Metallocenic Copolymers of Isotactic Propylene and 1‐Octadecene: Crystalline Structure and Mechanical Behavior

Summary: A set of copolymers of isotactic propylene and 1‐octadecene (CiPOD) and the corresponding isotactic poly(propylene) homopolymer (iPP) have been synthesized using a metallocene catalyst. The influence of the incorporation of this long chain comonomer on the structure and final properties exhibited by iPP has been examined. Wide‐angle X ray diffraction and optical microscopy have been used to analyze the effect of introducing 1‐octadecene comonomer within the iPP backbone. The initial monoclinic crystal lattice with a well‐developed lamellar morphology is transformed into a mesomorphic modification showing very small entities. All these structural changes significantly influence the mechanical behavior of these copolymers. Thus, stiffness and microhardness are diminished and the brittle‐ductile transition can be observed by simply varying composition when deformation takes place at room temperature. On the other hand, the intensity of the process associated with cooperative movements within the amorphous phase (β relaxation) significantly goes up with the incorporation of 1‐octadecene and its location is shifted to lower temperature because of the decrease in the crystallinity content.

X‐ray diffraction patterns at room temperature, with increasing comonomer content.     

The Development of Stereoerrors During the Homo‐ and Copolymerization of Propylene Using C2‐Symmetric Metallocene Catalysts – A Cautionary Note

Summary: A recent paper described the development of atactic sequences during the copolymerization of propylene and 1‐pentene using the C₂‐symmetric metallocene catalyst rac‐dimethylsilyl‐bis(2‐methylbenz(e)indenyl) zirconium dichloride. We have found similar stereoerrors, and showed that atactic material could in fact be extracted from the material, indicating that the catalyst in question had probably isomerized in solution, leading to a mixture of isotactic and atactic polymers.

     

Unique morphology of amorphous polystyrene synthesised by nickel bis(acetyl acetonate)/methylaluminoxane

Polystyrene synthesised at room temperature by nickel bis(acetyl acetonate)/methylaluminoxane is globally atactic and amorphous in solid state. Unexpectedly, the amorphous polystyrene displays, in addition to normal amorphous scattering, a Bragg X‐ray diffraction at 2θ = 14°. This sharp reflection has been related to the presence of individual isotactic polystyrene sequences, as shown by ¹³C NMR. The isotactic sequences are long enough so that they are likely to form 3₁ helices, but not necessarily significantly laterally ordered and crystalline in solid state.

WAXD diagrams of (1) polystyrene synthesised by Ni(acac)₂/MAO; (2) poly(styrene‐co‐norbornene), styrene content 28.4 mol‐%; (3) poly(styrene‐co‐norbornene), styrene content 9.5 mol‐%; (4) polynorbornene.     

Low‐Temperature Polymerization of Olefins in the Presence of Titanium Monoamidinate/MAO Catalyst

This paper reports the predominantly syndiotactic‐specific polymerization of propylene in the presence of titanium monoamidinate/methylaluminoxane (MAO) catalysts. The same catalysts, depending on the reaction conditions, also promote either predominantly 1,4‐cis or 1,4‐trans polymerization of 1,3‐butadiene and polymerization of styrene either to highly syndiotactic or to stereoirregular polymer. Some preliminary information about the features of propylene polyinsertion is also reported.

Expansion of the 20–24 ppm region of the ¹³C NMR spectrum of sample 2. The starred resonance at 21.75 ppm and the shoulders are not assigned.     

Unbridged bicyclic cyclopentadienyl zirconocene complexes: Their possible application as fluxional catalysts in propene polymerization

Three series of novel unbridged bicyclic cyclopentadienyl zirconium complexes, containing six‐, seven‐ and eight‐membered saturated rings fused to the cyclopentadienyl unit and bearing different substituents ( H,  CH₃,  Ph) in position 2, were used in combination with methylaluminoxane (MAO) for the polymerization of propene at different temperatures. All the catalysts have been shown to be active, the lowest activity being observed with the eight‐membered ring systems. With most catalysts the polymers obtained are fully atactic when the polymerizations are conducted at 30 °C, and become partially isotactic at lower temperatures. The ¹³C NMR analysis shows that in one case, that is, when the seven‐membered ring is associated with the phenyl substituent in position 2, a preponderance of the isotactic heptad in the methyl region of ¹³C NMR spectrum is observed, which allows us to hypothesize the formation of stereoblocks.

     

13C NMR Study of Copolymers of Propene with Higher 1‐Olefins with New Microstructures by ansa‐Zirconocene Catalysts

Copolymers of propene and higher 1‐olefins (1‐butene, 1‐pentene, 1‐hexene, 1‐heptene, 1‐octene, and 4‐methyl‐1‐pentene (4M1P)), prepared with rac‐Et(Ind)₂ZrCl₂ ( EI ) and rac‐Me₂Si(2‐MeBenz‐[e]Ind)₂ZrCl₂ (MBI), were comprehensively analyzed by ¹³C NMR spectroscopy. These catalysts known to produce isotactic polypropene lead to two vastly different families of copolymers under the chosen experimental conditions. All copolymers produced with EI possessed comparable isotacticities as well as similar stereosequences. Furthermore, these copolymers did not significantly differ from those of the reference propene homopolymer. However, the copolymers produced with MBI significantly differed both from the reference propene homopolymer and among themselves. In fact, in contrast to the corresponding highly isotactic homopolymer, the whole series of copolymers was characterized by rather low isotacticities. The degree of tacticity was strongly influenced by the comonomer type. A detailed ¹³C NMR analysis revealed that these copolymers are constituted by highly isotactic sequences and by atactic sequences of various lengths. It is proposed that the formation of atactic sequences is triggered by the insertion of a comonomer. It seems likely that MBI can shift from a stereoselective to a non‐stereoselective state due to an interaction with higher linear or branched comonomer.

¹³C NMR spectra of propene/1‐pentene (a) and propene/4‐methyl‐1‐pentene (b) prepared with MBI .     

Synthesis and Dielectric Study of New Liquid‐crystalline Polysiloxanes Presenting a Thioether Spacer

Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.

Example of an “interdigitated” structure observed by X‐ray analysis.     

Isotactic Poly(propylene) Crystallization: Role of Small Fractions of High or Low Molecular Weight Polymer

Summary: Two well‐characterized metallocene isotactic poly(propylene) (iPP) samples, one of high and one of low molecular weight, were blended together for studying the effects of a second component on quiescent and shear‐induced crystallization. A small amount of added high molecular weight (HMW) (up to 10 wt.‐%) polymer increases the quiescent crystallization rate. This was observed as a decrease in characteristic halftime of transmitted light intensity. The crystallization halftime increases again when adding more than 10 wt.‐% of HMW polymer. The crystallization halftime of pre‐sheared samples decreases with increasing HMW fraction and is lowest for the HMW sample by itself. For the specific shearing conditions (γ = 600, T_x = 145 °C), wide‐angle X‐ray diffraction (WAXD) images show the presence of the gamma (γ) crystalline phase of iPP for samples containing 25 wt.‐% of HMW and higher. DSC thermograms demonstrated higher crystalline fractions with increasing HMW fraction in pre‐sheared samples.

Optical micrograph of an iPP sample after quiescent crystallization at 145 °C.     

Stereoblock Copolymerization of Propylene and Methyl Methacrylate with Single‐Site Metallocene Catalysts

Sequential stereoblock copolymerization of propylene (P) and methyl methacrylate (MMA) using Group IV single‐site metallocene catalysts efficiently produces PP‐b‐PMMA stereodiblock copolymers. When activated with B(C₆F₅)₃, C₂‐symmetric rac‐Et(Ind)₂ZrMe₂ yields isotactic‐PP‐b‐isotactic‐PMMA diblock copolymer, whereas C_s‐symmetric Me₂Si(C₅Me₄)(tBuN)TiMe₂ affords atactic‐PP‐b‐syndiotactic‐PMMA diblock copolymer. In the copolymerization catalyzed by the C₂‐symmetric catalyst, a very small amount of PMMA homopolymer formed can be removed from the copolymer by extracting the bulk polymer product with boiling methylene chloride. However, separation of isotactic PP formed if any from the copolymer product approves very difficult, due to very similar solubility between the diblock copolymer and isotactic PP homopolymer in various high‐boiling chlorinated solvents. On the other hand, in the copolymerization catalyzed by the C_s‐symmetric catalyst, both PMMA and atactic PP homopolymers formed in small weight fractions during the copolymerization can be successfully removed from the predominant copolymer product by solvent extraction using boiling heptane. After successful removal of both homopolymers, for example, an atactic‐PP‐b‐syndiotactic‐PMMA diblock copolymer has high molecular weight (M _n = 21 100), narrow molecular weight distribution (PDI = 1.08), high PMMA incorporation (33.8 mol‐% of PMMA), and moderate syndiotacticity for the PMMA block ([rr] ≈ 80%). Furthermore, the comonomer composition in the copolymer can be controlled by the time for propylene polymerization and the conversion of MMA. A pronounced activator effect is observed; when the same C_s‐symmetric catalyst is activated with Ph₃CB(C₆F₅)₄, formation of homopolymers is predominated.

     

Novel Thermosetting Resins Based on 4‐(N‐Maleimido)phenylglycidylether, 4

Summary: A series of polymer‐clay nanocomposites were prepared by the simultaneous in situ curing of 4‐(N‐maleimido)phenylglycidylether/4,4‐diaminodiphenylmethane (MPGE/DDM) with the intercalation/exfoliation of various organo‐modified clays. The dispersion of the clays in the polymer matrix was produced by partial exfoliation and intercalation, as observed with X‐ray diffraction and transmission electronic microscopy. Clay modified with a carboxylic acid‐containing modifier showed enhancements with repesect to clay delamination in nanocomposite preparation. In comparison with the pristine resin, MPGE/DDM‐clay nanocomposites showed improved glass transition temperatures, thermal stability and flame retardance.

Preparation and characterization of polymer‐clay nanocomposites based on a new maleimide‐epoxy hybrid monomer.     

Unexpected Formation of Atactic Blocks in Propylene/1‐Pentene Copolymers from rac‐Me2Si(2‐MeBenz[e]Ind)2ZrCl2

Summary: Supplementary experimental findings are reported in addition to those presented in a previous paper dealing with the microstructure of propylene/1‐pentene copolymers prepared with rac‐Me₂Si(2‐MeBenz[e]Ind)₂ZrCl₂. The fractionation results which demonstrate that the atactic part of the copolymer can not be separated from the isotactic one confute the hypothesis suggested by other authors according to which the catalyst used could contain a percent of impurities of the meso (aspecific) form. This evidence is in agreement with the observed narrow polydispersities and the almost random distribution of the comonomers (r_P · r_Cm ≈ 1) which are typical of single site catalysts.

¹³C NMR methyl region of pentane‐soluble (a) and pentane‐insoluble (b) fractions of copolymer prepared with MBI .     

Structural Reasons for Restricted Backbone Motion in Poly(n‐alkyl methacrylates): Degree of Polymerization,Tacticity and Side‐Chain Length

Summary: The complex dynamics of poly(n‐alkyl methacrylates) is studied by advanced ¹³C NMR spectroscopy as well as mechanical and dielectric relaxation. Extended backbone conformations are identified as the molecular units involved in structural relaxation. From the variation in the degree of polymerization and a comparison with the presence of stereoregular sequences in the sample, the length of the extended units is determined to involve about five, at most ten monomeric units. Syndiotactic and isotactic sequences behave similarly. These findings are indicative of locally structured polymer melts.

     

Optically Active Poly[{methyl(1‐naphthyl)silylene}(o‐phenylene)methylene]‐Poly(ethylene glycol) Block Copolymer Micelles

Summary: Optically pure (+) and isotactic poly[{methyl(1‐naphthyl)silylene}(o‐phenylene)methylene] terminated with methylphenylchlorosilyl was obtained by the Pt‐catalyzed ring‐opening polymerization of optically pure 1‐methyl‐1‐(1‐naphthyl)‐2,3‐benzosilacyclobut‐2‐ene in the presence of methylphenylchlorosilane as a chain transfer agent. The polymer formed was transformed into a block copolymer by reacting the terminal chlorosilyl group with a commercial poly(ethylene glycol) monomethyl ether. The formation of micelles by the block copolymer in THF‐water mixtures was investigated by fluorescence and UV. More detailed information about the aggregation of the polymer in the micelles was obtained by circular dichroism spectroscopy. It was found that dense aggregates were formed at a concentration higher than the critical micelle concentration. This concentration was higher for lower molecular weight polymer, at higher temperatures, and in more hydrophobic solvent systems. The highly aggregated structure was altered by changing the solvent system.

     

Crystallization and Ring‐Banded Spherulite Morphology of Poly(ethylene oxide)‐block‐Poly(ε‐caprolactone) Diblock Copolymer

Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.

DSC heating curve for the PEO‐b‐PCL block copolymer.     

Lanthanide Metal‐Organic Frameworks as Ziegler–Natta Catalysts for the Selective Polymerization of Isoprene

The unprecedented ability of neodymium‐based metal organic frameworks (MOFs) as polymerisation pre‐catalysts towards isoprene is reported. Combined with methylaluminoxane (MAO) or modified MAO (MMAO), they afford mainly cis‐selective polyisoprene, up to 90.7%. Both the activity and the selectivity are tentatively ascribed to the intrinsic microstructure of the starting materials. Compared to conventional carboxylates, MOFs associated to an Al co‐catalyst are less active but the selectivity is found to be higher, and it may be modified by controlling the access to the pores, which would be favored at higher temperatures. Some residual crystalline MOF remains disseminated within the polymer matrix, as shown by X‐ray diffraction and X‐ray absorption spectroscopy studies.

     

Fine Structures in the Spherulites of Regioregular Poly(3‐dodecylthiophene)

Summary: In this work, we employed various techniques to cooperatively characterize the crystalline structure and morphology of a regioregular poly(3‐dodecylthiophene). We observed the spherulites in casting films first by polarized light microscopy and then further studied the fine structures within the spherulites by scanning and transmission electron microscopy. These studies showed that the stripe‐like structures with a width of ≈20 nm and a length of 100–500 nm are the basic building blocks of the spherulites. The small‐angle X‐ray scattering and wide‐angle X‐ray diffraction studies further confirm the existence of such the structures. Considering the stiff and unfolding feature of the macromolecules, we believe that the stiff macromolecules may adopt a special way to form the fine structure: the orientation of stiff macromolecules parallel to the longitudinal direction of the stripes without any chain folding.

     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Sulfonation of Poly(propylene) Films with Fuming Sulfuric Acid

Summary: Sulfonation is one of the most commonly used methods for the surface modification of polymers. In this study, the sulfonation of poly(propylene) (PP) films with fuming sulfuric acid has been investigated with the focus on the surface reaction. Analysis of the sulfonated PP films by X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) infrared spectroscopy, and chemical modification demonstrated the formation of C?C double bonds and sulfate groups in the sulfonation process. These results and a comparison with low‐density polyethylene (LDPE) films led us to propose a new sulfonation mechanism involving hydride abstraction and the formation of β‐sultones.

The here proposed mechanism of the sulfonation of poly(propylene) involves the formation of unstable β‐sultones.     

Influence of Surface Carbon Deposition on the Bulk Crystallization of Isotactic Polypropylene

Summary: The effect of a surface‐vacuum‐evaporated ultrathin carbon layer on the bulk crystallization behavior of isotactic polypropylene (iPP) films was investigated by means of polarized optical microscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction. Results obtained from both isothermal crystallization and constant cooling experiments indicate that surface carbon deposition on an iPP film can remarkably increase the crystallization ability of it during the melt recrystallization process. Optical microscopy observations show that the melt recrystallization of iPP with a carbon coating starts about 10 °C earlier than the pure iPP during a re‐cooling process of 1 °C · min^?1. Under isothermal crystallization conditions, a much shorter induction period for nucleation is required for the carbon‐coated iPP than the non‐carbon‐coated one. The wide‐angle X‐ray diffraction and DSC analyses further demonstrate a crystallinity increment of the carbon‐coated iPP with respect to its non‐carbon‐coated counterpart. This clearly indicates that the strong influence of the interfacial interaction between the vacuum‐evaporated carbon and the iPP film on its bulk crystallization can be extended deep into the bulk material.

An OM micrograph of a hot‐pressed partially carbon‐coated (top half) iPP film.     

Carbanions on Tap – Living Anionic Polymerization in a Microstructured Reactor

The paper describes the living anionic polymerization of styrenes to homo‐ and diblock copolymers in continuous flow, using a microstructured mixing set‐up (“microreactor”). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by “break‐seal” and “high vacuum” techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g · h^?1. Facile molecular weight adjustment is achieved by variation of the flow rates of initiator or monomer solutions. The polymerization of styrene in THF and cyclohexane was studied with respect to control of molecular weight and polydispersity. Furthermore, diblock copolymers with different block lengths and low polydispersities, consisting of styrene‐ and 4‐tert‐butoxystyrene blocks were synthesized, employing a second micromixer for a delayed introduction of the additional monomer. All materials were investigated by NMR‐spectroscopy, SEC/MALLS, and MALDI‐TOF mass spectrometry, confirming narrow molecular weight distributions (MWDs; 1.09–1.25), molecular weights in the range of 500–70 000 g · mol^?1, and complete end‐functionalization. No dimerization due to side reactions that would occur in the presence of oxygen was observed, evidencing efficient shielding of the apparatus from environmental influences.