Polycarbonates ring-opening polymerization

Extension of DKR to polymer chemistry would readily result in chiral polyesters, polycarbonates, or polyamides from an optically inactive monomer mixture. Scheme 10 describes three variants of chemoenzymatic catalysis applied in polymer chemistry that recently appeared in the literature. Route A uses AA and BB monomers to prepare chiral polymers from racemic/diasteromeric diols. Route B converts an enantiomer mixture of AB monomers to homochiral polymers. Route C is the enzymatic ring-opening polymerization of co-methylated lactones to homochiral polyesters. Details will be given in Sect. 3.4.2. 

Among the more common thermoplastics from ring opening polymerization of interest in composite processing are polylactams, polyethers, polyacetals, and polycycloolefins. It has also been shown that polycarbonates can be produced from cyclic carbonates [22], Anionic ring opening polymerization of caprolactam to nylon 6 is uniquely suited to form a thermoplastic matrix for fiber-reinforced composites, specifically by the reaction injection pultrusion process [23-25]. The fast reaction kinetics with no by-products and the crystalline... 

Polycarbonates, both aliphatic and aromatic, have been prepared by the ring opening polymerization of cyclic monomers or oligomers [22], Cyclic monomeric precursors are more common in aliphatic polycarbonates, but because of steric reasons aromatic polycarbonates can only be prepared from cyclic oligomers. Both cationic and anionic initiators have been examined and anionic initiators appear to be more efficient. 

Figure 1.8 Preparation of cyclic oligomers that yield polycarbonates by ring opening polymerization...

A kinetic study of the ring-opening polymerization (ROP) of trimethylene carbonate similarly afforded AG at 383 K of 101.9 kj mol-1, a value which was very close in energy to that found for the production of poly(TMC) from oxetane and C02. Hence, based on these experimental findings, the formation of polycarbonate from the oxetane and C02 coupling reaction was shown to occur via two different or concurrent pathways-that is, the intermediacy of TMC formation, and the subsequent polymerization and/or direct enchainment of oxetane and C02 (Figure 8.16). The presence of small amounts of ether linkages in the copolymer also supported this conclusion. 

Among the polycarbonates, PTMC in particular has been studied for biomedical use. PTMC is commonly derived by ring-opening polymerization (Fig. 9). The monomer, l,3-dioxan-2-one,is obtained by refluxing 1,3-propanediol in an excess of diethyl carbonate. Albertsson et al. have reported on the polymerization in bulk and solution using a number of initiators and catalysts [120,279, 280]. PTMC is aliphatic and has a low Tg (approximately -17 °C), it is thus in its... 

Takata et al. [99] found for two spiro orthocarbonates (119 and 121) having l,4,6,9-tetraoxaspiro[6.6]tridecane skeletons different cationic ring-opening polymerization behavior Irrespective of solvent, initiator, and temperature (from room temperature to 150°C), 119 gave polycarbonate (120), whereas 121 gave poly (ether-carbonate) (122). 

Transition metal catalyzed, ring opening polymerization Dispersion, cationic polymerization Homogeneous/precipitation, cationic polymerization Homogeneous, free radical/cationic polymerization Precipitation, free radical polymerization Dispersion, free radical polymerization Norbornene polymer, polycarbonate Isobutylene polymer Vinyl ether polymer Amorphous fluoropolymers Vinyl polymer, semicrystalline fluoropolymers Polyvinyl acetate and ethylene vinyl acetate copol5Tner... 

Other step-polymerization reactions of large cyclic monomers by entropically driven ring-opening polymerization have been reviewed (Hall and Hodge, 1999). An important example is the heating of cyclic bisphenol-A carbonates over a titanium isopropoxide transesterification catalyst to yield a polycarbonate with a relative molar mass of about 250000. This has also been performed under conditions of reaction injection moulding (Hall and Hodge, 1999). 

Al-Azemi, T.F., and Bisht, K.S. (1999) Novel functional polycarbonate by lipase-catalyzed ring-opening polymerization of 5-methyl... 

Chiral, hydroxy functional polycarbonates were prepared by the enzymatic ring opening polymerization (ROP) of a seven-membered cyclic carbonate (12) derived from L-tartaric acid (Scheme 11.3) [24]. Among others Novozym 435, PFL, and... 

Efficient methods for the synthesis of cyclic bisphenol-A polycarbonates have provided a practical technology for the rapid synthesis of high molecular weight bisphenol-A polycarbonates by anionic ring-opening polymerization as shown in Equation 7.29 [150]. A mixture of cyclic oligomers (M 1300) was polymerized with lithium... 

The most significant ahphatic polycarbonates are based upon DMTMC and TMC. They are made by the same ring-opening polymerization as glycoHde-based biodegradable polyesters. The homopolymers... 

The ring-opening polymerization of the cyclic carbonate methyl 4,6-0-benzylidene-2,3-6>-carbonyl-a-D-glucopyranoside has recently been described. This polymerizes at relatively low temperatures (60°C), without any elimination of carbon dioxide, to give polycarbonates in good yields and medium molecular weights [137]. 

Shen Y., Chen X., Gross R.A., Polycarbonates from sugars Ring opening polymerization of 1,2-0-isopropylidene-D-xylofuranose-3,5-cyclic carbonate (IPXTC), Macromolecules, 32, 1999, 2799-2802. 

Polycarbonates are also high melting rigid polymers. They were, therefore, also looked at for potential use in nonlinear optics. To achieve high molecular weights, some attempts were made to prepare them via ring opening polymerization. This, however, led to intractable materials. The cyclic structure can be shown as follows ... 

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