Sustainable,Stereoregular, and Optically Active Polyamides via Cationic Polymerization of ε‐Lactams Derived from the Terpene β‐Pinene

A convenient synthesis of sustainable polyamides, which contain side groups and stereocenters, starting from the biobased small terpene β‐pinene is reported. The polyamides, which are obtained via the pinene‐based lactam via ring‐opening polymerization, show excellent thermal properties, rendering this approach very interesting for the utilization of novel biobased and structurally significant high‐performance polymers and materials. Polymer masses and yields are shown to be dependent on different parameters, and the stereoinformation of the lactam monomer can thus be transferred into the polymer chain. In addition, another lactam side product can also be transformed to polyamides.

     

Convenient Method of Chain‐Growth Polycondensation for Well‐Defined Aromatic Polyamides

Summary: For the convenient synthesis of well‐defined poly(N‐octyl‐p‐benzamide)s with low polydispersities, the polycondensation of methyl 4‐octylaminobenzoate ( 1 ) was investigated. Methyl ester monomer 1 polymerized with lithium 1,1,1,3,3,3‐hexamethyldisilazide (LHMDS) in the presence of an initiator in tetrahydrofuran at −10 °C. The highly pure polyamide with a defined molecular weight and a low polydispersity is obtained after simple treatment of the reaction mixture with aqueous NaOH solution, followed by evaporation.

The chain‐growth polycondensation of 4‐octylaminobenzoic acid methyl ester ( 1 ) with lithium 1,1,1,3,3,3‐hexamethyldisilazide (LHMDS) to yield poly(N‐octyl‐p‐benzamide).     

Recent Developments in Polyether Synthesis

Polyethers, both aliphatic, such as poly(ethylene oxide), poly(propylene oxide), etc., and wholly aromatic ones, such as poly(phenylene oxide)s, are commercially important materials. Polymers belonging to the former class are primarily synthesized via a ring‐opening polymerization route, while those belonging to the latter are prepared via either oxidative coupling or nucleophilic aromatic substitution approaches. Polyethers that contain both aromatic and aliphatic units in their backbone are far less common. This review will discuss some of the recent advances in the preparation of polyethers, primarily focussing on those where the ether linkage is generated during polymerization. Although the standard ring‐opening polymerization (ROP) route toward aliphatic polyethers has witnessed several interesting developments in recent years, it will not be covered in this review. The last section deals with a new melt‐transetherification approach for the preparation of poly(xylylene alkylene ether)s developed in our laboratory.     

Enzyme‐Catalyzed Ring‐Opening Polymerization of Unsubstituted β‐Lactam

The synthesis of poly(β‐alanine) by Candida antarctica lipase B immobilized as novozyme 435 catalyzed ring‐opening of 2‐azetidinone is reported. After removal of cyclic side products and low molecular weight species pure linear poly(β‐alanine) is obtained. The formation of the polymer is confirmed with ¹H NMR spectroscopy and MALDI‐TOF mass spectrometry. The average degree of polymerization of the obtained polymer is limited to = 8 by its solubility in the reaction medium. Control experiments with β‐alanine as a substrate confirmed that the ring structure of the 2‐azetidinone is necessary to obtain the polymer.

     

Cyclic polymers: Synthetic strategies and physical properties

Syntheses of cyclic polymers including cyclic homopolymers, cyclic block copolymers, sun‐shaped polymers, and tadpole polymers are discussed on the basis of a differentiation between synthetic methods and synthetic strategies (e.g., polycondensation, ring–ring equilibration, or ring‐expansion polymerization). Furthermore, all synthetic methods are classified as kinetically or thermodynamically controlled reactions. Characteristic properties of cyclic polymers such as smaller hydrodynamic volume, lower melt viscosities, and higher thermostabilities are compared to the properties of their linear counterparts. Furthermore, the nanophase separation of cyclic diblock copolymers is discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 251–284, 2010     

Functional benzoxazines containing ammonium salt of carboxylic acid: Synthesis and highly activated thermally induced ring‐opening polymerization

1,3‐Benzoxazine monomers having ammonium salt of carboxylic acid have been developed. These 1,3‐benzoxazines 1a and 1b were easily synthesized from the corresponding tetrabutylammonium salts of glycine and β‐alanine, respectively. The glycine‐derived benzoxazine 1a exhibited remarkably high reactivity, which allowed its thermally induced ring‐opening polymerization in bulk at 100 °C, at which N‐methyl‐1,3‐benzoxazine 1d did not undergo the polymerization at all. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Sustainable Chiral Polyamides with High Melting Temperature via Enhanced Anionic Polymerization of a Menthone‐Derived Lactam

Polyamides are very important polymers that find applications from commodities up to the automotive and biomedical sectors, and their impact is continuously growing. The synthesis of structurally significant, chiral, and sustainable polyamides is described via a new, convenient, and solvent‐free anionic polymerization of a biobased ε‐lactam, which is obtained from the renewable terpenoid ketone l ‐menthone in a one‐step synthesis. These polyamides are shown to have outstanding structural and thermal properties, which are thus introduced via the structure and chirality of the natural lactam monomer and which are discussed and compared with those of petroleum‐based, established, and commercial polyamide Nylon‐6. X‐ray data reveal a remarkable degree of crystallinity in these green polymers and emphasize the impact of their structural features on the resulting properties.

     

Ring‐opening polymerization of 6‐hydroxynon‐8‐enoic acid lactone: Novel biodegradable copolymers containing allyl pendent groups

This article reports the synthesis and copolymerization of 6‐hydroxynon‐8‐enoic acid lactone. The ring‐opening polymerization of this lactone‐type monomer bearing a pendant allyl group led to new homopolymers and random copolymers with ε‐caprolactone and L ,L ‐lactide. The copolymerizations were carried out at 110 °C with Sn(Oct)₂ as a catalyst. The introduction of unsaturations into the aliphatic polyester permitted us to carry out different chemical transformations on this family of polymers. For example, this article reports the bromination, epoxidation, and hydrosylilation of the allyl group in the new polyester copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 870–875, 2000     

Three‐arm star block copolymers of ε‐caprolactone and acrylic acid: Synthesis and micellization behavior

A series of well‐defined three‐arm star poly(ε‐caprolactone)‐b‐poly(acrylic acid) copolymers having different block lengths were synthesized via the combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, three‐arm star poly(ε‐caprolactone) (PCL) (M_n = 2490–7830 g mol^?1; M_w/M_n = 1.19–1.24) were synthesized via ROP of ε‐caprolactone (ε‐CL) using tris(2‐hydroxyethyl)cynuric acid as three‐arm initiator and stannous octoate (Sn(Oct)₂) as a catalyst. Subsequently, the three‐arm macroinitiator transformed from such PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBuA) to construct three‐arm star PCL‐b‐P^tBuA copolymers (M_n = 10,900–19,570 g mol^?1; M_w/M_n = 1.14–1.23). Finally, the three‐arm star PCL‐b‐PAA copolymer was obtained via the hydrolysis of the PtBuA segment in three‐arm star PCL‐b‐P^tBuA copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance (¹H NMR), and Fourier transform infrared spectroscopy. The aggregates of three‐arm star PCL‐b‐PAA copolymer were studied by the determination of critical micelles concentration and transmission electron microscope. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Chain‐growth condensation polymerization approach to synthesis of well‐defined polybenzoxazole: Importance of higher reactivity of 3‐amino‐4‐hydroxybenzoic acid ester compared to 4‐amino‐3‐hydroxybenzoic acid ester

Application of chain‐growth condensation polymerization (CGCP) to obtain well‐defined polybenzoxazole (PBO) was examined. CGCP of both phenyl 3‐{(2‐methoxyethoxy)methoxy (MEM‐oxy)}‐4‐(octylamino)benzoate ( 1b ) (para‐substituted monomer) and phenyl 4‐MEM‐oxy‐3‐(octylamino)benzoate ( 3b ) (meta‐substituted monomer) was examined in the presence of metal disilazide base and phenyl 4‐nitro‐ or methylbenzoate 2 as an initiator. Polymerization of the latter monomer, but not the former, afforded polymer with controlled molecular weight based on the feed ratio of monomer to initiator and with a narrow molecular weight distribution. Accordingly, monomer 3c , in which the octyl group on the amino nitrogen of 3b was replaced with a 4‐(octyloxy)benzyl (OOB) group, was polymerized in the presence of lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS), phenyl 4‐methylbenzoate ( 2b ), and LiCl in THF at 0 °C to yield poly 3c with well‐defined molecular weight (M_n = 4520–9080) and low polydispersity (M_w/M_n ≤ 1.11). Treatment of poly 3c with trifluoroacetic acid simultaneously removed the MEM and OOB groups, affording poly(o‐hydroxyamide) (poly 4 ) without scission of the amide linkages. Cyclodehydration of poly 4 proceeded at 350 °C to yield PBO (poly 5 ), which was insoluble in organic solvents and acids. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1730–1736     

Simultaneous Chain‐Growth and Step‐Growth Polymerization—A New Route to Cyclic Polymers

Reinvestigation of numerous ring‐opening polymerizations by means of MALDI‐TOF mass spectrometry has evidenced that cyclic polymers were formed as the only reaction products or, at least, in large fractions. This finding is ascribed to the intermediate formation of difunctional chains having active end groups that can react with each other. Due to the low concentration of these difunctional chains cyclization is favored over chain extension according to the Ruggli–Ziegler dilution principle. A polymerization mechanism which usually favors the formation of cyclic polymers is the zwitterionic polymerization, but an exception from this rule is known. The following classes of monomers were discussed: α‐amino acid, N‐carboxyanhydrides (oxazolidine‐2,5‐diones), dithiolane‐2,4‐diones, 5,5‐dimethyl‐1,3,2‐dioxathiolan‐4‐one‐2‐oxide, salicylic acid O‐carboxyanhydride, L ‐lactide and D ,L ‐lactide, hexamethyl cyclotrisiloxane, and macrocyclic dithiocarbamates.

     

Phosgene‐free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α‐amino acids

We report a useful synthetic method of polypeptides using a series of urethane derivative of α‐amino acids (l ‐leucine, l ‐phenylalanine, l ‐valine, l ‐alanine, l ‐isoleucine, l ‐methionine), which are readily synthesized by N‐carbamoylation of tetrabutylammonium salts of α‐amino acids with diphenyl carbonate. Heating these urethane derivatives in N,N‐dimethylacetamide in the presence of n‐butylamine successfully gave the corresponding polypeptides with well‐defined structures through polycondensation with the elimination of phenol and CO₂. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigation showed that the resulting polypeptides had an n‐BuNH₂‐incorporated initiating end and an amino group at propagating end. These results strongly indicated that primary amines served as an initiator in this polycondensation system. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3726–3731     

Controlled synthesis and chemical modification of unsaturated aliphatic (Co)polyesters based on 6,7‐dihydro‐2(3H)‐oxepinone

A pure unsaturated cyclic ester, 6,7‐dihydro‐2(3H)‐oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with ?‐caprolactone (?CL) was initiated by aluminum isopropoxide [Al(OⁱPr)₃] at 0 °C as an easy way to produce unsaturated aliphatic polyesters with nonconjugated C?C double bonds in a controlled manner. The chain growth was living, as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer/initiator molar ratio. The polydispersity was reasonably low (weight‐average molecular weight/number‐average molecular weight ≤ 1.2). The homopolymerization of DHO2 was, however, not controlled because of fast intramolecular transesterification. Copolymers of DHO2 and ?CL were quantitatively oxidized with the formation of epoxides containing chains. The extent of the epoxidation allowed the thermal properties and thermal stability of the copolyesters to be modulated. The epoxidized copolyesters were successfully converted into thioaminated chains, which were then quaternized into polycations. No degradation occurred during the chemical modification. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2286–2297, 2002     

Polymerization of epoxidized vegetable oil derivatives: Ionic‐coordinative polymerization of methylepoxyoleate

Ring‐opening polymerization of epoxidized methyloleate (EMO) with various ionic‐coordinative initiators have been studied and compared with other internal epoxy monomers: benzyl 9,10‐epoxyoleoylether and cis‐4,5‐epoxyoctane. The structure and molecular weight of the resulting polymers have been studied by ¹H‐ and ¹³C‐NMR, MALDI‐TOF‐MS, and size exclusion chromatography analysis. Polymers with higher molecular weight than those obtained with conventional cationic catalyst are obtained. These materials have been found to consist of a complex mixture of cyclic and linear polymer chains with different chain ends that can be related to the catalyst nature and the occurrence of two main polymerization mechanisms, the cationic and the ionic‐coordinative. In the polymerization of EMO, transesterification by‐side reactions leading to ester linkages in the main chain have been identified. These undesired reactions have been suppressed by copolymerization with small amounts of tetrahydrofuran with no substantial decrease in the polymer yield and molecular weight. Finally, the polymerization of EMO has been tested in a larger scale to prepare a renewable resource‐based polyether as starting material to produce polyether polyols for polyurethane applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Poly(thioester)s

Syntheses and properties of aliphatic and aromatic polythioesters (PTEs) were reviewed including polythiocarbonates and polythiourethanes. The content is subdivided into the following sections: PTEs of aliphatic α‐mercapto carboxylic acid, PTEs of ω‐mercapto carboxylic acids, PTEs derived from α,ω‐dimercapto alkanes, aromatic poly(thioester)s, aliphatic poly(thiocarbonate)s, aliphatic poly(thiourethane)s and aromatic polythiocarbonates. The synthetic strategies reviewed in this article include anionic and cationic ring‐opening polymerizations, polycondensations in bulk, polycondensations in solutions, interfacial polycondensations and in vitro enzymatic polycondensations.     

Novel Aliphatic Polyesters Based on Functional Cyclic (Di)Esters

Recent progress in the chemical synthesis of novel aliphatic polyesters via ring‐opening polymerization of functional cyclic (di)esters are reviewed in this article. Syntheses of these functional aliphatic polyesters are being classified into three groups according to the structure of the cyclic monomers: (i) cyclic diesters, (ii) morpholine‐2,5‐dione derivatives, and (iii) cyclic esters. Progress in the synthesis and polymerization of monomers in each category is reported with an emphasis on controlled synthesis. The recent achievements have enabled the synthesis of a variety of novel aliphatic polyesters, including hydrophilic, halogenated, and unsaturated polyesters.

Structure of the most common R‐functionalized cyclic precursors of aliphatic polyesters.     

Cyclic poly(lactide)s via the ROPPOC method catalyzed by alkyl‐ or aryltin chlorides

A comparison of tributyltin chloride, dibutyltin dichloride, and butyltin trichloride as catalysts of ring‐opening polymerizations (ROPs) of l‐lactides at 160 °C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu₃SnCl, yield a uniform reaction product, namely cyclic poly(L‐lactide)s with weight average molecular weights (M_w's) in the range of 40,000–80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me₂SnCl₂ < Bu₂SnCl₂ < <Ph₂SnCl₂. In this series also, the most reactive catalyst yields cyclic polylactides, but the extent of cyclization varies with the molecular weight. The formation of cyclic polylactides is explained by ROP combined with simultaneous polycondensation involving end‐to‐end cyclization (ROPPOC method). ROP of meso‐lactide at 80 or 60 °C yields even‐numbered linear chains as main products, a result supporting the ROPPOC mechanism. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 952–960     

Controllable synthesis of bio‐based polylactide diols using an organocatalyst in solvent‐free conditions

Controllable synthesis of bio‐based polylactide (PLA) diols was realized by the ring‐opening polymerization (ROP) of lactide (LA) in the presence of 1,4‐butanediol (BDO) using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as an organocatalyst in solvent‐free conditions. The catalytic activity and conversion of LA could reach ∼1 kg g⁻¹ DBU and >97%, respectively, and the polymerization yielded polymers with narrow polydispersity index (PDI) (1.15–1.29). Interestingly, the number average molecular weight (M_n) of the obtained PLA diol was in excellent linear relation with the molar ratio of LA and BDO, and hence can be precisely controlled. The structure of the diol was clearly confirmed by ¹H and ¹³C NMR, FTIR, and MALDI‐TOF mass spectra, proving BDO as an initiation‐transfer agent to participate in the polymerization. Kinetic study of the ROP demonstrates a pseudo‐first‐order kinetic model and a controlled “living” nature. Notably, it is found that the glass transition temperature (T_g) of the diol significantly depends on the M_n. Furthermore, various chain transfer agents and organocatalysts can also be used to successfully synthesize well‐defined PLA diols. Especially, functional bio‐based dihydric alcohols such as 2,5‐furandimethanol (FDMO)‐initiated ROP in this system could result in fully bio‐based PLA diols with functionality. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 968–976     

Novel Photoresponsive Linear,Graft, and Comb‐Like Copolymers with Azobenzene Chromophores in the Main‐Chain and/or Side‐Chain: Facile One‐Pot Synthesis and Photoresponse Properties

Novel photoresponsive linear, graft, and comb‐like copolymers with azobenzene chromophores in the main‐chain and/or side‐chain are prepared via a sequential ring‐opening metathesis polymerization (ROMP) and head‐to‐tail acyclic diene metathesis (ADMET) polymerization in a one‐pot procedure using Grubbs ruthenium‐based catalysts. The diluted solutions of these as‐prepared copolymers containing azobenzene chromophores exhibit photochemical trans–cis isomerization under the irradiation of UV light, followed by their cis–trans back‐isomerization in visible light. The rates of photoisomerization are found to be slower than those of back‐isomerization, and the rate for the comb‐like copolymer is found to be from 3 to 7 times slower than that obtained for the linear or graft copolymer. This is ascribed to the differences in structure of the copolymers and the specific location of azobenzene chromophores in the copolymer, which favor a side‐chain graft structure.