摘要:

AbstractThe radical telomerization reactions of vinyl chloride or propylene with halomethanes were chosen as stereochemical models for studying the mechanism of stereoregular polymerization of the monomers.Conformational1H‐NMR analysis was used to assign the relative configurations of the racemic diad and triad telomer forms. The assignment was based on comparisons of the CH2‐proton geminal shifts in molecular fragments ‐CHX‐CH2‐CHX‐ and rotational equilibria of the racemic forms measured by NMR spectroscopy over a wide temperature range in solvents with different dielectric and magneto‐anisotropic properties. Complete iterative analysis of1H‐NMR spectra at 60 and 90 MHz was carried out by using the INDOR technique and the1H‐{D} spectra of partially deuterated model compounds, synthesized from various mono‐ and dideuterosubstituted vinyl chlorides.Statistical treatment of the distribution of the diad and triad forms allowed the stereochemical course of the propagating reactions of the 1,3‐substituted vinylic radicals to be determined at temperatures ranging from 55 to 200°C and pressures up to 8000 kg/cm2. From these statistical data and the conformational equilibria of the racemic diastereomeric forms, it was revealed that the stereoregularity of the studied and probably similar reactions with 1,3‐substituted vinylic radicals may be ascribed predominantly to the effect of the γ‐substituent. A dynamic model of a 1,3‐asymmetric induction and the mechanism of conformational control in stereoregular free‐radi

ISSN:0360-8905    

DOI:10.1002/polc.5070550123

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractWe have re‐examined the copolymerization of methyl methacrylate (MMA) and styrene in the presence of triethylaluminium at 273°K under visible light following recent claims that it was an alternating system. We applied gel‐permeation chromatography to establish that the polymers had monomodal distributions and could be regarded as coherent samples for analysis. Proton and13C‐NMR spectroscopy were used to determine the composition and structure of the copolymers and investigate the presence of complexes in the comonomer solutions. We found that the polymers produced are not strictly alternating. In the absence of excess, uncomplexed MMA, the system is a radical copolymerization of styrene and a 1:1 MMA‐AlEt3complex with reactivity ratios such that there is a strong tendency for styrene (S) and MMA (M) units to alternate. The alternating SMS triads were predominantly isotactic. Significant proportions of SSS, MMM and MMS triads could be

ISSN:0360-8905    

DOI:10.1002/polc.5070550124

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractIn the presence of excess water and potassium persulfate, N‐vinylpyrrolidone reacts to form 1,1‐bis(1′‐pyrrolidonyl)ethane. At lower water concentrations, potassium persulfate initiates the cationic polymerization of vinylpyrr

ISSN:0360-8905    

DOI:10.1002/polc.5070550125

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe pulse radiolysis of N‐vinylpyrrolidone and poly(vinylpyrrolidone) in aqueous solution has been studied. The absorption spectra of the intermediates produced have been measured and the kinetics of their disappearance studied. Further study is necessary before the precise structure of the intermediates can be describe

ISSN:0360-8905    

DOI:10.1002/polc.5070550126

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThis paper discusses the migration of singlet energy along polymer chains. This is a process of technical importance in that it can affect the efficiency with which the energy from an absorbed photon is transferred to some acceptor molecule which may then function as a photostabilizer or photosensitizer.When the side groups or unit chromophores on a chain are connected by strong electronic interactions (as in conjugated systems), the energy migration is extremely efficient, and it is probable that the energy is delocalized as a coherent exciton. The observed migration characteristics in poly(phenyl acetylene) and poly(p‐methoxyphenyl acetylene) are explained in terms of delocalization in a distribution of conjugated sequence lengths. In fluid solutions, segmental rotation maintains the distribution in dynamic flux, providing an “intersystem” ladder for the energy to be converted to long wavelength excitons, so that the effective migration distance is large and most of the fluorescence is long wavelength. In solids the distribution is static, effective migration distances are smaller, and the fluorescence contains an appreciable emission at shorter wavelengths from short sequ

ISSN:0360-8905    

DOI:10.1002/polc.5070550127

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe ESR spectra, due to trapped radicals produced by γ‐irradiation at 77°K, of random copolymers of styrene and methyl methacrylate of known composition and of the two parent homopolymers have been studied at 77°K. The yields of trapped radicals in the polymers were measured at several doses by double integration of the ESR spectra, and the G values for the production of radicals were calculated. The G(R) value for poly(methyl methacrylate) was calculated as 0.58 ± 0.2 and that for polystyrene as 0.05 ± 0.02. The variation of G(R) is not linear with polymer composition and is explained by a protective effect of the aromatic component resulting from energy transfer. Other chemical reactions and scavenging effects can be eliminated by consideration of the results from the analysis of the ESR spectra of the copolymers in terms of the homopolymers. It appears that different transfer mechanisms become operable as the copolymers are warmed up after irradiation a

ISSN:0360-8905    

DOI:10.1002/polc.5070550128

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractA series of deoxycholic acid inclusion compounds with vinyl and diene monomers were prepared, and their radiation‐induced polymerization was studied. In the case of 2,3‐dimethyl‐and 2,3‐dichlorobutadienes, highly 1,4‐trans tactic polymers were obtained, while in the case of acrylonitrile, an atactic polymer resulted. Stability of the deoxycholic acid adducts as well as polymerization characteristics are

ISSN:0360-8905    

DOI:10.1002/polc.5070550129

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe variables affecting the photosensitized copolymerization of monomers to cellulose using the simultaneous technique have been systematically investigated. Such variables include type of sensitizer, structure of monomer, and type of solvent. LOW molecular weight alcohols are particularly effective as grafting solvents, especially for styrene and methyl methacrylate. Polyfunctional acrylates predominantly homopolymerize rather than graft, as do acrylonitrile and acrylic acid. Vinyl acetate and 4‐vinylpyridine graft with little competing homopolymerization, although only the latter monomer gives reasonable yields at short conversion times. A Trommsdorff effect is observed for the styrene‐alcohol system. Novel copolymerization behavior is found when mixed alcohols are used as solvents for styrene grafting. Data from the photosensitized grafting are compared with corresponding studies using initiation by ionizing radiation. Results in both ultraviolet and ionizing radiation systems are interpreted in terms of common intermediates involving charge‐transfer bonded sp

ISSN:0360-8905    

DOI:10.1002/polc.5070550130

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe mutual γ‐irradiation method has been employed to graft methyl methacrylate (MMA) to polypropylene (PP) film in solutions open to the air. It was observed that grafting occurs only when the monomer solutions contain water. This effect of water has been related to a reduction in the oxygen solubility in aqueous solutions. There is some evidence that water affects the kinetics of the graft polymerizati

ISSN:0360-8905    

DOI:10.1002/polc.5070550131

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

ISSN:0360-8905    

DOI:10.1002/polc.5070550102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY