Polystyrene chain extension

The synthesis of comb-like polymers with regular branching (in contrast to random branching) has been performed in the following way 91) A linear polystyrene precursor fitted with carbanionic sites at both ends is reacted first with 1,1-diphenylethylene (to decrease the nucleophilicity of the sites) and then with a calculated amount of triallyloxytriazine to get chain extension. Each triazine residue still carries one allyloxy... 

The conformation of polymer chains in an ultra-thin film has been an attractive subject in the field of polymer physics. The chain conformation has been extensively discussed theoretically and experimentally [6-11] however, the experimental technique to study an ultra-thin film is limited because it is difficult to obtain a signal from a specimen due to the low sample volume. The conformation of polymer chains in an ultra-thin film has been examined by small angle neutron scattering (SANS), and contradictory results have been reported. With decreasing film thickness, the radius of gyration, Rg, parallel to the film plane increases when the thickness is less than the unperturbed chain dimension in the bulk state [12-14]. On the other hand, Jones et al. reported that a polystyrene chain in an ultra-thin film takes a Gaussian conformation with a similar in-plane Rg to that in the bulk state [15, 16]. 

Addition polymers, which are also known as chain growth polymers, make up the bulk of polymers that we encounter in everyday life. This class includes polyethylene, polypropylene, polystyrene, and polyvinyl chloride. Addition polymers are created by the sequential addition of monomers to an active site, as shown schematically in Fig. 1.7 for polyethylene. In this example, an unpaired electron, which forms the active site at the growing end of the chain, attacks the double bond of an adjacent ethylene monomer. The ethylene unit is added to the end of the chain and a free radical is regenerated. Under the right conditions, chain extension will proceed via hundreds of such steps until the supply of monomers is exhausted, the free radical is transferred to another chain, or the active site is quenched. The products of addition polymerization can have a wide range of molecular weights, the distribution of which depends on the relative rates of chain grcnvth, chain transfer, and chain termination. 

For the hydrosilylation reaction various rhodium, platinum, and cobalt catalysts were employed. For the further chain extension the OH-functionalities were deprotected by KCN in methanol. The final step involved the enzymatic polymerization from the maltoheptaose-modified polystyrene using a-D-glucose-l-phosphalc dipotassium salt dihydrate in a citrate buffer (pH = 6.2) and potato phosphorylase (Scheme 59). The characterization of the block copolymers was problematic in the case of high amylose contents, due to the insolubility of the copolymers in THF. 

Chain Extension of -U-Polystyrene Hiols. A two-stage chain extension of the. -kJ -polystyrene diols was accomplished by carboxylation of the diols with succinic anhydride followed by chain extension with a diepoxide. The succinic anhydride reaction was carried out 120-130°C under nitrogen. The reaction was monitored bj changes in the carbonyl bands at 1715 and 1740 cm in the infrared spectra of the reaction mixtures. The resulting dicarboxylic acid polymers were chain-extended in bulk at 130°C for 9 hours with Sow s HER diepoxide, equivalent weight =171, using bis( 3,5-diisopropylsalicylato)Cr (III) as the catalyst. 

To further test the functional purity of hydroxyl polymers prepared by the protected initiator and polymer route, two stage chain extensions of two polystyrene diols were carried out. The first stage involved conversion of the diols to acids with succinic anhydride the second stage involved chain extension with a diepoxide (Table III). If one assumes an overall conversion of 97-98%, a UP of 19 requires a functionality 1.93-1.95 based upon step-growth polymeri-... 

The simplest case of a polymer molecule which can undergo either cyclization or chain extension is that in which the groups are situated at each end of the polymer chain (which can react together). An example of this type of polymer is a,hydroxy-terminated polystyrene which reacts with a difunctional isocyanate, and our first studies were carried out with this reaction system. Obviously, the chain extension reaction leads to an increased specific viscosity, and cyclization leads to the reverse. 

For the subsequent generation of arborescent graft polystyrenes, a dramatic increase in rj0 was observed by Hempenius et al. [43] for each of the three series included in their study. However, despite this increase in viscosity, the rj0 for each of these is still lower than that of the linear homologue polystyrenes of the same overall molecular weight. This jump in viscosity is due to an increase in branch density which in turn results in increase in chain extension similar to that observed by Roovers [31] for highly branched star polymers. 

Block copolymers with hydroxyl segments were prepared by various ways An example utilizes the copper-catalyzed sequential copolymerizations of nBA and 2-[(trimethylsilyl)oxy]ethyl acrylate by the macroinitiator method into B-31 to B-33. The copolymers were then hydrolyzed into amphiphilic forms by deprotection of the silyl groups.313 A direct chain-extension reaction of polystyrene and PMMA with HEMA also afforded similar block copolymers with hydroxyl segments (B-34 and B-35).241-243 In block polymer B-36, a hydroxy-functionalized acrylamide provides a hydrophilic segment.117 Block copolymers of styrene and p-acetoxystyrene (B-37 to B-39), prepared by iron... 

The mechanismsof the acid effect has been extensively investigated (12-15, 21) whereas the current use of the polyfunctional monomers as enhancement additives in grafting is novel. The role of acid in these radiation grafting reactions is complicated and there is evidence that a number of pathways contribute to the overall enhancement effect. Thus mineral acid, at the levels used, should not affect the physical properties of the system such as swelling of the trunk polymer or precipitation of the grafted polystyrene chains. Instead evidence (12) indicates that the acid effect is due to a radiolytic increase in G(H) yields in the monomer-solvent system due to reactions similar to those depicted in Equations 1 and 2 for styrene-methanol. 

Figure 3. Fibrinogen sprayed onto surfaces of polystyrene (Panels A,B,C,and E), and carbon (Panel D). In panel E the alpha chain extension has been enzymatically removed. The scale bar represents 50nm.

Mechanistically, it is important to note that the presence of polyfunctional monomers in the grafting solution does not lead to a uniform enhancement in grafting. Instead, increased yields of copolymer are only observed at specific monomer concentrations. In the present experiments, polyfunctional monomers appear to have a dual function, namely to enhance the copolymerisation and also cross-link the grafted polystyrene chains. Such monomers have previously been used to extensively cross-link linear polymer chains. 

Miwa Y, Drews AR, Schlick S (2008) Unique structure and dynamics of poly(ethylene oxide) in layered silicate nanocomposites accelerated segmental mobility revealed by simulating ESR spectra of spin-labels, XRD, FTIR, and DSC. Macromolecules 41 4701-4708 Mohan SD, Mitchell GR, Davis FJ (2011) Chain extension in electrospun polystyrene fibres a SANS study. Soft Matter 7 4397-4404... 

---