摘要:

The radius of gyration of poly(styrene-b-butadiene) block copolymer micelles inn-heptane is measured by small angle X-ray scattering (SAXS). The results are compared with theoretical predictions, and good agreement is found, particularly for the appropriate scaling relations. It is argued that the radius of gyration of the micelles depends on both the molecular weight and the composition of the copolymers. The dominant factors which determine the micelle core and corona dimensions are identified.

ISSN:0008-4042    

DOI:10.1139/v85-041

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A method is demonstrated for the interpretation of the ultraviolet spectra of styrene-containing copolymers. This method is based on the use of model molecules to approximate the absorption behaviour of the known chromophores and on the statistical estimation of the average spectra of the unknown chromophores. The analysis yields directly the copolymer composition and an estimate of the background spectra which arise from the different arrangements of the styril units along the polymer chains. It is shown that reliable composition estimates are obtained for styrene – methyl methacrylate and styrene–acrylonitrile copolymers. The results from the interpretation of the spectra are discussed and compared with results obtained from the statistical copolymerization models.

ISSN:0008-4042    

DOI:10.1139/v85-042

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The cationic polymerization of 1,3-dioxolane and 1,3-dioxepane has been investigated to prepare "living" polymers and then to use them for copolymerization. Carbenium hexafluoroantimonate salts that are good initiators for tetrahydrofuran polymerization have been tested but produce unsatisfactory results with these acetals. In contrast, triflic anhydride, another good initiator for tetrahydrofuran polymerization, allows molecular weight control. Attempts to prepare block copolymers of two acetals by adding the second one to the first one under living conditions were unsuccessful because of randomization through transacetalization. Block copolymers containing a central block of polydioxepane and outer blocks of 1,2-dimethoxyethylene could be prepared by addition of the latter to living polydioxepane. Active polydioxolane reacts readily with polystyrene and leads to the formation of graft copolymers in the absence of gel.

ISSN:0008-4042    

DOI:10.1139/v85-043

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The13C nmr spectra of solids, acquired using the Cross Polarization/Magic Angle Spinning (CP/MAS) technique, are very sensitive to the detailed nature of crystalline packing. These effects are illustrated in the CP/MAS spectra of the α and β anomers of methyl-D-xylopyranoside. In the spectrum of the α anomer, which crystallizes with two molecules per unit cell, individual spectra can be resolved for the two molecules in the asymmetric unit of this crystal.

ISSN:0008-4042    

DOI:10.1139/v85-044

出版商:NRC Research Press    

年代:1985

数据来源: NRC