Dual polymerizations

This concept was further developed by Hawker and coworkers [193, 194], who performed dual living polymerizations from a single initiating molecule, without the requirement of an additional reaction. The compatibility of either NMRP or ATRP with the AROP of CL was demonstrated by the synthesis of a variety of well-defined block copolymers. The basic strategy followed for the dual polymerization is shown in Scheme 11.43. 

Scheme 11.43 Synthesis of block copolymers by dual polymerization including AROP and NMRP methods.

Less refined metallic species can be employed to perform dual polymerization processes. In 2007, Kong and Pan described the use of a simple [Cp2TiCl]/CuBr2... 

Construction of a dual-polymer electrochromic device (type iii memory device) that has two face-to-face polymer layers in each cell producing 400 (20 x 20) different combinations of absorptions was shown by Sonmez and Sonmez [84], In this study, several examples of this 3x3 pixel dual polymeric electrochromic device composed of red poly(3-alkylthiophene), green poly(2,3-di(thien-3-yl)-5, 7-di(thien-2-yl)thieno[3,4-fc]pyrazine] and blue PEDOT polymers, which switch at different wavelengths, were presented. These distinct absorption states have led to speculation that electrochromic polymers could be used for memory storage devices and computing functionalities. 

MountDuris, G., Silikas. N., and Eliades, G. (2004) Effect of sodium hypochlorite treatment on the molecular composition and morphology of human coronal dentin. /. Adhes. Dent, 6 (3), 175—182. Oook, S. et oL (2004) Influence of polymerization mode of dual-polymerized resin direct core foundation systems on bond strengths to bovine dentin. 

Blocked isocyanates are particularly helpful in dual cure mechanisms. In one instance, UV light first polymerizes an acrylate polymer containing hydroxyl groups. The system also contains a malonate ester-blocked isocyanate. The one-component system is heated, which starts the polymerization of the acrylate. Higher temperatures unblock the isocyanate, permitting the cure of the urethane to proceed [15]. 

Here, instead of an ordinary diol to react with ACPC, an azo-containing diol such as ACPO or AHPA was used to introduce two kinds of azo groups in the repeating unit. The decomposition temperature of newly incorporated azo groups were higher than that of the ACPC unit, and thus MAI shows dual decomposition temperatures so that a more labile azo group is specifically used for the first step polymerization and another... 

Another development has been the advent of the dual-cure resin cements. These are hybrids of glass polyalkenoate cements and methacrylates that set both by an add-base cementation reaction and by vinyl polymerization (which may be initiated by light-curing). In these materials, the solvent is not water but a mixture of water and hydroxyethylmethacrylate which is capable of taking dimethacrylates and poly(acrylic add)-containing vinyl groups into solution. In the absence of light these materials set slowly and... 

One of the most interesting recent developments has been the advent of the resin glass polyalkenoate cements (Antonucci, McKinney Stansbury, 1988 Mitra, 1989 Wilson, 1989, 1990 Mathis Ferracane, 1989 Minnesota Mining Manufacturing Company, 1989 Albers, 1990). They are dual-cure hybrids that set by a combination of acid-base and polymerization reactions, and there are several types. Polymerization is effected by either chemical or light initiation. 

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

An interesting development regarding the synthesis of block copolymers involves the use of bifunctional or dual initiators, which are compounds capable of performing two mechanistically distinct polymerizations. The advantage of this procedure is that there is no need for intermediate transformation or activation steps. If the different initiation sites are equally active for the... 

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