Thermal behaviour of highly stereoregular syndiotactic polypropene from homogeneous catalysts

Thermal characterization was carried out on highly stereoregular and regioregular syndiotactic polypropene (sPP) obtained with isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride and methylaluminoxane. The influence of molecular weight and syndiotacticity degree on the thermodynamic melting point (T°_m) of sPP were separately investigated by examining samples with a fully syndiotactic pentads content (rrrr) ranging from ca. 81% to ca. 94% and with an weight-average molecular weight (M?_w) ranging from 9,6 · 10⁴ to 17,3 · 10⁴. Upon excluding any influence of the molecular weight, the correlation between the rrrr pentads content and the T°_m of the samples led to the extrapolation of the thermodynamic melting point for a fully syndiotactic polypropene.     

Potentiometric titration of syndiotactic methacrylic acid/dimethacryloylamine copolymers

The potentiometric titration of syndiotactic methacrylic acid/dimethacryloylamine (MMA-MAI) copolymers is investigated. In contrast to copolymers studied before, MAA-MAI copolymers possess a highly syndiotactic backbone structure, a compositional statistics known from NMR-measurements, and a cyclic structure as a part of the chain. The statistics of the MAA-units and MAI-rings is nearly random with respect to the formation of imide rings, the rings introducing a trans and a gauche conformation for each ring. Plots of the apparent pK (pK_app) versus the degree of ionization α, or versus log [(1- α)/ α], indicate a change from a relatively dense coil (a-state) to an extended coil (b-state) when α is increased. The decisive parameter for pK_app in the b-state and for the conformational transition of the a-state to the b-state is the charge density on the chain β. The transition takes place for all copolymer compositions in an interval of Δβ ≈1 but the interval is situated at lower absolute values of β for the copolymers with higher contents of MAI-rings. The Δβ at lower β may be either due to a decrease in intramolecular attraction or to a higher electrostatic repulsion. The free enthalpy of the conformational transition is, however, approximately the same for copolymers with different MAI contents. This constancy of the free enthalpy points to a conformational transition which is energetically not much different for the MAA- and the MAI-units in the chain.     

Microstructure of syndiotactic polypropylenes prepared with heterogeneous titanium-based Ziegler-Natta catalysts

Polypropylenes produced with various heterogeneous titanium-based Ziegler-Natta catalysts were fractionated by solvent extraction technique. The infrared analysis of the fractions indicates the presence of a crystalline syndiotactic sequence, soluble in xylene at 20°C, and boiling hexane soluble fractions of all samples examined. Highly syndiotactic polypropylene (proportion of rrrr pentad is 0,50), comparable in syndiotacticity to the syndiotactic polymer prepared at ?78°C with a homogeneous vanadium catalyst, was separated from the xylenesoluble fraction of the polymer prepared with the system TiCl₃-Al(C₂H₅)₂Cl by means of elution column fractionation. The steric irregularities are mainly rrrm and rrmr (ratio ≈ 1:1), suggesting that the propagation is controlled mainly by end-groups. Chemical inversions, i. e., head-to-head or tail-to-tail linkages of propylene units, are practically absent, though they are seen in syndiotactic polypropylenes prepared with vanadium catalysts.     

Novel Olefin Block Copolymer,Polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene), Synthesized from Propene and 1,5‐Hexadiene by a Modified Stopped‐Flow Method

A block copolymer of propene and 1,5‐hexadiene, polypropene‐block‐poly(methylene‐1,3‐cyclopentane‐co‐propene) (PP‐b‐(PMCP‐co‐PP)), was synthesized using a modified stopped‐flow polymerization method with an MgCl₂‐supported Ziegler catalyst. Regarding the basic characteristics of the PP‐b‐(PMCP‐co‐PP), the block formation was investigated in detail. The obtained block copolymer showed a unimodal GPC curve without any peak in the low molecular weight region. It was also clear that the molecular weight of each part could be controlled by changing the polymerization time (from about 0.1 to 0.2 s). Furthermore, the elution pattern by temperature‐rising elution fractionation clearly showed that the block copolymer eluted in each temperature region between 20°C to 120°C was mainly composed of a unified component. Even after extraction with boiling heptane, the ¹³C NMR spectra of the block copolymer showed that the signals from PMCP‐co‐PP remained unchanged, but disappeared in the blend of polypropene and PMCP‐co‐PP. The differential scanning calorimetry results and optical microscopic observations indicated not only the formation of a block copolymer having a chemical linkage between polypropene and PMCP‐co‐PP, but also the regulation of the crystalline distribution in the block copolymer by changing the composition of each block part.     

Synthesis and basic characteristics of polypropene-block-poly(ethene-co-propene) by modified stopped-flow polymerization with an MgCl2-supported Ziegler catalyst

A well-defined diblock copolymer, polypropene-block-poly(ethene-co-propene), was synthesized by modified stopped-flow polymerization with an MgCl₂-supported Ziegler catalyst. The copolymer shows a unimodal gel permeation chromatography (GPC) elution curve without any material in the low molecular weight region. The molecular weight can be controlled by the polymerization time (ca. 0.1 to 0.2 s). Furthermore, the elution pattern by cross fractionation chromatography showed that the block copolymer eluted at each temperature region between 0°C to 120°C is composed of a uniform material. After extraction with heptane, the ¹³C NMR spectra showed that the signals from poly(ethene-co-propene) remain unchanged in the block copolymer but are absent in a corresponding polypropene/poly(ethene-co-propene) blend. The results of differential scanning calorimetry (DSC) and optical microscopic observation indicate not only the formation of a block copolymer with a chemical linkage between the polypropene block and the poly(ethene-co-propene) block, but also the regulation of the crystalline morphology in the block copolymer by changing the composition.     

Synthesis and characterization of branched polypropenes obtained by metallocene catalysis

The homopolymerization of propene, 4-methyl-1-pentene, 1-octene and the copolymerization of propene with 4-methyl-1-pentene and 1-octene, respectively, was carried out with the isospecific metallocene catalyst system rac-[(dimethylsilylene)bis(2-methylbenzo(e)indenyl)]zirconium dichloride/methylaluminoxane at 30°C in toluene. By variation of the monomer ratio, it is possible to produce copolymers in the entire composition range. The activity, the amount of comonomer insertion, and the molecular masses obtained in the propene/1-octene copolymerization are significantly higher compared to the respective values of the system propene/4-methyl-1-pentene. It is possible to synthesize polymers with glass transition temperatures ranging from −65 up to 26°C. Whereas the incorporation of more than 20 mol-% 1-octene leads to amorphous polymers, the propene/4-methyl-1-pentene copolymers with less than 15 and more than 60 mol-% 4-methyl-1-pentene are semicrystalline. All melting points vary in the range from 50 to 225°C. Wide angle X-ray scattering measurements indicate an increase of the γ-modification compared to the γ-modification with increasing comonomer content and crystallization temperature. Typical supermolecular morphologies different from spherulites and known for the γ-phase of the isotactic polypropene homopolymer are observed for the copolymers by polarized light microscopy.     

Miscibility behavior of syndiotactic and atactic polystyrene

Blends of atactic and syndiotactic polystyrene have a single composition dependent glass transition temperature. This does not confirm the miscibility of both polymers, however, unambiguously because there is only a small difference of 10°C in the glass transition temperatures of both neat polymers. Diffusion measurements of syndiotactic polystyrene and deuterated atactic polystyrene using the nuclear reaction D(³He,α)p confirm at least partial miscibility of both components. The average diffusion coefficient at 190°C is 2.3 ± 0.2 × 10^?15 cm²/s.     

