摘要:

AbstractTheQ‐eand Patterns of Reactivity schemes for the quantitative treatment of the reactions of polymer radicals both suffer from drawbacks which seriously limit their usefulness. Two revised versions of the Patterns of Reactivity scheme, in which all the necessary parameters are derived from experimental data, are summarised here. Both new schemes provide significantly more accurate assessments of monomer reactivity ratios and transfer constants than do their predecessor

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170501

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAdsorption and aggregation of carbosiloxane dendrimers on mica and pyrolytic graphite were investigated by scanning force microscopy (SFM). The aggregation process started from (i) single molecules which coagulated to (ii) clusters and (iii) fluid droplets followed by formation of (iv) a complete layer on the solid substrate. The molecules were displayed as a globular particle with a diameter of about 2.5 nm. Tapping SFM of the liquid was possible due to the fact that the dendrimer undergoes a transition to a viscoelastic state below the tapping frequency of about 360 kHz. Dynamic shear compliance experiments have shown a plateau of 5 · 10−7Pa−1around this frequency. Dendrimer droplets slowly spread into polygonal lamellae with a thickness of two molecular layers. The structures indicate a rather regular dense packing of the globular molec

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170502

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractA route to well‐defined side‐chain liquid‐crystalline polysiloxanes (ratio of weight‐to number‐average molar massesM̄w/M̄n<1.2 is reported. Anionic ring‐opening polymerization of pentamethylvinylcyclotrisiloxane yielded a poly(dimethylsiloxane‐co‐methylvinylsiloxane) backbone. A flexible disiloxane spacer was used to connect 4‐(ω‐alkenyloxy)‐4′‐cyanobiphenyl mesogenic molecules to the vinyl groups which belong to the backbone, leading to a side‐chain liquid‐crystalline polysiloxane (SCLCP) which has its mesogens distributed regularly along the main chain. Preliminary measurements indicate an electro‐optic switching time τs= 1 min at

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170503

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractLiquid‐crystalline (LC) block copolymers of lamellar morphology were prepared via anionic polymerization of polystyrene‐block‐1,2‐polybutadiene and subsequent introduction of a deuterated mesogen by polymer analogous reaction. Deuteron NMR measurements show that the first‐order nematic/isotropic transition in the block copolymer is changed to a critical behaviour under the influence of shear. In the nematic phase the order parameter is reduced with respect to the homopolymer, and there is no evidence of an isotropic boundary layer of the LC‐block at the nematic/isotropi

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170504

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractBiodegradable interpenetrating polymer network (IPN)‐structured hydrogels consisting of gelatin (Gtn) and dextran (Dex) were prepared by sequential crosslinking reactions of Gtn and methacryloylated Dex. Phase separation of these hydrogels is dominated by preparation conditions, i.e., above or below the sol‐gel transition temperature (Ttrans) of Gtn. Enzymatic degradation by either α‐chymotrypsin or dextranase is hindered for the IPN‐structured hydrogel prepared belowTtranswhereas this hydrogel is perfectly degradable in the presence of both enzymes. Such a specific feature of enzymatic degradation was not observed for the hydrogel prepared aboveTtrans. These results suggest that double‐stimuli‐responsive degradation of IPN‐structured hydrogels is related to their ph

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170505

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe first examples of poly(ferrocenylsilane)‐poly(carbosilane) random copolymers have been prepared via the transition metal‐catalyzed ring‐opening copolymerization of silicon‐bridged [1]ferrocenophanes and disila‐ or benzosilacy

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170506

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe disiloxane‐bridged zirconocene complexes, tetramethyldisiloxanediylbis (cyclopentadienyl)zirconium dichloride and tetramethyldisiloxanediylbis(cyclopentadienyl) dimethylzirconium initiate the homopolymerization of ethene as well as the copolymerization of ethene and α‐olefin with a modified methylaluminoxane as cocatalyst. The catalyst systems give resonable activity but the molecular weight of polyethene decreases drastically with increasing polymerization tempera

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170507

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPolymerization of propene at −78°C in the presence of a homogeneous catalytic system based on a Ni(II) diimine derivative and methylaluminoxane affords prevailingly syndiotactic crystalline poly(propylene) (rr triad content ≈80%).13C NMR analysis of the polymer microstructure indicates that the stereochemistry of the monomer insertion is controlled by the configuration of the methine carbon of the growing chain end (unlike‐1,3 asymmetric induction). This is the first example of stereospecific homopolymerization of propene promoted by a late transition metal ca

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170508

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe first radical polymerization of 1‐methoxy‐o‐quinodimethane(2)generated by thermal ring‐opening isomerization of 1‐methoxybenzocyclobutene(1)is described. The polymerization of1in the presence of a radical initiator afforded an MeOH‐insoluble polymer(3)in moderate yield at temperatures above 90°C. The structure of the obtained polymer is consistent with a ring‐opening polymerization. The yield of the polymer increased with the amount of initiator. Radical copolymerization with methyl acrylate was carried out. Treatment of 3 with acid gave poly(o‐phenylenevinylene)

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170509

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractBulk radical polymerization of styrene in the presence of nitronyl nitroxides (2‐(4‐substituted phenyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydroimidazolyl‐1‐oxyl 3‐oxide) was studied. All nitronyl nitroxides, like other nitroxyl radicals such as 2,2,6,6‐tetramethylpiperidine 1‐oxyl radical (TEMPO), act as reversible radical scavengers. The efficiency of controlling the polymerization is affected by the substituent at the 4′‐position. The efficiency increases with electron donating strength of 4′‐substituents, at least at the beginning of the reaction. However, the thermal stability of nitronyl nitroxides decreases in the same order. Thus, TEMPO is more suitable than nitronyl nitroxides for controlled/“living”

ISSN:1022-1336    

DOI:10.1002/marc.1996.030170510

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY