Comb PMMA

The core first method has been applied to prepare four-arm star PMMA. In this case selective degradation of the core allowed unambiguous proof of the star structure. However, the MWD is a little too large to claim that only four-arm star polymers are present [81], Comb PMMAs with randomly placed branches have been prepared by anionic copolymerization of MMA and monodisperse PMMA macromonomers [82], A thorough dilute solution characterization revealed monodisperse samples with 2 to 13 branches. A certain polydispersity of the number of branches has to be expected. This was not detected because the branch length was very short relative to the length of the backbone [83]. Recently, PMMA stars (with 6 and 12 arms) have been prepared from dendritic... 

Anotlier model system consists of polymetliylmetliacrylate (PMMA) latex, stabilized in organic solvents by a comb polymer, consisting of a PMMA backbone witli poly-12-hydroxystearic acid (PHSA) chains attached to it [10]. The PHSA chains fonn a steric stabilization layer at tire surface (see section C2.6.4). Such particles can approach tire hard-sphere model very well [111. 

The combinational contribution to AG,n for PMMA particles stabilized by PIB in 2-methylbutane is shown plotted as a function of temperature in Figure 3(a). The values of the parameters used in Equations 2 and 3 were u = 8 x 10- g cm-, a = 300 nm, >2 = 1.09 cm g- and V = 116.4 cnr mole- . The thickness of the steric barrier,L, was taken to be 25 nm and the particle separation, do, was fixed at 30 nm. It can be seen from Figure 3(a) that AGj (comb) is a positive quantity that becomes more positive as the temperature increases, indicating that in the absence of other contributions to AG, the particle would become more stable with increasing temperature. In the above calculation, we have assumed that the S function, Equation 3, remains invariant with temperature, which is incorrect. 

Catalytic chain transfer is used to control the molecular weight of PMMA commercially. The macromonomers produced by CCT show promise for synthesis of comb polymers. 

Highly stereoregular PMMA macromonomers, 14, prepared by Hatada and coworkers, have recently been fractionated by supercritical fluid chromatography into completely uniform fractions with no structural distribution [20,21]. They have been oligomerized with a radical (AIBN) or an anionic initiator (3,3-dimethyl-1,1-diphenylbutyllithium). After a new fractionation by SEC comb or star polymers of completely uniform architecture are obtained. No doubt, these samples will be most promising to investigate the branched structure-property relationship. 

Figure 7.9 Shear-stress dependence of the relative viscosity for dispersions in white spirit of acrylic copolymer particles of radius a = 157 nm at a volume fraction of p =0.40 for differing concentrations of nonadsorbing polyisobutylene polymer of molecular weight 411,000. The particles had been stabilized by addition of a comb-graft copolymer of PMMA backbone (which adsorbed to the particles) with non-adsorbing poly(12-hydroxystearic acid) teeth. The con-centrations (in weight per unit volume) of polyisobutylene are 1.0% ( ), 0.85%(B), 0.6%(D), 0.5%(V), 0.4%( ), and 0.1 %(0)- (From Bus-call et al. 1993, with permission from the Journal of Rheology.)...

Combination of a living ionic polymerization and a metal-catalyzed radical polymerization also leads to comb polymers, where both the molecular weights of the arm and main-chain polymers are well controlled. PMMA with poly(vinyl ether) arm polymers of controlled molecular weights (C-l) were prepared by the copper-catalyzed radical polymerization of methacrylate-capped macromonomers carrying a poly-(isobutyl vinyl ether), which were obtained by living cationic polymerization with a methacryloxy-capped end-functionalized initiator.428 Comb polymers with... 

PS, PS- -PI, and PS- PMMA comb-shaped polymers with well-defined molecular characteristics (Scheme 61). The PS- -PMMA graft copolymers were found to decompose in proton-containing media, while they were stable in organic solvents. 

Poly(methylmethacrylate) (PMMA) CH3 -(CHj-i-)- COOCH3 1.17-1.20 Balhroomfixtures, knobs, combs, flluminated signs... 

Another useful class of dispersants/emulsifiers are the graft copolymers consisting of one B chain and several A chains grafted on to the backbone. These graft copolymers are sometimes referred to as comb polymers. Examples of suitable B chains are poly(methyl methacrylate) (PMMA) or polystyrene, with A chains of PEO or PVP. The copolymer is usually prepared by grafting a macromonomer such as methoxy poly(ethylene oxide) methacrylate with poly(methyl methacrylate). 

Some polymers are linear—a long chain of connected monomers. PE, PVC, Nylon 66, and polymethyl methacrylate (PMMA) are some linear commercial examples found in this book. Branched polymers can be visualized as a linear polymer with side chains of the same polymer attached to the main chain. While the branches may in turn be branched, they do not connect to another polymer chain. The ends of the branches are not connected to anything. Special types of branched polymers include star polymers, comb polymers, brush polymers, dendronized polymers [1], ladders, and dendrimers. A cross-linked polymer, sometimes called a network polymer, is one in which different chains are connected. Essentially the branches are connected to different polymer chains on the ends. These three polymer structures are shown in Figure 1.3. 

Dispersion polymerizations in carbon dioxide using these various stabilizers can in general be carried out with high polymerization rates to produce polymers of high molecular weight that are recovered as 1-3 micron spherical particles. For example, polymerization at 65 °C and 205 bar, with PFAO as stabilizer and using AIBN as initiator, poly(methyl methacrylate) of Mn =200,000 to 315,000 have been produced [3b]. With a comb-like stabilizer at 65 °C and 380 bar poly(methyl methacrylates) (PMMA) in... 

Figure 2. Universal calibration plot. The figure symbols correspond to the following , linear polystyrene (PS) O, "comb" type polystyrene +, "star" type polystyrene A, heterograft copolymer x, polymethylmethacrylate (PMMA) 9, polyvinylchloride v > graft copolymer (PS/PMMA) , polyphenyl si loxane , polybutadiene, (redrawn with permission from ref. 52).

The method seems to be of wide application [36a] and was extended to block polymers with poly(thio-phene) (PT) sequences, (PS,-PT) and to poly(metha-crylate) blocks (PMMA) associated with PPP [36b]. The fact that these copolymer blocks have a micellar structure led to new organized polymers, with unexpected morphologies in the solid state, as for instance the regular honey-comb morphology obtained with PS,-PPP block copolymers [36]. 

PS-PMMA stat. copol o PS-PMMA comb o PS-PMMA heterograft... 

Reversible addition-fragmentation chain transfer polymerization (RAFT) polymerization of methyl acrylate was combined with cationic polymerization of THF to synthesize comb copolymers. Asymmetric star block copolymers based on polystyrene (PS), PTHF, and PMMA were synthesized by a combination of CROP and redox polymerization methods. Miktoarm star polymers containing poly(THF) and polystyrene arms were also obtained by combining CROP and ATRP methods. Another approach for the synthesis of block copolymers... 

Comb-shaped polymers are derived from polymerizing or copolymerizing macromonomers. Macromonomers can be synthesized by a variety of synthetic techniques. Asami and co-workers prepared a methacrylate-terminated polystyrene by anionic polymerization. The macromonomer was then polymerized using GTP [41] to yield an oligomer with a polystyrene backbone and PMMA grafts. McGrath and co-workers prepared a poly(dimethyl siloxane) macromonomer end-capped with a methacrylate group. This macromonomer was polymerized by GTP to yield a comb-shaped polymer with PDMS branches [19]. 

McGrath and co-workers synthesized a novel all-PMMA comb polymer by a combination of GTP and anionic polymerization (Scheme 7) [19]. The resulting comb had a = 2,48,600, with an average of 14 grafted PMMA chains per molecule. The grafted PMMA chain had a = 6300 and =... 

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