Bifunctional Initiator Research Articles

Mechanochemical Fluorescence Switching in Polymers Containing Dithiomaleimide Moieties.

Polymers that display useful mechanochemical responses, such as changes of their fluorescence characteristics, are attracting great interest. Here, we introduce the fluorescent dithiomaleimide (DTM) motif as a mechanofluorophore and report the mechanoresponse of two polymer types containing this motif. Poly(methyl acrylate) (PMA) and poly(ε-caprolactone)s (PCL) featuring one DTM moiety in the center of each chain (PMA-DTM and PCL-DTM) were synthesized by controlled radical and coordination-insertion ring-opening polymerizations using bifunctional DTM-containing initiators. Upon ultrasonic treatment of PMA-DTM or PCL-DTM of sufficiently high initial molecular weight, both the molecular weight and the fluorescence intensity decreased with similar kinetics, while no significant fluorescence changes were observed for DTM-free reference polymers. The results show that the DTM motif can serve as a mechanophore that displays a mechanically induced fluorescence turn-off.

Modeling of ethylene copolymerization in nonisothermal high‐pressure reactors using bifunctional initiators

Enhancing the performance of high‐pressure LDPE process is valuable for polymer industry. However, the severe thermodynamics requirement of high pressure and temperature hinders the reaction process from getting simultaneously high monomer conversion and polymer molecular weights. Bifunctional peroxides used as initiators can boost the polymerization rate and alter rheological polymer properties. This article proposes a new kinetics model of ethylene/butyl acrylate copolymerization with bifunctional initiators in a high‐pressure nonisothermal tubular reactor. Model predictions are compared with available data. A SQP optimization scheme is employed to determine a suitable wall temperature for each zone along the nonisothermal tubular reactor. In comparison with the monofunctional TBPPI peroxide, a lower amount of the bifunctional DHBPPI peroxide is needed to get a higher conversion in shorter residence time, but at the expense of higher thermal energy. The results also showed that polymers produced with bifunctional peroxides are significantly more branched. POLYM. ENG. SCI., 59:74–85, 2019. © 2018 Society of Plastics Engineers

Synthesis of Telechelic Poly(p-benzamide)s

Well-defined telechelic poly(benzamide)s were synthesized by chain-growth polycondensation of phenyl-4-amino benzoate and pentafluorophenyl-4-amino benzoate derivatives with a bifunctional initiator in the presence of LiTMP as base. The polymerization was carried out at −70 °C to prevent self-initiated polymerization. To confirm the control over molecular weight, different defined molecular weight polymers were synthesized and analyzed by GPC. Taking advantage of the labile ester end groups of these poly(benzamide)s, we carried out postpolymerization modifications to introduce different end functional groups such as alkyne, amine, alcohol, alkyl halide, and olefin suitable for different types of postpolymerization reactions. Successful end group modification was confirmed by 1H NMR spectroscopy and isotopically resolved MALDI-ToF mass spectrometry.

Low‐cost bifunctional initiators for bidirectional living cationic polymerization of olefins. III. centrally functionalized polyisobutylenes

ABSTRACTAllyl‐telechelic polyisobutylene (A‐PIB‐A) produced by the bis‐benzocyclobutane dichloride (bBCB‐diCl) initiator contains the bis‐benzocyclobutane (bBCB) fragment at the center of the macromolecule (A‐PIB‐bBCB‐PIB‐A). Thermolysis of A‐PIB‐bBCB‐PIB‐A quantitatively converts the central bBCB fragment to a substituted conjugated tetraene (A‐PIB‐tetraene‐PIB‐A). The structure of A‐PIB‐tetraene‐PIB‐A was anticipated from small molecule models and identified/quantitated by 1H NMR spectroscopy. This is the first time a reactive functional group was introduced at the statistical center of a (telechelic) PIB. Subsequently, the A‐PIB‐tetraene‐PIB‐A was peroxidized to an epoxy derivative. Reaction of the A‐PIB‐tetraene‐PIB‐A with HSCH2CH2OH produced HOCH2‐telechelic PIB containing a central CH2OH function, and hydrosilation with HSi(Me2)‐O‐Si(Me2)H produced SiH‐telechelic PIB with a central SiH function. Reactions with maleic anhydride, tetracyanoethylene, butyl lithium, and potassium permanganate have also been examined. In sum, A‐PIB‐bBCB‐PIB‐A and A‐PIB‐tetraene‐PIB‐A are useful intermediates for the synthesis of novel PIB‐based materials for various end uses under investigation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1140–1145

Combination of Photoinduced ATRP and Click Processes for the Synthesis of Triblock Copolymers

ABA type triblock copolymers possessing polystyrene as middle segment and poly(ε-caprolactone) (PCL) and poly(ethylene glycol) (PEG) as side segments were synthesized by combining two photochemical strategies, namely photoinduced atom transfer radical polymerization (ATRP) and click processes. For this purpose, α,ω-diazido functional polystyrene (N3-PS-N3) was synthesized by photoinduced ATRP using a bifunctional initiator, followed by a simple substitution of the chain end halides. Parallel to this, alkyne-PCL was synthesized by ring opening polymerization of ε-caprolactone, employing propargyl alcohol as initiator. For the synthesis of alkyne-PEG, industrially available PEG was functionalized by a simple esterification reaction using 5-pentynoic acid. After the syntheses of these alkyne functional polymers as clickable counterparts, they were reacted with N3-PS-N3 by photoinduced click reactions to prepare the desired triblock copolymers. All polymers were characterized by NMR, IR and GPC analyses.

A Straightforward Methodology for the Synthesis of α,ω-Telechelic Poly(dimethylsiloxane)s

In this work we report the synthesis of α,ω-telechelic poly(dimethylsiloxane)s (α,ω-PDMS) by employing a novel bifunctional initiator obtained from a commercially available siloxane precursor, diglycidylether-terminated poly(dimethylsiloxane) (PDMS-DGE). The synthetic strategy was easily followed by different colour changes, and involved the high-vacuum reaction of sec-Bu−Li+ with 1,1′-diphenylethylene (DPE) to afford the addition adduct (bright red) that was subsequently reacted with PDMS-DGE, promoting the nuclephilic ring-opening from epoxide-end chains. The resulting bifunctional initiator (light green) was then employed to polymerize hexamethyl(cyclotrisiloxane) monomer (D3) by using conventional anionic polymerization (from light green to pale yellow). From suitable terminating agents, silane (–SiH), vinyl (–CH=CH2), hydroxy (–OH), and even methacryloyl α,ω-PDMS were obtained. 1H NMR and FT-IR analyses confirmed the presence of the targeted functional groups in the resulting polymers. However, a careful siliconization procedure should be performed over glass surfaces during the fractionation of chlorosilane ampoules in order to avoid the presence of silanol moieties that decrease end-capping efficiency. This fact was observed not only from NMR but also from size exclusion chromatography (SEC) analyses, since narrow molar masses distributions (1.15 ≤ Mw/Mn ≤ 1.3) and a good control over the resulting molar masses were observed.

Low cost bifunctional initiators for bidirectional living cationic polymerization of olefins. II. hyperbranched styrene–isobutylene–styrene triblocks with superior combination of properties

ABSTRACTBoth bifunctional initiators, the new low cost bBCB‐diCl [4,9‐dichloro,2,4,7,9‐tetramethyl‐tricyclo[6.2.0.036]deca‐1(8),2,6‐triene] and the universally used “hindered” HDCCl [1‐(tert‐butyl)‐3,5‐bis(2‐chloropropan‐2‐yl)benzene] induce the living bidirectional block copolymerization of isobutylene (IB) followed by styrene (St), and produce PSt‐b‐PIB‐b‐PSt (SIBS) triblocks. We discovered that the molecular weights of triblocks kept significantly increasing long after St conversion reached completion during syntheses. Results were explained by the formation of blends consisting of the expected linear SIBS plus hyperbranched SIBS, HB(SIBS)n. The structure of high molecular weight (>106 g/mol) HB(SIBS)n was characterized by various techniques, and key properties of SIBS/HB(SIBS)n blends were investigated. The mechanism of HB(SIBS)n formation and the synthesis of SIBS/HB(SIBS)n blends was elucidated. The properties of SIBS/HB(SIBS)n blends are superior to those of SIBS. Thus, whereas SIBS exhibits ∼25 MPa tensile strength and ∼450% elongation, SIBS/HB(SIBS)n blends exhibit 25–27 MPa tensile strength and >400% elongation; deformation under constant load of SIBS is ∼12%, whereas that of SIBS/HB(SIBS)n is <1%; permanent set of SIBS is 1.3% whereas that of SIBS/HB(SIBS)n is <0.5%. SIBS/HB(SIBS)n blends also exhibit higher yield, yield strength, and toughness than SIBS. The microstructure/property relationship of HB(SIBS)n is discussed and the reasons for enhanced properties of SIBS/HB(SIBS)n blends are analyzed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 705–713

Low cost bifunctional initiators for bidirectional living cationic polymerization of olefins. I. isobutylene

ABSTRACTWe describe the discovery of novel low cost bifunctional initiators 2,4,7,9‐tetramethyl‐tricyclo[6.2.0.036]deca‐1(8),2,6‐triene‐4,9‐diol (bBCB‐diOH) and 4,9‐dichloro,2,4,7,9‐tetramethyl‐tricyclo[6.2.0.036]deca‐1(8),2,6‐triene (bBCB‐diCl), for living cationic bidirectional polymerization of olefins, for example, isobutylene. bBCB‐diOH was quantitatively synthesized in one step by UV radiation of commercially available diacetyl durene (DAD) and bBCB‐diCl by hydrochlorination of bBCB‐diOH. These molecules, in conjunction with TiCl4 coinitiator, initiate the living polymerization of isobutylene. Livingness was demonstrated by linear conversion versus molecular weight (MW) plots and narrow MW distributions. Polymerizations are slower than those initiated by the universally used “hindered” bifunctional initiator 5‐tert‐butyl‐1,3‐bis(1‐chloro‐1‐methyl)benzene and are suitable for rate studies. Herein, we report the synthesis, by the use of bBCB‐diCl, of relatively low MW (Mn < 3000 g mol−1) allyl‐telechelic polyisobutylene (PIB) used for the synthesis of PIB‐based polyurethanes and that of relatively high MW (Mn > 30,000) living PIB telechelics for the synthesis of thermoplastic elastomers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3716–3724

Bifunctional Initiators as Tools to Track Chain Transfer during the CROP of 2-Oxazolines.

Detailed kinetic studies during the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) are conducted using four bifunctional bromo-type initiators in N,N-dimethylformamide (DMF) at 140 °C. Serving as models to quantify chain transfer to monomer occurring during the CROP initiated by monofunctional initiators, size exclusion chromatography (SEC) resolves a second molar mass distribution with lower molar mass at initial [monomer] to [initiation site] ratios ([M]0 /[I]0 ) of 25, while the resolution is insufficient at [M]0 /[I]0 of 10. Slightly slow initiation is revealed at [M]0 /[I]0 = 25, which prohibits the derivation of chain transfer rates by fitting of the size exclusion chromatography (SEC) data. Although conventional kinetic plots give no indication of significant amounts of chain transfer, the molar mass distributions resolved by SEC can unambiguously be identified as such by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in both the high as well as the low m/z regions of the mass spectra.

Ultrafast SET-LRP with Peptoid Cytostatic Drugs as Monofunctional and Bifunctional Initiators.

To continue expanding the use of Single Electron Transfer-Living Radical Polymerization (SET-LRP) in applications at the interface between macromolecular science, biomacromolecules, biology and medicine, it is essential to develop novel initiators that do not compromise the structural stability of synthesized polymers in biological environments. Here, we report that stable 2-bromopropionyl peptoid-type initiators such as 1,4-bis(2-bromopropionyl)piperazine and 4-(2-bromopropionyl)morpholine are an alternative that meets the standards reached by the well-known secondary and tertiary α-haloester-type initiators in terms of excellent control over molecular weight evolution and distribution as well as polymer chain ends. SET-LRP methodologies in organic, aqueous, and biphasic organic-aqueous media were evaluated for this purpose.

Symmetrical polymer systems prepared using a degradable bifunctional atom transfer radical polymerization initiator: Synthesis, characterization, and cleavage

ABSTRACTLinear (co)polymers and dimethacrylate‐end‐linked polymer networks of methyl methacrylate with 2‐(dimethylamino)ethyl methacrylate, cleavable in the middle of the polymer chain, either under thermolysis or alkaline hydrolysis conditions, were prepared via atom transfer radical polymerization (ATRP) using a specially designed bifunctional degradable initiator. This initiator was 2,6‐pyridinediethanol di(2‐bromo‐2‐methyl propanoate) (PyDEDBrMeP), bearing two 2‐(pyridin‐2‐yl)ethyl ester moieties, known for their thermal and hydrolytic (alkaline conditions) lability. As a control, a more stable bifunctional ATRP initiator, 2,6‐pyridinedimethanol di(2‐bromo‐2‐methyl propanoate) (PyDMDBrMeP), was also synthesized together with the corresponding linear polymers and polymer networks prepared from it. Thermal or hydrolytic treatment of the polymers prepared using PyDEDBrMeP led to a reduction in the molecular weights of the linear polymers by a factor of two, and to the conversion of the polymer networks to soluble branched (star) structures, consistent with the expected cleavage of the initiator residue located in the middle of the polymer chain. Thermal treatment of the polymers prepared using PyDMDBrMeP did not affect their molecular weight due to the thermal stability of the (pyridin‐2‐yl)methyl ester group, while treatment under alkaline hydrolysis conditions resulted in complete cleavage, similar to the PyDEDBrMeP‐prepared polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2342–2355

A Rational Entry to Cyclic Polymers via Selective Cyclization by Self-Assembly and Topology Transformation of Linear Polymers.

A simple and effective synthetic route to cyclic polymers has been developed based on the following sequence: (i) selective cyclization of two self-complementary sec-ammonium-containing crown ether monomers to afford [c2] daisy-chain bifunctional initiators, (ii) living polymerization to afford the corresponding linear polymers, and (iii) a topology transformation of these linear polymers to furnish cyclic polymers. The key step in this sequence is the quantitative cyclization via self-assembly of two crown ether molecules with hydroxyl and sec-ammonium moieties. After the living polymerization, the linear polymers release the daisy-chain assembly to generate a cyclic topology. The specific advantages of the present synthetic protocol, i.e., procedural simplicity and concentration independence, are demonstrated by a gram-scale synthesis.

Synthesis of PS-b-PPOA-b-PS triblock copolymer via sequential free radical polymerization and ATRP

A novel ABA triblock copolymer comprising double-bond-containing poly(phenoxyallene) (PPOA) and polystyrene (PS) segments was synthesized by sequential conventional free radical polymerization and atom transfer radical polymerization (ATRP) via the site transformation strategy. A new bifunctional initiator containing azo and Br-containing ATRP initiating groups was prepared using 2-bromopropionyl chloride, hydroquinone, and 4,4′-azobis(4-cyanopentanoic acid) as starting materials. Conventional free radical homopolymerization of phenoxyallene with cumulated double bond was performed in toluene to provide a polyallene-based macroinitiator bearing ATRP initiating groups at both ends, which is stable under UV irradiation and free radical circumstances. PS-b-PPOA-b-PS triblock copolymer was then obtained by bulk ATRP of styrene initiated by PPOA-based macroinitiator. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1366–1372

Double-bond-containing polyallene-based triblock copolymers via phenoxyallene and (meth)acrylate

A series of ABA triblock copolymers, consisting of double-bond-containing poly(phenoxyallene) (PPOA), poly(methyl methacrylate) (PMMA), or poly(butyl acrylate) (PBA) segments, were synthesized by sequential free radical polymerization and atom transfer radical polymerization (ATRP). A new bifunctional initiator bearing azo and halogen-containing ATRP initiating groups was first prepared followed by initiating conventional free radical homopolymerization of phenoxyallene with cumulated double bond to give a PPOA-based macroinitiator with ATRP initiating groups at both ends. Next, PMMA-b-PPOA-b-PMMA and PBA-b-PPOA-b-PBA triblock copolymers were synthesized by ATRP of methyl methacrylate and n-butyl acrylate initiated by the PPOA-based macroinitiator through the site transformation strategy. These double-bond-containing triblock copolymers are stable under UV irradiation and free radical circumstances.

A Polymer Interfacial Modifier Synthesized by Living Anionic Polymerization: Incorporation of Inorganic Blocks to Chain Ends

As a polymer interfacial modifier, poly(methyl methacrylate) (PMMA) terminated with elemental blocks of polyhedral oligomeric silsesquioxane (POSS) has been exploited through the phenomenon of preferential segregation in PMMA films. The modifier synthesized by living anionic polymerization using a bifunctional initiator is segregated at the surface in the mixture of PMMA due to a “buoy” effect of the POSS blocks. This further results in the surface wettability of PMMA being regulated on the basis of the amount of the modifier fed into the matrix. Finally, it is shown that the amount of the modifier in the PMMA films affects the cell proliferation behavior via the wettability. image

LCST Behavior of Symmetrical PNiPAm-b-PEtOx-b-PNiPAm Triblock Copolymers

Poly(N-isopropylacrylamide) (PNiPAm) and poly(2-ethyl-2-oxazoline) (PEtOx) represent two polymer types that are well-known for their lower critical solution temperature (LCST) behavior in aqueous media. To synthesize triblock copolymers containing both polymers, a crossover of two different polymerization methods was applied using a bifunctional initiator for the living cationic ring-opening polymerization (CROP) of EtOx. Quantitative end-functionalization with a trithiocarbonate resulted in a bifunctional PEtOx macro chain transfer agent (CTA). A series of well-defined PNiPAm-b-PEtOx-b-PNiPAm triblock copolymers were obtained by subsequent reversible addition–fragmentation chain transfer (RAFT) polymerization of NiPAm. The influence of the PNiPAm to PEtOx ratio on the thermoresponsive properties was intensively investigated via turbidimetry, dynamic light scattering, cryo transmission electron microscopy, and 1H NMR studies, revealing hydrogen bonds between both copolymer segments that strongly lower the...

Synthesis and self-assembly of amphiphilic and biocompatible poly(vinyl alcohol)-block-poly(l-lactide) copolymer

Abstract Well-defined amphiphilic and biocompatible poly(vinyl alcohol)- block -poly( l -lactide) copolymers (PVA- b -PLLA) were synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT), ring opening polymerization (ROP), and click chemistry. First, an innovative azide-functionalized xanthate mediated chain transfer agent (CTA) [S-(3-azidopropyl propanamide)-( O -butyl xanthate)] was synthesized and used for vinyl acetate (VAc) polymerization through RAFT. Then, azide-terminated poly(vinyl acetate) (azide-PVAc) was converted to the corresponding azide-terminated poly(vinyl alcohol) (azide-PVA) through hydrolysis. Alkyne-terminated poly ( l -lactide) (alkyne-PLLA) was synthesized via ROP using a bifunctional initiator, having an alkyne and a hydroxyl group. Finally, azide-PVA and alkyne-PLLA were coupled by 1,3 cycloaddition click reaction to get PVA- b -PLLA. Synthesized azide-PVAc, azide-PVA, alkyne-PLLA and PVA- b -PLLA were characterized by size exclusion chromatography and 1 H NMR spectroscopy. The self-assembly of PVA- b -PLLA in water was investigated by transmission electron microscope, atomic force microscopy, dynamic light scattering and 1 H NMR spectroscopy. Spherical micelles in water were clearly observed. The critical micelle concentration of PVA- b -PLLA in water was determined by fluorescence spectroscopy, and it was decreased with increasing the molecular weight of PLLA block. PVA- b -PLLA exhibited low cytotoxicity which could be used in biomedical application.

Periodic introduction of a Hamilton receptor into a polystyrene backbone for a supramolecular graft copolymer with regular intervals

The Hamilton receptor group (–DADDAD–; D = hydrogen donor; A = hydrogen acceptor) was periodically introduced into a polystyrene backbone, starting from the ruthenium-catalyzed living radical polymerization of styrene with the Hamilton receptor-based bifunctional initiator.

Methacrylic Zwitterionic, Thermoresponsive, and Hydrophilic (Co)Polymers via Cu(0)-Polymerization: The Importance of Halide Salt Additives.

The synthesis of hydrophilic, thermoresponsive, and zwitterionic polymethacrylates is reported by Cu(0)-mediated reversible deactivation radical polymerization in water and/or water/alcohol mixtures. The predisproportionation of [Cu(I) (PMDETA)Cl] in water prior to initiator and monomer addition is exploited to yield well-defined polymethacrylates with full monomer conversions in 30 min. The addition of supplementary halide salts (NaCl) enables the synthesis of various molecular weight poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA475) (DPn = 10-80, Mn ≈ 10,000-40 000 g mol(-1)) with full monomer conversion and narrow molecular weight distributions attained in all cases (Đ ≈ 1.20-1.30). A bifunctional PEG initiator (average Mn ≈ 1000 g mol(-1)) is utilized for the polymerization of a wide range of methacrylates including 2-dimethylaminoethyl methacrylate, 2-morpholinoethyl methacrylate, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, and 2-methacryloyloxyethyl phosphorylcholine. Despite the high water content, high end group fidelity is demonstrated by in situ chain extensions and block copolymerizations with PEGMA475 yielding well-defined functional telechelic pentablock copolymers within 2.5 h.

Synthesis of diblock copolymers by combination of organocatalyzed ring-opening polymerization and atom transfer radical polymerization using trichloroethanol as a bifunctional initiator

This study reports an application of trichloroethanol (TCE) as a bifunctional initiator for the synthesis of block copolymers (BCPs) by organocatalyzed ring-opening polymerization (OROP) and atom transfer radical polymerization (ATRP). TCE was employed to synthesize a low dispersity poly (valerolactone) macroinitiator, which was subsequently used for the ATRP of tert-butyl methacrylate. While it is known that TCE can serve as an initiator in ATRP, the ability to induce polymerization under OROP is reported for the first time. The formation of well-defined BCPs was confirmed by gel permeation chromatography and 1H NMR. Computational studies were performed to obtain a molecular-level understanding of the ring-opening polymerization mechanism involving TCE as initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 563–569