Lipase‐catalyzed ring‐opening polymerization and copolymerization of cyclic dicarbonates

Ring‐opening polymerization of cyclic dicarbonates, cyclobis(hexamethylene carbonate) ( 1 a ) and cyclobis‐ (diethylene glycol carbonate) ( 1 b ), and their copolymerization with lactones have been carried out using lipase as catalyst. These carbonates were polymerized by Candida antarctica lipase under mild reaction conditions to give the corresponding polycarbonates. The enzymatic copolymerization with lactones proceeded to produce ester‐carbonate copolymers. The copolymerization of 1 b with 12‐dodecanolide produced the random copolymer, whereas the copolymer from 1 a and 12‐dodecanolide was not statistically random.     

Inter‐ and intramolecular ester exchange reactions in the ring‐opening polymerization of (D,L)‐lactide using lanthanide alkoxide initiators

Polylactide samples obtained by the ring‐opening polymerization of (D ,L )‐lactide by using different lanthanide alkoxide initiators were examined by SEC, ¹³C NMR and MALDI‐TOF MS techniques. The evidence of substantial transesterification was observed in the case of a polymerization initiated by lanthanum alkoxide and bimetallic aluminium‐yttrium alkoxide initiators. In the case of Y and Sm alkoxide initiators, the MWD remains narrow up to high conversions for reasonable polymerization times, but the prolongation of the post‐polymerization time increases the amount of ester‐exchange reactions. The extent of the transesterification reactions was evaluated on the basis of the intensity of the stereosequence resonances for the methine carbon signal in the ¹³C NMR spectra. MALDI‐TOF MS analysis revealed the presence of odd‐membered oligomers in all spectra. Thus, transesterification reactions occur from the beginning of the polymerization. Linear and cyclic oligomers were detected in some cases indicating the simultaneous occurrence of inter‐ and intramolecular exchange reactions. The microstructure analysis of the polymers by ¹³C NMR spectroscopy indicates a preference for a syndiotactic addition during the polymerization process.     

Preparation and characterization of poly(methyl-3,3,3-trifluoropropylsiloxane-co-dimethylsiloxane)

Methyl-3,3,3-trifluoropropylsiloxane (F)-dimethylsiloxane (D) random and block copolymers were prepared. The random copolymers were prepared by equilibrium copolymerization starting from a mixture of cyclic F and D siloxanes with potassium silanolate as the catalyst. The F-D block copolymer was prepared by sequential anionic living polymerization of strained cyclic trisiloxanes using butyllithium as initiator, first polymerizing D₃ then adding F₃ after consumption of D₃. The copolymer microstructure was established by means of ²⁹Si NMR, differential scanning calorimetry (DSC), and gel-permeation chromatography (GPC). Characteristic glass transition temperature (T_g) shifts were observed depending on the F:D ratio of the random copolymers. It was demonstrated that the tensile strength of the poly(methyl-3,3,3-trifluoropropylsiloxane)-poly(dimethylsiloxane) (PTFPMS-PDMS) blend system was improved when either of the copolymers was added.     

Novel block copolymers of 2‐vinylpyridine and ε‐caprolactone: Synthesis and characterization

Novel block copolymers based on 2‐vinylpyridine (2VP) and ε‐caprolactone (CL) have been synthesized via sequential anionic polymerization in tetrahydrofuran (THF). These block copolymers are expected to be promising pigment dispersing agents for TiO₂ in e. g. polyester powder coatings. Initiation of CL by the living P2VP polymer occurred instantaneously and without side reactions. Intramolecular transesterification reactions were not observed either. However, part of the living chains was deactivated immediately after the addition of CL, which yielded bimodal molecular weight distributions. This could be attributed to strong aggregation of the alkoxide chain ends. Addition of LiCl to the polymerization mixture prevented aggregation and resulted in well‐defined block copolymers. The block copolymers have been characterized with SEC, NMR and IR.     

Syntheses and Properties of Novel Copolymers of Poly(1,4‐dioxane‐2‐one) and Aliphatic Polycarbonate Based on Ketal‐Protected Dihydroxyacetone

Novel random copolymers of 1,4‐dioxane‐2‐one (DON) and 2,2‐ethylenedioxy‐1,3‐propanediol carbonate (EOPDC) are synthesized in bulk at 120 °C using Sn(Oct)₂ as a catalyst. The effects of different molar feed ratios of EOPDC/DON on the yield and molecular weight of the copolymers are investigated. The copolymers are obtained with a yield of 55.4–98%. The number‐average molecular weight of the copolymer is 0.49–4.18 × 10⁴ g mol^?1 with a polydispersity of 1.52–1.68. The poly(DON‐co‐EOPDC)s obtained are characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, gel‐permeation chromatography (GPC), and DSC. The hydrolytic degradation of the copolymer in phosphate buffered saline (PBS) is also investigated. The results show that both the hydrophilicity and the degradation rate of the copolymers increase with increasing copolymer DON content.     

Le poly(α-acétoxystyrène) et les copolymères de l'α-acétoxystyrène avec le styrène et styrènes substitués obtenus par polymérisation thermique. Etude de la microstructure et de la stabilité thermique des polymères

The microstructure of poly(α-acetoxystyrene), prepared from α-acetoxystyrene by bulk thermal polymerization, was studied by ¹H and ¹³C NMR spectroscopy. Anomalies observed in the NMR spectra could be ascribed to fragmentations with formation of benzoxy and acetoxy radicals followed by re-initiation. The thermal degradation of the polymer, resulting in the formation of polyphenylacetylene, rules out certain types of transfer. α-Acetoxystyrene was copolymerized with styrene or substituted styrenes and the NMR study (¹H and ¹³C) was limited to α-acetoxystyrene. The composition of the copolymer could be ascertained by means of the resonances of the quaternary carbons of the aromatic cycle. The copolymers were characterized by viscometry, GPC, and thermal degradation. Their compositions, except that of poly(α-acetoxystyrene-co-styrene) were determined by elemental analysis.     

Effects of Poly(N‐isopropylacrylamide) (PNIPAAm) on the Conformational Change of Poly(N 5‐hydroxyalkyl glutamine) (PHAG) in PHAG‐PNIPAAm Block Copolymer with Temperature

Diblock copolymers consisting of poly(N ⁵‐hydroxyalkylglutamine) (PHAG) and poly(N‐isopropylacrylamide) (PNIPAAm) were prepared by aminolysis with aminoalkanols of the side‐chain ester of poly(γ‐benzyl L ‐glutamate) (PBLG) as a part of PBLG‐PNIPAAm block copolymers. The molecular weight ratio of the initial PBLG to the resulting PHAG was nearly 0.35. The effect of PNIPAAm on the conformational change of PHAG in PHAG‐PNIPAAm block copolymers with temperature was investigated by circular dichroism. Poly[N ⁵‐(2‐hydroxyethyl)‐L ‐glutamine] (PHEG) and the PHEG‐PNIPAAm copolymer (GNE) stayed in a randomly coiled conformation whereas poly[N ⁵‐(3‐hydroxypropyl)‐L ‐glutamine] (PHPG), poly(N ⁵‐(4‐hydroxybutyl)‐L ‐glutamine) (PHBG), PHPG‐PNIPAAm copolymer (GNP), and PHBG‐PNIPAAm copolymer (GNB) underwent conformational transitions with temperature. The conformational change of the PHPG block in GNP copolymer occurred from an α‐helix to a random coil after the incorporation of PNIPAAm into the copolymer. The thermodynamic parameters of the thermally induced helix‐coil transition for PHBG and PHBG‐PNIPAAm in aqueous solution were calculated.     

Polymerization of Vinyl Acetate Initiated with Di‐tert‐butyl Perfumarate

The polymerization behavior of vinyl acetate ( 2 ) was studied in benzene using di‐tert‐butyl perfumarate ( 1 ) as an initiator. Low molecular weight polymer (M̄_n ≈ 3 000) is formed in the early stage of polymerization where 1 is substantially consumed by thermal decomposition, copolymerization with 2 , and chain transfer reactions through an addition‐substitution mechanism. As a result, the low molecular weight polymer formed in the early stage of polymerization contains five peroxy ester groups per polymer molecule. Then, the polymerization of 2 initiated with the low molecular weight polymer further proceeds to yield high molecular weight poly( 2 ) (M̄_n = 2.5–23×10⁴). Decomposition of the peroxy ester group of 1 in benzene was studied in the absence and in the presence of methyl methacrylate (MMA) or 2 . The activation energy of decomposition of the peroxy ester group of 1 is 118 kJ/mol in the absence of the monomers. The decomposition of the peroxy ester group of 1 is highly accelerated in the presence of MMA. The peroxy ester groups derived from 1 decompose in two stages in the presence of 2 . In the first stage, some of them are rapidly consumed mainly by the chain transfer reaction. In the second stage, the peroxy ester groups of copolymer from 1 and 2 decompose slowly.     

Synthesis,Characterization and In Vitro Cytotoxicity of Poly[(5‐benzyloxy‐trimethylene carbonate)‐co‐(trimethylene carbonate)]

The ring‐opening copolymerization of 5‐benzyloxy‐trimethylene carbonate (BTMC) with trimethylene carbonate (TMC) was described. The polymerization was carried out in bulk at 150°C using stannous octanoate as initiator. The influence of reaction conditions such as polymerization time and initiator concentration on the yield and molecular weight of the copolymers were investigated. The poly(BTMC‐co‐TMC)s obtained were characterized by FT‐IR, ¹H NMR, ¹³C NMR, GPC and DSC. NMR results of copolymer showed no evidence for decarboxylation occurring during the propagation. The relationship between the copolymer glass transition temperature and composition was in agreement with the Fox equation. The in vitro cytotoxicity studies of the poly(BTMC‐co‐TMC) (50 : 50) using 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay demonstrated that the copolymer has low cytotoxicity compared to poly[(lactic acid)‐co‐(glycolic acid)] (75 : 25).     

cis‐Specific Living Polymerization of 1,3‐Butadiene with CoCl2 and Methylaluminoxane

The polymerization of 1,3‐butadiene was conducted by CoCl₂ combined with methylaluminoxane (MAO) as a cocatalyst at 0 and 18°C. The uni‐modal molecular weight distribution curves of the resulting polymers shifted toward higher molecular weight regions and became narrower when increasing the polymerization time. The number‐average molecular weight increased linearly with polymerization time, while the polymer yield increased exponentially in the initial stage. As a consequence, the number of polymer chains, calculated from the polymer yield and M̄_n, increased gradually with polymerization time to reach a plateau value. These phenomena was interpreted based on a slow initiation system without any termination and chain transfer reaction. The microstructure of the polymer was determined by ¹H NMR and ¹³C NMR spectroscopy to be a cis‐1,4 structure in a 98–99% purity.     

Low Surface Energy Perfluorooctyalkyl Acrylate Copolymers for Surface Modification of PET

Summary: Copolymers of ω‐perfluorooctyalkyl acrylate C₈F₁₇‐(CH₂)_n′OC(O)CH?CH₂ with butyl acrylate were prepared by free radical polymerization. These compounds were characterized by ¹H and ¹⁹F NMR spectroscopy. Thermal properties were evaluated by DSC and TGA analysis. By changing the fluorinated monomer structure, i.e., the length of the hydrocarbon spacer between the perfluorinated side chain and the ester function, and the concentration of the perfluorooctyalkyl acrylate monomers, the surface properties of the resulting copolymers were greatly influenced. The copolymers exhibited low surface energies, the lowest recorded being 6 mJ · m^?2. XPS analysis indicated fluorine enrichment at the polymer‐air interface.

Molecular structure of the synthesized copolymer.     

Highly Water‐Soluble Rod–Coil Conjugated Block Copolymer for Efficient Humidity Sensor

In this report, the preparation of highly water‐soluble rod–coil conjugated block copolymer poly(3‐hexylthiophene)‐b‐polystyrenesulfonic acid (P3HT‐b‐PSSA) is demonstrated using a facile method with its moisture sensing properties. The block copolymer synthesis method comprises Kumada catalyst transfer polymerization and atom transfer radical polymerization from a bifunctional initiator followed by sulfonation of polystyrene using moderate reaction conditions. The polymerization results in the synthesis of well‐defined block copolymers with controllable block length. The successful synthesis of the block copolymer is studied by NMR and FTIR spectroscopy while optical and structural properties of the block copolymer are investigated using UV–vis, photoluminescence spectroscopy, XRD, and FESEM. In water, the block copolymer shows aggregated structure with crystalline core formed by rod‐like P3HT chain with absorption maxima at 558 nm, whereas in solid state the absorption maxima is blue shifted to 548 nm. The proton conductivity of the block copolymer P3HT‐b‐PSSA with ≈91% of PSSA (by weight) is measured from impedance study, and the values for bulk and grain conductivities are 5.25 × 10^?4 and 4.66 × 10^?6 S cm^?1, respectively, at room temperature. The as‐synthesized block copolymer shows a very high water uptake with maximum ≈80% in comparison with its initial weight. The I–V measurement of the device made from block copolymer shows nonlinear, rectifying characteristic and the current increases with increase of relative humidity (RH%). The block copolymer device shows well‐correlated systemic and reversible resistance change with RH both in doped and undoped state. It is believed that the interesting and highly reversible moisture‐sensitive electronic properties of this block copolymer will be useful for the fabrication of moisture‐sensitive polymer‐based flexible electronic devices.     

Copolymerization of glycolide and ϵ-caprolactone, 1. Analysis of the copolymer microstructure by means of 1H and 13C NMR spectroscopy

A detailed analysis of the structure of glycolide/ε-caprolactone copolymers was performed using ¹³C and ¹H NMR. All methylene and carbonyl carbons of glycolidyl and caproyl units in the ¹³C NMR spectra were found to be sensitive to the microstructure. The ¹H NMR spectra allow not only to determine the copolymer composition but also to analyze the chain microstructure. In the region of methylene protons of glycolide the resonance lines were ascribed to a series of compositional sequences, including those formed as a result of transesterification reactions. Equations are presented which allow to calculate the average lengths of comonomer blocks, the extent of transesterification, and the degree of randomness of the chain from both carbon and proton NMR spectra.     

Synthesis of Methacrylate‐Terminated Block Copolymers with Reduced Transesterification by Controlled Ring‐Opening Polymerization

This work presents a robust method to achieve the synthesis of low molecular weight polyesters via ring‐opening polymerization (ROP) initiated by 2‐hydroxyethyl‐methacrylate (HEMA) when using triazabicyclodecene (TBD) as catalyst. The effect that the HEMA:TBD ratio has upon the final reaction rate and final polymer molecular architecture is discussed. The optimum HEMA:TBD ratio and reaction conditions required to minimize competing transesterification reactions are determined, in order to synthesize successfully the target ROP macromonomer species containing only a single 2‐methacryloyloxyethyl end‐group. Additionally, to confirm the terminal end‐group fidelity of the product macromonomers and confirm TBD utility for block copolymer manufacture, a small series of di‐block polyesters are synthesized using TBD and shown to exhibit good control over the final polymer structure whilst negating the side transesterification reactions, irrespective of the monomers used.     

Synthesis of ethylene‐α‐olefin alternating copolymers with Et(1‐Ind)(9‐Flu)ZrCl2‐MAO catalyst system

Copolymerizations of ethylene and α‐olefins (4‐methyl‐1‐pentene, 1‐hexene, 1‐decene and 1‐hexadecene) were carried out with Et(1‐Ind)(9‐Flu)ZrCl₂‐MAO as the catalyst system. The degree of alternation in the resulting copolymers is higher than 92.1% for all the copolymers and close to 100% for ethylene‐1‐decene copolymer. Copolymerization behaviours focusing on the misinsertions during the polymerizations are investigated in detail from dyad and triad distributions estimated by ¹³C NMR analysis of copolymers. A reactivity ratio, r^B_E, was obtained for ethylene‐1‐hexene copolymers using a simplified two sites alternating mechanism and found to be 8.7, which is the same order of that reported in ethylene‐propene copolymerizations with Me₂C(3‐RCp)(Flu)ZrCl₂‐MAO as the catalyst system.     

Sodium Poly(α,L‐glutamate)/Ethylene Oxide‐Propylene Oxide (Block and Random) Copolymer Macromolecular Complexes. Method of Preparation and Structure of Complex

Macromolecular complexes of sodium poly(α,L ‐glutamate) (PGNA) (molecular weight (MW) 1, 49 and 71 k) and ethylene oxide‐propylene oxide tri‐block copolymer (MW 8 400) have been prepared by a novel method involving dehydration of reverse micelles (DRM method). This series of complexes was compared with the complexes of PGNA (MW 1, 49 and 71 k)/ethylene oxide‐propylene oxide random and tri‐block copolymers prepared by the common method involving evaporation of aqueous mixtures (EAM method). By the DRM process fifteen times more copolymer was incorporated in the pure macromolecular complex than by the EAM process. CD spectra of the EAM series of complexes showed formation of α‐helical PGNA conformation as evidenced by the observation of +ve peak at 194 nm and two –ve peaks at 201 and 221 nm. Formation of the α‐helical conformation is further supported by FT‐IR spectroscopy. On the other hand, CD spectra of the DRM macromolecular complexes showed neither α‐helical nor random conformation, and the spectra may be attributed to a distorted helical PGNA conformation. DSC studies revealed that the copolymers in EAM macromolecular complexes were intimately blended with PGNA, while in the DRM series only 65% of the copolymer were blended at the molecular level, with the rest present as a pure copolymer domain. ²³Na NMR spectra of both series of complexes showed presence of free sodium ions indicative of dissociated Na⁺—O dipolar interactions in aqueous solution. Hydrophobic interaction between PGNA and copolymer remained intact even in very dilute solutions of both series of complexes as observed by strong 2D‐NOESY ¹H NMR correlation between β and γ CH₂ groups of PGNA and CH₂ groups of copolymers. However, in the DRM series, only the CH₂ groups of PEO blocks of the PEO‐PPO‐PEO copolymer showed the 2D‐NOESY ¹H NMR correlation indicating that only the PEO blocks are involved in the complex formation. The PPO block that had no interaction with PGNA may have formed pure PPO domains. NMR data combined with the DSC, CD and FT‐IR data suggest that the structure of both series of macromolecular complex is a composite composed of copolymer molecules intimately interacting with PGNA chains. Interactions between β and γ groups of PGNA side groups with CH₂ groups of the copolymer are involved in forming the complex. 2D‐NOESY ¹H NMR correlation further indicate that both the DRM and EAM series of macromolecular complexes are stable in water for at least seven weeks.     

Synthesis and 13C CP MAS NMR spectroscopy of cellulose‐graft‐poly(N‐acetylethylenimine)

Starting from homogeneously prepared tosyl celluloses with DS_Tos values ranging from 0.2 to 1.8 poly(N‐acetylethylenimine) was grafted onto the cellulose backbone. Tosyl moieties served as starting centers for the living ring opening polymerization using 2‐methyl‐1,3‐oxazoline as the monomeric unit. The grafted products could be characterized by IR and ¹³C CP MAS NMR spectroscopy clearly indicating the loss of tosyl moieties as well as the occurrence of the N‐acetylethylenimine residues. ¹³C CP MAS NMR spectroscopy was also found to be an efficient tool for the quantification of grafted polymer after determination of the relaxation behavior of the various nuclei. Thus the grafting efficiency could be controlled by the DS_Tos of the starting tosyl celluloses, whereas the amount of monomer showed only a minor influence on the grafting density.     

One‐Pot Synthesis of Polyester–Polyolefin Copolymers by Combining Ring‐Opening Polymerization and Carbene Polymerization

The ring‐opening polymerization (ROP) of a cyclic ester using alkyl acetate carbene (ROCOCH:) is generated from diazoacetate as organocatalyst under microwave irradiation, which enables the one‐pot preparation of copolymers of polyester and polyolefin. The chemical structure of the polymerized product is characterized by NMR, Fourier transformed infrared (FTIR), and UV–vis spectroscopy. The incorporation of the azo group into the obtained copolymer is determined by elemental analysis, which indicates that 1.38–6.21% nitrogen is contained in the obtained copolymers. The influences of catalyst and microwave irradiation parameters on the polymerization are investigated. Both the microwave power and irradiation time have great influences on the copolymerization. Moreover, the molar mass of the obtained polymers is calculated with polystyrene standards, which gradually increases from 600 to 36 100 g mol^?1 as the reaction temperature increases from 60 to 120 °C. Poly­mer with of 36 100 g mol^?1 and PDI of 1.86 is produced under optimized conditions. The combination of ROP and carbene polymerization offers a new and convenient pathway to synthesize copolymers of polyesters and polyolefins.

     

Catalytic Oxyfunctionalization of Methyl 10‐undecenoate for the Synthesis of Step‐Growth Polymers

An efficient synthesis strategy for the preparation of two renewable polyesters and one renewable polyamide via catalytic oxyfunctionalization of methyl 10‐undecenoate, a castor oil derived platform chemical, is described. The keto‐fatty acid methyl ester (keto‐FAME) is synthesized applying a cocatalyst‐free Wacker oxidation process using a high‐pressure reactor system. For this purpose, catalytic amounts of palladium chloride are used in the presence of a dimethylacetamide/water mixture and molecular oxygen as sole reoxidant. The thus derived AB monomers (hydroxy‐esters, amine‐ester) are synthesized from the obtained keto‐FAME through Baeyer–Villiger oxidation and subsequent transesterification, reduction, or reductive amination, respectively. The resulting AB step‐growth monomers are then studied in homopolymerizations using 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene, DBU, and titanium(IV) isopropoxide as transesterification catalyst, yielding polymers with molecular weights (M _n) up to 15 kDa. The polyesters and the polyamide are carefully characterized by FTIR, SEC, ¹H‐NMR spectroscopy, and differential scanning calorimetry analysis.

     

Bioinspired All‐Polyester Diblock Copolymers Made from Poly(pentadecalactone) and Poly(2‐(2‐hydroxyethoxy)benzoate): Synthesis and Polymer Film Properties

The bioinspired diblock copolymers poly(pentadecalactone)‐block‐poly(2‐(2‐hydroxyethoxy)benzoate) (PPDL‐block‐P2HEB) are synthesized from pentadecalactone and dihydro‐5H‐1,4‐benzodioxepin‐5‐one (2,3‐DHB). No transesterification between the blocks is observed. In a sequential approach, PPDL obtained by ring‐opening polymerization (ROP) is used to initiate 2,3‐DHB. Here, the molar mass M_n of the P2HEB block is limited. In a modular approach, end‐functionalized PPDL and P2HEB are obtained separately by ROP with functional initiators, and connected by 1,3‐dipolar Huisgen reaction (“click‐chemistry”). Block copolymer compositions from 85:15 mass percent to 28:72 mass percent (PPDL:P2HEB) are synthesized, with M_n of from about 30 000–50 000 g mol^?1. The structure of the block copolymer is confirmed by proton NMR, Fourier‐transform infrared spectroscopy, and gel permeation chromatography. Morphological studies by atomic force microscopy (AFM) further confirms the block copolymer structure, while quantitative nanomechanical AFM measurements reveal that the Derjaguin–Muller–Toporov moduli of the block copolymers range between 17.2 ± 1.8 and 62.3 ± 5.7 MPa, i.e., between the values of the parent P2HEB and PPDL homopolymers (7.6 ± 1.4 and 801 ± 42 MPa, respectively). Differential scanning calorimetry shows that the thermal properties of the homopolymers are retained by each of the copolymer blocks (melting temperature 90 °C, glass transition temperature 36 °C).