Synthesis of Well‐Defined Polybenzamide‐block‐Polystyrene by Combination of Chain‐Growth Condensation Polymerization and RAFT Polymerization

Well‐defined diblock copolymers composed of poly(N‐octylbenzamide) and polystyrene were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of styrene with a polyamide chain transfer agent (CTA) prepared via chain‐growth condensation polymerization. Synthesis of a dithioester‐type macro‐CTA possessing the polyamide segment as an activating group was unsatisfactory due to side reactions and incomplete introduction of the benzyl dithiocarbonyl unit. On the other hand, a dithiobenzoate‐CTA containing poly(N‐octylbenzamide) as a radical leaving group was easily synthesized, and the RAFT polymerization of styrene with this CTA afforded poly(N‐octylbenzamide)‐block‐polystyrene with controlled molecular weight and narrow polydispersity.

     

Poly(p‐phenylenevinylene) Derivatives with Defined Conjugation Segments and Post‐Polymerization Modification with Sterically Enshrouded Chromophores

Two poly(p‐phenylenevinylene) derivative alternating copolymers ( P1‐I and P2‐I ) have been prepared featuring iodo substituents and m‐phenylene units to periodically disrupt conjugation. P1‐I was derivatized with various chromophores to yield P1a‐f . In P1a‐f , the chromophores were positioned within a sterically protected pocket shielding them from interchain interactions so that intrachain interactions between polymer segments could be observed. Solution and film properties of polymers have been examined. Post‐polymerization chromophore modification leads to new photophysical properties such as intramolecular charge transfer and fluorescent resonance energy transfer processes in some cases.

     

Alternating Poly(Pt‐salphen)‐(p‐phenyleneethynylene) as Phosphorescent Conjugated Linear‐Rod and Coilable Sensory Materials

Phosphorescent conjugated polymers consisting of alternating p‐phenylene‐ethynylene and ‘para‐’ or ‘meta‐type’ Pt(II)‐salphen luminophore units have been synthesized. Side‐arms bearing different substituents (n‐alkoxy and acetylated‐sugar) have afforded contrasting emission properties that are attributed to the polymer conformation, extent of π‐stacking interactions and differences in chemical structure. Intriguing selectivity in luminescent sensing of metal ions has been observed.

     

Nitroxide‐Mediated Polymerization of Styrene in a Continuous Tubular Reactor

Summary: Nitroxide‐mediated polymerization of styrene in a continuous tubular reactor has been demonstrated for the first time. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. The number average molecular weight increases linearly with conversion, and chain extension experiments were successful, indicating that the living nature of the polymerization is maintained in the tubular reactor.

Evolution of molecular weight as measured by GPC for chain‐extended latex in continuous tubular reactor.     

Synthesis and Characterization of Chitosan Grafted Oligo(L‐lactic acid)

Chitosan grafted oligo(L ‐lactic acid) copolymers with different length of side chain were prepared through the reaction of terminal aldehyde group of oligo(L ‐lactic acid) (OLLA) and amino groups of chitosan. The mean molecular mass of the grafting OLLA chain was ca. 600 ～ 5 000. The graft copolymers are soluble in DMSO, DMF and acetic acid. The synthesis method and structure described here provide chitosan‐g‐OLLA copolymers with broad applicability.

Structure of chitosan‐g‐oligo(L ‐lactic acid).     

Synthesis of Multiblock Polymer Containing Narrow Polydispersity Blocks

Summary: We have developed a new strategy to prepare multiblock polymers and copolymers via one‐ or two‐step polymerization using a polymerizable cyclic trithiocarbonate (CTTC), 4,7‐diphenyl‐[1,3]dithiepane‐2‐thione. CTTC undergoes ring‐opening process to incorporate a trithiocarbonate moiety. The trithiocarbonate moiety in turn, functions as a reversible addition fragmentation chain transfer (RAFT) agent. Through this mechanism, multiblock polystyrenes and polystyrene‐block‐ poly(butyl acrylate) copolymers containing various narrow polydispersity blocks can be prepared.

Integrated process of ring‐opening and RAFT polymerizations involving cyclic trithiocarbonates.     

Vapor‐Based Synthesis of Poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] and Its Use for Biomimetic Surface Modifications

Summary: The vapor‐based synthesis and characterization of a reactive polymer, poly[(4‐formyl‐p‐xylylene)‐co‐(p‐xylylene)] ( 1 ), have been reported. The reactive polymer coating enables the immobilization of oligosaccharides via the chemoselective aldehyde‐hydrazide coupling reaction.

     

Supramolecular Dynamics as Origin for Thermally Induced Insoluble‐to‐Soluble‐to‐Insoluble Transitions of Copolymers in Water

The synthesis of cationic mono‐(6‐O‐(1‐vinylimidazolium))‐ß‐cyclodextrin with toluenesulfonate as the corresponding anion is described. Free‐radical copolymerization of the resulting host–guest complex with N‐isopropylacrylamide or N,N‐diethylacrylamide yielded copolymers showing a temperature‐controlled solubility window in water. The impact of different anionic guests and salt concentrations on solubility behavior was investigated via turbidity measurements.

     

Photoinduced Fusion of Micro‐Vesicles Self‐Assembled from Azobenzene‐Containing Amphiphilic Diblock Copolymers

Poly(N‐isopropylacrylamide)‐block‐poly{6‐[4‐(4‐methylphenyl‐azo) phenoxy] hexylacrylate} (PNIPAM‐b‐PAzoM) was synthesized by successive reversible addition‐fragmentation chain transfer (RAFT) polymerization. In H₂O/THF mixture, amphiphilic PNIPAM‐b‐PAzoM self‐assembles into giant micro‐vesicles. Upon irradiation of light at 365 nm, fusion of the vesicles was observed directly under an optical microscope. The real‐time fusion process is presented and the derivation is preliminarily due to the perturbation by the photoinduced trans‐to‐cis isomerization of azobenzene units in the vesicles.

     

Soluble Polyimides from a New Dianhydride: 5′‐tert‐Butyl‐m‐terphenyl‐3,4,3″,4″‐tetracarboxylic Acid Dianhydride

A novel tert‐butyl‐containing dianhydride was prepared from readily available reagents. It was reacted with various aromatic diamines to prepare a set of polyimides containing tert‐butyl pendent groups. The resulting polyimides exhibit high molecular weights (high inherent viscosity), and a combination of desirable properties, such as good solubility in aprotic amide solvents and cresols, high glass transition temperatures (up to 320 °C), high thermal resistance, film‐forming capability and good mechanical properties.

     

Synthesis of Cyclopentadienyl Capped Polyethylene and Subsequent Block Copolymer Formation Via Hetero Diels‐Alder (HDA) Chemistry

In the current contribution it is demonstrated – for the first time – that poly(ethylene) ( = 1 400 as well as 2 800 g · mol⁻¹, PDI = 1.2) can be readily equipped with highly reactive cyclopentadienyl (Cp) end groups. The Cp terminal poly(ethylene) can subsequently be reacted in an efficient hetero Diels‐Alder (HDA) reaction with macromolecules (poly(isobornyl acrylate) ( = 4 600 g · mol⁻¹, PDI = 1.10) and poly(styrene) ( = 6 300 g · mol⁻¹, PDI = 1.13) featuring strongly electron withdrawing thiocarbonyl thio end groups, prepared via reversible addition fragmentation chain transfer (RAFT) polymerization employing benzylpyridin‐2‐yldithioformate (BPDF) as transfer agent. The resulting block copolymers have been analyzed via high‐temperature size exclusion chromatography (SEC) as well as nuclear magnetic resonance (NMR) spectroscopy. The current system allows for the removal of the excess of the non‐poly(ethylene) containing segment via filtration of the poly(ethylene)‐containing block copolymer. However, the reaction temperatures need to be judiciously selected. Characterization of the generated block copolymers at elevated temperatures can lead – depending on the block copolymer type – to the occurrence of retro Diels‐Alder processes. The present study thus demonstrates that RAFT‐HDA ligation can be effectively employed for the generation of block copolymers containing poly(ethylene) segments.

     

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.

     

Reversible Photocontrolled Swelling‐Shrinking Behavior of Micron Vesicles Self‐Assembled from Azopyridine‐Containing Diblock Copolymer

Poly(N‐isopropylacrylamide)‐block‐poly{6‐[4‐(4‐pyridyazo)phenoxy] hexylmethacrylate} (PNIPAM‐b‐PAzPy) was synthesized by successive reversible addition‐fragmentation chain transfer (RAFT) polymerization. In a water/tetrahydrofuran (H₂O/THF) mixture, amphiphilic PNIPAM‐b‐PAzPy self‐assembles into giant micro‐vesicles. Upon alternate ultraviolet (UV) and visible light irradiation, obvious reversible swelling‐shrinking of the vesicles was observed directly under an optical microscope. The maximum percentage increase in volume, caused by the UV light, reached 17%. Moreover, the swelling could be adjusted using the UV light power density. The derivation of this effect is due to photoinduced reversible isomerization of azopyridine units in the vesicles.

     

Multifunctional Poly(N‐vinylcarbazole)‐Based Block Copolymers and their Nanofabrication and Photosensitizing Properties

The synthesis of poly(N‐vinylcarbazole)‐based block copolymers functionalized with rhenium diimine complexes or pendant terpyridine ligands is reported. The copolymers are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and they exhibit interesting morphological properties as a result of the phase separation between different blocks. The rhenium complex polymer block may function as a photosensitizer, while the terpyridine‐containing polymer block can be used as the template for nanofabrication by selective deposition of zinc complexes.

     

Amphiphilic Block Copolymers from a Direct and One‐pot RAFT Synthesis in Water

The syntheses of amphiphilic block copolymers are successfully performed in water by chain extension of hydrophilic macromolecules with styrene at 80 °C. The employed strategy is a one‐pot procedure in which poly(acrylic acid), poly(methacrylic acid) or poly(methacrylic acid‐co‐poly(ethylene oxide) methyl ether methacrylate) macroRAFTs are first formed in water using 4‐cyano‐4‐thiothiopropylsulfanyl pentanoic acid (CTPPA) as a chain transfer agent. The resulting macroRAFTs are then directly used without further purification for the RAFT polymerization of styrene in water in the same reactor. This simple and straightforward strategy leads to a very good control of the resulting amphiphilic block copolymers.

     

Lower Critical Solution Temperature Properties of N‐Isopropylacrylamide‐Based Pseudopolyrotaxanes by Complexation with Cucurbituril[6]

Pseudopolyrotaxanes 4a and 5a are synthesized by two paths: a) directly from the pseudorotaxane, and b) by complexing with cucurbituril (CB[6]) in water at room temperature after the polymerization. Free radical copolymerization with CB[6] (un)complexed monomer and N‐isopropylacrylamide (NIPAAM) is carried out using a redox initiator in aqueous media at room temperature. The properties of pesudorotaxanes ( 4a and 5a ) and polymers ( 4 and 5 ) are investigated by TGA, DSC, and turbidity measurements. The lower critical solution temperatures of the NIPAAM‐containing copolymers and CB[6] are significantly higher than those of pure NIPAAM copolymers. The pseudopolyrotaxanes 4a and 5a have a higher thermal stability, as a result of threading of the CB[6] rings onto the polymer side groups.

     

Ultra‐Fast RAFT‐HDA Click Conjugation: An Efficient Route to High Molecular Weight Block Copolymers

The use of the reversible addition fragmentation chain transfer—hetero Diels–Alder (RAFT‐HDA) click reaction for the modular construction of block copolymers is extended to the generation of high molecular weight materials. Cyclopentadienyl end‐functionalized polystyrene (PS‐Cp) prepared via both atom transfer radical polymerization (ATRP) and the RAFT process are conjugated to poly(isobornyl acrylate) (PiBoA) (also prepared via RAFT polymerization) to achieve well‐defined block copolymers with molecular weights ranging from 34 000 to over 100 000 g · mol⁻¹ and with small polydispersities (PDI < 1.2). The conjugation reactions proceeded in a very rapid fashion (less than 10 min in the majority of cases) under ambient conditions of temperature and atmosphere. The present study demonstrates—for the first time—that RAFT‐HDA click chemistry can provide access to high molecular weight block copolymers in a simple and straight‐forward fashion.

     

Microwave Accelerated Polymerization of 2‐Phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine: Kinetics and Influence of End‐Groups on Glass Transition Temperature

Summary: The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine (PhOZI) with methyl tosylate (MeOTs) and butyl iodide (BuI) as initiators were performed in refluxing butyronitrile. Reaction kinetics under microwave irradiation was compared with conventional oil bath heating. The polymerization rates, under microwave irradiation, showed an acceleration by a factor of 1.8 (independently from the used initiator). The investigation of the thermal properties of the obtained poly(N‐benzoyl‐trimethyleneimine) showed the influence of molecular weight and end‐groups on the glass transition temperature.

The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine performed in refluxing butyronitrile.     

Novel Biodegradable Copolymers with a Periodic Sequence Structure Derived from Succinate Butan‐1,4‐diol,and Butan‐1,4‐diamine

Summary: Novel biodegradable copolymers derived from succinate, butan‐1,4‐diol, and butan‐1,4‐diamine were synthesized by two‐step polycondensation reactions. The obtained copolymers had a periodical‐sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.

Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine     

Design Criteria for Accurate Measurement of Bimolecular Radical Termination Rate Coefficients via the RAFT‐CLD‐T Method

The reversible addition‐fragmentation chain transfer chain length dependent termination (RAFT‐CLD‐T) technique allows a simple experimental approach to obtain chain‐length‐dependent termination rate coefficients as a function of conversion, k(x). This work provides a set of criteria by which accurate k(x) can be obtained using the RAFT‐CLD‐T method. Visualization of three‐dimensional plots varying all kinetic rate parameters and starting concentrations demonstrates that only certain combinations give an accurate extraction of k(x). The current study provides hands‐on guidelines for experimentalists applying the RAFT‐CLD‐T method.