Catalyst copolymer, preparation

The organometallic polymer shown in scheme 3 was synthesized using phosphoric acid, persulfate, or azobisisobutyronitrile (AIBN) as catalyst. Copolymers prepared with methyl methacrylate, styrene, and chloroprene as well as the homopolymer were crosslinked with formaldehyde. These polymers rmderwent reversible chemical oxidation with ceric sulfate. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Another soluble polymer-enlarged catalyst was synthesized and tested by Wandrey et a/.[57] The catalyst was prepared by a coupling of an oxazaborolidine via a hydrosilylation reaction to a methyl hydrosiloxane-dimethylsiloxane copolymer (Figure 4.40). The catalyst was used in the enantioselective borane reduction of ketones. 

The copolymer prepared without DEZ is clearly shown to be bimodal by GPC, with MJMn = 13.8 (Fig. 16). The GPC trace was deconvoluted into components of Mw 240,000 and 9600 g mol reflecting the differing propensities for hydrogen-induced termination between the two catalysts. The molecular weight distribution narrows as DEZ is added, as expected for an efficient chain shuttling polymerization ... 

Kragl 13) pioneered the use of membranes to recycle dendritic catalysts. Initially, he used soluble polymeric catalysts in a CFMR for the enantioselective addition of Et2Zn to benzaldehyde. The ligand a,a-diphenyl-(L)-prolinol was coupled to a copolymer prepared from 2-hydroxyethyl methyl acrylate and octadecyl methyl acrylate (molecular weight 96,000 Da). The polymer was retained with a retention factor > 0.998 when a polyaramide ultrafiltration membrane (Hoechst Nadir UF PA20) was used. The enantioselectivity obtained with the polymer-supported catalyst was lower than that obtained with the monomeric ligand (80% ee vs 97% ee), but the activity of the catalyst was similar to that of the monomeric catalyst. This result is in contrast to observations with catalysts in which the ligand was coupled to an insoluble support, which led to a 20% reduction of the catalytic activity. 

Fig. 1 NMR spectra in the carbonate region in CDCI3 of poly(propylene carbonate) A regioselective 94% head-to-tail selective copolymer prepared using a (salan)CrCl catalyst B regioirregular random polymer commercially available from Aldrich Chemicals...

These results suggest that the reaction conditions for the syntheses of PCEVE-NPVE and PCEVE-NNVE can be accomplished by the reactions of PCVE with any ratio of potassium cinnamate and PNP or PNN in one pot using a phase transfer catalyst. In addition, it is to be expected that PCEVE-NPVE and PCEVE-NNVE prepared from the reactions of PCVE have the same degree of polymerization if no side reactions occur during the substitution reactions. It is also expected that these copolymers are more random compared to the copolymers prepared from the cationic copolymerizations of the monomers, because the former is not affected by the monomer reactivity ratios. 

Solution (S-SBR) consists of styrene butadiene copolymers prepared in solution. A wide range of styrene-butadiene ratios and molecular structures is possible. Copolymers with no chemically detectable blocks of polystyrene constitute a distinct class of solution SBRs and are most like slyrcnc-buladicne copolymers made by emulsion processes. Solution SBRs with terminal blocks of polystyrene (S-B-S) have the properties of self-cured elastomers. They are processed like thermoplastics and do not require vulcanization. Lithium alkyls are used as the catalyst. 

POLYALLOMER RESINS. These are block copolymers prepared by polymerizing monomers in the presence of anionic coordination catalysts. The polymer chains in polyallomers are composed of homopolymerized segments of each of the monomers employed. The structure of a typical polyallomer can be represented as ... 

Although both linear polyethene and isotactic polypropene are crystalline polymers, ethene-propene copolymers prepared with the aid of Ziegler catalysts are excellent elastomers. Apparently, a more or less random introduction of methyl groups along a polyethene chain reduces the crystallinity sufficiently drastically to lead to an amorphous polymer. The ethene-propene copolymer is an inexpensive elastomer, but having no double bonds, is not capable of vulcanization. Polymerization of ethene and propene in the presence of a small amount of dicyclopentadiene or 1,4-hexadiene gives an unsaturated heteropolymer, which can be vulcanized with sulfur in the usual way. 