FTIR spectra and chain conformations in the crystalline forms and clathrates of syndiotactic poly(p-methylstyrene)

Infrared spectra of syndiotactic poly(p-methylstyrene) (s-PPMS) samples, exhibiting various crystalline forms and clathrate structures, are reported in this contribution. Bands due to the syndiotactic stereostructure, bands typical of the two different chain conformations observed in the crystalline structures and bands sensitive to intermolecular interactions typical of the different modes of packing of chains are pointed out. The observed similarities with the case of syndiotactic polystyrene are alos indicated. A complete assignment, via FTIR analysis, of the chain conformations, is presented for all the known crystalline forms and clathrates of s-PPMS.     

Propene polymerization with zirconocene catalysts supported on siloxane copolymers

A supported version of zirconocene catalysts on siloxane copolymers having 1,2,3,4-tetramethylcyclopentadienyl (Cp″)-fluorenyl (Flu) (I) or cyclopentadienyl (Cp)-fluorenyl (II) groups as substituents was prepared and applied to propene polymerization using methylalumoxane (MAO) or [Ph₃C][B(C₆F₅)₄] as cocatalyst. Catalyst (I), which was soluble in toluene, exhibited very low activity, whereas catalyst (II), which was composed of a toluene soluble (Cat-A) and an insoluble fraction (Cat-B), displayed a fairly high activity. Both catalysts (A and B) give a mixture of syndiotactic, atactic and a small quantity of isotactic polypropene, with a fraction of syndiotactic pentads ranging from about 50–75%. In contrast, the corresponding non-supported catalyst gives almost completely atactic polypropene.     

Crystal structure of the form I of syndiotactic poly(1-butene)

The crystal structure of the form I of syndiotactic poly(1-butene) is presented. According to the present analysis, chains having s(2/1)2 helical conformation are packed in an orthorhombic unit cell with a = 16,81 Å, b = 6,06 Å and c = 7,73 Å. The density is 0,96 g/cm³ with two chains in the cell (8 monomeric units), the space group is C222₁. Disorder, corresponding to the statistical presence of right- and left-handed helices in each site of the lattice, could be present. The space group for the completely disordered structure is Cmcm.     

Polymerization of propylene to syndiotactic polymer. IV. Addition to the double bond

By the study of differently deuterated homopolymers and copolymers of propylene it is demonstrated that the double bond addition is cis in the syndiotactic polymerization of propylene. Furthermore it is confirmed that the addition to the double bond is cis also in the isotactic polymerization.     

Bestimmung von sequenzlängenverteilungen hydrierter polyalkenylene durch metathese-abbau, 1. Homogen hydriertes polybutadien

Partially hydrogenated 1,4-polybutadiene is degraded into GC-detectable reaction products after olefin-metathesis with 4-octene in the presence of WCI₆/(CH₃)₄Sn. 1,4-polybutadiene is homogeneously hydrogenated with p-toluenesulfonohydrazide and serves as copolymer with non-hydrogenated and hydrogenated repeating units. Hydrogenated sequences up to an undecade are detectable. The experimental monomer sequence length distribution agrees satisfactorily with the theoretical one calculated under the assumption of an ideal statistical copolymer.     

Metathesis degradation of poly(butadiene-alt-propene)

Poly(butadiene-alt-propene) ( 1 ) was degraded by metathesis reaction using symmetric olefins (3-hexene and 4-octene) in chlorobenzene solution in the presence of WCl₆/(CH₃)₄Sn as catalyst. Identification of the degradation products by means of a combination of gas chromatography (GC) and mass spectrometry (MS) revealed small amounts of “defects” in the almost ideally alternating copolymer 1 . These were non-alternating sequences of 2-butenylene and methylethylene units, vinylethylene units and branching points. In addition, the metathesis degradation of 1 with 4 -octene was investigated kinetically between 15 and 40°C. The measurements confirm that the thermodynamically stable 4-methylcyclohexene is the final product. This can be formed directly from the polymer and via oligomeric products. The formation of these intermediates is preceded by an induction period. Their concentrations pass maxima, the positions of which depend on the size of the molecules and on the temperature.     

Poly(ε‐caprolactone) Single Crystals with Different Aspect Ratios Mediated by Counterion Exchange on the Basis of Hofmeister Series

Although polymeric single crystals fabricated from self‐assembly of block copolymers are reported, preparation of single crystals with different aspect ratios still remains a major challenge. In this work, a facile way is demonstrated to prepare poly(ε‐caprolactone) based single crystals with tunable aspect ratios through simple counterion exchange on the basis of the Hofmeister series. Briefly, after ion exchange from Brˉ (an ion‐containing triblock copolymer, poly(ethylene oxide)‐b‐poly(ε‐caprolactone)‐b‐poly(quaternized 2‐(dimethylamino)ethyl methacrylate)/ethyl bromide (PEO‐b‐PCL‐b‐qPDM‐Br)) to more hydrophobic anions, Iˉ, SCNˉ, PF₆ˉ and OTfˉ, respectively, morphological transitions from spheres to wormlike micelles and sphere to 2D platelet structure with an increasing aspect ratio are observed. The morphological transition depends on the essential hydrophilicity of the qPDM‐X segment and increasing crystallinity of the PCL core caused by ion exchange. These findings provide a facile approach to the preparation of polymeric single crystals with tunable aspect ratios.     

Syndiotactic styrene‐butadiene block copolymers synthesized with CpTiX3/MAO (Cp = C5H5, X = Cl,F; Cp = C5Me5, X = Me) and TiXn/MAO (n = 3, X = acac; n = 4, X = O‐tert‐Bu)

Copolymers sPS‐B consisting of blocks of syndiotactic polystyrene (sPS) and polybutadiene (B) have been prepared using CpTiX₃ (Cp = C₅H₅, X = Cl, F; Cp = C₅Me₅, X = Me) and TiX_n (n = 3, X = acetylacetonate (acac); n = 4, X = O‐tert‐Bu) activated with methylaluminoxane (MAO). If proper conditions are used, copolymers containing a range of styrene and butadiene molar fractions can be prepared. Structural analysis of these copolymers by means of ¹³C NMR spectroscopy allowed the assignment of different monomer diads (SS, SB, BB; S = styrene, B = butadiene) and the calculation of reactivity ratio products r₁·r₂. Differential scanning calorimetry (DSC) analysis further confirmed the block‐like structure of these copolymers. The melting points (T_m) of syndiotactic styrene sequences decrease as the styrene molar fraction decreases, whereas the glass transition temperature (Tg) increases with decreasing butadiene molar fraction in the copolymer. The polydispersity values (M_w/M_n) determined by GPC suggest that these copolymers are produced by a single site catalyst.     

Sequential reordering in condensation copolymers, 4. Crystallization-induced sequential reordering in poly(ethylene terephthalate)/polycarbonate copolymers as revealed by the behavior of the amorphous phases

An equimolar blend of poly(ethylene terephthalate) (PET) 3

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

and bisphenol-A-polycarbonate (PC) 4

2 Systematic structure-based IUPAC nomenclature: poly(oxycarbonyloxy-1,4-phenylene-1-methylethylidene-1,4-phenylene).

is studied by dynamic-mechanical thermal analysis (DMTA) and X-ray scattering after thermal treatment that enables transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples below the melting temperature of PET results in restoration of the crystallization ability. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions which closes the cycle of transformations from two homopolymers via block- and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demonstrating that their glass transition temperatures T_g's vary in accordance with the crystallinity changes. The random copolymer is characterized by a more or less homogeneous amorphous phase. In contrast to this, the mechanical mixture and the two block copolymers (the initial and that with the restored blocky structure) show DMTA peaks of two amorphous phases, clearly separated and with distinct individual T_g's. Viscosity measurements also demonstrate that the random copolymer significantly differs in its viscosity as compared to all other samples. These results represent a further evidence for the effect of block restoration via crystallization-induced sequential reordering.     

Solution properties of ultrahigh molecular weight polymers, 1. Methyl methacrylate-styrene 50:50 random copolymers

The paper is concerned with light scattering studies on solutions of ultrahigh molecular weight random copolymers of methyl methacrylate and styrene (50:50 mol/mol). The dependence of the radius of gyration and of the second virial coefficient on the weight-average molecular weight of the copolymers was established. The value of the steric factor of the copolymer compared to those of the corresponding homopolymers confirms the random character of the copolymer chain. The interpenetration function Ψ(Z), calculated on the basis of different theoretical approximations, is discussed for the expansion factor α_s³ > 7.     

Polymerization of olefins with the catalyst system (RCp)TiCl3 (R = H,CH3)/SiO2-common alkylaluminium activated with a suitable Lewis acid

The silica-supported catalyst (RCp)TiCl₃ (R = H, CH₃; Cp = cyclopentadienyl) was prepared by reaction of (RCp)TiCl₃ with silica gel. The resulting catalyst combined with common alkylaluminium as cocatalyst does not show any activity for olefin polymerization. However, the catalyst system is easily activated by adding a strong Lewis acid like (C₆H₅)₃C·B(C₆F₅)₄. Polymerization of propene and ethylene-propene copolymerization with this catalyst system gives atactic polypropene with frequent chemical inversion and a random copolymer whose structure is very similar to that produced with a homogeneous vanadium catalyst system, respectively.     

Novel thermotropic behavior of (diphenyl/phenyl-o-tolyl)phosphazene random copolymer

[(Ph₂PN)_0,76(Ph(o-tolyl)PN)_0,24] random copolymer (Ph: phenyl) was synthesized by the reaction of Ph₂POCH₂CF₃ and Ph(o-tolyl)POCH₂CF₃ with trimethylsilyl azide. Differential scanning calorimetry (DSC) measurements showed that this copolymer has a single glass transition at ≈ 80°C and transforms into a mesophase at 162 ～ 189°C depending upon the thermal history of the specimens. Lath shaped crystals with unit cell dimensions a = 1,30 nm, b = 1,13 nm and y = 87° (Form-I) were obtained from mixed dilute monochlorobenzene and p-xylene solution of the copolymer. Upon heating the specimens to 140°C, the “a” parameter of Form-I changes to a = 2,21 nm and the “b”, “y” remain unaltered (Form-II). When the specimens are cooled (10°C/min) from above T(1), the mesophase (δ-form) is “frozen in” and the δ-form specimens transform into Form-II by heating to 140°C. Another structure change (Form-III) occurs after the δ-form specimens were heated to 180°C followed by cooling below the glass transition temperature T_g. However, upon cooling the specimens slowly (0,2°C/min) from above T(1), Form-III results.     

Blends of Syndiotactic Polystyrene and Isotactic Polypropene Prepared Using a Ziegler‐Natta Catalyst Containing a Novel Donor

Blends of syndiotactic polystyrene (sPS) and isotactic polypropene (iPP) have been prepared using TiCl₄/MgCl₂/β‐diketone activated with methylaluminoxane (MAO). The influences of the Al/Ti ratio and the polymerization temperature on the catalyst activity and the blend composition have been investigated. It is shown that the polymerization temperature is an important factor in determining catalyst activity and the blend composition. Through controlling the polymerization conditions, blends containing a wide composition range of styrene/propene molar fractions can be prepared. The supported catalyst shows a good activity of about 1.5×10⁵ (g blend)·(mol Ti)^–1·h^–1. ¹³C NMR analysis allows the composition of the blends to be calculated. Dynamic mechanical analysis (DMA) reveals that the blends of sPS/iPP prepared this way are partially compatible; the two glass transition temperatures (T_g's) of the components shift towards each other. The values of T_g, as well as the peaks of sPS intensity, increase with an increasing molar fraction of styrene in the blend. When the sPS content is in the range of 59–80 wt.‐%, dual phase continuity occurs in the blends. The morphology found by microscopic observation is consistent with the DMA results.