摘要:

AbstractAmorphous and crystalline comb‐like poly(methacrylamides) containing cinnamoyl moieties in the side chain were synthesized and characterized. On UV‐irradiation these polymers and related monomeric model compounds undergoE‐Zphotoisomerization, [2 + 2] photocycloaddition and photo‐Fries rearrangement. The competition between these photoreactions was investigated in solution and solid films. The quantum yield of the photocycloaddition and the maximum of conversion of chromophores are much higher in solutions and in films for the crystalline homopolymer compared to the amorphous copolymer. The disappearance of crystallinity caused by isomerization in solution and in films caused by cycloaddition was demonstrated by means of DSC measurements. In films with side‐chain crystallinity the quantum yield of cycloaddition increases with rising temperature but falls drastically above the melting point. The crystallinity of the polymer influences photoreactivity of the cinnamoyl moiety, and, on the other side, photoisomerization and cycloaddition destroy the crystall

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930701

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this paper we studied the influence of the copolymerization of trimethylolpropane trimethacrylate (TRIM) with methyl methacrylate (MMA) on the pore structure of the resulting gels. TRIM and MMA were suspension‐copolymerized with toluene as pore‐forming agent. All gels have bimodal pore‐size distributions. The size distribution of large pores (r>50 Å) of the solvent‐free poly(TRIM‐co‐MMA) broadens when the TRIM/MMA ratio decreases. The size distribution of small pores (r<50 Å) shows sharp maxima for pores with a radius of 20 Å. In the swollen state the separation range for the poly(TRIM‐co‐MMA) particles of polystyrene standards varies with the TRIM/MMA ratio. The results of the porosity measurements of the swollen gels show good agreement with the results obtained from the dry gels. The porosity of the dry gels was studied with scanning electron microscopy, nitrogen adsorption/desroption and mercury porosimetry. The pore‐size distributions of the swollen poly(TRIM‐co‐MMA) gel particles were calculated from the size‐exclusion ch

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930702

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo polymeric amines, poly[(2‐aminopropyl)propyleneimine] (PI) and poly[(2‐aminoethyl)‐ethyleneimine] (PII), as well as the dodecyl‐ and imidazolylmethyl‐substituted derivative ofPI, were used for the hydrolysis ofp‐nitrophenyl acetate (PNPA), 4‐acetoxy‐3‐nitrobenzoic acid (ANBA) and some of their homologues, in order to elucidate the relations between their overall structure and their catalytic activities. All reactions were carried out at 28,7°C in aqueous solution, and followed spectrometrically using a catalyst concentration in large excess with respect to the substrate concentration (10−4mol · L−1). The reactions were found to obey pseudo‐first order kinetics. By plotting log[substrate] against time,k2(cat) and consequently the second‐order rate constantsk2were evaluated. The above mentioned polymers show hydrolysis constants which exceed the values obtained for tailor‐made partially substituted polyethyleneimines. Even when linear polythyleneimine was substituted for 42% with 2‐(2‐aminopropylamino)propyl groups,PIandPIIgivek2values which are 8 times higher towards PNPA, and 10 times higher towards ANBA, u

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930703

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA structural investigation is described of poly(L‐lactic acid) by best fitting of powder X‐ray diffraction patterns. The examined sample shows the already known pseudo‐orthorhombic α‐form, and it was possible to determine the location of the two 103polymeric helices in the unit cell and the size distribution of the crystallites. Furthermore, a study is reported of the crystallization kinetics of the above cited polymer by light depolarization measurements in an optical microscope. The crystallization kinetic constants in bulk were evaluated in a temperature range (70–165°C) wider than that previously resulting from measurements of radial growth of

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930704

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe formation and aggregation of primary particles in the beginning of emulsion polymerization was monitored by surface tension measurements, viscometry, electron microscopy, and static and dynamic light scattering. The dimensions of the primary particles in the emulsion polymerizations of vinyl acetate and methyl methacrylate are of the order of 3 – 5 nm. Immediately after the formation of primary particles these begin to aggregate. The stability of these particles is discussed and conclusions are drawn concerning the formation of new particles in the course of polymerization or in seeded polymerization experiment

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930705

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractL‐Lactide was polymerized with stannous 2‐ethylhexanoate (stannous octoate) in the presence of pentaerythritol to investigate multifunctional initiation. The prepared oligomers contain starshaped 4‐arm molecules when the mole ratio of [lactide]/[pentaerythritol]is above 32. The molecular weight of oligomers coincides with the [lactide]/[pentaerythritol]ratio, indicating that pentaerythritol in conjugation with stannous octoate is an initiator for the “living” polymerization of

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930706

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractRadical copolymerization of 4‐(trimethylsilyl)styrene (TMSS) with styrene were carried out to estimate the reactivity of TMSS. The monomer reactivity ratiosr1andr2in the radical copolymerization of TMSS (M1) with styrene (M2) were evaluated as 0,28 and 0,48, respectively. The valuer1·r2(= 0,13) being smaller than unity indicates that the trimethylsilyl group at para position behaves as an electron‐withdrawing substituent. Reactions of lithium diethylamide with TMSS in the presence of diethylamine, gave the 1:1 addition product 1‐[2‐(N,N‐diethylamino)‐ethyl]‐4‐(trimethylsilyl)benzene. Kinetic analysis showed that the second‐order rate constant (k) for this addition reaction is 34,4 · 10−4dm3· mol−1· s−1, which is by a factor of 2 larger than that for the reaction with styrene (k= 16,0 · 10−4dm3· mol−1· s−1). The fact is also compatible with the above consideration for ther1·r2values. Lithium diisopropylamide initiated anionic copolymerizations of TMSS with 1,4‐divinylbenzene (DVB) were also examined. The polymerizations proceed smoothly without any gel formation and the resulting copolymers are soluble in various common solvents such as benszene, tetrahydrofuran, chloroform, etc. Thus, novel organosilicon‐containing polymers having appropriate amounts of reactive pe

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930707

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractEthylene and propene were homopolymerized with 11 different metallocene‐methylalumin‐oxane (MAO) catalysts1–11using a constant set of parameters. The catalytic activity of the two unbridged and 9 ansa‐metallocenes as well as the properties of the polymers, such as molecular weight, width of molecular weight distribution, melting point, and, with polypropene, chain microstructure, were investigated. It was found that structure variations of the catalysts cause rather different catalytic behaviour, which further diversifies the performances with the two different monomers. In some cases this comparison allows insight into the nature of the influencing

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930708

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractBy X‐ray diffraction on polycrystalline powders and Fourier‐transform IR spectroscopy, some adducts MgCl2(C2H5OH)xwere studied, having different composition in the range fromx= 0 (α‐MgCl2) tox= 6. For 2

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930709

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reactions occurring during melt‐mixing of poly(ethylene terephthalate) and bisphenol‐A polycarbonate have been reconsidered. Certain evidence leads us to conclude that two reactions, usually disregarded in the literature, occur, which have to be considered in the general scheme along with the already described exchange reactions. These reactions lead to the formation of cyclic ethylene carbonate and of aromatic‐aliphatic ether moieties, and therefore introduce significant modifications in the chemical structure of the polymeric material resulting from melt‐mixing. An increase in the amount of aromatic‐aromatic ester groups and the formation of a significant amount of aromatic‐aliphatic ether moieties can be obtained depending on reaction

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930710

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY