Polymer steric interaction

An approximate expression first derived by Fisher (see Ref. [32] p. 460) for the adsorbed polymer steric interaction energy AGpoi t etween two spheres is ... 

Although it is apparent from the first two terms in Eq.(l) that the predicted influence of PEO molecular weight on Kp results from a delicate balance reflecting opposing influences of the protein-polymer and polymer-polymer steric interactions, it is clear that in order to evaluate the additive influences of these interactions, a more quantitative approach is needed. 

While steric factors do not directly affect the reactivity of the monomer, they can exert considerable influence on the structure and properties of the polymer. Steric interactions between substituents on adjacent monomers induce a distortion of the 7r-conjugated system, which results in a shortening of effective conjugation and hence in a drop in conductivity. 

The 1,1-disubstitution of chlorine atoms causes steric interactions in the polymer, as is evident from the heat of polymeri2ation (see Table 1) (24). When corrected for the heat of fusion, it is significantly less than the theoretical value of —83.7 kJ/mol (—20 kcal/mol) for the process of converting a double bond to two single bonds. The steric strain apparentiy is not important in the addition step, because VDC polymeri2es easily. Nor is it sufficient to favor depolymeri2ation the estimated ceiling temperature for poly (vinyhdene chloride) (PVDC) is about 400°C. 

The pattern presented by heats of polymerization of various monomers appears to be very well explained by two dominant factors elimination of resonance energy of conjugation, and steric interactions between substituents. The importance of the value of the heat of polymerization in determining the temperature above which reversal of the conversion of monomer to polymer occurs has been stressed by Dainton and Ivin. ... 

The contents of the nucleic acid bases in the poly-L-lysine derivatives were determined by UV spectra of the polymers after hydrolysis The polymers were hydrolyzed in 6 N-hydrochloric acid at 105°C for 24 hr, into lysine dihydrochloride and the carboxyethyl derivatives of the nucleic acid bases. The quantitative calculation was made relative to the standard sample of the carboxyethyl derivative of the nucleic acid bases. The analytical data are listed in Table 1. It was found that the thymine and uracil derivatives was completely substituted to polylysine. Low value in case of adenine base in the polymer may be attributed to the unstability of the activated ester, Ade-PNP (2), and may also be explained in terms of the steric interaction among bulky pendant groups of the polymer. When the poly-L-lysine containing about 50 mol % adenine units was again treated with Ade-PNP, the adenine unit content in the polymer increased up to 74 mol %(,] ). 

A second effect, widely believed to favour small ring formation concerns the steric interactions between the P- and N-skeletal substituents (Scheme 8). In this case steric interference between the N-substituents is minimised in four membered rings (25), but greater in larger rings or polymers 24). This effect could equally well apply to phosphorus substituents. 

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