Synthesis of New Hydrogels by Copolymerization of Poly(2‐methyl‐2‐oxazoline) Bis(macromonomers) and N‐Vinylpyrrolidone

New non‐ionic hydrogels were synthesized by radical homopolymerization of vinyl end‐functionalized poly(2‐methyl‐2‐oxazoline) bis(macromonomers), or by radical copolymerization of these bis(macromonomers) with N‐vinyl‐2‐pyrrolidone (NVP). The poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were synthesized through “living” cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline (MeOXA), using, simultaneously, the known “initiating” and “end‐capping” method for synthesis of macromonomers. Chloromethyl styrene was used as initiator and N‐(4‐vinylbenzyl)‐piperazine was used as the terminating agent. Well defined poly(2‐methyl‐2‐oxazoline) bis(macromonomers) were obtained with P_n = 4, 11, and 17. The hydrogel structures were characterized by high‐resolution magic angle spinning NMR technique and their solvent absorption capacity was tested by swelling experiments in different solvents. The bis(macromonomers) were characterized by NMR spectroscopy and gel permeation chromatography.

Schematic of polymerization     

Online monitoring of Silicone Network Formation by Means of In‐Situ Mid‐Infrared Spectroscopy

The ReactIR™ reaction analysis system was used to monitor the crosslinking copolymerization of trimethylsilyl methacrylate with α,ω‐methacryloyl‐terminated oligo(dimethylsiloxane). Characteristic infrared bands proved useful to determine the total methacrylate concentration. After less than 12 h at 60 °C using 0.14% 2,2′‐azoisobutyronitrile (AIBN), the methacrylate conversion during the crosslinking reaction exceeded 98%. The comparison of the crosslinking reaction with a methacrylate homopolymerization showed that significant autoacceleration occurred during network formation.

Time‐dependent monomer conversion [M]/[M]₀ for TMSMA homopolymerization (run H in Table 1) and the corresponding crosslinking polymerization (run N) as revealed by the peak at 1 326 cm⁻¹.     

Synthesis of a New Macromonomer from 2‐(Dimethylamino)ethyl Methacrylate Bearing 1‐(Isopropenylphenyl)‐1,1‐dimethylmethyl Isocyanate Group

Summary: The telomerization of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) with 2‐mercaptoethanol in acetonitrile shows that the telogen can react with the monomer by nucleophilic addition. It is to say that the tertiary amino group leads to nucleophilic addition rather than telomerization. The oligomers thus obtained were functionalized with 1‐(isopropenylphenyl)‐1,1‐dimethylmethyl isocyanate (TMI) in anhydrous toluene to afford macromonomers. These macromonomers were copolymerized with styrene and the r₁, r₂ ratio was determined according to Jaacks and Macret's methods. It was thereby demonstrated that the r₁ value for this type of monomer is close to zero.

Structure of the model molecule.     

Synthesis and Characterization of Alternating and Random Copolymer Brushes

Alternating free‐radical copolymerization of vinylbenzyl‐ and methacryloyl‐terminated macromonomers in the presence of Lewis acid was applied to the synthesis of prototype copolymer brushes composed of polystyrene/poly(ethylene oxide) (PS/PEO) alternating structure. Random copolymer brushes were also prepared by radical copolymerization of both macromonomers in the absence of Lewis acid. It was found from dilute solution properties that both copolymer brushes composed of short aspect ratio formed an ellipsoid‐like single molecule in solution. To discuss the intramolecular phase separation of PS/PEO brushes in solution, we determined the radius of gyration (R_g) and cross‐sectional radius of gyration (R_g,c) of copolymer brushes by small‐angle X‐ray scattering (SAXS) using Guinier's plots in DMF and styrene. We used styrene as a solvent to cancel each other out with the electron density of PS side chains. We made also clear the effect of branching topology on polymer crystallinity to be examined by comparing the copolymer brushes with corresponding linear PEO or PEO‐block‐PS block copolymer.

     

Controlled synthesis of anthracene‐labeled ω‐amine polystyrene to be used as a probe for interfacial reaction with mutually reactive PMMA

Anthracene‐labeled polystyrene (PS) end‐capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (m‐TMI). The m‐TMI co‐monomer (5.7 mol‐%) does not perturb the control of the radical polymerization of styrene. The pendant isocyanate groups of the copolymer chains of low polydispersity (M _w/M _n = 1.25) and controlled molecular weight (up to 35 000) have been derivatized into anthracene by a reaction with 9‐methyl(aminomethyl)anthracene. The anthracene‐labeled PS (ca. 2 mol‐% label) has been conveniently analyzed by size‐exclusion chromatography with a UV detector (SEC‐UV). Moreover, the ω‐bromide end‐group of the copolymer chains has been derivatized into a primary amine, making the labeled PS chains reactive towards non‐miscible poly(methyl methacrylate) (PMMA) chains end‐capped by an anhydride. The interfacial coupling of the mutually reactive PS and PMMA chains has been studied under static conditions (i.e., at the interface between thin PS and PMMA films) and successfully analyzed by SEC‐UV.

SEC‐UV traces for anth‐PS‐NH₂ (80 μg · ml⁻¹; sample A5; Table 1 ), and PMMA‐anh (80 μg · ml⁻¹; sample B1; Table 1 ).     

Heterofunctionalized Multiarm Star Polymers via Sequential Thiol‐para‐Fluoro and Thiol‐Ene Double “Click” Reactions

The successful postfunctionalization of multiarm star polystyrene (PS) with pentafluorophenyl and allyl moieties at the periphery is demonstrated employing modular thiol‐para‐fluoro and photoinduced radical thiol‐ene double “click” reactions, respectively. α‐Fluoro and α‐allyl functionalized PS (α‐fluoro‐PS and α‐allyl‐PS) are in situ prepared by atom transfer radical polymerization of styrene and their mixture is used as macroinitiator in a crosslinking reaction with divinyl benzene (DVB) yielding (fluoro‐PS)_m–polyDVB–(allyl‐PS)_m multiarm star polymer. It is found that the multiarm star polymer includes nearly identical number of arms possessing pentafluorophenyl and allyl moieties at the periphery. The obtained multiarm star polymer is then reacted with 1‐propanethiol through thiol‐para‐fluoro “click” reaction to give (propyl‐PS)_m–polyDVB–(allyl‐PS)_m multiarm star polymer, which is subsequently reacted with N‐acetyl‐l ‐cysteine methyl ester via radical thiol‐ene “click” reaction in order to give well‐defined heterofunctionalized (propyl‐PS)_m–polyDVB–(cysteine‐PS)_m multiarm star polymer, with higher molecular weight and narrow molecular weight distribution. Multiarm star polymers are characterized by using viscotek triple detection gel permeation chromatography, ¹H, and ¹⁹F NMR.

     

Synthesis of Polyacrylonitrile‐block‐Polystyrene Copolymers by Atom Transfer Radical Polymerization

Summary: The synthesis of polyacrylonitrile‐block‐polystyrene (PAN‐b‐PS) copolymers by atom transfer radical polymerization (ATRP) is reported. Chain extension of bromine terminated PAN macroinitiators with styrene was performed using a CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system and 2‐cyanopyridine as a solvent. The first‐order kinetic plots of styrene consumption showed a significant curvature, indicating a progressive decrease in the concentration of active species during copolymerization. The loss of the bromide end group was mainly ascribed to the elimination of HBr, as shown by ¹H NMR spectroscopy. By varying the molar ratio of either the catalyst or the monomer to the initiator, a series of PAN‐b‐PS copolymers were prepared, with polydispersities as low as 1.3, and molar compositions ranging from 8.6/91.4 to 35.5/64.5.

¹H NMR spectra of PAN‐b‐PS in DMF‐d₇ at 80 °C.     

Cyclodextrins in polymer synthesis: Steric retardation of the free‐radical polymerization in aqueous medium of 4‐vinylbenzaldehyde/methylated β‐cyclodextrin complex

4‐Vinylbenzaldehyde ( 3 ) was complexed with methylated β‐cyclodextrin ( 4 ) (me‐β‐CD) yielding the water soluble host‐guest complex ( 5 ). Radical polymerization was initiated with K₂S₂O₈/Na₂S₂O₅ in water at room temperature and also at 70 °C. The polymerization tendency of this complex ( 5 ) is lower compared to the styrene/me‐β‐CD‐complex ( 7 ). Also copolymerizations of 5 and complexed styrene ( 6 ) at these two temperatures were carried out and the results are discussed in respect to the behavior of the homopolymerization. The resulting polymers ( 8a‐k , 9a , 9b ) were characterized by SEC‐measurements and ¹H NMR spectroscopy. TEM‐measurements of the homopolymers 8f and 8k show differences in the particle size depending on the amount of me‐β‐CD.

TEM recordings of the polymers 8f (left) and 8k (right).     

One‐Pot Synthesis of Micelles with a Cross‐Linked Poly(acrylic acid) Core

Summary: Stable micelles with polystyrene (PS) as a shell and cross‐linked poly[(acrylic acid)‐co‐(ethylene glycol diacrylate)] as a core have been successfully prepared by reversible addition fragmentation chain transfer (RAFT) copolymerization of acrylic acid and ethylene glycol diacrylate in a selective solvent with PS‐SC(S)Ph as a RAFT agent. For the preparation of stable micelles, the RAFT polymerizations are carried out in different solvents: benzene, cyclohexane, and mixtures of tetrahydrofuran and cyclohexane. The monomer/PS‐SC(S)Ph molar ratio and molecular weight of the macro‐RAFT agent, PS‐SC(S)Ph, influence the RAFT polymerization and the formation of micelles.

Block copolymerization in selective solvent with the RAFT agent.     

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.

     

MADIX Polymerization of Captodative Ethyl α‐Acetoxyacrylate with Acrylate Monomers

Summary: MADIX homopolymerization of a captodative monomer, ethyl‐α‐acetoxyacrylate (EAA) was investigated using AIBN as an initiator and O‐ethyl‐S‐(1‐methoxycarbonyl)ethyl dithiocarbonate as a transfer agent at 70 °C in a mixture of iPrOH and H₂O. The experimental results revealed that this transfer agent had no effect on the polymerization reaction when compared with a free radical polymerization. Copolymerization of ethyl‐α‐acetoxyacrylate, with different acrylic monomers, such as butyl acrylate (BuA), acrylic acid, N,N‐(dimethylamino)ethyl acrylate and N,N‐dimethyl acrylamide, was then studied by MADIX polymerization using the same transfer agent. All the prepared copolymers were characterized by ¹H NMR and size exclusion chromatography, and the obtained results were in accordance with theoretical predictions regarding molecular weight and copolymer composition. Futhermore, the living character of the polymerization has been checked by the chain extension of poly(EAA‐stat‐BuA) with vinyl acetate (Vac) which led to poly(EAA‐stat‐BuA)‐block‐poly(VAc).

     

Synthesis and Characterization of α,ω‐Telechelic Polymers by Atom Transfer Radical Polymerization and Coupling Processes

Initiators for atom transfer radical polymerization (ATRP) bearing different functional groups (aldehyde, aromatic hydroxyl, dimethyl amino) were synthesized and characterized. Monotelechelics with low molecular weight were obtained by ATRP of styrene using these initiators in the presence of the CuBr/bpy catalytic complex. α,ω‐Telechelic polymers with double molecular weights with respect to the starting materials were prepared by coupling of monotelechelics under atom transfer radical generation conditions, in the absence of monomer, using CuBr as catalyst, tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) as a ligand, under Cu⁰ mediated reductive conditions and with toluene as solvent. Terminal Br atoms present in monotelechelic polystyrenes (PS) as a consequence of the ATRP mechanism also offer other routes for preparing telechelic polymers. Aldehyde functionalized polymer was etherified with hydroquinone furnishing telechelic PS with a molecular weight that was two times higher. All polymers were characterized by spectral methods (NMR, IR spectroscopy) as well as by GPC.

Synthesis of initiators for atom transfer radical polymerization bearing different functional groups, for example, aldehyde, aromatic hydroxyl, dimethyl amino.     

Synthesis of Well‐Defined Hybrid Macromonomers of Poly(ethylene oxide) and Their Reactivity in Photoinitiated Polymerization

Summary: α,ω‐Hybrid (hetero‐telechelic) poly(ethylene oxide) (PEO) macromonomers carrying both cationic and radical or anionic polymerizable vinyl end groups were newly synthesized by the living anionic polymerization of ethylene oxide (EO) initiated with partially K‐alkoxidated vinylic alcohols such as the monovinyl ether of tetramethylene glycol or di(ethylene glycol) and p‐vinylbenzyl alcohol (VBA), followed by reaction with methacryloyl chloride (MAC). They possess a couple of α‐ and ω‐end groups that can polymerize concurrently or selectively by radical and/or cationic or anionic mechanism. The reactivity of the radical and cationic species formed upon photolysis of benzophenone and triphenylsulfonium tetrafluoroborate towards these end groups were studied by means of ¹H NMR analysis following the disappearance of the respective olefinic groups. Studies with macromomonomers and model compounds revealed that photoexcited benzophenone abstracts hydrogen atoms from the PEO backbone to form radicals without added hydrogen donors. In the case of the sulfonium salt, both radical and cationic species are formed, which react with the respective functional groups. It was also shown that vinyl ether moieties react more readily than the methacrylate in both radical and cationic processes.

The general synthetic strategy followed for the preparation of the hybrid PEO macromonomers studied here.     

Amine‐Functionalized Polyacrylamide for Labeling and Crosslinking Purposes

Free radical copolymerization of acrylamide with N‐(3‐aminopropyl)‐methacrylamide yields water‐soluble polymers with randomly distributed pendent nucleophilic amine moieties. The copolymerization parameters were determined to be r₁ = 0.49 and r₂ = 0.85. A procedure which allows controlling the degree of functionalization and the molecular weight is described in detail. Copolymers with low amounts of functional groups were used to synthesize polymers with fluoresceine or rhodamine side groups as fluorescence labels. Furthermore, reaction of the amine moieties of the copolymers with glutaraldehyde under suitable conditions provides a way to generate polymer networks via random crosslinking of existent chains in a semi‐dilute solution.

     

Aliphatic Hyperbranched Copolyesters by Combination of ROP and AB2‐Polycondensation

Summary: Hyperbranched aliphatic copolyesters have been prepared by the copolymerization of ε‐caprolactone and 2,2‐bis(hydroxymethyl)butyric acid (AB₂‐monomer), catalyzed by (i) HfCl₄(THF)₂ and (ii) diphenylammonium trifluoromethanesulfonate (DPAT), respectively. In both cases, copolymerization by combined ROP/AB₂‐polycondensation was achieved. The degree of branching (DB) and consequently the density of functional groups of the resulting copolyesters were controlled by the comonomer ratio in the feed. Molecular weights in the range = 22 000–166 000 g · mol⁻¹ (GPC, PS standards) were obtained, with apparent polydispersity indices of 1.20 to 1.95. The DB was in the range 0.03–0.35. Remarkably, HfCl₄(THF)₂ appeared to cause no transesterification of the ester bonds in the hyperbranched polymer formed. Further esterification or functionalization of the hydroxyl end groups of the hyperbranched polymers is therefore possible in a convenient two step/one pot process. The prepared hyperbranched polycaprolactones can be used as multifunctional initiators for the ROP of ε‐caprolactone, which is also catalyzed by HfCl₄(THF)₂, resulting in multi‐arm star polymers. Diphenylammonium trifluoromethanesulfonate (DPAT) was also found to catalyze the combination of ROP and AB₂ polycondensation. However, the applicability of this system is restricted due to side reactions that can lead to crosslinking.

Synthesis of hyperbranched copolyesters by combined ROP/polycondensation.     

Propylene Polymerization with rac‐SiMe2(2‐Me‐4‐PhInd)2ZrMe2/MAO: Polymer Characterization and Kinetic Models

Poly(propylene)s were prepared with metallocene catalyst rac‐SiMe₂(2‐Me‐4‐PhInd)₂ZrMe₂/MAO (rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)dimethylzirconium/methylaluminoxane) in heptane solution at temperatures from 50 to 80 °C with varying concentrations of monomer, hydrogen, triisobutylaluminium (TIBA) and MAO. Polymer molar mass depended on the monomer, MAO, TIBA, and hydrogen concentrations and on polymerization temperature. The isotacticity was very high (mmmm > 95%), and only a slight decrease was detected at high temperatures. Regio selectivity was also high; the total amount of 2,1‐ and 3,1‐insertions was less than 0.4 mol‐%. Lowering the monomer concentration and raising the temperature increased the amount of 3,1 defects over the amount of 2,1 defects. End‐group analysis by ¹³C NMR spectroscopy revealed isobutyl and allyl end‐groups. Chain transfer to aluminium and β‐CH₃ elimination were concluded to be the dominating chain‐termination mechanisms. The importance of β‐CH₃ elimination increased with temperature. Hydrogen addition changed both the initiation and termination mechanisms as indicated by the presence of propyl, butyl and 2,3‐dimethylbutyl end‐groups. According to modeling studies, the molar mass follows a first‐order relationship with propylene and hydrogen concentrations, and a half‐order relationship with MAO concentration. Arrhenius‐type activation energy coefficients were 125 kJ · mol^?1 for β‐CH₃ elimination, 66 kJ · mol^?1 for chain transfer to aluminium, and 53 kJ · mol^?1 for chain transfer to hydrogen. A value of 45 kJ · mol^?1 was used for the propagation.

     

High‐Pressure Kinetics of Oxidative Copolymerization of Styrene with α‐Methylstyrene

This is the first report on the study carried out on high‐pressure free‐radical initiated oxidative copolymerization of styrene (STY) with α‐methylstyrene (AMS) at various temperatures (45–65 °C) at constant pressure (100 psi) and then at various pressures (50–300 psi) keeping the temperature (50 °C) constant. The compositions of the copolyperoxides obtained from the ¹H NMR spectra were utilized to determine the reactivity ratios of the monomers. The reactivity ratios indicate that STY forms an ideal copolyperoxide with AMS and the copolyperoxide is richer in AMS. The effect of temperature and oxygen pressure on the reactivity ratios of the monomers was studied. The rates of copolymerization (R_P) were used to determine the overall activation energies (E_a) and activation volume (ΔV^#) of copolymerization. The unusually higher values of the ΔV^# may be due to the pressurizing fluid oxygen which itself is a reactant in the copolymerization, the side reactions, and the chain‐transfer reactions occurring during copolymerizations.

The Arrhenius plots for the rate of the copolymerization of STY‐AMS‐O₂ system at 100 psi of oxygen pressure.     

Combining ATRP of Methacrylates and ROP of L,L‐Dilactide and ε‐Caprolactone

Coupling atom transfer radical polymerization (ATRP) and coordination‐insertion ring‐opening polymerization (ROP) provided a controlled two‐step access to polymethacrylate‐graft‐polyaliphatic ester graft copolymers. In the first step, copolymerization of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) was carried out at 80 °C at high MMA concentration by using ethyl 2‐bromoisobutyrate and [NiBr₂(PPh₃)₂] as initiator and catalyst, respectively. Kinetic and molar masses measurements, as well as ¹H NMR spectra analysis of the resulting poly(MMA‐co‐HEMA)s highlighted the controlled character of the radical copolymerization, while the determination of the reactivity ratios attested preferential incorporation of HEMA. The second step consisted of the ROP of ε‐caprolactone or L ,L ‐dilactide, in THF at 80 °C, promoted by tin octoate (Sn(Oct)₂) and coinitiated by poly(MMA‐co‐HEMA)s obtained in the first step. Once again, kinetic, molar mass, and ¹H NMR data demonstrated that the copolymerization was under control and started on the hydroxyl functions available on the poly(MMA‐co‐HEMA) multifunctional macroinitiator.

Comparison of the SEC traces for the poly(MMA‐co‐HEMA) macroinitiator P2 (line only), the polymethacrylate‐g‐PLA copolymer C2 (line marked by ○), and the polymethacrylate‐g‐PLA C3 (line marked by ?).     

Radical Copolymerization of α‐Trifluoromethylacrylic Acid with Vinylidene Fluoride and Vinylidene Fluoride/Hexafluoropropene

Summary: The radical copolymerization of α‐trifluoromethylacrylic acid (TFMAA) with vinylidene fluoride (VDF), initiated by tert‐butyl 2,2‐dimethyl peroxypropanoate (or tert‐butyl peroxypivalate) is presented. The kinetics of copolymerization were investigated from a series of eight reactions for which the initial [VDF]₀/[TFMAA]₀ molar ratios ranged between 15.0/85.0 and 89.4/10.6. The compositions of the copolymers, i.e. the molar ratios of VDF and TFMAA monomeric units, were determined mainly by ¹⁹F and ¹H NMR spectroscopy. According to the Tidwell and Mortimer method, the reactivity ratios, r_i, were assessed to be: r_VDF = 0.33 ± 0.09 and r_TFMAA = 0 at 55 °C, leading to copolymers of mainly alternating structure. Then, the radical terpolymerization of TFMAA with VDF and hexafluoropropene (HFP), initiated by 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane is described and the thermal properties of the materials produced are discussed.