Practical interest in high-molecular-weight poly (propylene oxide) centers in its potential use as an elastomer (19). Copolymerization of propylene oxide with allyl glycidyl ether gives a copolymer with double bonds suitable for sulfur vulcanization. Table IV shows the properties of elastomers made with a copolymer prepared with a zinc hexacyano-ferrate-acetone-zinc chloride complex. Also shown are the properties of elastomers made from partially crystalline copolymers prepared with zinc diethyl-water catalyst. Of particular interest are the lower room-... 

The NMR spectra of copolymers prepared by simultaneous oxidation of the two phenols and those prepared by sequential oxidation, in either order, are almost identical. The methyl peak is broadened, as is the peak caused by the protons of the pendant phenyl rings centered at 8 7.20 ppm, and all show the same peaks for aromatic backbone protons in about the same intensity ratios. The polymer obtained by oxidizing a mixture of DMP and the separately prepared homopolymer of MPP with a cuprous bromide-tetramethylbutanediamine catalyst, the procedure considered to have the best chance of producing a block copolymer, was completely random. 

The catalyst was prepared as in the previous examples, 9.9 grams of DPP was added, and oxidation continued at 60° C the volume was maintained about constant by periodic addition of benzene. After four hours, 7.3 grams of DMP was added, causing a sharp decrease in solution viscosity. Oxidation was continued for four hours after addition of the DMP. The copolymer, obtained in 8135 yield, had an intrinsic viscosity of 0.37 dl/g. 

As Zambelli (10) has summarized, ethylene-propylene copolymers prepared with syndiotactic specific catalysts contain both meso and... 

TABLE 1. Physical properties of copolymers prepared by bulk polymerization using bis[2-(2-ethoxyethoxy)-ethanolato-0,0, 0"] barium, ethyl benzene, and tri-n-octyl aluminum as the high trans catalyst mixture. 

Monocyclopentadienyl metallocene catalysts, (VII), not requiring methylalu-moxane as a co-catalyst were prepared by Canich [6] and used to prepare ethylene/a-olefin copolymers. 

Polymeric catalysts are also developed. For example, phospholene oxide modified divinylbenzene/styrene copolymers, as well as a polystyrene anchored triph-enylarsine oxide catalyst were prepared. The solid phase catalysts can be removed by filtration after partial conversion of an isocyanate to the carbodiimide. Such a catalyst is useful for the preparation of carbodiimide modified liquid MDl (4,4 -diisocyanatodiphenylmethane) products, which are of considerable commercial interest. 

The polymerizations were carried out in refluxing o-dichlorobenzene in the presence of 2-hydroxypyridine as catalyst. In the absence of catalyst, only low-molecular-weight polymers (IV <0.3 dL/g) could be isolated from solution. However, when 2-hydroxypyridine was used as a condensation catalyst, copolymers having IVs in excess of 0.45 dL/g could be prepared readily. The results are summarized in Table I. 

Data on a number of copolymers prepared with various catalysts are given in Table 19A [287]. An assumption in this work was that the small proportion of termonomer (ethylidene norbornene) did not interfere with E/ copolymerization. 

Both the early data and the more precise values given in Table 20A differ significantly from published estimates based on monomer and polymer composition (e.g. rj r2 = 0.60 in Table 19). As all the data relate to the, in general, more consistent soluble vanadium systems, this work reinforces doubts concerning the accuracy of much of the published information. A complication is that since C2 and C4 sequences are observed in ethylene/propene copolymers inverted head to head prop-ene units must be present and this will reduce the accuracy of analyses of EP sequences. In copolymers prepared by VC /AlEtj 4% of head to head propene sequences have been reported with the catalyst VCl4/AlEt2Cl which is syndiospecific for polypropene 8% of head to head sequences was found [295]. ... 

The coefficients 8.10 and 0.010 in the second equation are usually ascribed to the reactivity ratios rj and rj (Table 19). This catalyst produces poly-propene consisting mainly of syndiotactic stereoblocks, together with short disordered blocks resulting from head-to-head (hh) and tail-to-tail (tt) pro-pene enchainment and occasional isolated isotactic units, and if these features apply to copolymers prepared with vanadium catalysts, the reaction is in effect a terpolymerization. Locatelli et al. [322] derive the equation for monomer/polymer composition ratios... 

Observations on this system may not apply to other catalyst systems but the fact that abnormal addition of propene has been demonstrated in elastomeric E/P copolymers prepared under very different conditions makes it clear that, at the least, the values of and rj are approximations. It would be of interest to calculate (assuming, for example, that the ratio of the fractions of head-to-head and head-to-tail units equals the ratio of the corresponding rate coefficients) what differences from the true rj and T2 ratios would result from the occurrence of 5—10% of abnormal addition. 

Chung, T.C. Lu, H.L. Kinetic and micro structure studies of poly(ethylene-co-p-methylstyrene) copolymers prepared by metallocene catalysts with constrained ligand geometry. J. Polym. Sci. Pt. A Polym. Chem. 1998, 36, 1017. 

The addition copolymerization of norbornene-type monomers with a-olefins [21] forms the basis of EPDM (ethylene propylene diene monomer) technology. Incorporation of smaU amounts of DCPD or ethylidene norbornene (ENB) in olefinic vinyl addition polymers provides latent crosslink sites in EPDM elastomers. It is weU known in the hterature that incorporation of higher amounts of rigid, bulky multicychc olefins results in materials with higher TgS [22]. In fact, more recent work has concentrated on increasing the Tg of norbornene-type monomer/a-olefin copolymers [23]. The use of late transition metal catalysts to prepare such copolymers is reviewed in Section 4.3. 

Synthesised catalysts were named as NPML where N=percent crosslinking, P = styrene-divinyl benzene copolymer, M = Metal (Ru) and L=Ligand (DAP). The following catalysts were prepared. 

Sawamoto et aL used the RuCl2(PPh3)3/Al(OzPr)3 catalyst to prepare St/MMA copolymers [126]. They found that the polymerization proceeded well using 1-phenylethyl bromide as the initiator and that the composition of the copolymer matched the comonomer feed composition, or behaved azeotropically [126]. The polymers were well-defined, with predictable molecular weights and relatively low polydispersities (Mw/Mn<1.5). The reactivity ratios were similar to those determined from conventional free radical processes. Later work used a NiBr2(n-Bu3P)2 catalyst system for the ATRP of a 50/50 mixture of MMA/MA and MMA/nBA [127]. The results indicated that the copolymerization was controlled with copolymer Mn=ll,800 (Mw/Mn=1.47) and 12,500 (Mw/Mn=1.47),respectively. 

In comparison, block copolymers prepared using a copper catalyst and the halogen exchange technique had predictable molecular weights and narrower molecular weight distributions (cf. Fig. 17) [91]. There was no evidence of slow initiation and the outer pMMA blocks were more uniform. When Moineau et al. used this system, the mechanical properties were greatly improved relative to the copolymers prepared with the Ni catalyst [179]. It has also been reported that the proper choice of solvent also improves block copolymerization [180]. 

A number of block copolymers prepared with Ziegler-Natta catalysts have been reported however, in most cases the compositions may include significant amounts of homopolymer. The Ziegler-Natta method appears to be inferior to anionic polymerization for synthesizing carefully tailored block copolymers. Nevertheless, bock copolymers of ethylene and propylene (Eastman Kodak s Pofyallomers) have been commercialized. Unlike the elastomeric random copolymers of ethylene and propylene, these are high-impact plastics exhibiting crystallinity characteristics of both isotactic polypropylene and linear polyethylene. They also contain homopolymers in addition to block copolymers. 

Another field of investigation wherein IR spectroscopy and to a greater extent 13C NMR spectroscopy might give useful information is that of the sequence distribution in copolymers prepared with catalysts in which multiple active species are present (18,69, 78). 

The presence in the IR spectra of most C2-C3 copolymers prepared by Ziegler-Natta catalysts of the band at 13.3 p, characteristic of the rocking vibration of a sequence of two methylenes bound on both sides to tertiary carbon atoms (14), offers the possibility of quantitative evaluation of this phenomenon (9, 15, 25, 54, 77, 86, 91, 98). 

Vizen and Kissin (94) suggested that the distribution of active centres of a heterogeneous catalyst determines the distribution of compositions in the copolymer they derived formulas for calculating both composition and weight of copolymer fractions in relation to the stereospecificity of the active centres. The theoretical relationships were compared with experimental data, obtained in part by IR measurements, on composition distribution in a copolymer prepared with the catalytic system VC13—A1(C2H5)3. 

---