Unsaturated,biobased polyesters and their cross‐linking via radical copolymerization

Biobased, unsaturated polyesters derived from isosorbide, maleic anhydride, and succinic acid were synthesized and characterized. The presence of maleic anhydride units in the structure of the polyesters allowed converting them into cured coatings by radical copolymerization with crosslinking agents such as 2‐hydroxyethyl methacrylate, N‐vinyl‐2‐pyrrolidinone, acrylic acid or methacrylamide. The investigated polyesters were obtained via bulk polycondensation, catalyzed by titanium(IV) n‐butoxide. 2D NMR and MALDI‐Tof‐MS spectroscopy proved that this polymerization resulted in isomerization of maleic acid units into fumaric ones and in the formation of slightly branched structures by the reaction of isosorbide (end) groups with main chain unsaturated bonds. Moreover, some double bonds proved to have reacted with the condensation by‐product water. The resulting polyesters displayed the expected correlation between variables such as molecular weight and content of unsaturated bonds and their T_g values. Since the thermal properties of the obtained polyesters were appropriate for coating applications, the polymers were crosslinked with unsaturated monomers by radical copolymerization. The crosslinking process was studied using FTIR spectroscopy and by measurements of the soluble part of the cured coatings. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2885–2895, 2010     

Organocatalyzed Step‐Growth Polymerization through Desymmetrization of Cyclic Anhydrides: Synthesis of Chiral Polyesters

The polymerization of prochiral bis‐anhydrides with diols catalyzed by a cinchona alkaloid was shown to provide chiral polyesters in good yields and with high levels of stereocontrol. The structures of the polyesters were determined by ¹H and ¹³C NMR analyses, whereas their size was estimated by both size‐exclusion chromatography (SEC) and MALDI‐TOF mass spectrometry, which indicated that moderate degrees of polymerization were attained through this step‐growth polymerization. The enantioselectivity of the process was evaluated by using chiral HPLC analysis of the bis‐lactones resulting from a controlled chemoselective degradation of the polyesters. The best stereocontrol was reached for oligomers formed from bis‐anhydride and diol monomers bearing rigid aromatic spacers between the reactive functional groups. In this case, average enantioselectivities were comparable to those observed during ring‐opening of simple anhydrides with similar alcohols. In contrast, the use of more flexible spacers between reactive entities generally led to lower levels of stereocontrol.     

Novel functionalization routes of poly(ϵ‐caprolactone)

The aluminum alkoxide mediated ring opening polymerization of functional lactones, such as γ‐ethylene ketal‐ϵ‐caprolactone (TOSUO), γ‐(triethylsilyloxy)‐ϵ‐caprolactone (SCL) and γ‐bromo‐ϵ‐caprolactone (γBrCL), is a versatile route to polyesters containing ketal, ketone, alcohol and bromide groups. As result of living polyaddition mechanism, random and block copolymerization of ϵCL and γBrCL has been successfully carried out. The reactivity ratios are quite similar (1.08 for ϵ‐CL, and 1.12 for γBrCL). These random copolymers are semicrystalline when they contain less than 30 mol% of γBrCL, otherwise they are amorphous. No transesterification reaction occurs during the sequential polymerization of ϵ‐CL and γBrCL leading to block copolymers. Reaction of poly(ϵCL‐co‐γBrCL) with pyridine provides quantitatively a polycationic polyester. Furthermore, the reaction of this random copolymer with 1,8‐diazabicyclo[5.4.0] undec‐7‐ene (DBU) is a route to unsaturated polyesters, whose the non conjugated double bonds can be quantitatively converted into epoxides by reaction with m‐chloroperbenzoic acid (mCPBA). No chain degradation is detected during these derivatization reactions of poly(ϵCL‐co‐γBrCL).     

Insights into post‐polymerisation modification of bio‐based unsaturated itaconate and fumarate polyesters via aza‐michael addition: Understanding the effects of CC isomerisation

Development of renewable bio‐based unsaturated polyesters is undergoing a renaissance, typified by the use of itaconate and fumarate monomers. The electron‐deficient CC bond found on the corresponding polyesters allows convenient post‐polymerisation modification to give a wide range of polymer properties; this is notably effective for the addition of nucleophilic pendants. However, preservation of unsaturated functionality is blighted by two undesirable side‐reactions, branching/crosslinking and CC isomerisation. Herein, a tentative kinetic study of diethylamine addition to model itaconate and fumarate diesters highlights the significance of undesirable CC isomerisation. In particular, it shows that reversible isomerisation from itaconate to mesaconate (a poor Michael acceptor) is in direct competition with aza‐Michael addition, where the amine Michael donor acts as an isomerisation catalyst. We postulate that undesired formation of mesaconate is responsible for the long reaction times previously reported for itaconate polyester post‐polymerisation modification. This study illustrates the pressing need to overcome this issue of CC isomerisation to enhance post‐polymerisation modification of bio‐based unsaturated polyesters. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1935–1945     

Synthesis of narrow‐polydispersity degradable dendronized aliphatic polyesters

The divergent dendronization of an ?‐caprolactone‐based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug‐delivery scaffolds. The synthesis was performed through the tin(II) 2‐ethylhexanoate‐catalyzed polymerization of a γ‐functionalized ?‐caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth‐generation hydroxyl‐terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring‐opening polymerization of a second‐generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3563–3578, 2004     

Precision Aliphatic Polyesters with Alternating Microstructures via Cross‐Metathesis Polymerization: An Event of Sequence Control

Sequence‐regulated polymerization is realized upon sequential cross‐metathesis polymerization (CMP) and exhaustive hydrogenation to afford precision aliphatic polyesters with alternating sequences. This strategy is particularly suitable for the arrangement of well‐known monomer units including glycolic acid, lactic acid, and caprolactic acid on polymer chain in a predetermined sequence. First of all, structurally asymmetric monomers bearing acrylate and α‐olefin terminuses are generated in an efficient and straightforward fashion. Subsequently, cross‐metathesis (co)polymerization of M1 and M2 using the Hoveyda–Grubbs second‐generation catalyst (HG‐II) furnishes P1 – P3 , respectively. Finally, hydrogenation yields the desired saturated polyesters HP1 – HP3 . It is noteworthy that the ε‐caprolactone‐derived unit is generated in situ rather than introduced to tailor‐made monomers prior to CMP. NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) results verify the microstructural periodicity of these precision polyesters. Differential scanning calorimetry (DSC) results reflect that polyesters without methyl side groups exhibit crystallinity, and unsaturated polyester samples show higher glass transition temperatures than their hydrogenated counterparts owing to structural rigidity.

     

Photopolymerization of 1,6‐hexanedioldiacrylate initiated by three‐component systems based on N‐arylphthalimides

Three‐component photoinitiators comprised of an N‐arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron‐deficient N‐arylphthalimide resulted in a greater acrylate polymerization rate than an electron‐rich N‐arylphthalimide. Triplet energies of each N‐arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N‐arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron–proton transfer from an intermediate radical species to the N‐arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009–4015, 2004     

Enzyme‐Catalyzed Synthesis and Chemical Recycling of Polyesters

This article summarizes the enzyme‐catalyzed synthesis and chemical recycling of biodegradable aliphatic polyesters and poly(carbonate ester)s directed towards establishing green polymer chemistry. Lipase catalyzes the condensation polymerization of a hydroxy acid, diacid with diol, diacid anhydride with oxirane, and polyanhydride with diol, or the ring‐opening polymerization of lactones of small to large rings, and a cyclic diester to produce the corresponding polyesters. Also, lipase catalyzes the condensation polymerization of a dialkyl carbonate with diol, and the ring‐opening polymerization of a cyclic carbonate to produce the corresponding polycarbonates. These polyesters and polycarbonates were selectively degraded by lipase to produce repolymerizable oligomers. These chemical recycling systems using an enzyme will establish a novel methodology for sustainable polymer recycling. Finally, current trends in green polymer production using enzymes are discussed.     

Incorporation of poly(2‐acrylamido‐2‐methyl‐N‐propanesulfonic acid) segments into block and brush copolymers by ATRP

2‐Acrylamido‐2‐methyl‐N‐propanesulfonic acid (AMPSA) was successfully polymerized via atom transfer radical polymerization (ATRP) using a copper chloride/2,2′‐bipyridine (bpy) catalyst complex after in situ neutralization of the acidic proton in AMPSA with tri(n‐butyl)amine (TBA). A 5 mol % excess of TBA was required to completely neutralize the acid and prevent protonation of the bpy ligand, as well as to avoid side reactions caused by large excess of TBA. The use of activators generated by electron transfer (AGET) ATRP with ascorbic acid as reducing agent resulted in both increased conversion of the AMPSA monomer during polymerization (up to 50% with a 0.8 [ascorbic acid]/[Cu(II)] ratio) and much shorter polymerization times (<30 min). Block copolymers and molecular brushes containing AMPSA side chains were prepared using this method, and the solution and surface behavior of these materials were investigated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5386–5396, 2009     

Synthesis via ATRP,kinetics study and characterization (molecular‐morphological) of 3‐Arm star diblock copolymers of the (PS‐b‐P2VP)3 type

The synthesis of five homopolymers (PS)₃ and the corresponding diblock copolymer 3‐arm stars of the (PS‐b‐P2VP)₃ type is reported through atom transfer radical polymerization. Such star homo‐ and copolymers are prepared without any addition of solvent (bulk polymerization). The kinetics study results lead to the ability of predicting the best polymerization time with high values of monomer to polymer conversion, sufficient polydispersity indices and average molecular weights. Molecular characterization through size exclusion chromatography, viscometry, low‐angle laser light scattering, proton and carbon nuclear magnetic resonance spectroscopy (¹H NMR and ¹³C NMR, respectively) verified the successful synthesis of both homopolymer and copolymer 3‐arm star‐like architectures. Furthermore, the morphological characterization of the final copolymers is reported through transmission electron microscopy studies verifying the self‐assembly without any indication of homopolymer or Cu(I) traces. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 23–32     

Precision synthesis of sustainable thermoplastic elastomers from lysine‐derived monomers

Novel renewable thermoplastic elastomers were synthesized by sequential polymerization of lysine‐ and itaconic acid‐derived monomers. Ring‐opening polymerization of lysine‐based O‐carboxyanhydride monomer using diethylene glycol as an initiator gave well‐defined α,ω‐dihydroxy functionalized lysine‐derived polyesters. The M _n of these polyesters increased with the monomer conversion while retaining relatively narrow molecular weight distributions. Based on the successful controlled polymerization and esterification of α,ω‐dihydroxy with 2‐bromoisobutyryl bromide, the resultant Br‐PL‐Br macroinitiator was used for the atom transfer radical polymerization of N‐phenylitaconimide (PhII). Three poly(N‐phenylitaconimide)‐b‐polyester‐b‐poly(N‐phenylitaconimide) triblock copolymers were prepared containing 12 ? 25 mol% PPhII, as determined by ¹H NMR spectroscopy. The properties of the obtained triblock copolymer are evaluated as high‐performance and renewable thermoplastic elastomer materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 349–355     

ABA triblock copolymers with a ring‐opening metathesis polymerization/macromolecular chain‐transfer agent approach

Block copolymers containing polystyrene and polycyclooctene were synthesized with a ring‐opening metathesis polymerization/chain‐transfer approach. Polystyrene, containing appropriately placed olefins, was prepared by anionic polymerization and served as a macromolecular chain‐transfer agent for the ring‐opening metathesis polymerization of cyclooctene. These unsaturated polymers were subsequently converted to the corresponding saturated triblock copolymers with a simple heterogeneous catalytic hydrogenation step. The molecular and morphological characterization of the block copolymers was consistent with the absence of significant branching in the central polycyclooctene and polyethylene blocks [high melting temperatures (114–127 °C) and levels of crystallinity (17–42%)]. A dramatic improvement in both the long‐range order and the mechanical properties of a microphase‐separated, symmetric polystyrene–polycyclooctene–polystyrene block copolymer sample was observed after fractionation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 361–373, 2007     

Development of catalyst‐transfer condensation polymerization. Synthesis of π‐conjugated polymers with controlled molecular weight and low polydispersity

We describe the development of chain‐growth condensation polymerization for the synthesis of well‐defined π‐conjugated polymers via a new polymerization mechanism, catalyst‐transfer polymerization. We first studied the condensation polymerization of Grignard‐type hexylthiophene monomer with a Ni catalyst as a part of our research on chain‐growth condensation polymerization, and found that this polymerization also proceeded in a chain‐growth polymerization manner. However, the polymerization mechanism involving the Ni catalyst was different from that of previous chain‐growth condensation polymerizations based on substituent effects; the Ni catalyst catalyzed the coupling reaction of the monomer with the polymer, followed by the transfer of Ni(0) to the terminal C? Br bond of the elongated molecule. This catalyst‐transfer condensation polymerization is generally applicable for the synthesis of polythiophene with an etheric side chain and poly(p‐pheneylene), as well as for the synthesis of polyfluorene via the Pd‐catalyzed Suzuki–Miyaura coupling reaction. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 753–765, 2008     

Synthesis of hyperbranched polymers via proton‐transfer polymerization of acrylate monomer containing two hydroxy groups

The hyperbranched polymer 2 was produced via triphenylphosphine initiated polymerization of the acrylate monomer 1 containing two hydroxy groups. The reaction resulting in 2 is based on a Michael‐type addition followed by a proton‐transfer process. The molecular weights evaluated by VPO measurements were vanging between 1 170–2 700 g/mol. The results of the methanolysis experiments of the polymers were used to determine the degrees of branching, that ranged between 0.45 and 0.60. In this polymerization, the hydroxy groups of the monomer and of the polymer are latent propagating species, which are converted into the corresponding anions, which are the actual propagating species active during the proton‐transfer reactions. The proton‐transfer occur frequently during this polymerization in order to afford the formation of hyperbranched polymers.     

Hyperbranched polyesters based on polycondensation of 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid and 3,5‐dihydroxybenzoic acid

A series of hyperbranched polyesters was produced by the condensation of the monomer 3,5‐dihydroxybenzoic acid with 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid as a trifunctional central core. The monomer‐to‐core ratio was varied between 3 and 45. The resulting polymers were phenolic‐terminated polyesters. The degree of branching of the polyesters was calculated according to the method described by Fréchet and was found to be in the range of 0.7–0.8. The number‐average molecular weights calculated via ¹H NMR spectroscopic degree‐of‐polymerization values are in reasonable agreement with the predicted values derived from the monomer‐to‐core ratio for all prepared polyesters. Thermal and photophysical properties were also studied. Glass‐transition temperatures were determined by differential scanning calorimetry and were found to be relatively independent of the theoretical molar mass. The polyesters were found to be blue emitters, and the solutions exhibited intense fluorescence, with a maximum of 430 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3278–3288, 2005     

Oligoethylene‐end‐capped polylactides

Oligoethylene‐end‐capped polylactides were synthesized through the ring‐opening polymerization of L ‐lactide with alcohol‐terminated oligoethylenes as macroinitiators. The polymerization of L ‐lactide was carried out in bulk at 130 °C in the presence of stannous octoate and primary alcohols with four different molecular weights: 350, 425, 550, and 700 g/mol. The end‐capped copolymers that formed had a number‐average molecular weight of approximately 40,000 (weight‐average molecular weight/number‐average molecular weight = 1.7) according to gel permeation chromatography and were highly crystalline in comparison with the similarly formed homopolymer of L ‐lactide. The copolymer structure was characterized by Fourier transform infrared, NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and differential scanning calorimetry analysis. This work focused on developing more crystallizable and hydrolytically stable polylactide derivatives that could potentially be used as compatibilizers in polylactide–polyolefin blends or as nucleating agents for poly(L ‐lactide) or other polyesters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5257–5266, 2005     

Towards Truly Sustainable Polymers: A Metal‐Free Recyclable Polyester from Biorenewable Non‐Strained γ‐Butyrolactone

The first effective organopolymerization of the biorenewable “non‐polymerizable” γ‐butyrolactone (γ‐BL) to a high‐molecular‐weight metal‐free recyclable polyester is reported. The superbase tert‐Bu‐P₄ is found to directly initiate this polymerization through deprotonation of γ‐BL to generate reactive enolate species. When combined with a suitable alcohol, the tert‐Bu‐P₄‐based system rapidly converts γ‐BL into polyesters with high monomer conversions (up to 90 %), high molecular weights (M_n up to 26.7 kg mol^?1), and complete recyclability (quantitative γ‐BL recovery).     

Cyano Analogues of 7‐Azaindole: Probing Excited‐State Charge‐Coupled Proton Transfer Reactions in Protic Solvents

The interplay between excited‐state charge and proton transfer reactions in protic solvents is investigated in a series of 7‐azaindole (7AI) derivatives: 3‐cyano‐7‐azaindole (3CNAI), 5‐cyano‐7‐azaindole (5CNAI), 3,5‐dicyano‐7‐azaindole (3,5CNAI) and dicyanoethenyl‐7‐azaindole (DiCNAI). Similar to 7AI, 3CNAI and 3,5CNAI undergo methanol catalyzed excited‐state double proton transfer (ESDPT), resulting in dual (normal and proton transfer) emission. Conversely, ESDPT is prohibited for 5CNAI and DiCNAI in methanol, as supported by a unique normal emission with high quantum efficiency. Instead, the normal emission undergoes prominent solvatochromism. Detailed relaxation dynamics and temperature dependent studies are carried out. The results conclude that significant excited‐state charge transfer (ESCT) takes place for both 5CNAI and DiCNAI. The charge‐transfer specie possesses a different dipole moment from that of the proton‐transfer tautomer species. Upon reaching the equilibrium polarization, there exists a solvent‐polarity induced barrier during the proton‐transfer tautomerization, and ESDPT is prohibited for 5CNAI and DiCNAI during the excited‐state lifespan. The result is remarkably different from 7AI, which is also unique among most excited‐state charge/proton transfer coupled systems studied to date.     

Aza‐Michael addition reaction: Post‐polymerization modification and preparation of PEI/PEG‐based polyester hydrogels from enzymatically synthesized reactive polymers

The utility of aza‐Michael addition chemistry for post‐polymerization functionalization of enzymatically prepared polyesters is established. For this, itaconate ester and oligoethylene glycol are selected as monomers. A Candida Antarctica lipase B catalyzed polycondensation reaction between the two monomers provides the polyesters, which carry an activated carbon‐carbon double bond in the polymer backbone. These electron deficient alkenes represent suitable aza‐Michael acceptors and can be engaged in a nucleophilic addition reaction with small molecular mono‐amines (aza‐Michael donors) to yield functionalized linear polyesters. Employing a poly‐amine as the aza‐Michael donor, on the other hand, results in the formation of hydrophilic polymer networks. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 745–749     

The role of solvent‐ligated metal(II) complexes incorporating (fluoroalkoxy)aluminates as weakly coordinating anions in isobutylene polymerization

Nitrile‐ligated copper(II) and zinc(II) complexes comprising (fluoroalkoxy)aluminates as weakly coordinating anions (WCAs) have been synthesized and applied for the polymerization of isobutylene at room temperature (30°C). The polymers obtained are in the low and moderate molecular weight range and show characteristics of the highly reactive polyisobutylene. Results indicate that the fluoroalkoxy aluminate WCAs have even a higher tolerance toward water in IB polymerization than the earlier tested perfluoroborate WCAs. Studies showed that water plays an important role in the polymerization process, which indicates a polymerization mechanism similar to a proton‐initiated carbocation polymerization. The role of the WCAs and their importance for the room‐temperature polymerization process was re‐examined, and the effect of the addition of proton and electron donors including proton traps (2,6‐di‐tert‐butyl‐4‐methylpyridine or DTBP) was studied in detail. The polymerization reaction seems to be dominated by transfer reactions that lead to the high content of exo double bonds while propagation proceeds via conventional cationic polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013