Cationic Bottlebrush Polymers from Quaternary Ammonium Macromonomers by Grafting‐Through Ring‐Opening Metathesis Polymerization

Cationic bottlebrush homopolymers are polymerized using a grafting‐through approach by ring‐opening metathesis polymerization (ROMP) to afford well‐defined polymers. Quaternary ammonium macromonomers (MMs) are prepared by quaternizing tertiary amine MMs synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The quaternary ammonium MMs undergo ROMP to target molecular weights (M_n = 30 000–100 000 g mol^?1) and a low dispersity (? = 1.10–1.30). Halide‐ligand exchange between the third generation Grubbs catalyst (G3) and halide counter ions (bromide and iodide ions) of MMs changes the catalyst activity throughout ROMP, causing it to deviate from pseudo‐first order kinetic behavior; however, the polymerization still follows controlled behavior without significant catalyst termination. Increasing steric bulk of the MMs decreases the polymerization rate as well. Amphiphilic block copolymers are synthesized by sequential polymerization of quaternary ammonium MMs and polystyrene (PS) MMs. Using a PS macroinitiator affords block copolymers with lower ? values as compared to the less active cationic macroinitiator.     

Organobase‐Catalyzed Synthesis of Multiarm Star Polylactide With Hyperbranched Poly(ethylene glycol) as the Core

Multiarm star copolymers consisting of the polyether‐polyol hyperbranched poly(ethylene glycol) (hbPEG) as core and poly(L ‐lactide) (PLLA) arms are synthesized via the organobase‐ catalyzed ring‐opening polymerization of lactide using hbPEG as a multifunctional macroinitiator. Star copolymers with high molecular weights up to 792 000 g mol^?1 are prepared. Detailed 2D NMR analysis provides evidence for the attachment of the PLLA arms to the core and reveals that the adjustment of the monomer/initiator ratio enables control of the arm length. Size exclusion chromatography measurements show narrow molecular weight distributions. Thermal analysis reveals a lower glass transition temperature, melting point, and degree of crystallization for the star‐shaped polylactides compared to linear polylactide.     

Synthesis of 6‐Armed Amphiphilic Block Copolymers with Styrene and 2,3‐Dihydroxypropyl Acrylate by Atom Transfer Radical Polymerization

The controlled free radical polymerization of (2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methyl acrylate (DMDMA) was achieved by atom transfer radical polymerization (ATRP) in tetrahydrofuran (THF, 50%, v/v) solution at 90°C with the discotic six‐functional initiator, 2,3,6,7,10,11‐hexakis(2‐bromobutyryloxy) triphenylene (HBTP). The 6‐armed polyDMDMA with low polydispersity index (M̄_w/M̄_n = 1.52–1.32) was obtained. The copolymerization of DMDMA with styrene (St) using 6‐armed polySt‐Br as macroinitiator was carried out, and the GPC traces of the copolymers obtained were unimodal and symmetrical, indicating complete conversion of the macroinitiator into block copolymer. The star‐shaped block copolymers with different segment compositions and narrower polydispersity (1.21–1.24) were synthesized, and subsequent hydrolysis of the acetal‐protecting group in 1 N HCl THF solution produced poly[St‐b‐(2,3‐dihydroxypropyl)acrylate] [poly(St‐b‐DHPA)], which was verified by IR and NMR spectroscopy.     

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%.

     

Aggregation Behavior of Polystyrene/Poly(acrylic acid) Heteroarm Star Copolymers in 1,4‐Dioxane and Aqueous Media

Ionic heteroarm star copolymers bearing polystyrene (PS) and poly(acrylic acid) (PAA) arms (PS_nPAA_n) were prepared by quantitative hydrolysis of the poly(tert‐butyl acrylate) (PtBA) arms of the corresponding PS_nPtBA_n star copolymer. The aggregation properties of these copolymers were studied in various solvents. In 1,4‐dioxane PS₁₂PAA₁₂ (with nearly symmetrical PS and PAA arms) forms reverse micelles of low aggregation number (N_agg) and spherical morphology. In an 80 : 20 (v/v) 1,4‐dioxane/water mixture these micelles are transformed to regular micelles with an unexpectedly high N_agg and an elongated rod‐like structure. An abnormal behavior was observed in aqueous solutions of charged PS₂₄PANa₂₄ (with asymmetrical PS and PAA arms, W_PS = 19 wt.‐%) at low concentrations. A non‐equilibrium physical gel is formed, characterized by a very high viscosity and an elastic response upon oscillatory shearing.     

Tannic Acid‐Inspired Star‐Like Macromolecules via Temporally Controlled Multi‐Step Potential Electrolysis

Inspired by tea stains, a plant polyphenolic‐based macroinitiator is prepared for the first time by partial modification of tannic acid (TA) with 2‐bromoisobutyryl bromide. In accordance with the “grafting from” methodology, a naturally occurring star‐like polymer with a polar gallotannin core and a hydrophobic poly(n‐butyl acrylate) side arms is synthesized via a simplified electrochemically mediated ATRP (seATRP), utilizing multiple‐step potential electrolysis. To investigate the kinetics of the electrochemical catalytic process triggered by reduction of Cu(II) or Fe(III) catalytic complex in the presence of the multifunctional initiator, cyclic voltammetry measurements are conducted. The naturally derived tannin macromolecule shows narrow MWDs (? = 1.57). Moreover, solvolysis of the star polymer to cleave the side arms and characterize them indicates that all chains grow to the same length (homopolymers with M_w/M_n <1.17), which confirms the well‐controlled seATRP. The structure of the obtained TA‐based systems is characterized microscopically (AFM) and spectroscopically (¹H NMR, FT‐IR). Atomic force microscopy measurements precisely determine the diameters of the obtained star polymers (19.7 ± 3.3 nm). These new star polymers may find biomedical applications as drug delivery systems and antifouling or antimicrobial coatings.     

Synthesis of Di‐block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(tetrahydrofuran) by a Combination of Grignard Metathesis and Cationic Polymerizations

Poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was synthesized by cationic ring‐opening polymerization of tetrahydrofuran (THF) using a poly(3‐hexylthiophene) macroinitiator. Poly(3‐hexylthiophene) macroinitiator used for the ring‐opening polymerization of THF was synthesized by reacting the hydroxypropyl end‐group with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. ¹H NMR spectroscopy and SEC data confirmed the formation of the di‐block copolymers. Field‐effect mobility of poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was measured in a thin‐film transistor configuration and was found to be 0.009 cm² · V^?1 · s^?1.

     

N‐Isopropylacrylamide/2‐Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive Behavior

Summary: Tri‐arm star diblock copolymers, poly(2‐hydroxyethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) [P(HEMA‐b‐NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a two‐step ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well‐controlled polymerization of trifunctional macro‐initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature‐variable ¹H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I‐(HEMA₄₀‐NIPAAm₃₂₀)₃ solutions developed into core‐shell micelles with diameters of approximately 100 nm. I‐(HEMA₄₀‐NIPAAm₃₂₀)₃ was used as a representative example to elucidate the mechanism underlying temperature‐induced phase transition of copolymer solution. In this study we proposed a three‐stage transition process: (1) separately dispersed micelles state at ≈17–22 °C; (2) aggregation and fusion of micelles at ≈22–29 °C; (3) sol‐gel transition of PNIPAAm segments at ≈29–35 °C, and serious syneresis of shell layers.

Molecular architecture of Poly(HEMA‐b‐NIPAAm).     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.

     

Determination of the Kinetic Constants of the Telomerization of 10‐Undecenol with Alkyl Hydrogenphosphonate

Summary: The telomerization of 10‐undecenol with alkyl hydrogenphosphonate was studied in order to synthesize telomers of different molecular weights. The study showed that telomers from 10‐undecenol could be obtained despite the fact that the double bond has a low reactivity. The kinetic constant Kp²/K_Te was determined to be 7 × 10^?4 l · mol^?1 · s^?1 at 135 °C and the transfer constant C_T was 0.057. These values are normal for a low activity telogen such as hydrogenphosphonate and for slightly reactive monomers like 10‐undecenol.

SEC chromatogram of telomers obtained in the reaction of 10‐undecenol addition.     

Well‐defined N‐Isopropylacrylamide Dual‐Sensitive Copolymers with LCST ≈38 °C in Different Architectures: Linear,Block and Star Polymers

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is used to prepare temperature‐ and pH‐sensitive statistical copolymers with lower critical solution temperature (LCST) close to 38 °C at pH 7.4 based on N‐isopropylacrylamide and methacrylic acid derivative comonomers with a pK_a close to 6. Statistical copolymers are re‐activated to prepare amphiphilic block copolymers and star polymers with cross‐linked core. The LCST is maintained by varying the architecture; however, the LCST originated behaviour changes due to self‐aggregation. Statistical copolymers and short block copolymers show complex aggregation, whereas mid‐size block copolymers and star polymers show shrinkage of aggregate dimensions. The pH of the medium has a profound impact on the self‐assembling behaviour of the different polymer architectures.     

Acidolytic polymerization of N-methyldodecanelactam

The polymerization rate of 1-methylazacyclotridecan-2-one (N-methyldodecanelactam) ( 1 ) initiated with dodecanoic acid ( 2 ) can be described within the whole range of conversions in terms of the simple relation In ([ 1 ]₀/[ 1 ]) = k[ 2 ]₀t, in spite of the complexity of the overall reaction scheme. The rate constants (k) determined for 240, 260, and 280°C are 0,32, 1,21, and 3,4 kg · mol^?1 h^?1, respectively, and the constants of the Arrhenius equation are A = 6,6 · 10¹³kg · mol^?1 h^?1, E = 140 kJ · mol^?1. The resulting poly(N-methyldodecaneamide) ( 3 ) is a semicrystalline polymer (m.p. 65°C), soluble in polar organic solvents. The following constants of the Mark-Houwink equation were determined for solutions of this polyamide: for 5000 < M?_w < 150 000 g · mol^?1 at 25°C in THF (2-propanol), K = 0,124 (0,161) cm³ · g^?1, a = 0,59 (0,56); for 5 000 < M?_w < 80 000 g · mol^?1 at ?-temperature = 30,5°C in 1,4-dioxane, K = 0,215 cm³ · g^?1, a = 0,50. Analyses of molar masses, both theoretical and experimental (light-scattering, GPC, osmometry, end groups), indicate that at the polymerization temperature of 280°C side reactions already take place, reflected in random cleavage and in branching of chains.     

Thermodynamics of copolymerization of 1,3-dioxolane with 1,3-dioxepane and 1,3-dioxane

The equilibrium copolymerization of 1,3-dioxolane with 1,3-dioxepane in CH₂Cl₂ solution and with 1,3-dioxane without solvent is analyzed, and the equilibrium constants of homo- and cross-propagations are estimated and discussed. The corresponding thermodynamic parameters are calculated. The reported thermodynamic parameters of homopolymerization of 1,3-dioxane (ΔH_ss = ?3,1 kJ · mol^?1, ΔS_ss = ?35,5 J · mol^?1 · K^?1), were determined on the basis of the copolymerization data. Predictions of comonomer concentrations and microstructure of copolymers in the equilibrium copolymerization system are presented for any initial composition, on the basis of the determined equilibrium constants.     

PLP‐SEC Study into the Free‐Radical Propagation Rate Coefficients of Partially and Fully Ionized Acrylic Acid in Aqueous Solution

Summary: Propagation rate coefficients, k_p, for acrylic acid (AA) polymerization at 6 °C in aqueous solution were measured via pulsed laser polymerization (PLP) with the degree of ionization, α, varied over the entire range between 0 and 1. These measurements were carried out in conjunction with aqueous‐phase size‐exclusion chromatography (SEC). Strictly speaking, the reported k_p's are “apparent” propagation rate coefficients deduced from the PLP‐SEC data under the assumption that the local monomer concentration at the radical site is identical to overall monomer concentration. At an AA concentration of 0.69 mol · L^?1, the apparent k_p decreases from 111 000 L · mol^?1 · s^?1 at α = 0 to 13 000 L · mol^?1 · s^?1 at α = 1.0. The significant lowering of k_p with higher α is attributed to the repulsion between both monomer molecules and macroradicals becoming negatively charged. Addition of up to 10 mol‐% (with respect to AA) sodium hydroxide to the fully ionized aqueous AA solution leads to an enhancement of k_p up to 57 000 L · mol^?1 · s^?1.

Dependence of apparent k_p values on the degree of ionization of acrylic acid (a) and on pH (b) for aqueous polymerizations of acrylic acid.     

