摘要:

AbstractThis presentation asserts the importance of synthesis in the creation of new materials, the discovery of new phenomena, and the development of new or improved materials for high‐technology industries. It points to the neglect of synthesis and processing in American universities, and the response of the National Science Foundation to overcome this shortcoming in the futur

ISSN:0258-0322    

DOI:10.1002/masy.19920540103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0258-0322    

DOI:10.1002/masy.19920540104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo new methods for the synthesis of polyphosphazenes are described. The first is based on the catalyzed polycondensation of phosphoranimines using various catalysts and initiators. Certain mechanistic aspects of this process with reactive intermediates are discussed. Linear polymers are formed quantitatively at temperatures around 100 °C in a few hours (the thermal process requires a few days at 200 °C). The second method is based on the direct reaction between phosphonites and phosphinites with silyl azides. This reaction proceeds by phosphine azide intermediates and provides new polyphosphazene

ISSN:0258-0322    

DOI:10.1002/masy.19920540105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractAnionic and pseudoanionic polymerizations of ϵ‐caprolactone (CL) have been compared in terms of the principle relating reactivity with selectivity (reactivity‐selectivity principle, RSP). RSP can be formulated as follows: there are two reagents X and Y; reagent X reacts faster with substrates A and B than reagent Y does (i.e. kxa>kyaand kxb>kyb, where kxa, kya, kxband kybare the respective rate constants); moreover, reactions with A are faster than reactions with B (i.e. kxa>kxband kya>kyb); finally, if RSP is operative the inequality kya/kyb>kxa/kxbholds. Comparison of the anionic and pseudoanionic polymerizations of CL reveals that this system conforms to the RSP. Propagation on the …‐O−Na+ion pairs proceeds much faster than on the …−OAIR2covalent species (kp∓= 1,7 l/mol · s vs kpc= 3,0 · 10−2l/mol · s, THF solvent, 20°C). Propagation is accompanied by transesterification and cyclization. Formation of the cyclic dimer (with the rate constant kb(2)) was taken as a measure of an extent of these “side” reactions. Following selectivity coefficients ß = kp/kb(2) have been measured (in l/mol): 1, 55 · 103(…−O−Na+), 4, 6 · 104(…‐OAl(C2H5)2), and 7,7 · 104(…−OAl(i‐C4H9)2). Thus, kpc/kbc(2)>kp∓/kb∓(2). Therefore formation of the linear, high molar mass polymer is more pronounced i

ISSN:0258-0322    

DOI:10.1002/masy.19920540106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper concerns the recent progress in our search for new initiating systems for living cationic polymerization and the mechanisms involved therein, specifically focusing on:(a) Protonic acid/Lewis acid initiating systems for vinyl ethers;(b) Initiating systems for living cationic polymerization of styrene;(c) Multi‐functional initiating systems.In area (a), the design of counteranions was discussed relative to the principles of living cationic polymerization; in area (b), the first truly living cationic polymerization of styrene is described; and in area (c), the multi‐functional initiating systems led to tri‐armed polymers of vinyl ethers andp‐alkoxystyrenes with amphiphilic arm chains of uniform

ISSN:0258-0322    

DOI:10.1002/masy.19920540107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe cationic polymerization of alkenes and heterocyclics is compared in a critical way. After a brief introduction to the polymerizability of various monomers and efficiency of initiators, various active sites involved in propagation are discussed. They include covalent species, onium ions and carbenium ions of different degrees of association. Proportions and reactivities of these active sites are discussed for different monomers. Structure‐reactivity correlations for both systems are described. The construction of a general unifying theory of cationic polymerization is attempted, with peculiarities typical for each system pointed ou

ISSN:0258-0322    

DOI:10.1002/masy.19920540108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have begun an exploratory program on the synthesis of imines and azadienes (α, β‐unsaturated imines) to find the best structures for monomers which will form high polymers. Imines display a very wide range of stability from existing only in the gas phase or at liquid nitrogen temperatures to complete stability depending on the substituents on the nitrogen and carbon. Among the simple imines, benzylidene cyanamide gave oligomers of DP‐8 with either free radical or anionic initiators. Tricyanomethanimine, C4N4, could only be obtained in solution and spontaneously homopolymerized and copolymerized with paramethoxystyrene. Among the l‐azabutadienes, 1‐phenyl‐l‐aza‐1,3‐butadiene polymerized to reasonably high molecular weight polymers using anionic initiators. Cationic initiation was less successful and free radical initiators gave no polymers. Similarly, N‐carboethoxy‐3‐methyl‐l‐aza‐l,3‐butadiene gave moderate yields of polymers with modest molecular weights. Our conclusions at this stage of our investigations are that simple imines are a quite restricted class of monomers. On the other hand, owing to ease of synthesis and ability to polymerize the l‐azadienes represent

ISSN:0258-0322    

DOI:10.1002/masy.19920540109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCationic bulk polymerization of liquid crystalline phenyl benzoate and biphenyl vinyl ethers was performed using either thermal or photochemical initiation by onium salts. High molecular mass polymers having narrow molecular mass distribution were produced in high yields at very high temperatures (i.e., ≤ 120°).Seemingly, the polymerization system could stabilize the growing species and thus reduce the amount of chain transfer reactions. Thin films of the monomers were oriented in their liquid crystalline state by the use of conventional ordering techniques used for low molar mass liquid crystals. On subsequent polymerization the orientation was preserved giving liquid crystalline thin films having a very high degree of ord

ISSN:0258-0322    

DOI:10.1002/masy.19920540110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper reports the synthesis and characterization of hydroxyl functionalized poly(butyl vinyl ether) oligomers, and block copolymers comprised of poly(butyl vinyl ether) and poly(ϵ‐caprolactone). Using the HI/ZnI2initiating system in toluene at −20°C, monofunctional poly(butyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde or primary hydroxyl endgroups have been prepared. Furthermore, the primary hydroxyl end functionality has been utilized to initiate ring opening polymerization of ϵ‐caprolactone in the presence of stannous octanoate as the catalyst. This ring opening reaction provides an entry into new poly[(butyl vinyl ether)‐block‐poly(ϵ‐caprolacto

ISSN:0258-0322    

DOI:10.1002/masy.19920540111

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present paper describes the ring‐opening‐closing alternating copolymerization of cyclic phosphonites (2‐phenyl‐1,3,2‐dioxaphosphelane (1a), 2‐phenyl‐1,3,2‐dioxaphosphorinane(1b), 2‐phenyl‐1,3,2‐dioxaphosphepane(1c), and 2‐phenyl‐4H‐1,3,2‐benzodioxa phosphorin‐4‐one(1d)) with muconic acid(2a), succinaldehyde(2b), glutaraldehyde(2c), adipinaldehyde(2d), o‐phthalaldehyde(2e), acrylic anhydride(2f), methacrylic anhydride(2g), N‐methyl diacrylamide(2h), and N‐methyldimethacrylamide(2i). The reaction of a 1:1 monomer feed ratio, explained by a mechanism of propagation via zwitterion intermediates, proceeds without any added catalyst to give an alternating copolymer3involving ring‐opening of1and ring‐closing of2. The structure of copolymer3was determined by1H,13C NMR,31P NMR and IR s

ISSN:0258-0322    

DOI:10.1002/masy.19920540112

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY