Triple Detection GPC Research Articles

Hydrophilic Nonwoven Nanofiber Membranes as Nanostructured Supports for Enzyme Immobilization.

The high porosity, interconnected pore structure, and high surface area-to-volume ratio make the hydrophilic nonwoven nanofiber membranes (NV-NF-Ms) promising nanostructured supports for enzyme immobilization in different biotechnological applications. In this work, NV-NF-Ms with excellent mechanical and chemical properties were designed and fabricated by electrospinning in one step without using additives or complicated crosslinking processes after electrospinning. To do so, two types of ultrahigh-molecular-weight linear copolymers with very different mechanical properties were used. Methyl methacrylate-co-hydroxyethyl methacrylate (p(MMA)-co-p(HEMA)) and methyl acrylate-co-hydroxyethyl acrylate (p(MA)-co-p(HEA)) were designed and synthesized by reverse atom transfer radical polymerization (reverse-ATRP) and copper-mediated living radical polymerization (Cu0-MC-LRP), respectively. The copolymers were characterized by nuclear magnetic resonance (1H-NMR) spectroscopy and by triple detection gel permeation chromatography (GPC). The polarity, topology, and molecular weight of the copolymers were perfectly adjusted. The polymeric blend formed by (MMA)1002-co-(HEMA)1002 (Mw = 230,855 ± 7418 Da; Mn = 115,748 ± 35,567 Da; PDI = 2.00) and (MA)11709-co-(HEA)7806 (Mw = 1.972 × 106 ± 33,729 Da; Mn = 1.395 × 106 ± 35,019 Da; PDI = 1.41) was used to manufacture (without additives or chemical crosslinking processes) hydroxylated nonwoven nanofiber membranes (NV-NF-Ms-OH; 300 nm in fiber diameter) with excellent mechanical and chemical properties. The morphology of NV-NF-Ms-OH was studied by scanning electron microscopy (SEM). The suitability for enzyme binding was proven by designing a palette of different surface functionalization to enable both reversible and irreversible enzyme immobilization. NV-NF-Ms-OH were successfully functionalized with vinyl sulfone (281 ± 20 μmol/g), carboxyl (560 ± 50 μmol/g), and amine groups (281 ± 20 μmol/g) and applied for the immobilization of two enzymes of biotechnological interest. Galactose oxidase was immobilized on vinyl sulfone-activated materials and carboxyl-activated materials, while laccase was immobilized onto amine-activated materials. These preliminary results are a promising basis for the application of nonwoven membranes in enzyme technology.

Suppression of hydrolytic degradation in labile polymer networks via integrated styrenic nanogels

ObjectiveThe objective of this study was to demonstrate an approach with potential to increase the life of dental restorative polymers in water, by maintaining their strength and toughness with varied content of inert or reactive styrenic pre-polymeric additives. It was hypothesized that addition of styrene-co-divinylbenzene nanogels to a conventional dimethacrylate resin (e.g. TEGDMA) would reduce its susceptibility towards hydrolytic degradation, while maintaining equivalent mechanical properties. MethodsPolymerization kinetics and functional group conversions were determined by Fourier transform infrared spectroscopy. Triple-detection gel permeation chromatography was used for nanogel particle characterization. A goniometer was used to measure water contact angle on experimental and control photocured polymers. Hydrolytic degradation and mass loss evaluation was performed after extended water storage of an intentionally hydrolytically degradable polymer. Resin viscosity was determined rheometrically and polymer mechanical properties were evaluated using three-point flexural testing with TEGDMA-nanogel formulations. ResultsThe polymer network with highest level of nanogel loading (50 wt%) and the highest level of internal nanogel crosslinking (50 mol%) had the lowest degree of equilibrium swelling ratio and mass loss. The flexural modulus and ultimate strength of polymerized TEGDMA and styrenic nanogel-modified TEGDMA were not statistically different (p > 0.05). SignificanceDue to improved shielding throughout the bulk of methacrylate-based polymers, including an example with an intentionally hydrolytically labile network structure, and a dramatic decrease of water uptake while maintaining equivalent mechanical properties, styrenic nanogel additives especially in high loading levels provide an excellent alternative to eliminate the adverse effects of water and presumably salivary fluids.

Effects of extruder screw configurations on thermal properties of glass fiber‐reinforced polyamide 6 composites throughout the direct long‐fiber‐reinforced thermoplastics process

The direct long‐fiber‐reinforced thermoplastics (D‐LFT) process is a series of processes involving two twin‐screw extruders, a conveyer, and a compression molding machine. The second twin‐screw extruder is designed for mixing continuous fibers with polymer melt and plays an important role in the D‐LFT process. This study investigates effects of the screw configurations of the second extruder on thermal properties of glass fiber‐reinforced polyamide 6 (PA6) composites throughout the D‐LFT process. Two screw configurations, which generate low and high shear stress in composite melt (named the conveying and mixing screws, respectively), were used in the second twin‐screw extruder. Samples were taken from four different locations along the D‐LFT process and characterized using triple detection gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results suggested that the molecular weight of the PA6 matrix increased in the later stages of the D‐LFT process (i.e., after the second extruder) by branching of PA6 molecules. In addition, the mixing screw decreased the molecular weight of the PA6 matrix more than the conveying screw. However, such a decrease in molecular weight had little influence on the thermal stability and crystallization behavior of the composites. POLYM. COMPOS., 40:3500–3509, 2019. © 2019 Society of Plastics Engineers

“Push–push and push–pull” polystannanes

The synthesis and characterization of polystannanes with "push" or "pull" moieties attached to the tin backbone are described. Precursor tetra aryl- (1, 2) stannanes were converted to mono- (3) and dichloro- (4, 5) stannanes by either sequential chlorination or by redistribution reactions with SnCl4. Compounds 4 and 5 were transformed to polymerisable tin dihydride monomers 6 and 7 using a large excess (10×) of NaBH4. Homopolymer 8 with electron donating aryl substituents (p-MeOC6H4-) was synthesized by dehydrogenative polymerization using Wilkinson's catalyst. Attempts to prepare the homopolymer 9 with electron withdrawing aryl substituents (p-CF3C6H4-) from the dehydrocoupling of 7 using similar conditions led only to the formation of low molecular weight oligomeric species. Two alternating polymers, 10 and 11, were synthesized by condensation polymerization of (n-Bu)2Sn(NEt2)2 with monomers 6 or 7. The first was a "push-push" alternating polymer, 10, comprised of a repeating unit consisting of two different electron donating groups (p-MeOC6H4-, n-Bu) at neighboring tin centres. The second was a "push-pull" alternating polymer, 11, bearing both an electron donating group (n-Bu) and a strongly electron withdrawing substituent (p-CF3C6H4-) at neighboring tin atoms. All small molecule stannanes and tin-containing polymers were characterized by NMR (1H, 13C, 119Sn, and where required 19F) spectroscopy, MS or EA. The absolute molecular weights of tin polymers (8, 10, 11) were determined by triple detection GPC and in the range of 1.07 × 104 to 1.95 × 104 Da. Rapid photodegradation of polymers was observed by UV-Vis spectroscopy, with a slower degradation observed for the "push-pull" polymer, 11, compared to the "push-push" polymer, 10.

A powerful tool for preparing peripherally post-functionalized multiarm star block copolymer

A facile synthetic approach for the design of peripherally post-functionalized multiarm star block copolymer has been established by nucleophilic aromatic substitution reaction of pentafluorophenyl periphery functional multiarm star polymer with alcohol moieties of poly(ethylene glycol) (PEG-OH) under mild reaction conditions. For this purpose, α-fluoro-functionalized PS (α-fluoro-PS) was prepared by atom transfer radical polymerization (ATRP) of styrene (St) and was allowed to react with divinyl benzene (DVB) as a linking agent yielding (fluoro-PS)n–polyDVB multiarm star polymer. Then, (PEG)m–(PS)n–polyDVB multiarm star block copolymer was synthesized via nucleophilic addition of PEG-OH precursor with (fluoro-PS)n–polyDVB multiarm star polymer in the presence of sodium hydride in tetrahydrofuran at reflux for 3 h. Multiarm star polymers were characterized using triple detection gel permeation chromatography (TD-GPC), FT-IR, 1H NMR, 19F NMR and 13C NMR.

Linear, Star, and Comb Oxidation-Responsive Polymers: Effect of Branching Degree and Topology on Aggregation and Responsiveness.

Families of amphiphilic oxidation-responsive polymers (poly(ethylene glycol)-polysulfides) with different architectures (linear, 4, 6, and 8-armed stars and 10, 15, and 20-armed combs) and compositions (variable ethylene sulfide/propylene sulfide ratio) are prepared. In water, all the polymers assemble in spherical micelles, with critical micellar concentrations <0.01 mg mL-1 for all the branched polymers. Triple-detection gel permeation chromatography (GPC) and asymmetric field flow fractionation (AFFF) with dynamic and static light scattering detection, respectively, show an increasing compaction of the polymeric coil and a strong reduction of the aggregation number with increasing degree of branching. The key finding of this study is that the kinetics of the oxidative response sharply depend on the branching; in particular, it is highlighted that the degree of branching influences the lag time before a response can be observed rather than the speed of the response itself, a phenomenon that is attributed to a branching-dependent solubility of the oxidant in the polysulfide matrix.

Heterofunctionalized Multiarm Star Polymers via Sequential Thiol-para-Fluoro and Thiol-Ene Double “Click” Reactions

The successful postfunctionalization of multiarm star polystyrene (PS) with pentafluorophenyl and allyl moieties at the periphery is demonstrated employing modular thiol-para-fluoro and photoinduced radical thiol-ene double “click” reactions, respectively. α-Fluoro and α-allyl functionalized PS (α-fluoro-PS and α-allyl-PS) are in situ prepared by atom transfer radical polymerization of styrene and their mixture is used as macroinitiator in a crosslinking reaction with divinyl benzene (DVB) yielding (fluoro-PS)m–polyDVB–(allyl-PS)m multiarm star polymer. It is found that the multiarm star polymer includes nearly identical number of arms possessing pentafluorophenyl and allyl moieties at the periphery. The obtained multiarm star polymer is then reacted with 1-propanethiol through thiol-para-fluoro “click” reaction to give (propyl-PS)m–polyDVB–(allyl-PS)m multiarm star polymer, which is subsequently reacted with N-acetyl-l-cysteine methyl ester via radical thiol-ene “click” reaction in order to give well-defined heterofunctionalized (propyl-PS)m–polyDVB–(cysteine-PS)m multiarm star polymer, with higher molecular weight and narrow molecular weight distribution. Multiarm star polymers are characterized by using viscotek triple detection gel permeation chromatography, 1H, and 19F NMR.

Divergent Macrocyclization Mechanisms in the Cationic Initiated Polymerization of Ethyl Glyoxylate

We recently discovered that the cationic polymerization of o-phthalaldehyde generates cyclic poly(phthalaldehyde) in high yield, high molecular weight, and a high degree of cyclic purity. Given this surprising result, we pursued the cationic polymerization of ethyl glyoxylate to determine if the macrocyclization outcome is, in fact, a general trend of low ceiling temperature polyacetals. Using NMR spectroscopy, MALDI-TOF mass spectrometry, and triple detection GPC, we have uncovered divergent macrocyclization mechanisms in the cationic polymerization of ethyl glyoxylate. Backbiting is observed either via the backbone acetal or via the pendant ester to give disparate polymer products and unique polymer architectures. The favored route for cyclization is found to depend on both the monomer concentration and the initiating species. Understanding the underlying mechanisms of polymerization and the ability to rigorously control polymer structure has important implications for the design of new transient materials.

Cyclic Amphiphilic Random Copolymers Bearing Azobenzene Side Chains: Facile Synthesis and Topological Effects on Self‐Assembly and Photoisomerization

In this article, well-defined cyclic amphiphilic random copolymers bearing azobenzene side chains and pendent carboxyl moieties, cyclic-P(BHMEm -co-AAn )s, are synthesized by combining atom transfer radical polymerization (ATRP) with Cu(I)-catalyzed azide/alkyne cycloaddition (CuAAC) "click" reaction and selective hydrolysis of tert-butyl ester. Successful synthesis of the cyclic-P(BHMEm -co-AAn )s is fully characterized and verified via conventional gel permeation chromatography, triple detection gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared, and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. The cyclic topology induces profound effects on the glass transition temperatures, self-assembly behavior, and photoresponsive performance of the copolymers compared with their linear counterparts.

End Group Characterization of Poly(phthalaldehyde): Surprising Discovery of a Reversible, Cationic Macrocyclization Mechanism

End-capped poly(phthalaldehyde) (PPA) synthesized by anionic polymerization has garnered significant interest due to its ease of synthesis and rapid depolymerization. However, alternative ionic polymerizations to produce PPA have been largely unexplored. In this report, we demonstrate that a cationic polymerization of o-phthalaldehyde initiated by boron trifluoride results in cyclic PPA in high yield, with high molecular weight, and with extremely high cyclic purity. The cyclic structure is confirmed by NMR spectroscopy, MALDI-TOF mass spectrometry, and triple-detection GPC. The cyclic polymers are reversibly opened and closed under the polymerization conditions. Owing to PPA's low ceiling temperature, cyclic PPA is capable of chain extension to larger molecular weights, controlled depolymerization to smaller molecular weights, or dynamic intermixing with other polymer chains, both cyclics and end-capped linears. These unusual properties endow the system with great flexibility in the synthesis and isolation of pure cyclic polymers of high molecular weight. Further, we speculate that the absence of end groups enhances the stability of cyclic PPA and makes it an attractive candidate for lithographic applications.

The Effects of Gamma Irradiation on Medical Grade Poly(Methyl Methacrylate)

Within developing countries the most cost-effective polymer used in the fabrication of rigid intraocular lenses (IOLs) is poly(methyl methacrylate) (PMMA), for which gamma irradiation is increasingly being used as the preferred method of sterilisation. Medical grade PMMA samples sterilised using a dose of 29kGy of gamma irradiation, were immersed in a simulated aqueous humour solution (SAHS) (pH 7.4, 35 °C), and periodically removed to assess changes in their thermal and structural properties with respect to control samples. Triple-detection gel permeation chromatography indicated that substantial chain scission had occurred during gamma irradiation, an adverse effect that also resulted in a small increase in the rate of diffusion of the SAHS into the PMMA. The diffusion coefficient of SAHS into the gamma-sterilised PMMA was 2.7 ± 0.6 × 10−12 m2s−1, and that for the control samples was 2.0 ± 0.5 × 10−12 m2 s−1. Thermomechanical analysis revealed a decreasing Tg with time for samples incubated in SAHS, showing that the solution caused plasticisation irrespective of irradiation; however, the γ-sterilised PMMA had a Tg 7 °C lower than the control PMMA, which indicates the effect of the γ-irradiation on the rigidity of the polymer.

Various polycarbonate graft copolymers via diels–alder click reaction

AbstractIn this work, we used Diels–Alder click reaction for the preparation of various types of aliphatic polycarbonates (PCs). We first prepared a novel anthracene‐functionalized cyclic carbonate monomer, anthracen‐9‐ylmethyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate (2), followed by ring‐opening polymerization of this monomer to prepare PC with pendant anthracene groups (PC‐anthracene) using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU)/1‐(3,5‐bis(trifloromethyl)phenyl)‐3‐cyclohexylthiourea (TU) as the catalyst and benzyl alcohol as the initiator in CH2Cl2 at room temperature. Subsequently, the resulting PC‐anthracene (Mn,TDGPC = 6000 g/mol, Mw/Mn = 1.22) was grafted with a linear α‐furan protected‐maleimide terminated‐poly(methyl methacrylate) (PMMA‐MI) (Mn,GPC = 3100 g/mol, Mw/Mn = 1.31), or poly(ethylene glycol) (PEG‐MI) (Mn,GPC = 550 g/mol, Mw/Mn = 1.09), or a mixture of PMMA‐MI and PEG‐MI to yield well‐defined PC graft or hetero graft copolymers, PC‐g‐PMMA (Mn,TDGPC = 59000 g/mol, Mw/Mn = 1.22) or PC‐g‐PEG, or PC‐g‐(PMMA)‐co‐PC‐g‐(PEG) (Mn,TDGPC = 39900 g/mol, Mw/Mn = 1.16), respectively, using Diels–Alder click reaction in toluene at 110°C. The Diels–Alder grafting efficiencies were found to be over 97% using UV spectroscopy. Moreover, the structural analyses and the molecular weights of resulting graft copolymers were determined via 1H NMR and triple detection GPC (TD‐GPC), respectively. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Sequential double polymer click reactions for the preparation of regular graft copolymers

AbstractIn this study, graft copolymers with regular graft points containing polystyrene (PS) backbone and poly(methyl methacrylate) (PMMA), poly(tert‐butyl acrylate) (PtBA), or poly (ethylene glycol) (PEG) side chains were simply achieved by a sequential double polymer click reactions. The linear α‐alkyne‐ω‐azide PS with an anthracene pendant unit per chain was produced via atom transfer radical polymerization of styrene initiated by anthracen‐9‐ylmethyl 2‐((2‐bromo‐2‐methylpropanoyloxy)methyl)‐2‐methyl‐3‐oxo‐3‐(prop‐2‐ynyloxy) propyl succinate. Subsequently, the azide–alkyne click coupling of this PS to create the linear multiblock PS chain with pendant anthracene sites per PS block, followed by Diels–Alder click reaction with maleimide end‐functionalized PMMA, PtBA, or PEG yielded final PS‐g‐PMMA, PS‐g‐PtBA or PS‐g‐PEG copolymers with regular grafts, respectively. Well‐defined polymers were characterized by 1H NMR, gel permeation chromatography (GPC) and triple detection GPC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Design and synthesis by ATRP of novel, water-insoluble, lineal copolymers and their application in the development of fluorescent and pH-sensing nanofibres made by electrospinning

In this work, reverse Atom Transfer Radical Polymerization (ATRP) was used for synthesising novel water-insoluble lineal copolymers which were used for designing new fluorescent and pH-sensitive, nanostructured films based on nanofibre mats made by electrospinning. The copolymers are based on the copolymerization of fluorescein o-acrylate (fluorescent pH-sensitive monomer) with methyl methacrylate and hydroxyl ethyl methacrylate (principal framework of the copolymers) and 3-methacryloylaminopropyl-trimethylammonium chloride (positively charged monomer) or 2-acrylamido-2-methylpropane sulfonic acid (negatively charged monomer). The electrostatic properties of these copolymers were investigated, and perfectly adjusted to maintain the complete insolubility of these materials in aqueous media. The copolymers were also characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H-NMR) spectroscopy and by triple detection gel permeation chromatography (GPC). The synthesised copolymers are soluble in organic solvents such as tetrahydrofuran, acetone, and dimethylformamide. These facts make them highly versatile and very good candidates for the preparation of novel nanostructured, optical pH-sensitive sensing phases produced by different techniques such as electrospinning, spin coating, deep coating, spray dry, spray coating, etc., and with different structures, morphologies, and geometries for many different applications. To demonstrate these claims, we used these copolymers for providing highly fluorescent pH-sensitive nanofibres made by electrospinning. The selected flow rates and voltages of the electrospinning configuration allowed the collection of dry fibres in nonwoven mats. The nanofibres were characterised by scanning electron microscopy (SEM) and fluorescence microscopy and the fibre mats were successfully used for pH-monitoring in two different pH ranges (6.5–8 and 8–10) showing reversibility, high sensitive and low response times.

Block‐brush copolymers via ROMP and sequential double click reaction strategy

AbstractWe report an efficient way, sequential double click reactions, for the preparation of brush copolymers with AB block‐brush architectures containing polyoxanorbornene (poly (ONB)) backbone and poly(ε‐caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or poly(tert‐butyl acrylate) (PtBA) side chains: poly(ONB‐g‐PMMA)‐b‐poly(ONB‐g‐PCL) and poly(ONB‐g‐PtBA)‐b‐poly(ONB‐g‐PCL). The living ROMP of ONB affords the synthesis of well‐defined poly(ONB‐anthracene)20‐b‐poly (ONB‐azide)5 block copolymer with anthryl and azide pendant groups. Subsequently, well‐defined linear alkyne end‐functionalized PCL (PCL‐alkyne), maleimide end‐functionalized PMMA (PMMA‐MI) and PtBA‐MI were introduced onto the block copolymer via sequential azide‐alkyne and Diels‐Alder click reactions, thus yielding block‐brush copolymers. The molecular weight of block‐brush copolymers was measured via triple detection GPC (TD‐GPC) introducing the experimentally calculated dn/dc values to the software. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Graft copolymers via ROMP and Diels–Alder click reaction strategy

AbstractAnthracene‐functionalized oxanorbornene monomer and oxanorbornenyl polystyrene (PS) with ω‐anthracene end‐functionalized macromonomer were first polymerized via ring‐opening metathesis polymerization using the first‐generation Grubbs' catalyst in dichloromethane at room temperature and then clicked with maleimide end‐functionalized polymers, poly(ethylene glycol) (PEG)‐MI, poly(methyl methacrylate) (PMMA)‐MI, and poly(tert‐butyl acrylate) (PtBA)‐MI in a Diels–Alder reaction in toluene at 120 °C to create corresponding graft copolymers, poly(oxanorbornene)‐g‐PEG, poly(oxanorbornene)‐g‐PMMA, and graft block copolymers, poly(oxanorbornene)‐g‐(PS‐b‐PEG), poly(oxanorbornene)‐g‐(PS‐b‐PMMA), and poly(oxanorbornene)‐g‐(PS‐b‐PtBA), respectively. Diels–Alder click reaction efficiency for graft copolymerization was monitored by UV–vis spectroscopy. The dn/dc values of graft copolymers and graft block copolymers were experimentally obtained using a triple detection gel permeation chromatography and subsequently introduced to the software so as to give molecular weights, intrinsic viscosity ([η]) and hydrodynamic radius (Rh) values. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Multiarm star polymers with POSS at the periphery

AbstractAzide end‐functionalized polyhedral oligomeric silsesquioxane (POSS‐N3) was incorporated into the periphery of well‐defined alkyne‐polystyrene50‐poly(divinyl benzene) (alkyne‐PS50‐polyDVB) and alkyne‐poly(tert‐butyl acrylate)43‐poly(divinyl benzene) (alkyne‐PtBA43‐polyDVB) multiarm star polymers via highly efficient azide‐alkyne click reaction, resulting in POSS‐PS50‐polyDVB and POSS‐PtBA43‐polyDVB multiarm star block copolymers respectively, in the solution of tetrahydrofuran/N,N‐dimethyl formamide, CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) at room temperature for 24 h. Linear precursors and star polymers obtained in this study were characterized 1H NMR, gel permeation chromatography (GPC), and triple detection GPC (TD‐GPC). Absolute molecular weight, hydrodynamic radius, and intrinsic viscosity ([η]) values for all star polymers were determined by TD‐GPC. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Preparation of heat-resistant branched poly(styrene-alt-NPMI) by ATRP with divinylbenzene as the branching agent

Heat-resistant branched poly(styrene-alt-NPMI) has been prepared via atom transfer radical polymerization (ATRP) of styrene (St) and N-phenyl maleimide (NPMI) with divinylbenzene (DVB) as the branching agent in anisole at 80°C. Gas chromatography (GC) was used to determine the conversion of the reactants. Triple detection gel permeation chromatography (TD-GPC) was used to analyze the copolymers. The results show that the polymerization yields primary chains predominately in the early stages and the formation of branched molecules occurs mainly when conversion is higher than 50%. As expected, higher dosage of DVB in our investigation range favors the formation of polymers with higher degree of branching. All the resulting branched poly(styrene-alt-NPMI)s have glass transition temperature (Tg) above 175°C, extrapolated initial weight loss temperature (Ti) above 410°C and statistic heat-resistant index above 200°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Chain walking copolymerization of ethylene with cyclopentene – Effect of ring incorporation on polymer chain topology

Chain walking ethylene copolymerizations with cyclopentene (CPE) as the ring-forming comonomer were carried out in this study to investigate the tuning of polyethylene chain topology via the unique strategy of ring incorporation. Four sets of polymers containing five-membered rings on the polymer backbone at various low contents (in the range of 0–7.5 mol%) were synthesized by controlling CPE feed concentration at four different ethylene pressure/temperature combinations (1 atm/15 °C, 1 atm/25 °C, 1 atm/35 °C, and 6 atm/25 °C, respectively) using a Pd-diimine catalyst, [(ArN C(Me)–(Me)C NAr)Pd(CH 3)(N CMe)] +SbF 6 − (Ar = 2,6–( iPr) 2C 6H 3). The polymers were characterized extensively using 13C nuclear magnetic resonance (NMR) spectroscopy, triple-detection gel permeation chromatography (GPC), and rheometry to elucidate the chain microstructures and study the effect of ring incorporation on polymer chain topology. It was found that CPE was incorporated in the copolymers primarily in the form of isolated cis-1,3 ring units, along with a small fraction in the form of isolated cis-1,2 ring units. Significant linearization of polymer chain topology was achieved with ring incorporation in each of the three sets of polymers synthesized at 1 atm on the basis of the incrementally raised intrinsic viscosity curves in the Mark–Houwink plot and the significantly enhanced zero-shear viscosity of the polymer melts with the increase of ring content despite the decreasing polymer molecular weight. For the set of polymers synthesized at 6 atm/25 °C, the effect of ring incorporation on polymer chain topology was negligible or weaker due to their linear chain topology resulting at this polymerization condition. The results obtained in this study support the proposed blocking effect of backbone-incorporated rings on catalyst chain walking, and demonstrate that effective tuning of polyethylene chain topology from hyperbranched to linear can be conveniently achieved via CPE incorporation while without changing ethylene pressure or polymerization temperature.

Multiarm star block and multiarm star mixed-block copolymers via azide-alkyne click reaction

The synthesis of multiarm star block (and mixed-block) copolymers are efficiently prepared by using Cu(I) catalyzed azide-alkyne click reaction and the arm-first approach. α-Silyl protected alkyne polystyrene (α-silyl-alkyne-PS) was prepared by ATRP of styrene (St) and used as macroinitiator in a crosslinking reaction with divinyl benzene to successfully give multiarm star homopolymer with alkyne periphery. Linear azide end-functionalized poly(ethylene glycol) (PEG-N3) and poly (tert-butyl acrylate) (PtBA-N3) were simply clicked with the multiarm star polymer described earlier to form star block or mixed-block copolymers in N,N-dimethyl formamide at room temperature for 24 h. Obtained multiarm star block and mixed-block copolymers were identified by using 1H NMR, GPC, triple detection-GPC, atomic force microscopy, and dynamic light scattering measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 99–108, 2010