Supramolecular Thermoresponsive Hyperbranched Polymers Constructed from Poly(N‐Isopropylacrylamide) Containing One Adamantyl and Two β‐Cyclodextrin Terminal Moieties

Poly(N‐isopropylacrylamide) (PNIPAM) oligomer containing one adamantyl (AD) and two β‐cyclodextrin (β‐CD) moieties at the chain terminals, AD‐PNIPAM‐(β‐CD)₂, was synthesized by atom transfer radical polymerization (ATRP) and successive click reactions. In aqueous solution, AD‐PNIPAM‐(β‐CD)₂ spontaneously forms supramolecular thermoresponsive hyperbranched polymers via molecular recognition between AD and β‐CD moieties. To the best of our knowledge, this work represents the first report of the construction of supramolecular thermoresponsive hyperbranched polymers from well‐defined polymeric AB₂ building units.

     

Synthesis and properties of long‐chain branched poly(ether sulfone)s by self‐polycondensation of AB2 type macromonomers

Long‐chain branched poly(ether sulfone)s (PESs) were synthesized via self‐polycondensation of AB₂ macromonomers. The linear PES oligomers synthesized by self‐polycondensation of 4‐chloro‐4′‐(4‐hydroxyphenyloxy)diphenyl sulfone were terminated with 4‐(3,5‐methoxyphenoxy)‐4′‐fluorodiphenyl sulfone to form AB₂ macromonomer precursors. After conversion from methoxy to hydroxy groups, the AB₂ macromonomers were self‐polycondensed to form long‐chain branched PESs. NMR measurements support the formation of the target macromonomers ( = 2930–67,800 (g mol^?1); M_n = number average molecular weight) and long‐chain branched PESs. Gel permeation chromatography with multiangle light scattering measurements indicated the formation of high‐molecular‐weight (M_w) polymers over 10⁴. The root‐mean‐square radius of gyration (R_g) suggests that the shape of the long‐chain branched PES synthesized from small AB₂ macromonomers in solution is similar to that of hyperbranched polymers. Increasing resulted in larger R_g, suggesting a transition from hyperbranched to a linear‐like architecture in the resulting long‐chain branched PESs. Rheological measurements suggested the presence of strongly entangled chains in the long‐chain branched PES. Higher tensile modulus and smaller elongation at the break were observed in the tensile tests of the long‐chain branched PESs. It is assumed that the enhanced molecular entanglement points may act as physical crosslinks at room temperature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1825–1831     

A Facile Two‐Step Route to Branched Polyisoprenes via ABn‐Macromonomers

A facile two‐step synthesis for branched poly(isoprene)s (PI) based on polyaddition of AB_n‐type macromonomers is described. The synthesis of the macromonomers was achieved by anionic polymerization of isoprene and subsequent end‐capping of the polymers by addition of chlorodimethylsilane to the living carbanions. This led to PI‐based macromonomers with narrow polydispersity ( / < 1.15) and molecular weights in the range of 1 700 – 22 100 g · mol⁻¹. Synthesis of the branched polymers was carried out by a hydrosilylation‐based polymerization of the macromonomers. Characterization via SEC, SEC‐MALLS, coupled SEC‐viscosimetry and ¹H‐NMR‐spectroscopy supported the formation of branched structures. Interestingly, these branched polymers exhibited α‐values that were similar to those reported for hyperbranched polymers based on AB₂‐monomers.

     

Kinetic Analysis of A2 + AB2 Polymerization Approach

The kinetic model of the co‐polycondensation with A₂ and AB₂ type monomers is developed and the analytical expressions of the various molecular parameters of the products are derived rigorously. The monomer feed ratio (α) of A₂ to AB₂ significantly affects the molecular parameters and the critical condition of gelation. Gelation can be avoided if α is > . At the critical state, the degree of branching decreases firstly and reaches its minimum value at about α≈0.22. Then, it increases with increasing α‐value. In comparison with experimental results, non‐equal reactivity of the active groups should be considered.

     

Hyperbranched Polymers Formed through Irreversible Step Polymerization of AB2‐Type Monomer in a Continuous Flow Stirred‐Tank Reactor (CSTR)

Hyperbranched polymers formed through step polymerization of AB₂‐type monomer with equal reactivity for both B groups in a continuous flow stirred‐tank reactor (CSTR) are investigated theoretically. The weight fraction distribution at high molecular weight tail follows a power law, W (P ) ∝ P ^−1/ξ for ξ ≤ 0.5 with , where is the mean residence time. The degree of branching (DB) at the large degree of polymerization (P ) limit is DB _{P →∞} = 0.6 irrespective of the ξ‐value, which is larger than the case for the corresponding batch polymerization that gives DB _{P →∞} = 0.5. The relationship between the radius of gyration 〈s ²〉₀ and P shows that the hyperbranched polymers formed in a CSTR are very compact, and the 〈s ²〉₀‐values for large polymers are even smaller than the smallest possible case for a batch reactor with DB _{P →∞} = 1. For large polymers, the power law 〈s ²〉₀∝P ^1/3 holds, which is 〈s ²〉₀∝P ^1/2 for batch polymerization.

     

Universality in Branching Frequencies and Molecular Dimensions during Hyperbranched Polymer Formation: Step Polymerization of AB2 Type Monomer with Equal Reactivity

Hyperbranched polymer formation during step polymerization of AB₂ type monomer with equal reactivity of two B's is investigated theoretically, focusing the attention to the degree of branching (DB) and the mean square radius of gyration for the unperturbed chains, . It is found that the DB‐value at large degree of polymerization (P) limit, = 0.5 is unchanged during the whole course of polymerization. The average value of having the same P is invariant throughout the polymerization. The universal curve between and P agrees perfectly with that for the self‐condensing vinyl polymerization (SCVP), another method to synthesize hyperbranched polymers, when the reactivity ratio for SCVP, r_SCVP, is 2.589 that gives = 0.5. The power law, is found for large values of P.

     

A Convenient A2 + B3 Approach to Hyperbranched Poly(arylene oxindole)s

Summary: We developed a facile approach to hyperbranched polymers by applying a superelectrophilic reaction within an A₂ + B₃ strategy. A significant reactivity difference between the intermediate and the starting material was utilized to avoid gelation in the A₂ + B₃ polymerization. A number of hyperbranched poly(arylene oxindole)s were achieved in a one‐step polymerization and characterized by NMR spectroscopy and gel permeation chromatography. Moreover, further modifications at the interior and exterior of the resulting polymers were explored as well.

Structure of the hyperbranched polymers produced using the A₂ + B₃ approach.     

Controlling the Optical Properties of Hyperbranched Conjugated Polyazomethines through Terminal‐Backbone Interactions

A simple approach to tune the optical properties of the hyperbranched conjugated polymers by only adjusting the terminal‐backbone interactions has been reported in this article. Hyperbranched conjugated polyazomethines have been successfully prepared by the reaction of tetramine and dialdehyde. Not only varying the monomer feed ratio to change the quantity of terminal amino groups, but also adopting protonation or complexion with proper dopants (SnCl₂ and β‐cyclodextrin), can alter the interactions between amino terminals and imine bonds in the backbone. Correspondingly, the optical properties of the resulting hyperbranched polymers are controlled.

     

Linear‐Hyperbranched Amphiphilic AB Diblock Copolymers Based on Polystyrene and Hyperbranched Polyglycerol

Summary: A convenient three‐step strategy has been developed for the preparation of well‐defined amphiphilic, linear‐hyperbranched block copolymers by hypergrafting. The synthetic procedure is based on a combination of carbanionic polymerization with the alkoxide‐based, controlled ring‐opening multibranching polymerization of glycidol. A linear AB diblock copolymer polystyrene‐block‐polybutadiene (PS‐b‐PB) with narrow polydispersity was obtained by anionic copolymerization. Subsequent hydroxylation by hydroboration led to PS₅₀₈‐b‐(PB‐OH)₅₆, used as macroinitiator for the polymerization of glycidol under slow monomer addition conditions.

Structure of the linear‐hyperbranched amphiphilic AB diblock copolymer PS₅₀₈‐b‐(PB₅₆‐hg‐PG_x) and an AFM micrograph of its micellar core–shell structure observed after solution casting.     

Chain Walking Ethylene Copolymerization with an ATRP Inimer for One‐Pot Synthesis of Hyperbranched Polyethylenes Tethered with ATRP Initiating Sites

A one‐pot procedure for the synthesis of hyperbranched polyethylenes tethered with ATRP initiating sites by chain walking ethylene copolymerization with an acrylate‐type ATRP inimer, 2‐(2‐bromoisobutyryloxy) ethyl acrylate (BIEA) is reported. Because of its ability to incorporate acrylate‐type comonomers and tolerance toward the α‐bromoester group, the chain walking Pd‐diimine catalyst, [(ArNC(Me) (Me)CNAr)Pd(CH₃)(NCMe)]SbF₆ (Ar = 2,6‐(iPr)₂C₆H₃), allowed the successful synthesis of a series of hyperbranched copolymers tethered with 2‐bromoisobutyryl groups at different densities. These copolymers may serve as polyfunctional macroinitiators for the ATRP of functional monomers to further synthesize core‐shell structured functionalized copolymers with a hyperbranched polyethylene core grafted with side chains of the functional monomers.

     

Emulsion‐Induced Ordered Microporous Films Based on Micelles of Amphiphilic Poly(ethylene oxide)‐block‐Poly(methyl methacrylate) Diblock Copolymers

Well‐defined PEO‐b‐PMMA was prepared, initiated by macroinitiator PEO‐Br, by means of ATRP, where esterification of the terminal hydroxyl group of PEO with 2‐bromoisobutyryl bromide yielded a macroinitiator PEO‐Br. Highly ordered microporous films (hexagonal pattern) were constructed by emulsion micelles of such amphiphilic diblock copolymer formed from a solution with CHCl₃/H₂O/THF = 100:5:10 (v/v). We also constructed the microporous films using diblock copolymer by the current water‐assisted method.

     

Predicting the Change of MWD Caused by Interchange Reactions During Melt‐Mixing of Linear and Branched Polycondensates (AB2)

During mix melting of hyperbranched AB₂‐ and linear CD‐polycondensates distributive properties are changing by interchange reactions. Two mathematical modeling approaches are presented: (i) Simplified approach of monodisperse population of three‐arm stars undergoing interchange reactions, both analytical and by Monte Carlo simulations, assuming interchange as subsequent scission and recombination of fragments. (ii) Full system of interchange and polycondensation/hydrolysis reactions with Monte Carlo simulations and kinetic model describing reactions of free groups (A, B, C, D) and bonds (AB, CD, BC, AD). MC simulations show that the final molecular weight and branching distribution is attained after 10% of reaction time. The change of structure, from few large fragments to more, smaller ones, is slower.

     

Thioether‐Bearing Hyperbranched Polyether Polyols with Methionine‐Like Side‐Chains: A Versatile Platform for Orthogonal Functionalization

The synthesis of thioether‐bearing hyperbranched polyether polyols based on an AB/AB₂ type copolymerization (cyclic latent monomers) is introduced. The polymers are prepared by anionic ring‐opening multibranching copolymerization of glycidol and 2‐(methylthio)ethyl glycidyl ether (MTEGE), which is conveniently accessible in a single etherification step. Slow monomer addition provides control over molecular weights. Moderate dispersities (Đ = 1.48–1.85) are obtained, given the hyperbranched structure. In situ ¹H NMR copolymerization kinetics reveal reactivity ratios of r _G = 3.7 and r _MTEGE = 0.27. Using slow monomer addition, copolymer composition can be systematically varied, allowing for the adjustment of the hydroxyl/thioether ratio, the degree of branching (DB = 0.36–0.48), thermal properties, and cloud point temperatures in aqueous solution in the range of 29–75 °C. Thioether oxidation to sulfoxides enables to tailor the copolymers' solubility profile. Use of these copolymers as a versatile, multifunctional platform for orthogonal modification is highlighted. The methyl sulfide groups can be selectively alkoxylated, using propylene oxide, allyl glycidyl ether, or furfuryl glycidyl ether, resulting in functional hyperbranched polyelectrolytes. Reaction of the alcohol groups with benzyl isocyanate demonstrates successful orthogonal functionalization.

     

Hyperbranched Polymers Formed Through Irreversible Step Polymerization of AB2‐Type Monomer with Substitution Effect in a Continuous Flow Stirred‐Tank Reactor (CSTR)

A new Monte Carlo simulation method is proposed for the step polymerization of AB₂‐type monomer conducted in a continuous flow stirred‐tank reactor (CSTR). The effect of the second B group reactivity, represented by the reactivity ratio r is investigated. The degree of branching (DB) at large degree of polymerization (P ) limit, DB_{P →∞} does not change with the mean residence time . The value of DB_{P →∞} becomes larger by increasing r and is larger than the corresponding batch polymerization. The weight fraction distribution at high molecular weight tail follows a power law , and a simple formula to predict the power exponent α is proposed. The relationship between the radius of gyration 〈s ²〉₀ and P does not change with , and large polymers obtained in a CSTR are much more compact than those formed in batch polymerization. CSTR is advantageous to synthesize compact HB polymers, especially with a smaller r‐value.     

A Cationic Water‐Soluble Poly(p‐phenylenevinylene) Derivative: Highly Sensitive Biosensor for Iron‐Sulfur Protein Detection

Summary: A new water‐soluble cationic ammonium‐functionalized poly(p‐phenylenevinylene) (PPV‐NEtMe) was successfully synthesized and exhibited high sensitivity (K_sv = 6.9 × 10⁷ M ⁻¹) on rubredoxin, a type of anionic iron‐sulfur (Fe‐S) proteins. Further investigation showed that the biosensitivity of the cationic conjugated polymer is strongly dependent on the nature of the buffer solution and the concentration of the conjugated polymer used in the analyses.

The schematic diagram of anionic rubredoxin detected by PPV‐NEtMe.     

Polyurethanes Containing Indole‐Based Non‐Linear Optical Chromophores: from Linear Chromophore to H‐Type

Two new “H” type of indole‐based chromophores were designed and successfully introduced to the polymeric system, the resultant polymers demonstrated enhanced NLO effects, good processability, thermal stability and nearly excellent transparency, indicating the advantages of “H” type chromophore moieties. And they could be promising candidates for the practical applications as new photonic materials.

     

Modelling the Influence of Nanoparticles in the Phase Behaviour of an Epoxy/Polystyrene Mixture, 2

The influences of nanoparticle size and concentration on the thermodynamic behaviour of epoxy/polystyrene blends are evaluated in the framework of Ginzburg's simple analytical theory. Two approaches have been employed: NPEPO (for particles coated with epoxy groups) and NPFEN (for particles coated with phenyl groups). Using NPEPO, the particles are found to prefer the phase richer in epoxy, whereas the opposite occurs for NPFEN. The particles size significantly influences blend compatibility. When the particle radius R_p is about the same size as the radius of gyration R_g of PS, the compatibility of blends increases with particle concentration, whereas for R_p > R_g, higher particle concentrations do not clearly stabilize the polymeric blends.

     

Propylene Polymerization Performance of Isolated and Aggregated Ti Species Studied Using a Well‐Designed TiCl3/MgCl2 Ziegler‐Natta Model Catalyst

In propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts, it is known that the reduction of TiCl₄ with alkylaluminum generates Ti³⁺ active species, and at the same time, leads to the growth of TiCl_x aggregates. In this study, the aggregation states of the Ti species were controlled by altering the Ti content in a TiCl₃/MgCl₂ model catalyst prepared from a TiCl₃ · 3C₅H₅N complex. It is discovered that all the Ti species become isolated mononuclear with a highly aspecific feature below 0.1 wt.‐% of the Ti content, and that the isolated aspecific Ti species are more efficiently converted into highly isospecific ones by the addition of donors than active sites in aggregated Ti species.

     

Novel Chromophore‐Functionalized Poly[2‐(trifluoromethyl) adamantyl acrylate‐methyl vinyl urethane]s with High Poling Stabilities of the Nonlinear Optical Effect

Nonlinear optical vinyl polymers with high glass transition temperature (T_g) were prepared by the functionalization of a fluorinated acrylate‐methyl vinyl isocyanate copolymer. A modified pathway to obtain a thiophene bridged chromophore was worked out. Poled films of the polymers show a fairly high and stable nonlinear optical response, even at elevated temperatures.

The thiophene‐bridged chromophore, based on a substituted dicyanomethylene‐dihydrofuran acceptor, synthesized here.