摘要:

AbstractThe minimum structure of a poly(vinyl alcohol) block as a biodegradable segment in the polymer chain was estimated with respect to block length and its stereochemical configuration. It was found that poly(vinyl alcohol) block with a chain length of more than 3 monomeric units and having an isotactic structure is quickly biodegraded, in contrast to an atactic block having the same chain length, by poly(vinyl alcohol) (PVA) assimilating microbes and PVA‐dehydrogenase. It was also found that the substrate specificity of PVA‐dehydrogenase obtained from bothAlcaligenes faecalisKK314 andPseudomonassp. 113 P3 is quite simi

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961101

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractOne of the useful methods to improve the toughness of epoxy resin is by mixing the resin with poly(ether‐sulfone) (PES). In the present work, two hydroxyl‐terminated PESs with molecular weightsMn= 28 600 and 4 200 were used for blending with epoxy resin. The curing reaction of diglycidyl ether/bisphenol‐A (DGEBA) with 4,4′‐diaminodiphenyl sulfone (DDS) in the presence of hydroxyl‐terminated PES was studied by means of differential scanning calorimetry (DSC) and gel‐permeation chromatography (GPC). For the DGEBA‐DDS‐PES system with a stoichiometric ratio of epoxy and amino groups the DSC experimental results showed that at a fixed molecular weight of PES the curing reaction rate decreases with increasing PES concentration. At a fixed PES concentration (in the range of between 0 and 20 wt.‐% of PES), the DGEBA‐DDS system modified with hydroxyl‐terminated PES with lower molecular weight had a faster curing reaction rate at low conversion and a slower curing reaction rate at high conversion. The GPC results showed the evidence of etherification between low‐molecular‐weight PES with epoxy resin. However, very little etherification of high‐molecular‐weight hydroxyl‐terminated PES with epoxy resin was found. Based on the experimental results, a curing reaction mechanism of DGEBA with DDS in the presence of hy

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961102

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractBlock copolyetheresters1with poly(pentamethylenep,p′‐bibenzoate) segments and poly(ethylene oxide) segments were prepared by melt polycondensation of dimethylp,p′‐bibenzoate, 1,5‐pentanediol, and poly(ethylene glycol) (PEG) with molecular weights of 400, 1 000, or 2 000. The1H NMR analysis shows that the feed mole ratio of PEG to dimethylp,p′‐bibenzoate determines the composition of the block copolyetheresters. The differential scanning calorimetry (DSC) results indicate that some block copolyetheresters exhibit a monotropic smectic liquid‐crystalline phase due to the poly(pentamethylenep,p′‐bibenzoate) segments. The transitions depend on the content and the molecular weight of the PEG. The block copolyetheresters1show high water absorption due to the hydrophilic nature of the poly(ethylene oxide) segments. The water absorption increases with increasing PEG content. As the molecular weight of PEG increases, the water absorption incr

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIf gels are investigated in an analytical ultracentrifuge by means of sedimentation equilibrium experiments, so called soluble parts which are originally not incorporated into the network influence the swelling pressure equilibria of the gels. For gelatin/water, it can be shown that an irreversible process takes place which is dependent on the rotational speed of the experiment. Experimental evidence is given that soluble parts which are partly associated and aggregated to the polymer network can act as a branching and/or crosslinking agent. A model for this process is given. In such a case an application of the results of the swelling theory, e.g. that of Flory and Huggins assuming a constant number of network junctions, cannot be applied anymore. A universal procedure is described how swelling pressure equilibria can be identified, although the crosslinking density is changed. It can be shown that the gradient of the soluble parts, respectively the additional structural changes of the gel by the soluble parts, is reproducible and with it the swelling pressure equilibria. Furthermore the radial distribution of dyed soluble parts inside the gel phase is presented as a function of time during a sedimentation equilibrium run with a gelatin/water gel. It can be shown that the back diffusion process of the soluble parts in the gel is very slow and does not lead to the sedimentation‐diffusion equlibrium of free soluble parts in the considered time interval of 4 months. In combination with the detected fast sedimentation of the soluble component in the gel phase this gives further evidence for the association of the soluble parts to the gel network forming a gradient gel. The predicted formation of the anisotropic gel could be proved by a swelling experimen

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIn the present work the thermodynamic properties of 2,2‐dimethyltrimethylene carbonate (DTC) and poly‐2,2‐dimethyltrimethylene carbonate (PDTC) were studied by precise calorimetry. In adiabatic and dynamic vacuum calorimeters the temperature dependence of the heat capacity of DTC and PDTC was studied between 5 and 470 K. Temperature and enthalpies of physical transitions were determined, and in an isothermal calorimeter energies of combustion of the above compounds were measured. From the results the thermodynamic functionsC p0(T),H°(T)–H°(0),S°(T),G°(T)–H°(0) were calculated for various physical states of the monomer and the polymer from 0 to 470 K. The standard enthalpies of combustion and thermochemical parameters of formation ΔH f0, ΔS f0, ΔG f0of the objects studied were estimated atT=298,15 K andp= 101,325 kPa. The zero entropyS gl0(0) and configurational entropyS conf0of PDTC in the glassy state and the difference in zero enthalpies of the polymer in the glassy and crystalline statesH gl0(0)–H cr0(0) were estimated. The results were used to calculate the thermodynamic parameters of the bulk polymerization of DTC (ΔH pol0, ΔS pol0, ΔG pol0) in the range of 0 to 420 K. It was established that for the process DTC → PDTC, ΔG pol00 in the case of amorphous PDTC (glas

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dichlorides of commercial 1,4‐phenylenediacrylic acid3,3′‐(1,4‐Phenylene)di‐2‐propenoic acid.andN‐(4‐carboxyphenyl)‐trimellitimide were polycondensed with a chiral spacer prepared from (S)‐3‐bromo‐2‐methylpropanol and 4‐mercaptophenol. Optical microscopy revealed that all the resulting copoly(ester‐imide)s form an enantiotropic cholesteric melt and adopt a Grandjean texture upon slight shearing. The WAXD powder patterns indicate the formation of a layered structure in the solid state. Irradiation with UV light of wavelength ⩽ 360 nm allows crosslinkin

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe preparation of poly(amido‐amine)s and poly(ester‐amine)s via polyaddition between aromatic amines containing free or esterified carboxyl groups and compounds with activated double bounds [N,N′‐methylenebis(acrylamide), 1,4‐diacryloylpiperazine and 1,3‐propanediyl diacrylate] is described. The products obtained are typical polyelectrolytes, their solutions exhibiting anomalous viscosit

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

Abstract2‐(2‐Thienyl)ethyl methacrylate (2TEMA,1), 2‐(3‐thienyl)ethyl methacrylate (3TEMA,2) and 2‐(N‐pyrrolyl)ethyl methacrylate (PEMA,3) were synthesized and copolymerized with methyl methacrylate (MMA) by radical initiation with AIBN. The reactivity ratios for the system MMA/2TEMA were determined to berMMA= 0,57 ± 0,09 andr2TEMA= 0,90 ± 0,03. Thiophen was grafted into the copolymers from1–3via oxidative polymerization in nitromethane. The graft copolymers were soluble as aggregates, and films cast from these solutions reached conductivities in the range of

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRandomly branched (hyperbranched) Poly(3‐hydroxybenzoate), poly(3‐Hybe), was prepared by polycondensation of silylated 3‐acetoxybenzoic acid with either silylated 3,5‐diacetoxybenzoic acid or bis(trimethylsilyl) 5‐acetoxyisophthalate. The number of branching points was varied by changing the feed ratio of difunctional and trifunctional monomers.1H NMR and13C NMR spectroscopy proved the nearly random incorporation of the trifunctional “branching units”. Cocondensations with small amounts of acetylated bisphenol‐P allowed one to control the degree of polymerization (DP) and to determine the DP by1H NMR spectroscopy. However, analogous copolycondensations with silylated 2‐(4‐tert‐butylphenoxy)terephthalic acid failed. According to GPC measurements, weight‐average molecular weights above 105were obtained. DSC measurements revealed that the glass transition temperatures (Tg's) vary largely with the degree of branching (DB) and with the nature of the end‐groups. In the case of phenolic OH and acetate end‐groups, the relationshipTgvs. number of branching poin

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper describes preliminary work exploring the feasibility of preparing high‐performance nonlinear optical (NLO) materials based on the polyp‐phenylene (PPP) backbone. Three new monomer/NLO‐phores of the general formula: 4‐RSO2C6H4C(4‐XC6H4) (where R = 2,5‐dichlorophenyl;2a, X = H;2b, X = OCH3;2cX = N(CH3)2) were synthesized and then homopolymerized using catalytic nickel and stoichiometric zinc to produce the poly(p‐phenylenes),3a–c, respectively, as low‐molecular‐weight materials (number‐average molecular weightMn= 1800–6000). NLO‐phores2b–cand low‐molecular‐weight oligomers of3cwere dispersed in a poly(methyl methacrylate) (PMMA) host. Spin‐cast films of these guest‐host systems were subjected to corona poling above the glass transition temperature.Tg. Following poling, both monomer NLO‐phore/PMMA guest‐host systems displayed optical nonlinearity with second‐order nonlinear optical susceptibility χ(2)values of 1.7 pm/V and 0.9 pm/V for2cand2b, respectively. Both systems exhibited good temporal stability at room temperature, with about 12% loss in second harmonic signal over more than 100h. However, the oligomeric material3cdispersed in PMMA showed a smaller NLO signal when poled aboveTg. Attempts to induce dipolar asymmetry in the homopolymers3band3cwere unsuccessful. The observed response during poling and the relaxation of the chromophore orientation following poling, have been discussed in terms o

ISSN:1022-1352    

DOI:10.1002/macp.1995.021961110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY