Nitroxide-controlled free radical polymerization of a sugar-carrying acryloyl monomer

Controlled free radical polymerization of a sugar-carrying acrylate, 3-O-acryloyl-1,2 : 5,6-di-O-isopropylidene-α-D -glucofuranoside (AIpGlc), was achieved in p-xylene at 100°C by using a di-tert-butyl nitroxide (DBN)-based alkoxyamine as an initiator and dicumyl peroxide (DCP) as an accelerator. The polymerization gave low-polydispersity (1.2 < M_w/M_n < 1.6) polymers with predicted molecular weights. The same approach with a DBN-capped polystyrene (PS-DBN) as an initiator afforded block copolymers of the type PS-b-PAIpGlc. The acidolysis of the homopolymers and block copolymers gave well-defined glucose-carrying polymers PAGlc and PS-b-PAGlc, respectively. These amphiphilic PS-b-PAGlc block copolymers were observed to exhibit microdomain surface morphologies that differ for different copolymer compositions. This success opens up a new, simple route to the synthesis of well-defined sugar-carrying polymers of various architectures.     

Radical telomerization of vinyl acetate with chloroform. Application to the synthesis of poly(vinyl acetate)‐block‐polystyrene copolymers by consecutive telomerization and atom transfer radical polymerization

This paper demonstrates that radical telomerization and atom transfer radical polymerization (ATRP) can be combined in a two‐step procedure to prepare poly‐(vinyl acetate)‐block‐polystyrene (PVOAc‐b‐PSt) diblock copolymers. The first step consists in telomerizing VOAc with chloroform, leading to trichloromethyl‐terminated VOAc telomers CCl₃(VOAc)_nH. A detailed ¹H NMR analysis shows that nearly pure telomer structures are obtained over a broad range of DP_n values (up to at least 60 units). When ATRP of styrene is initiated with a model telomer adduct (CCl₃CH₂CH₂OAc), molecular weights increase linearly with monomer conversion and match theoretical values. Moreover, polydispersities are consistently low (1.22 < M_w/M_n < 1.38) throughout polymerization. Similarly, VOAc telomers (DP_n = 9 and 62) are good ATRP macroinitiators. The high purity of the resulting diblock copolymers is confirmed by GPC using RI/UV dual detection.     

Facile Synthesis of Helical Rod–Coil Block Polymers by the Combination of ATRP and Pd(II)‐Initiated Isocyanides Polymerizations

A bifunctional initiator containing propargyl bromoisobutyrate and alkyne‐Pd(II) (PBB‐Pd(II)) is designed and synthesized. The propargyl bromoisobutyrate unit of PBB‐Pd(II) can initiate the atom transfer radical polymerization (ATRP) of vinyl monomers, while the Pd(II) complex can initiate the polymerization of phenyl isocyanides. Both the ATRP and Pd(II)‐mediated isocyanide polymerization are proceeded in living/controlled manner. Thus, combining the two living polymerizations, a series of well‐defined block copolymers bearing rod poly(phenyl isocyanide)s and coil poly(acrylate) segments can be facilely prepared in high yield with tunable composition, controlled molar masses (M_ns), and narrow molar mass distributions (M_w/M_ns). What is more, benefiting from this synthetic strategy, well‐defined core cross‐linked star polymers are readily synthesized. Optically active block copolymers and star polymers can be facilely obtained by using chiral isocyanide monomers due to the formation of predominated one‐handed helix. The chiral star polymers show excellent enantioselective recognition ability in enantioselective crystallization of racemic compounds.     

Block copolymers by sequential group transfer polymerization: poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate)

Poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) (PMMA-block-PEHA) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate) with a methacrylate/acrylate unit ratio of 1:1 and 1:3, 16000 < M _n < 44000 and 1,9 < M _w/M _n < 2,5, were prepared by sequential group transfer polymerization using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane as initiator and tetrabutylammonium fluoride monohydrate as a catalyst in tetrahydrofuran at ?30°C, PMMA being the first block. The increase in M _n during the successive addition of monomers is linearly dependent on the (co)polymer yield and size-exclusion chromatography (SEC) curves are shifted towards higher molecular weights in comparison with PMMA macroinitiators. The block structure of the copolymers was also proven by extraction experiments. The presence of homopolymers in the copolymers was not detected. When the former copolymer is prepared in a reverse way (PEHA segment being the first), the MMA polymerization ceases at ≈ 43–45% conversion.     

Tuning Dispersity in Diblock Copolymers Using ARGET ATRP

Poly(methyl acrylate)‐b‐polystyrene with controlled molecular weight distribution of each block was synthesized via activators regenerated by electron transfer atom transfer radical polymerization. Polymers with tunable dispersity, in the range of M _w/M _n 1.32 to 2.0, were achieved by adjusting the concentration of the copper catalyst and reaction temperature, thereby controlling the rate of reversible deactivation reaction as well as the number of monomer units added during each activation cycle. Regardless of the increased dispersity, high chain‐end functionality was retained and the livingness of the macroinitiators was confirmed by chain extension, resulting in diblock copolymers with controlled dispersity in each block. Liquid chromatography under critical conditions was employed to determine if any macroinitiator remained in the final product.     

Chlorolanthanocene‐dialkylmagnesium systems for styrene bulk polymerization and styrene‐ethylene block copolymerization

The bulk polymerization of styrene has been investigated at 105°C in the presence of exclusively dialkylmagnesium or combination of chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmagnesium or n,s‐dibutylmagnesium, styrene polymerization proceeds via thermal self‐initiation, but is accompanied by a reversible transfer to dialkylmagnesiums to yield in turn oligostyrylmagnesium species; the latter are finally hydrolysed to oligostyrenes with M_n = 500–1 500 and M_w/M_n = 2.0–2.8. The analysis of the oligostyrenes by MALDI‐TOF mass spectrometry establishes the presence of ethyl and butyl headgroups, consistent with the transfer process. When the dialkylmagnesium is combined with a lanthanocene such as (C₅Me₅)₂NdCl₂Li(OEt₂)₂ ( 1 ), an increase in activity is obtained which is ascribed to additional styrene polymerization initiated by in situ generated alkyl(hydride)lanthanocene species. The influence of various reaction parameters on the performance of this system has been investigated. The oligostyrenes (M_n = 500–9 000) produced under optimum conditions have a relatively narrow molar mass distribution (M_w/M_n = 1.20–1.40) which can be explained in terms of an efficient transfer between the chain‐growing lanthanide and the oligostyrylmagnesium species. The MALDI‐TOF mass spectra of the oligostyrenes produced with various dialkylmagnesium‐lanthanocene combinations gives an insight into the initiation mechanism. Finally, the combination of butylethylmagnesium and Cp*₂NdCl₂Li(OEt₂)₂ has been used to achieve (styrene‐co‐ethylene) block copolymers.     

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.     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Anionic synthesis of well‐defined,poly[(styrene)‐block‐(propylene oxide)] block copolymers

Well‐defined, narrow molecular weight distribution (M_w/M_n ≤ 1.1) poly[(styrene)‐block‐(propylene oxide)] block copolymers with relatively high molecular weight poly(propylene oxide) blocks [e. g. M_n (PPO) = 10 000–12 000 g/mol] have been prepared by anionic polymerization. The polystyrene block (M_n = 5 000; M_w/M_n = 1.1) was prepared by alkyllithium‐initiated polymerization of styrene followed by chain‐end functionalization with ethylene oxide and protonation with acidic methanol. The resulting ω‐hydroxyl‐functionalized polystyrene was converted to the corresponding alkali metal salts with alkali metals (Na/K alloy, Rb, Cs) and then used to initiate block polymerization of propylene oxide in tetrahydrofuran. The effects of crown ethers (18‐crown‐6 and dicyclohexano‐24‐crown‐8) and added dimethylsulfoxide were investigated. Chain transfer to the monomer resulted in significant amounts of poly(propylene oxide) formation (50%); however, the diblock molecular weight distributions were narrow. The highest molecular weight poly(propylene oxide) blocks (12 200 g/mol) were obtained in tetrahydrofuran with cesium as counterion without additives.     

Living coordination polymerization of end‐allenyloxy poly(ethylene glycol) macromonomer by a π‐allylnickel catalyst

The living coordination polymerization of end‐allenyloxy poly(ethylene oxide)s ( 2A – 2C ) was carried out by [(η³‐allyl)NiOCOCF₃]₂ ( 1 ) in the presence of PPh₃ to produce narrowly dispersed polyallenes bearing poly(ethylene oxide) side chains. For instance, the polymerization of 2B (M_n = 590, [ 2 ]/[ 1 ] = 100) proceeded smoothly to give a polymer (M_n = 39 800, M_w/M_n = 1.13) in high yield. The molecular weight of poly( 2 ) could be controlled by the ratio of 2 to 1 and by the molecular weight of 2 . The block copolymers of 2B with various alkoxyallenes ( 3A – 3C ) or with 1‐phenylethyl isonitrile ( 3D ) were also obtained by the two‐stage copolymerization process (i. e., the polymerization of 2 , followed by that of 3A – 3D ). The resulting block copolymers were found to serve as polymeric surfactants in the polymer blend systems of PSt and PMMA.     

Polychloroalkane initiators in copper‐catalyzed atom transfer radical polymerization of (meth)acrylates

A series of polychloroalkanes CCl_nR_4‐n (n = 2, 3, or 4) was tested as initiators for atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and methyl acrylate (MA) using CuCl/2,2′‐bipyridine as the catalyst. 2,2‐Dichloropropane and 2,2‐dichloroethanol initiate the ATRP of MMA very slowly. 1,1,1‐Trichloroalkanes, RCCl₃, are good initiators. For all the R groups tested, the number‐average molecular weight M_n increases with conversion and polydispersities are low (1.1 < M_w/M_n < 1.3). The initiator efficiency factor increases with electrophilicity of the initiating radical (0.7 < f < 1). CCl₄ is a multifunctional initiator and the final M_n values are lower than targeted. This is explained by the generation of new polymer chains occurring once the third active site is created per chain. ATRP of MA initiated by CCl₃CH₂CF₂Cl or CCl₃C₈H₁₇ results in polymers with M_n values predetermined by the Δ [M]/[Initiator]₀ ratio (f close to 1) and narrow molecular weight distributions (M_w/M_n < 1.3 at high conversion). The polymerization is much slower than that of MMA, but can be considerably accelerated by use of Cu(0) metal while maintaining an excellent control over molecular weights and polydispersities.     

Amino-termined poly(L-lactide)s as initiators for the polymerization of N-carboxyanhydrides: synthesis of poly(L-lactide)-block-poly(α-amino acid)s

Poly(L -lactide)-block-poly(L -amino acids) block copolymers were prepared via polymerization of α-amino acid N-carboxyanhydrides with amino-terminated poly(L -lactide)s as macroinitiators. Two types of macroinitiators were used, one with an aminopropoxy head group (number-average molecular weight M _n = 22000) and the other one with a phenylalanine end group (M _n = 18000). The first macroinitiator was obtained by polymerization of (L ,L )-lactide with an initiator prepared in situ from diethylzinc Et₂Zn and N-tert-butoxycarbonyl-1-amino-3-propanol, followed by deprotection of the amino group. The second macroinitiator was obtained by endcapping of poly(L -lactide) with N-tert-butoxycarbonylphenylalanine and deprotection of the amino group. ¹H- and ¹³C NMR spectroscopies confirm the block structure of the copolymers obtained. In differential scanning calorimetry curves only one melting transition characteristic of the poly(L -lactide) block is observed, on further heating decomposition occurs. By thermogravimetry two steps of decomposition are observed, the first one being assigned to the decomposition of the poly(L -lactide) block, and the second one to that of the poly(amino acid) block, by comparison with the thermal behaviour of the corresponding homopolymers.     

Nitroxide-controlled free radical polymerization of p-tert-butoxystyrene. Kinetics and applications

The free radical polymerization of p-tert-butoxystyrene (BOS) in the bulk at 125°C “initiated” with the adduct of 2-benzoyloxy-1-phenylethyl and TEMPO (BS-TEMPO) was found to proceed in a “living” fashion, providing low-polydispersity PBOS and block copolymers of the type PBOS-b-PS, where TEMPO is 2,2,6,6-tetramethylpiperidin-1-oxyl and PS is polystyrene. The acidolysis of the polymers gave well-defined poly(p-vinylphenol) (PVP) polymers. The PVP-b-PS block copolymers were observed to exhibit lamellar and cylindrical microdomain morphologies depending on the copolymer composition. The rate of BOS polymerization is independent of the “initiator” (BS-TEMPO) concentration, being essentially equal to the rate of thermal polymerization. The polydispersity of PBOS depends on polymerization time but not on the degree of polymerization, under the studied experimental conditions.     

Living polymerization of several substituted acetylenes with WOCl4–Bu4Sn–tert‐BuOH (1 : 1 : 1) as a catalyst

Living polymerization of several substituted acetylenes was studied with a W‐based ternary catalyst, WOCl₄–Bu₄Sn–tert‐BuOH (1 : 1 : 1). [o‐(Trimethylsilyl)phenyl]acetylene forms a polymer with a narrow molecular weight distribution (MWD) (M_w/M_n 1.08). The living nature of this polymerization system was proved by both multistage polymerization and the conversion dependence of the polymer molecular weight. Linear internal alkynes (e. g., 5‐dodecyne) also yield polymers with a narrow MWD (M_w/M_n ∼︁ 1.10), which were proven to be obtained by living polymerization by examination of the conversion dependence of the polymer molecular weight. However, neither 1‐chloro‐1‐alkynes nor tert‐butylacetylene, polymerize in a living fashion with this catalyst. A block copolymer was selectively prepared by sequential polymerization of [o‐(trimethylsilyl)phenyl]acetylene and [o‐(trifluoromethyl)phenyl]acetylene.     

Protection and polymerization of functional monomers, 26. Synthesis of well-defined poly[4-(3′-butynyl)styrene] by means of anionic polymerization of 4-(4′-trimethylsilyl-3′-butynyl)styrene

Anionic polymerization of 4-(4′-trimethylsilyl-3′-butynyl)styrene ( 2 ) was carried out in THF at ?78°C for 0.5 h with oligo(α-methylstyryl)lithium, -dilithium, and -dipotassium. Poly( 2 )s possessing predicted molecular weights and narrow molecular weight distributions (M?_w/M?_n < 1.11) were quantitatively obtained in all cases. By sequential anionic copolymerization of 2 and styrene, novel block copolymers, polystyrene-block-poly( 2 ) starting either from living polystyrene or living poly( 2 ), were synthesized. After completion of the polymerization, there occurred some gradual deactivation of the propagating carbanion of poly( 2 ) at ?78°C. This deactivation reaction could be almost completely suppressed at ?95°C. The deprotection of poly( 2 ) was performed by treating with Bu₄NF in THF at 0°C for 1 h. The trimethylsilyl protecting group of poly( 2 ) was completely removed to afford a poly[4-(3′-butynyl)styrene] of a controlled molecular structure.     

Proton‐Conducting Poly(phenylene oxide)–Poly(vinyl benzyl phosphonic acid) Block Copolymers via Atom Transfer Radical Polymerization

Block copolymers containing poly(phenylene oxide) (PPO) and poly(vinyl benzyl phosphonic acid) segments are synthesized via atom transfer radical polymerization (ATRP). Monofunctional PPO blocks are converted into ATRP active macroinitiators, which are then used to polymerize a diethyl p‐vinylbenzyl phosphonate monomer in order to obtain phosphonated block copolymers bearing pendent phosphonic ester groups. Poly(phenylene oxide‐b‐vinyl benzyl phosphonic ester) block copolymers are hydrolyzed to corresponding acid derivatives to investigate their proton conductivity. The effect of the relative humidity (RH) is investigated. The proton conductivity at 50% RH and one bar of vapor pressure approaches 0.01 S cm^?1.     

Herstellung,charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren

An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 10⁵ < M < 3 · 10⁶), poly(α-methylstyrene)s (7 · 10⁴ < M < 4 · 10⁶), and block copolymers (2 · 10⁵ < M < 2,5 · 10⁶). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = M_w/M_n–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the two segment types yield light scattering measurements which give molecular weights M_w, radii of gyration 〈r²〉^1/2 and second virial coefficients A₂ with almost the same accuracy as in the case of homopolymers. The radii of gyration and the intrinsic viscosities of the block copolymers give no evidence for any “intramolecular phase separation” in the good solvent toluene. The coil conformation corresponds closely to that of the homopolymers.     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Use of Original ω‐Perfluorinated Dithioesters for the Synthesis of Well‐Controlled Polymers by Reversible Addition‐Fragmentation Chain Transfer (RAFT)

A series of five fluorinated dithioesters PhC(S)SRCH₂C_nF_2n+1 (where R represents an activating spacer and n = 6 or 8) was obtained in fair to high yields (57–88%). These transfer agents were successfully used in reversible addition‐fragmentation transfer (RAFT) of styrene (S), methyl methacrylate (MMA), ethyl acrylate (EA) and 1,3‐butadiene. Well‐chosen fluorinated dithioesters were able to lead to a good control of the radical polymerization of these monomers (i.e., molar masses of the produced polymers increased linearly with the monomer conversion and the polydispersity indexes ranging between 1.1 and 1.6 remained low). The relationship between the structures of the dithioesters and the living behavior of the radical polymerization of these above monomers is discussed and it is shown that the nature of the R group influences the living behavior from different contributions to radical stabilization. Furthermore, the RAFT process also yielded PMMA‐b‐PS and PEA‐b‐PS block copolymers bearing a fluorinated moiety.     

Thermal behavior and spherulitic superstructures of SBC triblock copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ε-caprolactone) (C) block

The dynamic crystallization and the melting behavior of polystyrene-block-poly(ε-caprolactone) (PS-b-PCL, short notation SC), polybutadiene-block-poly(ε-caprolactone) (PB-b-PCL, BC) and polystyrene-block-polybutadiene-block-poly(ε-caprolactone) (PS-b-PB-b-PCL, SBC) have been studied using differential scanning calorimetry. The copolymers with high molecular weight exhibit microphase separation into microphases consisting of polystyrene, polybutadiene and poly(ε-caprolactone) and partial crystallization of the corresponding PCL block. The crystallization occurs at temperatures below the PS glass transition. Depending on the block copolymer composition, crystallization takes place through a combination of heterogeneous and homogeneous nucleation. Isothermal crystallization was studied in order to determine the equilibrium melting point, T_m⁰, of the PCL block, which depends on the weight ratio w_PB: w_PCL. The crystallization kinetics was analyzed in terms of Avrami equation. A general decrease in the overall crystallization rate in the block copolymers relative to the equivalent PCL homopolymer was found. Additionally, the growth rate of the spherulites was followed using polarized optical microscopy. Depending on the composition and flexibility of the block connected to PCL, some copolymers showed ring-banded spherulites.