Grafting linear polymer

Dendronized, or dendritic-grafted linear polymers, are linear polymers that bear pendant dendrons along the repeat units. Although there have been a few reports of divergently prepared dendronized materials,138 371 372 the majority of the research in this field has focused on the convergent approach. Recently, the convergent synthesis of these materials has been optimized, and their preparation has been reviewed extensively elsewhere.373 375 The salient examples are, however, briefly mentioned below. 

Figure 3 72 Protein interaction with a cross-linked phase in comparison with a grafted linear polymer phase.

Chitosan, having a similar chemical backbone as cellulose, is a linear polymer composed of a partially deacety-lated material of chitin [(l-4)-2-acetamide-2-deoxy-/3-D-glucan]. Grafting copolymer chains onto chitosan can improve some properties of the resulting copolymers [48-50]. Yang et al. [16] reported the grafting reaction of chitosan using the Ce(IV) ion as an initiator, but no detailed mechanism of this initiation has been published so far. 

Recently it has been shown that anionic functionalization techniques can be applied to the synthesis of macromonomers — macromolecular monomers — i.e. linear polymers fitted at chain end with a polymerizable unsaturation, most commonly styrene or methacrylic ester 69 71). These species in turn provide easy access to graft copolymers upon radical copolymerization with vinylic or acrylic monomers. 

Fig. 14. Surface-grafted hyperbranched, branched, and linear polymers from ID to 3D...

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. 

Fig. 15. Schematic representation of the synthesis of hyperbranched, branched, and linear polymers grafted from functionalized silicon wafers SFM images and XPS spectra of the surface-grafted polymers. (Reproduced with permission from [48],Copyright 2001 American Chemical Society.)...

A graft copolymer consists of a linear Polymer chain of one type to which has been grafted side-chains of a different type of polymer. The formation of a graft copolymer can be brought about by either of two general methods ... 

In a recent review by Drake et al. 1 the surface activity of linear polymers and co-polymers is discussed, based on many recent references. They refer to the research correlating surface characteristics of siloxanes to the nature of end groups575 and to their concentration576 in linear polymers. A few examples of the recent work on siloxane migration to the interfaces, with the emphasis on the behavior of block577 and graft co-polymers,578 and their blends with... 

Fig. 5.9 Covalent grafting of (a) linear polymer and (b) dendrimer-like hyperbranched polymer of azo-functional porphyrin groups from alkyne functionalized CNTs. Redrawn from [122].

Fig. 9.19 Preparation of polymer brushes on solid surfaces by a) chemical grafting of end-functionalized linear polymers or selective adsorption of asymmetric block copolymers and b) by surface-initiated polymerization (SIP) using initiator functions on the solid surface. The depicted SAM bearing to-functionalities...

Recalling the demands on the polymer architecture of a polymer brush and the projected properties in terms of swelling, wetting and friction, as described in the theoretical work, the brush has to consist of linear polymer chains of the same length at high grafting densities. The closest approximation to this can be obtained by the living anionic SIP (LASIP). The experimental difficulties outlined mean that only relatively few examples of LASIP are documented in the literature. 

This contribution will provide a review of polylectrolytes as biomaterials, with emphasis on recent developments. The first section will provide an overview of methods of synthesizing polyelectrolytes in the structures that are most commonly employed for biomedical applications linear polymers, crosslinked networks, and polymer grafts. In the remaining sections, the salient features of polyelectrolyte thermodynamics and the applications of polyelectrolytes for dental adhesives and restoratives, controlled release devices, polymeric drugs, prodrugs, or adjuvants, and biocompatibilizers will be discussed. These topics have been reviewed in the past, therefore previous reviews are cited and only the recent developments are considered here. 

Graft polymers were obtained by mastication of a 60/40 blend of natural rubber and chlorosulphonated polyethylene (/). From 10-55% natural rubber was obtained as side chains. Grafting presumably proceeds by transfer of chlorine atoms to the rubber radicals to give grafting sites for combination with rubber radicals. Soluble linear polymers were also obtained by mastication for 50-180 min under nitrogen for a blend 50/50 of natural rubber and a polyurethane rubber (Vulcaprene A) (/). 

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. 

The molecular architecture of a polyphosphazene has a profound influence on properties. For example, linear and tri-star trifluoroethoxy-substituted polymers with the same molecular weight (1.2 x 104 or higher) have strikingly different properties.138 The linear polymers are white, fibrous materials that readily form films and fibers, whereas the tri-arm star polymers are viscous gums. One is crystalline and the other is amorphous. Cyclolinear polymers are usually soluble and flexible. Cyclomatrix polymers are insoluble and rigid. Linear polymers can be crystalline, but graft or comb polymers are usually amorphous. 

---