Effect of γ-irradiation and thermal annealing on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) subjected to γ-irradiation and thermal annealing has been studied for the first time with the use of thermomechanical spectrometry. The pseudonetwork structure of the copolymer contains an amorphous block (interjunction chains) and crystalline segments (branching points). The diblock amorphous and crystalline structure with a crystal structure fraction of 0.21 transformed into an almost completely amorphous structure with a crystallite fraction of 0.06 after the irradiation of the copolymer at a dose of 600 kGy. Thermal annealing at 483 K formed a new structure: a high-temperature amorphous block.     

Molecular–topological structure of tetrafluoroethylene–perfluoromethylvinyl ether copolymer irradiated with MeV protons

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoromethylvinyl ether has been studied for the first time before and after irradiation with 1- and 4-MeV protons. The pseudo-network structure of the copolymer contains an amorphous block and crystalline segments of macromolecules as branching points. After bombardment with protons, a high-temperature amorphous block is formed in the copolymer with simultaneous complete amorphization of the copolymer structure and a decrease in its molecular flow temperature. The surface of a target plate with a thickness of 500 μm that has not been directly exposed to proton bombardment preserves the molecular–topological structure of the initial copolymer.     

Effect of γ-irradiation on the molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether)

The molecular–topological structure of a copolymer of tetrafluoroethylene and perfluoro(propyl vinyl ether) before and after γ-irradiation has been studied for the first time. The pseudo-network structure of the copolymer contains an amorphous block and the crystalline segments of macromolecules serve as branching points. After γ-irradiation to a dose of 15 to 2380 kGy, polyassociative cluster-type entities have appeared in the initial copolymer in place of the crystalline branching points with simultaneous structure amorphization and a decrease in the onset temperature of molecular flow.     

Effect of γ-irradiation on the molecular-topological structure of the polyethylene matrix of glass-reinforced plastic

The molecular-topological structure of polyethylene (PE) and a PE matrix in a glass-reinforced plastic (GRP) after γ-irradiation of the plastic was studied by means of thermomechanical spectroscopy. The four-block topological structure of unirradiated PE (one amorphous block and three crystalline phases with different initial melting temperatures) is transformed into a three-block structure in the GRP already at a minimal radiation dose of 25 kGy. The intermediate crystalline phase disappears under these conditions, the molecular relaxation characteristics in all topological blocks alter, and chemical branching points appear in the pseudonetwork structure of the amorphous matrix block.     

Molecular-topological structure of γ-irradiated polytetrafluoroethylene

The molecular-topological structure of polytetrafluoroethylene (PTFE) has been studied in the range of ?100 to +450°C by thermomechanical spectrometry. Revealed in this temperature range is a fourblock topological structure composed of one amorphous (T _g = 16°C) and three crystalline (low-melting (T _m = 315°C), intermediate (T _m ¹ = 355°C), and high-melting (T _m ² = 388°C)) polymorphs. At a dose of 1 kGy, the long-range orientation of chains in the intermediate and high-melting crystalline blocks of PTFE is replaced by short-range orientation of the cluster association structure. At doses of 100?C500 kGy, the latter structure transitions to the amorphous state and the irradiated samples acquire a semicrystalline structure of the two-block type. The molecular-mass distribution function of interjunction chains of the pseudo-network of the amorphous block is bimodal in character and its maxima are noticeable shifted toward lower masses with an increase in the radiation dose. As the dose increases, the crystallinity decreases and the molecular mobility of amorphized chains is enhanced. As a result, both the glass transition and the molecular flow onset temperatures of the polymer are reduced.     

Effect of bombardment with helium ions on the molecular-topological structure and elemental composition of the surface of polytetrafluoroethylene

Irradiation of a polytetrafluoroethylene (PTFE) film with accelerated (1–5 MeV) helium ions at a fluence of 10¹⁵ ion/cm² has been studied. The efficiency of carbonization, defined as a decrease in the fluorine content and an increase in the carbon content on the surface of the polymer, increases with the incident ion energy. A characteristic feature of the topological structure of PTFE is the presence of four high-meltingpoint crystalline modifications, the “branching points” of the pseudo-network of the amorphous matrix block, in addition to a low-melting-point modification with the melting onset temperature of 13°C. After bombardment with 3–5 MeV ions, only two crystalline blocks remain in the polymer and a cluster block, which was not present in the unirradiated polymer, appears. The overall mass fraction of the crystalline structure in the irradiated polymer (0.48) is below that in the initial polymer (0.66), indicating amorphization of its structure.     

Effect of fast protons on the molecular—topological structure and surface properties of tetrafluoroethylene—hexafluoropropylene copolymer

The topologically diblock structure of a tetrafluoroethylene—hexafluoropropylene copolymer with a total weight fraction of crystalline structures of 0.07 is transformed into a fully amorphous matrix with a pseudo-network structure after irradiation with 1—4 MeV protons. Instead of crystalline branching points (as in the unirradiated copolymer), cluster structures have appeared in the matrix. Oxidative degradation processes that occur during the bombardment result in significant functionalization of the copolymer and a substantial increase in the surface free energy, its acid—base component, and surface polarity.     

IR-spectroscopic examination of polytetrafluoroethylene and its modified forms

The results of IR-spectroscopic examinations of the molecular and supramolecular structure of polytetrafluoroethylene and polymer materials thereof were summarized. It was shown that, upon heat, mechanical, and other treatment, as well as under radiation exposure, polytetrafluoroethylene preserves its chain-helical conformation, and the resulting modified forms consist of crystalline and amorphous phases in a ratio depending on the history of the sample. The degree of the structural ordering in the polymer decreases with increasing temperature and pressure. The formation of branched moieties and short macromolecules with double bonds (?CF=CF₂) in the terminal groups is specific for the process caused by thermal and radiation-induced degradation. The oxidation of the polymer macromolecules requires applying high irradiation doses and heating samples in an oxygen or air atmosphere.     

Effect of gamma radiation on the molecular-topological structure and properties of poly(vinylidene fluoride) and the matrix in a PVDF-based glass-reinforced plastic

The amorphous-topological structure of poly(vinylidene fluoride) (PVDF), the pseudo-network structure of which is formed by polyassociative entities of the cluster type and persists upon γ-irradiation up to 250 kGy, has been investigated. As a result of the processes involved in the fabrication of the glass-reinforced plastic (GRP), five crystalline modifications arise in the polymer matrix instead of cluster branching points in the initial PVDF, and the temperature of the molecular flow of the polymer matrix in the GRP rises from 410 to 593 K in comparison with the initial PVDF. The strength of GRP made of untreated glass cloth (110 MPa) is higher than that of the initial PVDF (86 MPa). However, when using glass cloth treated with a process sizing agent, the strength of the GRP increases up to 286 MPa. After γ-irradiation of the latter, upon which a sharp drop in the strength is observed immediately with the onset of GRP irradiation, the exposure of PVDF and GRP made of untreated glass cloth results in a drop in the strength only after 50 kGy. The irradiation eliminates the properties acquired by the polymer matrix during the fabrication of GRP, and the properties of the GRP polymer matrix approach those of the initial PVDF with an increase in the radiation dose.     

Study of Gamma-Irradiated Polyamide Using Thermomechanical Spectrometry and Radiothermoluminescence

The molecular–topological structure of polyamide before and after γ-irradiation has been first studied by thermomechanical spectrometry. The γ-irradiation with a dose up to 300 kGy does not change the topological structure of the polymer, the four-block pseudo-network structure of which contains crystalline segments of macromolecules and polyassociative entities of the cluster type in addition to low-and high-temperature amorphous blocks. During irradiation, only interblock mass transfer of the chain segments occurs, resulting in different dose-dependent values for the molecular weight of the chains, their weight fraction in each topological block, and the glass transition and molecular flow temperatures of the polymer. Radiothermoluminescence curves exhibit three maxima at 152, 200, and 330 K, of which the last one is detected in a temperature region close to the glass transition temperature of the high-temperature amorphous block on the thermomechanical analysis curve of the polymer.     

Effect of γ-irradiation on the molecular-topological structure of Viton® fluoroelastomers

The molecular–topological structure of a terpolymer based on vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene has been studied for the first time with the use of thermomechanical spectrometry. A five-block topologically amorphous and crystalline pseudo-network structure with crystallites, which have different initial melting temperatures, as branching points has been detected in the terpolymer at temperatures from–100 to 250°C. When γ-irradiated at a dose of 30 kGy, the crystalline blocks of high-temperature modifications assimilated into one cluster block with the formation of a pseudo-network with a 1.5fold increase in the block-average molecular weight and a decreased initial molecular flow temperature.     

Molecular-topological structure of γ-irradiated ftorlon polytetrafluoroethylene

Six topological structures (an amorphous and five crystalline blocks) have been detected in a polytetrafluoroethylene film with a pseudo-network structure. During the Γ-irradiation of the polymer in air, the crystalline fractions degrade and gradually convert into amorphous and cluster states with the increasing radiation dose. After irradiation at a dose of 90 kGy, the polymer loses its capability for crystallization and forms a completely amorphous topological structure. However, regardless of dose in the range of 3–90 kGy, the topological structure of the polymer irradiated in a vacuum remains unchanged and consists of amorphous, cluster, and crystalline blocks.     

Molecular-topological and thermal properties of gamma-irradiated alternating carbon monoxide-ethylene copolymer

Gamma-irradiation to a dose of up to 2000 kGy does not lead to substantial changes in the topological structure of a carbon monoxide copolymer with ethylene, thereby suggesting it high radiation resistance. The topological structure of unirradiated and irradiated copolymer samples is polyblock in nature having four crystalline phases as the branching “junctions” in the pseudo-network structure of its amorphous block. Copolymer molecular flow begins after completion of melting of its high-melting fraction and at an onset flow temperature of 484 ± 4 K regardless of the absorbed radiation dose. The irradiated and unirradiated copolymer releases the same gaseous products upon heating, and the irradiation itself does not affect the onset temperature of effective gas evolution.     

Crystal polymorphs of 6‐[(phenylcarbamoyl)oxy]hexa‐2,4‐diyn‐1‐yl isonicotinate

The title compound, C₁₉H₁₄N₂O₄, was found to have two crystal polymorphs, in which the molecular structures of the diacetylenic compound are broadly similar. The main structural difference between the polymorphs concerns the intermolecular hydrogen‐bonding motifs adopted, namely a one‐dimensional zigzag polymer linked by N—H…N(py) (py is pyridine) interactions in polymorph I and a centrosymmetric dimeric motif formed by N—H…O=C interactions in polymorph II. The diacetylene cores of the molecules stack along the a and b axes in polymorphs I and II, respectively. It was found that only the molecular arrangement in polymorph II satisfies Baughman's criterion to afford polydiacetylenes (PDAs) by thermal annealing or irradiation with light. This predicted polymerization activity was confirmed by experiment.     

Reversible Transformation between Amorphous and Crystalline States of Unsaturated Polyesters by Cis–Trans Isomerization

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T_g=18 °C) and crystalline (T_m=124 °C) states through cis–trans isomerization of the C=C bonds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer. A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides, such as epichlorohydrin, phenyl glycidyl ether, and (2,3‐epoxypropyl)benzene. These unsaturated polyesters with 100 % E‐configuration in the crystalline state were prepared by quantitative isomerization of their Z‐configuration analogues in the presence of a catalytic amount of diethylamine, while in the presence of benzophenone, irradiation with 365 nm UV light resulted in the transformation of about 30 % trans‐alkene to cis‐maleate form, thereby affording amorphous polyesters.     

Triphenylene-based discotic liquid crystals: star-shaped oligomers and branched-chain polymers

Liquid crystalline main-chain polymers based on a repeat hexaalkoxytriphenylene moiety have previously been made by the reaction of dihydroxytetraalkoxytriphenylenes with α,ω-dibromoalkanes catalysed by caesium carbonate in N-methyl pyrrolidone. We now show that the molecular weights of these polymers can be increased by adding ?5 wt% of a tribromide (a 1,3,5-trialkoxybenzene or trialkoxymethylbenzene with three ω-bromoalkyl substituents) to the reaction mixture. Studies of model oligomer systems show that, provided the ω-bromoalkyl chains are long enough, the presence of these branching points should not affect the formation of the Col_h mesophase. Indeed, if ?5 wt% of the tribromide is used in the synthesis of the polymer, it remains liquid crystalline. However, if >20 wt% of the tribromide is used, introducing a high degree of branching and cross-linking, the liquid crystal behaviour disappears.     

Polymerization of glycidol and its derivatives: A new rearrangement polymerization

Anionic (KOH) polymerization of glycidol, or its trimethylsilyl ether (TMSGE) followed by hydrolysis, gives a low molecular weight, largely amorphous polymer that is not the reported 1,3-polyglycidol but, based on ¹³C-NMR, largely a 1,4-poly(3-hydroxyoxetane) with much branching. This result is achieved by a simple rearrangement of the usual, propagating secondary oxyanion to a primary one. Substantial amounts of four dimers (5–10%), four trimers, and some tetramers were also found. One dimer was isolated and shown to be glycidyl glycerin, the usual thermal dimer from glycidol. Possible structures of the other dimers are proposed. The polymerization appears to begin with the rapid formation of the glycidoxy anion , formed by base abstraction of a proton from glycidol and by nucleophilic displacement of the SiMe₃ group from TMSGE. Other bases such as KOtert-Bu give similar 1,4 polymer for glycidol but, with TMSGE, there is considerable 1,3 polymerization. Detailed mechanisms are proposed. The polymer perpared from R-TMSGE with KOH was highly crystalline, high melting (166°C), H₂O soluble, isotactic poly(3-hydroxyoxetane). The cationic polymerization of tert-butyl glycidyl ether (TBGE) and TMSGE gave low molecular weight 1,3 polyethers. The TBGE polymer was all head-to-tail whereas the polyglycidol from TMSGE contained extensive head-to-head chain units with considerable branching. Mechanisms for these interesting differences are proposed.     

Structures and properties of different low density polyethylenes

Low density polyethylenes (LDPE) made by the known high pressure processes show significantly different molecular structures. When the reaction conditions are variable, e.g. in a tubular reactor (resinT) or in a system of two autoclaves with a lower temperature in the first reactor (resinA ₂ ^* ), the polymer shows a narrower molecular weight distribution, but wider distributions of long-chain and short-chain branching compared with a polymer produced at constant temperature and under practically ideal mixing in a stirred autoclave reactor (resinA). The polymerT displays a decrease in long-chain and short-chain branching with growing molecular weight and differs from sampleA in the type of long-chain branching and in the molecular shape.A-type molecules show tree-like branching and nearly globular shapes whereas theT-type molecules are characterized by comb-like branching and consequently have more extended (rod-like but flexible) conformations. These structures may be interpreted in terms of reaction kinetics. The differences in molecular structure lead to changes in the morphology. For example, the bulk density distributions of the polymersT andA ₂ ^* are narrower than that of polymerA although the latter has a much narrower short-chain branching distribution. The morphology (e.g. crystallinity and crystal size) is dominated by the tendency of short sidechains to accumulate in the amorphous phase and by the limited mobility of the molecules in the melt during crystallization. The proportion of short side-chains incorporated in the crystalline phase ranges from about 20% at high molecular weights to about 7% at low molecular weights for the resinsA andT. The physical and technological properties are closely related to molecular structure and morphology. They may be optimized by selecting suitable polymerization conditions, e.g. by use of a new two-autoclave process.In memoriam Prof. Dr. Dr. h. c. mult. Otto Bayer.Vorgetragen auf der Frühjahrstagung des Fachausschusses Polymerphysik der Deutschen Physikalischen Gesellschaft, Regensburg, 15.–17. März 1982.     

Isomorphic behavior of poly(aryl ether ketone) blends

Blends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number-average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature T_g versus composition exhibits a minimum deviation from linearity whereas the melting temperature T_m versus composition exhibits a pronounced maximum deviation from linear behavior. The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases T_m). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid-liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete. In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.     

Mechanism aspects of th e ring-opening polymerization of the episulfides compared to epoxides

The cis- and trans-2-butene episulfides polymerize with cationic catalyts differently than reported for the corresponding oxides. Where the cis-oxide gave amorphous disyndiotactic polymer, the cis-sulfide gives crystalline racemic diisotactic polymer since this polymer could be asymmetrically synthesized in optically active form. Also the same crystalline polymer was obtained with coordination catalysts. Where the trans-oxide gave only crystalline, meso-diisotactic polymer, the trans-sulfide gives mainly amorphous polymer which, in one case, did slowly crystallize. The difference between the trans forms appears due to the longer C? S bond which lowers steric hindrance and thus isomer selection in the attack of episulfide on the growing sulfonium ion to give less steroregular polymer. The difference in the cis forms may result from the sulfur atom in the last chain unit coordinating with the counterion. The greater hindrance around oxygen in the comparable oxide polymers may prevent the same mechanism from being utilized. The cationic polymerization of isobutylene sulfide gives both crystalline and amorphous polymer. NMR evidence indicates that the amorphous polymer results from substantial head-to-head, tail-to-tail polymerization, along with the expected head-to-tail polymerization. The same phenomenon occurs, but to a lesser extent, in cationic isobutylene oxide polymerizations. The preparation and properties of high molecular weight, head-to-tail isobutylene oxide and sulfide polymers from R₂Mg-NH₃ coordination catalysis are described.