ISSN:0959-8103    

DOI:10.1002/pi.1994.210330201

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractStyrene–isoprene A2B2star copolymers having two arms of polystyrene and two of polyisoprene have been synthesised. Two routes have been followed. In the first, 2 moles of polydienyl lithium were coupled, without loss of carbanionic character, by reacting with 1 mole of 1,3‐bis(1‐phenylethenyl) benzene. The difunctional adduct was then used to initiate the polymerisation of styrene in the presence of a small amount of triethylamine which served to ensure a rapid crossover. In the second route, 2 moles of polystyrl lithium were coupled with 1 mol of SiCl4in benzene; no attendant formation of three‐armed star was detected. Introduction of large excess of polyisoprenyl lithium, together with triethylamine as catalyst, generated the star which was isolated by fractional precip

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330202

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe ring‐opening polymerization of hexamethylcyclodisilazane (D2NMe), initiated by methyl triflate in 1,2‐dichloroethane, forms in the first, fast kinetic step both linear polymer and cyclic dimer (D4NMe). Subsequently a slow depolymerization process occurs leading to exclusively cyclotrisilazane (D3NMe). On the basis of kinetic measurements carried out using an adiabatic calorimetric technique and complementary experiments, mechanisms of both propagation, cyclization and back‐biting reactions are proposed. The influence of the reaction temperature was also studied; it is demonstrated that, at low temperature, polymerization does not lead to cyclic oligomer formation. In such conditions, the polymerization presents a ‘living’

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330203

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolystyrene macromonomers terminated with methacrylate, vinyl ether, or maleic half ester functionalities were evaluated in free radical initiated copolymerizations with vinyl chloride in aqueous suspension polymerization. Macromers® (M1) terminated with methacrylate disappeared very rapidly in copolymerization with vinyl chloride (M2). The relative reactivity ratio,r2, was determined to be 0.05 in good agreement with literature values of about 0.04. Vinyl ether‐terminated Macromers® had unexpectedly uniform reactivity with vinyl chloride in early conversion samples, but macromonomer conversion was incomplete. Macromers® having maleic half ester functionality were incorporated rapidly in vinyl chloride copolymerization at pH 2.5 (r2= 0.13). However, at pH 10 these Macromers® had reduced reactivity (r2= 0.34), which improved graft polymer uniformity. These Macromer® copolymerization relative reactivities are shown to be useful in predicting and controlling graft densities and graft polymer heterogeneity which influence morphology, processing, and mechanical prop

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330204

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe anionic polymerization of isoprene withn‐butyl lithium and polar modifier such as TMEDA and tripiperdinophosphine oxide were studied and kinetic and reactor models are proposed for these systems. Reactor conversion, molecular weight distribution and polymer glass transition temperature had been calculated from the model and compared favorably to the actual data for various combinations of reactor systems and operating conditions. Simulations of the model can be used to design reactor systems and predict polymer properties of large‐scale operations from results of small scale batch reactor r

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330205

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHigh yields of cyclic oligomeric carbonates can be prepared using an amine‐catalyzed reaction of bisphenol A–bischloroformate. We have studied the mechanistic aspets of this carbonate macrocyclization by the isolated study of key chemical events. Using stopped‐flow FT‐IR spectroscopy, we have found that the rate of carbonate formation between the intermediate acyl ammonium salt and 4‐isopropylphenol is the same for the acyl ammonium salt derived from tri‐n‐butylamine, triethylamine and diethylmethylamine. Previously, we found that conversion of acyl ammonium salt to urethane was also insensitive to amine structure while the formation of acyl ammonium salt is profoundly dependent on amine structure. These results are consistent with a mechanism in which the selectivity toward macrocyclization versus linear oligomer or high polymer formation is related to acyl ammonium salt

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330206

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractPolymerization of methyl methacrylate (MMA) by isotactic poly(methyl methacrylate) (PMMA) living anion, prepared witht‐C4H9MgBr in toluene at −60°C, was carried out at −78°C in the presence of trialkylaluminiums (R3Al; R = CH3, C2H5, andn‐C4H9) to obtain a stereoblock PMMA, isotactic PMMA‐block‐syndiotactic PMMA. Among the R3Als, (CH3)3Al gave most effectively the steroblock PMMA with narrow molecular weight distribution. The fraction ofrrtriad in the syndiotactic PMMA block increased with increase in the ratio of Al/Mg and reached about 76% at a ratio of Al/Mg ≥ 6. The method was also used to prepare stereoblock copolymer comprising isotactic PMMA block and syndiotactic block of butyl methacrylate. Stereocomplex formation and solution viscosity of the stereoblock PMMA we

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330207

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractStar‐branched poly(methyl methacrylate)s (PMMA) were synthesized by linking ‘living’ arms (produced by anionic polymerzation) with ethylene glycol dimethacrylate. Stars having arm molecular weights of 10000 and 40000 and between 4.9 and 18.7 branches were produced. The polymers were characterized using light scattering, size exclusion chromatography, and viscometry. It was found that well‐defined PMMA stars were obtained only at the higher (40000) arm molecular weight. The stars prepared using the lower molecular weight (c. 10000) arms contained very high molecular weight gel com

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330208

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstractω‐Formyl‐functionalized polystyrenes can be synthesized in quantitative yield by reacting poly(styryl)lithium (Mn= 2 × 103−8 × 103g/mol) in benzene with a 0.1−0.4 molar excess of 4‐morpholinecarboxaldehyde followed by methanol termination and precipitation into methanol. Narrow molecular weight distribution ω‐formyl‐functionalized polystyrenes were characterized by hydroxylamine end‐group titration, thin layer chromatography and both1H and13C NMR spectroscopy. The mechanism of the functionalization was studied by trapping the tetrahedral α‐amino alkoxide intermediate with diphe

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330209

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAnionic ring‐opening polymerization of thecisandtransisomers of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (cis‐ andtrans‐F3) and their mixtures was conducted under conditions that suppressed siloxane bond redistribution in order to preserve stereoregularity formed in the resulting poly[methyl(3,3,3‐trifluoropropyl)siloxane] (PMTFPS). Proton decoupled19F NMR of the resulting polymers was interpreted by assuming that the original stereoconfiguration of the monomer was preserved and that the monomer inserted with a roughly equal probability of forming meso or racemic configurations relative to the configuration of the reacting chain end. Polymers fromcis‐F3were solid and crystalline at room temperature while the more typical polymers from mixtures of isomers containing greater than 50%trans‐F3

ISSN:0959-8103    

DOI:10.1002/pi.1994.210330210

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY