the analysis of polyethylene

Field desorption mass spectrometry (FD-MS) has been evaluated for the analysis of low molecular weight polyethylene by using samples in the molecular weight range 600–2000 u as determined by gel permeation chromatography. The repeat units and end groups were characterized by FD-MS, but it was demonstrated that accurate molecular weight distribution data cannot be obtained for polyethylene by FD-MS because there is mass discrimination against the higher molecular weight polymers.     

Crystallinity and the effect of ionizing radiation in polyethylene. IV. Effect of segregation of low molecular weight chains on determination of main-chain scission in linear polyethylene

Different single crystal preparations of polyethylene with (unfractionated) and without (partially fractionated) low molecular weight chains were irradiated at room temperature. G(crosslink) was determined from the gel point. It is shown that in addition to the molecular weight and molecular weight distribution of polymers, G(crosslink) is determined by three more parameters: thickness of crystalline core, amount of amorphous surface layer, and degree of interlamellar contact. Unlike unfractionated polyethylene, partially fractionated polyethylene showed almost 100% gel at about 250 Mrad. To obtain the same amount of gel, unfractionated polyethylene required a much higher dose than that required by partially fractionated polyethylene. Molecular weight distribution of sol fractions of unfractionated and partially fractionated polyethylene was studied by gel permeation chromatography (GPC) and the solubility data analyzed by Charlesby–Pinner plots. It has been shown that the unattainability of 100% gel from unfractionated polyethylene is due to segregation of low molecular weight chains during crystallization which need very high doses for complete gelation.     

The morphology of ultradrawn polyethylene. I. Nitric acid etching plus gel permeation chromatography

Transparent strands of high-density polyethylene of unusually high c-axis orientation have been produced by a solid-state extrusion, involving pressure, temperature, and deformation, in an Instron capillary rheometer. Measured values for tensile modulus are higher than previously reported for any polyolefin. Previous modulus and electron microscopic data are consistent with a strand morphology comprised (≤20%) of of extended chain crystals. The remainder resembles an oriented fibrillar morphology such as found in highly drawn polyethylene. In the present study, fuming nitric acid etching of the ultraoriented strands, in combination with gel permeation chromatography (GPC), has provided incisive structural information. The strands exhibit ≥3X the resistance to acid degradation shown by conventionally drawn polyethylene. GPC molecular weight distributions (MWD) of etched samples show a single broad peak with a prominent high molecular weight tail. The crystal size, represented by the MWD, is in agreement with the crystal long period determined by small-angle x-ray scattering. The absence of multiple peaks in the etched MWD's is evidence of limited chain folding. The extended chain content, determined from the etched MWD's, is a strong function of strand formation temperature and is in agreement with the fraction of extended chains calculated from modulus measurements.     

Gel permeation chromatography of branched polyethylene

The effect of long-chain branching must be considered in gel permeation chromatography to evaluate the molecular weight polydispersity of branched polyethylenes. Osmotic molecular weights of fractions of branched polyethylene were correlated with elution volumes; weight-average and number-average molecular weights of a branched polyethylene were determined. Molecular weight changes on crosslinking polyethylene by ionizing radiation are accompanied by branching and cannot be simply interpreted by gel permeation chromatography.     

Gel Permeation Chromatography of Polymers from Wood

Abstract

Polymers from wood, including cellulose via the methylol derivative, are soluble in dimethyl sulfoxide (DMSO). To perform gel permeation chromatography of these high polymers, a packing material was sought which combined adequate pore size with stability in DMSO. Contrary to recommended practice, it was discovered that gel permeation chromatography in DMSO can be performed on prepacked, high-performance columns of μ-Styragel without adverse effects from bead swelling. When using the methylol derivative of cellulose, it is necessary to freeze dry the reaction mixture to obtain a product which gives reproducible results from gel permeation chromatography.     

Structural studies of ultrahigh-modulus polyethylene using nitric acid etching and gel permeation chromatography. II. Influence of polymer molecular weight,draw temperature,and annealing

The technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh-modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lengths less that 500 Å. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small-angle x-ray scattering. Possible reasons for these discrepancies are discussed.     

Polymer studies by gel permeation chromatography

Samples of polystyrene and poly(methyl methacrylate) have been prepared by bulk polymerization under conditions previously investigated in the literature. The molecular weight distributions were determined for early-conversion samples by gel permeation chromatography, and the experimental distribution curves were compared with calculated curves based on kinetic data. The agreement between the experimental and calculated curves was such as to indicate the utility of gel permeation chromatography in the investigation of polymer reaction kinetics and mechanisms.     

Investigation of the fold-surface problem in polyethylene single crystals with the nitric acid oxidation technique

Single-crystal preparations of polyethylene were treated with the selective oxidizing agent, fuming nitric acid. The degraded products were examined as regards layer thickness (by low-angle x-ray studies), chemical and weight changes, recrystallization and annealing treatments, and by broadline NMR, as part of a systematic investigation aimed at clarifying the nature of disordered material in single crystals. It emerges that there is a disordered-mobile region along the fold surface of the crystals in agreement with other parallel works along similar lines. In a more detailed analysis we can now decompose the nitric acid attack into components affecting the basal and side surfaces, respectively. Taking into account the recrystallization–annealing observations, we infer that the fold surface is heterogeneous with folds of more than one kind. These results were combined with a preliminary molecular weight distribution study by gel permeation chromatography. Taking into account all the available evidence, we are led to suggest a composite structure where surface looseness, coresponding to long loops and hairs, is superimposed on the more regular folded surface. This model is in the process of being tested. The problems concerning the assignment of a value to the amount of surface looseness are being discussed. In addition, a discontinuity in the thermal behavior of the crystals between 75 and 80°C. has been detected.     

Gel permeation chromatography and cellulose. II. Application of universal calibration

In previously reported work concerning the chain-length distributions obtained by gel permeation chromatography (GPC) in celluloses, degrees of polymerization (DP) of unusually high magnitude were reported. Later work in GPC has shown that the concept of relating extended nolecular chain length of different polymers to elution volume for obtaining molecular weight is not theoretically sound. Correlation of molecular hydrodynamic volume (indicated by the product of intrinsic viscosity and molecular weight) with elution volume has been found to place polymers of vastly different natures on a single curve, such is now designated universal calibration. Application of universal calibration to the determination of DP distributions in celluloses required a different method of converting counts to DP. This new procedure is described in detail. Weight-average DP's given by the procedure for samples of cellulose I, II, III, and IV were 5190, 4520, 4795, and 3390, respectively. These are decreases of 74–75% from the results obtained by the extended-chain procedure. The results compare favorably with the viscosity-DP's of the samples. Number-average DP's were 1580, 1040, 1140, and 490 for the four samples, respectively, these being decreases of 87–93% from the values formerly reported. The polymolecularity ratios for the samples are now unusually large, being 3.4, 4.7, 4.2, and 7.1, respectively.     

Electron beam crosslinking of poly(vinylmethyl ether)

The electron beam induced branching of poly(vinylmethyl ether) (PVME) in bulk and in isopropanol solutions has been studied by gel permeation chromatography. The branching probability of bulk PVME induced by high-energy electrons can be characterized by gel permeation chromatography and a simple probability constant obtained. In isopropanol solutions this branching probability is not constant as a function of dose and is found to decrease with decreasing concentration. These results indicate the importance of solvent effects on the crosslinking of PVME in isopropanol solution by electron beam radiation. © 1994 John Wiley & Sons, Inc.     

Melting behavior of drawn films from polyethylene single-crystal mats

Drawing of mats of linear polyethylene single crystals prepared from dilute solution is possible at temperatures above about 90°C. The structure and properties of the drawn specimens are much different from those ordinary drawn bulk polymer. Drawn mats have been investigated by differential scanning calorimetry. The characteristic experimental results are: (a) a broad melting curve, (b) considerable superheating depending on the rate of heating, (c) constancy of the melting point and the heat of fusion with annealing, (d) deviation from the relation between the heat of fusion and the density obtained for the drawn bulk specimens, (e) appearance of two melting peaks in samples annealed at temperatures above about 130°C. These results imply that the structure of the drawn mat is characterized by a larger number of the tie chains connecting the neighboring crystals (the structure postulated in earlier papers) than is the case in ordinary drawn bulk polymer. It can be concluded that the transformation of a fringed micellar type of structure to the folded lamellar structure may be difficult during annealing unless crystals melt and then recrystallize during cooling.     

