Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

The bromine chain‐end functionality of polystyrene (PSt) prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was analyzed using 500 MHz ¹H nuclear magnetic resonance (NMR). Bulk polymerization of styrene (St) was carried out with 50 ppm of copper in the presence of tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) ligand and tin(II) 2‐ethylhexanoate [Sn(EH)₂] reducing agent at 90 °C. Due to the use of a low concentration of an active Cu/ligand catalyst complex, it was possible to significantly decrease the occurrence of catalyst‐based side reactions (β‐H elimination). As a result, compared to PSt prepared via normal ATRP, PSt with improved chain‐end functionality was obtained. For example, at 92% monomer conversion in normal ATRP only 48% of chains retained chain‐end functionality, whereas 87% of the chains in an ARGET ATRP still contained halogen functionality. PSt with controlled molecular weight ( = 11 600 g · mol^?1, = 9 600 g · mol^?1) and narrow molecular weight distribution ( = 1.14) was prepared under these conditions. In addition, as a result of decreased frequency of side reactions in ARGET ATRP, PSt with relatively high molecular weight was successfully prepared ( = 185 000 g · mol^?1, = 1.35).

     

Anionic Ring‐Opening Polymerization of Propylene Oxide in the Presence of Phosphonium Catalysts at Various Temperatures

Anionic ring‐opening polymerization of propylene oxide in the presence of a potassium alkoxide initiator was accelerated by the addition of the bulky phosphonium salts tetrakis[cyclohexyl(methyl)amino]phosphonium‐, tetrakis[propyl(methyl)amino]phosphonium‐, and tetrakis[octyl(methyl)amino]phosphonium‐tetrafluoroborate. Dipropylene glycol (DPG) was partially deprotonated (5%) and used as initiator. The delocalization of the positive charge over five atoms promoted the formation of a separated ion‐pair, thus enhancing nucleophilicity and reactivity. The polymerization behavior of the counterions at varied temperatures was studied. Characterization of poly(propylene oxide)s by means of ¹H NMR spectroscopy, size exclusion chromatography (SEC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) showed low polydispersities and the absence of by‐products and impurities. The degree of polymerization (DP _n) for the polymers was in the range of 8–60 (M _n = 630–3 620 g · mol^?1) and M _w/M _n obtained was 1.03–1.35 and 1.11–1.32 for MALDI‐TOF‐MS and SEC, respectively. Values calculated from the titration of hydroxyl groups (OHV) showed good agreement. Determination of the total degree of unsaturation in the range 13–60 mmol · kg^?1 indicated larger amounts with decreasing polymerization rates and increasing polymerization temperatures.

The phosphonium salts Cy₄PBF, Pr₄PBF, and Oc₄PBF.     

Photocurable Shape‐Memory Copolymers of ε‐Caprolactone and L‐Lactide

Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol^?1), PCL diol ( = 10 000 g · mol^?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited R_f and R_r values above 90% at 45 °C for an extremely large tensile strain of 1 000%.

     

Enhanced Preparation of Alkoxyamine‐Functionalized Poly(p‐phenylene)s and Their Use as Macroinitiators for the Synthesis of Stimuli‐Responsive Coil‐Rod‐Coil Block Copolymers

Herein, the enhanced preparation of alkoxyamine‐functionalized poly(p–phenylene)s (PPP) via Suzuki polycondensation (SPC) using microwave irradiation is described. Microwave heating effects a drastic decrease of reaction times compared to conventional heating. By varying the diboronic acid esters within the polymerization process different chain lengths of PPPs ( = 1900?3600 g mol^?1) could be prepared. In addition, by exchange of the catalyst and base either preferably mono‐ or bis‐alkoxyamine‐terminated PPPs could be obtained. These macroinitiators are then applied for the nitroxide‐mediated radical polymerization (NMRP) of N–isopropylacrylamide (NIPAAm) to form PNIPAAm‐b‐PPP‐b‐PNIPAAm block copolymers ( = 24 900–38 400 g mol^?1, / = 1.54–1.67).     

Simple Trends in the Methylene Regions of the NMR Spectrum of Poly(propylene) and Ethylene‐Propylene Copolymers

Summary: The configurational sensitivity of the chemical shift of methylene carbons has been analyzed theoretically in terms of a perturbative approach. Theoretical results and computations have been applied successfully to new experimental data obtained from model compounds of the resonance. It has been shown that the carbon in position with respect to the first methine of a regioregular sequence follows the same simple trend of the corresponding carbon atoms in position. The tiny chemical shift spreadings of the resonance due to the relative configuration of the nearest methyl groups in and position showed a single inversion with respect to theoretical expectation.

Decomposition of a chain in subchains.     

Adducts of Polymeric Organolithiums with 1,1‐Diphenylethylene. Rates of Formation and Crossover to Styrene and Diene Monomers

The addition reactions of 1,1‐diphenylethylene (DPE) to polymeric organolithium (PLi) compounds and the crossover reactions of the resulting polymeric 1,1‐diphenylalkyllithiums with styrene, isoprene and butadiene monomers have been investigated and optimized. The addition of poly(styryl)lithium (PSLi) to one unit of DPE at 25 °C is complete in 6 and 8 h in benzene and cyclohexane, respectively. After 3 d at 25 °C, the extent of end‐capping with DPE was only 9% for poly(butadienyl)lithium and 15% for poly(isoprenyl)lithium. Addition of THF ([THF]/[PLi] = 15–40) promotes quantitative addition of poly(dienyl)lithiums to DPE within 1–4 hours at 25 °C. Crossover reactions of polymeric 1,1‐diphenylalkyllithiums (growth out) to styrene monomers are slow relative to crossover reactions to diene monomers. Crossover to diene monomers is complete within approximately 2 min at 25 °C and leads to well‐defined, narrow molecular weight distribution block copolymers ( = 1.01 with (out, calc) > 2 900 g · mol^?1). Crossover to styrene monomers requires 12 h and leads to broad molecular weight distributions ( > 1.1) and inefficient crossover if (out; calc) < 7 000 g · mol^?1 and the chain end concentration is ≤ 10^?3 M . Crossover to the styrene monomer is favored by low temperatures (5 °C), high chain end concentrations, and higher molecular weights of the growing block.

     

Reverse Atom Transfer Radical Polymerization of Methyl Methacrylate using a New Catalyst,Copper(II) N,N′‐Butyldithiocarbamate

Summary: The homogeneous bulk reverse ATRP using AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy as the initiating system has been successfully carried out for methyl methacrylate. Well‐controlled polymerizations with low polydispersities ( = 1.10–1.30) have been achieved. The revised number‐average molecular weights ( 's) increased linearly with monomer conversion and were close to the values. The polymerization rate followed the first‐order kinetics in monomer, while it is about 2.0 order in initiator concentration and 1.15 order in Cu(II) concentration. The k values for the homogeneous bulk reverse ATRP of MMA initiated by AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy (1:2:6) at 80, 90, 100 and 110 °C were 0.402 × 10^?4, 1.021 × 10^?4, 2.952 × 10^?4, and 3.687 × 10^?4 (s^?1), respectively. On the basis of the Arrhenius plot, the apparent activation energy was calculated to be ΔE = 87.1 kJ/mol. The obtained PMMA was functionalized with an ultraviolet light sensitive ω‐SC(S)N(C₄H₉)₂ group characterized by means of ¹H NMR spectroscopy, and which was also proved by its chain extension with fresh MMA under UV‐light irradiation at room temperature. A polymerization mechanism for this novel initiation system is proposed.

Dependence of and on the monomer conversion for the homogeneous bulk reverse ATRP of MMA at different concentration of catalyst.     

Flash‐Heating‐Enhanced Ring‐Opening Polymerizations of ε‐Caprolactone under Conventional Conditions

Summary: Flash conventional heating (FCH) and microwave heating (MH) were matched in their effects on the ROP of ε‐CL catalyzed by Sn(Oct)₂. The temperature of the ROP, heated by a hot salt bath, increased from room temperature to 215 °C within 3 min, which rose a little faster than that by MH (213 °C at 6 min), and the way of heating was considered as FCH. The kinetic results indicate that the chain propagation of PCL was significantly accelerated under FCH conditions and the ratio of the chain propagation rate constant by FCH to that by MH (k/k) was 4.48, if the concentrations of their propagating species were the same. The largest number‐average molar mass ( ) of PCL obtained by FCH was 13.0 × 10⁴ g · mol^?1 at 6 min, but that by MH was 4.1 × 10⁴ g · mol^?1 at 15 min. The ratio of the concentrations of propagating species under the two conditions was around one‐fifth at 4, 6, and 8 min.

Thermal and kinetic behavior of the ROP of ε‐CL.     

