Synthesis of Telechelic Oligomers via Atom Transfer Radical Polymerization, 3

Summary: ATRP of butyl α‐fluoroacrylate (FABu) was carried out at 90 °C using methyl 2‐bromoisobutyrate (2‐MBiB) as initiator and the homogeneous catalyst CuBr/1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA). Telechelic oligomers were obtained by coupling the bromo terminated polymers in the presence of Cu⁽⁰⁾ and 2,2′‐bipyridyl ligand. The ¹H and ¹⁹F NMR, SEC and MALDI TOF analyses show that the poly(FABu) chains recombination was the main reaction (80% yield). About 20% of disproportionation reaction also occurs in the process, whereas transfer reactions can be neglected.

Compounds produced by recombination, disproportionation and transfer during the coupling reaction of poly(FABu) oligomers.     

Cyclic Ladder Polymers by Polycondensation of Silylated Tetrahydroxy‐tetramethylspirobisindane with 1,4‐Dicyanotetrafluorobenzene

Summary: 5,5′,6,6′‐Tetra(trimethylsiloxy)‐4,4,4,4′‐tetramethyl‐1,1‐spirobisindane was polycondensed with 1,4‐dicyanotetrafluorobenzene under variation of solvent temperature, time, and feed ratio. Under optimized reaction conditions, all products detectable by MALDI‐TOF mass spectrometry (up to masses around 8 000 Da) proved to be cyclic ladder oligomers and polymers. In N‐methylpyrrolidone and dimethylsulfoxide odd‐numbered cycles were formed in addition to the prevailing even‐numbered ones. However, in sulfolane exclusively even‐numbered cycles were obtained (detectable up to masses around 10 000 Da), together with even‐numbered linear chains. Temperatures above 100 °C enhanced the molecular weights by side reactions. With the less reactive cyano‐2,3,5,6‐tetrafluorobenzene (CTB) again cycles were formed, but their content and the conversions were lower. Polycondensation of CTB up to 160 °C and all polycondensations of cyanopentafluorobenzene gave crosslinked products.

Synthesis of cyclic ladder polymers.     

Formation of Thermoresponsive Gold Nanoparticle/PNIPAAm Hybrids by Surface‐Initiated,Atom Transfer Radical Polymerization in Aqueous Media

Summary: We investigated the formation of thermoresponsive gold nanoparticle/poly(N‐isopropylacrylamide) (AuNP/PNIPAAm) core/shell hybrid structures by surface‐initiated, atom transfer radical polymerization (SI‐ATRP) in aqueous media and the effect of cross‐linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross‐linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush‐type and cross‐linked AuNP/PNIPAAm hybrids were characterized by Fourier‐transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering.

     

Rapid Synthesis and MALDI‐ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well‐defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5–8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30 000 g · mol^?1. MALDI‐ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths.

     

Synthesis of Polyphenylene Ether Derivatives: Estimation of Their Dielectric Constants

A series of poly(2‐alkyl‐6‐phenylphenylene ether)s were prepared by the oxidative polymerization of 2‐alkyl‐6‐phenylphenols. Their dielectric constants were approximately 2.5, whereas it was found that the phenyl group at the 6‐position clearly increased the Q factor of the polymer compared with poly(2,6‐dimethylphenylene ether), PPE. These values were qualitatively predicted from the polarizability and the molar volume calculated by the theoretical analysis of the unit structure at the HF/6‐31G* level.

     

Fluorinated Styrene‐ and Carbazole‐Based Cladding Polymer Layers for EO and NLO Polymer Devices

Novel polymer cladding materials were synthesized and their potential for use in optical waveguide devices was investigated. 9‐[2‐(2,3,5,6‐Tetrafluoro‐4‐vinylphenoxy)ethyl]‐9H‐carbazole and 1‐pentafluorophenylpyrrole‐2,5‐dione were used as comonomers for preparing the acrylic cladding copolymers. These showed a low resistivity (≈2 × 10¹³ Ω · cm) at room temperature and a low optical loss (?0.6 dB · cm^?1) at a wavelength of 1.55 µm. The refractive indexes and the glass transition temperatures of the polymer cladding materials can be controlled by the composition of the copolymers. The resulting polymers are good candidates for cladding materials for practical applications in devices.

     

Controlled Ring‐Opening Polymerization of Lactones and Lactide Initiated by Lanthanum Isopropoxide, 2. Mechanistic Studies

The mechanism of ring‐opening polymerization of some lactones and lactide initiated by lanthanum isopropoxide has been comprehensively investigated. NMR and viscosity analyses demonstrated that three active polymer chains grow per lanthanum atom and that, depending on the coordinating ability of the monomer, propagation proceeds on aggregated or unaggregated active species. It is also demonstrated that inter‐ and intramolecular side reactions are limited and that lanthanum‐based initiator selectivity in ring‐opening polymerization is analogous to that of aluminum ones.

Part of the proposed mechanism for the lanthanum alkoxide initiated polymerization of ε‐caprolactone.     

Synthesis and self‐assembly of polymers containing dicarboximide groups by living ring‐opening metathesis polymerization

Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.

     

NLO Behavior of Polymers Containing Y‐Shaped Chromophores

New polyurethanes containing Y‐shaped chromophores, symmetrical derivatives of 4‐(dicyanomethylene)‐2‐methyl‐6‐[p‐(dimethylamino)styryl]‐4H‐pyran, have been prepared. The polymers show high glass transition temperatures (T_g) and a good thermal stability. SHG measurements on poled polymer films of the synthesized polymers have been carried out and a maximum d₃₃ of 15 pm · V^?1 has been found at 1 368 nm fundamental wavelength. Time stability measurements on the most active polymer have shown that after the initial fast relaxation, the d₃₃ value remains constant at 80 °C for 60 d.

     

Low‐Temperature Polymerization of Olefins in the Presence of Titanium Monoamidinate/MAO Catalyst

This paper reports the predominantly syndiotactic‐specific polymerization of propylene in the presence of titanium monoamidinate/methylaluminoxane (MAO) catalysts. The same catalysts, depending on the reaction conditions, also promote either predominantly 1,4‐cis or 1,4‐trans polymerization of 1,3‐butadiene and polymerization of styrene either to highly syndiotactic or to stereoirregular polymer. Some preliminary information about the features of propylene polyinsertion is also reported.

Expansion of the 20–24 ppm region of the ¹³C NMR spectrum of sample 2. The starred resonance at 21.75 ppm and the shoulders are not assigned.     

Photocurable Shape‐Memory Copolymers of ε‐Caprolactone and L‐Lactide

Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol^?1), PCL diol ( = 10 000 g · mol^?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited R_f and R_r values above 90% at 45 °C for an extremely large tensile strain of 1 000%.

     

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

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

     

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.     

Model linear and star‐shaped polyisoprenes with phosphatidylcholine analogous end‐groups. Synthesis and association behavior in cyclohexane

Semitelechelic (ω‐), telechelic (α,ω‐), as well as 3‐ and 12‐arm star polyisoprenes (PI), end‐functionalized with the same dimethylamino group, were synthesized by anionic polymerization high vacuum techniques, using 3‐dimethylaminopropyllithium as initiator and chlorosilanes as linking agents. The dimethylamino groups were transformed to phosphatidylcholine analogues through reaction with 2‐ethoxy‐2‐oxo‐1,3,2‐dioxaphospholane. The association behavior of the phosphoro‐zwitterionic PI (PZw‐PI) was studied in cyclohexane by low angle laser light scattering, viscometry, and dynamic light scattering. The linear PZw‐PIs present relatively low weight‐average degree of association (N_w: 2–6), as compared with the corresponding sulfo‐zwitterionic PI (N_w: 10–45). The N_w values decrease with increasing molecular weight of the PI. In the case of the star PZw‐PI, the multiple intermolecular associations lead to the formation of gels, which break down by addition of a small amount of 1‐heptanol. In very dilute solutions and for high arm molecular weight stars, intramolecular dominates over intermolecular association.

     

Nuclear Magnetic Resonance Spectroscopy in Macromolecular Science

A historical overview of the role of NMR spectroscopy in macromolecular science in general and its coverage in “Macromolecular Chemistry and Physics” in particular is given. In the early days physics‐application to study molecular dynamics, partial alignment of macromolecules and phase separation prevailed, deduced from broad‐line solid‐state NMR. Only somewhat later, high‐resolution NMR in solution was established as an important tool for elucidating the chain microstructure. In the future, these two aspects are expected to merge.

Side group liquid crystalline polymers: ²H NMR has elucidated alignment and dynamics of these complex materials.     

The Fabrication of Very Small Miniemulsion Latexes from N‐Stearoylglutamate and Lauryl Methacrylate: Evidence for Droplet Budding

A new, biodegradable surfactant with high efficiency, N‐stearoyl‐di(sodium)glutamate (SDG), was used for miniemulsion polymerization of styrene and lauryl methacrylate (LMA). In the case of styrene, SDG produces latexes at least as small as those produced by sodium dodecyl sulfate (SDS), over a range of concentrations. In the case of LMA, a combination of SDG with an appropriate costabilizer allows one to obtain very small particles. With potassium persulfate (KPS) as initiator, the SDG/LMA system deviates significantly from the ideal miniemulsion, forming extremely small particles, which was speculatively attributed to a budding phenomenon.

The new, biodegradable surfactant, N‐stearoyl‐di(sodium)glutamate.     

Polyether Core‐Shell Cylinder–Polymerization of Polyglycidol Macromonomers

Summary: The synthesis and polymerization of macromonomers containing a polymerizable styrene head group and a tail of ethylene oxide derivatives of different character were investigated. The synthesis of macromonomers was based on living anionic polymerization of oxiranes. Two monomers were used: 1‐ethoxyethyl glycidyl ether (glycidol acetal), which after hydrolysis forms hydrophilic glycidol blocks and glycidyl phenyl ether forming hydrophobic blocks. Polymerizable double bonds were introduced by terminating the living chain with p‐(chloromethyl)styrene. The radical polymerization of the macromonomers was carried out in water with addition of a non‐polar solvent (benzene) and AIBN as initiator. Core‐shell polymers of different character and molar masses were obtained. The conversion of polymerized macromonomers was around 50%. However, the polymerization product could easily be separated from the reaction mixture.

     

Novel Phosphorous‐Containing Aromatic Polyethers – Synthesis and Characterization

Summary: The synthesis of novel phosphorous‐containing aromatic polyethers P‐PEEK and P‐PSU, based on poly(ether ether ketone)s (PEEK) and poly(ether sulfone)s (PSU) was carried out successfully by using phosphorous‐containing aromatic diols instead of bisphenol A in the usual synthesis procedure. The molecular weights of the P‐PEEKs and P‐PSUs obtained reflect both the influence of the different halogen components used and the lower thermal stabilities of the phosphorous‐containing diols compared to bisphenol A. However, polymers with sufficient molecular weights could be obtained, having interestingly high T_gs, high thermal stabilities as well as modified flame retardance properties depending on the diol type incorporated.

Comparison of the molecular weights of the synthesized P‐polyethers.     

Can the First Addition of Alkyl Radicals Play a Role in the Fate of NMP?

Values of k_d for the C? ON bond homolysis were measured for alkoxyamines based on imidazoline and imidazole nitroxides. They were analyzed in terms of polar/stabilization, steric, and entropic effects. k_d decreased with increasing electron‐withdrawing capacities of the groups attached to the nitroxide, but increasing with both the bulkiness of the group attached to the nitroxide and the presence of substituents on the ring. With three alkoxyamines, it was shown that the fate of the NMP of styrene depended on the type of initiating alkyl radical: successful for initiating 1‐phenylethyl radicals and unsuccessful for initiating p‐nitrophenyloxycarbonyl‐2‐prop‐2‐yl radicals.

     

Diene/polar monomer copolymers,compatibilisers for polar/non‐polar polymer blends. A controlled block copolymerisation with a single‐site component samarocene initiator

A well‐controlled two‐step process, the polymerisation of isoprene or isoprene/hex‐1‐ene copolymerisation followed by ε‐caprolactone polymerisation, affords trans‐polyisoprene or (trans‐polyisoprene/hex‐1‐ene copolymer)–poly(ε‐caprolactone) diblocks of various lengths. The single component initiator is an allylsamarocene compound. An atomic force microscopy study shows that these copolymers are efficient compatibilisers for poly(ε‐caprolactone) and polyisoprene blends.

Poly(ε‐caprolactone) chain growth from Sm–polyisoprene chain.