摘要:

AbstractThe ring‐opening polymerization of cyclic monomers shows the characteristic features of any addition polymerization or any physical aggregation process, in particular a ceiling temperature above which the formation of the aggregate (long‐chain polymer), under given conditions of monomer concentration, solvent and pressure, would involve a positive change of free energy and is therefore impossible. Conversely for a given temperature, pressure and solvent, there is an equilibrium monomer concentration below which long‐chain polymer cannot be formed. Cyclic monomers must therefore have a negative free energy of polymerization, under given conditions, if they are to be capable of undergoing a significant extent of ring‐opening polymerization. The effect of monomer structure, including ring size, on thermodynamic polymerizability is discussed, as well as the possibility of copolymerizing monomers which cannot themselves give homopolymers. Examples are given for various possible mechanisms of polymer

ISSN:0258-0322    

DOI:10.1002/masy.19910420103

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe polymerization features of the polymerization of heterocyclic monomers using anionic or coordinated anionic type initiators are examined. The chemical and configurational structure of initiating species depends on the regiospecificity of the ring‐opening reaction. Propagating rate constants, solvation and macrocyclisation phenomena are discussed. The structure and the chemical composition of stereospecific initiators are described. Different types of mechanisms (enantiomorphic sites and end‐chain) are illustrated. The dependence of selectivity on different parameters is discussed. Various aspects of chiral catalysis leading to stereoelective and enantiogenic processes are presented. Some examples of recent trends in anionic and stereospecific ring‐opening polymerization are

ISSN:0258-0322    

DOI:10.1002/masy.19910420104

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe main‐ and side‐reactions which can occur during cationic ring‐opening polymerizations of heterocyclic monomers are discussed. Based on these general reactions these polymerizations are classified into three groups. (1) Living (or “almost living”) polymerizations provide the possibility to produce polymers with predictable molecular weight, narrow molecular weight distributions and having functional end groups (by initiation and/or end‐capping). These polymerizations also allow the production of block and graft copolymers by sequential monomer additions. (2) Polymerizations which show temporary, i.e. reversible, termination reactions may be used to produce polymers with predictable molecular weights with molecular weight distributions of ≈2. Functional end groups may be introduced by end capping or chain transfer. These polymerizations generally lead to considerable fractions of cyclic oligomers. (3) Polymerizations which show irreversible termination reactions by the formation of stable, branched or (macro)cyclic onium ions. These polymerizations stop at limited conversions and are not suitable for the synthesis of well‐d

ISSN:0258-0322    

DOI:10.1002/masy.19910420105

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractA survey is provided which demonstrates the synthetic importance and variety of industrial applications that have developed for ring‐opening polymerization. The number of polymers produced this way is quite significant and includes the epoxides such as ethylene and propylene oxide and other cyclic ethers such as trioxane, tetrahydrofuran and the epoxy resins. Other important systems include the polylactams such as polycaprolactam (Nylon 6), the siloxane or silicone materials, polycaprolactone, and cycloolefins such as polynorbornene. Polyoxazolines are newer monomers which can be polymerized via cationic mechanisms to yield either hydrophilic or hydrophobic tertiary polyamides. Thus, the importance of the field is quite well established and continues to grow. Major applications in coatings, fibers, elastomers, adhesives, thermoplastics and thermosets, such as in composite matrix resins, have been develope

ISSN:0258-0322    

DOI:10.1002/masy.19910420106

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper reports a new copolymerization based on the novel concept, i.e., ring‐opening‐closing alternating copolymerization. The reaction of a cyclic monomer A and a noncyclic monomer B takes place without added initiator or catalyst to give a copolymer of structure having a ring‐opened unit from monomer A and a ring‐closed unit from monomer B in alternating arrangement. As monomer A, five, six and seven‐membered cyclic phosphonites are employed. As monomer B, on the other hand, are used muconic acid and dialdehydes. Combinations of these monomers A and B produced in all cases ring‐opened and closed 1 : 1 alternating

ISSN:0258-0322    

DOI:10.1002/masy.19910420107

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAluminium alkoxides, such as Al(OiPr)3or Et3‐pAl(O (CH2)2X)pwith 1≤p≤3, are very effective in initiating the polymerization of lactones, e.g.ϵ ‐ca‐prolactone and δ ‐valerolactone, and lactides (D,L‐ or L,L‐ isomers). The ring‐opening polymerization proceeds through a “coordination‐insertion” mechanism that involves the selective rupture of the acyl‐oxygen bond of the monomer and its insertion into an Al‐O bond of the initiator. Polymerization is typically “living” and allows block copolyesters with perfectly controlled molecular weight and composition to be prepared. Aluminium alkoxides carrying functional alkoxy groups (X = ‐Br, ‐CH2‐NEt2, ‐CH2‐CH=CH2, ‐CH2‐OC(O)‐C(Me)=CH2…) provide asymmetric telechelic polyesters (end‐groups being ‐X and ‐OH, respectively) and very interesting polyester macromonomers. Coupling the asymmetric telechelic chains via the hydroxyl end‐group ‐ or better its A1 alkoxide precursor ‐ is a straightforward way to

ISSN:0258-0322    

DOI:10.1002/masy.19910420108

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractCationic ring‐opening polymerization of e‐caprolactone using triethyloxonium hexafluorophosphate initiator in the presence of alcohol to produce low molecular weight polyester glycol was examined. The polymerization proceeded by an activated monomer mechanism; thus the polymer molecular weight increased directly with the monomer conversion. Polymerization of lactones other than ϵ‐caprolactone were also examined, and the overall rate of polymerization was in the order δ‐valerolactone>ϵ‐caprolactone>>β‐butyrolactone>diketene>

ISSN:0258-0322    

DOI:10.1002/masy.19910420109

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractAnionic polymerization of ϵ‐caprolactone conducted in THF solvent has been compared with polymerizations initiated with aluminium alkoxides. The latter processes have been kinetically analysed as the pseudoionic processes, i. e. with propagation proceeding by insertion. In the pseudoanionic reaction active species are aggregated. The methods of solving kinetic schemes involving aggregation ⇋ deaggregation equilibrium, followed by the chain growth on deaggregated species are described. These kinetic methods have been used to determine the propagation rate constants. The relationships between structures of the growing species and their reactivities have thus been determ

ISSN:0258-0322    

DOI:10.1002/masy.19910420110

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe anionic ring‐opening polymerization may result in a broad variety of homo‐ and copolycarbonates. Upon suitable selection of monomers, polymers with functional groups may be obtained which are eligible to cross‐linking reactions or exert a high degree of hydrophilicity. Copolymers with lactones are readily obtained, provided both polymerization reactions follow the same mechanism; the ring‐opening polymerization of cyclic carbonates is exclusively initiated by alcoholate ions and not by carboxylate anions. Since butyllithium is a suitable Initiator for the ring‐opening anionic polymerization of cyclic carbonates, living vinyl polymers may be used as initiators as well to obtain the respective blockcopolymers. Instead of living vinyl polymers obtained in the conventional manner, using carbanionic Initiators, also living polymers obtained by group transfer polymerization may be used as initiators for the ring‐opening polymerization of cyclic carbonates; the mechanism for the latter polymerization, however, then is rather a non‐metallic anionic one than a group trans

ISSN:0258-0322    

DOI:10.1002/masy.19910420111

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe preparation and polymerization of a variety of cyclic oligomeric carbonates containing diverse functionality is described. The preparation of bisphenols containing ether, amide, ester, urethane, etherketone, or ethersulfone functionalities is described. The functionalized bisphenols were converted to dichloroformates via phosgenation, and were subjected to cyclization reactions, forming cyclic oligomeric carbonates containing various functionality. Anionic, ring‐opening polymerization of the cyclic oligomers leads to high molecular weight polymers containing carbonate and other functionality. Depending on the nature of the functionalized bisphenol starting material, the product polymers may be alternating, block, or random copolymer

ISSN:0258-0322    

DOI:10.1002/masy.19910420112

出版商:Hüthig&Wepf Verlag    

年代:1991

数据来源: WILEY