Bulky pendant

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 %(,] ). 

Glass Transition Temperature Increases with the presence of bulky pendant groups stiffening groups as 1,4-phenylene chain symmetry polar groups cross-linking... 

Which protein would be more apt to be present in a helical conformation (a) a linear polyamide with small pendant groups or (b) a linear polyamide with bulky pendant groups ... 

All polymers discussed so far are homopolymers, i.e., they consist of multiple sequences of the same repeating unit. Regular linear homopolymers without bulky pendant groups, such as hdpe, are easily crystallized. However, the tendency for crystallization is reduced in copolymers, since they contain more than one repeating unit in the chain. Copolymers with random arrangements of repeating units in the polymer chain are generally amorphous. 

Bulky pendant groups also restrict segmental motion, and this effect on Tg values is enhanced when the pendant groups are polar. Thus polypropylene (PP) (Tg — 253 K) has a higher Tg than polyethylene (Tg — 147 K), and polyvinyl alcohol (PVA) (Tg = 358 K) has a higher Tg than either of these polyolefins. 

Polymers with little structural symmetry and with bulky pendant groups, such as atactic polystyrene (PS), are usually amorphous. Amorphous polymers have no long-range order, and their x-ray diffraction patterns are diffuse halos rather than the sharp peaks which are characteristic of crystalline polymers. 

Although atactic polymers with bulky pendant groups are usually amorphous, atactic polymers with small pendant groups, such as polyvinyl alcohol (PVA), may be made to be crystalline. Some polymers, such as PVC, may have long sequences of syndiotactic sequences in addition to atactic sequences, and hence are somewhat crystalline. 

Many copolymers are said to be internally plastidzed because of the flexibilization brought about by the presence of a second repeating unit in the polymer chain. In contrast. DOP and other liquid plastidzers are said to be external plastidzers. The presence of bulky pendant groups on the polymer increases segmental motion, and the flexibility of the polymer increases as the size of the pendant group increases. However, linear pendant groups with more than 10 carbon atoms reduce flexibility because of side chain crystallization. 

Amorphous atactic polymers with bulky pendant groups, such as pol-ystyrene (PS), which has the following repeating unit ... 

P-5 and P-7 are significantly blue shifted when compared with that of PPV, which again suggests the occurrence of a partial disruption of the coplanarity of the main chain 7T-system by the presence of the bulky pendants. The same phenomenon was described above for P-l-P-4. 

When the polymer chains are unsymmetricai, with repeat units of the type -(-CH2-CHX-)-, an additional restriction is imposed by steric effects depending on the size of the pendant group X. Bulky pendant groups hinder the rotation about the backbone and cause Tg to increase. 

It has been revealed by X-ray studies106,107) that in polyethylene the carbon-carbon bond distance is 1.54 A and the valence angle 108°, suggesting that the carbon atom in the polymer chain is tetrahedral. As all of the polyolefins including polyethylene possess helical coiled structure, the tetrahedral stereochemistry for the carbon atom in the polymer chain would persist in all of them. With bulky pendant groups linked to the polymer chain, this tetrahedral structure is most likely to be under considerable strain. For example, polyethylene, through a carbon-carbon bond scission in the polymer chain, forms the radical (XV) in which the unpaired electron and two C-H bonds on CH are in trans or gauche conformation with the two C 2-H bonds and the C T-Cn bond. The radical end... 

The lower activation energy for LLDPE compared to HDPE seems to be due to a storage of thermal energy by the crystallites caused by the presence of bulky pendant groups at the... 

When the polymer chains are unsymmetrical, with repeat units of the type -(-CH2-CHX-)-, an additional restriction is imposed by steric effects depending on the size of the pendant group X. Bulky pendant groups hinder the rotation about the backbone and cause Tg to increase. There is some evidence of a correlation between Tg and the size of the pendant group measured by its molar volume Vx-For example, T (°C) increases with increasing Vx (cm /mol) in the progressive series, polyethylene (Tg= —93, Vx = 3.7), polypropylene (Tg=—20, Vx=25.9) polypropylene (Tg=100, Vx=92.3), and poly(vinylnaphthalene) (Tg = 135, Vx= 143.9). 

Steric factors play an important role. A high is obtained when large pendant groups attached to the ehain restrict its internal rotation, and bulky pendant groups tend to impede crystallization, except when arranged regularly in isotactic or syndiotactic chains. 

Polarity, for example, has an influence on chemical stability (chlorine atom in polyvinyl chloride). Bulky pendant groups (phenyl residue in polystyrene) for example, move the glass transition temperature up and produce brittle, stiff plastics. 

New bis(ether anhydride)s containing flexible ether, isopropylidene groups, bulky pendant groups, noncoplanar biphenylene or kink linkages were synthesized. Almost all of the poly(ether imide)s derived from such novel bis(ether anhydride)s were soluble in the test solvents, including A-methyl-2-pyrrolidinone, A,A-dimethylacetamide (DMAc), pyridine, cyclohexanone, tetrahydrofuran and even in chloroform at room temperature. The high solubility of these poly(ether... 

The improvement in the solubility of the polyimides showed a similar tendency to that of the corresponding polyamides. For example, 2,5-di-f-butyl substituent in polymer backbone was too symmetrical for the solubility to be superior to that of /-butyl-substituted polymers From the solubility behaviors of the polyimides, therefore, it could be concluded that the incorporation of bulky pendant groups along the polymer chain gave the most effective enhancement in the solubility of polymers. (Fig. 2.8)... 

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