Branches, grafted

The dose and dose rate of irradiation are important factors in any radiation grafting system. In the direct method the total dose determines the number of grafting sites, while the dose rate determines the number of grafting sites, and the dose rate determines the length of the grafted branches. The length of the branches is also con-... 

The chain architecture and chemical structure could be modified by SCVCP leading to a facile, one-pot synthesis of surface-grafted branched polymers. The copolymerization gave an intermediate surface topography and film thickness between the polymer protrusions obtained from SCVP of an AB inimer and the polymer brushes obtained by ATRP of a conventional monomer. The difference in the Br content at the surface between hyperbranched, branched, and linear polymers was confirmed by XPS, suggesting the feasibility to control the surface chemical functionality. The principal result of the works is a demonstration of utility of the surface-initiated SCVP via ATRP to prepare surface-grafted hyperbranched and branched polymers with characteristic architecture and topography. 

The macroradicals of natural rubber react with those of the styrene elastomer, due to the presence of the very reactive 1,2 pendent vinyl groups in the latter. This mechanism leads to a structure where the styrene rubber forms a gel network with grafted branches of natural rubber. 

Tseng, W.C., Jong, C.M. (2003). Improved stability of polycationic vector by dextran-grafted branched polyethylenimine. Biomacromolecules, 4(5), 1277-1284. 

One method is to measure chain-transfer coefficients with low-MW analogues of the polymer. Thus Gilchrist (140) measured the rate at which 14C labelled decane was incorporated into polyethylene in the free-radical polymerization, and hence obtained an estimate of the transfer coefficient with methylene groups this was in fair agreement with another estimate obtained from the effect of the addition of fractions of linear polyethylene on the Mn of the branched polyethylene, which could be separated from linear polymer plus grafted branched polymer by column extraction. Low MW polymer may be used as a transfer agent Schulz and co-workers (189) obtained chain-transfer coefficients in styrene polymerization from the effect of added low MW polymer on Mn. 

Mori, Y., Y. Minoura and M. Imoto Vinyl polymerization. XXII. Determination of length and numbers of grafted branches of polystyrene on natural rubber. Makromol. Chem. 25, 1 (1957). 

Use of macromonomers as reactive (copolymerizable) surfactants in heterogeneous systems such as emulsion and dispersion constitutes an increasingly important application in the design of polymeric microspheres, as will be discussed later in Sect. 6. Here the macromonomers copolymerize in situ with some of the substrate comonomers to afford the graft copolymers, the grafts (branches) of which serve as effective steric stabilizers by anchoring their backbone onto the surfaces of the particles. In general, however, the copolymerization reactivities of macromonomers in such systems are not well understood yet. 

Comparison of the results in Fig. 10 with those in Fig. 7 makes it clear that the differences in monomer species, distribution of grafted branches, and the degree of decrystallization of wood result in quite different thermograms. 

The number- and weight-average degrees of the polymerization of the whole backbone having any grafted branches, PB,g and P B>g, are given by the following equations ... 

Fig. 3. Ratio of number-average DP of the mother polymer and number-average DP of the whole backbone having grafted branches, PB,g/PjB,0 5 a function of the average number of branches in one graft copolymer molecule, Ng o PB.g/PB.O at Nt- (),/. ., Ng- 1...

The MMA homopolymer and the unreacted PVA are removed from the reaction product by the selective extraction method. The grafted branch PMMA is separated from the backbone by oxidative cleavage of all 1,2-glycols of PVA (about 2 mole%)29 Molar masses of the isolated graft copolymers and the separated branches are osmo-metrically determined, after acetylation of hydroxyl groups in benzene. The chemical composition of the graft copolymers is determined from the saponification value of the acetylated sample. 

Fig. 22. Number of grafted branches formed per starting PVAc molecule (total polymer cone. = 5.0 g/dl and reaction time = 24 hr) (o) Mn = 9.22 x 104 ( ) M = 14.3 x 104...

The structure of graft copolymers is generally more complex than that of block polymers in that the trunk polymer may be joined to more than one grafted branch and the nature of the production of such copolymers is such that cross-linking also may occur. For this reason the microphase separation that is observed in graft copolymers alone is less distinct and regular than that seen with block copolymers of the same species. 

The monomer-up approach opens up the possibility of enzymatically grafting branched polysaccharides from functionalized substrates in order to make hybrid materials bearing a highly branched amylose part. Following the same route we are currently synthesizing hybrid materials bearing (hyper)branched polysaccharide structures as shown in Figure 9.11 with the described tandem reaction of two enzymes. 

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