摘要:

AbstractBinary mixtures of a thermoplastic engineering poly(ethylene terephthalate) (PETP) with a thermotropic liquid‐crystalline random copolyester (PCL) were prepared by melt blending the polymers in a screw extruder or by precipitating them from a solution in a common solvent. Differential scanning calorimetry and polarizing optical microscopy were used to study their thermal and morphological properties as a function of temperature and composition. At high temperature, the blends rich in PETP are isotropic liquids, those rich in PCL are nematic fluids, and those of intermediate compositions are formed of two phases in equilibrium, one liquid‐isotropic and one nematic. At low temperature, the blends are generally biphasic, with the two component polymers crystallized. The presence of crystallized PCL proved not to act as a nucleating agent towards the crystallization of PETP from the melt. A schematic phase diagram was drawn to summarize the thermal and morphological behaviour of the blends. Scanning electron microscopy studies of injection moulded samples revealed the presence of highly oriented fibrils when the composition exceeded roughly 50 wt.‐% in PCL. The bending elastic modulus of the injected blends with 75 wt.‐% of PCL surpasses that of the pure PCL, probably due to the presence of oriented high‐molecular‐weight PETP molecules. The particular dependence of the mechanical rigidity upon the concentration of PCL permits easily to determine conditions for the thermoform

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960701

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe anionic polymerizations of methyl methacrylate (MMA), isopropyl methacrylate (IPMA), andtert‐butyl methacrylate (TBMA) in THF in the presence of diethylzinc were investigated. The addition of diethylzinc to the reaction mixture remarkably lowers the polymerization rates of the methacrylates initiated with potassium diphenylmethanide to afford polymers with the predicted molecular weights and very narrow molecular weight distributions, while PMMA and poly(IPMA) produced with potassium diphenylmethanide in the absence of diethylzinc have rather broad molecular weight distributions. The stereospecificities of PMMA, poly(IPMA) and poly(TBMA) are not affected by diethylzinc. From the result of the block copolymerization of MMA with TBMA, it was found that the presistency of the anionic propagating end of PMMA is significantly enhanced by the addition of diethylzinc. The retardation of the polymerization rates and the enhancement of the persistency of the propagating end in the presence of diethylzinc may be caused by the weak coordination of diethylzinc toward the enolate anions at the propagating end group

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960702

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper describes a new class of reaction, group‐transfer alternating copolymerization (GTAC), between 2‐phenyl‐1,3,2‐dioxaphosphorinane (1) and trimethylsilyl 2‐(acryloyloxy)ethanesulfonate (2). The copolymerization took place without any added catalyst and proceeded via quantitative trimethylsilyl group‐transfer process to give a 1:1 alternating copolymer3ahaving a ketene silyl acetal group in the main chain. Results of spectroscopy as well as alkaline hydrolysis and bromination of the copolymer confirmed th

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960703

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPartially hydrolyzed ethylene/vinyl acetate copolymers (EVALVA) were modified by covalent binding of a heparin‐complexing poly(amido‐amine) (N2LL). The physicochemical characterisation of the starting and modified materials was carried out through thermal analysis, dynamic mechanical thermal analysis, mechanical tensile test, contact angle, potentiometric measurements, water uptake and FT‐IR spectroscopic measurements. The behaviour of this material in both the dry and the wet state was stressed, evidencing the different orientation of the chemical groups, which are buried or exposed according to whether its nature is hydrophilic or hydrophobic. The material was heparinised, and the presence of heparin was revealed by energy dispersive X‐ray analysis (EDAX) an

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960704

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA triphenylcarbinol (TPC) moiety‐containing cellulose derivative (TPC‐Cell) was prepared by a two‐step reaction. First, microcrystalline cellulose was dissolved in SO2‐diethyl‐amine‐dimethyl sulfoxide and homogeneously reacted withp‐bromobenzyl bromide to obtain tri‐O‐(p‐bromobenzyl)cellulose (BB‐Cell). Second, the BB‐Cell was reacted with butyllithium and then with Michler's ketone. The degree of substitution (DS) of the obtained ethanol‐soluble TPC‐Cell was up to 0,56. The leuco form of TPC moiety in TPC‐Cell showed a small extent of ionic dissociation in ethanol under irradiation with UV light of λ>290 nm, accompanied by a large extent of decomposition of the structure. With additions of acid and then of alkali, the TPC structure was reversibly isomerized from the leuco form to the colored from and then from the colored from to the leuco form. However, repeated cycles of the additions of acid and alkali resulted in considerable fat

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960705

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ionization of 1‐chloro‐1‐isobutoxyethane (IBVCI) in the presence of BCI3in CD2Cl2and CD2Cl2/CDCl3mixtures at variable temperatures was studied by1H NMR spectroscopy. The presence of only one NMR signal for the methine proton in the intermediate stage of ionization indicated a fast exchange between covalent and cationic species. The dependence of its chemical shift on the [BCI3]0/[IBVCI]0ratio was used to calculate the equilibrium constant of ionization at various temperatures, assuming only the ionization‐recombination process. The dependence of the calculate the equilibrium constant (Kapp) on the [BCI3]0/[IBVCI]0ratio indicated the involvement of additional side equilibria, including the formation of oxonium ions by the reaction between the carbocation and the ether functionality, and the complexation of Lewis acid by the ether group. The width at half‐height of the methine proton signal was used to calculate the apparent rate constant of the recombination of the counterions in the ion pairs (K appr). It was found thatK kappris larger in CDCI3/CD2CI2mixtures than in CD2CI2.When BCI3is present in excess, the calculated rate constants for ionization and recombination are higher than the reported rate constant of propagation for the cationic polymerization of isobutyl vinyl ether (IBVE). Attempts to use this finding in order to prepare well‐defined polymers were unsuccessful because of the consumption of BCI3through the addition reaction to the double bond

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960706

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPlasticizing agents are known to shift the material functions of polymer melts like raised temperatures to shorter times and to higher frequencies. The influence of dioctyl sebacate, dioctyl phthalate and bibenzyl on the viscoelastic properties of polystyrene melts is sized by shift factors which can be evaluated very exactly from the dynamic moduli in the rubber‐like liquid region. Besides, these shift possibilities enable us to enlarge the experimental window to the low frequency region for some decades. The typical diluent effect caused by the additives is quite similar to the one caused by not entangled polymer molecules. The lowering of the plateau modulus, i. e., the shift on the modul axis, is found to be equal to the square of the weight fraction of the polymer. The reduction of the relaxation times, i. e., the shift on the time or frequency axis, mainly is due to the increased fraction of free volume accounted for byA/Mn,c, whereArates the fraction created by one mole additive andA/Mn,cis the number‐average of the molar masses of polymer and additive. The influence of the free volume on the relaxation times is calculated with the aid of a Doolittle equation. The Concentration dependence of the time‐temperature shift factors is also accounted for byA/Mn,c. Therefore, besides the parameter A, only the three parameters used in (and known by) the analysis of the time‐temperature superposition principle, i. e., the fraction of free volume of the pure polymer (f), the thermal expansion coefficient off(αf) and the Doolittle parameterB, are needed for the calculation of the temperature‐dependent time‐concentration shift factors and of the concentration‐dependent time‐temperature shift

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960707

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractBased on unsteady diffusionkinetics, polyethylene(PE)‐graft‐polystyrene (PS) copolymers were designed and synthesized with a heterogeneous high yield titanium‐based catalyst by copolymerization of ethylene with a PS‐macromonomer using 1‐hexene as a short main agent to promote the incorporation of the PS‐macromonomer. The presence of 1‐hexene facilitated the diffusion of the PS‐macromonomer, giving rise to the significantly increased incorporation of the PS‐macromonomer. Compatibilization of blends of linear low density polyethylene (LLDPE)/poly(phenylene oxide) (PPO) with the PE‐g‐PS copolymer were investigated using scanning electron microscopy (SEM) and dynamic mech

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960708

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA novel type of biodegradable, pH‐sensitive hydrogels was synthesized by crosslinking ofN,N‐dimethylacrylamide copolymer precursors. These hydrogels contained azoaromatic crosslinks which may be degraded by the azoreductase activities in the colon. Hydrogel degradation experiments were performed bothin vitroandin vivo, using rat cecum contents and implantation into the rat cecum, respectively. In order to evaluate the influence of the detailed network structure on the degradation properties, the degradability of hydrogels synthesized by two different methods, i.e., crosslinking of polymeric precursors and crosslinking copolymerization, were compared. Two different patterns of the degradation of hydrogels were observed, i. e., a surface erosion process and a bulk‐degradation‐like process. The azo bond cleavage rate of hydrogels prepared by crosslinking of polymeric precursors was faster than that of hydrogels prepared by crosslinking copolymerization. The differences in the gel degradation pattern and the cleavage rate of azo bonds were attributed to the differences in the structure of the hydrogel network, i. e., the molecular weight of primary chains and the formation of chain entanglements. Under the experimental conditions used, the degradation ratein vivowas 3 to 5 times faster than thatin vitro.It appears that these hydrogels have a potential for colon‐specific drug

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960709

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe complex formation reaction of poly(vinyl ethers) of ethylene glycol (1), poly(vinyl ether) of diethylene glycol (2), copolymers of vinyl ether of ethylene glycol and vinyl butyl ether (3a–3c) with poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) was studied by conductimetric, viscometric and spectroturbidimetric methods in aqueous solution. It is shown that1and2do not form polycomplexes with PAA. While an introduction of hydrophobic vinyl butyl ether fragments into the structure of1enhances the complexation processes with respect to poly(carboxylic acids), the composition of the polycomplexes is independent of the mixing order of interacting components, temperature and composition of the copolymers. An addition of organic solvents to the aqueous solution of the polycomplexes leads to the cooperative destruction of polycomplex particles. An analysis of IR spectra of the polycomplex films shows the existence of COOH dimers, hydrogen bonds between hydroxyl groups and carboxylic groups as well as ester bo

ISSN:1022-1352    

DOI:10.1002/macp.1995.021960710

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY