Crystallization of trans-1,4-polyisoprene

Crystals of fractionated trans-1,4-polyisoprene (TPI) were grown from amyl acetate solution at two weight fractions, 5.7 × 10^?4 and 0.011; for the lower concentration a precooling followed by heating and then crystallization at temperatures in the 10–32°C range was used, while for the higher concentration this method and direct crystallization at a temperature T_C in the 0–32°C range were employed. The precooling method yielded samples crystallized in the α form, while direct crystallization led to formation of β-TPI at low T_C and α at higher T_C. The value for the DSC endotherm, characteristic of α-form melting, increased with increasing T_C, with a shift to lower values with increasing concentration for precooled samples. A β to α transformation was found to occur for synthetic unfractionated TPI when swollen with amyl acetate at 35°C for 17h. Swelling in n-butyl acetate for one day at 25°C or 17 h at 35°C also led to this transformation. From experimental results 74°C is chosen as the temperature at which the α and β forms coexist in the bulk, and this is used to calculate the enthalpy of fusion of β-TPI, yielding a value of 8.6 kJ mol^?1.     

The synthesis and modification of low relative molecular weight polybutadiene oligomers

Bulk precipitation polymerization and solution polymerization of butadiene with supported titanium catalyst TiCl₄/MgCl₂-Al(i-Bu)₃ using hydrogen as molecular weight regulator has been performed to synthesize low molecular weight oligomers of trans-1,4-polybutadiene. The effect of the polymerization conditions on the relative molecular weight and structure of the polymer have been studied. Increasing the hydrogen pressure and polymerization temperature resulted in the decrease of intrinsic viscosity of the polymer. By changing the hydrogen pressure, the mole percentage of trans-1,4-unit in the as-obtained polybutadiene can be adjusted, and the maximum value could reach 97%. The degree of crystallinity of the as-synthesized oligomers was about 8–50% with the melting point of form β at about 130–140°C and form α at about 50°C. Through the grafting maleic anhydride, the polar groups were introduced onto the polybutadiene macromolecular chain, which could broaden the application of the non-polar polybutadiene.     

In situ synchrotron X-ray scattering studies on the temperature dependence of oriented β-crystal growth in isotactic polypropylene

In this work, the growth dependence of oriented β-crystals in isotactic polypropylene (iPP) including their content, orientation and lamellar structures on the thermal treatment temperature (i.e. the final fusion temperature) is first investigated by in situ synchrotron X-ray diffraction/scattering. Interestingly, the dominance of oriented β-crystals is replaced by random α-crystals when the thermal treatment temperature in the range from 155 °C to 170 °C. This phenomenon is closely related to the nucleation efficiency of locally ordered domains of α-crystal and the template effect of residual α-crystals. Locally ordered domains of α-crystal are originated from the melting of β-crystals or (the partial melting of) α-crystals and β-α phase transformation. The orientation degree and lamellar structures of oriented β-crystals vary dramatically only when the thermal treatment temperature far exceeds the melting temperature of α-crystals. Comparably, the heat resistance of oriented β-crystals is stronger than the normal random ones.     

Equilibrium melting points of the low-melting and high-melting crystalline forms of trans-1, 4-polyisoprene

Equilibrium melting points in trans-1,4-polyisoprene were calculated from plots of crystallization temperature versus the experimentally measured melting points. The melting points were found to be 78 ± 1.7°C for the low-melting crystalline form and 87 ± 1.3°C for the high-melting form. Within the experimental error, melting points were independent of molecular weight above a number-average weight of 33,000.     

Polymorphism in polymers. I. The equilibrium melting temperature of two crystalline modifications of trans-1,4-polyisoprene

Dilatometric, calorimetric, and dissolution studies have been made of two crystalline modifications of trans-1,4-polyisoprene in order to determine their equilibrium melting temperatures. This parameter is of fundamental importance in the formal treatment of polymorphism in crystalline polymers. A consistent set of thermodynamic parameters has been derived for both crystalline modifications. The equilibrium melting temperature of the polymorph, which was previously observed to melt from carefully crystallized bulk material at 64°C, was calculated to be at least 82.4°C. The other form, which melts from the bulk at 74°C, has an equilibrium melting temperature of 79.5 ± 0.5°C. The trans-1,4-polyisoprene, crystallized by stirring n-butyl acetate solutions at 49°C, was found by x-ray diffraction to be in the first form and melts at 81.2 ± 0.5°C when very slow heating rates are applied. This melting temperature is very close to the independently derived equilibrium melting temperature and lends support to the possibility that extended chain crystals are present in these solution crystallized crystals. Using the newly found melting temperatures of the two crystalline modifications it can be derived from the free energies of fusion that the first crystalline form is more stable at temperatures above approximately 66°C, whereas the other form is more stable below this temperature.     

Solid-state polymerization of long-chain vinyl compounds. I. Effect of molecular arrangement on polymerizability of octadecyl methacrylate

γ-Ray-initiated postpolymerization of octadecyl methacrylate in polymorphic crystals and melt has been investigated to clarify the effect of molecular arrangement of the monomer on polymerizability. From thermal, x-ray, and infrared (IR) analyses this long-chain monomer exhibited three crystalline modifications that we refer to as α-, sub-α, and β-forms. The β-form (mp 28.7–29.7°C), which is obtainable from solution, is a stable state with triclinic chain packing. The α-form (mp 19.5–20.0°C), which is obtained first from the melt but transforms into β-form on storing, is a metastable state with hexagonal chain packing. The sub-α-form appears transiently in α→β transition. The polymerizability of octadecyl methacrylate in the β-form is extremely low, whereas the α-form can polymerize easily and the initial polymerization rate, saturated conversion, and polymer molecular weights increase with temperature. Polymerizability in the molten state at fairly high temperature is rather low, however. Thus maximum polymerizability is obtained just above the melting point of α-form. It has been found that particular orientation and suitable packing mode with some freedom of rotational motion of the monomer molecules in layered structure accelerate the polymerization reaction.     

Donor-acceptor complexes in copolymerization. L. Preparation and microstructure of chlorine-containing alternating conjugated diene–acceptor monomer copolymers

Neighboring monomer units cause significant shifts in the infrared absorption peaks attributed to cis- and trans-1,4 units in conjugated diene-acceptor monomer copolymers. Conjugated diene-maleic anhydride alternating copolymers apparently have a predominantly cis-1,4-structure, while alternating diene-SO₂ copolymers have a predominantly trans-1,4 structure. Alternating copolymers of butadiene, isoprene, and pentadiene-1,3 with α-chloroacrylonitrile and methyl α-chloroacrylate, prepared in the presence of Et_1.5AlCl_1.5(EASC), have trans-1,4 unsaturation. Alternating copolymers of chloroprene with acrylonitrile, methyl acrylate, methyl methacrylate, α-chloroacrylonitrile, and methyl α-chloroacrylate prepared in the presence of EASC-VOCl₃ have trans-1,4 configuration. The reaction between chloroprene and acrylonitrile in the presence of AlCl₃ yields the cyclic Diel-Alder adduct in the dark and the alternating copolymer under ultraviolet irradiation. The equimolar, presumably alternating, copolymers of chloroprene with methyl acrylate and methyl methacrylate undergo cyclization at 205°C to a far lesser extent than theoretically calculated, to yield five and seven-membered lactones. The polymerization of chloroprene in the presence of EASC and acetonitrile yields a radical homopolymer with trans-1,4 unsaturation.     

Study of crystallization kinetics of trans-1,4-polyisoprene

The concentrations and the growth rates of high- and low-melting type spherulites of trans-1,4-polyisoprene were measured in the temperature range 39–49°C. It was shown that above about 40°C., the crystallization rate of trans-1,4-polyisoprene is determined primarily by the radial growth rate of high-melting form (HMF) spherulites, whereas the predominance of the low-melting form (LMF) crystals below 40°C. can be attributed to the high rate of formation of LMF primary nuclei at lower crystallization temperatures. Temperature-independent rate parameters were calculated from optical and dilatometric measurements and were found to be in good agreement. Both the change in nucleation habit and spherulite growth rate with temperature can be explained on the basis of a lower end surface free energy of LMF crystals of trans-1,4-polyisoprene compared to that of the HMF crystals.     

Morphology and thermodynamic properties of solution-grown single crystals of trans-1,4-polybutadiene

The morphology and thermal behavior of trans-1,4-polybutadiene single crystals prepared from dilute solutions in n-heptane have been investigated by electron microscopy, wide-angle and low-angle x-ray diffraction, and differential scanning calorimetry. The thickness of the single crystals of trans-1,4-PBD is much greater, for the same undercooling, than that of other linear polymers. From the calorimetric study, convincing evidence of the presence, in the single crystals, of crystalline blocks of form 1 with two different thermodynamic stabilities is obtained and the relative amounts are calculated. From thermodynamic considerations we find a value of 75°C for the equilibrium transition temperature between forms 1 and 2, 139°C for the equilibrium melting temperature of form 2, and 31.2 erg/cm² for the fold-surface free energy of modification 2.     

Configurational characteristics of trans-1,4-polychloroprene: Experimental results on the unperturbed dimensions and their temperature coefficient

Polychloroprene [CCl?CH? CH₂? CH₂? ]_x of approximately 95% trans-1,4 stereochemical structure was prepared by low-temperature emulsion polymerization. Fractions, obtained by liquid–liquid precipitations were studied in toluene solutions at 30°C by viscometry and osmometry. In addition, force–temperature measurements were carried out on networks of the polymer in the amorphous state. The results obtained on the polymer solutions indicate that the unperturbed dimensions of trans-1,4-polychloroprene are essentially the same as those of trans-1,4-polybutadiene of the same molecular weight. This observation, that substitution of a relatively large Cl atom for one of the methine H atoms in the trans-1,4-polybutadiene repeat unit has little effect on the chain dimensions, suggests that this increase in substituent size is offset by the fact that the length of a C? Cl bond is very much greater than that of a C? H bond. The results obtained on the polymer networks indicate that the unperturbed dimensions of trans-1,4-polychloroprene decrease significantly with increasing temperature, as has also been reported for both trans-1,4-polybutadiene and trans-1,4-polyisoprene.     

Transitions in trans-1,4-polyisoprene

The melting transitions of both crystalline forms of trans-1,4-polyisoprene, as detected by differential thermal analysis, have been identified by attendant studies with optical microscopy and x-ray diffraction. The lower-melting (LM) form melts initially at a temperature which depends upon the crystallization temperature but which, under our experimental conditions, is between 45 and 53°C. If recrystallization is allowed to occur, the apparent final melting point, which depends upon the recrystallization temperature, is about 58°C. The initial melting point of the higher-melting (HM) form, also crystallization temperature-dependent, is upwards of 57°C. Under the most easily accessible experimental conditions, it may be obscured by the final melting of the LM-form. The apparent final melting point of the HM form is approximately 66°C. Conversion of the LM form into the HM form occurs only by fusion and crystallization. No evidence of a solid-solid transition was found. The rate of conversion is governed principally by the rate of nucleation at the conversion temperature. If fusion of the LM form is incomplete, recrystallization of the LM form takes place instead of conversion to the HM form.     

Purification, Characterization, and Heterologous Expression of a Thermostable β-1,3-1,4-Glucanase from Bacillus altitudinis YC-9

Purification, characterization, gene cloning, and heterologous expression in Escherichia coli of a thermostable β-1,3-1,4-glucanase from Bacillus altitudinis YC-9 have been investigated in this paper. The donor strain B. altitudinis YC-9 was isolated from spring silt. The native enzyme was purified by ammonium sulfate precipitation, diethylaminoethyl-cellulose anion exchange chromatography, and Sephadex G-100 gel filtration. The purified β-1,3-1,4-glucanase was observed to be stable at 60 °C and retain more than 90 % activity when incubated for 2 h at 60 °C and remain about 75 % and 44 % activity after incubating at 70 °C and 80 °C for 10 min, respectively. Acidity and temperature optimal for this enzyme was pH 6 and 65 °C. The open reading frame of the enzyme gene was measured to be 732 bp encoding 243 amino acids, with a predicted molecular weight of 27.47 kDa. The gene sequence of β-1,3-1,4-glucanase showed a homology of 98 % with that of Bacillus licheniformis. After being expressed in E. coli BL21, active recombinant enzyme was detected both in the supernatants of the culture and the cell lysate, with the activity of 102.7 and 216.7 U/mL, respectively. The supernatants of the culture were used to purify the recombinant enzyme. The purified recombinant enzyme was characterized to show almost the same properties to the wild enzyme, except that the specific activity of the recombinant enzyme reached 5392.7 U/mg, which was higher than those ever reported β-1,3-1,4-glucanase from Bacillus strains. The thermal stability and high activity make this enzyme broad prospect for industry application. This is the first report on β-1,3-1,4-glucanase produced by B. altitudinis.     

Four-center type photopolymerization in the crystalline state. VI. Kinetic and structural study of the polymerization of p-phenylenediacrylic acid diethyl ester

The effect of temperature on the four-center type photopolymerization has been investigated for p-phenylenediacrylic acid diethyl ester over a wide temperature range including crystal transition point (56°C) and melting point (96°C) of monomer. With the elevation of temperature between ?50 and 15°C, the polymerization rate in the initial stage increased and the degree of polymerization decreased monotonously, while the rate in the later stage decreased above ?25°C. With irradiation at above 25°C, the monomer crystals became sticky, and the polymerization was suppressed at the stage of oligomerization with low conversion. This tendency was enhanced above the crystal transition point, giving mainly dimer in low yield. Above the melting point, only radical polymerization occurred with the aid of oxygen. The steric configuration of the products in the crystalline state was 1,3-trans with respect to the cyclobutane ring. Peaks in NMR spectra of all products were assigned to the protons involved in four compounds up to tetramer. Various results obtained have been interpreted in terms of the change, as a function of temperature, from a topochemical polymerization which proceeds under a control of the monomer lattice to a photoinitiated vinyl-type polymerization in the disordered state. It is concluded that a rigid crystal lattice is indispensable for the four-center type photopolymerization to proceed smoothly.     

Polymorphic effects at the eutectic melting in the H2O–glycine system

Solid mixtures of ice with three glycine polymorphs were heated up to the eutectic melting and the DSC has detected the eutectic temperatures of ?2.8 °C for α-, ?3.6 °C for β-, and ?2.8 °C for γ-glycine. DSC peaks of the eutectic melting are rather strange in shape, indicating unclear processes in the solutions. Accurate DSC measurements of extremely small samples can probably provide us with the physicochemical tool for the investigation of polymorphic differences among different solutions. This may be important in relation to different bioavailability of solutions prepared from different polymorphs. Eutectic temperature of ?4.7 °C in water–glycine system allows us to suggest that the unknown polymorph of glycine exists.     

Cloning of LicB from Clostridium thermocellum and its efficient secretive expression of thermostable β-1,3-1,4-glucanase

β-1,3-1,4-glucanase is a widely used enzyme in brewing and in animal feed processing. To produce the bacterial enzyme at an industrial scale, the enzyme should be able to be secreted from microbial cells into fermentation broth and be stable in different conditions. In this study, the LicB gene encoding β-1,3-1,4-glucanase (lichenase) from Clostridium thermocellum was secretively expressed in a secretive strain, Bacillus subtilis WB800, with eight extracellular protease deletion which made LicB expressed obviously and reached 1.18 U/g cell mass. The secreted β-1,3-1,4-glucanase was found to be active from 40 °C to 80 °C and achieved the optimal activity at 80 °C. The enzyme also has a wide pH range (pH 4–11). The most common metal ions and chemicals were found to be inert on its activity. The property of LicB-encoded β-1,3-1,4-glucanase and its efficient secretive expression makes it a potential enzyme for industrial production and application.     

Radiation-induced cis–trans isomerization of polyisoprenes and temperature dependence of the equilibria

The cis-trans interconversion of polyisoprenes in solutions induced by γ-radiation in the presence of a sensitizer, which is any one of organic bromides or n-butyl mercaptan, was studied by using hevea and gutta percha as starting substances. The percentage cis remaining or converted after irradiation were determined by the infrared absorption. The equilibrium constants for the interconversion at 22, 60, and 100°C. were found to be 3.00, 5.25, and 7.33, respectively. The first-order rate constants for cis → trans and trans → cis isomerizations at 22°C. were calculated to be 9.05 and 2.91, respectively. The results were interpreted by the mechanism proposed by Golub, according to which the double bonds from π complexes with radiolytic fragments from sensitizers give a radical transition state capable of interconversion. However, our results showing that heating shifts the equilibrium toward trans isomer are not in accord with the mechanisms of the radiation-induced isomerization of polybutadiene of Golub and those for photoisomerization of aromatic azo compounds.     

Cationic ring-opening polymerization of 1,4-anhydro-2,3-di-O-benzyl-α-L-arabinopyranose and synthesis of L-arabinofuranan

1,4-Anhydro-2,3-di-O-benzyl-α-L -arabinopyranose (=1,5-anhydro-2,3-di-O-benzyl-β-L -arabinofuranose) (ABAP) was synthesized and underwent cationic ring-opening polymerization with several kinds of Lewis acids. All the polylmers prepared by Lewis acids as catalyst were found to consist of two different structural units, α-furanosidic and β-furanosidic units, and the structure of the polymers greatly depended on the polymerization conditions. Polymerization of ABAP with antimony pentachloride catalyst at 0°C for 42 h gave a polymer with the highest α content of 93%, and that at ?20°C for 3 h gave a polymer with the lowest (25%) α content. The other catalysts such as phosphorus pentafluoride, boron trifluoride etherate, niobium pentafluoride, and tantalum pentafluoride also afforded polymers with mixed structure of α-and β-furanosides. After debenzylation of poly(ABAP), a new polysaccharide, L -arabinofuranan was obtained.     

Polycondensation of bis(p-nitrophenyl) β-truxinate with diamine

Model reaction of bis(4-nitrophenyl) β-truxinate (BNPT) with aliphatic amines proceeded quantitatively at room temperature. Accordingly, polycondensation of BNPT with various diamines was carried out at room temperature or 80°C. During the polycondensation of BNPT with diamines, the precipitation of polymer or the observed gelation of polymerization solution occurred, which may limit the molecular weight of the polymer. On the other hand, the reaction of BNPT with 1,3-(4-piperidyl)propane (DPP) proceeded homogeneously to give the polymer with relatively high molecular weight, and the obtained polyamide (P-1e) showed excellent solubility in many solvents. The study of TG and DTA indicated that the obtained polymers were stable at lower temperature than around 270°C. The polymer prepared from the polycondensation of BNPT with hexamethylenediamine showed melting point and decomposition due to the imidation at 282°C. The photochemical reaction of these polymers was carried out in the film state. The irradiation of 254 nm light caused an absorption at 272 nm to appear and the molecular weight to decrease. This meant that the scission of cyclobutane ring in the main chain occurred to give cinnamamide structures. Also, the absorption at 272 nm decreased by the irradiation of 302.5 nm light. However, the UV spectrum of irradiated polymer did not agree with that of the original polymer. These results suggested that the dimerization of the resulting cinnamamide moieties occurred in the competition of their trans–cis-isomerization. On the other hand, the rate of scission of cyclobutane ring of P-1e was faster than that of the corresponding polyamide containing α-truxillamide structure.     

Effect of alkaline earth metal dopants on the thermal decomposition of the CaCO3-SiO2 system: Part II. Formation of dicalcium silicate

Mixtures of calcium oxide (taken as carbonate) and silica in 2:1 molar ratio containing varying amounts of MgO, SrCO₃ and BaCO₃ as dopants were subjected to thermal treatment up to 1450°C. The exothermic peaks at 1200°C and above (beyond the decomposition temperature of calcium carbonate) have been examined to elucidate the phases formed. The exothermic peak at 1210°C without dopant was found to conform to the β-dicalcium silicate phase with a significant amount of free lime and cristobalite along with small amounts of the γ-C₂S phase. MgO at 0.1–1% leads to the formation of β- and γ-dicalcium silicate phases at 1420–1430°C, while 5% MgO results in the formation of the β-C₂ S phase at 1360°C. SrCO₃, in the concentration range studied, leads to the stabilization of β-C₂S, but does not lower its temperature of formation. BaCO₃ at 0.1–1% assists in the formation of the β-dicalcium silicate phase, but 5% BaO forms a mixture of β- and α'_H-C₂S phases at a lower temperature.     

Pyrolysis—gas chromatography of networks

Cis-1,4-polybutadiene was exposed to different doses of β-radiation (5–100 Mrad), and polybutadiene samples with different contents of 1,2- and 1,4-isomers were exposed to equal doses of radiation (50 Mrad). The cross-linked products were characterized by sol—gel analysis, distribution of the molar masses of the sol fraction, determination of the degree of swelling and compressibility, and pyrolysed by means of a Curie-point pyrolyser at 770°C in 4 s. Evaluation of the pyrograms taken with the help of a capillary gas chromatograph proved that pyrolysis—gas chromatography enables statements regarding the micro-structure of these cross-linked polymers to be made through the degradation products 1-cis-2- and 1-trans-2-dimethylcyclopropane, 2-methyl-1,3-butadiene and trans-1,3-pentadiene in a very short time without much preparation of the samples. The peak areas of 1,3-butadiene and 4-vinylcyclohexane can be used to characterize the network density.