Ultrahigh draw ratios in polyethylene: Molecular weight effects

Removal of the ultrahigh molecular weight fraction in high-density polyethylene by hydrodynamic crystallization and analysis of the subsequent drawing behavior leads to the conclusion that the small portion of extremely long chains present in polymers with a log-normal molecular weight distribution is not necessary for the achievement of high draw ratios, that is, in excess of 30×. Furthermore, a certain minimum weight, and therefore chain length, is required for the attainment of high draw ratios. For example, paraffins with a molecular weight of 23,000 draw only up to about 5×. A logical extension of these concepts to other polymer systems is presented.     

Hyperbranched polycarbosilane macromonomers bearing oxazoline functionalities

Synthesis of hyperbranched polycarbosilanes by hydrosilylation of triallylsilane is reported. Soluble high molecular weight polymer was obtained in an uncontrolled bulk reaction. Addition of 2-(10-decen-1-yl)-1,3-oxazoline (i) afforded control over degree of polymerization (DP) and (ii) resulted in hyperbranched macromonomers. 17000 ≥ M _w ≥ 800 (GPC (PS)) was obtained. ²⁹Si NMR spectroscopy allowed identification of dendritic, branched, linear, and terminal silicon branch-points. A modified definition for the degree of branching yielded a value of 0.48 ± 0.05 (theory: 0.44).     

Evidence for chain transfer in the atom transfer radical polymerization of butyl acrylate

Poly(butyl acrylate) (PBuA) of high molecular weight was synthesized by atom transfer radical polymerization (ATRP) in ethyl acetate. Whereas for low molecular weight polymers, a linear increase of the number‐average molecular weight, M_n, versus conversion and narrow molecular weight distributions indicate the suppression of side reactions, a downward curvature in the plot of M_n versus conversion was observed for high molecular weights (M_n > 50 000). This effect is explained by chain transfer reactions, leading to branched polymers. GPC measurements with a viscosity detector give evidence for the branched structure of high molecular weight polymers obtained in ATRP. In addition, transfer to solvent or monomer is likely to occur.     

DETERMINATION OF BRANCHING DISTRIBUTION IN HIGH cis-1,4-POLYBUTADIENE BY GPC AND AUTOMATIC VISCOMETRY

Based on the methods reported by Ambler and Kraus, a method has been developed for the determination of long-chain branching distribution in polymers by the combined use of GPC and intrinsic viscosity data of polymer fractions. In this method, g_i, λ_i, G_i, m_i, the weight percentage of polymer that is branched, etc. can be used simultaneously to characterize the distribution, degree and content of branching in polymers. Some relations between molecular weight polydispersity and branching polydispersity in Nickel-based high cis-1,4-polybutadiene samples are discussed. It was found that the number of long branches λ. per unit molecular weight is a function of molecular weight and all of the samples are highly branched at a molecular weight of about 10~6.     

Radical polymerization in the presence of peroxide and reducing agent monomer for branched polymers

In this article, we report the radical polymerization in the presence of peroxide and commercially available or designed reducing agent monomer (RAM) for the preparation of branched poly(methyl methacrylate)s (PMMAs). The reaction behavior of the RAM was studied by NMR. Triple‐detection SEC (TD‐SEC) analysis was used to confirm the branching structure of the prepared PMMAs and to investigate the influence of peroxide concentration and RAM concentration on molecular weight and branched structure. The obtained branched PMMAs exhibited high molecular weights and relatively narrow polydispersities at high conversion of MMA. Interestingly, a significant increase in molecular weight and degree of branching of the obtained polymers are observed in higher BPO concentration, these results are quite different from that reported in the literature. The unique radical polymerization mechanism in the RAM/BPO redox‐initiated radical polymerization system resulted in branched PMMAs with high molecular weights at relatively high RAM and BPO concentrations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 833–840     

HyperMacs. Long Chain Branched Analogues of Hyperbranched Polymers Prepared by the Polycondensation of AB2 Macromonomers

We describe here a new strategy for the synthesis of polymers with highly branched architectures. The strategy involves the synthesis by anionic polymerization of well-defined AB₂ polystyrene macromonomers with molecular weights from 3,600 to 94,000 gmol⁻¹, which are then converted via a one-pot polycondensation reaction into high molecular weight, long-chain (hyper)branched architectures. Since the Hyperbranched structures are built up from condensation Macromonomers we have coined the term ‘HyperMac’ to describe these branched polymers. In this paper we report the synthesis of the HyperMacs, the optimal conditions for the polycondensation reaction and some preliminary characterization studies.     

Synthesis and performance of ansa-metallocene catalysts with substituted heterocyclic and indenyl ligands

Synthesis of new ansa-metallocene catalysts incorporating branched alkyl groups alpha to the bridgehead carbon of indenyl and thiapentalenyl ligands is reported. Me₂Si(2-Me-4-Ph-Indenyl)₂ZrCl₂ and Me₂Si(2,5-Me₂-3-Ph-Thiapentalenyl)₂ZrCl₂ type metallocenes with one and two isopropyl groups substituted for 2-methyl substitutents were prepared and used as procatalysts in propylene polymerizations and E/P copolymerizations. The 2-isopropyl groups influenced catalyst activity, molecular weight, and the relative amounts of microstructure errors. In contrast to procatalysts with only 2-methyl groups, polymer molecular weights increased in E/P copolymerizations with 2-isopropyl substituted complexes. The text was submitted by the authors in English.     

Architectural control of polystyrene physical properties using branched anionic polymerization initiated at ambient temperature

Ambient temperature-initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec-Butylithium-initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules.     

Homogeneous and multiphase poly(methyl methacrylate) graft polymers via the macromonomer method

Anionic and group transfer polymerization processes were used to synthesize controlled molecular weight methacryloyloxy functionalized poly(dimethylsiloxane) and poly(methyl methacrylate) macromonomers having a narrow molecular weight distribution and high percent functionality. These macromonomers were anionically copolymerized with methyl methacrylate (MMA) to afford poly(methyl methacrylate)-graft-poly(methyl methacrylate) (PMMA-g-PMMA) and poly(methyl methacrylate)-graft-poly(dimethylsiloxane) (PMMA-g-PDMS) polymers having not only narrow molecular weight distribution graft parts but also backbone parts. The PMMA-g-PDMS system was fractionated using supercritical chlorodifluoromethane to determine its chemical composition distribution (CCD). The CCD for the PMMA-g-PDMS copolymerized in a living manner was substantially more narrow than the free radically copolymerized material. The PMMA-g-PMMA system was used to study the dilute solution properties of branched homopolymers. The appropriateness of the universal calibration gel permeation chromatography (GPC) method for branched systems exhibiting long chain branching was reaffirmed.     

Ultra‐Tuning of the Rare‐Earth fcu‐MOF Aperture Size for Selective Molecular Exclusion of Branched Paraffins

Using isoreticular chemistry allows the design and construction of a new rare‐earth metal (RE) fcu ‐MOF with a suitable aperture size for practical steric adsorptive separations. The judicious choice of a relatively short organic building block, namely fumarate, to bridge the 12‐connected RE hexanuclear clusters has afforded the contraction of the well‐defined RE‐ fcu ‐MOF triangular window aperture, the sole access to the two interconnected octahedral and tetrahedral cages. The newly constructed RE (Y³⁺ and Tb³⁺) fcu ‐MOF analogues display unprecedented total exclusion of branched paraffins from normal paraffins. The resultant window aperture size of about 4.7 Å, regarded as a sorbate‐size cut‐off, enabled a complete sieving of branched paraffins from normal paraffins. The results are supported by collective single gas and mixed gas/vapor adsorption and calorimetric studies.     

短链支化对低分子量聚乙烯结晶及熔融行为的影响

研究了金属茂催化的低分子量支化聚乙烯和线性聚乙烯的结晶及熔融行为 ,发现支化聚乙烯的结构与线性聚乙烯相同为正交结构 ,但晶格略有膨胀 .支链的存在对熔融行为影响不大 ,两种聚乙烯的熔点均随结晶温度的升高而非线性增加 ,表现出低分子量样品的共同特征 .但支链的存在对结晶行为却有很大的影响 ,主要是由于支链的存在降低了晶体的结晶速率从而影响结晶过程 ,使得低分子量的支化聚乙烯的结晶行为与高分子量线性聚乙烯的结晶行为相似而与低分子量的线性聚乙烯不同 .动力学分析表明 ,低分子量的支化聚乙烯的结晶生长方式的转变温度比同等分子量的线性聚乙烯降低了约 2 0℃     

Organometallic polymers. XXV. Preparation of polyvinylferrocene

The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (M?_n ? 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.     

Obtaining aliphatic branched polycarbonates via simple copolymerization of trimethylene carbonate with cyclic carbonate containing pendant ester groups

Different possibilities for obtaining branched, functional carbonate copolymers are presented in this study. Copolymers were synthesized according to the ring‐opening polymerization (ROP) of the cyclic carbonate monomers, containing pendant ester groups. As an example, we chose copolymerization of ethyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate (MTC‐Et) with trimethylene carbonate (TMC), using zinc (II) and lanthanum (III) acetylacetonates as ROP initiators. The transesterification processes of ester groups in pendant, short chains, appearing during conducted copolymerization, led to the establishment of two different fractions: first‐branched and high molecular weight fraction and second‐linear and low molecular weight. The content of this high‐molecular‐weight fraction increased with both: the amount of MTC‐Et in started reaction mixture and the time of conducted copolymerization. Reactivity constants in studied reaction were determined. It was possible to obtain the copolymer fraction (ca. 30%) with molecular weight of up to a million g/mol, with a highly branched chain microstructure using lanthanum (III) acetylacetonate as initiator. Conclusions were based on detailed NMR analysis, determining microstructure of the copolymer chains and additionally on GPC and DSC measurement. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 808–819     

Effect of the monomer concentration on piperylene cationic polymerization in the presence of the TiCl4-trichloroacetic acid catalytic system

The effect of the monomer concentration on the kinetics of cationic polymerization of piperylene in the presence of the TiCl₄-trichloroacetic acid catalytic system and molecular weight of the produced polymer was studied. At high monomer concentrations, the high-molecular-weight peak related to the formation of the branched fraction appears in the molecular weight distribution curve of the produced polymer. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1310–1313, July, 2007.     

Round‐robin experiment in high‐temperature gel permeation chromatography

The results of an interlaboratory or round‐robin experiment in high‐temperature gel permeation chromatography (HT‐GPC) analysis are presented. The intention was to determine and raise awareness of interlaboratory reproducibility of HT‐GPC techniques. Fifteen laboratories performed analyses of five polyethylene samples and standards SRM 1475 and 1476. Reproducibility, as measured by the interlaboratory standard deviation (s_LAB), was greatly influenced by the breadth of the molecular weight distribution (MWD) and branching. The s_LAB values for the weight‐average molecular weight (M_w) of linear polyethylenes of narrow and broad MWDs were 4 and 14%, respectively. For branched polymers, GPC viscometry methods are shown to measure significantly higher molecular weights than the noncoupled GPC method, with higher variance. For branched polyethylenes measured with GPC viscometry, the reproducibility of M_w was characterized by s_LAB = 18%. Reproducibility of the SRM 1475 standard was better than for unknowns. The results for branched standard SRM 1476 emphasize the important role of the detection method in GPC but call into question the use of this material as a molecular weight standard. For single‐site polyethylene, only a handful of labs measured an MWD that closely matched the Flory distribution. Qualitatively, the responses indicate that many variations in instrument and analytical methods exist among laboratories; this is partly a reflection of the development and refinements that this technique must yet undergo before a truly standard method is widely accepted and practiced. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 905–921, 2002     

Branched polymers through redox emulsion polymerization using peroxide monomer as the branching agent

Redox emulsion polymerization to branched vinyl polymers in the presence of 2-(tert-butylperoxy)ethyl methacrylate (BPEMA), ferrous sulfate, and sodium formaldehyde sulfoxylate (SFS) is reported in this paper. The peroxide monomer BPEMA containing alkyl peroxide was designed for high stability during preparation and storage. Nuclear magnetic resonance spectroscopy (NMR), Raman, and triple-detection size-exclusion chromatography (TD-SEC) measurements were used to reveal the polymerization procedure and provide evidence of branching structure. In the case of polymerization at St₁₀₀-BPEMA_1.0-FeSO_{4 0.5}-SFS_0.2, the molecular weight increased and decreased with conversion below and above 75% monomer conversion, respectively. The decreasing of molecular weight with monomer conversion came from the increased viscosity of the micelle, which makes it difficult for the formed macromolecules containing vinyl group to participate into polymerization. Finally, the molecular weight reached a value of M_{n. SEC} = 439,200 g/mol at 92.2% conversion. In addition, the Zimm branching factor, g', also decreased and increased with conversion below and above 60% conversion, respectively, and then the g' finally attends a value of 0.41, showing high degree of branching. Branched poly(methyl methacrylate) was also prepared through this strategy, showing a versatile approach to branched vinyl polymers.     

Randomly branched bisphenol A polycarbonates. I. Molecular weight distribution modeling,interfacial synthesis,and characterization

Randomly branched bisphenol A polycarbonates (PCs) were prepared by interfacial polymerization methods to explore the limits of gel‐free compositions available by the adjustment of various composition and process variables. A molecular weight distribution (MWD) model was devised to predict the MWD, G, and weight‐average molecular weight per arm (M_w /arm) values based on the composition variables. The amounts of the monomer, branching agent, and chain terminator must be adjusted such that the weight‐average functionality of the phenolic monomers (F_OH ) was less than 2 to preclude gel formation in both the long‐ and short‐chain branched (SCB) PCs. Several series of SCB and long‐chain branched PCs were prepared, and those lacking gels showed molecular weights measured by gel permeation chromatography–UV and gel permeation chromatography–LS consistent with model calculations. In SCB PCs, the minimum M_w /arm that could be realized without gel formation depended on both composition (molecular weight, terminator type) and process (terminator addition point, coupling catalyst) variables. The minimum M_w /arm achieved in the low molecular weight series studied ranged from ∼3300 to ∼1000. The use of long chain alkyl phenol terminators gave branched PCs with lower glass‐transition temperatures but a higher gel‐free minimum M_w /arm. SCB PCs where M_w /arm was less than ∼M_c spontaneously cracked after compression molding, a result attributed to their lack of polymer chain entanglements. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 560–570, 2000     

Reaction rate of crosslinkings by using a metallated polymer. II. Intermolecular and intramolecular crosslinkings at the second state

Lithium-metallated styrene–p-benzylstyrene copolymer was reacted with the branched polymer with chlorine groups at the pendant chain ends (multifunctional branched polymer) in tetrahydrofuran (THF) at 25°C. The rate constant was estimated from the changes in the concentration of metallated polymer by using photometrical measurements. The various reaction conditions were chosen and it became clear that the rate constants of intermolecular (k₂₀) and intramolecular (k_3intra) crosslinkings were derived separately at the second stage. k₂₀ showed a constant value in spite of the molecular weight of crosslinker chains and was about equal to the rate constant of the grafting. The rate of intramolecular crosslinking at the second stage increased with decreasing the molecular weight of pendant chains of multifunctional branched polymer.     

茂金属聚乙烯的非等温结晶行为及其动力学研究

为探索分子量和支链含量对聚乙烯非等温结晶过程的影响,选用3组样品:(1)不同分子量的无支链线形聚乙烯;(2)低分子量的支链含量不同的试样;(3)高分子量的支链含量不同的试样.用DSC研究了这3组样品的非等温结晶动力学.结果表明:(1)与支链含量相比,分子量大小对结晶的影响是次要的,但高分子量样品的结晶度比低分子量样品低;(2)支链对聚乙烯的非等温结晶有重要影响,在支化聚乙烯中起决定作用;(3)无论是高分子量试样还是低分子量试样,支化含量增加,聚乙烯的结晶温度、结晶度、结晶动力学以及晶体的熔点等显著降低.     

Branching by reactive end groups. II. Synthesis,branching, and melt rheology of (meth)acrylate/p‐t‐butylphenol‐coterminated bisphenol a polycarbonates

(Meth)acrylate/p‐t‐butylphenol (PTBP)‐coterminated bisphenol A polycarbonates (PCs) were prepared by interfacial processes and subsequently were reacted at high temperatures (≥200 °C) to form new branched polymers. Two interfacial methods were used to prepare the precursor linear PCs, one with (meth)acryloyl chloride [(M)AC] and the other with (meth)acrylic acid [(M)AA]. Both processes involve phosgenation in the presence of catalytic amounts of triethylamine. The process that used (M)AC formed disproportionately large amounts of bisphenol A di(meth)acrylate, whereas the process using (M)AA required about 50% more phosgene to achieve high (M)AA conversions than typical interfacial PC processes. The branching of the acrylate/PTBP PCs occurred with heating at temperatures greater than or equal to 250 °C. The molecular weight and degree of branching depended on the mole ratio of the thermally reactive and nonreactive coterminators, the total amount of coterminators, and the reaction conditions. The functionality of the branch points formed appeared to be dependent on the acrylate concentration. The branching of the methacrylate/PTBP PCs required the presence of a free‐radical initiator and temperatures up to about 200 °C. The methacrylate end group was less effective than the acrylate on a molar basis in increasing the branched polymer molecular weight and degree of branching. The melt rheology of the branched acrylate/PTBP PCs showed the expected increase in low shear viscosity and shear rate sensitivity with increasing weight‐average molecular weight and acrylate‐end‐group concentration. Small changes in the total terminator concentration and, therefore, the linear precursor polymer molecular weight produced large effects in the low shear rate melt viscosity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2340–2351, 2000