Nitroxide‐Mediated Radical Polymerization of N‐tert‐Butylacrylamide

The nitroxide‐mediated polymerization of N‐tert‐butylacrylamide (TBAM) in DMF at 120 °C using SG1/DEPN and AIBN has been investigated. Linear growth in number‐average molecular weight ( ) versus conversion and narrow molecular weight distributions (MWDs) with high livingness were obtained up to ≈8 000 g · mol^?1. For higher molecular weights, the MWDs gradually became broader with low molecular weight tailing, and deviated downwards from theoretical values. Quantitative analyses of MWDs, along with specifically designed conventional radical polymerizations at 120 °C, were consistent with chain transfer to monomer limiting the attainable . This finding can be equally applied to existing literature polymerizations of TBAM.

     

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).     

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).

     

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.     

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%.

     

Click‐Chemistry: An Alternative Way to Functionalize Poly(2‐methyl‐2‐oxazoline)

CROP has been used to synthesize well‐defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3‐diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α‐azido‐POXZ, = 3.58 × 10³ g · mol^?1) or both ends (α,ω‐azido‐POXZ, = 6.21 × 10³ g · mol^?1) of the macromolecular chain. The Huisgen 1,3‐dipolar cycloaddition has been investigated between azido‐POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, ¹H NMR, and SEC.

     

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.     

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 .     

Synthesis of AB2 3‐ and AB4 5‐Miktoarm Star Copolymers Initiated from Dendritic Tri‐ and Penta‐Functional Initiators by Combination of Ring‐Opening Polymerization of ε‐Caprolactone and Nitroxide‐Mediated Radical Polymerization of Styrene

Summary: Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators. Initially, two kinds of dendritic initiators having one benzylic OH and two or four TEMPO‐based alkoxyamine moieties were prepared. Using them, ROP of ε‐caprolactone was carried out at room temperature to give poly(ε‐caprolactone)s carrying two or four alkoxyamine moieties. NMRP of styrene from the poly(ε‐caprolactone)s was carried out at 120 °C to give AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers, which were analyzed by ¹H NMR and SEC. The increased linearly with conversion and the were in the range 1.10–1.37, showing that well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were formed.

Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators.     

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.

     

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.     

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.

     

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.     

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.     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

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.

     

Aliphatic‐Aromatic Hyperbranched Polyesters by Polycondensation of Potassium 3,5‐Bis(bromomethyl)benzoate: Formation of Cyclic Structures

Aliphatic‐aromatic hyperbranched polyesters of reasonable degrees of branching (DB's) but of relatively low molar masses were prepared from 3,5‐bis(bromomethyl)benzoic acid ( 2a ). 2a was synthesized by radical bromination of 3,5‐dimethylbenzoic acid. The polymerization of 2a and that of the potassium salt of 2a ( 2K ), both carried out in the presence of a potassium monocarboxylate (RCOOK), led to directly derivatized polyesters. Polyesters bearing free ? CH₂Br groups were obtained by polymerization of 2K alone or in the presence of 2,4,6‐tris(bromomethyl)mesitylene (TBMM) or by polymerization of 2a in the presence of RCOOK provided that 1 ≤ [RCOOK]/[ 2a ] < 2. These polyesters were later derivatized by reaction with RCOOK. In all cases, RCOOK can be chosen in order to introduce, in the polyesters, reactive functional groups such as unsaturated (double or triple bond) and hydroxy ones. The NMR analysis of polymers has shown that a cyclic dimer (C₂) was formed in most cases. Its amount depends on the process of polymerization and on the experimental conditions. The of polyesters was found to be correlated with the amount of C₂. The MALDI‐TOF analysis of polymers confirmed the formation of cycles and showed that both the polymerization of 2K in the presence of TBMM and that of 2a in the presence of some particular RCOOK's led to the formation of acyclic macromolecules.

Expanded aromatic region of the ¹H NMR spectrum of a polymer showing the six characteristic resonances H, H, H, H, H and H of the cyclic dimer C₂.     

Migration of Additives in Polymer Coatings: Phosphonated Additives and Poly(vinylidene chloride)‐Based Matrix

Summary: The living radical terpolymerization of vinylidene chloride (VC₂), methyl acrylate (MA), and dimethyl‐2‐methacryloxyethylphosphonate (MAPHOS) was performed at 70 °C in benzene by a reversible addition fragmentation chain transfer (RAFT) process to yield a gradient terpolymer of controlled molecular weight ( = 5 800 g · mol⁻¹, I_p = 1.53) with a molar composition of 75:14:11 (VC₂/MA/MAPHOS). Such terpolymers, hydrolyzed (phosphonic acid groups) or not, were used as polymeric additives in coating formulations based on a poly(VC₂‐co‐MA) copolymer matrix ( = 63 300 g · mol⁻¹, I_p = 1.99, VC₂/MA = 80:20 molar ratio). The formulations were spun cast on stainless steel surfaces and the coatings were observed by scanning electron microscopy (SEM) coupled with X‐ray analyses (EDX). The hydrolyzed additive was shown to both segregate and migrate towards the metal interface, leading to a preferential organization of the coating. Hence, the matrix at the air surface acts as a barrier to gas while the additive ensures adhesion at the polymer/metal interface.

SEM photograph of a section of the coating with formulation 4 [poly(VC₂‐co‐MA‐co‐MAPHOS(OH)₂) (75:14:11)].     

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.     

Accessing Chain Length Dependent Termination Rate Coefficients of Methyl Methacrylate (MMA) via the Reversible Addition Fragmentation Chain Transfer (RAFT) Process

Summary: The RAFT‐CLD‐T methodology is demonstrated to be not only applicable to 1‐substituted monomers such as styrene and acrylates, but also to 1,1‐disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 °C. The evolution of the chain length dependent termination rate coefficient, k, was constructed in a step‐wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k_t in MMA polymerizations is compatible with the composite model for chain length dependent termination. For the initial chain‐length regime, up to a degree of polymerization of 100, k_t decreases with α (in the expression k = k · i^−α) being close to 0.65 at 80 °C. At chain lengths exceeding 100, the decrease is less pronounced (affording an α of 0.15 at 80 °C). However, the data are best represented by a continuously decreasing non‐linear functionality implying a chain length dependent α.