Narrow Molar Mass Distribution Research Articles

On the Role of Tin Catalysts in Step-Growth Polymerization Reactions

Organotin compounds have been used to catalyze the condensation of various α,ω-dihydroxyl terminated organosiloxane diols. This tin catalyzed reaction extends the length of siloxane chains and it also produces narrow molar mass distribution polyorganodisilanols (Mw/Mn = 1.4). The reaction occurs between a variety of siloxanes that are terminated with hydroxyl groups and it does not depend on the organic side groups connected to silicon for the systems studied here. These systems include silicon atoms bearing dimethyl, methylphenyl or methyl 1,1,1 trifluoropropyl substituents. The organotin catalyst in the reaction facilitates the organosilanol condensation releasing water as a byproduct. However it does not appear to facilitate the opening of siloxane bonds nor the redistribution of siloxane bonds under the conditions employed here. Copolymerization of linear oligomeric dimethylsiloxane diol and linear oligomeric methylphenylsiloxanediol was found to give a relatively equal reactivity of homo polymerization and hetro polymerization in the condensation and randomly alternating segmented block copolymers that were formed. The reaction kinetics of the polymerization was used to experimentally verify the fact that there is a chain length dependence of the reacting silanol end-groups. The molar mass values during the polymerizations were determined using gel permeation chromatography. The chromatography, viscosity and FTIR results demonstrate that the reactivity of the hydroxyl end-groups in the polycondensation reaction decreases upon increasing the chain length of the siloxane. It therefore appears that these tin catalyzed siloxane systems deviate from the widely demonstrated hypothesis of Paul Flory on the “equal reactivity of functional groups” for step-growth polymerizations.

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3- and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol−1, narrow molar mass distribution (PDI ≤ 1.2) and high end group functionality (∼90%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.

Bulk Ring-Opening Transesterification Polymerization of the Renewable δ-Decalactone Using an Organocatalyst.

The bulk ring-opening polymerization of renewable δ-decalactone using 1,5,7-triazabicyclo[4.4.0]dec-5-ene was carried out at temperatures between 7 and 110 °C. The equilibrium monomer concentration for reactions within this temperature range was used to determine the polymerization thermodynamic parameters (ΔHp = -17.1 ± 0.6 kJ mol-1, ΔSp = -54 ± 2 J mol-1 K-1) for δ-decalactone. The polymerization kinetics were established and high molar mass poly(δ-decalactone) was prepared with a glass transition temperature of -51 °C. Poly(δ-decalactone) samples with controlled molar mass and narrow molar mass distributions were realized by controlling the monomer conversion and initiator concentration. A high molar mass poly(lactide)-poly(δ-decalactone)-poly(lactide) triblock copolymer with a low polydispersity index was prepared by simple sequential addition of monomers. The product triblock exhibited two distinct glass transitions temperatures consistent with microphase segregation.

Functionalization of Titanium Surfaces with Polymer Brushes Prepared from a Biomimetic RAFT Agent

Well-defined dopamine end-functionalized polymers were synthesized by employing the reversible addition–fragmentation chain transfer (RAFT) polymerization technique. tert-Butyl acrylate, N-isopropylacrylamide, and styrene monomers were polymerized in the presence of azobis (isobutyronitrile) and a new catechol-based biomimetic RAFT agent incorporating a trithiocarbonate unit. All RAFT polymerizations exhibited pseudofirst-order kinetics, a linear increase of the number-average molar mass (Mn SEC) with conversion and narrow molar mass distributions (polydispersity <1.2). The resulting homopolymers exhibited the electroactive catechol and the ω-trithiocarbonyl end groups. Subsequent immobilization of dopamine end-functionalized polymers on titanium surfaces was monitored by using a surface plasmon resonance (SPR) sensor, and the resulting films were characterized by contact angle, infrared ATR spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS).

Radical polymerization and preliminary microbiological investigation of new polymer derived from myrtenol

A new methacrylic monomer derived from myrtenol, an essential oil possessing biocidal properties extracted from Myrtus communis L., was prepared in one step and named myrtenyl methacrylate. Conventional radical polymerization was performed in solution with 2,2′-azobis(2-methylpropionitrile) as thermal initiator in the temperature range 60–80 °C. Influences of reaction time, temperature and initiator concentration on monomer conversion and molar masses were studied. Controlled radical polymerization experiments were performed using the Atom Transfer Radical Polymerization techniques, leading to the formation of polymers with controlled molar masses and narrow molar mass distribution. Microbiological tests of these (macro)molecules were carried out using planktonic and adhesion tests with gram-positive and gram-negative bacteria in order to evaluate their antibacterial properties.

α,ω‐Functionalized Poly(2‐Oxazoline)s Bearing Hydroxyl and Amino Functions

AbstractNovel α,ω‐functionalized amphiphilic lipopolymers are prepared that are composed of a proximal lipid moiety and a hydrophilic poly(2‐oxazoline)‐based (POx) polymer chain. The synthesis begins from bifunctional lipoinitiators, which are asymmetrically protected as tert.butyldiphenylsilyl (TBDPS) ethers, followed by cationic living ring‐opening polymerization of 2‐oxazolines in a one‐pot multistep reaction. This results in polymers with defined terminal end groups and narrow molar mass distributions. All protective groups involved can be readily cleaved in a single step reaction keeping the structure of the polymer intact, giving access to (lipo)polymers with a variety of defined identical or chemical orthogonal α,ω‐functionalities. The synthetic strategy is a versatile tool for the preparation of defined polymer–drug or polymer–protein conjugates or asymmetric functionalized model lipid membranes for the quantitative study of membrane‐associated phenomena such as transmembrane transport and cell adhesion/recognition. magnified image

Elasticity of polystyrene melts filled with silica nanoparticles: Influence of matrix polydispersity

It has recently been shown that the linear elastic steady-state compliance J e 0 reacts very sensitively on the addition of nanoparticles to a polymer melt. This effect can be attributed to an interaction between the particles and the matrix molecules. Creep-recovery experiments have evolved as a very suitable tool to measure J e 0, because the time window can be extended wide enough to detect the processes underlying the interactions. Whereas the effect of the particle geometry on J e 0 has already been investigated to some extent, the influence of the molecular structure of the matrix is still an open question. Therefore, in this study investigations of two polystyrenes with different molar masses and distributions and composites with 1 vol.% silica nanoparticles each are reported. One polystyrene is an anionic product (aPS) with a narrow molar mass distribution, the other a radically polymerized sample (PS 158K) with a broader molar mass distribution. Due to their molecular structures the unfilled polymers already differ significantly in their rheological properties. The linear steady-state elastic compliance is found to be J e 0 = 1.9 × 10 −5 Pa −1 for the aPS and J e 0 = 2.5 × 10 −4 Pa −1 for the PS 158K, which is in agreement with the literature. Investigations on nanocomposites with a poly (methyl methacrylate) of M w/M n = 1.5 as the matrix have shown that the elasticity, measured by J e 0 in the creep-recovery experiment, strongly increases with the specific surface area of the nanoparticles added. Also for the PS composites an increase of J e 0 was found by adding 1 vol.% of silica nanoparticles. However, the relative increase strongly depends on the elasticity of the unfilled matrix. Whereas for the PS 158K an increase of J e 0 of only 70% is found, it is much larger, namely 470%, in the case of the anionic PS.

Phosphoric and phosphoramidic acids as bifunctional catalysts for the ring-opening polymerization of ε-caprolactone: a combined experimental and theoretical study

The ring-opening polymerization of e-caprolactone catalyzed by the phosphoric acid (PhO)2P(O)OH (PA) or the phosphoramidic acid (PhO)2P(O)NH(SO2CF3) (PAA) has been investigated experimentally and computationally. The two catalysts promote polymerization under mild conditions, with PAA being slightly more active than PA. The controlled character of the polymerization has been examined thoroughly, and the polymerization conditions were optimized so as to afford well-defined polycaprolactones of molar masses up to 15 000 g mol−1 and narrow molar mass distributions. Density Functional Theory calculations support a bifunctional mechanism for these organo-catalyzed ROPs, with participation of both the acidic proton and basic PO (/SO) moiety of the phosphoric and phosphoramidic acids.

A synthetic approach to a fullerene-rich dendron and its linear polymer via ring-opening metathesis polymerization

Through the esterification of an acyl chloride functionalized fullerene precursor with dendritic alcohol, a fullerene-rich dendron containing a norbornene unit at the focal point is prepared for ring-opening metathesis polymerization to obtain its linear polymer with a unimodal and narrow molar mass distribution (PDI = 1.08) by a progressive addition of catalysts.

Boron‐functionalized poly(3‐hydroxybutyrate)s from hydroboration of poly(allyl‐β‐hydroxyalkanoate)s: Synthesis and insights into the microstructure

AbstractThe controlled ring‐opening polymerization of racemic allyl‐β‐butyrolactone (rac‐BLallyl) in toluene or in bulk, catalyzed by the discrete β‐diiminate zinc amido [(BDIiPr)Zn(N(SiMe3)2)] (1) or {amino‐methoxy‐bis(phenolate)}yttrium amido [(ONOOtBu)Y(N(SiHMe2)2)(THF)] (2) complexes, in association with an alcohol, gave poly(β‐hydroxyalkanoate)s (PHAs) with allylic side chains. These PHAsallyl exhibit either a slightly isotactic‐enriched (Pm = 0.61) or highly syndiotactic‐enriched (Pr = 0.82) backbone structure, respectively, with high molar mass (Mn up to 21,100 g mol−1) and narrow molar mass distribution values (1.05 &lt; Mw/Mn &lt; 1.28), as evidenced by detailed 13C NMR and size exclusion chromatography analyses. Postpolymerization rhodium‐catalyzed hydroboration of the resulting PHAsallyl with pinacolborane quantitatively afforded the corresponding PHAsboron. Introduction of boron into the pendant chains did not alter neither the structure of the polymer backbone nor the macromolecular features (Mn, Mw/Mn, and stereoregularity). However, differential scanning calorimetry analyses revealed a significant increase of the glass transition temperature on modifying the allyl for the boron function in these PHAs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Living/controlled hex-1-ene polymerization initiated by nickel diimine complexes activated by non-MAO cocatalysts: Kinetic and UV–vis study

Living/controlled polymerization of hex-1-ene initiated by nickel diimine catalysts of general form [ArN=C(1,8-naphthalenediyl)C=NAr]NiBr2 activated by simple organoaluminium compounds was investigated. Polyhexenes with a very narrow molar mass distribution and molar mass controlled by the monomer/initiator ratio were prepared using diethylaluminiumchloride, ethylaluminiumdichloride and methylaluminiumdichloride as cocatalysts for nickel complexes 1 (Ar = 2,6-iPr2C6H3) and 2 (Ar = 2-tBuC6H4). Nickel complexes with smaller aryl substituents (3, Ar = 2,6-Me2C6H3; 4 Ar = 2,4,6-Me3C6H2; 5, Ar = 2,6-Et2C6H3) undergo transfer reactions significantly. For the most bulky complex 1 activated by ethylaluminiumdichloride living hex-1-ene polymerization was achieved, proved by the reinitiation of polymer growth upon the addition of fresh monomer. The effect of Al/Ni ratio on the activity of the catalytic systems was studied by dilatometry. The catalytic systems were investigated by UV–vis spectrometry and a new interpretation of their absorption spectra was suggested.

Ring‐opening polymerization of cyclic esters promoted by phosphido‐diphosphine pincer group 3 complexes

AbstractPhosphido‐diphosphine Group 3 metal complexes 1–4 [(o‐C6H4PR2)2P‐M(CH2SiMe3)2; R = Ph, 1: M = Y, 2: M = Sc; R = iPr, 3: M = Y, 4: M = Sc] are very efficient catalysts for the ring‐opening polymerization (ROP) of cyclic esters such as ε‐caprolactone (ε‐CL), L‐lactide, and δ‐valerolactone under mild polymerization conditions. In the ROP of ε‐CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (∼4 × 104 molCL/molI h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of ε‐CL and L‐lactide is feasible by combining complexes 1–4 with 5 equiv of 2‐propanol. Polymers with controlled molecular parameters (Mn, end groups) and low polydispersities (Mw/Mn = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ‐valerolactone, complexes 1–4 showed the same activity observed for lactide (L‐ and D,L‐lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac‐β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Solution behavior of 4-arm poly( tert-butyl acrylate) star polymers

This paper reports the synthesis of 4-arm poly( tert-butyl acrylate) stars of different molar masses up to 10 6 g/mol by the “core-first” method using ATRP. All obtained stars have a monomodal and narrow molar-mass distribution (<1.2). The dilute-solution properties of these star polymers were investigated in good solvents (tetrahydrofuran and acetone). Gel permeation chromatography and dynamic and static light scattering were used to measure the hydrodynamic properties including intrinsic viscosity [ η], radius of gyration R g , hydrodynamic radius R h , second virial coefficient A 2 and diffusion coefficient D 0 . These data were used to establish relationships between these parameters and the molar mass of 4-arm poly( tert-butyl acrylate) stars. The branching parameters g and g ′ and the shape factor ρ were calculated for all obtained star polymers.

Design of new amphiphilic triblock copoly(2-oxazoline)s containing a fluorinated segment

New amphiphilic triblock copoly(2-oxazoline)s, containing hydrophobic domains with fluorine-containing blocks, were synthesized. Using microwave radiation as heating source, triblock copolymers with narrow molar mass distributions were obtained by the sequential addition of 2-ethyl-2-oxazoline, 2-(1-ethylheptyl)-2-oxazoline, and 2-(2,6-difluorophenyl)-2-oxazoline. The polymers obtained were characterized by size exclusion chromatography, 1H NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). To investigate the incorporation of all three monomers into the triblock copolymers, a model polymer was prepared with shorter blocks exhibiting a suitable length to be measured in the reflector mode of a MALDI-TOF MS. In addition, kinetic investigations on the homopolymerizations of all monomers were performed in nitromethane at 140 °C, yielding the polymerization rates under these conditions. DSC measurements of poly(2-(1-ethylheptyl)-2-oxazoline) and poly(2-(2,6-difluorophenyl)-2-oxazoline)) revealing glass transitions at about 33 and 120 °C, respectively. The thermal analysis of a blend of the two polymers showed two glass transitions revealing demixing, which could be an indicating for the immiscibility of the two components in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Syndiotactic-specific polymerization of methyl methacrylate with tert-butyllithium/trialkylaluminum in dichloromethane

By using dichloromethane as a polymerization solvent, syndiotactic-specific polymerization of methyl methacrylate with t-BuLi in the presence of large excess of tributylaluminum at –78 °C proceeded more rapidly than in toluene and gave st-PMMA (rr = 90%) with narrow molar mass distribution. This method allows us to prepare st-PMMA with molar mass up to 350 × 103 in 48 h.

Synthesis and morphology of model PS‐b‐PDMS copolymers

AbstractTrue model linear poly(styrene‐b‐dimethylsiloxane) PS‐b‐PDMS copolymers were synthesized by using sequential addition of monomers and anionic polymerization (high‐vacuum techniques), employing the most recent experimental procedures that allow the controlled polymerization of each monomer to obtain blocks with controlled molar masses. The model diblock copolymers obtained were analyzed by using different techniques, such as size‐exclusion chromatography, 1H NMR, Fourier transform infrared spectroscopy, small angle X‐rays scattering (SAXS), and wide angle X‐rays scattering (WAXS). The PS‐b‐PDMS copolymers obtained showed narrow molar mass distribution and variable PDMS content, ranging from 2 up to 55 wt %. Compacted powder samples were investigated by SAXS to reveal their structure and morphology changes on thermal treatment in the interval from 30 to 200 °C. The sample with the highest PDMS content exhibits a lamellar morphology, whereas two other samples show hexagonally packed cylinders of PDMS in a PS matrix. For the lowest PDMS content samples, the SAXS pattern corresponds to a disordered morphology and did not show any changes on thermal treatment. Detailed information about the morphology of scattering domains was obtained by fitting the SAXS scattering curves. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3119–3127, 2010

A complete hyaluronan hydrodynamic characterization using a size exclusion chromatography–triple detector array system during in vitro enzymatic degradation

Size exclusion chromatography coupled with triple detection (online laser light scattering, refractometry, and viscosimetry) (SEC–TDA) was applied for the study of hyaluronan (HA) fragments produced during hydrolysis catalyzed by bovine testicular hyaluronidase (BTH). The main advantage this approach provides is the complete hydrodynamic characterization without requiring further experiments. HA was hydrolyzed using several BTH amounts and for increasing incubation times. Fragments were characterized in terms of weight and number average molecular weights ( M w and M n, respectively), polydispersity index ( M w/ M n), hydrodynamic radius ( R h), and intrinsic viscosity ([ η]). The Mark–Houwink–Sakurada (MHS) curves (log [ η] versus log M w) were then derived directly. Fragments covering a whole range of M w (10–900 kDa) and size ( R h = 4–81 nm) and presenting a rather narrow distribution of molar masses ( M w/ M n = 1.6–1.7) were produced. From the MHS curves, HA conformation resulted in a change from a random coil toward a rigid rod structure while decreasing the M w. HA enzymatic hydrolysis in the presence of a BTH inhibitor was also monitored, revealing that inhibition profiles are affected by ionic strength. Finally, a comparison of the kinetic data derived from SEC–TDA with the data from rheological measurements suggested different strengths of the two methods in the determination of the depolymerization rate depending on the hydrolysis conditions.

Encapsulation Using Hyperbranched Polymers: From Research and Technologies to Emerging Applications

Dendritic macromolecules, such as hyperbranched polymers are increasingly being studied in the context of encapsulation. The intensive research on encapsulation using hyperbranched polymers is motivated by factors such as a cost-effective polymer synthesis and a customizable property profile. Hence, in the past few years, hyperbranched polymers have been employed as carriers for several guest molecules such as dyes, pharmaceuticals, cosmetics, catalysts, and aromatic hydrocarbons. However, hyperbranched polymers compete not only with perfectly structured dendrimers but also with conventional carrier molecules in terms of price and performance criteria such as processability, loading capacity, delivery efficiency and/or reduction of toxic side effects. This article aims at reviewing the research and development (R&D) in the field of encapsulation using hyperbranched polymers. Based on a summary of the most relevant R&D results and encapsulation technologies in this area, progress and challenges are discussed and new emerging applications are described. The most prominent emerging applications include the encapsulation and/or controlled release of (i) unstable or sensitive components (such as those used in the field of personal care), (ii) pharmaceutical substances (using hyperbranched carrier polymers with a narrow molar mass distribution), and (iii) inorganic nanoparticles to design versatile nanoreactors for catalytic applications.

Kinetic studies of surface‐initiated atom transfer radical polymerization in the synthesis of magnetic fluids

AbstractWe present results from kinetic studies on the surface‐initiated atom transfer radical polymerization in the preparation of polymer brush‐coated magnetic particles from a heterogeneous system. It is shown that a controlled reaction behavior and a reproducible surface functionalization with end‐tethered polymers are achieved, although the reaction advances gradually from a biphasic solid–liquid mixture to a stable colloidal dispersion of the nanoobjects. Although the initiator‐functional magnetite nanoparticles initially form a precipitate, the formation of a polymer layer on the particle surface in the course of the reaction contributes to a sterical stabilization in dispersion. We thoroughly investigated the development of the initial heterogeneous system with time and in various concentration regimes by simultaneously monitoring the monomer conversion, molar mass, the hydrodynamic diameter of the nanoobjects, and the magnetite content of the dispersions at different reaction times. The results indicate first‐order chain growth kinetics with respect to the monomer and narrow molar mass distributions, demonstrating good control on the particle architecture. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

Hydrodynamic Analysis of Well-Defined Flexible Linear Macromolecules of Low Molar Mass

Samples of poly(styrene−diphenylethylene) copolymers of narrow molar mass distribution were studied by molecular hydrodynamic methods. The values of velocity sedimentation coefficient, frictional ratio, translational diffusion coefficient, and intrinsic viscosity were measured in toluene. It is shown that the method of velocity sedimentation, coupled with the numerical solution of the Lamm equation (Sedfit program), can be considered as an absolute method of molar mass determination. The correlations between the hydrodynamic values and the molar mass were obtained. A new Multi-HYDFIT program was applied to obtain the conformational parameters of poly(styrene−diphenylethylene) copolymer chains unaffected by intrachain excluded volume effects.