Polylactones, 2 Copolymerization of glycolide with β-propiolactone, γ-butyrolactone or δ-valerolactone

Numerous copolymerizations of glycolide with β-propiolactone, γ-butyrolactone or δ-valerolactone were conducted either in bulk or in nitrobenzene solution at temperatures in the range of 20 to 150°C. Three classes of catalysts were used, namely acidic catalysts initiating cationic polymerizations, complexing catalysts initiating insertion mechanisms, and anionic catalysts. The molar composition of the copolyesters was determined from ¹H NMR spectra and the sequence distribution of the comonomers from ¹³C NMR spectra. No reasonable copolymerization of glycolide and βhyphen;propiolactone was obtained at 20°C in nitrobenzene, whereas all catalysts yielded copolyesters at 100°C. In the case of glycolide/γ-butyrolactone only bulk copolymerizations at 60°C with acidic initiators were successful. Under other conditions only homopolymerization of glycolide was observed. Copolymerizations of glycolide and γ-valerolactone were performed in bulk and in nitrobenzene with both acidic and complexing initiators, whereas anionic initiators only caused homopolymerization of glycolide. Acidic initiators favored the incorporation of δ-valerolactone, whereas the complexing initiators favored the incorporation of glycolide. The crystallinity of the glycolide/δ-valerolactone copolymers was characterized by means of differential scanning calorimetry, and a good agreement with the expectations from both molar composition and sequence distribution was found.     

Crystallization of polypeptides in the course of polymerization, 7. Crystallization of poly(γ-methyl-L-glutamate), poly(γ-benzyl-L-glutamate) and poly(β-benzyl-L-aspartate)

Heterogeneous polymerizations of γ-methyl-L -glutamate N-carboxy anhydride (NCA), γ-benzyl-L -glutmate NCA, and β-benzyl-L -aspartate NCA were carried out using butylamine as initiator in acetonitrile at 30°C. The oligomer chains formed in the beginning of the polymerization crystallized into the antiparallel β-form and thereafter the α-helical chains grew from the active sites of the β-chains. The polymerization of γ-methyl-L -gultamate NCA proceeded to 100% conversion and accordingly gave rise to high molecular weight poly(γ-methyl-L -glutamate). The polymerizations of γ-benzyl-L -glutamate NCA and β-benzyl-L -aspartate NCA stopped at 54% and 16%, resp. The levelling-off of the conversion at such low values, in spite of the α-helical chain growth, may be due to the occlusion of the active chain ends of the resultant poly(γ-benzyl-L -glutamate) and poly(β-benzyl-L -aspartate) into the crystals. It was concluded that the interlamellar crystallization was induced by the intermolecular interaction between the benzyl groups of the polymer side chains, giving rise to the occlusion of the active growing chain ends into the interstices of the crystal formed during the polymerization.     

Spontaneous copolymerization of 1-(2-hydroxyethyl)aziridine with β-butyrolactone, 14

The copolymerization of 1-(2-hydroxyethyl)aziridine ( 1 ) as nucleophilic monomer with β-butyrolactone ( 2 ) as electrophilic monomer without initiator in solution at 45°C was investigated. Copolymers were characterized by IR and ¹H NMR spectroscopy. By elemental analyses it could be shown that their compositions depend on the monomer ratio in the feed. From the copolymer composition and ¹H NMR spectra it was possible to suggest four probable copolymer structures.     

Investigation of γ-irradiated syndiotactic poly(2-methylheptyl methacrylate) using NMR spectroscopy

Syndiotactic poly(2-methylheptyl methacrylate) which was γ-irradiated at room temperature to a dose of 1600 kGy was investigated by NMR spectroscopy. The ¹H and ¹³C resonances for the macromolecular chain were assigned by using the 2D and the DEPT (distortionless enhancement by polarization transfer) technique. The spin-echo modified 2D NMR pulse sequence was used to investigate the small molecules and new structures which were formed during γ-irradiation. The radiation mechanisms for cleavage of the side chain from the main chain and formation of double bonds from both the main chain and the side chain have been formulated based upon the NMR analysis.     

Preparation,properties and biodegradation of stereoregular copolymers of (R,S)-3-butyrolactone and 4-butyrolactone

Copolymers obtained from the copolymerization of (R,S)-3-butyrolactone ((R,S)-3-BL) and 4-butyrolactone (4-BL) catalyzed by isobutylaluminoxane were compared in structure and properties to copolymers having the same types of repeating units produced by Alcaligenes eutrophus when grown with an appropriate substrate or substrate or substrate mixtures. Copolymers with 4-BL contents up to 33 mol-% were prepared and characterized by ¹H NMR, ¹³C NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The copolymers had a sequence distribution of 3-hydroxybutyrate (3-HB) and 4-hydroxybutyrate (4-HB) units which were non-random in that very few, if any, sequences of more than two successive 4-HB units were present. The 3-HB units are believed to be separated into isotactic (R) and (S) blocks, but thermal analysis by DSC showed that both the glass transition temperatures and melting temperatures decreased in a regular manner with increasing contents of 4-HB units. Number average molecular weights of the copolymers (M _n) ranged from 7000 to 15000. Biodegradation tests with a bacterial hydrolase showed that the biodegradation rates increased with increasing contents of 4-HB units, as is the case for the equivalent bacterial copolymers.     

Synthesis and ring-opening polymerization of α-chloromethyl-α-methyl-β-propiolactone

α-Chloromethyl-α-methyl-β-propiolactone (CMMPL) was synthesized by dehydrohalogenation of α,α-dichloromethyl-β-propionic acid which was obtained by chlorination of α,α-hydroxymethyl-β-propionic acid (DMPA). Due to high strain of the four-numbered ring, CMMPL can be polymerized by ring-opening with or without an initiator. Both electrophiles like trifluoroacetic acid (TFAA) and nucleophiles like triethylamine (TEA) and pyridine, as well as organometallic compounds such as stannous octoate [Sn(Oct)₂)], aluminium triisopropoxide [Al(OⁱPr)₃] and tetrabutyl orthotitanate [Ti(OC₄H₉)₄], were found to be effective initiators. The polymerization can be conducted by either solution or bulk polymerization. P(CMMPL) is insoluble in almost all organic solvents at room temperature. An endothermic peak (ca. 214 ˜ 250°C) attributed to the melting transition of P(CMMPL) was observed in DSC curves. P(CMMPL) tends to have high crystallinity (40% ˜ 60%) as demonstrated by its X-ray diffraction patterns, and the crystallinity was found to vary with the types of initiator used.     

Polylactones, 7. The mechanism of cationic polymerization of β-propiolactone and ϵ-caprolactone

Homopolymerisations of β-propiolactone and ?-caprolactone, initiated by means of methyl trifluorosulfonate, triethyloxonium tetrafluoroborate or acetylium perchlorate, were investigated. Both ¹H and ¹³C NMR spectra proved that the alkylating initiators yield polyesters with alkyl ester end groups, indicating a chain growth via alkyl-oxygen cleavage of the lactone. At temperatures below 100°C cationic polymerizations initiated by alkylating reagents were found to proceed via end groups which may cause degradation due to back-biting. When ?-caprolactone was reacted with excess methyl triflate, high concentration of triflate ester end groups were formed, whereas in the case of β-propiolactone active end groups were not detectable by ¹H NMR spectroscopy. Initiation with acetylium perchlorate yielded a polyester with acetate end groups. Acetate end groups were also obtained, when “living” polymers, initiated with methyl triflate, were reacted with acetic anhydride. It could be shown that the formation of acetate end groups does not indicate an electrophilic attack at the endocyclic oxygen. Furthermore, it is discussed that any experimental evidence for a cationic chain growth via acyloxygen bond cleavage is lacking.     

Synthesis of α- and ω-norbornenyl-polybutadiene macromonomers and their ring-opening metathesis polymerization

Norbornene-ended polybutadiene (PBu) macromonomers have been prepared via two different routes: α-norbornenyl-polybutadiene was derived from a norbornene-containing carbanionic initiator, whereas ω-norbornenyl samples were obtained through deactivation of living polybutadienyl anions by a norbornene-based deactivator. Out of four alkylidene complexes tried, the molybdenum alkylidene complex that contains two alkoxide ligands was found to be the most suitable initiator for the ring-opening metathesis polymerization of these macromonomers.     

Synthesis of poly[isobutyl (2S,3R)-3-benzyloxyaspartate]

A chiral poly(3-substituted isobutyl D -aspartate) 12 was synthesized by polymerization of the chiral β-lactam 11 derived from D -glyceraldehyde. The new polyamide was characterized by elemental analyses, and infrared, ¹H- and ¹³C nuclear magnetic resonance spectroscopies. The molecular weight was estimated as 543 000 and 230 000 on the basis of viscosimetric measurements and gel-permeation chromatography, respectively. Polyamide 12 is soluble in a variety of organic solvents including chloroform.     

Sulfur-containing optically active polymers, 1. Synthesis and chiroptical properties of poly(γ-ketosulfide)s derived from (−) (2R, 3R)-1,4-dimercapto-2,3-butanediol

The synthesis of optically active poly(γ-ketosulfide)s from bis-Mannich bases or α,β,α′,β′-unsaturated ketones and (?) (2R, 3R)-1, 4-dimercapto-2,3-butanediol, is described. The corresponding low-molecular-weight analogs were also synthesized. The products were fully characterized and their stereochemical features investigated by NMR. The relations between chiroptical and conformational properties in solution were also studied by circular dichroism measurements. Although an appreciable local asymmetric induction on the chromophores belonging to the starting achiral co-reagent is observed, the macromolecules do not display any occurrence of ordered secondary structures due to a low stereoregularity degree orginated by the presence of randomly distributed constitutional repeating units having different diastereomeric configurations.     

13C NMR study of the tacticity of poly(propylene oxide)s prepared by polymerization with α,β,γ,δ-tetraphenylporphyrin/AlEt2Cl as initiator system: An example of first-order markovian statistics in ring-opening polymerization

Racemic and enantiomerically enriched poly(propylene oxide)s were prepared using α, β, γ, δ-tetraphenylporphyrin/AlEt₂Cl as initiator system. Triad tacticity of the polymers was analyzed by ¹³C NMR spectroscopy (62,89 MHz). A predominance of isotactic triads was observed in the case of the racemic polymer, corresponding to a non-random distribution of configurational units in the polymer chain. A model correlating tacticity with enantiomeric excess of starting monomer in the case of a first-order Markovian distribution was established. Good agreement between experimental results and calculated triad contents (according to the model previously described) was observed for enantiomerically enriched polymers. This indicates a steric control by the last unit of the growing chain end. The influence of the size of the substituent was examined for the case of poly(1,2-epoxybutane). The origin of the chain-end effect is discussed.     

Polymer conformation and NMR chemical shifts, 9. Poly(α-methylene-γ-butyrolactone)

The conformational energies of poly(α-methylene-γ-butyrolactone) are calculated and compared with those of poly(methyl methacrylate). In spite of the structural resemblance of these two polymers, the patterns of the energy contour maps are clearly distinguishable from each other; the energy barriers between rotational isomeric states are appreciably higher in the former than in the latter polymer. The calculation indicates large non-bonded interactions between the protons in one lactone ring and those in the adjacent lactone rings. The broad NMR spectrum of poly(α-methylene-γ-butyrolactone) apparently reflects its rigid conformational structure. ¹H and ¹³C NMR chemical shifts are calculated by theoretical shielding calculations based on conformational analysis. Much lower magnetic field resonances of the O? CH₂ and α-CH₂ carbons in poly(α-methylene-γ-butyrolactone) as compared with those of the O? CH₃ and α-CH₃ carbons in poly(methyl methacrylate) are well reproduced by the calculation. The shift to lower magnetic field is mainly attributed to paramagnetic shielding derived from the interaction between O? CH₂ carbon and α-CH₂ carbon. Tacticity- and conformation-dependent ¹H and ¹³C NMR chemical shifts of poly(α-methylene-γ-butyrolactone) are well interpreted on the basis of the conformational analysis.     

Copolymerization via zwitterion, 8. β-butyrolactone and 2-ethyl-2-oxazoline

2-Ethyl-2-oxazoline (ETOX) as nucleophilic monomer and β-butyrolactone (BUL) as electrophilic monomer were copolymerized in bulk in the absence of initiator at 45°C. Copolymers were characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy. The copolymer composition was determined by elemental analysis and by ¹H NMR spectroscopy. All copolymers contain a BUL:ETOX mole ratio greater than one.     

Production of poly(β-hydroxyalkanoates) with β-substituents containing terminal ester groups by Pseudomonas oleovorans

Pseudomonas oleovorans was grown separately on the methyl, ethyl and tert-butyl esters of octanoic, nonanoic and decanoic acid in attempts to obtain poly(β-hydroxyalkanoates), PHAs, with ester groups at the terminal position of the β-substituent. The growth rate increased from methyl to tert-butyl esters, but the rate for the slowest growing substrates, the methyl esters, could be accelerated by using special feeding techniques, either by prefeeding with sodium acetate or by cofeeding with a good growth and polymer producing substrate, sodium octanoate. For the ethyl esters the prefeeding technique had minimal success, but a considerable increase of the growth rate was achieved by starting the bacterial growth with a pre-culture that was grown on the substrate under investigation. Tert-butyl nonanoate as the substrate gave the most rapid growth, but the growth rate was not influenced by special feeding techniques. All of these substrates formed copolymers which contained up to eight different repeating units and some had terminal ester groups on alkane side chains of varying lengths. The use of methyl esters as substrates resulted in the incorporation of a reasonably high degree of pendant methyl ester groups in the polymer produced, and the amount of repeating units carrying pendant ester groups dependend directly on the oxygen supply available to the bacterial culture. The fermentation of substrates with ethyl ester groups resulted in the formation of copolymers containing either unsubstituted units or units containing either ethyl or methyl ester groups, or both. The reason for this unexpected behavior was not clarified. The large tert-butyl ester group was not maintained as a substituent group in the polymer, but instead, growth on this substrate always resulted in producing polymers consisting of the unsubstituted repeating units expected from the corresponding carboxylic acid alone.     

Controlled synthesis of α,β-difunctional poly(hexafluoropropylene oxide)

An improved method is described for the preparation of difunctional poly(hexafluoropropylene oxide) of moderate molecular weight (M _n ≈ 6000) in good yield (>80 wt.-%). With the dependence of chain transfer constant on initiator concentration known, at least under controlled conditions, good molecular-weight control can be achieved.     

Photoconductivities of poly[γ-(β-N-carbazolylethyl)-L-glutamate] and its charge-transfer complex with 2,4,7-trinitrofluorenone

Poly[γ-(β-N-carbazolylethyl)-L -glutamate] (PCLG) was prepared by polymerizing the monomer which was synthesized by adapting the NCA method to a reaction product between L -glutamic acid and N-(β-hydroxyethyl)carbazole. PCLG films were prepared on a quartz Nesa (In₂O₃) plate by casting technique. The charge-transfer complex could be successfully formed only near the surface of the PCLG film by immersing the PCLG film into either a benzene or a methyl ethyl ketone solution of 2,4,7-trinitrofluorenone (TNF), since both benzene and methyl ethyl ketone were poor solvents for PCLG and suitable solvents for TNF. A photocell was formed by depositing a translucent gold electrode with vaccum evaporation onto the immersed film. For a small content of TNF in both the immersed films and the homogeneously mixed films of PCLG with TNF, the photocurrent of PCLG was successfully sensitized by TNF, but the sensitized photocurrents retained the relation I>I in a similar way as the photocurrent of PCLG alone, where I was the photocurrent under illumination onto the positive Au electrode and vice versa. On the other hand, as the TNF content increased, I became remarkably greater than I. The PCLG polymer, therefore, can behave as a p-type photoconductor, while the well-doped PCLG-TNF complex can behave as an n-type photoconductor.     

Copolymerization via zwitterion, 5. β-butyrolactone and 2-methyl-2-oxazoline

The zwitterionic copolymerization of 2-methyl-2-oxazoline (MOX) as nucleophilic monomer with β-butyrolactone (BUL) as electrophilic monomer was investigated in bulk and in solution (CH₃CN) at 45°C. The copolymer composition was around 1,5/1,0 (BUL/MOX) as was established by ¹H NMR. ¹H and ¹³C NMR spectroscopy were used to identify the copolymers. The IR spectroscopy supported the NMR results. On the other hand, the copolymers behave as polyelectrolytes, according to viscosity determinations. A copolymerization mechanism through a zwitterion species is suggested.     

Crystallization kinetics of β-phase poly(propylene)

Crystal growth rates of spherulites of β-phase poly(propylene)s and of an ethylene/propene block copolymer, crystallized from the melt, have been investigated in the temperature range of 122 to 146°C. On the basis of the regime theory, a transition between regime II and III is found at ΔT ≈ 37–43,5 K. The nucleation constant for β-phase poly(propylene)based on the current theory of crystal growth was determined, and the fold surface free energy of β-phase poly(propylene) was estimated from the nucleation constant for different samples to lie between 48,2 and 55,2 erg/cm² (1 erg = 10^?7 J).