Exploring Reaction Kinetics of a Multi‐Site Ziegler‐Natta Catalyst Using Deconvolution of Molecular Weight Distributions for Ethylene‐Hexene Copolymers

Industrial ethylene‐hexene copolymer samples produced using a supported Ti‐based Ziegler‐Natta catalyst were deconvoluted into five Flory molecular weight distributions (MWDs). Relationships between reactor operating conditions and deconvolution parameters confirmed that temperature and hydrogen and hexene concentrations influenced the MWD. The two sites that produced low‐molecular‐weight polymer responded similarly to changes in reactor operating conditions, as did the three sites that produce high‐molecular‐weight polymer. Increasing hexene concentration resulted in relatively more polymer being produced at the two low‐molecular‐weight sites and less at the high‐molecular‐weight sites. The information obtained will be useful for making simplifying assumptions during kinetic model development.

     

On the Contraction Factor of Star‐Branched Polymers with Flory‐Distributed Arms

More than fifty years ago, Zimm and Stockmayer calculated the average contraction factor of star‐branched polymers (stars) with uniformly distributed arms to be 6f/{(f + 1)(f + 2)}. Since then this contraction factor has also been used for stars with other arm distributions. In this paper we determine the (probability) density function of the contraction factor of stars with arms with a Flory (most probable) distribution and conclude that this function is equal to that for stars with uniformly distributed arms. Other arm distributions, however, lead to different contraction factor density functions. The moments of the contraction factor distribution were precisely determined with the aid of a recursion method. The stochastical behavior of the contraction factor of stars was applied to size‐exclusion chromatography (SEC) analysis and showed that upward correction of the crude SEC data is necessary to determine the proper molecular‐mass distribution of stars.     

Microphase separation in block‐random copolymers of styrene, 4‐acetoxystyrene,and 4‐hydroxystyrene

“Block‐random” copolymers—where one or more blocks are themselves random copolymers—offer a flexible modification to the usual block copolymer architecture. For example, in a poly(A)‐poly(A‐ran‐B) diblock consisting of monomer units A and B, the interblock segregation strength can be continuously tuned through the B content of the random block, allowing the design of block copolymers with accessible order‐disorder transitions at arbitrarily high molecular weights. Moreover, the development of controlled radical polymerizations has greatly expanded the palette of accessible monomer units A and B, including units with strongly interacting functional groups. We synthesize a range of copolymers consisting of styrene (S) and acetoxystyrene (AS) units, including copolymers where one block is P(S‐ran‐AS), through nitroxide‐mediated radical polymerization. At sufficiently high molecular weights, near‐symmetric PS‐PAS diblocks show well‐ordered lamellar morphologies, while dilution of the repulsive S‐AS interactions in PS‐P(S‐ran‐AS) diblocks yields a phase‐mixed morphology. Cleavage of a sufficient fraction of the AS units in a phase‐mixed PS‐P(S‐ran‐AS) diblock to hydrogen‐bonding hydroxystyrene (HS) units yields, in turn, a microphase‐separated melt. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2106–2113, 2009.     

Highly fluorinated low‐molecular‐weight photoresists for optical waveguides

A series of highly fluorinated polymers were synthesized by copolymerization of 2,3,4,5,6‐pentafluorostyrene (PFS) and fluorinated styrene derivate monomer (FSDM). Their chemical structure were confirmed by ¹H NMR, ¹³C NMR, and ¹⁹F NMR spectra. The refractive index and cross‐linking density of the polymers can be tuned and controlled by monitoring the feed ratio of comonomers. A series of negative‐type low‐molecular‐weight fluorinated photoresists (NFPs) were prepared by composing of fluorinated polystyrene derivates (FPSDs), diphenyl iodonium salt as a photoacid generator (PAG) and solvent. The polymer films prepared from NFP by photocuring exhibited excellent chemical resistance and thermal stabilities (T_d ranged from 230.5 to 258.1 °C). A clear negative pattern was obtained through direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides was measured to be 0.25 dB/cm at 1550 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Molecular Weight Development during Simultaneous Chain Scission,Long‐Chain Branching and Crosslinking, 1

A general matrix formula is proposed for the weight‐average molecular weights of the polymer systems formed through simultaneous scission, branching and crosslinking of N types of chains, assuming the chain connection statistics are Markovian. For the polymerization systems in which chains are generated consecutively, such as for free‐radical polymerization, the present theory can be applied by increasing the number of chain types N to infinity, by considering the chains formed at different times as different types of chains. The gel point determination reduces to the eigenvalue problem and the present theory extends the classical gelation theory to non‐random, history‐dependent reaction systems. From the mathematical point of view, this theory is capable of describing complex molecular build‐up processes through end‐linking, T‐ and H‐shaped chain connections, irrespective of reaction/reactor types used.

Schematic representation of the 0^th generation segment and the connection to the 1^st generation segments.     

Role of sodium dodecylbenzenesulfonate in 2,2,6,6‐tetramethy‐1‐piperidinyloxy‐mediated styrene miniemulsion polymerization

In studying 2,2,6,6‐tetramethy‐1‐piperidinyloxy (TEMPO)‐mediated styrene miniemulsions, we have observed that the surfactant sodium dodecylbenzenesulfonate (SDBS) not only provides colloidal stability but also influences the rate of polymerization. Increasing the SDBS concentration results in higher polymerization rates, although the molecular weight distribution and particle size distribution are not significantly impacted. We have also examined another common sulfonate surfactant, DOWFAX 8390. In contrast to SDBS, DOWFAX 8390 does not affect the polymerization rate. Furthermore, DOWFAX‐stabilized polymerizations are slower than SDBS‐stabilized polymerizations. TEMPO‐mediated bulk styrene polymerizations are also accelerated significantly in the presence of SDBS. Although the mechanism for the rate acceleration is unknown, the experimental evidence suggests that SDBS is participating in the generation of radicals capable of propagating, thereby reducing the TEMPO concentration within the particles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5974–5986, 2006     

Flow‐Induced Polymer Degradation During Ink‐Jet Printing

We report for the first time evidence of flow‐induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having either less than 100 kDa or greater than approximately 1 000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco‐elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro‐symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

     

Original crosslinking of poly(vinylidene fluoride) via trialkoxysilane‐containing cure‐site monomers

The synthesis of fluorinated monomers bearing an ω‐trialkoxysilane function (4,5,5‐trifluoropent‐4‐ene‐1‐trimethoxysilane and 4,5,5‐trifluoropent‐4‐ene‐1‐triethoxysilane), their radical copolymerization with vinylidene fluoride (VDF), and the crosslinking of resulting copolymers are presented. The silicon‐containing fluoromonomers were prepared from a three step‐reaction from ClCF₂CFClI, last step being the hydrosilylation of 1,1,2‐trifluoro‐1,4‐pentadiene with trialkoxysilane. The copolymerizations of these silicon‐containing fluoromonomers with VDF led to original PVDF bearing pendant trialkoxysilane functions. Their microstructures, characterized by NMR showed that VDF was the more incorporated. These latter ones were crosslinked in the presence of moisture at 200 °C leading to insoluble materials stable in solvents, oils, water, and to acids. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3896–3910, 2006     

Calculation of Molecular Weight Distributions in Non‐Linear Free‐Radical Polymerization Using the Numerical Fractionation Technique

Mathematical Modeling of non‐linear polymerization systems subject to gel formation is a challenging endeavor. At the gel point, the second and higher molecular weight moments diverge to infinity making it impossible to obtain the molecular weight distribution (MWD). The numerical fractionation (NF) technique utilizes a refinement of the method of moments to model non‐linear polymerization systems that form gel. Since the method of moments yields results in terms of average quantities, some information is lost when reconstructing the MWD using NF. As a consequence, a broad shoulder appears at the high chain length end of the MWD tail. This study demonstrates that the validity of the gamma distribution deteriorates for the broader branched polymer generations and evaluates the performance of various alternative model distributions. Proper selection of the model distribution enhances the NF‐reconstructed MWD.     

Solid‐phase incorporation of gaseous carbon dioxide into oxirane‐containing copolymers

Carbon dioxide was incorporated into poly(glycidyl methacrylate‐co‐methyl methacrylate) by a solid‐phase reaction, which transformed the pendent oxirane moieties into cyclic carbonate moieties, with quaternary ammonium halide catalysts. The incorporation of carbon dioxide into the copolymer led to soluble carbonate‐containing polymers, whereas the incorporation of carbon dioxide into the glycidyl methacrylate homopolymer produced an insoluble product. The copolymer composition, reaction temperature, and catalyst amount affected the incorporation efficiency and the side reaction that caused crosslinking. Effective incorporation was achieved under the following reaction conditions: the glycidyl methacrylate content was less than approximately 50%, the temperature was greater than the glass‐transition temperature, and the catalyst concentration was 1.5–6 mol %. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3812–3817, 2004     

Deconvolution of Molecular Weight Distributions Using Dynamic Flory‐Schulz Distributions

Summary: The deconvolution of molecular weight distributions (MWDs) may be useful for obtaining information about the polymerization kinetics and properties of catalytic systems. However, deconvolution techniques are normally based on steady‐state assumptions and very little has been reported about the use of non‐stationary approaches for the deconvolution of MWDs. In spite of this, polymerization reactions are often performed in batch or semi‐batch modes. For this reason, dynamic solutions are proposed here for simple kinetic models and are then used for deconvolution of actual MWD data. Deconvolution results obtained with dynamic models are compared to deconvolution results obtained with the standard stationary Flory‐Schulz distributions. For coordination polymerizations, results show that dynamic MWD models are able to describe experimental data with fewer catalytic sites, which indicates that the proper interpretation of the reaction dynamics may be of fundamental importance for kinetic characterization. On the other hand, reaction dynamics induced by modification of chain transfer agent concentration seem to play a minor role in the shape of the MWD in free‐radical polymerizations.

This Figure illustrates that MWDs obtained at unsteady conditions should not be deconvoluted with standard steady‐state Flory‐Schulz distributions.     

Reconstruction of the Chain Length Distribution for Vinyl‐Divinyl Copolymerization Using the Numerical Fractionation Technique

A proposed theory for evaluating the chain length distribution (CLD) using the numerical fractionation (NF) technique was extended to the vinyl‐divinyl (VDV) copolymerization. The CLD is reconstructed for this system, in which pendant double bond propagation leads to crosslinking and gel formation. The method was earlier developed for a non‐linear free‐radical polymerization scheme where chain transfer to polymer and termination by combination resulted in gel formation. The VDV study presented indicates that the proposed method of weighted summation (WS) accurately predicts the resulting CLDs evaluated using NF.

Comparison of the overall polymer NF and the direct solution CLDs near the gel point.     

Microwave‐assisted suzuki coupling reaction for rapid synthesis of conjugated polymer–poly(9,9‐dihexylfluorene)s as an example

Long reaction period (dozens of hours) is often required for the synthesis of conjugated polymers by palladium‐catalyzed Suzuki polymerization reaction. This work shows that microwave can accelerate Suzuki polymerization to realize the ultra‐rapid synthesis of conjugated polymers, here poly(9,9‐dihexylfluorene)s (PDHFs) as an example. The effects of reaction conditions on the polymerization have been systematically investigated, including the mode of microwave irradiation, microwave power, reaction temperature, reaction time, solvents, catalyst species, and catalyst concentrations. Compared with the conventional heating method (oil bath) for the synthesis of PDHFs (48 h, M_w = 20,000 g/mol), Suzuki polymerization under optimized microwave condition can yield PDHFs with higher molecular weight (M_w = 40,000 g/mol) in a much shorter time (14 min). The structures of obtained PDHFs samples are fully characterized spectroscopically, demonstrating well‐defined PDHFs have been prepared through microwave‐assisted (MA) Suzuki polymerization reaction. In addition, the mechanism of MA Suzuki polymerization is proposed preliminarily. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Ion‐exchange resins. III. Functionalization–morphology correlations in the synthesis of some macroporous,strong basic anion exchangers and uranium‐sorption properties evaluation