Gel permeation chromatographic studies of the degradation of polyethylene with fuming nitric acid. III. Fibrous stirring-induced crystals

Fibrous crystals of polyethylene are produced by crystallization from agitated solutions in xylene. If crystallization temperature is maintained between 97°C and 108°C these fibers are free from overgrowth effects and are seen to consist of flat, striated ribbons. This material was treated with fuming nitric acid, and the molecular weight distribution of the degradation product was analyzed by gel permeation chromatography. This distribution was found to consist of a low molecular weight peak and an exceptionally resistant high molecular weight tail over a wide range of degradation times in quantitative agreement with the serrations developed during the nitric acid attack. This is consistent with the fibers possessing a composite folded and extended chain structure. The lateral pulling out of smooth fibrils from the original fibers in the course of certain electron microscope sample preparation methods is consistent with the presence of chain-folded material and might account for the structureless fibrils reported in the literature. Partially successful attempts to obtain the extended chain portion in pure form by selective dissolution are mentioned together with some low-angle x-ray results.     

Study of the Isothermal Bulk Polymerization of Methacrylic Acid and Some Methacrylic Acid Esters by Differential Scanning Calorimetry

Abstract

The course of the isothermal bulk polymerization of methacrylic acid and some methacrylic acid esters differing in the length of the ester group was studied by differential scanning calorimetry at different temperatures. The enthalpies of polymerization, the residual monomer content, the overall reaction rate constants, and the overall activation energies were calculated. The molecular weight averages of the synthesized polymers before and after the gel effect were measured by gel permeation chromatography.     

乙丙三元胶的功能化研究

用马来酸二丁酯（ＤＢＭ）对乙丙三元胶（ＥＰＤＭ）进行了功能化，在烃链上导入极性基团，以改善ＥＰＤＭ与含极性基团聚合物的相容性．红外光谱表明功能化反应确已发生．用电子顺磁共振波谱仪（ＥＳＲ）研究了热引发的机理，产物的功能化率由皂化水解反应测定；产物交联程度由凝胶量间接表征；用凝胶渗透色谱法（ＧＰＣ）表征产物的分子量分布。研究了反应温度、反应时间、单体用量和引发剂用量等对产物功能化率和凝胶量的影响。     

Effect of molecular structure on polyethylene melt rheology. II. Shear-dependent viscosity

The investigation of the effect of molecular structural variables on the melt viscosity of polyethylene was extended to the shear dependent region by application of a reduced variables treatment following, in a formal sense, that of Bueche. Viscosity–shear rate data were obtained for a series of experimentally polymerized linear polyethylene samples having a range of molecular weights and molecular weight distributions as characterized primarily by gel permeation chromatography. These data could be superimposed on a single reduced variables flow curve using parameters which were a function only of temperature, limiting Newtonian viscosity, M?_w, and M?_w/M?_n. The same treatment was successfully applied also to branched (low-density) fraction data discussed in a previous paper, with additional correction for long-chain branching. However, different reduced variables curves were obtained for the branched and linear cases.     

Analysis of sodium polycarboxylates in detergents by size exclusion chromatography

Summary This paper describes the quantitative analysis and preparative isolation of sodium polycarboxylates in detergents by means of gel permeation chromatography. An analytical monitoring method separates the polymers from other low molecular detergent ingredients within 10 minutes. There is no separation of the various molecular weight polycarboxylate macromolecules themselves. They elute from the column as a single narrow peak at the exclusion volume. A second preparative gel filtration method allows isolation of polycarboxylates in amounts necessary for further characterization. Appropriate sample pretreatments and possible interferences are discussed.     

Polymeric fullerene hydrides. Birch reduction of [60] fullerene polymers from solution-based photopolymerization and free radical polymerization reactions

Fullerene polymers represent a new class of carbon materials for potential hydrogen storage applications. Poly[60]fullerene polymers were obtained by covalently linking [60]fullerene molecules in photochemical reactions. [60]Fullerene polymers were also prepared in free radical reactions of [60]fullerene with radical initiator benzoyl peroxide. The polymeric [60]fullerene materials were hydrogenated under Birch reduction conditions. The hydrides, which contain ≈3.5% (wt/wt) of hydrogen, were characterized by use of gel permeation chromatography, NMR, FT-IR, and elemental analysis. The results are compared with those of monomeric [60]fullerene hydrides.