Polylactones, 67

Summary: Spirocyclic initiators were prepared by condensation of Ge(OEt)₄ and tetra(ethylene glycol), TEG, or PEG‐2000 ( = 2 000 Da). These spirocycles were used as initiators for the ring‐expansion polymerization of L ‐lactide in chlorobenzene at 120 °C. The resulting cyclic block copolymers were reacted in situ with aliphatic dicarboxylic acid dichlorides (ADADs) or with hexamethylene diisocyanate (HMDI) to achieve chain extension. The reaction conditions were optimized via model reactions. The isolated Ge‐free multiblock copolymers were characterized by viscosity and by ¹H NMR measurements. In selected cases SEC measurements and MALDI‐TOF mass spectrometry were conducted. The mass spectra revealed small amounts of cyclic oligo‐ and polylactides, whereas the high molecular weight multiblock copolymers did not “fly”.

Structure of spirocyclic Ge‐initiator used here.     

New Functional Block Copolymers via RAFT Polymerization and Polymer‐Analogous Reaction

The synthesis of block copolymers consisting of nonfunctional and reactive blocks is reported. The precursor polymers are ABA triblock copolymers, consisting of S/VBC or MMA/GMA and prepared via RAFT polymerization. The reactive blocks are converted into blocks with new functionalities that are hard to achieve by direct polymerization. The new polymers are either amphiphilic, with acidic or basic blocks on the outside and a nonfunctional core, or have functionalities that are useful for further reactions like thiol‐ene or alkyne‐azide click reactions. Reaction success and degree of functionalization are determined via FTIR, elemental analysis, and MALDI‐TOF MS. The stability of the RAFT functionalities during the modification reactions is analyzed.     

Aliphatic Polyesters of Butyne‐1,4‐Diol

Polyesters of butyne‐1,4‐diol (ByD) and aliphatic dicarboxylic acids (ADAs) were prepared in three different ways. Method I is based on the transesterification of ByD with the dimethyl esters of ADAs in bulk. Although catalyst and temperature were varied, only oligomers were obtained, because even at 220 °C the conversions were far from complete. Higher molar masses resulted from method II, the acid‐catalyzed polycondensation of ByD with sebacic acid, but this method yielded a high fraction of ether groups. The best results were obtained from method III, which consisted of pyridine‐catalyzed polycondensations of ByD and various ADA dichlorides at 0–20 °C. SEC measurements yielded corrected number average molecular weights ( ) up to 20 000 Da. The success of this method depended largely on the excess of the ADA dichloride in the feed ratio. MALDI‐TOF mass spectrometry evidenced that under optimized reaction conditions the chain‐growth was mainly limited by cyclization. With the exception of the polysuccinate, all polyesters were rapidly crystallized materials with melting temperatures in the range of 50–90 °C.

     

Well‐defined N‐Isopropylacrylamide Dual‐Sensitive Copolymers with LCST ≈38 °C in Different Architectures: Linear,Block and Star Polymers

Reversible addition‐fragmentation chain transfer (RAFT) polymerization is used to prepare temperature‐ and pH‐sensitive statistical copolymers with lower critical solution temperature (LCST) close to 38 °C at pH 7.4 based on N‐isopropylacrylamide and methacrylic acid derivative comonomers with a pK_a close to 6. Statistical copolymers are re‐activated to prepare amphiphilic block copolymers and star polymers with cross‐linked core. The LCST is maintained by varying the architecture; however, the LCST originated behaviour changes due to self‐aggregation. Statistical copolymers and short block copolymers show complex aggregation, whereas mid‐size block copolymers and star polymers show shrinkage of aggregate dimensions. The pH of the medium has a profound impact on the self‐assembling behaviour of the different polymer architectures.     

New Polymer Syntheses, 112

Bis(4‐chlorophenyl)sebacate (BCPS) was polycondensed with 1,12‐diamino‐4,9‐dioxadodecane or with its bistrimethylsilyl derivative in three different solvents with variation of time and temperature. The highest molecular weights were obtained in dimethylsulfoxide at 60 °C. The highest fraction of cyclic polyamides was detected by MALDI‐TOF mass spectrometry in the samples with the highest molecular weights. Numerous polycondensations of BCPS and 1,13‐diamino‐4,7,10‐trioxatridecane were performed with variation of solvent, time and temperature. Again the best results were obtained in dimethylsulfoxide at 60 °C. The fraction of cyclic polyamides increased with higher average molecular weights of the samples. The MALDI‐TOF mass spectrum of the sample with the highest molar mass (M _n ca. 30 000 Da) exclusively displayed mass peaks of cycles (detected up to 13 000 Da). No side reactions were observed.

MALDI‐TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60 °C/48 h (no. 3, Table 1 ).     

Polylactones, 53. Formation of Cyclic Polyesters in the Combined Ring‐Expansion Polymerization/Ring‐Opening Polycondensation of Lactones

Ring‐expansion polymerizations of β‐D ,L ‐butyrolactone (β‐BL) or ε‐caprolactone (ε‐CL) were initiated with 2,2‐dibutyl‐2‐stanna‐1,3‐dioxepane (DSDOP) and the monomer‐initiator ratio (M/I) was varied. The resulting tin‐containing polylactones were polycondensed in situ either with succinyl chloride (in the case of β‐BL) or with suberoyl chlorid (for ε‐CL). The reaction conditions were optimized towards high molecular weights by the addition of bipyridine. The isolated tin‐free polylactones were characterized by MALDI‐TOF mass spectrometry. In the best spectra cyclic poly(ε‐caprolactone)s were detected up to masses around 10 600 Da and cyclic poly(β‐butyrolactone)s up to masses around 17 000 Da. In addition to the cyclic polyesters linear chains having alcoholic OH and/or CO₂H group were found. These results suggest that the chain growth is limited by cyclization and by incomplete conversion of the functional groups.     

Star Block Copolymers Through Nitroxide‐Mediated Radical Polymerization From Polyhedral Oligomeric Silsesquioxane (POSS) Core

A series of star block copolymers were prepared through nitroxide‐mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core‐first polymerization. Eight N‐alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q₈M POSS) with 1‐(2‐(allyloxy)‐1‐phenylethoxy)‐2,2,6,6‐tetramethylpiperidine (allyl‐TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa‐N‐alkoxyamines POSS (OT‐POSS) were used as platform to synthesize star polystyrene‐POSS ((PS)₈‐POSS) homopolymer and diblock copolymers of poly(styrene‐block‐4‐vinylpyridine)‐POSS ((PS‐b‐P4VP)₈‐POSS) and poly(styrene‐block‐acetoxystyrene) ((PS‐b‐PAS)₈‐POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS‐b‐PAS)₈‐POSS, the poly(styrene‐block‐vinyl phenol) ((PS‐b‐PVPh)₈‐POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self‐assembled structures of these star block copolymers based on POSS were characterized by ¹H NMR, FTIR, SEC, TEM, and SAXS analyses.

     

Synthesis,Characterization, and Photopolymerization of Novel Phosphonated Resins, 2

New phosphonated cross‐linked polymers were synthesized from telomers obtained by reaction between 10‐undecenol and dialkyl hydrogenphosphonates. Telomers were studied using MALDI‐TOF MS. It was proven that side products were produced, corresponding to cross‐esterification reactions of dialkyl hydrogenphosphonate on telomers and to radical additions of telomer on 10‐undecenol. The same behavior was also observed with allyl alcohol. Telomers were then converted to resins by methacrylation reactions. Finally, photopolymerization of the different resins synthesized was achieved and influence of the nature of the phosphonate group (diester, monoacid and diacid) was also evaluated.

     

“Tree‐Shaped” Copolymers Based on Poly(ethylene glycol) and Atactic or Isotactic Polylactides: Synthesis and Characterization

“Tree‐shaped” copolymers constituted by an m‐PEG trunk and poly(L ‐lactide) or poly(D ,L ‐lactide) branches were obtained. The m‐PEG was functionalized at the terminal chain with two (G1) and four (G2) hydroxyl groups, then reacted with Al(CH₃)₃ to produce aluminum alkoxide species, active as initiators in the ROP of L‐ or D ,L‐ lactide. Copolymers were characterized by ¹H and ¹³C NMR, GPC and DSC, and compared with analogous linear copolymers. Characterization of a low‐molecular‐weight G1 copolymer confirmed the architecture. GPC curves showed monomodal and narrow molecular weight distribution for all the samples, while the melting points of the copolymers seemed more correlated to the architecture than to the composition.

     

Dibromomaleimide Derivative as an Efficient Polymer Coupling Agent for Building Topological Polymers

The dibromomaleimide derivative, N‐(4‐bromobutyl)‐dibromomaleimide (dBMIB), is found to be a highly efficient coupling agent to dimerize thiol‐terminated hydrophilic polymers by substituent reaction. When mono‐thiol poly(ethylene oxide) (PEO₄₅‐SH) is mixed with dBMIB in an equivalent molar feed in water, a dimer of PEO₄₅ with a maleimide unit located at the chain center, (PEO₄₅)₂MIB, is obtained quantitatively. The dBMIB is also used to dimerize thiol‐ terminated poly(N‐(2‐acryloyloxyethyl) pyrrolidone) and poly(N,N‐dimethyl acrylamide). Moreover, the butylene bromide of (PEO₄₅)₂MIB is transferred into a butylene azide, which is allowed to react with alkynyl‐terminated polystyrene to give a A₂B miktoarm star polymer via a copper‐catalyzed azide–alkyne cycloaddition coupling reaction.     

Reversible Hydrogels from an Ampholytic An(B‐b‐C)n Heteroarm Star Block Terpolymer

An asymmetric, amphiphilic, A_n(B‐b‐C)_n heteroarm star block terpolymer bearing polystyrene and poly(2‐vinyl pyridine)‐block‐poly(acrylic acid) arms, was synthesized by anionic polymerization, using an extending “in‐out” method and a post polymerization deprotection reaction. Due to the pH‐dependent protonation/deprotonation equilibrium of the P2VP/PAA blocks, a rich phase behavior was observed as a function of pH. At pH = 2, the star terpolymers form a physical hydrogel through a solvent‐induced sol/gel transition in a DMF/water solvent mixture. The gelation mechanism was attributed to a jamming effect mediated by increasing the dielectric permittivity of the medium.

     

Synthesis and Micellization of Star‐Shaped Poly(ethylene glycol)‐block‐Poly(ε‐caprolactone)

Summary: The relationship between the architecture of block copolymers and their micellar properties was investigated. Diblock, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymers based on poly(ethylene glycol) and poly(ε‐caprolactone) were synthesized. Micelles of star‐shaped block copolymer in an aqueous solution were then prepared by a solvent evaporation method. The critical micelle concentration and the size of the micelles were measured by the steady‐state pyrene fluorescence method and dynamic light scattering, respectively. The CMC decreased in the order di‐, 3‐arm star‐shaped and 4‐arm star‐shaped block copolymer. The size of the micelles increased in the same order as the CMC. Theory also predicts that the formation of micelles becomes easier for 4‐arm star‐shaped block copolymers than for di‐ and 3‐arm star‐shaped block copolymers, which qualitatively agrees with the experiments.

     

Poly[2,7‐(9,9‐dihexylfluorene)]‐block‐Poly(2‐vinylpyridine) Rod–Coil Star‐block Copolymers: Synthesis,Micellar Structures,and Photophysical Properties

The first successful synthesis of conjugated rod–coil star block copolymer, (PF‐b‐P2VP)_n, containing conjugated poly[2,7‐(9,9‐dihexylfluorene)] (PF), and coil‐like poly(2‐vinylpyridine) (P2VP) by combining a Suzuki coupling reaction and living anionic polymerization is reported. With increasing methanol content in THF/methanol mixtures (PF‐b‐P2VP)_n symmetric star‐block copolymers maintain spherical micelles, but PF‐b‐P2VP asymmetric diblock copolymers vary from spherical micelles to vesicles. Both the absorption and emission spectra of PF‐b‐P2VP blue shift with increasing methanol content, suggesting an “H‐type” aggregation. However, (PF‐b‐P2VP)_n star‐block exhibits no shift in absorption but a red shift in the emission spectra, indicating a different type of aggregation. These results suggest the significance of polymer architectures on microphase‐separated morphologies and photophysical properties.

     

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.     

Successive Synthesis of Multiarmed and Multicomponent Star‐Branched Polymers by New Iterative Methodology Based on Linking Reaction between Block Copolymer In‐Chain Anion and α‐Phenylacrylate‐Functionalized Polymer

A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.

     

Architecturally and Chemically Modified Poly(1,3‐cyclohexadiene)

Star‐shaped, star‐block‐linear, and hyperbranched poly(1,3‐cyclohexadiene) (PCHD) (co)polymers were synthesized through a convergent living anionic polymerization process or via addition of divinylbenzene. Chemical modification of star‐shaped PCHDs, including aromatization, hydrogenation, fluorination, and sulfonation, was carried out in order to manipulate the physical and thermal properties of these materials. The obtained (co)polymers were characterized by gel permeation chromatography, ¹H NMR, DSC, and thermal gravimetric analysis in order to elucidate their molecular weights, molecular weight distributions, chemical nature, and physical and thermal properties. The synthetic approaches described herein offer routes to novel structure and functionality in PCHD‐based materials.

     

Multicyclic Poly(ether ketone)s by Polycondensation of 1,3,5‐Tris(4‐fluorobenzoyl)benzene with Various Diphenols

Summary: 1,3,5‐Tris(4‐fluorobenzoyl)benzene (TFBB) was polycondensed with silylated 4,4′‐dihydroxybiphenyl, bisphenol‐A or 4‐tert‐butylcatechol in N‐methylpyrrolidine with K₂CO₃ as a promoter. The TFBB/diphenol feed ratio was varied from 1.0:1.0 to 1:0:1.5. Partial cross‐linking was observed with the stiff 4,4′‐dihydroxybiphenyl, even at the 1.0:1.0 ratio. With bisphenol‐A, no gelation took place up to a feed ratio of 1.0:1.3, indicating a high cyclization tendency. With 4‐tert‐butylcatechol, no cross‐linking occurred up to the 1.0:1.5 ratio, proving an even higher cyclization tendency. The formation of cyclic, bicyclic and multicyclic oligo‐ and polyethers was detected by means of MALDI‐TOF mass spectrometry for all reaction products. These results demonstrate that increasing chain stiffness reduces the influence of cyclization. Cyclization proved unavoidable, however, and a high cyclization tendency prevents the formation of hyperbranched and networked structures.

     

A Novel Bifunctional Trithiocarbonate for Styrene and Methacrylate RAFT Polymerization

The synthesis of butane‐1,4‐bis(phenylacetonitrile trithiocarbonate) and its application as a new chain transfer agent for controlled radical polymerization is reported. It is a bifunctional trithiocarbonate for the polymerization of methacrylates, and styrenic monomers and therefore a novel type of RAFT agent. Linear growth of molar masses with conversion and narrow molecular weight distributions are obtained. ABA triblock copolymers are successfully synthesized in two steps. MALDI‐TOF MS and SEC prove the living character of the polymers and uniform growth of both functionalities. The pre‐equilibrium kinetics are analyzed by SEC to determine transfer coefficients. The P(GMA) blocks are used as precursor for polymer‐analogous reactions.

     

Multicyclic Poly(ether sulfone)s Derived from Tris(4‐hydroxyphenyl)ethane

Polycondensations of 4,4′‐difluorodiphenylsulfone with tris(4‐hydroxy phenyl)ethane were performed in DMSO with variation of feed ratio and concentration. For feed ratios of 1.0:1.3–1.0:1.5, soluble multicyclic poly(ether sulfone)s were obtained when the monomer concentration was below 0.05 M . The conversions were never complete under standard conditions, and doubling the reaction time yielded perfect multicyclic products free of endgroups; however, a small fraction of the product was crosslinked under these conditions. Quite similar results were obtained with 4,4′‐dichlorodiphenylsulfone at higher temperatures. When K₂CO₃ was replaced by tertiary amines, conversions and molecular weights were lower. The multicyclic poly(ether sulfone)s were characterized by MALDI‐TOF mass spectrometry, SEC, and DSC measurements. Broad molecular weight distributions with polydispersities in the range of 2.4–3.9 were found, and, surprisingly, two glass transitions were detectable in the DSC heating curves.