Reactivity in radical and anionic copolymerizations of 4-(trimethylsilyl)styrene. Synthesis of soluble poly{(1,4-divinylbenzene)-co-[4-(trimethylsilyl)styrene]}

Radical copolymerization of 4-(trimethylsilyl)styrene (TMSS) with styrene were carried out to estimate the reactivity of TMSS. The monomer reactivity ratios r₁ and r₂ in the radical copolymerization of TMSS (M1) with styrene (M2) were evaluated as 0,28 and 0,48, respectively. The value r₁ · r₂ (= 0,13) being smaller than unity indicates that the trimethylsilyl group at para position behaves as an electron-withdrawing substituent. Reactions of lithium diethylamide with TMSS in the presence of diethylamine, gave the 1:1 addition product 1-[2-(N,N-diethylamino)-ethyl]-4-(trimethylsilyl)benzene. Kinetic analysis showed that the second-order rate constant (k) for this addition reaction is 34,4 · 10^?4 dm³ · mol^?1 · s^?1, which is by a factor of 2 larger than that for the reaction with styrene (k = 16,0 · 10^?4 dm³ · mol^?1 · s^?1). The fact is also compatible with the above consideration for the r₁ · r₂ values. Lithium diisopropylamide initiated anionic copolymerizations of TMSS with 1,4-divinylbenzene (DVB) were also examined. The polymerizations proceed smoothly without any gel formation and the resulting copolymers are soluble in various common solvents such as benszene, tetrahydrofuran, chloroform, etc. Thus, novel organosilicon-containing polymers having appropriate amounts of reactive pendent vinyl groups are easily synthesized.     

Visible Light–Induced RAFT Polymerization of Methacrylate with 4‐(N,N‐diphenylamino)benzaldehyde as Organophotoredox Catalyst and the Effect of Temperature on the Polymerization

With UV–vis absorption in the range of 270–435 nm, 4‐(N,N‐diphenylamino)benzaldehyde (DPAB) takes efficient photoreduction quench with 4‐cynao‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP). The polymerization rates of methyl methacrylate (MMA) are 0.019, 0.056, and 0.102 h^?1 at 33, 40, and 50 °C, respectively, in the presence of DPAB and CTP under visible‐light irradiation. Dark reaction produces no PMMA at 50 °C for 120 h. The living feature is demonstrated by linearly increasing M_n with the monomer conversions and narrow polydispersity index (PDI), chain extension, and block polymerizations with benzyl methacrylate (BnMA) and poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). With PMMA‐CTP (M_n = 6800, PDI = 1.17), chain extension gives PMMA with M_n = 15 900 and PDI = 1.15. With PMMA‐CTP (M_n = 6000, PDI = 1.21) as macro‐RAFT, PMMA‐b‐PBnMA of M_n = 12 600 (PDI = 1.44) and M_n = 18 500 (PDI = 1.31) are prepared. These results support that there is a positive synergistic effect between polymerization temperature and visible‐light irradiation on the photo‐RAFT without losing the living features.     

Configurational double bond selectivity in the epoxidation of hydroxy-terminated polybutadiene with m-chloroperbenzoic acid

The selectivity of the three different double bonds (CIS, TRANS and VINYL) of hydroxyterminated polybutadiene regarding epoxidation was evaluated, using m-chloroperbenzoic acid in toluene below room temperature (?10°C, ?5°C, 0°C and 5°C). To determine the kinetic constants for the three configuratons (k_1,cis = (2,59–0,6) × 10^?2 L · mol^?1 · min^?1; k_{2, trans} = (5,35–0,82) × 10^?2 L · mol^?1 · min^?1; k_{3, vinyl} = (0,97–0,01) × 10^?2 L · mol^?1 min^?1), ¹H and ¹³C NMR was used along with a system of three parallel equations. The activation energy values were also evaluated (E_{a, cis} = 53,9 kJ · mol^?1; E_{a, trans} = 70,7 kJ · mol^?1 and E_a, vinyl = 261,1 kJ · mol^?1) for the three double bond types.     

Bioinspired All‐Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(2‐(2‐hydroxyethoxy)benzoate): Synthesis and Polymer Film Properties

The bioinspired diblock copolymers poly(pentadecalactone)‐block‐poly(2‐(2‐hydroxyethoxy)benzoate) (PPDL‐block‐P2HEB) are synthesized from pentadecalactone and dihydro‐5H‐1,4‐benzodioxepin‐5‐one (2,3‐DHB). No transesterification between the blocks is observed. In a sequential approach, PPDL obtained by ring‐opening polymerization (ROP) is used to initiate 2,3‐DHB. Here, the molar mass M_n of the P2HEB block is limited. In a modular approach, end‐functionalized PPDL and P2HEB are obtained separately by ROP with functional initiators, and connected by 1,3‐dipolar Huisgen reaction (“click‐chemistry”). Block copolymer compositions from 85:15 mass percent to 28:72 mass percent (PPDL:P2HEB) are synthesized, with M_n of from about 30 000–50 000 g mol^?1. The structure of the block copolymer is confirmed by proton NMR, Fourier‐transform infrared spectroscopy, and gel permeation chromatography. Morphological studies by atomic force microscopy (AFM) further confirms the block copolymer structure, while quantitative nanomechanical AFM measurements reveal that the Derjaguin–Muller–Toporov moduli of the block copolymers range between 17.2 ± 1.8 and 62.3 ± 5.7 MPa, i.e., between the values of the parent P2HEB and PPDL homopolymers (7.6 ± 1.4 and 801 ± 42 MPa, respectively). Differential scanning calorimetry shows that the thermal properties of the homopolymers are retained by each of the copolymer blocks (melting temperature 90 °C, glass transition temperature 36 °C).     

Highly Branched Poly(arylene ether)s via Oligomeric A2 + B3 Strategies

Summary: Branched poly(arylene ether)s were prepared in an oligomeric A₂ + B₃ polymerization of phenol endcapped telechelic poly(arylene ether sulfone) oligomers as A₂ and TFPPO as trifunctional monomer B₃. The molar mass of the A₂ oligomer significantly influenced the onset of gelation and the DB. A high level of cyclization during polymerization of low molar mass A₂ oligomers (U₃ = 660 and U₆ = 1 200 g · mol^?1) led to a high conversion of functional groups in the absence of gelation, and the level of cyclization reactions in the polymerization decreased as the molar mass of the A₂ oligomer was increased. The pronounced steric effect in the polymerization of higher molar mass A₂ oligomers (U₈ = 1 800 and U₁₆ = 3 400 g · mol^?1) resulted in low reactivity of the third aryl fluoride in the B₃ monomer. As a result, only slightly branched (U₈ = 1 800 g · mol^?1) or nearly linear (U₁₆ = 3 400 g · mol^?1) high molar mass products were obtained with higher molar mass A₂ oligomers. The branched polymers exhibited lower Mark‐Houwink exponents and [η] relative to linear analogs, and differences between the branched polymers and linear analogs were less significant as the molar mass of the A₂ oligomers was increased due to a decrease in the overall DB.

     

Macroion-pairs and macroions in the kinetics of polymerization of hexamethylene oxide (oxepane)

Cationic polymerization of oxepane (hexamethylene oxide) ( 1 ) in CH₂Cl₂ and C₆H₅NO₂ as solvents was initiated with 1,3-dioxolan-2-ylium hexafluoroantimonate ( 2 ). Dissociation constants (K_D) of the ion-pairs of polyoxepane into ions were measured: K_D (in CH₂Cl₂, T = 25°C) = 2,8·10^?5 mol·l^?1 [ΔH_D = ?3,8 kJ·mol^?1 (?0,9 kcal·mol^?1), ΔS_D = ?98 J·mol^?1·K^?1 (?23,4 cal·mol^?1·K^?1)]; K_D (in C₆H₅NO₂, T = 25°C) = 1,6·10^?3 mol·l^?1 [ΔH_D = ?7,1 kJ·mol^?1 (?1,7 kcal·mol^?1), ΔS_D = ?78 J·mol^?1·K^?1 (?18,7 cal·mol^?1·K^?1)]; these values are close to those of the ion-pairs of polytetrahydrofuran. Rate constants k_p⁺ and k_p^±, determined from the kinetic measurements for degrees of dissociation of macroion-paris ranging from 0,02 to 0,21 (in CH₂Cl₂) and from 0,09 to 0,7 (in C₆H₅NO₂), were found to be identical within an experimental error of kinetic measurements. The activation parameters of propagation were measured and their dependences on the polarity of the polymerization mixtures are discussed.