Branching in poly

Short branching has also been verified in poly(vinyl acetate), poly(vinyl chloride), and various polyacrylates. Branching in poly(vinyl acetate) and polyacrylates involve the intramolecular backbiting mechanism as in polyethylene [Adelman and Ferguson, 1975 Heatley... 

An important objective of this research was to determine directly the molecular weights and the molecular weight distribution of polystyrene branches in poly(buta-diene-g-styrene). 

In a study of chain-transfer constants of the monomeric vinyl acetate it was found that the formation of nonhydrolyzable branches is virtually negligible while hydrolyzable branches are formed at position 1 of Structure 1 by a terminal double-bond reaction rather than by a polymer-transfer reaction. The long nonhydrolyzable branches in poly(vinyl alcohol) are, presumably formed almost exclusively by a polymer transfer mechanism [35]. 

The NMR spectroscopy of poly(vinyl chloride), which was reduced with tributyltin hydride, showed that the original polymer contained a number of short four-carbon branches [300]. This, however, may not be typical of all poly(vinyl chloride) polymers formed by free-radical polymerization. It conflicts with other evidence from NMR spectroscopy that chloromethyl groups are the principal short chain branches in poly(vinyl chloride) [301, 302]. The pendant chloromethyl groups were found to occur with a frequency of 2-3/1,000 carbons. The formation of these branches, as seen by Bovey and coworkers, depends upon head to head additions of monomers during the polymer formation. Such additions are followed by 1,2 chlorine shifts with subsequent propagations [301, 302]. Evidence from still other studies also shows that some head to head placement occurs in the growth reaction [303]. It was suggested that this may be not only... 

Branching in poly(vinyl chloride) has been studied using > C n.m.r. by reduction of C—Cl bonds to C—H(D) bonds with LiAlH4 or LiAlD to give polyethylene with short branches (—CHjCl) and also longer branches. Branches with —CH2CI end-groups have also been detected in the H spectra of poly(vinyl chloride) itself. Also in poly(vinyl chloride) H n.m.r. spectra, the structures... 

Figure 9.17 Plot of log [i ]M versus retention volume for various polymers, showing how different systems are represented by a single calibration curve when data are represented in this manner. The polymers used include linear and branched polystyrene, poly(methyl methacrylate), poly(vinyl chloride), poly(phenyl siloxane), polybutadiene, and branched, block, and graft copolymers of styrene and methyl methacrylate. [From Z. Grubisec, P. Rempp, and H. Benoit, Polym. Lett. 5 753 (1967), used with permission of Wiley.]...

Trilialophenols can be converted to poly(dihaloph.enylene oxide)s by a reaction that resembles radical-initiated displacement polymerization. In one procedure, either a copper or silver complex of the phenol is heated to produce a branched product (50). In another procedure, a catalytic quantity of an oxidizing agent and the dry sodium salt in dimethyl sulfoxide produces linear poly(2,6-dichloro-l,4-polyphenylene oxide) (51). The polymer can also be prepared by direct oxidation with a copper—amine catalyst, although branching in the ortho positions is indicated by chlorine analyses (52). 

The hydrodynamic volume separation mechanism of SEC, along with the different molecular size/weight relationships of branched and linear polymers of identical chemical composition, can be exploited with the SEC/LALLS method to gain information about polymer branching. In the studies described in this paper both conventional SEC and SEC/LALLS are used to obtain data about branching in samples of poly(vinyl acetate) (PVA) and polychloro-prene (PCP). 

Canali et al.17 reported the use a linear poly(tartrate) ligand in the asymmetric epoxidation of allylic alcohols. Moderate results were obtained. They also reported the use of branched/crosslinked poly(tartrate), which gave moderate to good results in the asymmetric epoxidation of allylic alcohols. As shown in Scheme 4-9, when L-(+)-tartaric acid and 1,8-octanediol are heated... 

Interestingly, no chiral induction was apparent when a / -branched polymer, poly( -decyl-2-methylpropylsilylene), PD2MPS, was spin-coated onto a film of 88. It is likely that the /3-branching position results in a very stiff, locked conformation for PD2MPS, which, due to the relative weakness of the van der Waals interaction, is not obedient to the command from the PSS helical surface-tethered chains. 

It is notable that the GC samples in Table 4.1 are much too short for the Intermediate Zone formula to apply out to 120 ns. The formulas for subsequent zones of C (t) (Eqs. 4.38—4.41) are employed as needed and yield the same value of a for both 230- and 590-bp samples.(146) The 590-bp sample initially exhibited a threefold higher value, which relaxed over several months, during which time many very small fragments dissociated from, or annealed out of, the predominant 590-bp species. This was tentatively attributed to the presence of branched structures, which exhibit high affinity sites for ethidiuny in the original material. Both gel electrophoretic and electron microscopic 147 1 evidence for branched structures in poly(dG-dC) were noted.(146) The 500-bp length from gel electrophoresis was confirmed by sedimentation.(146)... 

McKee MG, Elkins CL, Park T, Long TE. Influence of random branching on multiple hydrogen bonding in poly(alkyl methacrylate)s. Macromolecules 2005 38 6015-6023. 

Under a variety of conditions, plasmid DNA undergoes a dramatic compaction in the presence of condensing agents such as multivalent cations and cationic polymers. Naked DNA coils, typically with a hydrodynamic size of hundreds of nanometers, after condensation it may become only tens of nanometer in size. Contrary to proteins which show a unique tertiary structure, DNA coils do not condense into unique compact structure. Cationic polymers execute their gene carrier function by their condensation effect on gene materials and, furthermore, their protection effect on DNA from nuclease digestion. Currently, the most widely used cationic polymers in research include linear or branched PEI (poly (ethyleneimine) (161-165), polypeptides such as PLL (poly-L-lysine) (166-169), PLA (poly-L-arginine) (170). 

The group X transferred may be H or halogen. Attack on the CH2 groups in the polymer, or on pendent groups, such as — COO CH3 in poly (vinyl acetate), would produce similar effects in the case of poly (vinyl acetate) branches attached via the acetate group can be removed by hydrolysis, unlike those formed by attack on hydrogen atoms linked to main chain carbons. 

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