Hans R. Kricheldorf

Polylactones: 31. Sn(II)octoate-initiated polymerization of L-lactide: a mechanistic study

Abstract The polymerization of L-lactide was catalysed with Sn(II)2-ethylhexanoate (SnOct 2 ) in the presence or absence of benzyl alcohol. The molecular weights parallel the lactide/benzyl alcohol ratio, but never the lactide/Sn ratio. 1 H n.m.r. spectroscopy revealed the existence of benzylester and −CH(CH 3 )OH end-groups. Polymerizations conducted at low lactide/catalyst ratios in the absence of an alcohol yield polylactide with a low content of 2-ethylhexanoate end-groups. 1 H and 119 Sn n.m.r. spectroscopy of CHCl 3 solutions also demonstrated that SnOct 2 forms strong complexes with both benzyl alcohol and ethyl lactate and weaker complexes with lactide. A similar but weaker complexation was also detected for Bu 2 SnOct 2 in combination with either benzyl alcohol or lactide. A new polymerization mechanism is discussed, assuming the reaction between lactide and OH end-groups bound to a Sn atom via two sp 3 d 2 orbitals.

Syntheses and application of polylactides

Polylactides can be prepared by direct polycondensation of lactic acid, or better, by ring-opening polymerization of cyclic dilactides (usually called lactides). These lactides exist in the form of four stereoisomers two of which (L,L- and rac. -D,L-) are technically produced in large quantities. These lactides can by polymerized via four different classes of initiators and reaction mechanisms. The characteristics mechanistic and preparative features of the cationic polymerization, anionic polymerization and of the coordination-insertion mechanism are described. Furthermore, copolymerizations of lactides with glycolide or epsilon-caprolactone and their analytical problems are discussed. Finally, a new type of wound dressing based on transparent are resorbable films of copolylactides is mentioned.

Polylactones: 23. Polymerization of racemic and mesod,l-lactide with various organotin catalysts—stereochemical aspects

Abstract Racemic and meso d,l -lactide were polymerized at 90 or 120°C in xylylene or at 120, 150 and 180°C in bulk. Furthermore, copolymerizations of racemic d,l -lactide and l,l -lactide were conducted at 180°C in bulk. Tributyltin methoxide (Bu3SnOMe), dibutyltin dimethoxide (Bu2Sn(OMe)2) and Sn(II) octoate were used as initiators. Despite high yields only low molecular weights were obtained with both tin methoxides. Sn(II) octoate gave significantly higher molecular weights. The stereosequences were analysed by 1H and 13C n.m.r. spectroscopy on the basis of tetrad effects. The signal assignments are discussed. Bu3SnOMe and Bu2Sn(OMe)2 are effective transesterification catalysts and cause ‘back-biting’ degradation even at 90°C. In all series of polymerizations initiated with tin methoxides two tendencies are detectable: increasing randomization of the stereosequence with increasing reaction time and with higher reaction temperatures. In contrast, Sn(II) octoate does not cause transesterification at ≤ 120°C and even at 180°C randomization of the stereosequences is slow.

“Sugar Diols” as Building Blocks of Polycondensates

Abstract The term sugar diols is used throughout this review as a nickname for diols that are usually derived from saccharides. Typical examples of such “sugar diols” are the bicyclic ethers L-sorbitol (A), L-iditol (z), and L-mannitol (3),—where 1 and 1 are commercial monomers. Furthermore, the acetals 4, 5, 6, and 7 should be mentioned, which are all commercial. These sugar diols have recently attracted increasing interest as monomers for the synthesis of various polycondensates. Several reasons are responsible for this tendency. 1. All sugar diols can be prepared from saccharides (although other synthetic routes may also be available) and thus are monomers based on renewable resources. 2. Most sugar diols (e.g., 1–4 and 7) are nontoxic and their polyesters derived from aliphatic dicarboxylic acids are sensitive to hydrolysis. Such aliphatic polyesters will degrade in the course of several months in contact with warm neutral water and thus are considered to be useful biodegradable materials. 3. All suga...

Silicon in polymer synthesis

From the contents: Polymerization of Si-containing Vinylmonomers and Acetylenes.- Group Transfer Polymerization.- Polysiloxanes and Polymers Containing Siloxane Groups.- Poly(organosilane)s, Poly(carbosilane)s, Poly(organosilazane).- Polycondensation of Silylated Monomers.- Miscellaneous Applications of Silicon Reagents.- Chemical Modification of Polymers and Surfaces.- Appendix A: Silicon-based thermoset resins.- Appendix B: Silylation, Silylating Agents.

Macrocycles 2. Living macrocyclic polymerization of ε‐caprolactone with 2,2‐dibutyl‐2‐stanna‐1,3‐dioxepane as initiator

e-Caprolactone was polymerized in bulk at 80°C with 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) as initiator. The reaction time was varied for monomer/initiator molar ratios of 20, 100 and 500. A rapid and complete conversion of the monomer and only slight transesterification or back-biting degradation were found after longer reaction times. However, significant acceleration of these side reactions was observed at 180°C. Regardless of the M/I ratios and of the reaction time the polydispersities were nearly constant. Number average molecular weights (M n s) as obtained from GPC measurements are larger than the values obtained from end-group analyses by 15-25% and increase with increasing molar ratio M/I (at 100% conversion). The living character of the Sn-O end-groups was demonstrated by acylation with 4-nitrobenzoyl chloride and by the synthesis of a macrocyclic block copolyester containing β-D,L-butyrolactone.

New polymer syntheses: 6. Linear and branched poly(3-hydroxy-benzoates)☆

Abstract Synthesis of poly(3-hydroxybenzoate) were conducted in three ways: (a) condensation of the novel monomer, 3-(trimethylsiloxy)benzoyl chloride in bulk and in solution, (b) bulk condensation of 3-acetoxybenzoic acid, (c) condensation of 3-hydroxybenzoic acid by means of phosphorus reagents in solution. The bulk condensation of 3(trimethylsiloxy)benzoyl chloride gave the best results with respect to both yields (89–99%) and molecular weights ( Mn = 10 000–14 000). Because amorphous poly(3-hydroxybenzoate) is soluble in various solvents the molar weights could be determined by both vapour pressure osmometry and 1 H n.m.r. endgroup analyses. Crystalline poly(3-hydroxybenzoate) was only obtainable by solvent induced crystallization; yet not by annealing. Glass transition ( Tg = 145°C) and melting point ( Tm =181°–185°C) were determined by means of differential scanning calorimetry and torsion pendulum. Branched poly(3-hydroxybenzoate) was prepared by condensation of 3-(trimethylsiloxy) benzoyl chloride and 3,5-(bistrimethylsiloxy) benzoyl chloride. Thus, for the first time a branched polycondensate was obtained which did not crosslink regardless of the conversion.

Polylactones: 32. High-molecular-weight polylactides by ring-opening polymerization with dibutylmagnesium or butylmagnesium chloride

The dibutylmagnesium (Bu2Mg)-initiated polymerizations of l-lactide at 120°C in bulk yielded poly(l-lactide) of low molecular weights (ηinh ⩽ 0.4 dlg−1 in CH2Cl2), regardless of reaction time and initiator concentration. Higher molecular weights were obtained in solution when carried out in the presence of ethers. The addition of crown ethers to polymerizations conducted in toluene at 0°C gave the best results, with ηinh values up to 3.0 dlg−1 (in Ch2Cl2), corresponding to number-average molecular weights (Mns) the order of 3 × 105g mol−1. These high-molecular-weight poly(l-lactide)s possess almost complete optical purity and show melting temperatures of ∼170°C. Relatively high-molecular-weight poly(d,l-lactide)s were also obtained by the Bu2Mg-initiated polymerizations of racemic- or meso-d,d-lactides, with ηinh values up to 1.4 dl g−1 (in CH2Cl2), corresponding to Mn = 105, being found. The Grignard reagent, BuMgCl, gave somewhat better results than Bu2Mg when used as an initiator for l-lactide in bulk. However, BuMgCl is not reactive enough to initiate satisfactory polymerizations in solution at temperatures ⩽25°C.

Polylactones, 42. Zn L-lactate-catalyzed polymerizations of 1,4-dioxan-2-one†‡

1,4-Dioxan-2-one (DOXA) was polymerized by means of Zn L-lactate (ZnLac 2 ) as catalyst in bulk. Upon systematic variation of the temperature, the reaction time and the monomer/catalyst (M/C) mole ratio the highest molecular weights were obtained at 100°C and M/C ratios between 2000 and 4000. However, long reaction times (8-14d) were required to obtain optimum results. Zinc chloride proved to be a somewhat less reactive catalyst, whereas zinc bromide proved to be as efficient as ZnLac 2 . Addition of benzyl alcohol as a coinitiator at a fixed DOXA/ZnLac 2 ratio allowed a systematic control of the molecular weight. Furthermore the formation of benzyl ester endgroups was detected. Moreover, ZnLac 2 allows the incorporation of various bioactive alcohols or phenols (e.g. testosterone, stigmasterol, ergocalciferol, cortisone, α-tocopherol) in the form of ester endgroups. Finally several properties of polydioxanone are reported and discussed, such as solubilities, IR, 1 H NMR and 13 C NMR spectroscopic data and thermogravimetric analysis.

New polymers of carbonic acid. XXV. Photoreactive cholesteric polycarbonates derived from 2,5-bis(4'-hydroxybenzylidene)cyclopentanone and isosorbide

Several binary copolycarbonates were prepared by polycondensation of 2,5-bis(4-hydroxybenzylidene)cyclopentanone, BHBC, with methylhydroquinone, MHQ, hydroquinone 4-hydroxybenzoate, HQHB, or isosorbide. Furthermore, five ternary copolycarbonates were prepared based on the aforementioned monomers. All polycondensations were conducted in pyridine with trichloromethyl chloroformate as condensing agent. All polycarbonates were characterized by elemental analyses, viscosity and DSC measurements, IR and 1 H- and 13 C-NMR spectroscopy, optical microscopy, and the WAXS powder pattern. All isosorbides containing binary and ternary copolycarbonates were found to form a cholesteric melt, but only three of them were capable to form a stable Grandjean texture upon shearing.