摘要:

AbstractOrganometallic rhodium complexes are described which are highly efficient initiators for the ring‐opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy‐functional silanes in high yields without competing ring‐opening polym

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300101

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA method of analysis of copolymerization systems involving multiple reaction pathways is presented. The method involves fractionation and separate analysis of the individual product populations comprising each sample. Modification of the Kelen–Tüdos linearization techniques into the form necessary to deal with high conversion copolymerizations involving multiple reaction pathways is presented. The method is applied to the ionizing radiation initiated copolymerization of styrene derivatives in dichloromethane, in which case simultaneous copolymerization via cationic and free radical mechanisms is found to occur. Reactivity ratios corresponding to each mechanism are calculated and discuss

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300102

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractPolymerization of 4‐methyl‐2‐oxetanone (1) initiated with potassium acetate‐dibenzo‐18‐crown‐6 complex (2) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (kp,ktr,kri, andKassand respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constantskp:kt:kriis fairly constant and equal to 10−4: 10−6: 10−6, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4‐methyl‐2‐oxetanone) with\documentclass{article}\pagestyle{empty}\begin{document}$\bar M_n$\end{document}as high as 1.7 × 104and\documentclass{article}\pagestyle{empty}\begin{document}${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$\end{documen

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300103

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn the presence of SiH containing cocatalysts, dicobaltoctacarbonyl has been found to very efficiently catalyze the ring‐opening polymerization of cyclic ethers, especially epoxides, as well as certain vinyl monomers. The reaction conditions employed are very similar to those used in Co2(CO)8catalyzed hydrogenation and hydrosilylation reactions. Detailed investigations have been carried out to elucidate the nature of the active species for this catalytic system. A cationic mechanism is proposed based on the experimental results of those investigati

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300104

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractNew linear triblock thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by two glassy endblocks of various styrenic polymers have been synthesized by living carbocationic polymerization by sequential monomer addition. First isobutylene (IB) was polymerized by a bifunctionaltert‐ether (dicumyl methyl ether) initiator in conjunction with TiCl4coinitiator in CH3Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at −80°C. After the living narrow molecular weight distribution PIB midblock ($\[\bar M_n\]$= 1.1–1.2) has reached the desired molecular weight, the styrenic monomers together with an electron pair donor (ED) and a proton trap (di‐tert‐butylpyridine, DtBP) were added to start the blocking of the glassy segments from the living ⊕PIB⊕ chain ends. Whilep‐methylstyrene (pMeSt),p‐t‐butylstyrene (ptBuSt) and indene (In) gave essentially 100% blocking to the corresponding glassy endblocks, the blocking of 2,4,6‐trimethylstyrene (TMeSt) and α‐methylstyrene (αMeSt) were ineffective. Uncontrolled initiation by protic impurities was prevented by the use of DtBP. In the simultaneous presence of DtBP and the strong EDN,N‐dimethylacetamide (DMA), TPEs with good mechanical properties (10–20 MPa tensile strength, 300–600% elongation) were prepared. The products exhibit a low and a high temperatureTgcharacteristic of phase separated rubbery and glassy domains. The service temperature of these new TPEs exceeds that of PSt–PIB–PSt triblock copolymers due to the higherTgs (PpMeSt = 108, PptBuSt = 142 and PIn = 220–240°C) of the outer blocks. TheTgof the glassy blocks can be regulated by copolymerizing two styrene derivatives; a triblock copolymer with outer blocks of poly(pt‐butylstyrene‐co‐indene) showed a single glassy transitionTg= +165°C, i.e., in between that of PptBuSt and PIn. Virgin TPEs have been repeatedly compression molded without deterioration of physical properties. The high melt flow index obtained with a TPE containing PptBuSt endblocks suggests superior processability relative to those with PSt end‐blocks. The tensile strength retention at 60°C of the former TPE is far superior to that

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300105

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe redox bistelomerization of allyl acetate with telogens which exhibit α, ω‐di(trichloromethyled) end groups catalyzed by copper, iron salts, or a ruthenium complex led to monoadducts and telechelic oligomers. These diacetates were quantitatively changed into diols. Such compounds have been characterized by both1H‐ and13C‐NMR. A reactivity series has been determined and shows that both end groups must be activated to obtain the expected telechelic products in satisfactory

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300106

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe study of rare earth coordination catalysts for polymerization of 1‐octene has been successfully carried out for the first time. Some features and kinetic behavior of polymerization of 1‐octene by Nd(naph)3–AIEt3catalyst system in tetrachloro‐methane are described. The overall polymerization activation energyEameasured was 74.5 kJ/mol and the rate equation could be expressed asRp=kp[Nd] [M](kp= 3.21 × 10−3L/mol s, at 50°C). The catalytic activity of various rare earth elements in Ln (naph)3and ligands in NdL3for the polymerization was compared. A 1‐octene oligomer with double bonds was obtained. It is either a white or pale yellow waxy semi‐solid. Its number‐average molecular weight is about 103and the molecular weight distributi

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300107

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractPoly(alkylene phosphate)s bearing regularly distributed uracil moiety in the main chain have been obtained. The synthetic procedure consists of condensation of bis(diethylamino)‐methoxyphosphine withN1,N3‐bis(2′‐hydroxyethyl) uracil followed by oxidation, dealkylation, and transformation to the resulting sodium polysalt. The final polymer (\documentclass{article}\pagestyle{empty}\begin{document}$\bar M_n \approx 10^4 $\end{document}) as well as the intermediate products were characterized by1H‐,13C‐, and31P‐NMR

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300108

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe combination membrane of poly(1‐trimethylsilyl‐1‐propyne) with enormously high permeability and poly(vinylimidazole)‐bound porphinatocobalt with selective oxygenbinding ability was prepared. Oxygen transport through the membrane was facilitated in terms of oxygen transport via the latter domain as a fixed oxygen‐carrier, and this oxygen permeability maintained fo

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300109

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractAlternate syntheses of polyarylate from dimethyl iso/terephthalate (DMI/DMT) and bisphenol‐A (BPA) or bisphenol‐A diacetate (BPAOAc) were investigated using a variety of catalysts. The model exchange of DMT with 4‐t‐butylphenol with loss of methanol proceeded moderately rapidly at rather low temperature (170°C) to produce to mono‐ and di‐t‐butylphenyl terephthalates. Dibutyltin oxide is the preferred catalyst. Alkali metal phenoxides are almost as effective but were less soluble. The model reaction of DMT with 4‐tert‐butylphenyl acetate involving loss of methyl acetate gave comparable results using dibutyltin oxide as catalyst. Based on these model results, polycondensations of DMI/DMT with BPAOAc under optimal conditions, gave polyarylate having an inherent viscosity 0.34 dL g−1in quantitative yield and light brown color. Polycondensation with BPA was unsatisfactory in terms of yield, molecul

ISSN:0887-624X    

DOI:10.1002/pola.1992.080300110

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY