Haupt- und seitenkettenkristallinität bei isotaktischen poly(1-alkylethylen)en, 3. Änderung der ordnungszustände bei den höheren homologen

The higher homologues for isotactic (it) poly(1-alkylethylene)s (from it-poly(1-dodecylethylene) to it-poly(1-eicosylethylene)) show three polymorphic modifications. The modification of highest order crystallizes in an orthorhombic structure (modification I). This modification is formed during melt crystallization at a cooling rate ? < 2,5 K·s^?1. The main-chain conformation is a quaternary helix. The side-chains are tilted 130,6° against the axes of the helices and crystallize like orthorhombic polyethylene. The DSC-curves of these homologues in modification I show the endotherm of melting and an endotherm at a temperature, about 25 K to 30 K below the melting temperature. The endotherm at the lower temperature is caused by atactic material in the samples, by only partially ordered crystallites in isotactic material, and by the change of conformation of some CH₂-groups of the side-chains near the main chain.     

Haupt- und seitenkettenkristallinität bei isotaktischen poly(1-alkyläthylen)en, 1. Thermoanalytische und röntgenographische untersuchungen an den höheren homologen

The main-chain and side-chain crystallinity of several isotactic poly(1-alkylethylene)s from poly(1-dodecylethylene) to poly(1-eicosylethylene) have been investigated by X-ray diffraction and thermoanalysis. The DSC curves of the samples which were melted and rapidly quenched indicate three first-order transitions. At low temperatures a crystal modification with an arrangement of closely packed parallel side-chains is observed. Heating of the samples changes the modification: The main-chains crystallize in a helical conformation, the side-chains assume an orthorhombic order. The side-chain crystallinity of the higher homologues of poly(1-alkylethylene)s predominates if the number of methylene groups in the side-chains increases.     

Kristallisationskinetik von polymeren 2. mitteilung: Untersuchungen der anwendbarkeit der AVRAMI - Gleichung auf den kristallisationsverlauf von polyäthylensuccinat

The crystallization of polyethylene succinate has been studied dilatometrically in the temperature range 0 to 80 °C. The temperature-time behaviour of the sample during the crystallization was also determined and three different time vs. temperature curves were observed, for one of which the AVRAMI equation is applicable. The crystallization is interpreted in terms of the AVRAMI equation and the degree and the range of validity of this equation is investigated. It is found that the time exponent n has the value 3 below the temperature of 65 °C. and thereafter decreases with increasing temperature. For partially molten samples the time exponent persists at the value n = 3 also at higher temperatures. The AVRAMI diagram, at temperatures higher than 65 °C. shows a break which is due to the contact of spherulites. A discussion of the n-values shows the applicability of the AVRAMI equation in a definite temperature range.     

Haupt- und seitenkettenkristallinität bei isotaktischen poly(1-alkylethylen)en, 2. Röntgenographische,kalorimetrische und ramanspektroskopische untersuchungen am it-poly(1-eicosylethylen)

Isotactic poly(1-eicosylethylene) shows three polymorphic modifications. The orthorhombic modification I is formed during melt crystallization at a cooling rate ?<2,5K.s^?1. The dimensions of the unit cell are calculated to be a=0,75 nm, b=8,8 nm and c=0,67 nm. The heat of fusion is 145J.g^?1, the melting point is 363K. The monoclinic modification II is crystallized from the polymer solution (a=0,53 nm, b=10,8 nm, c=0,77 nm, β=94°). The heat of fusion amounts to 120J.g^?1, the melting point is 356K. Modification III is formed during rapid quenching of the melt. The side-chains crystallized closely packed in layers. Modification III shows no main-chain crystallinity. The heat of fusion is 40J.g^?1, the melting point is 348 K. The crystal field splitting in the Raman spectrum of modification +1418/1440cm^?1 indicates an arrangement of the side-chains as in orthorhombic polyethylene with two chains in the subcell. The subcells of both modifications II and III contain only one chain each.     

Telechele Oligomere, 3. Oligoäthylene durch radikalische Polymerisation mit Diacylperoxiden als Initiator

The possibility of the formation of telechelic oligoethylenes was investigated by analyses of the reaction products of dihexanoyl peroxide and ethylene. High temperatures (>200°C) result mainly in linear paraffins having an even number of C-atoms (combination product). A reaction temperature of 95°C, however, gives mainly the uneven numbered paraffins. The reason is an induced decomposition of dihexanoyl peroxide caused by growing alkyl radicals abstracting H at the β-position to the carbonyl group. This induced decomposition of dihexanoyl peroxide is also observed in the absence of ethylene.     

Bestimmung der langkettenverzweigung von hochdruckpolyäthylen durch streulicht- und viskositätsmessungen

Linear and branched polyethylene were fractionated by solvent gradient chromatography. The fractions were characterized by light scattering and viscosity measurements. The relationship between the molecular weight and the limiting viscosity number and that between the molecular weight and the radius of gyration in α-chloronaphthaline at 127°C were determined. The exponent of the equation between the ratio 〈g_η〉Θ of the limiting viscosity numbers of branched and linear fractions of the same molecular weight M_w and the corresponding ratio 〈g_η〉_Θ,w of the radii of gyration for Θ-conditions was By this equation, the long chain branching of high pressure polyethylene can be determined from 〈g_η〉, the ratio of the limiting viscosity numbers in thermodynamically good solvents, which is within the experimental limits of error identical to 〈g_η〉_Θ in a Θ-solvent. Almost independent of the molecular weight, for the branched polyethylene fractions 1,4 long chain branching points per 1000 C-atoms were obtained.     

Polymorphie,kristallinität und schmelzwärme von poly(ε-caprolactam), 2. Kalorimetrische untersuchungen

The transition between the amorphous state and 3 crystalline modifications of poly(ε-caprolactam) (polyamide-6) has been investigated in Part 1 by IR spectroscopy. With these results as background the relation between heat of fusion ΔH* and specific volume v is now investigated as a function of crystallization temperature and time, using isothermal crystallization conditions from the melt as well as cold crystallization. The changes of ΔH* and v, which occur in the course of isothermal crystallization, allow qualitative statements on crystallinity changes and transitions between different crystalline modifications as a function of crystallization temperature. Quantitative results are obtained only in rare special cases, if either only one of the 3 crystalline modifications (α, γ, γ*) is formed or if the amount of one further modification is independent of crystallization time. Additionally, the situation is complicated by the fact, that for constant molecular weight and identical crystallization conditions the results strongly depend on (a) the origin of the polyamide-6 pellets and (b) the mechanical prehistory of the melt. The reasons for these difficulties are differences in the number of (a) heterogeneous and (b) orientation-induced homogeneous nuclei. This results in strongly varying crystallization rates, which has a considerable influence upon the relation between ΔH* and v.     

Die temperaturabhängigkeit von abbau und vernetzung bei der γ-bestrahlung von polyäthylenoxid

Three samples of polyethylene oxide (P?_n between 100 and 200) have been γ-irradiated at various temperatures in the pre-gel region. Changes in number and weight average molecular weight have been determined and therefrom 100-eV-yields of crosslinking G(X) and main chain scission G(S) calculated. At room temperature G(S) amounts to 2.0 and G(X) to 1.8. Whereas crosslinking and degradation are only slightly enhanced with increasing temperature below the melting point, a significant increase to G(S) = 4.2 and G(X) = 4.0 occurs at the transition to the liquid state. Above the melting point both G(S) and G(X) are independent of temperature up to the highest temperature (120°C). The increase at the phase transition is considered to be due to the higher mobility of the macromolecules in the liquid state in conjunction with a diminuation of cage recombination of geminate macroradicals produced by main chain scissions. At high temperatures the H-atom-abstraction from intact macromolecules by end group macroradicals is favored. Hereby additional side group macroradicals are formed.     

Isothermal Crystallization of Poly(ε‐caprolactone) in Blend with Poly(styrene‐co‐acrylonitrile): Influence of Phase Separation Process

Summary: The isothermal crystallization process of poly(ε‐caprolactone) (PCL) and its blend with styrene‐acrylonitrile random copolymer containing 27.5 wt.‐% acrylonitrile has been investigated as a function of crystallization and melting temperatures for different melting times in the vicinity of the lowest critical solution temperature (LCST)‐type phase diagram using DSC. The obtained results showed that the isothermal crystallization kinetics from the melt of PCL in the blend was greatly affected by the presence of SAN. For a given crystallization temperature, the crystallization half time (t_0.5) in the case of PCL/SAN = 80/20 blend was much longer than the corresponding value for pure PCL. This depression in the crystallization kinetics of PCL in the blend was mainly attributed to the favorable interaction between the two components and the reduction in chain mobility as a result of increasing the T_g by adding the amorphous component (SAN). In addition, the value of t_0.5 was found to be independent of the melting temperature (T_m) and melting time for pure PCL. The isothermal crystallization kinetics for samples that were crystallized after decomposition into different stages of phase separation were also investigated. A major acceleration in the crystallization kinetics was observed isothermally for the samples that had undergone phase separation in the early and middle stages. The isothermal crystallization kinetics was also analyzed based on the Avrami approach. Although the crystallization kinetics was accelerated to a great extent by the liquid‐liquid phase separation, no change in the crystallization mechanism could be predicted. Furthermore, the phase separation process of PCL/SAN blend has been studied indirectly by following the variation in t_0.5 at different melting temperatures and melting times above the LCST phase diagram.

Melting temperature, T_m, dependence of crystallization half time, t_0.5.     

Reaktionen bei der Bestrahlung von poly(N-chloramid)en

On irradiating poly(N-chloroamide)s in films or in solution in the range of 325–375 nm carboxamide groups are formed. The irradiated polymer contains chlorine which is linked to C-atoms. This reaction can certainly not be explained with an intramolecular photorearrangement but with a sequence of photoreactions and dark reactions satisfactorily accounting for all observations.     

Zur Taktizität von Poly(α-methylstyrol), 4. Das 1H- und 13C-NMR-Spektrum des 1,3,3-Trimethyl-1-phenylbutyllithium

The structure of 1,3,3-trimethyl-1-phenylbutyllithium ( 1b ), which is a model compound for the active chain end in the polymerisation of α-methylstyrene with butyllithium, was investigated with ¹H and ¹³C NMR spectroscopy. The carbon-13 chemical shift of the αC-atom in benzene and tetrahydrofuran as solvent suggests a substantial sp² hybridisation. The rotation of the aromatic ring around the bond (C₆H₅)? αC is hindered at room temperature. In benzene as solvent the carbon-13 resonances of the αC-atom and the aromatic C-atoms are strongly broadened. This broadening, caused by exchange reactions or ¹³C-⁷Li-coupling, can be interpreted by an interaction of the lithium atom with the aromatic ring. This interpretation of the ¹³C NMR spectra leads to a structure, in which the lithium is not located at the αC-atom but in the space over the bond (C₆H₅)? αC.     

Über die Bruttokinetik der Thermooxidation von Hochdruckpolyäthylen

The oxidation of molten foils (20μm) from high pressure polyethylene at 157°C and at 650 Torr (= 867 mbar) oxygen pressure was studied and kinetically analyzed for the period of maximum rate. The oxygen uptake, weight increase, and hydroperoxide formation start with a rate different from zero; the initial rate of carbonyl groups and volatile products is practically zero. The absorbed oxygen, except in the initial stage, shows a distribution of the ratio 1:1 between the polymer (predominantly as carbonyl groups) and volatile products (such as water). The average number of C-atoms in the volatile fragments was estimated from kinetic data to be 6 per O-atom.     

Polyketone materials: control of glass transition temperature and surface polarity by co- and terpolymerization of carbon monoxide with higher 1-olefins

Highly soluble alternating 1-olefin/carbon monoxide copolymers with olefin monomers (H₂C?CH? R) containing 4, 5, 6, 10, 14, 16 and 18 C-atoms in the R-substituents were prepared by the use of dicationic palladium(II) phosphine catalysts and an optimized amount of methanol as activator. In terpolymerization experiments the influence of icosene-CO or octadecene-CO units, distributed randomly along a propene-CO or ethene-CO copolymer backbone, on molecular weight, glass transition temperature and on the surface polarity of films casted from solution has been investigated. As the length of the α-olefin side chain increases, the glass transition temperature (T_g) of the copolymer is reduced from room temperature to almost ?60°C. For octadecene-CO and icosene-CO copolymers side chain crystallization occurs, leading to elastic materials. Contact angle measurements, performed on water drops located on the surface of selected co- and terpolymer films demonstrate the wide range of surface polarity which can be covered by simple copolymerization of polar CO groups with apolar alkenes.     

Investigation of the Melting and Crystallization Behavior of Random Propene/α‐Olefin Copolymers by DSC and CRYSTAF

The melting and crystallization behavior of random propene/higher linear α‐olefin copolymers synthesized with the catalyst system (CH₃)₂Si(2‐methylbenz‐[e]indenyl)₂ZrCl₂/MAO were investigated. According to Flory's theory, the melting point depression is linearly related to the amount of comonomer incorporated irrespective of the nature thereof. The crystallization temperature decreased as well linearly with increasing comonomer content, but was independent of the comonomer type. The comonomer amount had an equally depressant effect on the melting temperature and on the crystallization temperature regardless of whether the crystallization occurred from melt or from dilute solution.     

Crystallization,melting and morphology of poly(hexamethylene sulfide)

Poly(hexamethylene sulfide) fractions, ranging in molecular weight from 4600 to 20000, were isothermally crystallized from the melt state in the temperature range 50–70°C. The dependence of the melting temperature on the crystallization temperature was analyzed in experiments involving low and high levels of crystallinity. The equilibrium melting temperature corresponds to 366 K and the enthalpy of fusion was found to be 40,5 cal/g (= 170 J/g). The isothermal overall crystallization rates were analyzed using dilatometric and calorimetric techniques. The Avrami exponent is an integral value, n = 3, and the crystallinity varies with increasing molecular weight from 65% to 55%. The morphology is spherulitic and it was found that the growth rate is linear in the whole range of crystallization temperatures. The temperature coefficient of the crystallization was analyzed using nucleation theory, and comparison between dilatometric and growth data revealed that the overall rate and growth rate-temperature coefficients are approximately equal.     

Isothermal Crystallization Kinetics of Poly(ε‐caprolactone) with Tetramethyl Polycarbonate and Poly(styrene‐co‐acrylonitrile) Blends Using Broadband Dielectric Spectroscopy

Summary: Phase behavior and isothermal crystallization kinetics of poly(ε‐caprolactone) (PCL) blends with tetramethyl polycarbonate (TMPC) and poly(styrene‐co‐acrylonitrile) with 27.5 wt.‐% acrylonitrile content have been investigated using broadband dielectric spectroscopy and differential scanning calorimeter. An LCST‐type phase diagram has been observed for PCL/SAN blend while all the different blend compositions of PCL/TMPC were optically clear without any phase separation structure even at high temperatures up to 300 °C. The composition dependence of T_gs for both blends has been well described by the Gordon‐Taylor equation. The phase diagram of PCL/SAN was theoretically calculated using the Flory‐Huggins equation considering that the interaction parameter is temperature and composition dependent. The equilibrium melting point of PCL depressed in the blend and the magnitude of the depression was found to be composition dependent. The interaction parameters of PCL with TMPC and SAN could not be calculated from the melting point depression based on Nishi‐Wang approach. The isothermal crystallization kinetics of PCL and in different blends was also investigated as a function of crystallization temperature using broadband dielectric spectroscopy. For pure PCL the rate of crystallization was found to be crystallization temperature (T_c) dependent, i.e., the higher the T_c, the lower the crystallization rate. The crystallization kinetics of PCL/TMPC blend was much slower than that of PCL/SAN at a constant crystallization temperature. This behavior was attributed to the fact that PCL is highly interacted with TMPC than SAN and consequently the stronger the interaction the higher the depression in the crystallization kinetics. It was also attributed to the different values of T_g of TMPC (191 °C) and SAN (100 °C); therefore, the tendency for crystallization decreases upon increasing the T_g of the amorphous component in the blend. The analysis of the isothermal crystallization kinetics was carried out using the theoretical approach of Avrami. The value of Avrami exponent was almost constant in the pure state and in the blends indicating that blending simply retarded the crystallization rate without affecting the crystallization mechanism.

Dielectric constant, ε′, of pure PCL, blends of PCL/TMPC = 80/20 and PCL/SAN = 80/20 as a function of crystallization time at 47 °C and 1 kHz.     

Influence of composition on the melt crystallization of isotactic random propylene/1-butene copolymers

The influence of composition on the overall rate of isothermal crystallization of isotactic random propylene/1-butene copolymers is investigated. At a constant crystallization temperature a small fraction of 1-butene co-units inserted along a polypropylene chain causes a drastic reduction in the overall rate of crystallization. Further it is found that for a given rate of crystallization it is possible to crystallize the isotactic polypropylene at lower crystallization temperature by adding along the chain a small amount of 1-butene as comonomer. The equilibrium melting temperature, the surface free energy of folding, the enthalpy and the entropy of fusion decrease with increasing the contents of 1-butene in the copolymer samples.     

Poly(ethylene‐co‐ethyleneoxyethylene terephthalate)s: synthesis and non‐isothermal crystallization behavior

A series of random copolyesters of reasonably high molecular weight was synthesized with varying composition by melt copolycondensation of dimethyl terephthalate (DMT) with ethylene glycol (EG) and diethylene glycol (DEG). Composition and molecular weight of the copolyesters were determined by ¹H NMR spectroscopy and viscometry, respectively. The copolyesters containing DEG of ≤ 40 mol‐% are crystallizable, whereas those with DEG of > 40 mol‐% are amorphous. For the copolyesters containing DEG of ≤ 13 mol‐% which were crystallized isothermally, the melting behavior was investigated by means of differential scanning calorimetry (DSC). Three endotherms were found to be influenced by the crystallization temperature and composition, and the equilibrium melting temperatures were determined. In addition, the non‐isothermal crystallization behavior was investigated by DSC and analyzed by both Ozawa and modified‐Avrami approaches. Regardless of the composition, the value of the Ozawa exponent ranges from 2.4 to 2.6, depending on the temperature, whereas the value of the Avrami exponent ranges from 2.5 to 3.2, depending on the cooling rate. These results indicate that the nucleation and growth mechanisms of the copolyesters are independent of their composition. However, the crystallization rate is decreased by incorporating DEG units into the polymer backbone and also by lowering the cooling rate. Furthermore, incorporating DEG units into the polymer backbone increases the crystallization activation energy.     

Cristallisation de poly(oxyéthylène)s segmentés

Two homologous series of segmented poly(oxyethylene)s, comprising from 1 to 4 blocks, were studied by differential scanning calorimetry, dilatometry and low-angle X-ray scattering. The polymers used were synthesized by condensation of α,ω-dihydroxy poly(oxyethylene)s with molecular weights of 2750 and 10600, respectively, upon 2,4-toluene diisocyanate. It was shown that the structure of these polymers is lamellar as for the usual poly(oxyethylene)s, but the degree of crystallinity and the melting temperature decrease appreciably with increasing degree of condensation. The thickness of the lamellae of the two-block polymers increases drastically and stepwise with crystallization temperature, exactly as in the case of weakly polydisperse, ordinary poly(oxyethylene)s. On the other hand, the thickness of the lamellae is little affected by the crystallization temperature for tri- and tetra-block polymers. The conclusion is drawn that this is due to a blocking of the urethane groups during the annealing process. As these groups are excluded from the crystalline domains, they play the same rǒle as end groups of the chains in ordinary poly(oxyethylene)s.     

Die Kationische ε-Caprolactam-Polymerisation. V. Die quantitative Bestimmung der N-Acyllactam-Gruppen bei der Initiierung mit wasserfreien Säuren und die Konzentrationsänderung der Endgruppen während der Polymerisation

As a contribution to the elucidation of the mechanism of the cationic polymerization of caprolactam initiated by anhydrous acids, e.g. HCl, the variation of the concentration of some functional groups of the oligoamides and polyamides formed was investigated. In particular, the concentration of the C-terminal N-acyllactam groups was determined by IR-spectroscopy and by potentiometric titration of the carboxylic groups formed upon alkaline hydrolysis. An improved polymerization technique was developed leading to a complete exclusion of traces of oxygen and moisture and, hence, to more reproducible results. The dependence of the concentration of different functional groups on the polymerization conditions (temperature, reaction time, initiator concentration) was examined. In the initial state of the polymerization acyllactam and ammonium endgroups are formed to equal amount, i.e., one of each group per initiating lactam hydrochloride molecule. This confirms the earlier(^1–4) established mechanism of the initiation reaction under formation of oligo-ε-aminocaproyl caprolactams. The concentration of the acyllactam groups then reaches a maximum and decreases again due to side reactions before becoming constant. At high temperatures the concentration of the basic endgroups (as hydrochlorides) becomes equal to that of the initiator after reaching the equilibrium and then remains constant during the total polymerization time. The concentration of caprolactam hydrochloride drops to a very low equilibrium value. The course of the polymerization also depends on temperature. Above 170°C increasing side reactions occur leading to the disappearance of acyllactam groups and to the formation of a midine and carboxylie groups which were detected by IR-spectroscopy. The occurrence of the side reactions strongly depends on the acidity of the medium.