The synthesis and characterization of a series of macroporous, strong basic anion exchangers (SBAEs), with an average pore radius higher than 50 nm, and the evaluation of their sorption properties for uranyl chlorocomplexes from HCl solutions are reported. Finely divided macroporous styrene–divinylbenzene (S–DVB) copolymers with a narrow distribution of beads sizes, diameters within the range of 90–200 μm, were prepared for this purpose with 2‐ethyl‐1‐hexanol as a porogen, at a high dilution of monomers (D ≥ 0.55 mL/mL). Chloromethyl groups were introduced with (CH₂O)_n/Me₃SiCl as a chloromethylation agent in the presence of a Lewis acid as a catalyst (TiCl₄, SnCl₄, and FeCl₃) in CHCl₃ as a reaction medium. SnCl₄ and FeCl₃ gave comparable chloromethylation degrees in the same reaction conditions. TiCl₄ was not efficient as a catalyst in the chloromethylation with this reagent. Diethyl‐2‐hydroxyethylamine was used as a tertiary amine to prepare SBAEs. Structural and morphological characteristics were determined after every functionalization step of the macroporous network. Both the chloromethylation, in the presence of FeCl₃ as a catalyst, and the amination reactions determined a significant decrease of the pore volume, in the whole range of the nominal crosslinking degree, comparative with the starting copolymer. The specific surface area and the average pore radius varied in a different way as a function of the nominal crosslinking degree. Thus, the specific surface area increased and the average pore radius decreased after chloromethylation and amination for copolymers with a DVB content lower than 10 wt %. Small decreases of the specific surface area and the average pore radius were observed after chloromethylation and amination reactions for copolymers with a DVB content higher than 10 wt %. SBAEs were also characterized by thermogravimetric analysis and sorption capacity for uranyl chlorocomplexes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2451–2461, 2004     

Span‐Length Distributions of Star‐Branched Polymers

Many relations between the physical, rheological or mechanical properties of linear polymers and their molar mass are well known. For disperse polymers, parameters that express these relations are typically related to (a combination of) the moments of the molar‐mass distribution. Properties of branched, nonlinear polymers have been far more difficult to describe in the form of general relations. Monodisperse star polymers or regular stars, with a distinct number of arms and equal arm length, are the simplest member of the family of branched polymers and have served as model compounds in many studies. For these regular stars, the relation between zero shear viscosity and arm or span length has been determined. To establish equivalent relations for disperse star‐branched polymers, it is important to assess the span‐length distribution and its moments; these parameters can be calculated when the distribution of the molar mass of the arms of a star‐branched polymer is known, for instance, for a known polymerization mechanism.

Span‐length probability functions of star‐branched polycondensates with x_n = 100: f = 1 (•), f = 2 (○), f = 3 (▪), f = 5 (□), and f = 10 (+).     

Ethylene polymerization behavior of Cr(III)‐containing montmorillonite: Influence of chromium compounds

Montmorillonite was treated with Cr(NO₃)₃, Cr(acetate)₃, and Cr(acac)₃ to give three catalyst precursors, Cr‐MMT‐1 , Cr‐MMT‐2 , and Cr‐MMT‐3 , respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr‐MMT‐1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr‐MMT‐1 and mostly the outer surface region for the other two catalysts. Aluminosilicate‐supported Cr catalysts exhibited reactivity similar to that of Cr‐MMT‐2 and Cr‐MMT‐3 . However, more of the low‐molecular‐weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n‐Bu₂Mg and Et₂Zn in the place of Et₃Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high‐molecular‐weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272–2280, 2009     

Polymerization of an epoxy‐containing silacyclobutane and its application to networked polymer synthesis

Polymerization of a silacyclobutane having an epoxy moiety and its application to networked polymer synthesis were examined. Four‐membered ring‐opening polymerization of silacyclobutane having a 3,4‐epoxybutyl group on the silicon atom (OBMSB) was achieved by using a platinum vinyldisiloxane complex with keeping the epoxy ring unchanged. Copolymerization of 1,1‐diethylsilacyclobutane (DESB) with OBMSB by using the same catalyst effectively gave the corresponding copolymers [poly(DESB‐co‐OBMSB)]. Thermal properties of the polyOBMSB, polyDESB, and poly(DESB‐co‐OBMSB) were investigated by DSC and TGA. Cast films of the obtained polymers with 1‐naphthylmethylmethyl‐p‐hydroxyphenylsulfonium hexafluoroantimonate, a small amount of thermally latent acid generator were prepared. Heating the films at 80 °C for 2 h gave crosslinked networked polycarbosilanes through cationic ring‐opening of the epoxy moieties. Thermal and mechanical properties of the networked polymers were investigated by TGA, DSC, and tensile strength measurements. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3400–3405     

Development and application of novel ring‐opening polymerizations to functional networked polymers

This Highlight gives an overview of the recent progress in development of new ring‐opening polymerizations (ROPs) and their applications to functional networked polymers in our group. The described ROPs involve thermally induced polymerization of 1,3‐benzoxazine, anionic alternating copolymerizations of epoxides and lactones, and those exhibiting equilibrium nature. These ROPs were successfully applied to the syntheses of the relevant networked polymers, leading to their distinctive features such as high thermal stability, small volume shrinkage, and selective decrosslinking ability, which enabled design and development of next generation materials. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4847–4858, 2009     

Incorporating glycidyl methacrylate into block copolymers using poly(methacrylate‐ran‐styrene) macroinitiators synthesized by nitroxide‐mediated polymerization

Methyl methacrylate/styrene (MMA/S), ethyl methacrylate/styrene (EMA/S) and butyl methacrylate/styrene (BMA/S) feeds (>90 mol % methacrylate) were copolymerized in 50 wt % p‐xylene at 90 °C with 10 mol % of additional SG1‐free nitroxide mediator relative to unimolecular initiator (BlocBuilder^®) to yield methacrylate rich copolymers with polydispersities _w/ _n = 1.23–1.46. k_pK values (k_p = propagation rate constant, K = equilibrium constant) for MMA/S copolymerizations were comparable with previous literature, whereas EMA/S and BMA/S copolymerizations were characterized by slightly higher k_pK's. Chain extensions with styrene at 110 °C initiated by the methacrylate‐rich macroinitiators (number average molecular weight _n = 12.9–33.5 kg mol^?1) resulted in slightly broader molecular weight distributions with _w/ _n = 1.24–1.86 and were often bimodal. Chain extensions with glycidyl methacrylate/styrene/methacrylate (GMA/S/XMA where XMA = MMA, EMA or BMA) mixtures at 90 °C using the same macroinitiators resulted frequently in bimodal molecular weight distributions with many inactive macroinitiators and higher _w/ _n = 2.01–2.48. P(XMA/S) macroinitiators ( _n = 4.9–8.9 kg mol^?1), polymerized to low conversion and purified to remove “dead” chains, initiated chain extensions with GMA/MMA/S and GMA/EMA/S giving products with _w/ _n ～ 1.5 and much fewer unreacted macroinitiators (<5%), whereas the GMA/BMA/S chain extension was characterized by slightly more unreacted macroinitiators (～20%). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2574–2588, 2009