摘要:

AbstractTetramethylammonium 3‐aminopropyl dimethylsilanolate, readily prepared from bis(3‐aminopropyl) tetramethyldisiloxane and tetramethyl‐ammonium hydroxide pentahydrate, has been found to serve as a highly effective catalyst for the ring opening polymerization of cyclic siloxanes with an end blocker such as bis(3‐aminopropyl) tetramethyldisiloxane to give aminopropyl terminated linear polydimethylsiloxanes. By following a novel two stage procedure, even high molecular weight (5,000–55,000 g/mol) silicone diamines were able to be prepared in a high state of purity; chain extension reactions of these diamines with diisocyanates gave a series of high molecular weight silicone polyureas with good elastomeric p

ISSN:0959-8103    

DOI:10.1002/pi.4990240302

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractMagnetic resonance imaging has been used to spatially map the time course of the bulk polymerisation of methylmethacrylate. Both two‐dimensional projection and slice‐selective techniques have been employed. Image intensities give qualitative information about viscosity, reaction rates and the localised extent of polymerisation. The importance of proton relaxation measurements in drawing quantitative conclusions is stres

ISSN:0959-8103    

DOI:10.1002/pi.4990240303

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPoly(L‐α,ω‐diaminobutyric acid) having azo aromatic side chains was synthesized by the water‐soluble carbodiimide procedure. The photoresponsive properties of the polypeptide poly[N7‐p‐(phenylazo)benzoyl‐L‐α,ω‐diaminobutyric acid] (PPABLDBA) due to thetrans(about 71%, under visible light)cis(under ultraviolet light) photoisomerization of the azo aromatic moieties in the side chains were investigated by absorption and circular dichroism spectroscopy in hexafluoro‐2‐propanol (HFIP). The starting slightly turbid solution oftrans‐PPABLDBA becomes clear on irradiation at 360 nm, accompanied by photoconversion of the conformer of the azo moieties tocis. The backbone conformation of PPABLDBA in HFIP is right‐handed helical (helical content, about 60%) when the azo moieties aretrans(71%), while the conformation is random coil whencis. The backbone conformational transition of PPABLDBA from helical to coil is mostly reversible u

ISSN:0959-8103    

DOI:10.1002/pi.4990240304

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractPolyetherurethaneureas are increasingly used as implants in the human body, where they come in contact with body fluid. Most of the reported properties of polyetherurethaneureas have been determined in the dry state. The present work deals with the properties of these materials in aqueous systems. A number of linear polyetherurethaneureas based on polyethoxyglycol and polypropoxyglycol of different molecular weights, 4,4′‐diphenylmethane diisocynate, 1,3‐propanediamine and 1,6‐hexanediamine have been prepared. Their swelling characteristics and phase composition in phosphate buffer solution are evaluated. The role of water in changing various properties of polyetherurethaneureas is di

ISSN:0959-8103    

DOI:10.1002/pi.4990240305

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe results of ultrasonic irradiation of polystyrene solutions in toluene, benzene and carbon tetrachloride are described. The effect of a range of conditions such as ultrasonic intensity, solution concentration and varying solvents were investigated. The non‐random nature of the degradation process was clearly demonstrated and the effect of different solvents was interpreted in terms of their thermodynamic propertie

ISSN:0959-8103    

DOI:10.1002/pi.4990240306

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe elastic and viscous properties of polymer melts may be affected by the shear history of the polymer. The extrudate swell of a polymer melt is primarily a manifestation of the elasticity of the polymer melt. In this study, a single screw extruder was used to impose different shear histories on a polystyrene polymer which was processed with and without added plasticizer. The extrudate swell and apparent viscosity of these melts were measured with a capillary rheometer. These characteristics of unplasticized polystyrene are almost not affected by the various preshearing processes. However, the extrudate swell and viscosity of polystyrene containing plasticizer are affected by plasticizer level, shear history and thermal history. After most of the plasticizer in the presheared plasticized polystyrene was extracted, the extrudate swell was still lower than that of the parent sheared polystyrene with the same shear history and the same plasticizer content. These results were obtained without significant changes in molecular weight.Shear modification by conventional process equipment may become impractical if the shear field intensity or dwell time of the material in the apparatus is limited. In such cases, shear refinability by standard process equipment may be observed if the coupling density in the polymer is reduced by some additional means, such as blending with a plasticizer.

ISSN:0959-8103    

DOI:10.1002/pi.4990240307

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThermal properties were investigated using differential scanning calorimetry of blends of vinylidenefluoride‐tetrafluoroethylene (VDF‐TFE) copolymer and polymethylmethacrylate. Curie transition behavior was strongly dependent on the crystallization temperature. A Curie temperature was shown in pure VDF‐TFE copolymer and in the blend with 91 wt % VDF‐TFE copolymer, which were crystallized above the Curie temperature. The samples crystallized above the Curie temperature showed higher melting temperatures than those crystallized below the Curie temperature, resulting in an upturn of slope at high temperatures in the Hoffman‐Weeks plot. The polymer‐polymer interaction parameter was calculated to be −0·165 at 130°C from the equilibrium melting temperatures, indicating miscibility of the

ISSN:0959-8103    

DOI:10.1002/pi.4990240308

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe UV‐induced copolymerization of methyl methacrylate (MM) with 2,2′‐thiobisethanol dimethacrylate (TEDM) and MM with 2,2′‐oxybisethanol dimethacrylate (OEDM) was investigated for a wide range of the diester content (6‐80 mol%) in the initial mixture. The influence of the feed composition on the course of copolymerization was determined. It was found that there exists a minimum on the plot of maximum yield of soluble copolymer versus diester content at a diester content of 30 mol%. The total copolymer yields were lower in the case of mixtures containing TEDM comonomer. Determination of the reactivity ratios gave the following values: for MM + TEDMra= 0·21,rb= 4·59 and for MM + OEDMra= 0·55.rb= 4·42. A possible explanation of the results obtain

ISSN:0959-8103    

DOI:10.1002/pi.4990240309

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInhibition of a double base propellant surface with a good percentage of nitro bodies in the propellant composition is a rather difficult process. One of the methods of inhibiting the surface is to use unsaturated polyesters with free radical cure having high exotherm as a barrier coating. This system has been improved by using a 1:1 mix of photocurable vinyl ester with pendant —OH groups and unsaturated polyester that underwent room temperature free radical cure. Adhesion of the barrier coat to the propellant surface through its —OH groups was stronger than the propellant strength itself. Additional layers of commercially available unsaturated polyester could be easily grafted on to the barrier coat through chemical c

ISSN:0959-8103    

DOI:10.1002/pi.4990240310

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0959-8103    

DOI:10.1002/pi.4990240313

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY