摘要:

AbstractThermal degradations of samples of poly(methyl methacrylate), prepared with different anionic initiators, were compared. It could be shown that the polymers prepared with 1,1‐diphenylhexyllithium and with the tetramer of α‐methylstyrene degrade in one step at temperatures higher than 300°C, whereas those prepared with cumylcesium exhibit two degradation steps, one at temperatures lower and one at temperatures higher than 300°C. By means of end group analysis and molecular weight determinations it could be concluded that the low temperature degradation step of poly(methyl methacrylate), prepared with cumylcesium, involves initiation at the polymer chai

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900301

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPolymers containing azo groups and CC‐double bonds were crosslinked by heating to the temperature at which cleavage of the azo functions covalently linked to the polymer backbone takes place. The crosslinking process was characterized by swelling experiments and by DSC. From the reaction enthalpy the number of polymer chains initiated by one radical was estimated. Swelling experiments and DSC showed that the crosslinking efficiency of the radicals increases with the temperature at which the azo groups are split off and with the instability of the radicals. Polymers containing also functions with different thermostability were used for selective stepwise network formatio

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900302

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractUnsymmetrical azo compounds of the general structurem‐RC6H4NNC(OCOCH3) (R1) (R2) (2–4), in which R stands for H, CH3, CHCH2or a polymeric residue, were irradiated with light of λ ≥ 330 nm. Depending on the substituents R1and R2and the reaction temperature trans‐cis isomerization or/and decomposition was observed. Polymers containing azo groups and CC‐double bonds can be crossl

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900303

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe photodehydrochlorination of four poly(vinyl chloride) (PVC) samples of different tacticities, as studied previously, was compared with that of a PVC sample after being modified to various degrees by nucleophilic substitution with sodium benzenethiolate (NaBT). In order to separate the influence of substituted structures from that of the chromophoric group grafted onto the polymer, a series of PVC mixtures withsec‐butyl phenyl sulfide (BPT), of compositions similar to those of modified polymers was also studied. The evolution of HCl was found to be a linear function of the absorbed dose in all cases. The quantum yield of dehydrochlorination, ΦHCl, as obtained from the slopes, appeared to decrease with the isotactic content. The results suggest specific isotactic triads to be markedly reponsible for the photodehydrochlorination, which would account for a mechanism based on the occurrence of chlorines of low dissociation energy at such tria

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900304

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractA new, general functionalization reaction for polymeric organolithium compounds was developed based on their quantitative reaction with 1,1‐diphenylethylene derivatives. The utility of this method was demonstrated by preparation of 4‐hydroxyphenyl‐terminated polystyrene (2b) by reaction of polystyryllithium in benzene at room temperature with 1‐[4‐(tert‐butyldimethylsiloxy)phenyl]‐1‐phenylethylene (1a) followed by hydrolysis with dilute hydrochloric acid. The course of the functionalization reaction was monitored by ultraviolet‐visible spectroscopy at 406 nm. Polystyrene2bwas characterized by size exclusion chromatography, thinlayer chromatography, membrane osmometry, end‐group titration and both1H and13C NMR spectroscopy. All experimental evidence is consistent with quantitative functionalization via the 1,1‐diphen

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900305

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractChain extension of hydroxyl‐ or vinyl‐terminated poly(dimethylsiloxane) was carried out with difunctional end‐linking agents that are similar in their structure to the higher functionality end linkers used for model network formation. Values of the number‐average molecular weight of the polymers before and after chain extension were determined by gel permeation chromatography. In this way, values of the extent of reaction,p, were determined for different stoichiometric ratios,r. They were found to be in the range 0,5–1,0, with the largest values generally corresponding torclosest to unity. Increase in reaction time increasesp, but increase in the amount of catalyst did not show any discernible effect. The overall results show that at least under some conditions, the analogous reactions using end linkers of functionality three or higher should produce nearly perfect model

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900306

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractPolypropylenes produced with various heterogeneous titanium‐based Ziegler‐Natta catalysts were fractionated by solvent extraction technique. The infrared analysis of the fractions indicates the presence of a crystalline syndiotactic sequence, soluble in xylene at 20°C, and boiling hexane soluble fractions of all samples examined. Highly syndiotactic polypropylene (proportion ofrrrrpentad is 0,50), comparable in syndiotacticity to the syndiotactic polymer prepared at −78°C with a homogeneous vanadium catalyst, was separated from the xylenesoluble fraction of the polymer prepared with the system TiCl3‐Al(C2H5)2Cl by means of elution column fractionation. The steric irregularities are mainlyrrrmandrrmr(ratio ≈ 1:1), suggesting that the propagation is controlled mainly by end‐groups. Chemical inversions, i. e., head‐to‐head or tail‐to‐tail linkages of propylene units, are practically absent, though they are seen in syndiotactic polypropylenes prepared wi

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900307

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe chiral catalyst ethylene(bisindenyl)zirconiumdichloride/methylaluminoxane, which is soluble in hydrocarbons, allows the polymerization of cyclic alkenes, e. g. cyclopentene, to form isotactic polymers. No ring opening reaction occurs. To reduce the high melting point of the polycyclopentene, copolymers with ethylene were synthesized. The copolymerization of cyclopentene with ethylene shows similar reaction rates as found for the homopolymerization of ethylene. From13C NMR spectroscopically calculated rates of incorporation of cyclopentene or cycloheptene in the polymers the copolymerization parameters can be deduced. With increasing polymerization temperature from −10 to 20°C ther1values rise significantly from 80 to 300. Up to 10 mol‐percnt; of cyclopentene monomeric units in the polymer the comonomer is incorporated statistically, whereas a higher content of comonomer leads to two‐block for

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900308

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe reaction kinetics for the group transfer polymerization (GTP) oftert‐butyl methacrylate (TBMA) using a silyl ketene acetal initiator and a nucleophilic catalyst are investigated. The reaction is shown to be of first order in both monomer and catalyst concentrations. The “livingness” of this system appears to be influenced by the reaction temperature. At temperatures above −20°C, deactivation is observed, with its severity increasing with increasing temperature. This deactivation is attributed to a depletion of catalyst by side reactions. It was demonstrated that reactivation is made possible by the addition of more catalyst. This result is in contrast to the anionic polymerization of TBMA, where no deactivation was observed even at ambient temperature. At temperatures below −20°C no deactivation is observed; however, at these temperatures, the reactions manifest induction periods with lengths increasing with decreasing temperature. The rate constants are lower than those for the GTP of methyl methacrylate (MMA) by a factor of 1,5 to 2. The following Arrhenius parameters were obtained for the propagation rate constants: activation energy,Ea= (19,1± 3) kJ/mol, preexponential factor, log10A= (7,05± 0,3). These values are comparable with those obtained for MMA. The molecular weight distributions are similar to those obtained in the GTP of MMA, i.e. the ratio of weight‐to number‐average molecular weights is rather high for low monomer conversions and narrows toM̄w/M̄n≥ 1,3 for full conversion. This is attributed to the rates of the catalyst

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900309

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe concentration‐dependent decrease of the entropy of polymer chains in polymer solutions is treated by Monte Carlo simulation technique and by blob analysis. The results suggest the existence of a universal relation for this dependence over a broad concentration range. Differences between the observed combinatorial entropy of the multichain system and the behaviour proposed by mean‐field treatments as well as implications for treatments of the melting entropy of a polymer are pointed

ISSN:0025-116X    

DOI:10.1002/macp.1989.021900310

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY