Anionic copolymerization of ω-lactams with ω-lactones

Copolymerizations of ε-caprolactam, α-pyrrolidone or α-piperidone with ε-caprolactone or δ-valerolactone have been carried out in the presence of alkali metal. It has been shown that in copolymerizations of ε-caprolactam or α-pyrrolidone with ε-caprolactone and α-pyrrolidone with δ-valerolactone conversions of above 70 % and reduced viscosities of above 0.5 in m-cresol at 35°C for all compositions were obtained. In the case of copolymerization of ε-caprolactam with δ-valerolactone at 180°C a conversion of 25 % and a reduced viscosity of 0.5 were obtained, but the polymer was polycaproamide, while at 90°C the conversion was 50 % but the polymer was polyvalerolactone. In copolymerizations of α-piperidone with ε-caprolactone or δ-valerolactone the copolymer contained only polyester. A mechanism is proposed for the copolymerization of ω-lactams with ω-lactones with alkali metal, which involves chain propagation by the stepwise addition of the lactam ring at an end of the chain molecule and by the stepwise addition of the lactone ring at the other end of the chain molecule, resulting to a certain extent in the formation of polyester and polyamide segments. This mechanism is supported by experimental results obtained through the reaction in the presence of alkali metal salts of ω-lactam, data on infrared analyses and elementary analyses, and by experimental results obtained through measurements of physical properties of these copolymers.     

Anionic polymerization of β-nitrostyrenes

The rate of polymerization of β-nitrostyrene initiated by sodium alkoxide was setudied gravimetrically. The rate was found to be first order with respect to monomer concentration and first order with respect to initiator concentration. Rate constants in the order of 0,25 dm³ · mol^?1 · s^?1 were obtained at 15°C, 20°C, and 25°C for the polymerization of β-nitrostyrene, p-methoxy-β-nitrostyrene, and p-methyl-β-nitrostyrene initiated by sodium methoxide and by sodium ethoxide. The activation energy of polymerizations initiated by sodium methoxide and by sodium ethoxide was ～24 kJ · mol^?1 and ～ 16 kJ · mol^?1, respectively. The number average degree of polymerization of poly(β-nitrostyrene)s was determined by polymerization of the monomer in the pressence of ¹⁴C-alkanol. This is the first time that accurate number average molar masses of poly(β-nitrostyrene)s have been reported since conventional methods of molar mass determination cannot be used owing to the insolubility of these polymers in most common organic solvents.     

Cationic copolymerization of α,β-disubstituted ethylenes. Investigations on propagation reaction

To elucidate the feature of the propagation reaction in cationic polymerization, the studies on the effect of a β-methyl group on the reactivity of vinyl ethers and styrenes are summarized. Although the electron density on a β-carbon is decreased by β-methyl substitution, the β-methyl group increases the reactivity of vinyl ethers. Therefore, in the transition state of the propagation reaction of vinyl ethers, it is estimated that a propagating chain interacts with π-electrons of the α-carbon and ethereal oxygen in addition to the β-carbon. Cis-propenyl ethers have been reported to be several times as reactive as trans-propenyl ethers in a non-polar solvent. However, in a polar solvent, cis- and trans-propenyl ethers show nearly the same reactivity, and with isopropyl and tert-butyl propenyl ethers having a bulky alkoxyl group, the trans-isomer is found to be more reactive than the cis-isomer. These phenomena are interpreted by the transition state model proposed above.     

Anionic block polymerization of β-lactones initiated by potassium solutions, 1. Synthesis of poly(4-methyl-2-oxetanone-block-2-oxetanone)

The block polymerization of 4-methyl-2-oxetanone (β-butyrolactone) with 2-oxetanone (β-propiolactone) proceeds fast with a yield of more than 90%, in the presence of potassium solutions in THF containing 18-crown-6. Poly(4-methyl-2-oxetanone-block-2-oxetanone) polymers having the expected molecular weight and composition are formed by this way. Their glass transition and melting temperatures as well as their melting enthalpies, determined by DSC, show a strict correlation with block polymer composition.     

Synthesis of New Homopolyester and Copolyesters by Anionic Ring‐opening Polymerization of α,α′,β‐Trisubstituted β‐Lactones

Summary: Novel polyester and copolyesters have been prepared by anionic ring‐opening polymerization of racemic 4‐alkyloxycarbonyl‐3,3‐dimethyl‐2‐oxetanones that had been synthesized in five steps from diethyl oxalpropionate used as chemical precursor. The anionic polymerizations, realized in bulk or in solution with tetraethylammonium benzoate as initiator, led to a homopolymer and copolymers with high molecular weights and polydispersity indices close to unity. These features can be explained by the presence of two methyl groups on the same carbon atom in the lactone, preventing transfer reactions to the monomer. Preparation of seeds and re‐initiation by addition of fresh monomer confirmed a living process. The hydrolysis of poly[(R,S)‐3,3‐dimethylmalic acid] under physiological conditions yielded (R,S)‐3,3‐dimethylmalic acid. A terpolymer was also prepared for biological studies related to its use as biodegradable materials for tissue regeneration.

Structure of poly[(R,S)‐3,3‐dimethylmalic acid].     

Formation of macrozwitterions in the polymerization of β-lactones initiated by tertiary amines. 2nd communication on macrozwitterions1

End group analysis by NMR spectroscopy and by various chemical methods as well as dipole moments of the carefully purified polymer obtained from propiolactone or pivalolactone and trimethylamine prove the following zwitterion structure: Theoretical aspects of chain initiation with formation of zwitterions are discussed and some physical properties of macrozwitterions are investigated.     

Copolymerization of styrene with α-chloromaleic anhydride, 2. Spontaneous copolymerization in 1,4-dioxane

α-Chloromaleic anhydride (CMA) copolymerizes spontaneously with styrene (ST) at a higher rate than maleic anhydride (MA), and α,α′ -dichloromaleic anhydride (DCMA) does not copolymerize, even in the presence of a radical initiator. The results obtained from the copolymerization of ST with CMA in 1,4-dioxane in the absence of a radical initiator are as follows: the copolymerization is strongly accelerated by UV-irradiation; the monomer reactivity ratios of ST and CMA at 60°C are 0,06 and 0,00, respectively; the over-all activation energy of the copolymerization is 77,4 kJ · mol^?1 (18,5 kcal · mol^?1); the maximum rate of copolymerization at a constant total monomer concentration is observed at a mole fraction of ST of 0,4 to 0,5. The rate of copolymerization at equimolar feed composition is of second order with respect to the total monomer concentration. From the results obtained here and shown in the preceding paper, it was inferred that initiating radicals for the spontaneous copolymerization are formed through a charge transfer (CT) complex between the comonomers.     

Preparation and investigation of optically active polyesters from α-ethyl-α-phenyl-β-propiolactone, 1

α-Ethyl-α-phenyl-β-propiolactone ( 7 ) of an optical purity up to 95% was prepared; the resolution of the two optical antipodes was carried out with the optical active precursor ethyl 2-aminomethyl-2-phenylbutyrate ( 5 ), and the optical purity was determined by ¹H NMR analysis using europium salt shift reagents. The solution and thermal properties of the corresponding polyesters 8 , as obtained by anionic ring opening polymerization, were investigated. It was found that the inherent viscosity increased with the optical purity of the lactone. Distinct differences in the melting behaviour were found between the racemic and the optically active polymers; the ideal melting temperature T_M⁰ for the pure enantiomeric polymer was estimated to about 535 K.     

Direct copolymerization of L-lactic acid with γ-butyrolactone in the absence of catalysts

The copolymerization of L -lactic acid (LA) with γ-butyrolactone (BL), performed without catalyst at 200°C under nitrogen in order to obtain a relatively low-molecular-weight copolymer, proceeds via direct condensation between linear LA and linear 4-hydroxybutyric acid produced by hydrolysis of the cyclic BL. The copolymers were characterized with respect to the copolymerizability (¹³C NMR spectroscopy), composition (¹H NMR spectroscopy), molecular weight (terminal group analysis and gel permeation chromatography), and crystallinity (differential scanning calorimetry). The copolymerizability of BL is low, e. g., the contents of BL units in the copolymers were found to be 12, 16, and 19 mol-% for initial BL contents in the monomer feed of 30, 50, and 70 mol-%, respectively, in which copoly(LA/BL) is composed of blocks of lactyl units separated by single γ-oxybutyryl unit.     

Oligomerization and copolymerization of γ-butyrolactone — a monomer known as unable to homopolymerize, 1. Copolymerization with ε-caprolactone

Copolymerization of γ-butyrolactone (γBL) with ε-caprolactone (εCL) initiated with aluminium isopropoxide trimer ([Al(OⁱPr)₃]₃, (A₃)) is described. Copolymers with molecular weights (M _n) up to 3 · 10⁴ and containing up to 43 mol-% repeating units derived from γBL are prepared. Their molecular weight is controlled by the concentrations of the consumed comonomers and the starting concentration of initiator {M _n = (86.09 · [γBL]_c + 114.14 · [εCL]_c)/3[Al(OⁱPr)₃] + 60.10}. ¹³C NMR and DSC data are indicative of a pseudoperiodic or random copolymer structure.     

Thermodynamic and hydrodynamic properties of aliphatic polyesters, 1. Solubility,intrinsic viscosity,and molecular weight of poly(β-propiolactone)

Absolute molecular weight, intrinsic viscosity, refractive index increment, refractive index, partial specific density, solubility and molecular weight distribution of poly(β-propiolactone) is studied. The measured molecular weights range from 40000 up to nearly 1000000. The relationship between intrinsic viscosity and molecular weight [η] = 0,0259 · M ml/g (CHCl₃, 30,0°C) shows that the polymer molecule is a linear flexible chain.     

Developmental expression of the αIELβ7 integrin on T cell receptor γδ and T cell receptor αβ T cells

A novel monoclonal antibody, 2E7, was shown by immunoprecipitation to be reactive with the α_IELβ7 integrin and was employed to analyze the expression of this integrin in lymphocyte subsets and during T cell ontogeny. In adult lymph nodes, α_IEL was expressed at low levels by 40–70% of CD8⁺ T cells and < 5% of CD4⁺ T cells. However, virtually all intestinal intraepithelial lymphocytes and ?20% of lamina propria CD4⁺ T cells were 2E7⁺, indicating a preferential expression of this integrin on mucosal T cells. Examination of α_IEL integrin expression during thymus ontogeny revealed that ?3–5% of fetal or adult thymocytes were 2E7⁺. Interestingly, early in fetal thymus ontogeny, ?40% of 2E7⁺ cells expressed T cell receptor (TcR)-γδ and this subset persisted through birth. A developmental switch occurred such that 2E7⁺ TcR^? CD4^?8⁺ cells detected on fetal day 19 were followed by 2E7⁺ TcR-αβ CD4^?8⁺ cells in the neonatal thymus. The latter population persisted throughout thymus ontogeny into adulthood. Interestingly, a subset of TcR-γδ Vγ3⁺ day 16 fetal thymocyte dendritic epidermal cell (DEC) precursors were 2E7⁺, but all mature DEC expressed high levels of α_IEL integrin, suggesting that the α_IEL integrin was acquired late in DEC maturation. This possibility was strenghthened by immunohistochemical localization of the majority of 2E7⁺ γδ and αβ T cells to the medullary regions of the thymus. Overall, the results demonstrate a developmentally ordered expression pattern of the α_IELβ₇ integrin that suggests a common function for this integrin during TcR-γδ and -αβ CD4^?8⁺ T cell thymocyte development or perhaps in effector functions for these subsets.     

Asymmetric induction in the copolymerization of (–)-3-(β-styryloxy)menthane with styrene

Asymmetric induction in the copolymerization of (–)-3-(β-styryloxy)menthane (1) with styrene was investigated. The copolymers obtained in the presence of BF₃ · OEt₂ are optically active. The absolute value of the specific rotation of the copolymers was found to be higher than that of the homopolymeric mixture, whatever the composition. After ether cleavage reaction of the copolymers, the products are still optically active. The result suggests that an asymmetric induction takes place in the polymer main chain.     

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.     

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.     

Cationic graft copolymerization of tetrahydrofuran with partially α-brominated polystyrene

Partially α-brominated polystyrene was first prepared from commercial polystyrene and N-bromosuccinimide by the Wohl-Ziegler reaction. It was treated with silver perchlorate to initiate cationic graft copolymerization with tetrahydrofuran leading to polystyrene-graft-polytetrahydrofuran. The influence of reaction time, reaction temperature, initial concentrations of silver perchlorate and partially α-brominated polystyrene, etc., on the graft polymerization was studied. It partially α-brominated polystyrene with a bromination degree of 5–15% was used, a leather-like graft copolymer was obtained with a high grafting efficiency at or below 0°C.     

Role of the thymus in the generation of skin-homing αβ and γδ virgin T cells

Current models of lymphocyte traffic suggest that homing specificities of T cells to tissues such as skin are generated outside the thymus as a result of activation of naive T cells by antigen in lymph nodes. Virgin T cells are thought to home to high endothelial venules in lymph nodes, but are thought to be unable to home to extra-lymphoid tissues such as skin. We used the technique of in situ labeling of the thymus with fluorescein isothiocyanate to examine the homing specificities of authentically naive T cells in vivo, immediately after their export from the thymus. We report that homing specificities for skin as well as lymph node are imprinted on T cells inside the thymus, independent of antigen. We also show that both αβ and γδ emigrant T cells exhibit homing patterns to skin and lymph nodes which are identical to those of mature T cells. Our findings demonstrate a key role for the thymus in the induction of skin-homing specificities on T cells indicating that skin-homing specificities of T cells are not generated solely outside the thymus as a result of the activation of virgin T cells by antigen. The migration of thymic emigrants to extra-lymphoid tissues within a few hours of leaving the thymus may have implications for mechanisms of peripheral self-tolerance. This pathway provides an opportunity for direct virgin T cell interactions with self components only expressed in the periphery at a time when emigrants may be more susceptible to tolerance induction than mature circulating T cells.