Uniform triblock oligomers with a central methylene block and outer oxyethylene blocks terminated by methoxy groups, CH,(OCH,CHz)mO(CH,)n(OCHzCHz)~OCH, (E,CnE,), were prepared and studied in the solid state by X-ray diffraction, differential scanning calorimetry and Raman spectroscopy. Both fully crystalline and partly-crystalline structures were found, with chains in wholly trans-planar and mixed trans-planar/helical conformations. Comparison is made with previous results for triblock oligomers of type CnE,Cn and diblock oligomers of type CnEm.The crystallinities o b s e r~e d~-~) in stable layer crystals of uniform C,E,,C, triblock oligomers are listed below. POE: n 5 2 Completely crystalline helical oligo(oxyethy1ene) chains. I: n < 10 Crystalline oxyethylene blocks, liquid-crystalline methylene blocks, helical oxyethylene blocks and trans-planar methylene blocks orientated normal to the end-group plane. 11: 10 5 n 5 26 Completely crystalline, helical oxyethylene blocks orientated normal to the end-group plane, trans-planar methylene blocks tilted at an angle of 61 111: n 2 26Crystalline methylene blocks, liquid-crystalline oxyethylene blocks, trans-planar oxyethylene and methylene blocks orientated normal to the end-group plane.Chain folding is observed in type I11 structures of series C,E,,C,, the fold being in the trans-planar, liquid-crystalline oxyethylene block. Oligomers C,E,C, with m ranging from 9 to 45 have been studied, and oligomers C,E,,C, can form chain folded type I1 structures with the fold in the helical, crystalline oxyethylene block7). Nonequilibrium structures may be formed, depending on the crystallisation conditions. These include structures in which the whole oligomer chain is tilted7).The structures of uniform diblock oligomers are less well documented. Several authors9* lo, 12) have reported Raman spectroscopic studies, which give valuable information on chain conformation. Diffraction studies 8, indicate similar structures to those established for the uniform C,E,C, triblock oligomers, but with some distinctly 'diblock' features, e. g. bilayer structures in the C,E,OH oligomers.In this paper we report on the crystallinity of uniform triblock oligomers with a central methylene block and outer oxyethylene blocks terminated by methoxy groups: with respect to the end group plane. CH3(OCHzCHJ,0 (CH,),(OCH2),0CH3So far as we are aware, uniform block oligomers of this type have not been studied before. TWO series of samples were prepared E,C,,E, m = 3, 6, 9, 12, 15 E,Cz3E, m = 3, 6, 9, 12The general methods of preparation have been described previously13). In this work an a,wdibromo-n-alkane was reacted under alkaline conditions (Williamson reaction) with either (a) an a-methyl-o-hydroxy-oligo(oxyethy1ene) or (b) an a-hydro-whydroxy-oligo(oxyethy1ene) and the product then methylated. In both procedures the triblock product was purified by preparative-scale gel permeation chromatography followed by recrystallisation. Experimental partDibromoalkanes 1,12-Dibromododecane (n = 12) was purchased ...
Low-frequency Raman spectra were recorded for a-methy1,w-hydroxyoligo(oxyethylene)s, CIEmOH with m in the range 4-16, Le., 14-50 chain atoms. Longitudinal acoustical mode (LAM) frequencies were identified and compared with those determined previously for a-hydro,whydroxyoligo(oxyethylene)s and a-methy1,o-methoxyoligo(oxyethy1ene)s. On the basis of the linear crystal model of Minoni and Zerbi, the two most prominent bands in the low-frequency spectra were assigned to the LAM-1 and LAM-3 modes of the H-bonded dimer crystallized in a bilayer structure. ' h n t addrm: European Vinyls Corp. ((1) Campbell. C.; Viras. K.; Booth, C. J. Polym. Scl., Polym. Phys. Ed., (2) Viras, K.; Teo, H. H.; Marshall. A.; Domszy, R. C.; King, T. A,; Booth, (3) Viras, K.; King, T. A.; Booth, C. J. Polym. Sei., Polym. Phys. Ed.in press. C.Infrared absorption spectral bandshapes are examined theoretically for the OH stretching vibration in hydrogen-bonded complexes in solution. Two distinct dephasing mechanisms are considered: the indirect mechanism in which the OH vibration is coupled to one or more internal vibrations in the complex, which are in turn coupled to the solvent, and the direct mechanism in which the OH vibration is directly coupled to the solvent. Attention is focused on intramolecularly H-bonded complexes for which extensive spectral data are available for a range of solvent polarity. It is concluded for the complexes considered that the direct mechanism is dominant. In particular, good fits to the experimental data are obtained via this mechanism for spectral width features in a given solvent and as a function of solvent polarity. Some distinctions between intra-and intermolecularly H-bonded complexes are given, and some suggestions for further work are made.
Low‐frequency Raman spectra were recorded for α‐methyl, ω‐methoxy‐oligo(oxyethylene)s, C1EmC1 with m in the range 4–25 (i.e., 15–78 atoms). Longitudinal acoustical mode (LAM‐1) frequencies were identified and compared with those determined previously for α‐hydro, ω‐hydroxy‐oligo (oxyethylene)s. Nonlinear relationships between LAM‐1 frequency and reciprocal chain length were explained as an effect of intermolecular end forces.
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