Copolymerisation block copolymers

By block copolymerisation so that one component of the block copolymer has a Tg well below the expected service temperature range (e.g polypropylene with small blocks of polyethylene or preferably polypropylene with small amorphous blocks of ethylene-propylene copolymer). 

The applicability of organolanthanide metallocenes as polymerisation catalysts can also be seen from the results of the block copolymerisation of ethylene and methyl methacrylate. The persistence of the lanthanide-alkyl bond has been utilised to prepare ethylene copolymers with polar poly(methyl methacrylate) blocks. For this purpose, ethylene is introduced as the first monomer into the polymerisation system with the samarocene catalyst, and then methyl methacrylate is polymerised, which leads to block copolymer formation [532-534] ... 

A single reactor system is used to make olefin homopolymers and random copolymers. Two reactors are operated in series for the production of block copolymers (impact copolymers). An inert conveying gas (nitrogen) is used to maintain the fluidised bed in the reactor for impact copolymerisation [43,51]. 

Interesting evidence supporting the mechanism of polymerisation of acetylenes via carbene species is provided by the block and random copolymerisation of acetylenic monomers with cycloolefins. For instance, block copolymers of acetylene and cyclopentene with the WC —AlEtCT catalyst [41] and block copolymers of acetylene and norbornene with the (MeA. Oj2W(=NAr)= CHMe3 catalyst [42] have been obtained moreover, random copolymers of phenylacetylene and norbornene with the WC16 catalyst have also been obtained [149, 150],... 

Since oxiranes are representative heterocyclic monomers containing an endo-cyclic heteroatom, and the most commonly polymerised of such monomers, they have been subjected to copolymerisations with heterocyclic monomers containing both an endocyclic and an exocyclic heteroatom. Coordination copolymerisations of heterocyclic monomers with different functions are focused on oxirane copolymerisation with cyclic dicarboxylic acid anhydride and cyclic carbonate. However, the statistical copolymerisation of heterocyclic monomers with an endocyclic heteroatom and monomers with both endocyclic and exocyclic heteroatoms have only a limited importance. Also, the block copolymerisation of oxirane with lactone or cyclic dicarboxylic acid anhydride is of interest both from the synthetic and from the mechanistic point of view. Block copolymerisation deserves special interest in terms of the exceptionally wide potential utility of block copolymers obtained from comonomers with various functions. It should be noted, however, that the variety of comonomers that might be subjected to a random, alternating and block polymerisation involving a nucleophilic attack on the coordinating monomer is rather small. 

Block copolymers characterised by different backbone structures of well-defined block lengths have been obtained from oxiranes and other heterocyclic monomers in the presence of catalysts that are effective at bringing about living polymerisations. Aida et al. [127,188,189,195,196] applied aluminium porphyrins and Teyssie et al. [125,197,198] applied bimetallic /i-oxoalkoxidcs for block copolymerisations in systems involving oxirane lactone, oxirane oxirane/cyclic acid anhydride, and oxirane/cyclic acid anhydride lactone as block forming units and obtained respective polyether polyester and polyester polyester block copolymers. Such copolymers seem to be of exceptionally wide potential utility [53]. 

Alternating copolymers may be considered as homopolymers with a structural unit composed of the two different monomers. Random copolymers are obtained from two or more monomers, which are present simultaneously in one polymerisation reactor. In graft polymerisation a homopolymer is prepared first and in a second step one or two monomers are grafted onto this polymer the final product consists of a polymeric backbone with side branches. In block copolymerisation one monomer is polymerised, after which another monomer is polymerised on to the living ends of the polymeric chains the final block copolymer is a linear chain with a sequence of different segments. 

The present volume is particularly concerned with the use of the different modes of controlled radical polymerisation for the preparation of copolymers such as random copolymers, linear block copolymers, as well as graft copolymers and star-shaped copolymers. It also presents the combination of controlled radical polymerisation with non-controlled radical copolymerisation, cationic and anionic polymerisation,both of vinyl monomers and cyclic monomers, and ringopening metathesis polymerisation. 

Ethylene has a symmetrical monomer, so the concept of tacticity does not apply. Consequently, the crystallinity of polyethylene is controlled either by chain branching or by copolymerisation. Copolymers are classified into random and block copolymers (Fig. 2.7) depending on whether the monomer locations are random, or whether long blocks of each monomer exist. Polyethylene copolymers are random. The figure suggests that the local composition of a random copolymer is the same as that of the monomer mixture. However, in a batch copolymerisation, monomers tend to add to the end of a growing chain at different rates. The monomer ratio drifts as the polymerisation proceeds, so polymer formed at the end of the polymer-... 

Near-IR spectroscopy (10000-4000/cm) was successfully used to monitor conversion dining conventional, anionic solution polymerisation of styrene and isoprene to homopolymers and block copolymers. The conversion of the vinyl protons in the monomer to methylene protons in the polymer was easily monitored under conventional (10-20% solids) solution polymerisation conditions. In addition to the need for an inert probe, high sampling frequencies were required since polymerisation times ranged from 5s in tetrahydrofuran to 20 minutes in cyclohexane. Preliminary data indicate that near IR is capable of detecting sequence distribution for tapered block copolymers, geometric isomer content, and reactivity ratios for free-radical copolymerisation. 20 refs. USA... 

SEC chromatogram (Figure 5) shows a shift of the block copolymer to higher molecular weights upon styrene polymerization without the formation of an additional shoulder. Further investigations copolymerisation of the BLG-NCA and styrene using doubleheaded initiators with amido-amidate and NMP groups are necessary. 

Fatty-acid chains with oxazoline end groups have been synthesised by the two mechanistic routes shown in Scheme 4.25 and their polymerisations and copolymerisations reviewed [122]. Block copolymers of conventional alkyl oxazolines... 

Natural polystyrene has a strong tendency to crack, and can only be used in most potential applications when modified to form high-impact or toughened polystyrene grades or ABS. It can be toughened by polybutadiene, butadiene-acrylonitrile copolymer rubber, or SBS or SEBS block copolymers. The rubber can be added before or after polymerisation of the styrene monomer. In the case of polybutadiene, two reactions take place styrene polymerisation, and graft copolymerisation of the styrene with the polybutadiene. A brief outline of this operation is available on the Dynasol website (www.dynasolesastomers.com). 

It is possible to chemically string chains of different polymers together (forming block copolymers or through randomised copolymerisation) or physically melt different polymers into a blend to gain beneficial synergised properties. These altered properties are also determined by the above two factors, ie, intra- and inter-polymer molecular interactions. These are the fundamental characteristics of polymer interactions at molecular scales. 

Copolymerisation is another approach to improve the mechanical behaviour of polymers, especially their ductility. In copolymerisation, different monomers are used to form the chain molecules. There are several possibilities to arrange the monomers, shown in figure 8.26. The monomers can alternate alternating copolymerisation) or can be arranged irregularly random copolymerisation). In block copolymers, there are longer chain segments of one type... 

PP homopolymer is copolymerised with ethylene. In block copolymers, the ethylene content is much higher than the random copolymers. The copolymerised part of the material is rubbery and forms a separate dispersed phase within the PP matrix. As a result, block copolymerised PP is much tougher than homopolymerised PP and can withstand higher impact even at low temperatures but at the expense of transparency and softening point. The main applications of the block copolymerised PP are similar to those of elastomer-modified PP but where the impact property requirement is not that critical. 

---