Critically Evaluated Rate Coefficients for Free‐Radical Polymerization, 4

Propagation rate coefficients, k_p, which have been previously reported by several groups for free‐radical bulk polymerizations of cyclohexyl methacrylate (CHMA), glycidyl methacrylate (GMA), benzyl methacrylate (BzMA), and isobornyl methacrylate (iBoMA) are critically evaluated. All data were determined by the combination of pulsed‐laser polymerization (PLP) and subsequent polymer analysis by size‐exclusion chromatography (SEC). This so‐called PLP‐SEC technique has been recommended as the method of choice for the determination of k_p by the IUPAC Working Party on Modeling of Polymerisation Kinetics and Processes. The present data fulfill consistency criteria and the agreement among the data from different laboratories is remarkable. The values for CHMA, GMA, and BzMA are therefore recommended as constituting benchmark data sets for each monomer. The data for iBoMA are also considered reliable, but since SEC calibration was established only by a single group, the data are not considered as a benchmark data set. All k_p data for each monomer are best fitted by the following Arrhenius relations: CHMA: , GMA: , BzMA: , iBoMA: . Rather remarkably, for the methacrylates under investigation, the k_p values are all very similar. Thus, all data can be fitted well by a single Arrhenius relation resulting in a pre‐exponential factor of 4.24 × 10⁶ L · mol^?1 · s^?1 and an activation energy of 21.9 kJ · mol^?1. All activation parameters refer to bulk polymerizations at ambient pressure and temperatures below 100 °C. Joint confidence intervals are also provided, enabling values and uncertainties for k_p to be estimated at any temperature.

95% joint confidence intervals for Arrhenius parameters A and E_A for cyclohexyl (CHMA), glycidyl (GMA), benzyl (BzMA), and isobornyl (iBoMA) methacrylate; for details see text.     

Synthesis and Properties of Novel Fluorinated Poly(phenylene‐co‐imide)s

A new class of high‐performance materials, fluorinated poly(phenylene‐co‐imide)s, were prepared by Ni(0)‐catalytic coupling of 2,5‐dichlorobenzophenone with fluorinated dichlorophthalimide. The synthesized copolymers have high molecular weights ( = 5.74 × 10⁴–17.3 × 10⁴ g · mol^?1), and a combination of desirable properties such as high solubility in common organic solvent, film‐forming ability, and excellent mechanical properties. The glass transition temperature (T_gs) of the copolymers was readily tuned to be between 219 and 354 °C via systematic variation of the ratio of the two comonomers. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 66.7–266 MPa, 2.7–13.5%, and 3.13–4.09 GPa, respectively. The oxygen permeability coefficients ( ) and permeability selectivity of oxygen to nitrogen ( ) of these copolymer membranes were in the range of 0.78–3.01 barrer [1 barrer = 10^?10 cm³ (STP) cm/(cm² · s · cmHg)] and 5.09–6.25, respectively. Consequently, these materials have shown promise as engineering plastics and gas‐separation membrane materials.

     

Stereokontrolle. IV. Konstitutionseinflüsse bei radikalischen Polymerisationen

A compensation effect exists between the quantities (ΔH ? ΔH) and (ΔS ? ΔS) in the free radical polymerization of a monomer in different solvents ΔH, ΔH, ΔS, and ΔS are the activation enthalpies and entropies, resp. for the formation of isotactic and syndiotactic dyads. The quantities ΔΔH and T₀ are by definition independent of the temperature of polymerization and other polymerization conditions and thus a pair of constants characteristic for each monomer. A linear relationship between ΔΔH and T₀ has been found for acrylic and vinyl monomers each. Both true activation and conformational effects seem to be responsible for the stereocontrol in free radical polymerizations.     

Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.     

α,ωn‐Heterotelechelic Hyperbranched Polyethers Solubilize Carbon Nanotubes

The synthesis of novel linear‐hyperbranched (linhb) polyether block copolymers based on poly(ethylene oxide) and branched poly(glycerol), bearing a single pyrene or myristyl moiety at the α‐position of the linear chain is described. The polymers exhibit low polydispersity ( < 1.3) and controlled molecular weights ( = 5 000 g · mol^?1). The mainly hydrophilic block copolymers with multiple hydroxyl end groups readily dissolve multiwalled carbon nanotubes (MWCNTs) in water by mixing and subsequent sonification, resulting in noncovalent attachment of the linhb hybrid structure to the carbon nanotubes (CNTs). Transmission electron microscopy (TEM) was employed to visualize the solubilized nanotubes; after sulfation of the multiple hydroxyl groups the polymer layer was detected in the TEM images.

     

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

The technique of SPPLP EPR, which is single‐pulse pulsed‐laser polymerization (SPPLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain‐end) radical termination of acrylates. Measurements are performed on methyl acrylate, n‐butyl acrylate, and dodecyl acrylate in bulk and in toluene solution at ?40 °C. The reason for the low temperature is to avoid formation of mid‐chain radicals (MCRs), a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite‐model behavior for chain‐length‐dependent termination (CLDT) rate coefficients, , is found in this work. However, lower and more reasonable values of α_s, the exponent for variation of at short chain lengths, are found in the present study. Most likely this is because of the absence of MCRs, thereby validating the methodology of this work. Family‐type termination behavior is observed, with the following average parameter values adequately describing all results, regardless of acrylate or the presence of toluene: α_s = 0.79, α_l = 0.21 (long chains) and i_c ≈ 30 (crossover chain length). All indications are that these values carry over to termination of acrylate chain‐end radicals at higher, more practical temperatures. Further, these values largely make sense in terms of what is understood about the physical meaning of the parameters. Variation of the rate coefficient for termination between monomeric radicals, , is found to be well described by the simple Smoluchowski and Stokes–Einstein equations. This allows easy prediction of for different alkyl acrylates, solvent, and temperature. Through all this the unrivalled power of SPPLP EPR for measuring and understanding (chain‐length‐dependent) termination rate coefficients shines through.

     

Synthesis of Poly(lauryl acrylate) by Single-Electron Transfer/Degenerative Chain Transfer Living Radical Polymerization Catalyzed by Na2S2O4 in Water

Living radical polymerization of lauryl acrylate was achieved by SET/DTLRP in water catalyzed by sodium dithionite. The work describes the synthesis of a highly hydrophobic and polar monomer in aqueous medium. The plots of versus conversion and ln[M]₀/[M] versus time are linear, indicating a controlled polymerization. This method leads to α,ω-diiodopoly(lauryl acrylate)s that can be further functionalized. The MWDs were determined using a combination of three detectors: RALLS, DV, and RI. The method studied in this work represents a possible route to prepare well-tailored macromolecules made of LA in environment friendly reaction medium. The syndiotactic content is 75%.

     

Rheological Investigation of Shear Induced‐Mixing and Shear Induced‐Demixing for Polystyrene/Poly(vinyl methyl ether) Blend

Full Paper: The phase behavior of polystyrene (PS) and poly(vinyl methyl ether) (PVME) blend has been investigated rheologically as a function of temperature, composition and oscillating shear rate as well as different heating rates. An LCST (lower critical solution temperature)‐type phase diagram was detected rheologically from the sudden changes in the slopes of the dynamic temperature ramps of G′ at given heating and shear rate values. The rheological cloud points were dependent on the heating rate, , and oscillating shear rate, . The cloud points shifted a few degrees to higher temperatures with increasing and reached an equilibrium value (heating rate independent) at °C/min. The phase diagrams of the blends detected at = 0.1 and 1 rad/s were located in lower temperature ranges than the quiescent phase diagram, i.e., oscillating shear rate induced‐demixing at these two values for the shear rate. On the other hand, at = 10 rad/s, the phase diagram shifted to higher temperatures, higher than the corresponding values found under quiescent conditions, i.e., shear induced‐mixing took place. Based on these two observations, shear induced‐demixing and shear induced‐mixing can be detected rheologically within a single composition at low and high shear rate values, respectively, and this is in good agreement with the previous investigation using simple shear flow techniques. In addition, the William, Landel and Ferry (WLF)‐superposition principle was found to be applicable only in the single‐phase regime; however, the principle broke‐down at a temperature higher than or equal to the cloud point. Furthermore, different spinodal phase diagrams were estimated at different oscillating shear rates based on the theoretical approach of Ajji and Choplin.

Spinodal phase diagrams at different oscillating shear rates.     

Synthesis and Surface Attachment of ABC Triblock Copolymers Containing Glassy and Rubbery Segments

Summary: The synthesis of an ABC triblock copolymer containing glassy and rubbery segments was conducted using a combination of living anionic and atom transfer radical polymerizations (ATRP). A poly(dimethylsiloxane) (pDMS) macroinitiator ( = 6 200; = 1.19) was prepared by living anionic ring‐opening polymerization, followed by hydrosilation reactions to incorporate 2‐bromoisobutyrate end groups for initiation of ATRP. The ATRP of styrene (S) using the pDMS macroinitiator yielded a diblock copolymer ( = 66 730; = 1.38). Chain extension of the pDMS‐b‐pS macroinitiator with 3‐(dimethoxymethylsilyl)propyl acrylate (DMSA) by ATRP yielded an ABC triblock copolymer. The latter reactive segment was covalently attached to silanol groups on a silicon wafer. The presentation of either glassy pS or flexible pDMS segments of the brushes attached to the surface was reversibly controlled by treatment with selective solvents for each segment.

Surface immobilization of pDMS‐b‐pS‐b‐pDMSA triblock copolymer to Si wafer. Treatment of brush with toluene, methanol, or annealing yields brush with hard pS surface. Treatment with hexane selectively solvates pDMS, and the soft layer is presented to the brush surface.     

Xanthate‐Mediated Controlled Radical Polymerization of N‐Vinylcarbazole

Summary: Well‐defined poly(N‐vinylcarbazole) [poly(NVC)] was synthesized by macromolecular design via interchange of the xanthates (MADIX)/reversible addition‐fragmentation chain transfer (RAFT) polymerization. The homopolymers with controlled molecular weights ( = 3 000–48 000) and low polydispersities indices ( = 1.15–1.20) were obtained by the polymerization of NVC with AIBN in the presence of O‐ethyl‐S‐(1‐phenylethyl) dithiocarbonate as a xanthate‐type chain transfer agent (CTA). Good control of the polymerization was confirmed by the linear first‐order kinetic plot, the molecular weight controlled by the monomer/CTA molar ratio, linear increase in the molecular weight with the conversion, and the ability to extend the chains by the second addition of the monomer.

Radical polymerization of NVC in the presence of CTA and plot of number‐average molecular weight (circles) and polydispersity (squares) as a function of conversion.     

Hydrolytic Polycondensation of Bisphenol‐A‐Bischloroformate Catalyzed by Phase‐Transfer Catalysts

The hydrolytic interfacial polycondensation of bisphenol‐A‐bischloroformate was performed with four different phase‐transfer (PT) catalysts: N‐butylpyridinium bromide, triethylbenzylammonium (TEBA) chloride, tetrabutylammonium hydrogen sulfate, and tetraphenylphosphonium bromide. These polycondensations were conducted at 5 or 35 °C initial reaction temperature. The resulting polycarbonates were characterized by viscosity and SEC measurements and by MALDI‐TOF mass spectrometry. The four PT catalysts gave quite different results with respect to molecular weight and formation of cyclic polycarbonates. The highest molecular weights (number average, and weight average, ) were obtained with TEBA‐Cl. Lower temperatures and high feed ratios of TEBA‐Cl proved to be favorable for both high molecular weights and high fractions of cycles. Cyclic polycarbonates were detectable in the mass spectra up to 14 kDa (technical limit of the measurements). Low molecular weights in combination with unreacted chloroformate groups proved that the other PT‐catalysts were less efficient under the given reaction conditions.

MALDI‐TOF mass spectrum of the polycarbonate No. 3b .     

Direct Synthesis of Controlled Poly(styrene‐co‐acrylic acid)s of Various Compositions by Nitroxide‐Mediated Random Copolymerization

Styrene and acrylic acid were copolymerized under controlled conditions, in 1,4‐dioxane solution at 120 °C and 2 bar, using an alkoxyamine initiator based on the N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl) nitroxide, SG1. A broad composition range from 90/10 to 10/90 was investigated. With slightly different initiator concentrations and a similar initial proportion of free SG1 (4.5 mol‐% with respect to the initiator) the polymerizations exhibited very similar rates, irrespective of the proportion of acrylic acid in the comonomer mixture (80% conversion within 8 h). In all cases, the copolymers presented number average molar masses, , that increased linearly with overall monomer conversion, and polydispersity indexes that ranged between 1.2 and 1.4. Moreover, followed the calculated values, based on the initial concentrations of monomers and initiator. The variation in the initiator concentration allowed to target various molar masses, but some limitation appeared at low initiator concentration owing to chain transfer to 1,4‐dioxane. From the kinetic data, the reactivity ratios were determined: r_A = 0.27 ± 0.07 for acrylic acid and r_S = 0.72 ± 0.04 for styrene. Depending on the initial comonomer composition, chains exhibited no or small composition drift, and hence a slightly pronounced gradient structure.

Reactivity ratios for acrylic acid and styrene.