摘要:

AbstractNew polycondensation reactions of active diphenyl carbonates and diphenyl carbamate with diamines were developed for the synthesis of high‐molecular‐weight polyureas. The kinetics and mechanism of carbonic acid active esters aminolysis model reactions were studied. Possible side reactions including nucleophilic substitution reaction were investigated as well. It is shown that novel methods advantageously distinguish from traditional methods of polyureas synthesis by low tendency to side reactions and facilitate the synthesis of linear polyureas and copolyureas. It is found thatN,N′‐bis(trimethylsilylated) diamines and salts of diamines as monomers can be successfully used in these reactions. Bioanalogous polymers promising for biomedical application — polyureas based onL‐lysine — were synthesized using novel polycondensat

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941201

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe ring‐opening polymerization of L‐lactide with stannous octoate was investigated in the presence of pentaerythritol. By this way it was possible to prepare higher molecular weight star‐shaped poly(L‐lactide)s compared with the linear ones obtained by stannous octoate only. The weight‐average molecular weights of linear and star poly(L‐lactide)s were measured by light scattering analysis from hexafluoro‐2‐propanol solution, and the respective Mark‐Houwink equations were derived. The second virial coefficient and the intrinsic viscosity of the star polymers were lower than those of the linear ones, which confirms the star‐

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941202

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractAs a design for a biodegradable functional polymer, compositionally homogeneous poly[(sodium acrylate)‐co‐(vinyl alcohol)] [P(SA‐co‐VA)], containing varying amounts of vinyl alcohol groups as biodegradable segments were prepared and their biodegradability and builder performance in detergent formulations were analyzed with respect to the successive vinyl alcohol length. It was found that the acrylate copolymers having more than 80 mol‐% vinyl alcohol content showed biodegradability. That is, P(SA‐co‐VA) having a vinyl alcohol chain length of more than about 5–6 is cleaved by PVA‐degrading microbes. This indicates that the vinyl alcohol blocks, which act as biodegradable segments, should be incorporated into the polymer chain in such a manner that they are accepted as substrates by the PVA

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941203

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA series of small peptides consisting of the repeating sequence Asn‐Pro‐Asn‐Ala, and their Gly‐substituted analogs, having one of the Asn residues replaced by Gly, have been synthesized to investigate the role of Asn side‐chain amido groups in stabilizing the secondary structure of the Asn‐Pro‐Asn‐Ala tetrapeptide unit. Analyses of the1H NMR data obtained in dimethyl sulfoxide (Me2SO) revealed that the secondary structure of the tetrapeptide sequence is stabilized by virtue of the two Asn residues preceding and following Pro. The sequence‐specific turn structure, which is proposed here as the most probable conformer for the tetrapeptide unit, contains at most three intra‐molecular hydrogen bonds: between backbone CO of Asn preceding Pro and backbone NH of Asn following Pro (inverse γ turn), between side‐chain NHEand backbone CO of the same Asn following Pro, and between side chain CO of Asn preceding Pro and

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941204

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractPoly(alkylene phosphate)s of low molecular weight were synthesized by polytransesterification of dialkyl phosphonates with poly(ethylene glycol)s (PEG). These poly(alkylene phosphonate)s were then converted into poly(alkylene phosphate)s by using the Atherton‐Todd reaction in methanol as a solvent. The compound 2‐phenylethylamine was immobilized on these polymers via ionic bonds. These immobilizations were achieved by both alkylation and dealkylation reactions. The final products from these reactions are the polyanions. The structures of these products were determined by a combination of1H,31P and31C NMR spectrosc

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941205

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractEquilibrium constants were determined for the formation of cyclic oligomers of the general formula\documentclass{article}\pagestyle{empty}\begin{document}$ {\hbox{-\hskip-5pt-\hskip-5pt-}[({\rm CH}_3})_2 {\rm Si \hbox{---} Si(CH_3})_2\hbox{---} {\rm O\hbox{-\hskip-6.5pt-}]}_n , n = 2 - 6$\end{document}, in the polymerization of then= 2 homologue, octamethyl‐1,4‐dioxa‐2,3,5,6‐tetrasilacyclohexane (1). The formation of a linear polymer is thermodynamically favoured in bulk and in concentrated solutions. The equilibrium concentration of cyclics is little dependent on temperature. The six‐membered ring,n= 2, used here as a monomer, is the most abundant cyclic in the equilibrium mixture. Kinetics of the conversion of1during the polymerization initiated with CF3SO3H, CH3SO3H and CF3COOH was studied in methylene dichloride solution. In its first stage, the reaction follows first order, but it slows down at higher monomer conversion. The order of the reaction with respect to the acid is two. Some kinetic features of the polymerization initated with CF3SO3H were similar to those exhibited by the polymerization of octamethylcyclotetrasiloxane (D4). In particular small amounts of additional water have rather small effect on the rate, but change to a considerable extent the entropy and enthalpy of activation. The concentration of cyclic oligohomologues passes through a maximum during monomer conversion, which indicates the kinetic enhancement of the cyclisation process. This observation is somewhat similar to those in the polymerization of hexamethylcyclotrisiloxane (D3). However, in contrast to the polymerization of D3and similarly to the polymerization of D4, the excessive formation of oligomers being multiples of the monomer is not

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941206

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRate coefficients of termination and transfer in the free‐radical polymerization of 1,3‐butadiene in chlorobenzene were determined in the temperature range 318 K

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941207

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractRubber modification of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO)/crosslinked polystyrene (CPS) semi‐interpenetrating polymer networks (semi‐IPNs) was studied using polybutadiene (PB), a linear styrene‐butadiene‐styrene (SBS) triblock cocpolymer and a star‐shaped SBS multi‐block copolymer, at different composition ratios. The materials, obtained by reactive compression moulding of mixtures containing PPO, an elastomer, styrenic monomers and crosslinker (divinylbenzene), show a very high glass transition temperature (Tg), high dimensional stability and good

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941208

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo‐dimensional heteronuclear single quantum coherence — total correlation spectroscopy (2D HSQC‐TOCSY) was used to make end‐to‐end sequential assignments and determine stereochemical configuration at the triad, tetrad and pentad levels of poly(acrylic acid). The pseudo three‐dimensional experiment allows heteronuclear (13C‐1H) as well as homonuclear (1H‐1H) corelations in a single 2D NMR experiment. The stereochemical configuration assignment is based on sequential identification of neighboring species. For example, ammrtetrad resonance (methylene‐13C) is determined by its correlations to themmandmrtriad resonances (methine) that constitute it. Hence, it is independent of chemical shift and peak intensity estimates that are requisites of the conventional method. This self‐consistent technique enables absolute assignments of all magnetically unique tetrads and some of the pentad resonances. In addition, some resonances in the methylene and methine regions that have been difficult to characterize by conventional techniques were unequivocally assigned to endgroup resonances and other polymerization by‐products of the low‐molecular‐

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941209

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractSynthesis and radical polymerization of allenyl ethers with oligo(oxyethylene) moieties (1a–1c: CH2CCHO(CH2CH2O)mCH3,m= 3 − 1) were examined. The polymerization of1a(m= 3) in bulk with 2,2′‐azoisobutyronitrile as initiator at 60°C gives the polymer2ain 51% yield with 75% of the double bonds remaining in the polymer chain (estimated by1H NMR). The polymers2a–2care hydrophilic, soluble in protic solvents such as water and methanol, and are subject to crosslinking upo

ISSN:0025-116X    

DOI:10.1002/macp.1993.021941210

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY